An effective voltage control loop for a deep flux-weakening in IPM synchronous motor drives

An interior permanent magnet synchronous machine drive exhibits an inherent wide speed range capability. In order to exploit this peculiar characteristic while assuring the lowest power losses, a proper control algorithm has to be used. In particular, as long as the required voltage is below the limit imposed by the available DC bus, the control algorithm must command the maximum torque per ampere operation ensuring the minimum copper losses and in turn the maximum efficiency. If the voltage limit is reached, the flux of the permanent magnets has to be weakened to exploit the whole speed range of the machine while keeping a stable operation. For machines having a short circuit current within the current limit, the maximum torque per voltage locus has to be tracked to reach the maximum speed. A novel voltage control loop able to drive the machine in all the aforementioned working conditions is presented in this work. This is combined with a field oriented current control and it determines the two current references to govern the drive operations. The result is a motor drive able to operate the machine in compliance with current and voltage rating constraints without speed limits. Additional merits of the proposed scheme are the ease of implementation and the simple design. The effectiveness of the proposed control algorithm is verified through simulations and experimental tests.