PWM Voltage Actuator
Digital current controllers are used in grid-side inverters, generator-side inverters, electrical drives, and many other applications. Their purpose is to control the electrical current injected into the grid or the electrical current supplied to the windings of an electrical machine. Desired goals include quick and accurate suppression of any errors between the desired current, also called the current reference, and the actual current obtained from the current sensors. Ideally, digital current controllers should provide the means for an error-free tracking of the current reference profiles even in the presence of the input disturbances (i.e., sudden changes of the reference) and the voltage disturbances (sudden changes of the line voltages, back-electromotive forces, and similar). The driving force in current controllers is the voltage supplied to the load, wherein the load could be either the LCL filter in grid-side inverters or the ac machine stator winding in electrical drives. In essence, the current controller uses the current error to calculate the required voltage that would drive detected error back to zero. The controller outputs such voltage as a signal called the voltage reference. It takes the voltage actuator to generate the actual voltage that corresponds to the voltage reference. In other words, the voltage actuator is an amplifier that turns the voltage reference signals into power circuit voltages.