Design and control of a 10kw three-phase grid-tied back to back inverter

Abstract

Inverters in back to back (B2B) connection are utilized to convert the voltage and frequency of the power source to another format. Typical application of inverters is the wind power system. This study presents a B2B inverter for equal voltage and frequency format conversion in which one inverter works to get power from the grid to charge the DC capacitor and another inverter returns most of the active power back to the grid and retain a few powers to maintain the DC-link voltage. The power grid affords only the power loss of the inverters, which benefits the test of the inverter rated above 10kW under general distribution line. A proportional-resonant (PR) controller in a stationary frame in place of a proportional-integral (PI) controller in a synchronous frame was adopted to condition the B2B inverter AC current for grid connection due to the advantages such as instantaneous tracking capability as well as low-cost computational resources. To mitigate the startup transient for grid connection, the instantaneous grid voltage was feedforwarded to the inverter voltage command. The B2B inverter was run according to the proposed control strategy under various conditions such as the reactive power control and the active and reactive power controls. Experimental results show that the power returns to the power grid is close to originally put in and the proposed B2B inverter can be tested under the distribution line with the power capability over 10kW.