Dual Three-phase Permanent Magnet Synchronous Machines Research Articles

Current Harmonics and Unbalance Suppression of Dual Three-Phase PMSM Based on Adaptive Linear Neuron Controller

A strategy of current harmonics and unbalance suppression based on the vector space decomposition control with adaptive linear neuron (ALN) controller for the dual three-phase permanent magnet synchronous machine (DTP-PMSM) drive system is proposed in this paper. According to the conventional vector space decomposition theory, the compensation voltages from the ALN controller in the dq-frame and dqz-frame are employed to suppress the 5th and 7th current harmonics and unbalances. Compared with the VSD control using only the PI controller, the current harmonics and unbalance are sufficiently suppressed in the proposed strategy. In addition, unlike the resonant controller discretized by conventional Tustin transformation, the ALN controller has no resonant pole shift to the desired resonant frequency. Therefore, the harmonic suppression effect of the proposed strategy exhibits better performance than the VSD control with the resonant controller, especially in the high-speed region. Finally, the feasibility and effectiveness of the proposed strategy are validated by experimental results under both steady and transient states.

Sensorless Control Design of High-Speed Electric Drives in Discrete-Time Domain for Mild-Hybrid Turboprop Aircraft Applications

High-speed Permanent Magnet Synchronous Machine (PMSM) sensorless control design is not without challenges, especially when the ratio of power electronic modulation frequency to electrical fundamental frequency (M-F ratio) is relatively low. The Model Reference Adaptive System (MRAS) is a mature sensorless control method and has been widely used in industrial drives. There, an observer is commonly used to estimate rotor speed and angle using machine voltages and currents. The estimated angle is then further implemented for voltage and current frame transformations. Thus, the MRAS sensorless control is indeed a strong-coupled, multi-variable and nonlinear system. This paper proposes a detailed MRAS sensorless control system design method in discrete-time domain for high speed drives with relatively low M-F ratio with good system stability confidence. A detailed discrete local-linearized small-signal model is developed and state-space evolution matrix of current closed-loop system has been derived. The system stability can be defined and analysed with its maximum eigenvalue and the controller design is to make sure that the maximum eigenvalue is falling within the stable region. This proposed design method has been validated on a dual three-phase PMSM by simulation and experiment results with selected stable design point.

Analysis of Inter-Turn Short Circuit Faults in Dual Three-Phase PMSM for Electromechanical Actuator

Dual three-phase permanent magnet synchronous machine (DTPM) is an attractive choice for electromechanical actuator owing to its advantages of double redundancy, high power density and high reliability. However, the winding insulation is susceptible to the high thermal and mechanical stress, which will lead to the inter-turn short circuit faults (ITSCF) and poses threat to the safety of the machine system. Moreover, the ITSCF of DTPM is not only limited to single-phase, but also occurs between adjacent phases. Therefore, in this paper, the characteristics of single-phase and phase-to-phase ITSCFs are investigated and compared while the short-circuit contact resistance is considered. Firstly, a general mathematical model for single-phase and phase-to-phase ITSCFs are established, and the expressions of short circuit current (SCC) and output torque are derived. Then, the characteristics of flux density, back-EMF, SCC, fault phase current and output torque of the different fault models are compared by finite element analysis. It is demonstrated that when the contact resistance is not zero ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_f</i> ≠0), the amplitude of SCC and the third harmonic content of fault phase current are inversely proportional to the contact resistance and proportional to the number of short-circuit turns. In addition, the amplitude of SCC, torque ripple and braking torque caused by a phase-to-phase ITSCF will be larger than those of the single-phase ITSCF under the same fault conditions, especially when the contact resistance is small. Finally, an experimental prototype is made and tested to validate these analyses.

Generalized Predictive Current Control for Dual-Three-Phase PMSM to Achieve Torque Enhancement Through Harmonic Injection

The output torque capability of a dual-three-phase permanent magnet synchronous machine (DTP-PMSM) can be increased by intentionally injecting proper harmonic currents, which can be beneficial in some applications that require high torque density. To achieve this, current references containing multiple harmonic components with time-varying frequencies must be accurately tracked by the current controllers, which can hardly be achieved by conventional control methods. Fortunately, to track these complex but predetermined current references, generalized predictive control (GPC) shows unique advantages for its characteristic of multi-step prediction and receding horizon optimization. In this paper, a current control strategy based on GPC is proposed for the DTP-PMSM, which enhances the output torque capability by tracking the harmonic current references with high accuracy in both phase and magnitude. Parameter tuning and model mismatch issues of the proposed GPC are discussed. The effectiveness and merits of the proposed control strategy are validated by comparison study based on simulation and experiments.

Fundamental PWM Excitation Based Rotor Position Estimation for a Dual Three-Phase Permanent Magnet Synchronous Machine

Two rotor position estimation methods for a dual three-phase (DTP) permanent magnet synchronous machine (PMSM) are investigated in this article, where the rotor position is estimated by exploiting the saliency of the motor through the phase current derivative measurement during the fundamental PWM excitation of a standard six-phase two-level inverter. It is found that in a DTP PMSM, the wide speed range rotor position estimation is possible not only in the torque-producing subspace, but also in the harmonic subspace. The principle and practical implementation of the methods are explained in details. The experimental results verify the effectiveness of the proposed rotor position estimation methods.

Optimal switching sequence control for current stress reduction of DC-link capacitors in dual-three phase PMSM drives

The safety and installation space of DC-link capacitor is crucial for dual-three phase permanent magnet synchronous machines (DTPMSM) drives in industrial applications. Reducing the capacitor current stress can contribute to decrease the designed capacitor value and install size, thus enhance safety of drives fed by two parallel inverters. Therefore, an optimal switching sequence control scheme for DTPMSM drives is proposed to reduce the DC-link capacitor current stress in this paper. For DTPMSM drives, the maximum four adjacent voltage vectors control (MFAVC) method is usually adopted due to its control flexible and stability characteristic. Based on MFAVC, the capacitor current can be derived though the current reconstruction theory to reorder the current amplitude over one switching period. Through the rearrangement of voltage vector and duration, the theoretical analysis of capacitor current reduction is presented. On this basis, the optimal switching sequence control method can be implemented based on the minimized current sum of the two inverters. The performance of proposed method has been evaluated via. comparatively experimental tests on a prototype 3 kW DTPMSM drive, which shows superior features on reducing capacitor current stress. Furthermore, it is also found that the proposed method is helpful to redesign a small capacitor value for DTPMSM drives.

Sensorless Control of Dual Three-Phase Permanent Magnet Synchronous Machines—A Review

This paper presents an overview of various sensorless control methods, with a focus on dual three-phase permanent magnet synchronous machines (DTP-PMSM). Owing to the important role that DTP-PMSMs play in motion-control applications in industry, most academic researchers and industry activists seek to reduce costs and size while increasing the capability and efficiency of motion applications. This has led to an increase in the number of publications about multiphase machines in recent years. The purpose of this article is to review the most important sensorless control techniques, which are divided into two main categories, namely saliency-based control method for low-speed range and model-based control method for high-speed range. Both methods are subdivided into other categories, with a focus on DTP-PMSMs. The methods are compared with each other for the purpose of selecting the most suitable control technique for implementation in applications such as ship propulsion, wind turbines, and aerospace.

Open-Phase Fault-Tolerant Control Strategy for Dual Three-Phase Permanent Magnet Synchronous Machines Without Controller Reconfiguration and Fault Detection

Due to high power-transforming capability and excellent fault-tolerant performance, dual three-phase permanent magnet synchronous machines (DT-PMSMs) are widely used in high-reliability applications. Concerning on the remedial strategy for DT-PMSMs under open-phase faults, the conventional method is to reconfigure the controller or the current references in order to obtain optimum postfault performances. Two different control schemes should be separately designed for normal and fault conditions, respectively. Meanwhile, related fault detection measures need to be adopted and the inherent fault detection delay will further result in transient performance deterioration. In order to solve these problems, this article proposes a control strategy, which can achieve natural fault-tolerant capability of DT-PMSMs without additional fault detection algorithm. With the proposed control method adopted, reconfiguration of the control structure and modification of the current command are not required. Thus, the control scheme is simplified. The transition from the healthy to the postfault operation can be improved, meanwhile, the steady-state performances in prefault and postfault situations can be guaranteed. The proposed strategy can be generally applied to single open-phase faults and multiple open-phase faults in DT-PMSMs. Experimental validations are presented on a 1 kW DT-PMSM platform to prove the effectiveness of the proposed strategy.

Zero-sequence Current Suppressing Strategy for Dual Three-phase Permanent Magnet Synchronous Machines Connected with Single Neutral Point

Dual three-phase permanent-magnet synchronous machines (DTP-PMSM) connected with a single neutral point provide a loop for zero-sequence current (ZSC). This paper proposes a novel space vector pulse width modulation (SVPWM) strategy to suppress the ZSC. Five vectors are selected as basic voltage vectors in one switching period. The fundamental and harmonic planes and the zero-sequence plane are taken into consideration to synthesis the reference voltage vector. To suppress the ZSC, a non-zero zero-sequence voltage (ZSV) is generated to compensate the third harmonic back-EMF. Rather than triangular carrier modulation, the sawtooth carrier modulation strategy is used to generate asymmetric PWM signals. The modulation range is investigated to explore the variation of modulation range caused by considering the zero-sequence plane. With the proposed method, the ZSC can be considerably reduced. The simulated and experimental results are presented to validate the effectiveness of the proposed modulation strategy.

Analysis and Fault-Tolerant Control for Dual-Three-Phase PMSM Based on Virtual Healthy Model

Dual-three-phase permanent magnet synchronous machines (DTP-PMSMs) are famous for their fault-tolerant capability. However, the complex modeling, high copper loss, and torque ripple under postfault operation limit their further application. In this article, a fault-tolerant control (FTC) strategy is developed for DTP-PMSMs under the open-phase fault (OPF) with straightforward modeling and smooth output torque. The virtual healthy DTP-PMSM model, where the coordinate transformation, the modulation strategy, and the controller structure remain unchanged under OPF, is adopted in the proposed FTC scheme. And the current references are derived in sinusoidal waves with minimum copper loss. The inaccurate transmission of control signals under OPF is also focused on. Comprehensive theoretical analysis shows the relationship between the controller output voltage and the actual stator voltage should be considered in the proposed FTC strategy; otherwise, distortion in torque and current will be introduced. The voltage compensation is utilized to compensate for the voltage difference and ensure the smooth torque output. Besides, a quasi proportional resonance controller is designed to further suppress the residual torque ripple. The proposed strategy will not induce complex implementation and heavy computation burden. The simulation and experimental results prove the analysis and the effectiveness of the proposed strategy.

Electromagnetic Performance Prediction for the Symmetrical Dual Three-phase Surface-mounted PMSM under Open-phase Faults Based on Accurate Subdomain Model

The paper presents an accurate analytical subdomain model for predicting the electromagnetic performance in the symmetrical dual three-phase surface-mounted permanent magnet synchronous machine (PMSM) under open-phase faulty conditions. The model derivations are extended from previous accurate subdomain models accounting for slotting effects. Compared with most conventional subdomain models for traditional three-phase machines with nonoverlapping winding arrangement, the subdomain model proposed in this paper applied for the 24-slot/4-pole dual three-phase machine with symmetrical overlapping winding arrangement. In order to investigate the postfault electromagnetic performance, the reconfigured phase currents and then current density distribution in stator slots under different open-circuit conditions are discussed. According to the developed model and postfault current density distribution, the steady-state electromagnetic performance, such as the electromagnetic torque and unbalanced magnetic force, under open-circuit faulty conditions are obtained. For validation purposes, finite element analysis (FEA) is employed to validate the analytical results. The result indicate that the postfault electromagnet performance can be accurately predicted by the proposed subdomain model, which is in good agreement with FEA results.

A Novel Space Vector PWM Technique With Duty Cycle Optimization Through Zero Vectors for Dual Three-Phase PMSM

In this paper, a novel space vector pulse width modulation (SVPWM) technique with duty cycle optimization through zero vectors for dual three-phase (3-ph) permanent magnet synchronous machines (PMSMs) is proposed. Dual 3-ph PMSMs can be optimally controlled in vector space decomposition, which allows controls of the fundamental component and main low-frequency harmonics separately in two orthogonal subspaces, i.e., αβ and xy subspaces. However, the space voltage vector modulations of voltage references in two subspaces are not independent, because each voltage vector possesses its unique and fixed spatial location in two subspaces. Therefore, many SVPWM techniques intend to extend the modulation capability by designing the voltage vector selection principle, but the duty cycle saturation determines the limit of phase voltage regardless of the voltage vector selection principle. Therefore, a simple SVPWM technique with duty cycle optimization by adjusting dwell times of zero vectors is developed to offer a reasonable modulation capability with reduced switching frequency and no complex voltage vector selection principle. The linear modulation range is explained as well. Finally, the experimental results validate the performance of the proposed SVPWM technique through voltage injection and closed-loop current control.

Six-Step Operation of a Symmetric Dual Three-Phase PMSM With Minimal Circulating Currents for Extended Speed Range in Electric Vehicles

Automotive applications demand high efficiency, good reliability, and a wide operating speed range within limited dc bus voltage constraints. In this article, a zero degree displacement dual three-phase permanent magnet synchronous machines (PMSM) is derived from an original three-phase PMSM to enhance the power rating as well as the operating speed range. The proposed topology can be used as an alternative to the conventional configuration of three-phase PMSM with a bidirectional dc–dc converter for electric vehicles. Even though the commonly used dual three-phase PMSM with split-phase winding eliminates the sixth harmonic torque pulsation, a large circulating current is generated during six-step operation, which results in additional stator copper loss. In this article, six-step operation of the symmetric dual three-phase PMSM with zero degree winding displacement is proposed to achieve maximum inverter utilization. Both harmonic circulating current and torque pulsation were observed to be within satisfactory levels using this configuration. A changeover algorithm is also proposed to enable a smooth transition between closed-loop current vector control during low and medium speed operation to open-loop six-step voltage angle control for high speed operation. The performance of the proposed method is experimentally validated on a 3-kW dual three-phase PMSM drive.

A Novel High Torque Density Dual Three-Phase PMSM With Low Space Harmonic Content

A novel 36-slot/14-pole dual three-phase permanent magnet synchronous machine (PMSM) is proposed to suppress non-working space harmonics in the synthesized magnetomotive force (MMF) and improve torque density simultaneously. The machine adopts unequal coil-turns winding and special stator core which includes two different types of slots, namely double-layer slots (DLSs) and single-layer slots (SLSs). The special structure of the machine improves the working space harmonic and eliminates lower non-working space harmonics in MMF, which leads to torque promotion and permanent magnet (PM) loss reduction. Harmonic content in MMF of the proposed machine is derived from theoretical analysis and verified by finite element (FE) calculation. Besides, the proposed machine is compared with existing machines, from aspects of MMF, back electromotive force (EMF), torque, losses, efficiency, unbalanced magnetic force (UMF), and torque-speed characteristic. The proposed machine has higher torque density, higher efficiency, and lower PM loss than existing machines.

Torque Ripple Suppression Based on Optimal Harmonic Current Injection in Dual Three-Phase PMSMs Under Magnetic Saturation

Dual three-phase permanent magnet synchronous machines (DTP-PMSMs) have received increasing attention from the industry and academia due to their advantages in lower burden on power inverters when operating in high power applications compared to the three-phase counterparts and low torque ripples. In this article, it reveals that the favorable low torque ripple characteristic of DTP-PMSM is undermined in the high power and overload operating mode. To solve this problem, this article proposes a novel torque ripple suppression strategy based on optimal harmonic current injection. A mathematical torque ripple model of DTP-PMSM considering the cross-coupling effects between <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d–q</i> axis and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> - <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> axis is built. And based on this model, a detailed analysis is carried out to obtain the optimal harmonic current. The theoretical analysis also guarantees that the induced machine loss is minimum. Moreover, the proposed strategy has good dynamic performance since the algorithm involves no iterative computation and is computationally effective, which is proved on a laboratory DTP-PMSM system. The effect of parameter variation is also discussed and tested. The experiment results prove that the influence of magnetic saturation on torque ripple can be effectively suppressed.

Suppression of Major Current Harmonics for Dual Three-Phase PMSMs by Virtual Multi Three-Phase Systems

Dual three-phase (DTP) permanent magnet synchronous machine (PMSM) systems exhibit high current harmonics due to low impedance to voltage disturbance such as inverter voltage errors and back-EMF harmonics. This article proposes a concept of virtual multi three-phase systems to achieve independent regulation of the current harmonics in a DTP PMSM system. The virtual multi three-phase currents are first reconstructed by appropriately shifting the phase of original physical DTP currents, and then decomposed with the help of vector space decomposition techniques. As a result, the fundamental and the major current harmonics, i.e., the 5th, 7th, 11th, and 13th, can be completely separated in several isolated subspaces, where the independent current control loops can be easily designed and implemented. Compared with existing methods, the steady-state and dynamic-state performance of current harmonic regulation are enhanced by the proposed virtual multi three-phase systems and the effectiveness is validated by experimental.

Space-Vector-Optimized Predictive Control for Dual Three-Phase PMSM With Quick Current Response

This article proposes a scheme of space vector optimization for model predictive control (MPC) of dual three-phase permanent magnet synchronous machine (DTP-PMSM), which aims to restrain the current harmonics under the condition of low inductance. The multiphase electric motor possesses the characteristics of quick current variation rate by means of the low inductance. Especially incorporating with MPC schemes, its advantage of quick response shows promising prospects for various applications such as robotics, aerospace and medical devices. However, such a characteristic of low inductance requires shorter control period, which means that the traditional MPC cannot be implemented to suppress the current harmonics since the performance of the power switching devices and the digital controller limits the arbitrary increasing of the control frequency, which has nearly unexplored in previous studies. In order to address such an issue, this article presents the space-vector-optimized model predictive control (SVO-MPC) for the DTP-PMSMs with low inductance by presynthesizing space vectors to eliminate harmonics in the harmonic frame and optimizing the zero vector to deal with quick current response. As a result, the proposed SVO-MPC can remarkably improve the steady and dynamic control performance, while the traditional MPC almost fails at commonly-adopted control frequency. Finally, simulated and experimental results are both given to verify the feasibility of the proposed SVO-MPC for DTP-PMSMs with quick current response.

Multi-Virtual-Vector Model Predictive Current Control for Dual Three-Phase PMSM

This paper proposes a multi-virtual-vector model predictive control (MPC) for a dual three-phase permanent magnet synchronous machine (DTP-PMSM), which aims to regulate the currents in both fundamental and harmonic subspace. Apart from the fundamental α-β subspace, the harmonic subspace termed x-y is decoupled in multiphase PMSM according to vector space decomposition (VSD). Hence, the regulation of x-y currents is of paramount importance to improve control performance. In order to take into account both fundamental and harmonic subspaces, this paper presents a multi-virtual-vector model predictive control (MVV-MPC) scheme to significantly improve the steady performance without affecting the dynamic response. In this way, virtual vectors are pre-synthesized to eliminate the components in the x-y subspace and then a vector with adjustable phase and amplitude is composed of two effective virtual vectors and a zero vector. As a result, an enhanced current tracking ability is acquired due to the expanded output range of the voltage vector. Lastly, both simulation and experimental results are given to confirm the feasibility of the proposed MVV-MPC for DTP-PMSM.

Current Injection-Based Simultaneous Stator Winding and PM Temperature Estimation for Dual Three-Phase PMSMs

This article proposes a current injection-based simultaneous stator winding and permanent magnet (PM) temperature tracking technique for dual three-phase permanent magnet synchronous machines (PMSMs). The estimation models involving winding and PM temperatures are derived for different control strategies with the cancelation of inductances. To improve the tracking performance, a Kalman filter is used for simultaneous winding and PM temperature estimation. Compared with the existing methods, the proposed simultaneous winding and PM temperature estimation technique is independent of the voltage-source nonlinearity effect and is applicable to various machine operating conditions. The main features of the proposed method are underscored by the cancelation of inductance and the elimination of the need for a lookup table. The test results on a laboratory dual three-phase PMSM are used to validate the proposed method under different speed and torque conditions.

Harmonic Current Suppression of Dual Three-Phase PMSM Based on Model Predictive Direct Torque Control

The traditional direct torque control (DTC) method will produce a larger harmonic current in the x, y subspace when applied to a dual three-phase permanent magnet synchronous machine (DTP-PMSM) because the voltage vector used for DTC is not equal to zero in the x, y harmonic subspace. To mitigate this problem, in this manuscript, a model predictive direct torque control (MPDTC) method is proposed to eliminate the harmonic current in DTP-PMSM. The spatial distribution characteristic DTP-PMSM voltage vector is analyzed; then, the table of vector group can be obtained according to DTC, and each vector group can be combined to obtain the zero-voltage vector in the x, y subspace. According to the cost function, MPDTC selects the vector group and obtains the optimal vector sequence combination to eliminate the harmonic current in the x, y subspace. Furthermore, the MPDTC achieves closed-loop control of harmonic currents in the x, y subspace. The MPDTC can also eliminate harmonic currents caused by other factors. The simulation results show that the method of MPDTC can effectively suppress the harmonic current of DTP-PMSM.