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n array power with the available so the proposed simple CV algori Tr [The PV array generated power is shown in corresponding to the input radiation. Comparing the PV Fig. (8 a) ar radiation indicated that the PV generated power matches the solar radia MPP for each solar radiation condition is rapidly tracked by hm. Similarly, shows the variations of the voltage and current at he voltage at the PV-PCC is maintained almost invariant except during the fault it is red current response is the same as at the wind-PCC. It is also ion. T Fig. (8 luced to zero value. T verified that a very low transient is recording in t exchanged power of the grid-connected PV system due to the proposed full decoupled current control strategy in d-g coordinates. PV-PCC. ne b) ne ne Fig. 8: Dynamic response of the PV array, (a) generated maximum power and (b) voltage and current

Figure 8 n array power with the available so the proposed simple CV algori Tr [The PV array generated power is shown in corresponding to the input radiation. Comparing the PV Fig. (8 a) ar radiation indicated that the PV generated power matches the solar radia MPP for each solar radiation condition is rapidly tracked by hm. Similarly, shows the variations of the voltage and current at he voltage at the PV-PCC is maintained almost invariant except during the fault it is red current response is the same as at the wind-PCC. It is also ion. T Fig. (8 luced to zero value. T verified that a very low transient is recording in t exchanged power of the grid-connected PV system due to the proposed full decoupled current control strategy in d-g coordinates. PV-PCC. ne b) ne ne Fig. 8: Dynamic response of the PV array, (a) generated maximum power and (b) voltage and current

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A single line diagram of the micro grid system studied in this paper is illustrated in Fig. 1. It consists of 22 kV network, 600 kW wind turbine and 200 kW PV panel. The average wind speed is 10 m/s at 40 m above ground level. The wind turbines are connected to the network through 800kVA, 690V/22kV transformers. The turbines are coupled to induction generators and have fixed capacitors, rated speed of 12 m/s. Local loads are included in the system with total active and reactive power of 400 kW and 100kVAR, respectively. The PV arrays are connected to the grid through DC/DC boost converter and DC/AC 3-phase two-level inverter. After inversion the arrays are interfaced to the distribution network through 6 kV/22 kV transformer. In the case of installing fixed capacitor for induction generator excitation, the system may need additional source of reactive power from the grid to enhance system performance. blades is changed. The extracted power of wind turbine depends on three main factors: available wind power, the power curve of the machine and the ability of the machine's response to wind fluctuation. The expression for power produced by the wind is given by [5]:
A single line diagram of the micro grid system studied in this paper is illustrated in Fig. 1. It consists of 22 kV network, 600 kW wind turbine and 200 kW PV panel. The average wind speed is 10 m/s at 40 m above ground level. The wind turbines are connected to the network through 800kVA, 690V/22kV transformers. The turbines are coupled to induction generators and have fixed capacitors, rated speed of 12 m/s. Local loads are included in the system with total active and reactive power of 400 kW and 100kVAR, respectively. The PV arrays are connected to the grid through DC/DC boost converter and DC/AC 3-phase two-level inverter. After inversion the arrays are interfaced to the distribution network through 6 kV/22 kV transformer. In the case of installing fixed capacitor for induction generator excitation, the system may need additional source of reactive power from the grid to enhance system performance. blades is changed. The extracted power of wind turbine depends on three main factors: available wind power, the power curve of the machine and the ability of the machine's response to wind fluctuation. The expression for power produced by the wind is given by [5]:
The current source I,, represents the photocurrent of the cell. The relationships between the PV cell output current and terminal voltage is given by: Using the physics of p-n junctions, a PV cell can be modeled as a DC current source in parallel with a diode that represents the most effective current escaping due to diffusion mechanisms. Two resistances, R, and R,, are included to model the contact resistances and internal PV cell resistance respectively. A solar cell equivalent circuit is usually represented [7], as shown in Fig. 2.
The current source I,, represents the photocurrent of the cell. The relationships between the PV cell output current and terminal voltage is given by: Using the physics of p-n junctions, a PV cell can be modeled as a DC current source in parallel with a diode that represents the most effective current escaping due to diffusion mechanisms. Two resistances, R, and R,, are included to model the contact resistances and internal PV cell resistance respectively. A solar cell equivalent circuit is usually represented [7], as shown in Fig. 2.
Fig4.a: Boost with MPP block diagrams IGBTs at high frequency according to the varying duty cycle. The fast switching action of the boost converter decouples the dynamics of the PV array due its changes in voltage or current from that of the DC link capacitor, which offers good performance under changing weather conditions. The other advantage of using the boost converter is to increase the array voltage to higher levels suitable for grid interconnection. A phase locked loop was used to lock on the grid frequency in such a way that V, was set to zero [8]. If the grid voltage is relatively constant, Ig and I, can be used to control real and reactive power injections from the PV array. In order to inject real power from t PI controller to follow he inverter, Iy was controlled using a specified reference signal Ig REF; reactive power injection was set to zero and thus I, = 0, as displayed in Fig.(4.b). T link capacitor. A constant DC voltage across means that the power t matches the power going out to the inverter previously mentioned, was controlled to be the he Ig per Was extracted hat goes into it from t he input power Pj,to t by the DC-DC conver extract Iy rer from the error mismatch between MPP of the PV array o er. The PI controller was used to from the DC he capacitor he PV array 11, 14]. As he capacitor utput power according to the following relation: Pin and Pout
Fig4.a: Boost with MPP block diagrams IGBTs at high frequency according to the varying duty cycle. The fast switching action of the boost converter decouples the dynamics of the PV array due its changes in voltage or current from that of the DC link capacitor, which offers good performance under changing weather conditions. The other advantage of using the boost converter is to increase the array voltage to higher levels suitable for grid interconnection. A phase locked loop was used to lock on the grid frequency in such a way that V, was set to zero [8]. If the grid voltage is relatively constant, Ig and I, can be used to control real and reactive power injections from the PV array. In order to inject real power from t PI controller to follow he inverter, Iy was controlled using a specified reference signal Ig REF; reactive power injection was set to zero and thus I, = 0, as displayed in Fig.(4.b). T link capacitor. A constant DC voltage across means that the power t matches the power going out to the inverter previously mentioned, was controlled to be the he Ig per Was extracted hat goes into it from t he input power Pj,to t by the DC-DC conver extract Iy rer from the error mismatch between MPP of the PV array o er. The PI controller was used to from the DC he capacitor he PV array 11, 14]. As he capacitor utput power according to the following relation: Pin and Pout
The samples of input wind speed and solar radiation are displayed in Fig. (5). 3-phase fault is applied on the feeders connecting the grid with the two PCC of the wind turbine
The samples of input wind speed and solar radiation are displayed in Fig. (5). 3-phase fault is applied on the feeders connecting the grid with the two PCC of the wind turbine
and PV array. This fault is initiated at 1.5 s and cleared after 100ms.Due to lack of space selected simulation results are displayed to summarize the system response under normal operation and for a 3-phase fault conditions.
and PV array. This fault is initiated at 1.5 s and cleared after 100ms.Due to lack of space selected simulation results are displayed to summarize the system response under normal operation and for a 3-phase fault conditions.
Fig. 6: Dynamic response of the grid variables (a) Voltage and current (b) active and reactive power Figure (6) shows the dynamic response of the grid voltage, current, active and reactive power. During the fault condition the current and power supplied by the grid are rapidly increased and return back to its normal value after fault clearing. Similarly, Fig. (7) Shows voltage, current, active and reactive power injected at wind-PCC. During the fault the voltage magnitude at wind-PCC is dropped to 0.75 pu and the injected wind power is consequently decreased.
Fig. 6: Dynamic response of the grid variables (a) Voltage and current (b) active and reactive power Figure (6) shows the dynamic response of the grid voltage, current, active and reactive power. During the fault condition the current and power supplied by the grid are rapidly increased and return back to its normal value after fault clearing. Similarly, Fig. (7) Shows voltage, current, active and reactive power injected at wind-PCC. During the fault the voltage magnitude at wind-PCC is dropped to 0.75 pu and the injected wind power is consequently decreased.
Fig.7: Dynamic response of wind energy conversion system variables at wind-PCC (a) Voltage and current (b) active and reactive power
Fig.7: Dynamic response of wind energy conversion system variables at wind-PCC (a) Voltage and current (b) active and reactive power
The instantaneous value of inverter phase voltage, inverter modulation index m, the DC-link capacitor voltage and the boost converter duty cycle are displayed in Fig. (9) for 3- phase fault at 5 km from PV-PCC. Similar system behavior is obtained for another case with the fault at 5 km from wind-PCC. This can be attributed to the short feeder lengths in micro-grids. As shown in Fig. (7,8), the generating units reached their stable state after tripping the fault. The simulation results validate the robustness of the control scheme for constant speed wind turbine and PV-MPP tracking. The DC link controller regulated the capacitor voltage at approximately 7000 V. The dc link voltage is varied around its set value due to the capacitive charging according to the available daily solar radiation and discharge during night. The modulation index of the VSI is controlled to adjust the magnitude of the instantaneous voltage at the PCC. The duty cycle is adjusted for MPP tracking of the available solar radiation.
The instantaneous value of inverter phase voltage, inverter modulation index m, the DC-link capacitor voltage and the boost converter duty cycle are displayed in Fig. (9) for 3- phase fault at 5 km from PV-PCC. Similar system behavior is obtained for another case with the fault at 5 km from wind-PCC. This can be attributed to the short feeder lengths in micro-grids. As shown in Fig. (7,8), the generating units reached their stable state after tripping the fault. The simulation results validate the robustness of the control scheme for constant speed wind turbine and PV-MPP tracking. The DC link controller regulated the capacitor voltage at approximately 7000 V. The dc link voltage is varied around its set value due to the capacitive charging according to the available daily solar radiation and discharge during night. The modulation index of the VSI is controlled to adjust the magnitude of the instantaneous voltage at the PCC. The duty cycle is adjusted for MPP tracking of the available solar radiation.
Fig.9: Dynamic response of power conditioning system variables for 3- phase fault 5 km from PV-PCC (a) instantaneous inverter voltage (b) modulation index (c) Dc-link voltage (d) duty cycle of boost converter.
Fig.9: Dynamic response of power conditioning system variables for 3- phase fault 5 km from PV-PCC (a) instantaneous inverter voltage (b) modulation index (c) Dc-link voltage (d) duty cycle of boost converter.
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Environmental SciencePhotovoltaic system
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