Online loop gain monitoring technology for power converters in weak grids

Abstract

Under the weak grid condition, the grid-connected inverter is very easy to cause control system instability due to the insufficient control bandwidth, so stability monitoring is extremely important to ensure the healthy and stable operation of the inverter. In this paper, a scheme is adopted to measure the control bandwidth and phase angle margin of the grid-connected inverter for microgrid online. The scheme is based on Middlebrook's loop gain measurement technique and is applicable to any control loop of a microgrid power converter. The basic idea of the method is to inject small signals into the inverter's control loops of current and voltage to be measured, measure its loop gain, and then obtain real-time control bandwidth and phase angle margin information. This paper describes in detail the theoretical analysis, as well as the specific parameter design method. In order to verify the correctness of the theoretical analysis, a Simulink simulation model is used, thus proving that the online measurement method has good performance and can be extended to all the common linear control loops of power converters.