Three-level shunt power quality controller（SPQC）can be used to solve a variety of shunt power quality problems in three-phase four wire distribution system intensively. Three-leg and four-leg neutral point clamped（NPC）topologies have been widely used as the mainstream scheme but with the lack of reasonable choice in different scenarios. A unified topology is proposed

which can be used to guide the parameter optimization of different topologies

and realize the quantitative comparison of compensation performance. The inherent neutral point potential oscillation of three-level structure seriously affects the hardware security and compensation effect of the device. For different discrete topologies

the pulse width modulation（PWM）strategy is improved to minimize the neutral point potential oscillation in the time scale of each switching cycle

instead of the additional voltage balancing loop in the traditional control strategies.Finally

the simulation results verify the effectiveness of the theoretical results and the improved strategies.