DC-link voltage Control for a Three-Phase Active Infeed Converter with Power Decoupling Circuit

Reducing the DC-link capacitance of a voltage source converter (VSC) by means of an active power decoupling circuit - also known as power pulsation buffer (PPB) - affects the structure of the voltage control loop. In this paper a three-phase two-level IGBT converter in conjunction with a shunt type PPB based on a bidirectional SiC buck/boost converter is investigated. Measured DC-load current and calculated AC-grid instantaneous power are used as feed-forward variables to improve the transient performance while reducing the PPB loading. Hence the system can handle DC-load steps in the range of its nominal current without experiencing large voltage excursions. Combining both IGBT and SiC technology reflects in the actuators individual dynamic behavior which is justified by a factor of 16 in switching frequency. Although the PPB actuator serves as the main contributor directly after the load-step time instant, the VSCs dynamic is of major importance for long term stability and PPB auxiliary capacitor sizing. The system analysis presented here gives an elementary insight in designing the voltage controllers and shows the dependencies between both VSC and PPB actuator while stabilizing the DC-link voltage. Small signal transfer function for the VSC actuators is evolved and used in the design process. Averaging modelling technique is adopted to verify the proposed control scheme.