To assure the effective performance of controller over wide range of system operations and to increase the transient stability of the system, a supplementary fuzzy logic controller (FLC) based on the Mamdani's fuzzy inference method is designed for the PI controller input. FLC generates the required small change for voltage to control the magnitude of the injected voltage. The centroid defuzzyfication technique is used is this fuzzy controller.
The below fig describes the FLC structure. In this case, a two–input, one–output FLC is considered. These two inputs will be evaluated using a fuzzy logic-based control algorithm and an output signal is produced. The input signals are voltage error and rate of change of voltage error and the resultant output signal is the voltage for PI controller. By employing Fuzzy Controller the ripples are reduced to a great extent even when the χvalue is selected above 23. Sinusoidal tracking is even more accurate with the addition of fuzzy controller into the system. Fig.8. Fuzzy logic controller structure There are two linguistic variable for each input variable, including, “Positive” (P), and “Negative” (N). For the output variable there are three linguistic variables, namely, “Positive” (P), “Zero” (Z) and “Negative” (N). Fig. (8a) Membership function of input 1 (error voltage) Fig.(8b) Membership function of input 2 (rate of change in error voltage) Fig.(8c) Membership function of output The rules used for the FLC are chosen as follows: If o is P and d is P, then m is P. If o is P and d is N, then m is Z. If o is N and d is P, then m is Z. If o is N and d is N, then m is N. SIMULATION RESULTS AND DISCUSSION The first two tests are used for verifying whether the condition of χ is efficient to accommodate the inverter to different operating conditions. The last two tests confirmed that the proposed voltage regulator is possible to achieve tight regulation in the PCC bus voltage. (Test 1) Adapt System Damping to Source Impedance When source impedance changes in a PV system, the PCC bus voltage will not be constant and is inclined to disturbance, which not only intrudes with SPLL performance but also decays the current response. When two response curves between Figs 9 and 10 are …show more content…
(χ = 27, Kp= 3.2516, b = 2134.7; χ = 16.5, Kp= 2.1180, b = 1365.2.)
Fig.10. System responses of Test 1 (L = 10.0 mH, vdc = 450 V, i∗=0.333 pu) when there is a step change in χ from 25.5 to 16. (χ = 25.5, Kp=3.0894, b = 2024.7; χ = 16, Kp= 2.0642, b = 1328.6.)
B. (Test 2) Adapt System Damping to Solar Irradiation
When solar irradiation increases, the PV array would equip the PV inverter with more voltage.The output current of the PV inverter should be increased to acquire more power from the PV array. To relieve the tracking error for the high-irradiation case, a high value of χ compared to Test 1 should be taken up. The best method to decrease the current deviation is to alter χ to decline the control gains to adapt PV inverter to the changed solar irradiation. The consequence of altering χ to the changed solar irradiation is shown in Figs. 11 and 12, which confirms that χ has prominent influence on the current response.
Fig.11. System responses of Test 2 (L = 0.0 mH, vdc= 550 V, i*= 0.5 pu) when there is a step change in χ from 27.0 to 18.7. (χ = 27, Kp=3.2516, b = 2134.7; χ = 18.7, Kp= 2.3552, b =
The below fig describes the FLC structure. In this case, a two–input, one–output FLC is considered. These two inputs will be evaluated using a fuzzy logic-based control algorithm and an output signal is produced. The input signals are voltage error and rate of change of voltage error and the resultant output signal is the voltage for PI controller. By employing Fuzzy Controller the ripples are reduced to a great extent even when the χvalue is selected above 23. Sinusoidal tracking is even more accurate with the addition of fuzzy controller into the system. Fig.8. Fuzzy logic controller structure There are two linguistic variable for each input variable, including, “Positive” (P), and “Negative” (N). For the output variable there are three linguistic variables, namely, “Positive” (P), “Zero” (Z) and “Negative” (N). Fig. (8a) Membership function of input 1 (error voltage) Fig.(8b) Membership function of input 2 (rate of change in error voltage) Fig.(8c) Membership function of output The rules used for the FLC are chosen as follows: If o is P and d is P, then m is P. If o is P and d is N, then m is Z. If o is N and d is P, then m is Z. If o is N and d is N, then m is N. SIMULATION RESULTS AND DISCUSSION The first two tests are used for verifying whether the condition of χ is efficient to accommodate the inverter to different operating conditions. The last two tests confirmed that the proposed voltage regulator is possible to achieve tight regulation in the PCC bus voltage. (Test 1) Adapt System Damping to Source Impedance When source impedance changes in a PV system, the PCC bus voltage will not be constant and is inclined to disturbance, which not only intrudes with SPLL performance but also decays the current response. When two response curves between Figs 9 and 10 are …show more content…
(χ = 27, Kp= 3.2516, b = 2134.7; χ = 16.5, Kp= 2.1180, b = 1365.2.)
Fig.10. System responses of Test 1 (L = 10.0 mH, vdc = 450 V, i∗=0.333 pu) when there is a step change in χ from 25.5 to 16. (χ = 25.5, Kp=3.0894, b = 2024.7; χ = 16, Kp= 2.0642, b = 1328.6.)
B. (Test 2) Adapt System Damping to Solar Irradiation
When solar irradiation increases, the PV array would equip the PV inverter with more voltage.The output current of the PV inverter should be increased to acquire more power from the PV array. To relieve the tracking error for the high-irradiation case, a high value of χ compared to Test 1 should be taken up. The best method to decrease the current deviation is to alter χ to decline the control gains to adapt PV inverter to the changed solar irradiation. The consequence of altering χ to the changed solar irradiation is shown in Figs. 11 and 12, which confirms that χ has prominent influence on the current response.
Fig.11. System responses of Test 2 (L = 0.0 mH, vdc= 550 V, i*= 0.5 pu) when there is a step change in χ from 27.0 to 18.7. (χ = 27, Kp=3.2516, b = 2134.7; χ = 18.7, Kp= 2.3552, b =