Three phase inverter grid voltage feed forward method under unbalanced operating conditions

A method for controlling a grid-connected three phase reactive power compensation inverter to counteract unbalanced grid voltage conditions, said method comprising:

• receiving, by an inverter controller, inputs including measured three phase grid voltage signals and measured three phase grid-inverter current signals from sensors, and direct and quadrature reference current signals;
• computing, using a processor in the inverter controller, predictive feedforward voltages from the measured grid voltage signals, including converting three phase grid voltages to positive sequence direct and quadrature components for each measurement sample, and computing direct and quadrature predictive feedforward voltages for a next control cycle based on two measurement samples from a previous control cycle, where the measurement samples are taken at a time at an end of the previous control cycle at a time 75% through the current control cycle;
• performing, using the processor, control calculations using a decoupled double synchronous reference frame (DDSRF) algorithm, where the DDSRF algorithm uses the predictive feedforward voltages along with the measured and reference current signals as inputs, and the DDSRF algorithm produces a two phase alpha-beta (αβ) reference voltage signal as output;
• converting the two phase αβ reference voltage signal to switching commands using a Space Vector pulse width modulation (PWM) algorithm;
• and
• providing the switching commands to a switch driver board in the inverter to control operation of bridge arm power switches in the inverter, where the switching commands cause the inverter to counteract the unbalanced grid voltage conditions by providing a different current amplitude to each grid phase.

A controller for controlling a grid-connected three phase inverter to counteract unbalanced grid voltage conditions, said controller comprising:

• a processor configured in accordance with a set of non-transitory instructions stored within a memory associated with the processor to:
• receive inputs including measured three phase grid voltage signals and measured three phase grid-inverter current signals from sensors, and direct and quadrature reference current signals;
• to perform control calculations using a decoupled double synchronous reference frame (DDSRF) algorithm, where the DDSRF algorithm uses predictive feedforward voltages along with the measured and reference current signals as inputs, and the DDSRF algorithm produces a two phase alpha-beta (αβ) reference voltage signal as output, where the predictive feedforward voltages are computed by the processor from the measured grid voltage signals, including converting the measured three phase grid voltages to positive sequence direct and quadrature components for each measurement sample, and computing direct and quadrature predictive feedforward voltages for a next control cycle based on one or more measurement samples from a previous control cycle;
• and
• a duty cycle controller operably associated with and configured to control a plurality of inverter switches based on the two phase αβ reference voltage signal.