Independent vector control of two permanent magnet synchronous motors fed by a four-leg inverter

This paper proposes the independent drive system of two permanent magnet synchronous motors (PMSMs) fed by a four-leg inverter (4LI) with vector control method. The 4LI consists of four legs and two capacitors connected in a series. There are independent speed and position controls of two PMSMs fed by a 4LI with vector control, but there are known to have several disadvantages. First, the pulse width modulation (PWM) technique in three-phase voltage source inverter (VSI) is not directly applicable for the 4LI because only two phases must be modulated. Second, the characteristics of speed and position drive are unstable when the voltage drift of neutral point of the two capacitors is happened. This paper shows the expanded two-arm modulation to obtain balanced three-phase AC voltage. Also, this paper proposes the compensation method for voltage of two-split capacitors. Next, the independent speed drive of two PMSMs fed by the 4LI with the vector control system is demonstrated by the experimental results. Besides, the independent position drive of two PMSMs fed by the 4LI with the vector control system is demonstrated by the simulation results.