A single-phase D-STATCOM inverter for distributed energy sources

Currently many utilities are resistant to the idea of increasing the penetration of distributed energy sources on distribution systems. The majority of distribution systems in the United States are radial and provide utilities with no communication or feedback on the low-voltage side of the substation. This makes the dynamic control of feeder lines very limited with time steps that are well above the variable power output of wind turbines and solar installations. This is in part due to the added technical difficulties associated with maintaining compliance with IEEE standards. This paper presents the design of a unique inverter with D-STATCOM capability for small to mid-sized (10kW-20kW) permanent magnet wind installations. The proposed inverter can actively regulate VARs on individual feeder lines at a programmable output while providing the variable output power of the renewable energy source. The aim is to provide utilities with distributive control of VAR compensation and power factor correction on feeder lines. The designed inverter utilizes a multi-level voltage-source converter (VSC) topology. Reactive power control is achieved by modulation index control. Active power control is achieved by phase-shift-angle control and VSC harmonics are eliminated by the optimized harmonic stepped waveform technique (OHSW). All simulations were done in MATLAB.