Current control of permanent magnet synchronous machines. Experimental and simulation study

The control structure of a PWM (pulsewidth modulation) inverter-fed sinusoidal synchronous motor commonly includes two or three current control loops. Previous simulation studies have shown that the three-loop structure should be preferred: hence the neutral-point voltage can move freely. To obtain the same results with the two-loop structure, a more complex control variable limitation strategy is compulsory. However, the three-loop structure is very sensitive to imperfections in the control system (gain errors and offsets). Simulation and experimental results for both structures are compared and the influence of a neutral-point voltage (NPV) feedback loop to cancel homopolar errors in the three-loop structure is discussed