The development of power electronics technology gives ample of opportunity for the grid integration of renewable in an efficient way. Commonly pulse width modulated voltage source inverter is widely used for this purpose. The control technique of grid integrated inverters plays a major role for the reduction of harmonic and improvement of power quality in the system. The most commonly used current control technique for the control of the inverter is hysteresis current controller strategies. But the main drawback hysteresis current controller is the uneven switching frequency and higher harmonic distortion. In this paper a hysteresis current controller with offset band for three phase grid integrated pulse width modulated voltage source inverter has been implemented for considerable reduction of harmonic distortion and better power quality. The MATLAB-Simulink environment is used to model, study and simulate the system.
- Hysteresis Current Controller (HCC)
- Total Harmonic Distortion (THD)
- Pulse width modulated voltage source inverter (PWM VSI))
Fig. 1. Overall Block diagram for three phase grid connected PWM-VSI
EXPECTED SIMULATION RESULTS
Fig. 2. Result of (a) DC Link Voltage (b) Grid voltage (c) grid current
Fig. 3. Grid current and reference current during change in load
Fig. 4 Current Error for HCC
Fig. 5. Active Power of load during change in load
Fig. 6. Reactive Power of load during change in load
Fig. 7. Result for HCC in steady state condition (a) DC link voltage (b) grid voltage (c) Grid current (d) THD
Fig. 8 Result of three phase grid current for HCC with offset band
Fig. 9 Grid current and reference current during change in load
Fig. 10. Current Error for HCC with offset
Fig. 11. Zero state of the inverter
Fig. 12. THD for HCC with offset band
The HCC with offset scheme is implemented to achieve lower THD and power quality improvement of the three phase grid connected PWM-VSI. The result obtained from simulation is compared with HCC system. The result reveals that the HCC with offset scheme has lower THD i.e. 2.10% as compared to HCC which is 3.22% and also the average switching frequency is less due to the zero level in the inverter output voltage. The another advantage of HCC with offset scheme is, average value of the current error is smaller as compared to HCC which can be verified by comparing the result of current error of both the schemes. It implies the power quality is superior in case of HCC with offset band.
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