Parallel operation of series-connected PWM voltage regulators without control interconnection

A novel current-sharing control scheme is presented that can parallel opera te multiple series-connected pulse-width modulation (PWM) voltage regulator s (VRs) directly with no control interconnection The current-sharing contro l is dedicated for both fundamental and harmonic components. The fundamenta l current-sharing is controlled by the Q-V droop and P-delta shift scheme. while the harmonic current sharing is controlled by the resistive droop sch eme. Both schemes have the feature of no real impedance connection between the VR and the load. Instead. the required impedance for executing both sch emes is simulated in the control circuits. As a result, the VRs are tightly connected and thus have a lower output impedance. Other features include a ccurate voltage regulation, low voltage distortion and tolerance for parame ter mismatch. Two 1kV prototype capacitor current-controlled single-phase V Rs with three-arms rectifier-inverter topology are designed and implemented , The effectiveness is demonstrated by some experimental results.