Variable Flux Permanent Magnet Synchronous Machines Research Articles

Torque Pulsation Reduction During Magnetization in Variable Flux Machines

This paper proposes two methods to minimize the pulsating torque during magnetization in a variable flux - permanent magnet synchronous machine (VF-PMSM). The VF-PMSM is demagnetized and remagnetized by injecting a current pulse to achieve the high speed and high torque requirements. During demagnetization and remagnetization, a d – axis current pulse is injected to change the magnetization state (MS). These MS changing current pulses will change the magnet flux linkage based on the amplitude of the pulse. However, the injected d – axis current abruptly changes the magnet torque as well as reluctance torque and results in a pulsating torque. Since the remagnetization current is much higher than the machine rated current, the pulsating torque is more severe during the remagnetization process. Thus, it is preferred to magnetize the magnet at zero speed and unloaded conditions. To solve this problem, a q – axis current reference during the remagnetization is determined by two different methods: voltage limit method and load torque method. The derived q – axis current reduces the torque pulsation during the remagnetization. The effectiveness of the proposed scheme is experimentally verified on a manufactured VF-PMSM prototype.

Design, modelling and analysis of a hybrid-magnet variable-flux PMSM with variable series-parallel magnetic circuit

Variable-flux permanent magnet synchronous machines (PMSMs) which use low-coercive-force permanent magnets have gained a lot of attention as a perspective alternative in the variable-speed driving application for their advantages of operating with improved efficiency in higher speed through adjusting the variable-flux PMSMs’ magnetization states. A hybrid-magnet variable-flux machine which has the variable series-parallel magnetic circuit is investigated. Magnetization state and magnetic circuit type of this variable-flux PMSM are adjustable. This machine’s equivalent magnetic circuit (EMC) model at different magnetization states is established and evaluated. This model can precisely represent the complicated and changeable magnetic circuit in variable-flux PMSMs and provide an effective way for the operating principle and performance analysis. The electromagnetic performances are investigated in detail. The magnetization state variation’s range is wide. Magnetizing/demagnetizing current is small. By fully using reluctance torque, variable-flux PMSM’s torque ability improves greatly. The ratio of high efficiency area in total torque-speed operating area increases obviously. The efficiency during high speed operation also increases. This machine has advantages and overcomes limitations of variable-flux machine which has series magnetic circuit or parallel magnetic circuit.

Study of a High-Efficiency Series–Parallel-Connected Hybrid-PM Variable-Flux Permanent Magnet Synchronous Machine

Variable-flux permanent magnet synchronous machines (PMSMs) are considered as a promising candidate in electric vehicle industry for their ability to operate in a wide speed range with high efficiency by manipulating the magnetization state dynamically. A novel high-efficiency series–parallel-connected hybrid-PM variable-flux PMSM is proposed in this article. The topology and operating principle are introduced. The performances, including magnetization/demagnetization ability, PM stability, and torque ability, are analyzed and compared with other hybrid-PM variable-flux PMSMs. The results show that the proposed machine retains the advantages and overcomes the limitations of the existing structures. The steady-state efficiency-maximizing magnetization state adjustment strategy is proposed and evaluated. The torque-speed range is expanded and the proportion of high-efficiency region increases obviously by using this strategy. The efficiency-maximizing magnetization state adjustment strategy considering magnetization state adjustment loss is proposed and evaluated with the worldwide harmonized light vehicles test cycle (WLTC). The efficiency during the whole driving circle is significantly improved by adopting the proposed strategy.

Permanent Magnets Aging in Variable Flux Permanent Magnet Synchronous Machines

Permanent magnet synchronous machines (PMSMs) operation above base speed is typically achieved by injecting negative d -axis current to produce flux weakening. However, this mode of operation increases copper, stator/rotor core, and permanent magnet (PM) losses, penalizing the efficiency and increasing the risk of demagnetization. Variable flux PMSMs in which PMs are magnetized/demagnetized during normal operation of the machine have been proposed to avoid the use of flux weakening current. However, PM aging due to magnetization/demagnetization cycles has not been thoroughly studied yet. This article analyzes the variation of NdFeB, SmCo, and AlNiCo PMs properties, including magnetic, electric, and thermal, resulting from magnetization/demagnetization cycles.

Analysis of Magnetic Properties of AlNiCo and Magnetization State Estimation in Variable-Flux PMSMs

Variable-flux permanent-magnet synchronous machines have gained a lot of attention for their ability to expand the speed range and reduce loss over an electric vehicle drive circle by manipulating magnetization state (MS) dynamically. In this paper, a combined-magnet-pole variable-flux machine (CMP-VFM) using both AlNiCo and NdFeB is analyzed. To obtain the variation laws of MS quickly and precisely, a 3-D neural-network hysteresis model of AlNiCo is proposed, and the accuracy and time consumption of the proposed neural-network hysteresis model are evaluated. In order to optimally utilize the speed expansion and loss minimization capability with precise MS control, a flux observer based on model reference adaptive theory is proposed for the closed-loop flux control of CMP-VFM and validated by simulations. The simulation results prove that the accuracy of the proposed adaptive flux observer is almost not affected by parameter disturbance.

A Novel Variable-Flux Permanent-Magnet Synchronous Machine With Quasi-Series Magnet Configuration and Passive Flux Barrier

Variable flux permanent magnet synchronous machine (VF-PMSMs) has drawn considerable attention due to the capability of operating in a wide speed range with overall high efficiency. The conceptual machine firstly proposed employs AlNiCo magnets characterized by low H c and (BH) max as sole magnetomotive force (MMF) source [1]. Various topologies have been further developed to enhance the torque density by employing both low coercive-force PMs (AlNiCo) and high coercive-force PMs (NdFeB) [2], [3]. The magnet configuration could be classified to parallel configuration and series configuration, as shown in Fig. 1 (a) and (b). In parallel configuration, part of MMF generated by NdFeB magnets exerts on AlNiCo magnets, which leads to low working point and even unintentional demagnetization of AlNiCo magnets under on-load operation. Preceding defects could be avoided in series configuration due to the support of NdFeB magnets to AlNiCo magnets, but several times of demagnetizing current are required to fulfill the demagnetization process and the magnetization state variation range is usually limited. In this paper, a topology of VF-PMSM with quasi-series magnet configuration and passive flux barrier is proposed, which exhibits both advantages of high torque density of series configuration and easily achievable demagnetizing current of parallel configuration.

Enabling Driving Cycle Loss Reduction in Variable Flux PMSMs Via Closed-Loop Magnetization State Control

Variable flux permanent magnet synchronous machines (VF-PMSMs) have recently been proposed to reduce driving cycle losses in electric vehicle traction motors via magnetization state (MS) manipulation. This paper presents a closed-loop MS control method to enable reliable loss minimization control of VF-PMSMs. The MS is estimated at every sample instant and is used as a feedback for closed-loop control. Under most circumstances, the proposed method maintains precise torque control even during the MS manipulation transient by using a deadbeat-direct torque and flux control (DB-DTFC) framework. The state-of-the-art high-speed flux trajectory generation method for MS manipulation is integrated in the new closed-loop method to allow MS manipulation up to the maximum speed within the inverter voltage limit. The effectiveness of the proposed methods, in terms of driving cycle loss reduction capability and its thermal impact, is evaluated experimentally by emulating the road load using the dynamometer load motor.

Variable Flux Permanent Magnet Synchronous Machine (VF-PMSM) Design Methodologies to Meet Electric Vehicle Traction Requirements with Reduced Losses

Variable flux permanent magnet synchronous machines (VF-PMSMs) in which the magnetization state of low coercive force permanent magnets can be actively controlled to reduce losses in applications that require wide-speed operation have been proposed recently. While prior focus has been on achieving magnetization state manipulation without oversizing the inverter and obtaining higher torque capability, this paper extends the design objectives to include the power requirements of an electric vehicle traction motor over its entire speed range. Finite-element methods are used to study the effect of combinations of low coercive-force and high coercive-force permanent magnets arranged in either series or parallel on the performance of VF-PMSMs. While both configurations help improve the torque density, only the series configuration can help improve the high speed power capability. Experimental results showing the variable magnetization state property, torque-speed capability, and loss reduction capability of a series magnet configuration VF-PMSM test machine are presented.

Magnet Temperature Effects on the Useful Properties of Variable Flux PM Synchronous Machines and a Mitigating Method for Magnetization Changes

Variable flux permanent magnet synchronous machines (VF-PMSMs) use permanent magnet magnetization as an additional degree-of-freedom to reduce losses based on operating conditions (e.g., at medium to high speeds, losses are reduced by using a lower magnetization). Magnet properties are known to be dependent on temperature; therefore, the magnet temperature effects on magnetization manipulation and maximum torque properties in VF-PMSMs are investigated in this paper with FEA simulations and experiments. Increased magnet temperature changes the available range of attainable magnetization levels and makes demagnetization occur more easily; therefore, a different current angle and magnetization are needed for maximum torque operation. The temperature effects on high speed magnetization manipulation methods, which are needed for driving cycle loss reduction and full power capability, are evaluated with simulation and experiments on a prototype 80 kW traction machine. A closed loop method for magnetization manipulation that mitigates the effect of temperature is proposed.