High performance sensorless speed vector control of SPIM Drives with on-line stator resistance estimation

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Abstract

The aim of this paper is to implement a sensorless Indirect Stator Field Oriented Control (ISFOC) of Single-Phase Induction Motor Drive (SPIMD) with stator resistance tuning. The proposed method for the estimation of speed is based only on measurement of stator currents. A very simple identification algorithm using d-axis stator current error for identifying the stator resistance is proposed. Experimental results for SPIMD are presented and analyzed by using a dSpace system with DS1104 control board based on the Digital Signal Processor (DSP) TMS320F240. Simulated results are compared with experimental results on a test 1.1 kW SPIM setup. The agreement between simulated and experimental results proves the validity of the proposed method.

Introduction

The continuous increasing of energy requires the companies to take into account the energy saving and budgetary. The Single-Phase Induction Motor (SPIM) is widely used for fixed-speed operation in a wide variety of HVAC (Heating, Ventilation and Air-Conditioning) commercial and industrial applications, such as blowers, compressors, fans, conveyors, air conditioners, machine tools and pumps. A tested and economic solution is the use of variable frequency converter to control the speed of the SPIM for HVAC applications. Variable speed process of this motor drive will give us improved performances and energy saving. Therefore, this is a current topic of research interest. A number of works have reported the improvement of SPIM efficiency up to now. By cost reduction of variable-speed drives during the 1990s, their utilization for driving SPIMs gradually increased. Some references have presented various power converter topologies for variable-speed Single-Phase Induction Motor Drive (SPIMD) [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]. Most researchers of two-phase inverters have selected the two-leg type as a model configuration, and lately they have taken an increasing interest in the three-leg type. A practical topology has to conform to: low implementation cost, easy control, reduced complexity and high lifetime. This paper presents a voltage source inverter topology with three-leg for SPIMD systems. A more suitable method to supply the SPIMD with an orthogonal voltage system implies a six-transistor bridge, originally proposed in [1], [5], [7], [9], [11]. Recently, Indirect Stator Field Oriented Control (ISFOC) of SPIMD has been receiving wide attention in the literature [1], [4], [5]. All high performance vector controlled SPIMD require accurate rotational speed information for feedback control. This information is provided by a speed sensor. The use of this sensor implies more electronics, higher cost and lower reliability, difficulty in mounting in some cases such as motor drives in harsh environment and high speed drives, increase in weight, increase in size and increase electrical susceptibility [17]. The speed sensorless vector control of induction motors has been receiving increased research attention during many years. The speed estimation of field-oriented control SPIMs has been rarely presented so far. In fact, the asymmetrical models of SPIM cause extra complexity in the latter case. In the existing literature, some approaches have been suggested for speed sensorless SPIM in [12], [13], [14], [15], [16]. In paper [16], the authors suggested to estimate the motor speed using rotor voltage vector which is defined in complex domain. The sensorless speed control strategy using Model Reference Adaptive Systems (MRAS) techniques is based on the comparison between the outputs of two estimators when motor currents and voltages must still be measured [18]. The MRAS algorithm sensorless speed vector control of three phase induction motor drive is sensitive to resistance variation [18]. A vast majority of speed estimation schemes require an accurate knowledge of all the motor parameters, including the stator resistance. To overcome this problem, on-line tuning stator resistance variation of the SPIM is essential in order to maintain the dynamic performance of a sensorless ISFOC drive. Recently, many works have been developed using different approaches to estimate rotor speed and stator resistance. In general, all of the methods rely on stator current measurement and predominantly require information regarding stator voltages as well. In order to overcome the problems of system complexity and cost, a sensorless speed control for SPIMD using ISFOC strategy is evaluated in this paper. The novelty of this work is the association of a sensorless speed control for SPIMD with stator resistance tuning and dynamic feedforward decoupling scheme. The estimated speed is obtained only from the main and auxiliary windings stator currents measurements and the q-axis current reference generated by the control algorithm. The error signal of the measured q-axis current from its reference value feeds a Proportional plus Integral (PI) controller. This last one delivers the estimated slip frequency. In order to estimate the rotor speed, the estimated slip frequency is subtracted from the synchronous angular frequency. The error between d-axis stator current and that generated by the control algorithm allows us the on-line estimation of stator resistance estimation by using a pure integral controller. Simulation and experimental results are presented to demonstrate the main characteristics of this method for sensorless ISFOC of SPIMD system and to validate the methodology and the modelling approach employed in this work.

Section snippets

Single-phase induction motor model

The dynamic model for the SPIM in a stationary reference frame can be described by the following equations:vsα=Rsdisα+dϕsαdtvsβ=Rsqisβ+dϕsβdt0=Rrirα+dϕrαdt+ωrϕrβ0=Rrirβ+dϕrβdt-ωrϕrαϕsα=Lsdisα+Msrdirαϕsβ=Lsqisβ+Msrqirβϕrα=Lrirα+Msrdisαϕrβ=Lrirβ+MsrqisβTe=np(Msrqisβirα-Msrdisαirβ)Because of the unbalance of the stator windings of the single-phase machine, vector control algorithm requires some adaptation to be applied to this type of machine. As was done in [1], [5] to drive the symmetrical

Indirect Stator Field Oriented Control

From (3), (4), (5), (6), (7), (8), (10), (12) it is possible to derive dynamic equations, which relate stator fluxes to stator currents, as:dϕsα1dt+1τrϕsα1+ωrϕsβ1=Lsdτrisα1+σdLsddisα1dt+ωrk2σqLsqisβ1dϕsβ1dt+1τrϕsβ1-ωrϕsα1=k2Lsqτrisβ1+k2σqLsqdisβ1dt-ωrσdLsdisα1whereσd=1-Msrd2LsdLr,σq=1-Msrq2LsqLr,τr=LrRrThe vector model for the stator-flux control written for an arbitrary frame (denoted by the superscript a) using Eqs. (13), (14) are given by:dϕs1adt+1τrϕs1a+j(ωa-ωr)ϕs1a=Lsdτris1a+σdLsddis1adt+j(

Feedforward decoupling controller

For ISFOC, the d-axis of the reference frame is oriented along the stator flux vector, which means Φsd = Φs1 and Φsq = 0. The dynamic model of the SPIM can be represented according to the usual d-axis and q-axis components in a synchronous rotating frame as:vsd1=vd-Ed=Rsd(τsd+τr)τr1+σdτsdτrτsd+τrsisd1-k2σqLsqωslisq1-ϕs1τrvsq1=vq-Eq=k2Rsq(τsq+τr)τr1+σqτsqτrτsq+τrsisq1+σdLsdωslisd1+ωrϕs1whereEd=k2σqLsqωslisq1+ϕs1τrEq=-σdLsdωslisd1-ωrϕs1The Ed and Eq are, respectively, the d- and q-back electromotive

Slip speed estimation

The simulation results studied in [1] show that the q-axis current error varies almost linearly according to the slip frequency for a reference speed of 1500 r/min with nominal load torque applied to the SPIM. Thus, it is possible to use the q-axis current error for the estimation of slip speed.

From Eq. (19), we obtain the following q-axis reference current with stator flux reference and slip angular frequency estimationsisq1=-1σdτrisq1+ϕs1σdLsdωsl-ωslisd1The component error between

Experimental implementation

We have tested the controller at nominal and zero speed command with load torque applied for sensorless speed controlled SPIMD. An experimental setup is developed to evaluate the proposed method for the estimation of speed. A schematic overview of the implemented setup is given in Fig. 5 and a photograph of the experimental test system is shown in Fig. 6. The motor used in the experimental system is loaded by a magnetic powder brake. The experimentation has been carried out using

Conclusion

The paper presents a parallel estimator that enables simultaneous estimation of rotor speed and stator resistance for SPIM. A simple and rather accurate method for speed estimation has been presented that is able to perform at nominal, low and zero sensorless speed control of SPIMD. The sensorless control method using slip angular speed estimation with stator resistance tuning is based on the measured and reference d, q axis stator currents of SPIM. The results were satisfactory and the

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