Department of Electrical Engineering, Southern Taiwan University Practical sensorless control for...

Department of Electrical Engineering, Southern Taiwan University

Department of Electrical Engineering, Southern Taiwan University

Practical sensorless control for inverter-fed BDCM compressors

Practical sensorless control for inverter-fed BDCM compressors

Student: Chien-Chih HuangTeacher: Ming-Shyan Wang Date : 2011.04.27

CHEN H.C., CHANG Y.C., HUANG C.K.: ‘Practical sensorless control for inverter-fed BDCM compressors’, IET Electric Power Appl., 2007, 1, (1), pp. 127–132

Department of Electrical Engineering, Southern Taiwan UniversityDepartment of Electrical Engineering, Southern Taiwan University 22

Outline

AbstractIntroductionSystem configurationSensorless circuits

Terminal-voltage analysisDesign of sensorless circuitsDesign resultsSensorless-commutation table

Sensorless controlStarting strategyLimitationsPractical sensorless control

Experiment ResultsConclusionReferences


Abstract

Brushless DC motors (BDCMs) possess higher efficiencies than the conventional induction motors and BDCMs have therefore been used widely in inverter-fed compressors.

Since the Hall position sensors cannot work well in the high-temperature environment of refrigerants,sensorless control schemes play an important role in the application of inverter-fed BDCM compressors.


Abstract

The sensorless circuits used have been analysed in detail to find the design rules of the circuit parameters for various compressor motors.

The limitations of sensorless control are discussed to develop a practical speed controller for BDCM compressors.

The developed starting strategy and sensorless algorithms are presented and digitally implemented.

Some experimental results are displayed to demonstrate the proposed sensorless speed control for BDCM compressors.


Introduction

During the last decades, more and more researchers have focused their attention on energy-saving technology and promoted the development of high-efficiency products.

It has been concluded that inverter-fed compressors (or called variable-speed compressors) are the key to increasing system efficiency and reducing energy consumption.


Introduction

To commutate the motor current adequately, the actual rotor positions are required in normal BDCM operation.

Unfortunately, in the refrigeration application,high-temperature refrigerants will surround the compressor motor and commonly used rotor-position sensors such as Hall elements cannot be used to sense the positions.

To solve this problem, many sensorless control methods have been proposed.


System configuration

Fig. 1 System configuration of the sensorless speed control


System configuration

Fig. 2 Waveforms of the BDCM operation


Terminal-voltage analysis

As shown in Fig. 1, we can express the terminal voltagesVx as

Since ｜ VZX ｜ is generally smaller than ｜ EX ｜ in motor operationVZX can be neglected and thus (1) can be rewritten as

VX = VN + EX + iXZX = VN + EX + VZX X=U ， V ， W (1)

VXN = VX － VN E≒ X X=U ， V ， W (2)


Design of sensorless circuits

Fig. 3 Sensorless circuits



The transfer function between the terminal voltage VU and thenew signal vU can be derived as



Note that the near-90°phase shifting occurs at a frequency ten times higher than the cut-off frequency of the lowpass filter.

The DC-filtering stage designed here is to prevent the DC and low-frequency components from appearing in the filtering signals.

The main function of the last PWM-filtering stage is to attenuate the high-frequency component in signals. Thus, its cut-off frequency fcut3 must be placed far smaller than the PWM frequency

f PWM and larger than the highest frequency (PωrHigh/120).


Design results

The PWM switching frequency is fpwm = 8 kHz and the 4P BDCM compressor is operating during the speed range between 1000 rev/min (=ωrLow) and 6000 rev/min (=ωrHigh) to yield variable cooling capability.

It is sensible to select the individual resistor and capacitor values as follows to meet the design rules (8)–(10).

R1 = 470 kΩ ， R2 = 47 kΩ ， R3 = 30 kΩR4 = 470Ω ， C1 = C2 = 2.2μF ， C3 = 0.47μF


Design results

Fig. 4 Responses of resulting sensorless circuits for different values of resistor R4 (a) Amplitude response (b) Phase response


Sensorless-commutation table

Fig. 2 Waveforms of the BDCM operationA B C D E F A

Table 1: Sensorless-commutation table


Starting strategy

Fig. 5 Timing diagram of proposed starting strategy


Starting strategy

The period Tn of each commutation state in starting strategy is obtained as

and the synchronous speed orsyn can be formulated as

Then, (12) can be rewritten as


Limitations

Fig. 6 Limitations of the sensorless controlled BDCM(a) Torque against speed (b) Power against speed


Practical sensorless control

Fig. 7 Proposed sensorless speed controller for actual BDCM compressors


Practical sensorless control

The BDCM speed or in revolutions per minute is obtained from the period TU of signal HU through counting in the MCU timer:

The above limiting lines Tmin will be considered in our sensorless speed controller. After obtaining the frontend input current iin through the current transformer (CT) and the A/D peripherals shown in Fig. 1, we can estimate the input power estimate . Then, the estimated power will be co-ordinated in Fig. 6b to decide the speed limit or;lim it as shown in Fig. 7

PP


Experimental results

Fig. 8 Voltage and current waveforms at 5400 rev/min withdifferent values of R4(a) R4=2kΩ(b) R4=470Ω



Fig. 9 Critical waveforms at different speeds(a) 900 rev/min(b) 1800 rev/min(c) 2700 rev/min



Fig. 9 Critical waveforms at different speeds(d) 3600 rev/min(e) 4500 rev/min(f) 5400 rev/min



Table 2: Experimental data of developed BDCMcompressor


ConclusionThis paper develops a sensorless controller for BDCM compressors where the operating limitations of inverter-fed BDCM compressors and sensorless control are considered.

To improve the current waveforms, the sensorless circuits are designed and implemented.

The control algorithms, including the starting strategy, the sensorless commutation table and the speed-control loops, are all implemented digitally in MCU.


References1 Murakami, H., Honda, Y., Kiriyama, H., Morimoto, S., and Takeda, Y.: ‘The performance comparison of SPMSM, IPMSM and SynRM in use as air-conditioning compressor’. Proc. IAS’99, 1999, pp. 840–845

2 Soong, W.L., Kliman, G.B., Johnson, R.N., White, R.A., and Miller, J.E.: ‘Novel high-speed induction motor for a commercial centrifugal compressor’, IEEE Trans. Ind. Appl., 2000, 36, (3), pp. 706–713

3 Llzuka, K., Uzuhashi, H., Kano, M., Endo, T., and Mohri, K.: ‘Microcomputer control for sensorless brushless motor’, IEEE Trans. Ind. Appl., 1985, 21, (4), pp. 595–601

4 Moreira, J.C.: ‘Indirect sensing for rotor flux position of permanent magnet AC motors operation in a wide speed range’. Proc. IAS’94, 1994, pp. 401–407

5 Ogasawara, S., and Akagi, H.: ‘An approach to position sensorless drive for brushless DC motors’, IEEE Trans. Ind. Appl., 1991, 27, (5), pp. 928–933

6 Chen, H.C., and Liaw, C.M.: ‘Current-mode control for sensorless BDCM drive with intelligent commutation tuning’, IEEE Trans. Power Electron., 2002, 17, (5), pp. 747–756


References7 Chen, Z., Tomita, M., Doki, S., and Okuma, S.: ‘An extended electromotive force model for sensorless control of interior permanentmagnet synchronous motors’, IEEE Trans. Ind. Electron., 2003, 50, (2), pp. 288–295

8 Shao, J., Nolan, D., and Hopkins, T.: ‘Improved direct back EMF detection for sensorless brushless DC (BLDC) motor drives’. Proc. APEC’03, 2003, pp. 300–3059 Chen, H.C., Chang, Y.C., Lin, S.P., Huang, C.M., Chen, Y.C., and Liang, K.Y.: ‘Sensorless control for DC inverter-fed compressors’. Proc. APEC’04, 2004, pp. 1106–1110


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