**7. Conclusion**

134 Electrical Generation and Distribution Systems and Power Quality Disturbances

constant in modified ramp type current controller, delta modulator as limited switching frequency. Switching frequency is varying more with hysteresis band in hysteresis current controller. Modified ramp type current controller is giving good system power factor

Vector control of grid connected voltage source inverter is implemented in MATLAB/simulink. Simulation results are obtained for different current controllers. The discussion of the results as follows: vector control in virtual grid flux oriented reference frame is having an capability to decouple the active and reactive powers flowing into grid, which we can seen from the waveforms of active and reactive powers for three current controllers. Reactive power flowing into grid is almost zero in all the controllers to ensure unity power factor operation of grid. Total harmonic distortion of three current controllers is as follows 1. For hysteresis current controller percentage of THD is 4.41 2. For current regulated delta modulator percentage of THD is 4.74 and 3. For modified ramp type current controller percentage of THD is 2.68. Among all the current controllers modified ramp type current controller is having fewer harmonics in grid current, which ensures fewer ripples in three phase active power following into grid, and current regulated delta modulator having more harmonics in grid current which leads to more ripple is three phase active power following into grid. The switching frequency of modified ramp type current controller is 2 KHz it is a constant value at its ramp generator frequency. In Current regulated delta modulator switching frequency is limited to 2 KHz, but the variation of frequency with in fundamental period cannot be controlled. In hysteresis current controller the switching frequency is varies with load parameters and hysteresis band, switching frequency when hysteresis band 20 is equal to 2.72 KHz. Form the above discussion modified ramp type current controller has constant switching frequency. The power factor by using modified ramp type current controller is very good then compared to other current controllers. The following table 1 shows the switching frequency, THD, power factor for three current

Current control THD Switching frequency Power factor

Hysteresis 4.41 2.72 KHz 0.9989

Delta modulator 4.74 2 KHz 0.9973

Modified ramp type 2.68 2 KHz 0.9996

Table 1. Comparison of three current control techniques of grid connected VSI

compared to other controllers.

**6. Discussion** 

controllers.

Analysis of different current control techniques for synchronous grid flux oriented control of grid connected voltage source inverter is presented in this chapter. For effectiveness of the study MATLAB/simulink is used here in GUI environment. Vector control in grid flux oriented reference frame is having capable of decoupling active and reactive powers following into grid, which we could see form figures of active and reactive powers for three current controllers. Reactive power following into grid is zero for all current control techniques to ensure the grid at unity power factor operation. There is a slight variation in power factors of three current controllers which is due to variation of percentage of THD in three current controllers. The DC link voltage is maintained at 2200V which is the set value of DC link voltage by using DC link voltage controller which controls the active current reference flows in the grid. The total harmonic distortion is less in modified ramp type current controller compared to other two current controllers. The switching frequency of modified ramp type current controller is maintained at 2 KHz which decreases the switching losses of power semiconductor devices compared to other current controllers where the switching frequency varies with load parameters. There is a less ripple in three phase active power for modified ramp type current controller compared to other two current controllers. Form the above discussion modified ramp type current controller is more advantages then other two current controller in grid connected voltage source inverter.
