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Fig.11 Two-phase stationary stator fluxes due to speed changes with full loading. Fig.12 Two-phase stationary stator fluxes due to speed changes with full loading and parameters variation.

Figure 11 Two-phase stationary stator fluxes due to speed changes with full loading. Fig.12 Two-phase stationary stator fluxes due to speed changes with full loading and parameters variation.

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Fig.1 System diagram of a typical DTC PMSM drive system. DTC strategy give a fast and good dynamic performance and can be considered as an alternative to the FOC strategy therefore, in recent years the industrial application areas of the high performance AC drives based on DTC technique have gradually increased due to the following advantages over the field oriented control technique, such as: (i) Excellent dynamic performance. (ii) Precise and quick control of stator flux and electromagnetic torque. (ili) Absence of coordinate transformation, which reduce the complexity of algorithms involved in FOC. (iv) Robust against machine parameters variations. (v) No current control oops. A DTC Drive system, which is based on a pre-fixed hysteresis bands for both torque and flux controllers, suffers from a varying switching frequency, which is a function of a motor speed, stator/ rotor fluxes, and stator voltage; it is also not constant in steady state. At low speed, an appreciable evel of acoustic noise is present, which is mainly due to the ow inverter switching frequency. The high frequency is imited by the switching characteristics of the power devices. Therefore, there will be large torque ripples and distorted waveforms in currents and fluxes. Thus there will be a varying device switching frequency. Variable switching frequency is undesirable and is limited by the thermal condition of the switching devices and maximum switching frequency of the devices. Therefore, there will be a large torque ripples and distorted waveforms in currents and fluxes.
Fig.1 System diagram of a typical DTC PMSM drive system. DTC strategy give a fast and good dynamic performance and can be considered as an alternative to the FOC strategy therefore, in recent years the industrial application areas of the high performance AC drives based on DTC technique have gradually increased due to the following advantages over the field oriented control technique, such as: (i) Excellent dynamic performance. (ii) Precise and quick control of stator flux and electromagnetic torque. (ili) Absence of coordinate transformation, which reduce the complexity of algorithms involved in FOC. (iv) Robust against machine parameters variations. (v) No current control oops. A DTC Drive system, which is based on a pre-fixed hysteresis bands for both torque and flux controllers, suffers from a varying switching frequency, which is a function of a motor speed, stator/ rotor fluxes, and stator voltage; it is also not constant in steady state. At low speed, an appreciable evel of acoustic noise is present, which is mainly due to the ow inverter switching frequency. The high frequency is imited by the switching characteristics of the power devices. Therefore, there will be large torque ripples and distorted waveforms in currents and fluxes. Thus there will be a varying device switching frequency. Variable switching frequency is undesirable and is limited by the thermal condition of the switching devices and maximum switching frequency of the devices. Therefore, there will be a large torque ripples and distorted waveforms in currents and fluxes.
Direct Torque and Flux Control (DTFC), also termed Direct Torque Control (DTC), has been developed by German and Japanese researchers for use in torque control of high power servo drives. Recently, it has provided an industrial alternative to the field oriented control strategy. DTC is a control philosophy exploiting the torque and flux producing capabilities of ac machines when fed by a simple voltage source inverter that does not require current regulation loops, still attaining similar performance to that obtained from a vector control drive [4,16,17,18].
Direct Torque and Flux Control (DTFC), also termed Direct Torque Control (DTC), has been developed by German and Japanese researchers for use in torque control of high power servo drives. Recently, it has provided an industrial alternative to the field oriented control strategy. DTC is a control philosophy exploiting the torque and flux producing capabilities of ac machines when fed by a simple voltage source inverter that does not require current regulation loops, still attaining similar performance to that obtained from a vector control drive [4,16,17,18].
Fig.3 Stator flux vector locus and different possible switching voltage vector lies in sector 1. The motor torque is estimated from Equation (5). Then from Fig.2 the inputs to the switching table block are the torque and flux error, and the stator flux angle information are used to select the suitable switching pattern. Many voltage selection strategies can be utilized as widely discussed in Refs. [16,25,26,27,28,29]. Each strategy affects the drive performance in terms of torque and current ripple, switching frequency, and torque response [21,23,24].
Fig.3 Stator flux vector locus and different possible switching voltage vector lies in sector 1. The motor torque is estimated from Equation (5). Then from Fig.2 the inputs to the switching table block are the torque and flux error, and the stator flux angle information are used to select the suitable switching pattern. Many voltage selection strategies can be utilized as widely discussed in Refs. [16,25,26,27,28,29]. Each strategy affects the drive performance in terms of torque and current ripple, switching frequency, and torque response [21,23,24].
Table (1) Optimum selection table for DTC.
Table (1) Optimum selection table for DTC.
Fig.4 Complete Simulink model of DTC of PMSM drive system. type of the controller used and the type of disturbance imposed on the system. The mathematical model of each considered subsystem is used here to form the SIMULINK model for each subsystem. The complete dynamic models of the direct torque control of PMSM drive systems is shown in Fig.4.
Fig.4 Complete Simulink model of DTC of PMSM drive system. type of the controller used and the type of disturbance imposed on the system. The mathematical model of each considered subsystem is used here to form the SIMULINK model for each subsystem. The complete dynamic models of the direct torque control of PMSM drive systems is shown in Fig.4.
Fig. 5 Dynamic performance of reference and actual speed with full loading.
Fig. 5 Dynamic performance of reference and actual speed with full loading.
Figure 7 and 8 indicate the performances of rotor flux due to speed changes. It is noted that the motor flux maintained constant in this speed range while, a distorted and changed flux magnitude especially at the transient instant and at speed reversal with DTC as indicated.
Figure 7 and 8 indicate the performances of rotor flux due to speed changes. It is noted that the motor flux maintained constant in this speed range while, a distorted and changed flux magnitude especially at the transient instant and at speed reversal with DTC as indicated.
Fig. 6 Dynamic performance of reference and actual speed with full loading and parameters variation.
Fig. 6 Dynamic performance of reference and actual speed with full loading and parameters variation.
Fig. 8 The performances of rotor flux due to speed changes with full loading and parameters variation.
Fig. 8 The performances of rotor flux due to speed changes with full loading and parameters variation.
Fig.9 The performances of the motor reference and actual torque corresponding to speed changes with full loading. Figures 9 and 10 show the performances of the motor reference and actual torque corresponding to speed changes in forward and reverse direction as indicated. Also, the reference and actual torque takes their maximum value to provide the accelerating torque at the beginning of the transient instant. The output of speed controller is the reference torque while, the actual torque is the estimated one.
Fig.9 The performances of the motor reference and actual torque corresponding to speed changes with full loading. Figures 9 and 10 show the performances of the motor reference and actual torque corresponding to speed changes in forward and reverse direction as indicated. Also, the reference and actual torque takes their maximum value to provide the accelerating torque at the beginning of the transient instant. The output of speed controller is the reference torque while, the actual torque is the estimated one.
Fig.10 The performances of the motor reference and actual torque corresponding to speed changes with full loading and parameters variation
Fig.10 The performances of the motor reference and actual torque corresponding to speed changes with full loading and parameters variation
Fig.13. Two-phase stationary reference frame currents due to speed changes with full loading. Figures 15 and 16 show the flux position angle or the electrical rotor position ramp signal at 4000 rpm where the flux position angle is varying in a linear shape from (0 to 360) degree or from (0 to 6.2832) radian in estimations as indicated. Figure 15 shows the effect of speed reversal on two-phase stationary reference frame flux components and the associated flux position angle. From these figures it is noted that, when the speed is in forward direction of rotation the slope of the flux position is positive. Also, when the speed in backward direction the slope of the flux positions is negative. At the instant of speed reversal, the two-phase stationary reference frame flux components reverses their phase sequences with maintaining their amplitude constants. Consequently, the slope of the flux position is reverse from positive slope to negative slope when speed change from forward to backward direction of rotations and vice versa.
Fig.13. Two-phase stationary reference frame currents due to speed changes with full loading. Figures 15 and 16 show the flux position angle or the electrical rotor position ramp signal at 4000 rpm where the flux position angle is varying in a linear shape from (0 to 360) degree or from (0 to 6.2832) radian in estimations as indicated. Figure 15 shows the effect of speed reversal on two-phase stationary reference frame flux components and the associated flux position angle. From these figures it is noted that, when the speed is in forward direction of rotation the slope of the flux position is positive. Also, when the speed in backward direction the slope of the flux positions is negative. At the instant of speed reversal, the two-phase stationary reference frame flux components reverses their phase sequences with maintaining their amplitude constants. Consequently, the slope of the flux position is reverse from positive slope to negative slope when speed change from forward to backward direction of rotations and vice versa.
Fig.14 Two-phase stationary reference frame currents due to speed changes with full loading and parameters variation.
Fig.14 Two-phase stationary reference frame currents due to speed changes with full loading and parameters variation.
Fig.15 The flux position angle or the electrical rotor position ramp signal at 4000 rpm when speed reversal.
Fig.15 The flux position angle or the electrical rotor position ramp signal at 4000 rpm when speed reversal.
Fig.16 The flux position angle or the electrical rotor position ramp signal at 4000 rpm when speed reversal and parameters variation.
Fig.16 The flux position angle or the electrical rotor position ramp signal at 4000 rpm when speed reversal and parameters variation.
running under different conditions. Test results are compared with simulation and the necessary discussions are implemented. The experimental results of this proposed drive system are based mainly on PMS motor and displayed facilities using four-channel digital storage oscilloscope "Tektronix- TDS2014". The results are recorded by snap shots of different examined cases and then analyzed when required. Fig.17 Connection diagram of the implemented DTC system.
running under different conditions. Test results are compared with simulation and the necessary discussions are implemented. The experimental results of this proposed drive system are based mainly on PMS motor and displayed facilities using four-channel digital storage oscilloscope "Tektronix- TDS2014". The results are recorded by snap shots of different examined cases and then analyzed when required. Fig.17 Connection diagram of the implemented DTC system.
Fig.19 Performance of the rotor position at 500 rpm forward speed. Fig.18 Performance of the steady state estimated two-phase current components corresponding to 500 rpm forward speed.
Fig.19 Performance of the rotor position at 500 rpm forward speed. Fig.18 Performance of the steady state estimated two-phase current components corresponding to 500 rpm forward speed.
Figure 18 shows the performance of the steady state estimated two-phase direct and quadrature current components corresponding to 500 rpm forward speed and Fig.19 indicates the performance of the flux position or rotor position at 500 rpm forward speed. Also, they have nearly sinusoidal waveforms without any ripples and the flux position angle, is varying in a linear shape from (0 to 360) degree as indicated in figure 19.
Figure 18 shows the performance of the steady state estimated two-phase direct and quadrature current components corresponding to 500 rpm forward speed and Fig.19 indicates the performance of the flux position or rotor position at 500 rpm forward speed. Also, they have nearly sinusoidal waveforms without any ripples and the flux position angle, is varying in a linear shape from (0 to 360) degree as indicated in figure 19.
Fig.23 Close view of the rotor position when the speed is reversed from forward to backward at 500 rpm. A little distorted and improved current waveform is obtained by using the direct torque control technique. Increasing the switching frequency reduces the current ripples but this is restricted with the maximum switching frequency of the power transistor, this will case higher switching losses. A compromise between the quality of the output current and the inverter switching losses is the key of the switching frequency choice [16].
Fig.23 Close view of the rotor position when the speed is reversed from forward to backward at 500 rpm. A little distorted and improved current waveform is obtained by using the direct torque control technique. Increasing the switching frequency reduces the current ripples but this is restricted with the maximum switching frequency of the power transistor, this will case higher switching losses. A compromise between the quality of the output current and the inverter switching losses is the key of the switching frequency choice [16].
Fig.22 Close view of the two-phase current components when the speed is reversed from forward to backward at 500 rpm. When speed is reversed from backward to forward Figs.22, 23, 24 and 25, the drive system gives a very fast and smooth dynamic response. Also, the steady state speed when reversed from forward to backward and vice versa is reached in approximately 250 ms. As indicated from these figures the use of DTC gives a fast and better response in transient and in steady state periods therefore, a good dynamic response is obtained.
Fig.22 Close view of the two-phase current components when the speed is reversed from forward to backward at 500 rpm. When speed is reversed from backward to forward Figs.22, 23, 24 and 25, the drive system gives a very fast and smooth dynamic response. Also, the steady state speed when reversed from forward to backward and vice versa is reached in approximately 250 ms. As indicated from these figures the use of DTC gives a fast and better response in transient and in steady state periods therefore, a good dynamic response is obtained.
ee a _ _ ~ a Fig.21 performance of the rotor position at 500 rpm at reverse direction. Fig.20 performance of the two-phase current components at 500 rpm at reverse direction.
ee a _ _ ~ a Fig.21 performance of the rotor position at 500 rpm at reverse direction. Fig.20 performance of the two-phase current components at 500 rpm at reverse direction.
| Fig.25 Close view of the rotor position when the speed is reversed from backward to forward at 500 rpm. Fig.24 Close view of the two-phase current components when the speed is reversed from backward to forward at 500 rpm.
| Fig.25 Close view of the rotor position when the speed is reversed from backward to forward at 500 rpm. Fig.24 Close view of the two-phase current components when the speed is reversed from backward to forward at 500 rpm.
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