Z-SOURCE INVERTER BASED BOOSTED VOLTAGE FLUX-WEAKENING CONTROL OF SPMSM

Abstract

This thesis gives a brief analysis of field-oriented control strategy for flux-weakening and maximum torque per ampere (MTPA) operation of permanent magnet synchronous motor (PMSM). Features such as higher efficiency, smaller size, faster dynamic response and large torque-to-inertia ratio makes the application of PMSM suitable for the electric vehicle (EV). However, because of permanent magnet on rotor, i.e., constant flux, permanent magnet (PM) motors have small constant power speed range (CPSR). This drawback limits the application of PMSM in EV’s where wide speed operation, above base speed, is required. The high-speed operation under constant power zone can be extended either by (1) increasing the output voltage of drive or (2) by using flux weakening control methods. However, the dc bus limits the output voltage of a conventional drive. Further, the high-speed operation, i.e., above base speed is limited by the voltage constraint from the drive side which is the maximum voltage a conventional inverter can output. Ultimately, this is in-turn depends on dc bus voltage rating and usually application like EVs has limited dc bus normally rated for 200 to 600 volts. That’s why in this thesis an advanced flux-weakening algorithm is introduced aimed for providing wide constant power operation namely, boosted voltage flux-weakening (BVFW), based on the Z-source inverter (ZSI). A ZSI has voltage boosting abilities and is immune to shoot-through issues. This flux-weakening strategy overcomes the voltage constraint in electrical drives fed from a conventional inverter by utilizing the voltage boosting ability of Z-source Inverter (ZSI) for a wide speed operation, i.e., above base speed. In comparison to other flux weakening control strategies, this method can provide wide constant power speed range (CPSR) with higher torque generation. Moreover, the maximum boost control method is also been discussed for controlling the shoot-through state of ZSI. In order to validate the feasibility and merits of the ZSI based flux-weakening algorithm, a SPMSM drive with MTPA and BVFW controls based on ZSI has been simulated in MATLAB/SIMULINK and its performance is compared with other conventional flux-weakening strategies.