Optimized Design of Stationary Frame Three Phase AC Current Regulators

Abstract

Current regulation plays an important role in modern power electronic AC conversion systems. The most direct strategy to regulate such currents is to use a simple closed loop proportional-integral (PI) regulator, which has no theoretical stability limits as the proportional and integral gains are increased, since it is only a second order system. However, pulsewidth modulation (PWM) transport and controller sampling delays limit the gain values that can be achieved in practical systems. Taking these limitations into account, this paper presents an analytical method to determine the best possible gains that can be achieved for any class of practical linear AC current controller. The analysis shows that the maximum possible proportional gain is determined by the plant series inductance, the DC bus voltage and the transport and sampling delays, while the maximum possible integral gain is determined primarily by the transport and sampling delays. The work is applicable to stationary frame PI regulators, stationary frame controllers with back electromotive force compensation, stationary frame P+ resonant (PR) controllers, and synchronous <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> frame controllers, since they all have identical proportional and integral gains that must be optimized for any particular application.