The steady frequency three-phase AC can be changed into the AC which frequency is continuously adjusted in the experiment unit composed of rectifier, inverter, control circuit, and relay safeguard circuit.

• SPWM三相变频实验单元能够把频率固定的三相交流电变换成频率连续可调的三相交流电，它主要包括交直变换、逆变、控制和继电保护电路。