Discrete Resonant Control for wide frequency range operation of power converters

Proportional Resonant Control (PRC) is a well-known control technique applied on ac systems in order to ensure zero steady state error for sinusoidal references. However, this control technique is not suitable to operate in a variable frequency environment, which is typically found on weak micro grids and aircraft systems. Once the controller is designed, the resonant frequency is fixed, and therefore no zero steady state error can be ensured under operating frequency fluctuations. This paper extends the resonant control approach to operate in a larger frequency range in order to be applied in power inverters and achieving zero steady state error. A back-to-back topology case is studied, connected to a distorted supply (with variable frequency) feeding a critical load. The load-connected to the back-to-back topology- requires a given frequency and amplitude voltage which is easily achieved if the grid side converter successfully regulates the dc link voltage. In addition, a desired power factor at the point of common coupling can also be imposed. The approach is based in a discrete implementation of the PRC, where its resonant frequency tracks the grid frequency, independently of grid frequency variations. This issue is mathematically demonstrated and tested with accurate results.