Multiphase drives offer enhanced fault-tolerant capabilities compared with conventional three-phase ones. Their phase redundancy makes them able to continue running in the event of faults (e.g., open/short-circuits) in certain phases. Moreover, their greater number of degrees of freedom permits improving diagnosis and performance, not only under faults affecting individual phases, but also under those affecting the machine/drive as a whole. That is the case of failures in the dc link, resolver/encoder, control unit, cooling system, etc. Accordingly, multiphase drives are becoming remarkable contenders for applications where high reliability is required, such as electric vehicles and standalone/off-shore generation. Actually, the literature on the subject has grown exponentially in recent years. Various review papers have been published, but none of them currently cover the state-of-the-art in a comprehensive and up-to-date fashion. This two-part paper presents an overview concerning fault tolerance in multiphase drives. Hundreds of citations are classified and critically discussed. Although the emphasis is put on fault tolerance, fault detection/diagnosis is also considered to some extent, because of its importance in fault-tolerant drives. The most important recent advances, emerging trends and open challenges are also identified. Part 1 provides a comprehensive survey considering numerous kinds of faults, whereas Part 2 is focused on phase/switch open-circuit failures.

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A Comprehensive Survey on Fault Tolerance in Multiphase AC Drives, Part 1: General Overview Considering Multiple Fault Types

Multiphase machines are very convenient for applications that require high reliability. In this two-part survey, the state of the art about fault tolerance in multiphase drives is reviewed. In Part 1, an overview including numerous fault types was presented, along with fundamental notions about multiphase drives. Here, in Part 2, the focus is placed on phase/switch open-circuit (OC) faults in particular, which have received the most attention in the literature. Phase OC failures involve OCs in stator phases or in converter-machine connections, and switch/diode OCs are frequently dealt with similarly or identically. Thanks to the phase redundancy of multiphase drives, their operation can be satisfactorily continued under a certain number of OCs. Nonetheless, the procedure to follow for this purpose is far from unique. For given OC fault conditions, numerous fault-tolerant possibilities can be found in the literature, each of them with different advantages and disadvantages. Moreover, a great variety of methods have also been devised to detect and diagnose phase/switch OC failures so that, as soon as possible, the most appropriate fault-tolerance measures are applied. Thus, given the broad literature about tolerance to phase/switch OC faults in multiphase drives, the survey presented here is expected to be of great interest for the research community and industry.

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A Comprehensive Survey on Fault Tolerance in Multiphase AC Drives, Part 2: Phase and Switch Open-Circuit Faults

To heighten the position estimation accuracy of sensorless control of interior permanent magnet synchronous motor (IPMSM), an improved full-order sliding mode observer (FSMO) based on novel phase-locked loop (PLL) is proposed in this article. By contrast with the traditional FSMO, the improved FSMO (IFSMO) with piecewise power function has merits of higher estimation accuracy and more chattering suppress capability, which is beneficial to the position sensorless drives. Based on that, to pledge the rotor position observation precision of the IFSMO during wide speed range, a variable sliding mode gain related to the rotor speed is designed. However, due to the inverter nonlinearity and rotor spatial harmonics, the extended back electromotive force contains high-order harmonics, which will reduce the estimation accuracy of PLL and cause notable position error. Therefore, a novel PLL with complex bandpass filter as the preprocessing stage that features high estimation accuracy, high filtering capability, and fast dynamic response is proposed. Meanwhile, the linearized model and parameter design of the proposed PLL is developed, and hence the stability of the designed PLL is analyzed by the derived linearized model. The availability of the proposed sensorless strategy is verified via experiments on 2-kW IPMSM drive. 

Estimated Position Error Suppression Using Novel PLL for IPMSM Sensorless Drives Based on Full-Order SMO

Multiphase electrical machines are advantageous for many industrial applications that require a high power rating, smooth torque, power/torque sharing capability, and fault-tolerant capability, compared with conventional single three-phase electrical machines. Consequently, a significant number of studies of multiphase machines has been published in recent years. This paper presents an overview of the recent advances in multiphase permanent magnet synchronous machines (PMSMs) and drive control techniques, with a focus on dual-three-phase PMSMs. It includes an extensive overview of the machine topologies, as well as their modelling methods, pulse-width-modulation techniques, field-oriented control, direct torque control, model predictive control, sensorless control, and fault-tolerant control, together with the newest control strategies for suppressing current harmonics and torque ripples, as well as carrier phase shift techniques, all with worked examples.

Advances in Dual-Three-Phase Permanent Magnet Synchronous Machines and Control Techniques

For the dual three-phase interior permanent magnet synchronous machines (DT-IPMSMs), open-phase fault can cause current unbalance and degrade the drive performance. This article proposes a fault tolerant maximum torque per ampere (FT-MTPA) control for DT-IPMSMs, which can maximize the ratio of the average torque to the stator current and minimize the fault-induced torque ripple. In the proposed approach, optimal FT-MTPA solution is derived and theoretically proven, and current rms is considered as one design constraint to ensure the equivalent loss to the healthy condition. The proposed FT-MTPA control ensures the smooth switching between fault tolerant control and healthy control without inducing noticeable torque ripple. Compared with existing methods, the proposed approach is computation-efficient and fast in achieving the FT-MTPA control, which is critical to practical applications with fast changing loads. Moreover, this article derives the optimal solution from the faulty MTPA model with fault induced terms considered to ensure high torque. Experiments and comparisons with existing methods are conducted to evaluate the proposed approach on a laboratory DT-IPMSM.

Fault Tolerant Maximum Torque Per Ampere (FT-MTPA) Control for Dual Three-Phase Interior PMSMs Under Open-Phase Fault

For dual three-phase interior permanent magnet synchronous machines (DT-IPMSMs), open-phase fault (OPF) can result in significant average torque reduction and harmonics in the output torque and speed, which prevent the machines from a reliable and safe operation. Indeed, these adverse effects are mainly due to significant harmonics in the stator currents caused by OPF. This article investigates fault-tolerant control (FTC) of DT-IPMSM under OPF and proposes a computation-efficient FTC solution to maximize the average torque and minimize the fault-induced torque and speed ripples. In the proposed FTC, the open-phase model is first derived, and optimal stator currents are then derived to achieve maximized average torque and minimized fault-induced torque harmonics. The computation efficiency enables the proposed solution, the capability of FTC, under both the steady-state and transient conditions. Moreover, the proposed FTC can eliminate the harmonic current components in the torque contributing frame and, thus, reduce the harmonic losses, and nonlinear inductance maps are employed to consider magnetic saturation. The proposed FTC is compared with existing methods and evaluated with experiments on a laboratory DT-IPMSM under various operating conditions.

Computation-Efficient Solution to Open-Phase Fault Tolerant Control of Dual Three-Phase Interior PMSMs With Maximized Torque and Minimized Ripple

For interior permanent magnet synchronous machines (IPMSMs), maximum torque per ampere (MTPA) control aims to find the MTPA angle to maximize the control objective (the ratio of output torque to stator current). This article proposes a novel online polynomial curve fitting technique for fast and accurate MTPA angle detection, which is motivated by the fact that the objective increases before MTPA angle and decreases after MTPA angle. This article proposes a polynomial-based objective model and identifies the polynomial parameters from a few test data for direct MTPA angle calculation. The proposed approach can avoid the time-consuming search process resulting in fast detection speed in comparison to existing search-based methods. In implementation, the current angle is set to a few test values to obtain the data for online curve fitting and MTPA angle calculation, in which there is no need of machine inductances and PM flux linkage. Moreover, the proposed polynomial model is analyzed to obtain the number of test data required for fast and accurate MTPA angle detection. The proposed approach is validated with extensive experiments and comparisons with existing methods on a laboratory IPMSM.

Fast Maximum Torque Per Ampere (MTPA) Angle Detection for Interior PMSMs Using Online Polynomial Curve Fitting

During the operation of permanent magnet synchronous motor (PMSM), accurate parameter identification plays an important role in high-performance motor control, especially in a situation where the parameters can vary nonlinearly significantly. This paper proposes an estimation method that combines extended Kalman filtering (EKF) and least squares method to identify the parameters of PMSM under the influence of magnetic saturation. This paper improves the PMSM model by establishing an inductance model considering magnetic saturation at first. Thereafter, EKF and least squares based method is proposed to estimate the magnetic flux and variation of inductances. The proposed method can accurately identify the machine parameters especially under the condition of magnetic saturation situation. The effectiveness of the proposed method is verified by simulation on the improved PMSM model.

Extended-Kalman-Filter-Based Magnet Flux Linkage and Inductance Estimation for PMSM Considering Magnetic Saturation

In this paper, an event-triggered active disturbance rejection control (ET-ADRC) method is designed for the battery-supercapacitor hybrid energy storage system (HESS) in electric vehicles (EVs). The proposed method combines the advantages of the ADRC method and the event-triggered mechanism. It inherits the fast response from the ADRC-based control module, which has an inner PI current loop and an outer ADRC voltage loop. To improve the computational efficiency, an event-triggered control module is adopted by utilizing the system state information at the last triggering and current sampling time. When the state error exceeds the preset range, the ADRC-based control module is triggered and the control signals are updated; otherwise, the ADRC-based control module is halted with unchanged control signals. A series of simulation cases have been conducted for the verification of the response speed and computational efficiency of the proposed method. A scaled-down hardware platform is set up to carry on the experiments. The experimental results demonstrate that under the similar voltage ripples the proposed ET-ADRC method responses faster than the conventional PI method and reduces the computational burden to almost 60% of the original ADRC method.

Event-Triggered Active Disturbance Rejection Control for Hybrid Energy Storage System in Electric Vehicle

Accurate and fast parameter estimation is essential for efficient operation and control of permanent magnet synchronous machine (PMSM). In this paper, a novel multi-parameter decoupling estimation method based on multi-state measurement is proposed to analyze and estimate the important parameters including winding resistance, permanent magnetic flux linkage, and $d-q$ axis inductances. An improved PMSM model containing inverter distorted voltage and nonlinear inductance considering magnetic saturation is established at first, then the model is decoupled to reduce the cross influences among the parameters and improve the computation efficiency through model dimension reduction according to the proposed decoupling method, and finally each parameter is estimated from multi-state voltage and torque measurement with improved efficiency and accuracy. This decoupling method separates the resistance and the inductance based on electromagnetic torque and reluctance torque, which is the crucial part of the estimation method proposed in this paper. Experiment on a PMSM driving system and comparison with existing methods are conducted to show that the proposed estimation method can improve the accuracy of estimation and calculation efficiency.

Yu Han

Papers

Computation-Efficient Solution to Open-Phase Fault Tolerant Control of Dual Three-Phase Interior PMSMs With Maximized Torque and Minimized Ripple

Fast Maximum Torque Per Ampere (MTPA) Angle Detection for Interior PMSMs Using Online Polynomial Curve Fitting

Extended-Kalman-Filter-Based Magnet Flux Linkage and Inductance Estimation for PMSM Considering Magnetic Saturation

Event-Triggered Active Disturbance Rejection Control for Hybrid Energy Storage System in Electric Vehicle

Efficient Nonlinear Multi-Parameter Decoupled Estimation of PMSM Drives Based on Multi-State Voltage and Torque Measurements