Comparative analysis of voltage and current source inverter topologies for standalone system

A three-phase inverter plays an important role in the standalone system. It converts the variable direct current (DC) input into alternating current (AC) output that can be fed into on-grid or off-grid for commercial or domestic usage. Three-phase inverters are classified into voltage source inverter (VSI) and current source inverter (CSI). VSI is commonly used in industrial due to its stable operation and low cost. However, VSI need to operate with an extra converter stage which is a DC-DC converter for the voltage boosting purposes. In contrast, CSI inherits voltage-boosting capability may become an alternative option to VSI with a DC-DC converter. Yet, there are not many research on CSI that dedicated on the voltage boosting capability. A three-phase inverter is knowingly work with control system to maintain the output voltage and frequency within the standard specification limits. However, the conventional voltage-controlled VSI and current-controlled CSI are not a straightforward comparison due to their different output-controlled parameters. A voltage-controlled CSI has been reported yet there is no recent work reported in comparing with a voltage-controlled VSI. Thus, this research focuses on comparing the voltage-boosting capability of CSI and VSI in both open-loop and closed-loop conditions. For closed-loop condition, a voltage-controlled is proposed for both inverters. The performance of VSI and CSI are simulated using MATLAB/Simulink.Three types of modulation techniques namely SPWM, THIPWM and SVM are implemented to investigate the voltage boosting capability feature of the inverters. Then, the same design of voltage-controlled synchronous frame PI control system is proposed for both VSI and CSI. Under open-loop steady-state operation, CSI has implicit its voltage boosting capability by providing a fundamental output that is on average 55% higher than VSI. Yet, CSI suffer high THD percentage as compared to VSI for the same switching frequency. This high THD shortcoming can be easily resolved by using a simple CL filter. Next, for closed-loop control system operation, VSI and CSI with voltage-controlled synchronous frame PI control system are proved to have good reference tracking and harmonic rejection and suitable to be implemented for household application or for a standalone system. Interestingly, CSI with voltage-controlled synchronous frame PI control system able to achieve a wider range of output due to the voltage boosting capability and provide a better quality of output waveform as compared to VSI. This research concludes that CSI has implicit voltage boosting capability that provides a fundamental output on average 55% higher than VSI and provide a better quality of output waveform. A comparative analysis of VSI and CSI in this research plays an important guidance in the selection of suitable inverter topology to fulfil industrial usage or off-grid application.