A Novel Approach for Dc Balancing in Three-Level Neutral Point Clamped Inverter Based Statcom

Achieving stable DC bus voltage across the splitcapacitor bank presents a significant technical hurdle in threelevel Neutral Point Clamped (NPC) inverters, particularly within grid-connected applications link Static Synchronous Compensators (STATCOMs), where rapid dynamic response and high power quality is considered essential. The unbalance in the split DC-link capacitors often tends to result in neutral point voltage drift, delivering distorted output voltages, increased stress on devices, instability in system operation, voltage shifting onto one capacitor and even affects STATCOM functionalities resulting in degraded reactive power control. This paper presents a novel approach for mitigating DC bus voltage unbalance in a threelevel Neutral point clamped inverter based STATCOM. Unlike traditional methods which solely rely on passive balancing, this method efficiently balances the DC link voltages by modifying the reference in response to the unbalance occurred. A simple but efficient algorithm has been realised to analyze the unbalance and suitably alter the reference so as to balance the voltage in the series connected DC link Capacitors. The method has been implemented and has been validated in a 50kVAR STATCOM system. Results demonstrate better regulation in voltage on implementating the algorithm