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A Novel Sensorless-Drive Method to SRM by Impressing Pulse-Voltage on a Single Phase 11A Novel Sensorless-Drive Method to SRM by Impressing Pulse-Voltage...

    A Novel Sensorless-Drive Method to SRM by Impressing Pulse-Voltage on a Single Phase 1

    A Novel Sensorless-Drive Method to SRM by

    Impressing Pulse-Voltage on a Single Phase

    印加單相脈衝電壓於切換式磁阻馬達之

    無檢測器驅動法

    Chung-Neng Huang

    黃崇能

    國立台北科技大學車輛工程系

    Abstract

    Due to a lot of drawbacks exist at present in the sensorless drive methods of Switched Reluctance Motor (SRM)[1]-[7]; a new conception is proposed in this paper. The feature of the proposal is: only one unexcited phase is required to be impressed pulse voltage for detecting the rotor position. Consequently, both of the control circuit and algorithm are simplified. Furthermore, since the mechanism for determining the impressed timing of the pulse voltages is introduced into the control system, the negative torque and noise resulting from the residual currents can be extremely eliminated. In addition, for the sake of the proposed method is quite simple, instead of expensive Digital Signal Processor (DPS) the entire experimental system can be implemented by Field Programmable Gate Array (FPGA). The appropriateness and efficiency of the proposed method are confirmed through the comparison of those results from simulation studies and experiments.

Keywords: Switched Reluctance Motor, Sensorless Drive, Pulse Voltage, and FPGA.

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2 臺北科技大學學報第三十七之一期

    摘要

    為改善目前存在於切換式磁阻馬達無檢測器驅動法之缺點(對此(本文提出一個新的方法(來解決這些問題。 此法的特點為: 一,只要單一非激磁相印加以脈衝電壓即可檢測出轉子位置。因此(在硬體設備及控制程式上都可以被簡化。二,導入脈衝電壓印加時機的決策機構。如此一來(因殘存電流所導致之負轉矩可被精確地去除(所以馬達運轉穩定且噪音減小。又所提案之驅動法相當地簡單(故可利用FPGA以取代昂貴的DSP來完成。最後(本文將所提方法進行電腦模擬(並與實機試驗作比較(以驗證該方法之可行性與有效性。

關鍵詞;切換式磁阻馬達!無檢測器驅動法!脈衝電壓, FPGA

    投稿受理時間: 92 10 15 審查通過時間: 93 1 2

    Nowadays, owing to the remarkable growth I. Introduction

    of power electronic technology, various subjects

    to AC motors have been progressed. Where, the In the recent years, the rapid industriali-

    application of SRM is worthy of note. Since the zation makes the demand on automatic

    framework of SRM is only built of silicon-steel production equipment increase. Where, electric

    laminations in both rotor and stator, it is not only motors have been taken as the main drivers to

    quite simple in structure but also solidly enough those production facilities. In order to further

    to operate in high speed driving and the serious extend the application of electric motors, the

    environments with high temperature or vibration. improvement of motor performance is strongly

    Furthermore, for the reason of no winding loss desired. However, since the problems as brush

    occurring in rotor as it existing in permanent discharge and commutator sparks involving with

    magnet synchronous motors (PMSM), the the unavoidable abrasion between brushes and

    efficiency of SRM is better than those of commutator to DC motor occur frequently, the

    induction motors. According to those desirable conservative periodical inspection is required.

    features and advance performance of SRM as Consequently, the growing tendency toward the

    simple structure, high reliability and low cost, it substitution of AC motors for the DC ones to

    is adoptable to be the low-cost variable-speed solve the problems.

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    drivers in many industrial applications as Since the proposed method is quite simple, changeable speed motors, starters of aircraft, the experimental system can be implemented by hydraulic pumps, fans, blowers and the driving instead of the expensive DSP to a simple analog starters of scooters, electric mobiles etc.. and digital circuit as FPGA. The appropriateness

    A Novel Sensorless-Drive Method to SRM by Impressing Pulse-Voltage on a Single Phase 3 However, SRM has not been put into and efficiency of the proposed method are practical applications widely for the problems of confirmed through the comparison of those large torque ripple, acoustic noise and low results from simulation studies and experiments. power factor. In addition, since most of

    conventional position sensors for SRM drive are II. Estimation of Rotor Position

     & Determination of Exciting weak in structure, it is damageable in high

    Timing temperature, noise or vibration environments.

    That is, the applications of SRM are constrained.

    A. The Nature of SRM Until now, the methods of driving SRM by

     sensorless control have been variously proposed [1]-[7], but above studies are still far from stator practical application. In this paper, a simple and

     rotor practical method to improve the drawbacks of

     those sensorless drive methods by the

     Positive Negative conception of impressing pulse voltage is Torque Torque inductance proposed. Here, two key contributions will be

     achieved:

     1. Instead of impressing pulse voltage into all Rotor Position θ [deg.] rotor position phases of SRM, there is only one unexcited

    Fig.1. Correlation of Rotor Position and phase required. This conception much

    Variation Inductance simplifies the control circuits and algorithm.

    2. A new mechanism is introduced into the The torque generation of SRM bases on the control system to determine the exciting reluctance characteristic as well as the one of a timing of pulse voltage. By which, the conventional motor which can be expressed by negative torques and noise resulting from the rotor position θ and magnetic energy W. residual currents of inductive windings can be W (1) Tcompletely eliminated.

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    In addition, if the nonlinear characteristic of pulse voltages must be hold until the excitation magnetic material is neglected [8], the magnetic to driven phase completely (the slop of energy can be future expressed as: inductance is positive). Consequently, for the accurately impressing pulse voltages on all 4 臺北科技大學學報第三十七之一期 phases, it makes the control system of sensorless

    drive be complicated. Moreover, since the value 12 (2) WL()iof residual current is larger, the current 2

    corresponding to pulse voltage is easy to be Through the combination of (1) and (2), the

    vanished. It will cause the serious error in correlation between magnetic torque and space

    calculation of impressing timing. distribution of inductance can be obtained. For the improvement of above drawbacks 1()L2exiting in conventional methods, the sensorless (3) Tidrive of SRM based on impressing voltage pulse 2 with a low-pass filter is proposed in this paper. (3) shows that if the slope of inductance is The conception of proposed method is shown in positive, the positive excitation can generate the Fig. 2. From the top of Fig. 2 are single-phase torque in positive. Similarly, a negative torque is inductance waveforms, the corresponding phase formed in the interval of negative slope [9]-[12]. and pulse currents, respectively. At last, by Here, giving a 6/4 poles 3-phase SRM as an introducing a second-order low-pass filter, the example as shown in Fig. 1 which is adopted in pulse currents can be turned into an approximate this paper. Suppose the rotor is on 0 degree sinusoidal waveform. Noticeably, the peaks of when its pole comes into line with stator pole the sinusoidal waveform and the waveform of and forms the maximum inductance. On the inductance variation are in inverse. Wherewith, other hand, the minimum inductance occurs

    when the rotor pole leaves from stator pole with

    45 degrees. That is, the cycle of inductance

    variation is 90 degrees in this case. In order to generate the continuous rotating torque, the

    excitation switching to each phase should be

    corresponding to rotor position in turn. However, since the excited phase is changing, the

    estimation of rotor position is required.

    B. Impressing Pulse Voltage on

    Single Phase

    In order to prevent from the occurrence of

    negative torque during the estimation period of

    the rotor position of SRM can be estimated by it. rotor position, the impressing of high-frequency

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    A Novel Sensorless-Drive Method to SRM by Impressing Pulse-Voltage on a Single Phase 5

     Start exciting timing Start exciting timing of Phase Bof Phase A

    Start exciting timing of Phase C

    La1 Phase BPhase A Phase C

    conventional method can be eliminated

    completely. It does facilitate the extension in

    La3 La2 speed control range of SRM. 0

    Fig.3. Determination of Exciting Timing lagging angle θThreshold 1 by Threshold Values Threshold 2

    Threshold 3 III. Simulation Study

    0

    A. Mechanism of Sensorless Drive

    Fig.2. Estimation of Inductance For the proposed method in confirmation of Variation by Low-pass Filter appropriateness and effectiveness, the simulation

    studies are given in this chapter. The simulation C. Exciting Timing Based on mechanism of sensorless drive is modeled by

    Threshold Values MATLAB/Simulink and shown in Fig. 4. Where,

    Fig. 3 shows the three phases of SRM the speed control of this model is based on the inductance waveforms and the output waveform comparison of triangular waveform. The block of the low-pass filter. Suppose that a lagging PVM (pulse timing modulation) is functioned to phase angle θ is between the waveforms of determine the exciting timing of high-frequency filter output and the inductance variation of an pulse voltage as soon as the residual current is optional phase A which is depending on the down to zero. In the block of SLP (sensorless magnetic characteristic and motor speed. processor), only the pulse currents are picked up Continuously, by availing of the phase angle θ, and introduced into the low-pass filter to the reference values as threshold 3,2 and 1 can estimate the rotational speed of SRM. By the be obtained. These thresholds are corresponding way, the lagging angle of filter output can be to those points La1, La2 and La3 on the found and available to calculate the excitation inductance waveform of phase A and as well as timing.

    the start points of exciting timing for phase B, However, since a satisfactory performance phase C and phase A, respectively. of the low-pass filter cannot be obtained if the Consequently, not only the exciting timings of rotation of SRM does not speed up on a certain all phases can be estimated by only impressing value, it still requires a position sensor to offer on a single phase but also the negative torques the data of rotor position to drive when start up. resulting from residual currents in the

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6 臺北科技大學學報第三十七之一期

     LT proportional and integral gains of PI controller DC Voltage ST

    are 2 and 1, respectively, the frequency of !;

    + PWM PI VE voltage pulse is 7[kHz], the band off frequency CV SRM Model of second order low-pass filter is 280[Hz] with VI

    no load. SW PT GS GS speed [rpm] PVM !? Va 6000

    SLP 5000 ia 4000 SP 3000 Motor speed 2000 Assigned speed 1000 CV Converter SW Switch switch to sensorless procedure on 0.2[S ] ω Motor speed 0 0 1 2 3 4 5 6 7 8 9 10 ωe Estimated speed time [S] ω* Assigned speed LT Load torque Fig.5. Simulation Results from 3000 [rpm] ST Step-up torque

    GS Gate signals of three phases ?4000 [rpm] ?5000 [rpm] PT Pulse timing

    VE Excited voltage Load torque [N.m] VI Inverse voltage 0.12 PVM Pulse timing modulation 0.1 SLP Sensorless processor 0.08 SP Sensor procedure 0.06 0.04 0.02 Fig.4. The Mechanism of Sensorless Drive

     0 0.5 1.0 1.5 2.0 2.5 3.0 Whereby, as soon as the motor speed is upon a time [S]

    Speed [rpm] certain speed, the mechanism automatically 4000 switches to sensorless drive mode. 3000 assigned speed 2000 motor speed 1000 B. Calculation Results 0 0.5 1.0 1.5 2.0 2.5 3.0

    Through the simulation model in Fig. 4, the time [S]

    results are shown in Fig. 5. Here, the conditions Fig.6.2 Simulation Result following the

     Speed Command on 3000[rpm] with of calculation are set as following: the sampling

     time is 0.01[ms], DC voltage is 100[V], the

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    A Novel Sensorless-Drive Method to SRM by Impressing Pulse-Voltage on a Single Phase 7

     Loading Increase from 0~0.1[Nt-m]

    As the results shown in Fig. 5, the speed command is set on 3000[rpm] in the beginning. ?. Experimental Demonstration

    Sensor was used to step up the motor until 0.2[S]

     then the model is switched to sensorless drive

    ss mode. Continuously, the speed command is

     rrchanged to 4000[rpm] and 5000[rpm] on 3[S]

    0.2 mm0.2 mm and 6[S], respectively. Whereupon, the 40 mm40 mm

     75 mm75 mmeffectiveness of speed control by the proposed

     method can be confirmed.

     In addition, the simulation of sensorless drive coped with the situation of loading Fig.7 the Basic Structure and variations is held and shown in Fig. 6.2. Here, Components of SRM

     the simulation conditions are set as above ones as motor step up by sensor until 0.2[S] with no Table?Specifications of SRM

     load. Core Material 50H290

    For examining the stability of speed control 30 deg Stator Pole Arc. (β) s

    in the situation of loading variation, the speed 30 deg Rotor Pole Arc. (β) r

    Stack Length 42 mm command is set and fixed on 3000[rpm]. The

    2Cross Section of Winding Space 87 mm load is jumped up to 0.05[Nt-m] from 1[S] and 0.1[Nt-m] from 2[S] as shown in Fig. 6.1. From Yoke Thickness 8 mm the simulation results in Fig. 6.2 shows that even Shaft Radius 12 mm the load is changed but the speed is still Winding/Pole 28 turns

    following with the command and maintain in SRM converter stable operation. Wherewith, the effectiveness of

    the proposed method coped with the situation of

    loading variations can be confirmed. V dc

    Gate signal V i Impressed Sensorless Pulse Timing Driving Unit

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    shown in Fig. 2, the phase current and exciting 8 臺北科技大學學報第三十七之一期 signal are used in the block Sensorless Driving

    Circuit. Let the extracted current pulse of one

     phase through the low-pass filter, the exciting timing of three phases can be found by three Fig.8. Experimental Circuit

    thresholds. Exciting Signal The experimental conditions are set as: the 0

     decreased gain of phase voltage is 1, frequency Phase Current

     0 of voltage pulse is 7[kHz] and the band-off

     frequency of second order filter is 210[Hz]. The Phase Voltage

     0 experiment results are shown in Fig. 10 and 11,

     respectively. Fig. 10 shows the effectiveness of Commutation

     the sensorless drive circuit, whereby a stable 0 Voltage Pulse rotation of SRM can be maintained as well as by 0

    sensor drive. Furthermore, the waveforms of Fig.9. Determination of

     Impressing Timing filter output, gate signals for impressing voltage

     pulse, phase voltage and current are shown in

    In order to demonstrate the practical use of Fig. 10 from up to down, respectively. The the proposed method, an experiment of waveform of phase current shows that the timing sensorless drive is held. As the basic structure of of voltage pulse is exactly impressed. SRM shown in Fig. 7, a 6/4 poles, 3 phases In order to find the optimal PI gains as Kp SRM is applied. The basic driven circuit is an and Ki, the program of PI control is introduced asymmetrical half-bridge converter as shown in into the experiment and under the conditions as: Fig. 8 [13]. the decreased gain of phase voltage is 12/30,

    The function of the block Impressed Pulse source voltage is 30[V], frequency of voltage Timing in Fig. 8 is shown in Fig. 9. Where, the pulse is 7[kHz] and the band-off frequency of decreased phase voltage resulting from residual second order filter is 280[Hz]. In addition, the current is commutated through the absolute sampling frequency is 5[kHz], the carrier value circuit, then it outputs the voltage pulse to frequency is 2[kHz], the proportional gain kp is impress one phase of SRM. Continuously, in 0.001; the integral gain ki is 0.001 in the control order to obtain the extracted current pulse as program of DSP [13]-[15]. In Fig. 12, it shows a

     250

considerable performance of speed following in

    both ranges of speed up from 3000 to 5000[rpm]

    and speed down from 5000 to 2000[rpm]. The results of the experiments confirm the Control Performance of Motor Speed Fig.12 A Novel Sensorless-Drive Method to SRM by Impressing Pulse-Voltage on a Single Phase 9 effectiveness of sensorless adjustable-speed 3000 [rpm] ? 4000 [rpm] ? 5000 [rpm] ?

     4000 [rpm] ? 3000 [rpm] ?2000 [rpm] drive method.

     Sensorless Drive V. Conclusions

     This paper proposed a practical useful sensorless drive method to SRM based on

    magnetic characteristic of motor. By the two 500[rpm]

    important contributions, the controllable range of speed can be further extended than it is done 5[s] by conventional method. Since the mechanism of the proposed method is quite simple, the Fig.10 Experimental Result with Source entire control system can be implemented with

    instead of expensive DSP to a simple analog and Voltage 5[V], 2500[rpm]

    digital circuit as FPGA [17]. The appropriateness and efficiency of the proposed method are confirmed through the comparison Filter output of those results from simulation studies and

    experiments. Gate signal

    Phase Voltage Acknowledgement 5[ms] Phase Current This work was supported in part by the National Science Council of the R.O.C. under Fig.11 The Waveforms Measured from Grant NSC92-2622-E-027-015 -CC3. Sensorless Drive Circuit

     Conference

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    1000[rpm]

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