Utility Power Supply Based on Indirect Matrix

8/8/2019 Utility Power Supply Based on Indirect Matrix

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978-1-4244-4547-9/09/$26.00 2009 IEEE TENCON 2009

Utility Power Supply Based on Indirect MatrixConverter for Electromagnetic Stirrer

Yang Mei, Xiaofan Ji, Zhengxi LiPower Electronics and Motor Drive Engineering Center,

North China University of TechnologyBeijing, China

E-mail: [email protected]

Kai SunState Key Lab of Power Systems

Department of Electrical Engineering,Tsinghua University,

Beijing, China

Abstract Indirect matrix converter (IMC) has some attractive

advantages compared to back-to-back PWM converters and

conventional matrix converters. In this paper, indirect matrix

converter is applied to feed electromagnetic stirrer (EMS) as a

utility power supply. According to the technical requirements by

electromagnetic stirrer, the output current of power supply

should be controlled with high precision and fast dynamic

response both in magnitude and frequency. Hence, a outputcurrent control method based on vector control technique is

developed in this paper, which is realized together with the

SVPWM of indirect matrix converter. Simulations using

MATLAB verify the effectiveness of the developed control

methods. Some experimental results validate the practical

feasibility of this power supply.

Keywords- electromagnetic stirrer; power supply; indirectmatrix converter; vector control

I. INTRODUCTIONElectromagnetic stirring (EMS) technology has been widely

used in metallurgy industry, not only in the steel-making, but

also in the smelting of nonferrous metal (like aluminum alloy).The applications of EMS in metallurgy introduce someattractive merits: 1) The purity of metal liquid can be enhancedduring the process of molding; 2) The surface quality of thefoundry blank can be improved; 3) The casting characteristic ofalloy steel can be improved; 4) The compression ratio of steel-rolling process can be reduced; 5) The speed of continuousfoundry blank can be accelerated. According to the industrialapplications of EMS, there are some technical requirements forthe power supply of EMS: 1) the output current of powersupply should be controlled with high precision and fastdynamic response both in magnitude and frequency; 2) Thepower supply of EMS should has high input power factor andlow harmonic currents injected into power grid [1][2].

Indirect matrix converter (IMC), also named two-stagematrix converter, has obtained much attention in AC-AC powerconversion field during recent years [3]-[5]. Compared withback-to-back PWM converters, IMC exhibits good input/output performances similar as conventional direct matrix converter,such as sinusoidal input/output currents, adjustable input powerfactor, and compact system design because of no large energystorage components. Since IMC involves a practical dc-link, ithas much more attractive characteristics over conventional

direct matrix converter, such as zero current switching in therectifier stage, simple clamping circuit, and decoupled control between the rectifier stage and the inverter stage. Thesecharacteristics improve the efficiency and reliability of IMC. Inaddition, the IMC using RB-IGBT has much higher energyconversion efficiency than back-to-back PWM converters andconventional direct matrix converter [6].

In order to utilize the good characteristics of IMC andrealize high performance EMS, a utility power supply based onIMC is developed in this paper. IMC is usually applied to driveAC motors with motor speed and torque control. However, thekey control issue of EMS power supply is the output currentregulation. In order to fulfill the technical requirements byEMS, an output current control method is developed, which is based on the vector control technique. Simulations usingMATLAB and experiments on a 6kW prototype are conductedto verify the developed control strategy.

II. THEORETIC ANALYSIS AND CONTROL STRATEGYA. Basic Principles

The basic principle of EMS is to execute contact-lessstirring in metal liquid by using electromagnetic force. TheEMS can be considered as a motor with large air-gap, in whichthe inductor operates as a stator and the metal liquid is like arotor. When a AC current with variable frequency is fed intothe winding of EMS, a flux will be exist in the metal liquid,which induces current. The interaction between this inducedcurrent and the flux results in electromagnetic force. The metalliquid will be driven to move by this force on a specificdirection. Hence, the task of the power supply for EMS is to provide AC currents with variable frequencies. The powersupply for EMS can be classified into two categories: three-

phase output or two-phase orthogonal output. In this paper, thepower supply with three-phase balanced output is investigated.Usually, the EMS works in low frequency range according todifferent applications: 1) 0.5-12Hz for mold electromagneticstirring (MEMS); 2) 12-30Hz for final electromagnetic stirring(FEMS).

B. System ConfigurationThe system configuration of the utility power supply based

on IMC for EMS is shown in Fig.1. The IMC consists of input

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LC filter, rectifier stage, clamping circuit, and inverter stage.The EMS is expressed by three-phase inductor windings.

Figure 1. Configuration of utility power supply based on IMC for EMS

C. Control Strategy of Indirect Matrix ConverterThe control diagram of the IMC based power supply for

EMS is shown in Fig.2. Since the IMC has a practical dc-link,conventional SVPWM strategy can be used on the rectifierstage and the inverter stage respectively, which involves two processes: input current SVPWM for the rectifier stage andoutput voltage SVPWM for the inverter stage. The reference

output voltage vector (represented by ,U U ) is provided by

the output current controller, and the reference input current

vector (represented byiref

I ) is determined by the input voltages

and input displacement angle through the input power factor

control. The detailed modulation process is presented in [7].

In addition, a two-step zero current switching (ZCS)commutation method, which was proposed in [7], is employedfor the commutation control of the bi-directional switches inthe rectifier stage.

D. Output Current Control MethodIn order to regulate the output current magnitude and the

output frequency accurately and rapidly, a control method based on the vector control technique for output current isdeveloped.

As shown in Fig.2, the principle of this control method issimilar as the flux oriented vector control technique of ACmotor drives, while the speed control loop is omitted and thecoordinate transformation angle is calculated according tooutput frequency f and sampling time t. The output currentshave been transformed into d-q reference frame. Themagnitude of output current can be controlled through setting

the values ofidref, iqref.

III. SIMULATION STUDYIn order to verify the developed control method described

in Section II, the simulations using MATLAB are conductedunder the steady-state and the dynamic state during frequencychange and magnitude change. In the simulations, a three-phase Y-connected R-L load is used to emulate the winding of

EMS. The load resistance and load inductance in each phase

are 2.92and 0.371H respectively.

Figure 2. Control diagram of utility power supply based on IMC for EMS

The output currents of IMC at steady-state are shown inFig.3 in terms of 5Hz and 25Hz. In the simulation, thereference current magnitude is set at 5A. Hence, the reference

values of d-axis and q-axis current are 6.1237A ( 5 2 / 3 ) and0A respectively. As can be seen, the waveforms are sinusoidaland the magnitudes are controlled with high precision.

a. output frequency 5Hz

b. output frequency 25Hz

Figure 3. Output currents of IMC at steady-state

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The simulation results of the dynamic operation are shownin Fig.4. In the simulation of the output frequency change, thecurrent magnitude is set at 5A. In the simulation of the currentmagnitude change, the output frequency is set at 10Hz. As can be seen, the output currents follow the change commandquickly and accurately, even without oscillation.

a. output frequency change (10Hz -15Hz)

b. current magnitude change (5A - 3A)

Figure 4. Output currents of IMC at dynamic state

IV. EXPERIMENTSA 6kW prototype of indirect matrix converter using RB-

IGBT has been developed, as shown in Fig.5. It mainlyincludes main power circuit, input LC filter, RB-IGBT gatedrive circuit, signal processing circuit, DSP/CPLD control

board and heat sink. The rectifier stage is constructed by theRB-IGBT module 18MBI100W-060A from Fuji Electric.SVPWM algorithm for IMC and motor control techniques arerealized by DSP (F2812) and CPLD (EMP9320LC84). ThisIMC prototype is employed to feed a induction motor withoutrotating, whose three-phase stator is used to emulate thewinding of EMS. The resistance and inductance of the stator in

each phase are 2.92and 0.371H respectively, which is thesame as those in simulations.

The experimental input waveforms of IMC at steady-stateare shown in Fig.6. As can be seen, the input current is almostsinusoidal and in phase with input voltage. This means thepower factor of the developed EMS power supply at grid sideis near 1.

Figure 5. Prototype of indirect matrix converter

Figure 6. Input phase voltage (blue: 10V/div) and current (green: 0.5A/div)

The experimental output waveforms of IMC at steady-stateare shown in Fig.6, including output line-to-line voltage andline current. As shown in Fig.7(a), in the first test the output

frequency is set at 5Hz, and current magnitude is set at 1.5A;As shown in Fig.7(b), in the second test, the output frequencyis set at 25Hz and the current magnitude is set at 0.5A. As canbe seen, the currents of EMS power supply are well controlledwith accurate frequency and amplitude.

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a. line voltage (dark blue:50V/div) and line current (light blue:1A/div)(output frequency 5Hz)

b. line voltage (dark blue:25V/div) and line current (light blue:1A/div)(output frequency 25Hz)

Figure 7. Output waveforms of IMC under steady-state

V. CACULATIONIn this paper, a RB-IGBT based IMC is applied to construct

a utility power supply for EMS. According to the technicalrequirements by EMS, a output current control method basedon vector control technique is developed, which is realizedtogether with the SVPWM of IMC.

Simulation results by using MATLAB, which includesgood steady-state waveforms and well-controlled dynamicresponses, verify the effectiveness of the developed controlmethod.

Experimental results on a 6kW RB-IGBT IMC prototypeshow the practical feasibility and good input power quality ofthe developed EMS power supply. Further experimental resultswill be presented in final paper.

ACKNOWLEDGMENT

The authors would like to appreciate the financial supportby National Natural Science Foundation of China (50607012).

REFERENCES

[1] Xiaolei Wang, Qingfu Li, Two phase electromagnetic stirring inverterbased on space vector oriented control, Foundry Technology, vol.26,No.11, 2005, pp.1061-1064. (in Chinese)

[2] Ovidiu Pesteanu, Electromagnetic mould stirring with higher supplyfrequency, ISIJ International, vol.48, No.2, 2008, pp.251-253.

[3] L. Wei, T. A. Lipo, and H. Chan, Matrix converter topologies withreduced number of switches, Proceedings of IEEE PESC02, vol.1,2002, pp. 57-63.

[4] J. W. Kolar, M. Baunann, F. Schafmeister, and H. Ertl, Novel three-phase AC-DC-AC sparse matrix converter, Proceedings of IEEEAPEC2002, 2002, pp.777-791.

[5] C. Klumpner, F. Blaabjerg, Using reverse blocking IGBTs in powerconverters for adjustable speed drives, Proceedings of IEEE IAS2005,vol.3, 2005, pp.1516-1523.

[6] Y. A.-R. I. Mohamed and T. K. Lee, Adaptive self-tuning MTPAvector controller for IPMSM drive system, IEEE Trans. on EnergyConversion, vol.21, No.3, 2006, pp.636-644.

[7] Gang Li, Kai Sun, Lipei Huang, A novel algorithm for space vectormodulated two-stage matrix converter, Proceedings of ICEMS2008,2008, pp.1316-1320.

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Utility Power Supply Based on Indirect Matrix