Back EMF Sensorless-Control Algorithm for High-Dynamic Performance PMSM

Adviser : Y.S. KungStudent :Jin-Mu Lin

IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 57, NO. 6, JUNE 2010,P.2092~2100

Fabio Genduso, Rosario Miceli, Member, IEEE, Cosimo Rando, and Giuseppe Ricco Galluzzo

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Outline

Abstract Introduction Control-algorithm description Experimental results Conclusion Appendix References

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Abstract

1. a low-time-consuming and low-cost sensorless-control algorithm for high-dynamic performance permanent-magnet synchronous motors.

2. This control algorithm is based on the estimation of rotor speed and angular position starting from the back electromotive force space-vector

determination without voltage sensors by using the reference voltages given by the current controllers instead of the actual ones.

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3. This choice obviously introduces some errors that must be vanished by means of a compensating function.

4. The mathematical structure of the estimation guarantees a high degree of robustness against parameter variation as shown by the sensitivity analysis reported in this paper.

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Introduction

1. in field-oriented control for brushless machines, the exact knowledge of the rotor angular position is needed.

2. when the rated power of an electrical machine is small or fractional,the electrical-drive comprehensive cost will raised.

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3. the signal transmission between sensor and control systems can be subjected to electromagnetic interference (EMI) coming from external sources, producing an error in measurement that may be significant for feedback control.

4.So in this paper, a novel low-time-consuming and low-cost sensorless-control algorithm for PMSM drives, both surface or IPM mounted.

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Control-algorithm description

A. PMSM Mathematical Model

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8

the torque expression

in (1) becomes

Because of the constant PM flux, the torque depends only on the quadrature component of the stator current.

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B. Description of the Estimator

Assuming a balanced three-phase system, the expression of the back EMF space vector components is

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The argument of the back EMF clearly is not the real rotor position.

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A simple analysis on the machine model at steady state with id = 0 gives the following expression for correct rotor position:

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Let T be the lag time introduced by the inverter and be the first term of (4),

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Now, after substitution, considering a well-known calculus formula for the increment of functions, we can write

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and developing the partial derivatives of the incremental term

, we get

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Now, neglecting all harmonics, consider that and are, respectively, cosine and sine functions of ωt. The same can be

said for and . In particular, it is

where V is the rms value of the stator voltage.

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It is now clear that T being very small compared with 2π/ω

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In this way, our previous expansion of (8) reduces to

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that in a more compact form becomes

cos(ϕ) being the power factor in the motor operation and V , I,and E are, respectively, the rms values of the stator voltages,currents, and back EMF.

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Equation (12) may be written also in complex-number form

where ( ) denotes the complex conjugate.∗

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Furthermore, as with = 0, the motor drive operates with near-unity power actor, (12) can be further simplified as follows:

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Introducing these speed- and current-offset corrections in (4), one finally gets a suggestion for the first expression of

“estimated” position

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Fig. 2 shows the sum of speed and current offsets

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Equation (15) may be rewritten in a differential form by substituting with the derivative of

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C. Estimator Realization

Taking the presence of the PI into account, the ultimate estimator-equation form is

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Estimator block diagram.(Fig.3.)

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Experimental results

A. Description of the Test Bench 1) an IPMSM; 2) a controlled hysteresis brake; 3) a digital signal processing and control

engineering(dSPACE) board; 4) a resolver (used only for comparison purpose).

A master Power PC 604E and a Ti slave DSP of the type TMS320F240.

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Test bench for IPMSM electrical-drive machine.(Fig.4.)

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B.Results and Discussion

1) step change in motor speed from 400 up to 4000 r/min (nominal speed) and back again to 400 r/min.

2) sudden application of a 1.8-N · m load torque while the motor runs at 4000 r/min speed.

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Comparison between (solid line) real and (dashed line) estimated speed during the execution of test n. 1. Fig. 5.

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(Solid line) Real and (dashed line) estimated position during the execution of test n. 1.

Fig. 6.

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Comparison between (solid line) real and (dashed line) estimated rotor position during the execution of test n. 2. Fig. 7.

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Comparison between (solid line) real and (dashed line) estimated rotor speed during the execution of test n. 2. Fig. 8.

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Estimation error for rotor speed during the execution of test n. 2.

Fig. 9.

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Conclusion

this paper, a low-time-consuming and low-cost sensorless-control algorithm for PMSM without voltage probes for position and speed estimation has been introduced, discussed, and experimentally verified.

Drive starting is made with open-loop operation.

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in the proposed control systems, the reference voltages instead of the actual voltages are used for the back-EMF estimation,therefore eliminating the presence of voltage probes.

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Clearly, the presented correction method is intended, above all, to make the electrical drive cheaper and suitable for industrial drives both surface or internal mounted PM working within the nominal speed range, as, for example, for spindle drives, while the field weakening is not taken into account.

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