A new speed synchronization technique for a three PMSM

This paper deals with a speed synchronization technique for multi motors (three motors or more) systems which emphasizes minimizing synchronization error between the motors. Such synchronization is essential in electric vehicles with multi motor tracking systems. Synchronization techniques such as master reference, master slave, cross coupling and electronic virtual line shafting (EVLS) are well known. Master reference and master slave techniques are widely used in industries to minimize tracking error to a speed reference. Cross coupling and EVLS techniques are widely used in systems that focus on synchronization due to tightened coupling between motors. The cross coupling technique is only applicable for two motors systems while the EVLS is quite complex and it requires load inertia estimation. This paper offers a new speed synchronization technique where cross coupling is combined with master slave technique so that it could be applied for speed synchronization for three motors systems. PID controller which is tuned by the Ziegler Nichols method is used for speed control. The Routh criterion is used to find feedback gains for relative speed control between the motors, while hysteresis current control is used for control strategy and modulation technique. The proposed cross coupling-master slave (CC-MS) combined method has been evaluated through computer simulation using Matlab-Simulink
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. In the simulation, three permanent magnet synchronous motors (PMSMs)in a multi motors system are loaded by the same values of 9 Nm at different times. PMSM1 is loaded at 0 second until 0.9 second, PMSM2 is loaded at 0 second until 0.5 second, and PMSM 3is loaded at 0 second until 0.3 second. Simulation results show overshoot of 25%, peak time 0.01 second, settling time 0.05 second, with almost no synchronization error as long as the load is unchanged. When there is load change at one PMSM, steady state error occurs only during 0.03 seconds. It can be concluded that the proposed CC-MS combined method can be applied to a three motors system with good synchronization performance.