Proposal of a nine-switch inverter that can independently control amplitude and frequency for two loads

When two three-phase loads are controlled, two methods exsist. One is to provide two inverters to control two loads. The other is to connect two loads with one inverter in parallel. However, the former makes an experimental apparatus and a cost grow. On the other hand, the latter can not control two loads independently. Thus we propose a novel Nine-Switch inverter that can independently control two three-phase loads. In Fig. 1, the structure of the Nine-Switch inverter is shown. This inverter has nine switches and is made from combined two threephase inverters with three common switches. One is configured with switches UH, VH, WH, UM, VM, WM, the other is configured with switches UM, VM, WM, UL, VL, WL. The upper inverter is called Inv1, and lower is called Inv2 in the following. Gate signals for the swiches are generated from PWM modulation shown as in Fig. 2. UL, VL, WL are closed when Inv1 is driven, and UH, VH, WH are closed when Inv2 is driven because of this carrier wave form. A simulaton is carried out to verify the validity of the proposed inverter. In this simulation, different reference is imposed to each inverter. The reference for Inv1 is a three-phase sin wave of amplitude 10 [V] and frequency 320 [Hz], and the reference for Inv2 is a three-phase sin wave of amplitude 10 [V] and frequency 640 [Hz]. A three-phase LR load is connected with each inverter. A value of resistance is 47 [Ω] and inductance is 15000 [μH]. In Fig. 3, the simulation result is shown. To verify the simulation result, an experiment is conducted. Parameters of the experimental system are set as same as the simulation case. In Fig. 4, the experimental result is shown. This result is almost similar to the simulation result. Thus it can be confirmed that the proposed inverter works correctly.