Controlling inverters to maintain total harmonic distortion of output voltage and current

摘要

The total harmonic distortion (THD) of the output voltage and output current of an inverter is maintained within required ranges simultaneously. The inverter output voltage, the current from/to the grid and the grid voltage are measured and a control signal is generated to be converted into pulse-width-modulation signals to drive the inverter switches. The controller consists of a current outer loop and a voltage inner loop. Both the inner-loop and outer-loop controllers have an internal model having high gains at the fundamental and all harmonic frequencies of interest. The difference of the current reference and the current from/to the grid is fed into the outer-loop current controller and the output of the first internal model is fed into a transfer function block, of which the output is added onto the grid voltage to generate the voltage reference for the inner-loop controller. The difference of the voltage reference and the inverter output voltage is then fed into the internal model of the inner-loop voltage controller, of which the output is fed into another transfer function block to generate the control signal for the inverter, which is then converted into pulse-width-modulated signals to drive the inverter switches.