Kaiyuan Lu

A Simple Startup Strategy Based on Current Regulation for Back-EMF-Based Sensorless Control of PMSM

Back-EMF-based sensorless control of permanent magnet synchronous machines (PMSMs) is preferred in many industrial applications due to its control simplicity and high machine efficiency. Position estimation based on the back-EMF is most reliable in the medium-to high-speed range. For applications where low-speed operation is not required, a simple-structure back-EMF-based sensorless controller coupled with a simple startup procedure offers an attractive low-cost solution. This paper proposes a new startup procedure based on closed-loop current regulation. Compared to the existing methods, the new starting method can work under different load conditions and allows smooth transition from the startup procedure to the back-EMF-based sensorless control mode. In order to determine the successful use of the proposed method in various applications, it stability under different load conditions is discussed in detail. The proposed method is robust when it comes to the motor parameter variation and can be used for both surface-mounted PMSMs (SPMSMs) and interior PMSMs. The method presented in this paper is validated using the experimental results on an SPMSM. A general design guideline is also given.

An Active Damping Technique for Small DC-Link Capacitor Based Drive System

A small dc-link capacitor based drive system shows instability when it is operated with large input line inductance at operating points with high power. This paper presents a simple, new active damping technique that can stabilize effectively the drive system at unstable operating points, offering greatly reduced input line current total harmonic distortion. The proposed method requires only a first-order, high-pass filter with a gain. Active damping voltage terms, linked directly to the dc-link voltage ripple through gain units, are injected to the drive machine for stabilizing the operating points. The stabilizing effect of the active damping terms is demonstrated for an induction machine based drive system. The effects of the added damping terms on the machine current and dc-link voltage are analyzed in detail. A design recommendation for the proposed active damping terms is given. Experimental results verifying the effectiveness of the new active damping method are presented.

Design Considerations of Permanent Magnet Transverse Flux Machines

Permanent magnet transverse flux machine (PMTFM) is well known for its high torque density and is interested in various direct-drive applications. Due to its complicated 3-D flux components, design and design optimization of a PMTFM is more difficult and time consuming than for radial flux electrical machines. This paper addresses two important design considerations for PMTFM - the influence of permanent magnet leakage flux, which plays an important role in the determination of machine output torque, and the leakage inductance. A new simple method to provide a quick estimation of the armature leakage inductance is proposed, avoiding use of complicated 3-D equivalent reluctance network model to estimate the circumferential armature leakage flux component, and the pole face fringing flux component. Analysis results are supported by 2-D, and 3-D finite element (FE) analysis results, and measurement results on a prototype surface-mounted PMTFM.

Artificial Inductance Concept to Compensate Nonlinear Inductance Effects in the Back EMF-Based Sensorless Control Method for PMSM

The back EMF-based sensorless control method is very popular for permanent magnet synchronous machines (PMSMs) in the medium- to high-speed operation range due to its simple structure. In this speed range, the accuracy of the estimated position is mainly affected by the inductance, which varies at different loading conditions due to saturation effects. In this paper, a new concept of using a constant artificial inductance to replace the actual varying machine inductance for position estimation is introduced. This facilitates greatly the analysis of the influence of inductance variation on the estimated position error, and gives a deep insight into this problem. It also provides a simple approach to achieve a globally minimized position error. A proper choice of the artificial machine inductance may reduce the maximum position error by 50% without considering the actual inductance variation in the control algorithm. Analytical and experimental results are given for validating the proposed theory.

Minimum-Voltage Vector Injection Method for Sensorless Control of PMSM for Low-Speed Operations

In this paper, a simple signal injection method is proposed for sensorless control of permanent-magnet synchronous machine (PMSM) at a low speed, which ideally requires one voltage vector only for position estimation. The proposed method is easy to implement, resulting in low computation burden. No filters are needed for extracting the high-frequency current signals for position estimation. The use of low-pass filters (LPFs) in the current control loop to obtain the fundamental current component is not necessary. Therefore, the control bandwidth of the inner current control loop may not need to be sacrificed. The proposed method may also be further developed to inject two opposite voltage vectors to reduce the effects of inverter voltage error on the position estimation accuracy. The effectiveness of the proposed method is demonstrated by comparing with other sensorless control method. Theoretical analysis and experimental results are given for validating the proposed new sensorless control method.

Single-Phase Hybrid Switched Reluctance Motor for Low-Power Low-Cost Applications

This paper presents a new single-phase, Hybrid Switched Reluctance (HSR) motor for low-cost, low-power, pump or fan drive systems. Its single-phase configuration allows use of a simple converter to reduce the system cost. Cheap ferrite magnets are used and arranged in a special flux concentration manner to increase effectively the torque density and efficiency of this machine. The efficiency of this machine is comparable to the efficiency of a traditional permanent magnet machine in the similar power range. The cogging torque, due to the existence of the permanent magnetic field, is beneficially used to reduce the torque ripple and enable self-starting of the machine. The starting torque of this machine is significantly improved by a slight extension of the stator pole-arc. A prototype machine and a complete drive system has been manufactured and tested. Results are given in this paper.

Analysis and Design of Double-Sided Air Core Linear Servo Motor With Trapezoidal Permanent Magnets

In order to reduce the thrust ripple of linear servo system, a double-sided air core permanent magnet linear servo motor with trapezoidal shape permanent magnets (TDAPMLSM) is proposed in this paper. An analytical model of the motor for predicting the magnetic field in the air-gap at no-load is introduced. This model is derived based on the equivalent magnetization intensity method, and its accuracy is validated by using the results obtained from the finite-element method. The key dimensions that affect the air-gap magnetic field are analyzed based on the analytical model, and the design is optimized by using genetic algorithm. A thrust ripple reduction of 70.6% is achieved by optimization. The proposed analytical model may be used for a quick and reliable design and design optimization of the TDAPMLSM.

Determination of High-Frequency

This paper presents a reliable method for the experimental determination of high-frequency d- and q -axis inductances for surface-mounted permanent-magnet synchronous machines (SMPMSMs). Knowledge of the high-frequency d- and q-axis inductances plays an important role in the efficient design of sensorless controllers using high-frequency signal injection techniques. The proposed method employs a static locked-rotor test using an ac +dc power supply. By injecting a high-frequency rotating voltage vector into the machine, the d- and q-axis inductances may simultaneously be determined with no need to change the rotor position. Measurements are carried out at steady state. The recording of instantaneous waveforms using a dedicated data acquisition system is avoided. In this paper, experimental results are presented, on a commercial SMPMSM, using the proposed method.

d

With the development of electric vehicles, increasing attention is paid to the selection of motor type for a specific vehicle application. Candidate drives include induction, reluctance, permanent magnet and transverse flux motor types. Calculations for these four machine types have been done to suit EV applications. In this paper, an analytical method is employed to extend these calculation results to general cases. The transverse flux machine (TFM) is taken as the reference machine and compared with the other types of machines by describing the main differences between them. Thus, the main characteristics of each machine type may be compared. In the paper, the TFM provides the best power and torque density at low speed with high efficiency, and seems suitable for EV application.

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This paper presents a sensorless-controlled, low-cost, low-power, and variable-speed drive system suitable for fan and pump applications. The main advantages of this drive system are the low system cost, simple converter structure, and simple but robust sensorless control technique. The drive motor is a special hybrid switched reluctance motor. The proposed sensorless control method beneficially utilizes the stator side PM field and its performance is motor parameter independent. The unique low-cost drive system solution, simple and robust sensorless control features of this drive system, is demonstrated in detail in this paper. Important design details for practical implementation of the sensorless control algorithm are included. The complete drive system performance is validated using a prototype drive system.