Flux-weakening Control Strategy Research Articles

Flux Weakening Controller Design for Series-Winding Three-Phase PMSM Drive Systems

Series-winding three-phase PMSMs have a higher bus voltage utilization than the conventional three-phase PMSMs with star connection. This topology is suitable for applications with a limited bus voltage. However, the zero-sequence current controller will reduce the bus voltage utilization of the series-winding PMSMs, which causes problems in the flux-weakening controller design. The conventional flux-weakening control algorithms will cause the series-winding PMSMs to enter the overmodulation region early and degrade the performance of the zero-sequence current suppression algorithm. In this paper, a new flux-weakening controller with a dynamic fundamental voltage limit (FW-DFVL) is designed for the series-winding three-phase PMSM traction system. Firstly, the space vector modulation method combines the proposed virtual zero-sequence vectors to realize both the fundamental current generation and the zero-sequence current suppression. The accurate bus voltage utilization in the fundamental current subspace can be derived from the proposed modulation method. Secondly, the gradient descent method generates the flux-weakening d-axis reference current with the dynamic fundamental voltage, which will converge faster than the conventional PI-based flux-weakening control scheme. Thirdly, the flux-weakening controller in the overmodulation region is also designed where the zero-sequence current will no longer be suppressed. The bus voltage utilization is Vdc in this operation mode. Finally, both the simulation and experimental results are utilized to verify the effectiveness of the proposed FW-DFVL, where faster dynamic performance and higher bus utilization are observed.

Flux-Weakening Controller Design of Dual Three-Phase PMSM Drive System With Copper Loss Minimization

The performance of flux-weakening controllers in the multiphase permanent magnets (PM) machines depends on the accurate fundamental voltage limit derivation, and the minimal copper loss design in the flux-weakening operation region has not been well discussed. In this article, the accurate fundamental voltage limit with considering harmonic current suppression is derived at first. Then, two control concepts are addressed, and the corresponding flux-weakening control strategies are designed with the gradient descent method. In the first control strategy, both the fundamental and harmonic voltage vectors are feasible, resulting in the larger amplitude of the phase currents. The second control strategy obtains higher bus voltage utilization by an additional transition stage. At the same time, the harmonic currents cannot be further suppressed in the flux-weakening operation region. Third, the copper loss per electrical cycle is calculated, and a switching scheme is designed to obtain lower copper loss in the flux-weakening operation region. Finally, both strategies are successfully implemented in a dual three-phase PMSM. Moreover, the proposed switching scheme obtains minimal copper loss in the whole flux-weakening operation region.

Review of Flux-Weakening Algorithms to Extend the Speed Range in Electric Vehicle Applications With Permanent Magnet Synchronous Machines

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.

Improved Flux Weakening Control Strategy for Five-Phase PMSM Considering Harmonic Voltage Vectors

This article proposes a novel flux weakening scheme for five-phase PMSM with active harmonic currents injection. The conventional flux weakening control schemes applied in the five-phase PMSM do not consider the voltage limit drop in the fundamental subspace due to the harmonic current controller. Thus, the derivation between the reference current trajectory and actual current trajectory would cause the current distortion when applying deadbeat current controller (DBCC). This article analyses the precise voltage limit circles considering the voltage drop caused by the resistance and harmonic currents control at first. Then, a feed-forward flux weakening control algorithm is designed to optimize the current trajectory online. The gradient descent method is used to ensure the converge speed and stability of the optimized current trajectory. Thirdly, the peak value of phase currents would be clipped by the harmonic currents to prevent the inverter current limit, where a new non-linear harmonic current controller is designed to precisely control the harmonic currents. Finally, the DBCC and modified SVPWM technology are utilized to generate the duty cycle. The proposed improved flux weakening control strategy is successfully implemented in an interior five-phase PMSM, and the performance demonstrate the effectiveness of this strategy.

Deep flux weakening control strategy for IPMSM with variable direct axis current limitations

Deep flux weakening control strategy for IPMSM with variable direct axis current limitations

Voltage Control of IPMSM Servo Drive in Constant Power Region With Intelligent Parameter Estimation

A novel voltage control scheme for an interior permanent magnet synchronous motor (IPMSM) servo drive in the constant power region with intelligent estimation of the motor parameter is proposed in this study. In the novel voltage control scheme, a feedforward voltage angle controller is proposed where an intelligent parameter estimation method by using a wavelet fuzzy neural network (WFNN) is developed to estimate the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis inductance online. In this study, in order to minimize the copper loss, a flux-weakening (FW) control scheme under maximum phase voltage is developed first. Then, an adaptive backstepping based nonlinear controller (ABNC) considering nonzero <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current is developed to improve the robustness of the speed control. The Lyapunov stability theorem is used to derive the adaptive law of the online estimation of the lumped uncertainty to ensure the asymptotical stability of the ABNC. Moreover, a feedforward voltage angle controller is developed for the voltage control where the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current controller is retained in order to ensure the steady-state performance of the control system. Furthermore, the WFNN is adopted to estimate the actual <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis inductance value online for the feedforward voltage angle controller to improve the dynamic response. In addition, some experimental results are demonstrated to verify the effectiveness of the proposed voltage control scheme with ABNC in the constant power region.

An enhanced feedforward flux weakening control for high‐speed permanent magnet machine drive applications

Permanent magnet machines have been used in the high-speed drive applications due to their high-efficiency, high-power-density, and wide-speed range characteristics. However, control of such high-speed permanent magnet machines machine is always challenging and proper flux-weakening controller design is essential to achieve high performance of these machines. In this paper, an improved feedforward flux-weakening control scheme for interior permanent magnet synchronous machine (IPMSM) drives are proposed. The proposed method identifies optimal d-axis and q-axis currents under different operation regions using maximum-torque-per-ampere curve, voltage limit, and current limit curves with a fast Newton–Raphson algorithm. To ensure the optimal performance of the control mechanism, effects of inductance variations due to the magnetic saturation are considered and an innovative high-frequency staircase voltage injection method is used to identify the q-axis inductance. The experimental results show that compared with other existing flux-weakening methods, the proposed technique can improve the DC-link voltage utilisation without the need to tune any controller gains and can fully utilise maximum available torque with desirable transient performance.

Co-Design Optimization of Direct Drive PMSGs for Offshore Wind Turbines Based on Wind Speed Profile

This paper presents a new method to optimize, from a working cycle defined by torque and speed profiles, both the design and the control strategy of permanent magnet synchronous generators (PMSGs). The case of a 10 MW direct-drive permanent magnet generator for an Offshore wind turbine was chosen to illustrate this method, which is based on the d–q axis equivalent circuit model. It allows to optimize, with a reduced computation time, the design, considering either a flux weakening control strategy (FW) or a maximum torque per Ampere control (MTPA) strategy, while respecting all the constraints—particularly the thermal constraint, which is characterized by a transient regime. The considered objective is to minimize the mass and the average electric losses over all working points. Thermal and magnetic analytical models are validated by a 2D finite element analysis (FEA).

Improvement on Flux Weakening Control Strategy for Electric Vehicle Applications

This paper proposes an optimized flux weakening (FW) control strategy for interior permanent-magnet synchronous electric motor to address the critical issues that could occur under torque setpoint transition in flux weakening region, due, for example, to an emergency braking. This situation is typical in electric vehicles where the electrical machines operate over a wide speed range to reach high power density and avoid gearboxes. Two modified traditional flux weakening strategies are proposed in this paper to improve torque control quality during high speed torque transition. The proposed modified control strategies were validated both by Matlab/Simulink simulations, modeling the power train of a light vehicle application, and extensive experimental tests on a dedicated test bench.

Maximum Torque per Voltage Flux-Weakening Strategy With Speed Limiter for PMSM Drives

This article presents an enhanced flux weakening (FW) control scheme for permanent magnet synchronous motors, 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 as speed limit, without interfering between them until this limit is achieved. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -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 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> plane throughout the maximum torque per ampere, constant torque, current and voltage limit, maximum torque per voltage, and constant speed strategies without switching the algorithm. Simulations and experimental results from a real exterior-rotor interior permanent magnet synchronous motor direct-drive e-motorbike verify the effectiveness of the proposed method.

High-speed control strategy for permanent magnet synchronous machines in electric vehicles drives: Analysis of dynamic torque response and instantaneous current compensation

Flux-weakening control strategy of interior permanent magnet synchronous machines have a massive significance to enlarge the operational speed of electric vehicles (EVs) and to facilitate the power integration. However, how to keep the torque stability and achieve the fast response should be given the top priority. In order to facilitate the flux-weakening control application on EVs, a novel flux-weakening control strategy with fast transient current response is proposed. In detail, the change of dynamic voltage margin and its response are analyzed in this paper. Accordingly, the flux-weakening control is proposed through the collaborative control of the dynamic current compensation and the d-axis current-error adjustment. To fully evaluate effectiveness of proposed strategy, the traditional PI-based voltage-closed flux-weakening and the low-pass-filter method are constructed for comparison. The simulation and experimental results illustrate that the proposed strategy can achieve the fast torque response and also have the capacity to reduce the torque fluctuation of the stable state.

Parameters Compensation of Permanent Magnet Synchronous Motor in Flux-Weakening Region for Rail Transit

This article proposes a dual-parameters compensation control method to improve the torque accuracy of permanent magnet synchronous motor (PMSM) in flux-weakening region for rail transit. For the sake of the feature that six-step operation is the essential operation of rail transit and switching frequency is very low, the proposed method works on the single q-axis current regulator-variable voltage angle (SQCR-VVA) flux-weakening control strategy for PMSM operation. Based on SQCR-VVA flux-weakening control, impact of inaccurate parameters is analyzed in seven different conditions, and inaccurate parameters (d-axis inductance, q-axis inductance and permanent magnet flux linkage) result in the errors on d-axis current response and d-axis feed forward voltage. In order to eliminate the impact of the three parameters at the same time, dual compensation regulators are applied to the proposed method. Error of q-axis inductance is identified by the d-axis voltage regulator. The whole impact of inaccurate d-axis inductance and permanent magnet flux linkage is eliminated by the d-axis current regulator. The proposed method is subsequently tested on PMSM and shows quite good performance on the improvement of torque accuracy.

An Improved UDE-Based Flux-Weakening Control Strategy for IPMSM

Interior permanent magnet synchronous motors (IPMSMs) are usually used in electric vehicle drives and in other applications. In order to enlarge the speed range of IPMSMs, the flux-weakening control method is adopted. The traditional flux-weakening control strategy degrades the control performance because of parameter mismatches caused by variation of motor parameters. An improved uncertainty and disturbance estimator (UDE)-based flux-weakening control strategy is proposed for IPMSM drives in this paper. The parameter tuning method in the UDE-based control is improved. In addition, a flux-weakening adjusting factor is put forward to reduce the torque fluctuation when the operation point switches between the constant torque region and the flux-weakening region. This factor can be adjusted online by a lookup table. Finally, the validity of proposed method is verified by the simulation and experimental results. The results show that the proposed control strategy can effectively enhance the robustness of the system in the flux-weakening region, and make the system switch more smoothly between the constant torque region and the flux-weakening region.

Hybrid excited permanent magnet machines for electric and hybrid electric vehicles

This paper reviews various hybrid excited (HE) machines from the perspective of location of PM and DC excitation, series/parallel connection of PM and DC excited magnetic fields, and 2D/3D magnetic fields, respectively. The advantages as well as drawbacks of each category are analyzed. Since an additional control degree, i.e. DC excitation, is introduced in the HE machine, the flux weakening control strategies are more complex. The flux weakening performance as well as efficiency are compared with different control strategies. Then, the potential to mitigate the risk of uncontrolled overvoltage fault at high speed operation is highlighted by controlling the field excitation. Since additional DC coils are usually required for HE machines compared with pure PM excitation, the spatial confliction inevitably results in electromagnetic performance reduction. Finally, the technique to integrate the field and armature windings with open-winding drive circuit is introduced, and novel HE machines without a DC coil are summarized.

Stepwise Magnetization Control Strategy for DC-Magnetized Memory Machine

A memory machine (MM) equipped with hybrid permanent magnets (PMs), i.e., NdFeB and low coercive force PMs, exhibits acceptable torque capability at low speeds and high efficiency at high speeds. Previous literatures have addressed that the constant power speed range (CPSR) of MMs can be further extended by online PM flux control and the requirement of the flux-weakening (FW) inverter current can be reduced as well. Nevertheless, how to coordinate the d -axis vector FW and PM magnetization control over a whole operating range in a reasonable manner remains unreported. Therefore, this paper proposes and implements a stepwise magnetization control strategy on a dc-magnetized MM based on the operating characteristics under various PM magnetization states and speed ranges. The configuration, principle, and mathematical model of the investigated machine are introduced first. Then, the proposed control strategy is established by dividing the operating envelop into several FW regions and an appropriate FW control scheme is utilized at each stage. It demonstrates that the CPSR can be effectively extended by simply applying the demagnetizing current pulses in several steps. This simplifies the control efforts considerably without resorting to continuous PM flux control and frequent actions of the switching devices. The effectiveness of the proposed control strategy is verified by experimental results.

Optimal Three-Dimensional Current Computation Flux Weakening Control Strategy for DC-Biased Vernier Reluctance Machines Considering Inductance Nonlinearity

An optimal three-dimensional current computation flux weakening control strategy for dc-biased Vernier reluctance machines (VRMs) is proposed in this paper. Compared with permanent magnet synchronous machines, dc-biased VRMs have an additional degree of freedom to regulate the rotor flux through variable dc-biased armature current. The conventional flux weakening control strategy does not utilize the adjustable dc field current, and the output capacity in the flux weakening region is limited. In this paper, the optimal three-dimensional current distribution is calculated at the intersection of current and voltage constraint. Meanwhile, in order to maintain the armature voltage within the voltage constraint, the inductance nonlinearity is reflected by constructing the inductance table. The algorithm provides maximum output capability and high efficiency for dc-biased VRMs despite the changes in inductance parameters in the whole flux weakening region. Finally, the effectiveness of the proposed control strategy is validated by experimental results for a prototype machine.

Optimal flux‐weakening control of a new five‐phase FT‐IPM motor based on DTC and SVPWM for electric vehicle applications

This study proposes two flux-weakening control strategies for a new five-phase fault-tolerant interior-permanent-magnet (FT-IPM) motor, in which direct torque flux-weakening control (DTFWC) and space vector pulse width modulation (SVPWM)-based vector flux-weakening control (SVMFWC) are adopted. To achieve the reduced computation and the good operating performance such as minimised copper loss, improved dynamic response performance, and constant power operation in FW region, the multi-objective optimisation without complex non-linear optimisation algorithms for the DTFWC and SVMFWC are developed. In addition, the two proposed strategies have the same control objective but realised with two different ways. The reducing copper loss is obtained in DTFWC by reducing flux-weakening current with the full utilisation of DC-link voltage, while the reducing copper loss is gained in SVMFWC by decreasing the required current amplitude with maximum output torque per ampere current. Furthermore, the effectiveness of the proposed DTFWC and SVMFWC strategies is verified by simulation and experimental results.

The Design of a Permanent Magnet In-Wheel Motor with Dual-Stator and Dual-Field-Excitation Used in Electric Vehicles

The in-wheel motor has received more attention owing to its simple structure, high transmission efficiency, flexible control, and easy integration design. It is difficult to achieve high performance with conventional motors due to their dimensions and structure. This paper presents a new dual-stator and dual-field-excitation permanent-magnet in-wheel motor (DDPMIM) that is based on the structure of the conventional in-wheel motor and the structure of both the radial and axial magnetic field motor. The finite element analysis (FEA) model of the DDPMIM is established and compared with that of the conventional in-wheel motor. The results show that the DDPMIM achieves a higher output torque at low speeds and that the flux-weakening control strategy is not needed in the full speed range.

Magnetic Saturation Aids Flux-Weakening Control: Using Lookup Tables Based on a Static Method of Identification for Nonlinear Permanent-Magnet Synchronous Motors

For a given power voltage, the usual fluxweakening control of permanent-magnet synchronous motors (PMSMs) is based on two independent current regulators to expand the speed range of linear PMSMs. Therefore, the magnetic saturation is not often taken into account in these control strategies. Many authors have worked on this topic in recent years, but questions remain about the optimization of the flux-weakening space. In this article, by taking into account the magnetic saturation, an optimal flux-weakening control scheme has been developed. The proposed method is based on a lookup table that provides the current set points according to the speed and power voltage measurements. To implement this control strategy, two steps are required. The first presents a specific characterization scheme of PMSMs. The second shows how to build lookup tables for the flux-weakening control by using an optimization algorithm under constraints, based on obtained identification results. An example is given to illustrate each step of this study. Please be advised that the control scheme carried out in this article is under patent by Piaton et al.

Analysis of Effective Control Strategy for IPMSM Driven by Electric Vehicles

Field oriented control strategy for IPMSM for electric vehicle is analyzed considering the different operation conditions of elective vehicle. Maximum torque/current control and flux weakening control strategy based on voltage feedback compensation for demagnetizing current are adopted for IPMSM and SVPWM technology establishes motor control system. The Venucia Chenfeng 2014 version Lingfeng electric vehicle is the study subject carrier, ACR and ASR double closed-loop control used for simulation analysis and illustrate that this control system applied to electric vehicle drive system has small torque ripple and good static and dynamic response characteristics.