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Drive Systems

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Drive systems refer to the mechanical and electrical components that transmit power and control motion in machines and vehicles. This field encompasses the design, analysis, and optimization of systems that convert energy into mechanical work, including motors, gears, and control systems, to achieve desired performance and efficiency.
lightbulbAbout this topic
Drive systems refer to the mechanical and electrical components that transmit power and control motion in machines and vehicles. This field encompasses the design, analysis, and optimization of systems that convert energy into mechanical work, including motors, gears, and control systems, to achieve desired performance and efficiency.

Key research themes

1. How do advanced control strategies enhance the dynamic torque response in induction machine drive systems?

This theme investigates the development and implementation of control algorithms—specifically within Direct Torque Control (DTC) frameworks—to achieve fast and precise torque control in induction motors, with a focus on methods that balance torque response speed and system simplicity.

Distraction Osteogenesis in Irradiated Rabbit Mandibles With Adjunctive Hyperbaric Oxygen Therapy
by henry Ferguson

2014, Journal of Oral and Maxillofacial Surgery

Key finding: Proposes a minor but effective modification to the DTC hysteresis comparator flux error status which enables the selection of the voltage vector producing the largest tangential flux component, thereby achieving significantly... Read more
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Simple Dynamic Overmodulation Strategy for Fast Torque Control in DTC of Induction Machines with Constant Switching Frequency Controller
by Tole Tole

2014

Key finding: Introduces a straightforward dynamic overmodulation approach by adjusting flux error signals feeding into the switching table, allowing the DTC system to operate in six-step mode for the fastest torque response, even in field... Read more
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A simple dynamic overmodulation strategy for fast torque control in DTC of induction machine with constant switching frequency controller
by Tole Tole

2014

Key finding: Demonstrates that by modifying flux hysteresis comparator outputs prior to voltage vector selection, the DTC method can deliver a fast torque transient response under constant switching frequency control. The paper compares... Read more
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2. What are the key hardware and software components involved in effective drive system simulation and control implementation?

This theme focuses on the integration of motor models, power converters, and control algorithms within simulation environments, as well as the practical realization of control strategies using embedded hardware, highlighting methods to verify performance during design and implementation of drive systems.

Drive System Simulation and Implementation
by Faeka Khater and 
1 more
mohamed ibrahim

2015

Key finding: Classifies major drive system components—motors, power converters, controllers—and summarizes control algorithm implementation options including PID, adaptive, and AI-based controllers. It emphasizes simulation software... Read more
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3. How does external vibration impact the performance of disk drives and what factors mitigate these effects?

This theme addresses the sensitivity of consumer-grade versus enterprise-class disk drives to external vibrations generated by adjacent drives, quantifying performance degradation and identifying packaging as a key factor in reducing vibrational impact on drive bandwidth and reliability.

Performance Impact of External Vibration on Consumer-Grade and Enterprise-Class Disk Drives
by Thomas Ruwart

2025, 22nd IEEE / 13th NASA Goddard Conference on Mass Storage Systems and Technologies (MSST'05)

Key finding: Empirically quantifies that consumer-grade disk drives experience a 10%-15% reduction in read bandwidth and 25%-40% reduction in write bandwidth due to vibrations from neighboring drives, while enterprise-class drives are... Read more
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4. What are the emerging power electronic technologies and control strategies driving renewable energy systems integration?

This theme investigates the role of power electronics in enabling high-efficiency energy conversion technologies for renewable sources such as wind and photovoltaic systems, focusing on converter topologies, reliability, grid integration control (including grid support through reactive power and low voltage ride-through), and trends for cost and reliability improvements.

Power electronics - key technology for renewable energy systems
by Florin Iov

2024

Key finding: Provides a comprehensive overview of power converter technologies and control methods essential for integrating wind and photovoltaic renewable energy systems into electrical grids. Emphasizes demands such as reliable power... Read more
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Power electronics-key technology for renewable energy systems
by Florin Iov

2022

Key finding: Describes a DSP-based three-phase inverter power electronic interface for a 70 kW microturbine distributed generation system supporting both grid-connected and islanded operation. The controller allows seamless switching... Read more
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Power electronics-key technology for renewable energy systems
by Florin Iov

2022

Key finding: Describes a DSP-based three-phase inverter power electronic interface for a 70 kW microturbine distributed generation system supporting both grid-connected and islanded operation. The controller allows seamless switching... Read more
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5. How do novel data storage architectures and disk hardware design approaches address increasing data density and recording limitations?

This theme explores hardware solutions such as shingled write disk technology and on-disk XOR computation engines in RAID systems to overcome conventional magnetic recording limits and to optimize storage efficiency and reliability, focusing on sequential write constraints, data layout optimizations, and improved parity update mechanisms.

Design Issues for a Shingled Write Disk System
by Darrell D E Long and 
3 more
Ethan L Miller
Jehan-Francois Paris
Thomas J E Schwarz

2016

Key finding: Analyzes the trade-offs of shingled writing to enable ~2.3× higher areal density by overlapping written tracks, requiring sequential writes instead of random writes. Presents new disk data structures optimized for sequential... Read more
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The Designs of RAID with XOR Engines on Disks for Mass Storage Systems
by David Du

2023

Key finding: Proposes integrating exclusive-or (XOR) computation capability into individual disks to offload parity updates from centralized RAID controllers, significantly reducing data traffic and computational bottlenecks during write... Read more
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A brief history of disk drive control
by Daniel Abramovitch

2022, IEEE Control Systems

Key finding: Provides an extensive historical overview of disk drive servo control evolution from early magnetic disks to modern hard drives. Highlights how advances in control system design, including improved feedback algorithms, servo... Read more
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Related Topics

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    • All papers in Drive Systems

    Power Electronics and Control of Renewable Energy Systems
    by Mihai Ciobotaru and 
    1 more
    Florin Iov

    2007, 2007 7th International Conference on Power Electronics and Drive Systems

    The global electrical energy consumption is still rising and there is a demand to double the power capacity within 20 years. The production, distribution and use of energy should be as technological efficient as possible and incentives to... more
    Ireland’s grid code is very demanding in respect with the fault duration while Denmark has the lowest short circuit time duration with only 100 msec. However, Denmark’s grid code requires that the wind turbine shall remain connected to the electrical network during successive faults which is a technical challenge.
    Fig. 1. Power electronic system with the grid, load/source, power converter and control.
    inree important issues are OF concem using sucn a system. The first one is reliability; the second is efficiency and the third one is cost. For the moment the cost of power semiconductor devices is decreasing 1+5 % every year for the same output performance and the price pr. kW for a power electronic system is also decreasing. An example of a mass-produced and high competitive power electronic system is an adjustable speed drive (ASD). The trend of weight, size, number of components and functions in a standard Danfoss Drives A/S frequency converter can be seen in Fig. 2. It clearly shows that power electronic conversion is shrinking in volume and weight. It also shows that more integration is an important key to be competitive as well as more functions become available in such a product. Fig. 2. Development of standard adjustable speed drives for the last four decades.
    Fig. 3. Development of power semiconductor devices in the past and in the future [36].
    Wind turbines capture power from the wind by means of aerodynamically designed blades and convert it to rotating mechanical power. The number of blades is normally three. As the blade tip-speed should be lower than half the speed of sound the rotational speed will decrease as the radius of the blade increases. For multi- MW wind turbines the rotational speed will be 10-15 rpm. The most weight efficient way to convert the low- speed, high-torque power to electrical power is to use a gear-box and a standard fixed speed generator as illustrated in Fig. 4. Fig. 4. Converting wind power to electrical power in a wind turbine [19].
    The development in wind turbine systems has been steady for the last 25 years and four to five generations of wind turbines exist and it is now proven technology. t is important to be able to control and limit the converted mechanical power at higher wind speed, as he power in the wind is a cube of the wind speed. The power limitation may be done either by stall control the blade position is fixed but stall of the wind appears along the blade at higher wind speed), active stall (the blade angle is adjusted in order to create stall along the blades) or pitch control (the blades are tured out of the wind at higher wind speed) [6], [7]. The basic output characteristics of these three methods of controlling the power are summarized in Fig. 6. Fig. 6. Power characteristics of different fixed speed wind turbine systems.
    It uses a wound rotor induction generator (WRIG) and it has been used by the Danish manufacturer Vestas Wind Systems since the mid 1990’s. Fig. 8. Partial variable speed wind turbine with variable rotor resistance.
    This configuration corresponds to the so called Danish concept that was very popular in 80’s. This wind turbine is fixed speed controlled machine, with asynchronous squirrel cage induction generator (SCIG) directly connected to the grid via a transformer as shown in Fig. 7. Fig. 7. Fixed speed wind turbine with directly grid connected squirrel-cage induction generator.
    Fig. 11. Control of a wind turbine with doubly-fed induction generator (WT Type C).
    Another solution for the electrical power control is to use the multi-pole synchronous generator. A passive rectifier and a boost converter are used in order to boost the voltage at low speed. The system is industrially used today and it is shown in Fig. 12. Fig. 12. Control of active and reactive power in a wind turbine with multi-pole synchronous generator (WT Type D).
    Fig. 15. Active stall wind farm with a DC-link grid connection. Another possible DC _ transmission system configuration is shown in Fig. 16, where each wind turbine has its own power electronic converter, so it is possible to operate each wind turbine at an individual optimal speed. A common DC grid is present on the wind farm while a full scale power converter is used for the on-shore grid connection.
    Fig. 16. Wind farm with common DC grid based on variable speed wind turbines with full scale power converter. A comparison of these possible wind farm topologies is given in Table 2.
    According to this demand the wind turbines must be able to control the active in the Point-of-Common- Coupling (PCC) in a given power range. The active power is typically controlled based on the system frequency e.g. Denmark, Ireland, Germany [51]-[57] so that the power delivered to the grid is decreased when the grid frequency rise above 50 Hz. A typical characteristic for the frequency control in the Danish erid code is shown in Fig. 17. On the contrary other grid codes, e.g. Great Britain [58] specifies that the active power output must be kept constant for the frequency range 49.5 to 50.5 Hz, and a drop of maximum 5% in the delivered power is allowed when frequency drops to 47 Hz.
    Fig. 18. Regulation function for active power implemented in wind farm controller required by the Danish grid codes: a) delta control, b) balance control, c) absolute production constraint and d) system protection.
    Fig. 20. Requirements for reactive power control in the Irish grid code for wind turbines [54]. Reactive power is typically controlled in a given range. The grid codes specify in different ways this control capability. The Danish grid code gives a band for controlling the reactive power based on the active power output as shown in Fig. 19.
    The Irish grid code specifies e.g. the reactive power capability in terms of power factor as shown in Fig. 20.
    The general structures of a single-phase and three- phase PLL including the grid voltage monitoring are presented in Fig. 43a and Fig. 43b respectively. Usually, the main difference among different single- phase PLL methods is the orthogonal voltage system generation structure.
    Fig. 44. Adaptive control of the grid-connected inverter [138].
    The German transmission grid code for wind power specifies that the wind power units must provide a reactive power provision in the connection point without limiting the active power output as shown in Kin OT
    On the other hand Germany and Spain requires grid support during faults by reactive current injection up to 100% from the rated current [55], [56] and [59] as shown in Fig. 23. Fig. 23. Reactive current support during faults as specified in the German grid code [55].
    The PV cell is an all-electrical device, which produces electrical power when exposed to sunlight and connected to a suitable load. Without any moving parts inside the PV module, the tear-and-wear is very low. Thus, lifetimes of more than 25 years for modules are easily reached. However, the power generation capability may be reduced to 75% ~ 80% of nominal value due to ageing. A typical PV module is made up of around 36 or 72 cells connected in series, encapsulated in a structure made of e.g. aluminum and tedlar. An electrical model of PV cell is shown in Fig. 24. Fig. 24. Electrical model and characteristics of a PV cell.
    Typical curves of a PV cell current-voltage and power-voltage characteristics are plotted in Fig. 25a and Fig. 25b respectively, with insolation and cell temperature as parameters.
    inverters are characterized by high efficiency and low cost pr. kW. However, the energy yield of the PV plant decreases due to module mismatching and potential partial shading conditions. Also, the reliability of the plant may be limited due to the dependence of power generation on a single component: a failure of the central inverter results in that the whole PV plant is out of operation. Fig. 26 Structures for PV systems: a) Central inverter, b) String inverter and c) Module integrated inverter [71].
    The PV inverter technology has evolved quite a lot during the last years towards maturity [66]. Still there are different power configurations possible as shown in Fig. 27.
    The isolation is typically acquired using a transformer that can be placed on either the grid frequency side (LF) as shown in Fig. 28a or on the high-frequency (HF) side in the dc-dc converter as shown in Fig. 28b. The HF transformer leads to more compact solutions but high care should be taken in the transformer design in order to keep the losses low.
    In order to keep the magnetic components small high switching frequencies in the range of 20 — 100 kHz are typically employed. The full-bridge converter is usually utilized at power levels above 750 W. The advantages of this topology are: good transformer utilization — bipolar magnetization of the core, good performance with current programmed control — reduced DC magnetization of transformer. The main disadvantages in comparison with push-pull topology are the higher active part count and the higher transformer ratio needed for boosting the dc voltage to the grid level.
    In Fig. 30b a practical example [70] using a simple boost converter is shown.
    Fig. 32. Practical example of a PV system without DC-DC converter and with a full-bridge converter and isolation grid side transformer. Fig. 31. General diagram of a PV system without DC-DC converter and with isolation transformer. A PV inverter topology is presented in Fig. 32, in which a line frequency transformer is used. For higher power levels, self-commutated inverters using thyristors may be used [70].
    In Fig. 33b, a typical transformer-less topology is shown using PWM IGBT inverters. This topology can be used when a large number of PV panels are available connected in series producing in excess of the grid voltage peak at all times.
    Fig. 35. Single-stage PV grid-connected system.
    Classical Fl control with grid voltage teed-lorward (vg) [13], as depicted in Fig. 36a, is commonly used for current-controlled PV inverters, but this solution exhibits two well known drawbacks: inability of the PI controller to track a sinusoidal reference without steady-state error and poor disturbance rejection capability. This is due to the poor performance of the integral action.
    Fig. 38. The flowchart of the dp-P&O method. The experimental results show that the dP-P&O method performs superior to the traditional P&O during rapidly changing irradiance, resulting in higher dynamic efficiency, see Fig. 39.
    cri’ (Wey Fig. 39. The instantaneous efficiency of the traditional P&O method can decrease to below 80% during rapidly increasing and decreasing irradiation, while the efficiency of dP-P&O is not affected.
    Fig. 37. Measurement of the power between two MPPT sampling instances.
    In Fig. 40c a new control strategy of input power is proposed. The new element introduced is a power feed- forward. The computed value of t he current amplitude reference using the PV power (P,,) and the RMS value of the ac voltage (Vacrms) is added the de voltage controller (/,) resu amplitude reference (I .). Using t re forward the dynamic of the PV 0 the output value of ting in an ac-current he input power feed- system is improved being known the fact that the MPP1 [ is rather slow.
    Fig. 41. Maximum trip times for both voltage amplitude and frequency according to the standard IEC61727 [86]. Grid-connected converter systems rely on accurate and fast detection of the phase angle, amplitude and frequency of the utility voltage to guarantee the correct generation of the reference signals. This is also required by the relevant grid codes which are country specific and can vary also in respect to the generation system (e.g. PV systems, wind turbines, fuel cell, etc). The grid codes may refer to different standards for distributed generation systems. These standards impose the operation conditions of the grid-connected converter systems in terms of grid voltage amplitude and frequency. Considering grid voltage monitoring requirements for interconnection of PV systems to the grid, the standard IEC61727 [86] and IEEE 929 [87] are given as examples. These standards apply to utility- interconnected PV power systems operating in parallel with the utility and utilizing static (solid-state) non- islanding inverters for the conversation of DC to AC.
    Fig. 45. Bode plot of plant for different values of the grid inductance L in case of using an LCL filter. According to [130] different techniques, as presented in [131]-[136] can be used for line impedance measurements. It is noticeable that, usually, these methods use special hardware devices. Once the inputs are acquired by voltage and current measurement, the processing part follows, typically involving large mathematical calculations in order to obtain the impedance value.
    The method proposed in [139] is based on producing a perturbation on the output of the power converter that is in the form of periodical injection of one or two voltage harmonic signals (see Fig. 49). The single harmonic injection uses a 600 Hz signal and the double harmonic injection uses a 400 Hz and 600 Hz signals, respectively. During the perturbation, the current response(s) at the same frequency as the injected signal(s) is/are measured. The value of the grid impedance is estimated using two different signal processing algorithms. The DFT technique is used for the single harmonic injection and the statistic technique is used for the double harmonic injection (see Fig. 50). Fig. 49. Harmonic injection methods [139]: a) single harmonic injection; b) double harmonic injection.
    Fig. 52. Islanding operation test setup for IEEE 929-2000 standard [87].
    Fig. 53. Wind turbine market share by manufacturer (end of 2005). ihe Danish company VESIAsS Wind systems A/S was still on the top position among the largest manufacturers of wind turbines in the world, followed by GE Wind, as the second largest in the world. German manufacturers ENERCON, Gamesa and Suzlon are in third, fourth and fifth positions, respectively. Notice that, the first four largest suppliers (Vestas, Gamesa, Enercon, GE Wind) had much larger markets with the first leading positions, compared to the others.
    PV solar electricity is also a booming industry; since 1980, when terrestrial applications began, annual installation of photovoltaic power has increased to above 750 MWp, the cumulative installed PV power in 2004 reaching approximately 2.6 GWp [159] and [160].
    Fig. 54. Wind World share of yearly installed power for the considered wind turbine concepts (see Fig. 7 to Fig. 10).
    Fig. 56. Development and prognoses of specific cost and production quantity for the PV inverter of nominal powers between | and 10 kW during two decades (j indicates specific prices of products on the market [162].
    Table 1. System comparison of wind turbine configurations. D. Control of Wind Turbines
    Table 2. Comparison of wind farm topologies. investment, maintenance and reliability. This may be different depending on the planned site. htt. § Sansa not wenn Bios beacnl nwa Some European countries have at this moment dedicated grid codes for wind power. These requirements reflect, in most of the cases, the penetration of wind power into the electrical network or a future development is prepared.
    Appendix I. Review of connection requirements for wind power in European grid codes [7].
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    Power electronics - key technology for renewable energy systems
    by Yongheng Yang

    2011, 2011 2nd Power Electronics, Drive Systems and Technologies Conference

    The electrical energy consumption continues to grow and more applications are based on electricity. We can expect that more 60 % of all energy consumption will be converted and used as electricity. Therefore, it is a demand that... more
    Fig. 1. Annual and cumulative installed Wind Power Capacity from 1985 to 2009 (source: BTM Consult).
    Fig. 2. Wind turbine market share distributed by manufacturers in 2009. (source: BTM Consult).
    Fig. 3. Cumulative PV installed capacity from 2000 to 2009 (source: EPIA, http://www.epia.org) [78]. The annual growth rate is still very high (>30%) especially for the last 3 years. As in the previous years the vast majority o f new capacity was installed in EU with Germany as dominating the market followed by Spain and Italy. USA market is also growing fast According to Pho ton Magazine, the prices for PV modules are decreased by the end of 2009 to around 1.5-2 €/Wp with stronger trends for using thin film technology in order to reach the psychological threshold of 1 €/Wp, which really will trigger the mass- penetration of PV as an energy and power source. In addition to the PV module cost, the cost and reliability of PV inverters are also important issues. The inverter cost share represents about 10-15% of the total investment cost of a grid connected PV system.
    The prices for PV inverters in the 1-10 kW range are show this n in Fig. 4. It can be seen that the inverter cost of power class has decreased by more than 50 % during the last decade. The main reasons for this reduction are the increase of the production quantities the implementation of new system technologies . string-inverters). A further 50 % reduction of the ific cost is anticipated during the coming decade h requires the implementation of specific measures in the development and the manufacturing processes.
    rotational speed will decrease as the radius of the blade increases. For multi-MW wind turbines the rotational speed is 8-13 rpm. So far the most weight efficient way to convert the low-speed, high-torque power to electrical power is to use a gear-box and a standard fixed speed generator as illustrated in Fig. 5
    Fig. 6. Roadmap for wind turbine technology from wind to electricity [7].
    betters oe yi Fig. 7. Power characteristics of different wind turbine systems. Passive stall is based on fixed speed operation. The development in wind turbine systems has been steady for the last 35 years [3]-[35] where four to five generations of wind turbines have been developed and the power capacity has increased by a factor of 100. In a wind turbine it is essential to be able to control and limit the converted mechanical power at higher wind speeds, as the power in the wind is a cube of the wind speed. It is also important to maximize the energy capture from the wind below maximum power production. The power limitation is done either by stal control (the blade position is fixed but stall of the wind appears along the blade at higher wind speed), active stall (the blade angle is adjusted in order to create stal along the blades) or pitch control (here the blades are turned out of the wind at higher wind speed). The basic output characteristics of a wind turbine using these three methods of controlling the power are summarized in Fig. 7.
    Fig. 9. Partial variable speed wind turbine with variable rotor resistance. ~ Tt uses a wound rotor induction generator (WRIG) and it has been used by since the mid 1990's. The generator is directly connected to the grid. The rotor winding of the generator is connected in series with a controlled resistance, whose size defines the range of the variable speed (typically 0-10% above
    Fig. 10. Variable speed wind turbine with partial scale power converter. This configuration is known as the doubly-fed induction generator (DFIG) concept, which gives a variable speed controlled wind turbine with a wound rotor induction generator (WRIG) and partial power- scale frequency converter (rated to approx. 30% of nominal generator power) on the rotor circuit. The topology is shown in Fig. 10. The stator is directly connected to the grid, while a partial-scale power converter controls the rotor frequency and thus the rotor speed. The power rating of this partial-scale frequency converter defines the speed range (typically +30% around synchronous speed). Moreover, this converter performs the reactive power compensation and a smooth grid connection. The control range of the rotor speed is wider compared to the variable rotor resistance type. The smaller frequency converter makes this concept attractive from an economical point of view. In this case the power electronics is enabling the wind turbine to act as a dynamic power source to the grid. However, its main drawbacks are the use of slip-rings and the protection schemes/controllability in the case of grid faults.
    Fig. 8. Fixed speed wind turbine with directly grid connected squirrel-cage induction generator. See See ee eS Se he ee ee Pe This configuration corresponds to the so called Danish concept that was very popular in 80’s. This wind turbine has a fixed speed controlled machine, with asynchronous squirrel cage induction generator (SCIG) directly connected to the grid via a transformer as shown in Fig. 8. This concept needs a reactive power compensator to reduce (almost eliminate) the reactive power demand from the turbine generators to the grid. It is usually done by continuously switching capacitor banks following the power production variation (5-25 steps Smoother grid connection occurs by incorporating a soft-starter as shown in Fig. 8. Regardless the aerodynamic power control principle in a fixed speed wind turbine, the wind fluctuations are converted into mechanical fluctuations and further into electrical power fluctuations. These can yield to voltage fluctuations at the point of connection in the case of a weak grid.
    Fig. 12. Two-level back-to-back voltage source converter for wind turbines. (2L BTB).
    Fig. 16. Three-level Neutral Point Clamped and five-level H-bridge converter for wind turbines. (3L-NPC + 5L-HB).
    Fig. 14. Three-level H-bridge back-to-back converter for wind turbines. (3L-HB BTB).
    Fig. 15. Five-level H-bridge back-to-back converter for wind turbines. (5L-HB BTB). With the same voltage rating switching devices, 5L- HB BTB can achieve five level output voltage, and doubled voltage amplitude compared to the 3L-HB BTB solution. These features enable smaller output filter and less current rating in the switching devices as well as in the cables [38], [45].
    The DC/DC converters with medium frequency transformer (MFT) operate at several kHz to dozens of kHz, the transformer size is thereby reduced. Because of the cascaded structure, this configuration can be directly connected to the transmission power grid (10 kV-20 kV) with high output voltage quality, filter-less design, and the redundancy ability [47]-[49]. Fig. 17. Cascade H-bridge back-to back converter for wind turbines with Medium Frequency Transformer. (CHB-MFT).
    Fig. 18. Converter cell of the Cascade H-bridge back-to-back converter with Medium Frequency Transformer.
    Another solution for the electrical power control is to use the multi-pole synchronous generator and a full scale power converter. A passive rectifier and a boost converter can be used in order to boost the voltage at low speed. The system is industrially used today and it is shown in Fig. 21.
    Fig. 23. Regulation functions for active power control implemented in wind farm controller required by the Danish grid codes. a) delta control, b) balance control, c) absolute production constraint and d) system protection.
    All considered grid codes require fault ride-through capabilities for wind turbines to overcome grid faults. Voltage profiles are given specifying the depth of the voltage dip and the clearance time as well. One of the problems is that the calculation of the voltage during all types of unsymmetrical faults is not very well defined in some grid codes. The voltage profile for ride-through capability can be summarized as shown in Fig. 26. Fig. 26. Voltage profile for fault ride-through capability in European grid codes for wind power [61]. Ireland’s grid code is very demanding in respect to the fault duration while Denmark has the lowest short circuit time duration with only 100 ms. However, the grid code in Denmark requires that the wind turbine shall remain connected to the electrical network during successive faults, which is a technical challenge.
    Fig. 25. Requirements for reactive power provision of generating units without limiting the active power output in the German transmission grid code [55].
    Fig. 24. Danish grid code demands for the reactive power exchange in the PCC [51], [52].
    Some typical curves of a PV cell current-voltage and power-voltage characteristics are shown in Fig. 29.
    Fig. 28. Ideal equivalent circuit of a PV cell.
    Fig. 27. Reactive current support during faults as specified in the German grid code [61].
    Fig. 30. Different grid-connected PV inverter structures. a)C entral inverter; b) String inverter; c) Module inverter; d) Multi-string inverter. The Multi-String concept is a flexible solution, having a high overall efficiency of power extraction, due to the fact that each PV string is individually controlled.
    Fig. 31. Comparison of commercial PV inverters in terms of efficiency, weight and volume [79].
    Fig. 32. Parasitic capacitance in PV panels [73].
    Fig. 33. Transformer-less PV system showing the parasitic capacitance between the PV and the grounded frame of the array anc the path of the alternating ground leakage current.
    Fig. 35. Experiments on full-bridge topology. 1) bipolar output of the converter, 2) the voltage to ground (DC- terminal of the PV array), 3) the leakage ground current for the single-phase inverter with bipolar PWM.
    Fig. 34. Full-bridge topology with bipolar PWM. The H-Bridge is a well-known topology and it is made up of two half bridges. This topology has also been used in motor drives and UPS applications. To control the four switches in this topology several PWM techniques can be implemented. The simplest one is the bipolar PWM, which modulates switches T1-T4 (see Fig. 34) complementary to T2-T3, resulting in a two evel output voltage. The conversion efficiency is reduced due to the fact that during the free-wheeling period the grid current finds a path and flows back to the DC-link capacitor. Fig. 35 shows some measurements on such a converter.
    Using the H-Bridge topology with different PWM schemes than the bipolar one, will result in unipolar output vo switching the unipo the freew. tage (+Vdc, 0 and -Vdc) that has twice the frequency. The advantage of this method is that the grid side filter needs to be much smaller due to ar output voltage of the converter and also due to the fact that the frequency of the output voltage is twice the switching frequency. Furthermore, during heeling period, the grid current finds a path through the short-circuited output of the converter, either through T1-T3, as shown in Fig. 36 or similarly through T2-T4. On the other hand, there is a significant disadvantage using unipolar PWM transformer-less PV systems, regarding the voltage to ground of the PV array and the ground leakage currents. As shown in Fig. 37, the modulation strategy generates a varying common-mode voltage. An FFT of the voltage to ground, as detailed in Fig. 38, shows that voltage components at the switching frequency have very high amplitudes in the range of Vac.
    Fig. 37. Experiments on a full-bridge topology with unipolar PWM. 1) unipolar output of the converter, 2) voltage to ground (DC- terminal of the PV array), 3) leakage ground current for the single- phase inverter with unipolar PWM.
    Fig. 39. Highly Efficient and Reliable Inverter Concept (HERIC) showing path of the current during the zero voltage state, for positive load current [104]. To keep high efficiency and all the advantages given by the unipolar PWM, but still have the common-mode behavior as in case of the bipolar PWM, the H-Bridge topology may be modified [104], the Highly Efficient and Reliable Inverter Concept (HERIC). The modification includes two extra switches (T5-T6) each connected in series with a diode. During the zero voltage vector, depending on the sign of the reference voltage, either T5 of T6 are tured ON, while T1, T2, T3 and T4 are all in their OFF state and the PV array is disconnected from the grid. In this way there is a possibility to achieve the zero voltage state and the output voltage will be unipolar, having the same frequency as the switching frequency and there will be no high frequency fluctuations present at the DC terminals of the PV array. Furthermore, the efficiency of the inverter is still kept high, because during the freewheeling period, the load current is short-circuited through T5 or T6, depending on the sign of the grid current.
    Fig. ‘40. H5-topology for high efficiency. Path of the current in the case of positive voltage state, for positive load current.
    Fig. 41. Single-phase topology with DC decoupling used for transformerless PV systems. Another topology using the DC decoupling method is the one presented in [106], which adds two extra switches and two extra diodes to the H-Bridge topology as shown in Fig. 41. The modulation strategy is also a hybrid type. The active voltage vector is achieved by switching T5-T6 with high frequency. Switches T1-T4 are switched with the grid frequency and in anti-parallel to T2-T3, depending on whether the reference voltage is in the positive or negative half period. In this way the output voltage of the converter will be a unipolar voltage, like in case of the HERIC and H5 topologies.
    Another solution for generating the zero voltage state can be done using a bidirectional switch made of one GBT and one diode-bridge [109]. The topology is shown in Fig. 42, using the bidirectional switch, as an auxiliary component with a grey background. This bidirectional switch is clamped to the midpoint of the DC-link capacitors in order to fix the potential of the PV array also during the zero voltage state when T1-T4 and T2-T3 are open. An extra diode is used to protect from short-circuiting the lower DC-link capacitor.
    Fig. 44. Patented topology from Refu Solar [111] for single-phase PV -inverter.
    The NPC topology is suitable for transformer-less PV systems, since the voltage to ground is constant in case of both terminals of the PV. The only drawback for the single-phase NPC topology is the high DC-link voltage, which has more than twice the grid peak voltage and might reach voltages higher than the allowed maximum system voltage, therefore a boost stage is needed before the inverter, which decreases the overall efficiency of the whole PV system. The Neutral Point Clamped (NPC) topology was introduced some years ago in [110] and has mostly been used for applications in AC drives. The voltage to ground measured at both PV array terminals is constant, when the switching ripple is not taken into consideration. This is due to the connection of the neutral line of the middle point of the DC-link that fixes the potential of the PV array to the grounded neutral [108]. Fig. 43 shows this topology.
    Fig. 45. Conergy topology used for single-phase converter [112].
    It is also shown in Fig. 47, where the voltage to ground varies with the switching frequency and changes according to the PWM strategy. Fig. 47. Measurements for 3FB topology. 4) shows the voltage to ground of the DC+ terminal [250V/div]. Fig. 46. FFT of voltage to ground for the 3FB topology.
    frequency and multiples of it, having high amplitude using a 3FB topology.
    System comparison of wind turbine configurations.
    Comparisons of the multilevel solutions for wind turbines.
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    A DQ synchronous frame controller for single-phase inverters
    by Mohammad Monfared

    2011

    This paper deals with design of a synchronous frame control strategy for single-phase inverter-based islanded distributed generation (DG) systems. Although, implementation of these regulators requires a minimum of two independent phases... more
    Fig. 1 shows the converter system considered in this in- vestigation, which includes an insulated-gate bipolar transistor (IGBT) bridge configuration driven from constant voltage DC bus and an LC filter. Note that the assumption of a constant DC voltage is reasonable if the DC capacitance is large or if DC bus voltage ripple compensation is included within the PWM control algorithm [9]. Salient parameters for the system are shown in Table I. The bilinear differential equations that describe the large- signal dynamic behavior of this converter are presented as
    Fig. 2. A simplified model of the single phase inverter A simple time-continuous model of the inverter derived from the above equations is shown in Fig. 2, where the full-bridge is replaced by mVac, assuming that the inverter switching frequency, f;, is much higher than the frequency of the modulating signal, ™m.
    "Eq into (11), the . W + transfer function between the real voltage error Hy and the Finally, by substituting Eg = Notice, the transfer function H (s) has very high gain at
    Fig. 6. Block diagram of inner current loop Once the inner current loop design is finished, the next step is to fine-tune the parameters of the voltage feedback loop. Fig.
    Fig. 7. Bode plots of ic /ig and ic/to
    Fig. 9. Variation of closed loop poles of the system with respect to Ky. (a) and (b): 0 < Kp < 2, K; = 80, K = 15. (c) and (d): 0 < Kp < 2, Ki = 80, kK = 80.
    Fig. 10. Variation of the harmonic impedance with respect to Kp. (arrow direction indicates increasing value of Kp)
    Fig. 11. Simulation results for the proposed controller under a resistive load. (a): output voltage vo (solid line) together with output voltage reference v? (dashed line), (b): tracking error E(t).
    Fig. 12. Simulation results for the multiloop PI controller under a resistive load. (a): output voltage vo (solid line) together with output voltage reference v* (dashed line), (b): tracking error E(t).
    Fig. 13. Simulation results for the proposed controller under a triac controlled load. (a): output voltage vo and load current io, (b): tracking error E(t harmonics spectrum.
    Fig. 14. Simulation results for the proposed controller under a rectifier load. (a): output voltage vo and load current io, (b): tracking error E(t) harmonic spectrum
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    Power Electronics and Control of Renewable Energy Systems
    by Florin Iov

    2007, 2007 7th International Conference on Power Electronics and Drive Systems

    The global electrical energy consumption is still rising and there is a demand to double the power capacity within 20 years. The production, distribution and use of energy should be as technological efficient as possible and incentives to... more
    descriptionView Paperarrow_downwardDownload
    A simple dynamic overmodulation strategy for fast torque control in DTC of induction machine with constant switching frequency controller
    by Tole Tole

    2009

    This paper presents a simple dynamic overmodulation method to obtain a quick dynamic torque response in Direct Torque Control with constant switching frequency (will be referred as DTC-CSF) induction machines. A fast dynamic torque... more
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    Parallel Operation of Power Factor Corrected AC-DC Converter Modules With Two Power Stages
    by Aravind Pothana

    2007, 2007 7th International Conference on Power Electronics and Drive Systems

    Page 1. PEDS 2007 Parallel Operation of Power Factor Corrected AC-DC Converter Modules With Two Power Stages Aravind Pothana Department of Electrical Engineering Indian Institute of Technology Madras Chennai, India 600036 Email:... more
    descriptionView Paper
    Simple Dynamic Overmodulation Strategy for Fast Torque Control in DTC of Induction Machines With Constant-Switching-Frequency Controller
    by Tole Tole

    2011, IEEE Transactions on Industry Applications

    This paper presents a simple dynamic overmodulation method to obtain a quick dynamic torque response in Direct Torque Control with constant switching frequency (will be referred as DTC-CSF) induction machines. A fast dynamic torque... more
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    Power Electronics and Control of Renewable Energy Systems
    by Mihai Ciobotaru

    2007, 2007 7th International Conference on Power Electronics and Drive Systems

    The global electrical energy consumption is still rising and there is a demand to double the power capacity within 20 years. The production, distribution and use of energy should be as technological efficient as possible and incentives to... more
    descriptionView Paperarrow_downwardDownload
    A D-Q synchronous frame controller for single-phase inverters
    by Josep M. Guerrero

    2011, 2011 2nd Power Electronics, Drive Systems and Technologies Conference, PEDSTC 2011

    This paper deals with design of a synchronous frame control strategy for single-phase inverter-based islanded distributed generation (DG) systems. Although, implementation of these regulators requires a minimum of two independent phases... more
    descriptionView Paperarrow_downwardDownload
    Power electronics - key technology for renewable energy systems
    by Florin Iov

    2011, 2011 2nd Power Electronics, Drive Systems and Technologies Conference

    The electrical energy consumption continues to grow and more applications are based on electricity. We can expect that more 60 % of all energy consumption will be converted and used as electricity. Therefore, it is a demand that... more
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    Comparison of basic direct torque control designs for permanent magnet synchronous motor
    by Mohamad N Abdul Kadir

    2007, 7th International Conference on Power Electronics and Drive Systems, PEDS 2007

    In the production of high quality materials by a heat treatment, it is indispensable to accurately predict the temperature inside the furnaces being employed. Mathematical modelling allows one to optimize the operating conditions of... more
    Figures used in the abstract Figure 1: Temperature in empty kiln
    Figure 2: Temperature in kiln filled with clay-like material
    descriptionView Paperarrow_downwardDownload
    Power electronics-key technology for renewable energy systems
    by Florin Iov

    2011

    The electrical energy consumption continues to grow and more applications are based on electricity. We can expect that more 60 % of all energy consumption will be converted and used as electricity. Therefore, it is a demand that... more
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    A complete excitation-shaft-bearing model to overcome the shaft induced voltage and bearing current
    by Reza Kazemi Golkhandan

    2011, 2011 2nd Power Electronics, Drive Systems and Technologies Conference

    This paper proposes a complete distributed model for investigating the induced shaft voltage and bearing current in turbo generators due to the interaction with the static excitation systems. This undesirable voltage affects the... more
    Fig .1: Static excitation system
    Another solution to the shaft voltage is applying symmetrical filters on DC-side of the rectifier in order to eliminate high frequency peaks in rectifier output voltage and prevent them entering to the field winding. By this procedure a applied to the field winding and shaft voltage reduces to a harmless value. This passive filter is connected symmetrically to both terminals on DC-side of rectifier. The appropriate values of resistance and capacitance chosen for the passive filter are 10 ohms and 2uF. These values insure damping high frequency peaks of voltage and prevent them entering to the field winding. This procedure results in reduction of shaft voltage. Connection of the designed passive filter to the system is depicted in Fig .3.
    Fig .3: Connection of the passive filter to the DC side of rectifier
    Fig .4: Voltage applied to the field winding of the proposed model According to the simulation results, it can be concluded that under symmetrical conditions and without any grounding brush, only common mode voltage contributes to the shaft voltage. The voltage applied to the field winding is a saw- tooth voltage with the base frequency of six times the base frequency of the system. This voltage is the DC output voltage of rectifier and is depicted in Fig .4. As depicted in Fig. 5, shaft voltage measured on exciter end (EE) and turbine end (TE) of generator is a periodic wave form with the base frequency of 150Hz. High frequency peaks, created by switching of rectifier, are also superimposed on the shaft voltage
    “ig .6: Field winding voltage in the case of applying the proposed passive filter Simulation results in the case of applying the proposed passive filter to the derived model of the system is shown in Fig .6, 7. Fig .6 shows the voltage applied to the field winding. This voltage does not have high frequency peaks which existed in the previous section.
    Fig .5: Shaft to ground voltage on (EE) without applying any solution
    Fig .7: Shaft to ground voltage on (EE) in the case of applying the proposed passive filter Shaft voltage on exciter end (EE) of generator is shown in Fig .7. It is significant that in the case of applying the passive RC filter to the DC side of the rectifier in the static excitation system, peaks of shaft voltage reduced from 115 volts, in the simple model, to 30 volts.
    Fig .9: RMS value of shaft to ground voltage on the exciter end of generator in the case of applying passive filter
    Fig .8: RMS value of shaft to ground voltage on the exciter end of generator According to the simulation results it can be concluded that applying passive RC filter on DC side of the rectifier reduced high-frequency peaks of field voltage and hence reduced shaft voltage to a harmless value. RMS values of shaft voltage on exciter end of generator (EE) in simple model of the system and in the model with passive RC circuit are depicted in Fig. 8, 9. It can be concluded that applying passive RC filter to the input of field winding reduced RMS value of shaft voltage from 37.3 volts to a value beneath 6 volts and of course this value is low enough to ensure that bearing currents do not damage the journal bearings.
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