This paper presents an enhanced Flux Weakening (FW) control scheme for Permanent Magnet Synchronous Motors (PMSMs), focused on electric vehicle applications. The novelty of the proposed algorithm is the integration in a unified scheme of both the accelerator pedal as torque reference and the cruise speed limiter (CSL) as speed limit, without interfering between them until this limit is achieved. The dq-axis current references are calculated from the proposed algorithm by using a polar coordinate system and a per-unit system. The latter is based on the characteristic machine parameters which aim to ease and simplify the algorithm implementation. Moreover, it takes advantage of the smooth transition between the Low Back Electromotive Force (LBEF) zone and the FW zone thanks to a voltage loop which changes the current-vector angle. Another fundamental merit of the proposed scheme is its capacity to work in all the dq-plane throughout the Maximum Torque per Ampere (MTPA), Constant Torque (CT), Current and Voltage Limit (CVL), Maximum Torque per Voltage (MTPV) and Constant Speed (CS) strategies without switching the algorithm. Simulations and experimental results from a real exterior-rotor Interior Permanent Magnet Synchronous Motor (IPMSM) direct-drive emotorbike verify the effectiveness of the proposed method.
This article reviews Flux-Weakening (FW) algorithms for Permanent Magnet Synchronous Machines (PMSMs), focusing on the automotive sector, especially in electric and hybrid electric vehicles. In the past few years, the spread of Electric Vehicles (EVs) has improved the technology of electric machines and their control to achieve more compact and competitive solutions. PMSMs are the most widespread electric machines used in EVs thanks to their high-power density and potential operation at constant power range during high speed. Such high speed implies a high electromotive force. An FW technique is mandatory to reduce the electromagnetic flux generated by the electric machine due to the voltage limits of the traction inverter and the energy source. This article classifies and analyses the state-of-the-art FW control strategies by comparing their main advantages and drawbacks. The Vector Current Control (VCC) method that regulates the modulus of the applied voltage is the most common one in the literature thanks to i) its robustness to parameter modification and model unsureness, ii) low computational complexity, and iii) high dynamic response and control stability.
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