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Simple Direct Power Control of Three-Phase. PWM Rectifier Using Space-Vector. Modulation (DPC-SVM). Mariusz Malinowski, Member, IEEE, Marek Jasinski, ...
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 51, NO. 2, APRIL 2004

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Simple Direct Power Control of Three-Phase PWM Rectifier Using Space-Vector Modulation (DPC-SVM) Mariusz Malinowski, Member, IEEE, Marek Jasin´ski, Student Member, IEEE, and Marian P. Kazmierkowski, Fellow, IEEE

Abstract—This paper proposes a novel and simple direct power control of three-phase pulsewidth-modulated (PWM) rectifiers with constant switching frequency using space-vector modulation (DPC-SVM). The active and reactive powers are used as the pulse width modulated (PWM) control variables instead of the three-phase line currents being used. Moreover, line voltage sensors are replaced by a virtual flux estimator. The theoretical principle of this method is discussed. The steady-state and dynamic results of DPC-SVM that illustrate the operation and performance of the proposed system are presented. It is shown that DPC-SVM exhibits several features, such as a simple algorithm, good dynamic response, constant switching frequency, and particularly it provides sinusoidal line current when supply voltage is not ideal. Results have proven excellent performance and verify the validity of the proposed system. Index Terms—Converter control, harmonics, power-factor correction, power quality, sensorless control.

I. INTRODUCTION

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OST three-phase rectifiers use a diode bridge circuit and a bulk storage capacitor. This has the advantages of being simple, robust, and low in cost. However, a diode rectifier results in only unidirectional power flow, low power factor, and high level of harmonic input currents. Therefore, a three-phase pulsewidth-modulated (PWM) rectifier (Fig. 1) is a more interesting solution for industrial application thanks to viable advantages such as: • bidirectional power flow; • low harmonic distortion of line current; • regulation of input power factor to unity; • adjustment and stabilization of dc-link voltage; • reduced dc filter capacitor size. PWM rectifiers were applied by most global companies (Siemens, ABB, and others) like an ac/dc/ac converter or a dc distributed power system (Fig. 2) [12], [13]. Development of control methods for PWM boost rectifiers was possible thanks to advances in power semiconductor devices and digital signal processors, which allow fast operation Manuscript received May 28, 2002; revised December 2, 2003. Abstract published on the Internet January 13, 2004. This work was supported by the Foundation for Polish Science (FNP). This paper was presented at the 28th Annual Conference of the IEEE Industrial Electronics Society, Seville, Spain, November 5–8. The authors are with the Institute of Control and Industrial Electronics, Warsaw University of Technology, 00-662 Warsaw, Poland (e-mail: [email protected]; [email protected]; [email protected]). Digital Object Identifier 10.1109/TIE.2004.825278

and cost reduction. It offers possibilities for implementation of sophisticated control algorithms. Appropriate control can provide both the rectifier performance improvements and reduction of passive components. Various control strategies have been proposed in recent works on this type of PWM rectifier [2], [4], [8]–[10]. A well-known method of indirect active and reactive power control is based on current vector orientation with respect to the line voltage vector [voltage-oriented control (VOC)] [2], [4], [10]. VOC guarantees high dynamics and static performance via internal current control loops. However, the final configuration and performance of the VOC system largely depends on the quality of the applied current control strategy [3]. Another less known method based on instantaneous direct active and reactive power control is called direct power control (DPC) [8], [9]. Both strategies mentioned do not perform sinusoidal current when the line voltage is distorted. Only a DPC strategy based on virtual flux instead of the line voltage vector orientation, called VF-DPC, provides sinusoidal line current and lower harmonic distortion [5], [7]. However, among the well-known disadvantages of the VF-DPC scheme are: • variable switching frequency (difficulties of LC input filter design); • violation of polarity consistency rules (to avoid switching over dc-link voltage); • high sampling frequency needed for digital implementation of hysteresis comparators; • fast microprocessor and A/D converters required. Therefore, it is difficult to implement VF-DPC in industry. All the above drawbacks can be eliminated when, instead of the switching table, a PWM voltage modulator is applied. This paper presents a new simple method of line voltage sensorless DPC with constant switching frequency using space-vector modulation (DPC-SVM). II. DPC DPC is based on the instantaneous active and reactive power control loops [8], [9]. In DPC there are no internal current control loops and no PWM modulator block, because the converter switching states are selected by a switching table based on the instantaneous errors between the commanded and estimated values of active and reactive power. Therefore, the key point of the DPC implementation is a correct and fast estimation of the active and reactive line power.

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Fig. 1. Representation of three-phase PWM boost rectifier.

Fig. 2.

DC distributed power system.

A. Virtual Flux Estimator

then, similarly to (3) a VF equation can be presented as [11]

It is possible to replace the ac-line voltage sensors with a virtual flux estimator, which gives technical and economical advantages to the system such as simplification, isolation between the power circuit and control system, reliability, and cost effectiveness. The voltages imposed by the line power in combination with the ac-side inductors are assumed to be quantities related to a virtual ac motor as shown in Fig. 3(a). Thus, and represent the stator resistance and the stator leakage inductance of the virtual motor and line-to-line voltage: , , would be induced by a virtual air-gap flux. In other words the integration of the voltages leads to a virtual flux , in stationary - coordinates [Fig. 3(b)] [1]. (VF) vector (1) where (2)

(4) Based on the measured dc-link voltage and the duty cythe virtual flux components cles of modulator are calculated in stationary ( – ) coordinates system in the block (P&VF) as follows: (5a) (5b) B. Active and Reactive Power Estimator The measured line currents , and the estimated virtual , are used to the power estimation flux components [5], [7]. Using (3) the voltage equation can be written as (in practice, can be neglected) (6) Using complex notation, the instantaneous power can be calculated as follows:

When we establish, that [2] (3)

(7a)

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9

Fig. 3. (a) Three-phase PWM rectifier system with ac side presented as virtual ac motor. (b) Reference coordinates and vectors: —virtual flux vector of line; —virtual flux vector of converter; —virtual flux vector of inductor; u —converter voltage vector; u —line voltage vector; u —inductance voltage vector; i —line current vector.

9

9

(7b) where denotes conjugate of the line current vector. The line voltage can be expressed by the VF as

(8) where denotes the space vector and its amplitude. For VF-oriented quantities, in – coordinates [Fig. 3(b)] and using (7) and (8), (9)

Fig. 4. Block scheme of VF-DPC.

(10) and

which gives

(11a)

(11b)

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Fig. 5.

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(a) Block scheme of DPC-SVM. (b) Block scheme of DPC-SVM estimators (P&VF).

For sinusoidal and balanced line voltage the derivatives of the flux amplitudes are zero. The instantaneous active and reactive powers can be computed as [5]

TABLE I PARAMETER USED IN SIMULATION STUDY OF DPC-SVM

(12a) (12b)

C. Block Scheme of DPC Fig. 4 shows the configuration of conventional DPC, where the commands of reactive power (set to zero for unity power factor) and active power (delivered from the outer proportional–integral (PI) dc voltage controller) are compared with the estimated and values [(12a) and (12b)], in reactive and active power hysteresis controllers, respectively. The digitized and the line voltage vector position variables , form a digital word, which by accessing the address of the lookup table selects the appropriate voltage vector according to the switching table [7].

However, disturbances superimposed on the line voltage influence directly the line voltage vector position in the control system. Sometimes, this problem is overcome by phase-locked loops (PLLs) only, but the quality of the controlled system depends on how effectively the PLLs have been designed. Therefore, it is easier to replace angle of the line voltage vector by angle of VF vector , because is less sensitive than to disturbances in the line voltage, thanks to the natural low-pass behavior of the integrators in the

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Fig. 7. Simulated basic signal waveforms and line current harmonic spectrum under distorted (5% of fifth harmonic) line voltage for DPC-SVM. From the top: line voltage, line current, and harmonic spectrum of the line current (THD 2.4%).

=

where (14a)

Fig. 6. Simulated basic signal waveforms and line current harmonic spectrum under purely sinusoidal line voltage for DPC-SVM. From the top: line voltage, line current, instantaneous active and reactive power, and harmonic spectrum of the line current (THD 2.1%).

=

estimator [(5a) and (5b)]. For this reason, it is not necessary to implement PLLs to achieve robustness in the flux-oriented scheme.

III. BLOCK SCHEME OF DPC USING SPACE-VECTOR MODULATION (DPC-SVM) The concept of DPC and VF can also be applied to new control scheme. The DPC-SVM with constant switching frequency uses closed-loop power control, as shown in Fig. 5. The (set to zero for unity power commanded reactive power factor operation) and (delivered from the outer PI dc voltage (power flow between the supply controller) active power and the dc link) values are compared with the estimated and values (12(a) and (b)), respectively. The errors are delivered to PI controllers, where the variables are dc quantities, which eliminates steady-state error. The output signals from the PI controllers after transformation described as (13)

(14b) are used for switching signals generation by the space-vector modulator (SVM). IV. SIMULATION RESULTS To study the operation of the DPC-SVM system under different line conditions, the PWM rectifier with the whole control scheme has been simulated using SABER software. The main electrical parameters of the power circuit and control data are given in Table I. The simulation study has been performed with two main objectives in mind: • explaining and presenting the steady-state operation of the proposed DPC-SVM with a purely sinusoidal and distorted supply line voltage; • presenting the dynamic performance of DPC. The simulated waveforms for the proposed DPC-SVM are shown in Fig. 6. These results were obtained for purely sinusoidal supply line voltage. Similarly, Fig. 7 shows results for distorted (5% of fifth harmonic) line voltages. DPC-SVM provides sinusoidal line current (Figs. 6 and 7) and low total harmonic distortion (THD) for ideal (THD 2.1%) as well for distorted (THD of line of line current current 2.4%) line voltage. This is thanks to low-pass filter behavior of the integrators used in (5). Therefore, each of the

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Fig. 8. Simulated basic signal waveforms under step change of the load. From the top: line voltage, line current, and instantaneous active and reactive power.

Fig. 10. Experimental waveforms with distorted line voltage for DPC-SVM. From the top: line voltage, line currents (10 A/div), and harmonic spectrum of line current (THD 2.6%).

=

Fig. 9. Configuration of laboratory setup.

th harmonics in power estimator (12) and the angle of VF are reduced by factor . vector The excellent dynamic behavior under a step change of the load is presented in Fig. 8. The coupling between active and reactive power is practically unobservable. V. EXPERIMENTAL RESULTS The laboratory setup (Fig. 9) consists of commercial Danfoss inverter VLT 5000 series (5.2 kVA) controlled by the dSpace DS1103 board inserted into a PC-Pentium and

Fig. 11. Transient of the step change of the load in the DPC-SVM, load increasing. From the top: line voltages, line currents (10 A/div), and active and reactive power.

a resistor as a load. The mixed RISC/DSP digital controller based on two microprocessors (PowerPC604e–333 MHz and TMS320F240–20 MHz) and four high-resolution analogto-digital (A/D) converters (0.8 s–12 bit) provide very fast processing for floating-point calculations. Steady-state operation of DPC-SVM for significantly distorted line voltage is shown in Fig. 10. DPC-SVM provides sinusoidal current and

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REFERENCES

Fig. 12. Transient of the step change of the load in the DPC-SVM, load increasing. From the top: dc-link voltages (20 V/div) and line currents (5 A/div).

low THD. The dynamic behavior under a step change of the load is shown in Figs. 11 and 12. VI. CONCLUSION A line voltage sensorless DPC with constant switching frequency (DPC-SVM) for a three-phase PWM boost type rectifier has been presented. The DPC-SVM system constitutes a viable alternative to the conventional control strategies and it has the following features and advantages. • No line voltage sensors are required; • The noise-resistant power estimation algorithm is easy to implement in a DSP. • The control algorithm is simple, which gives the possibility of implementing it in an inexpensive microcontroller (e.g., TMS 2406). • It has a lower sampling frequency (than a conventional DPC [8]). • Coordinate transformation and decoupling between active and reactive current is not required. • No current regulation loops are required. • It has good dynamics. • It offers sinusoidal line currents (low THD), for ideal and distorted line voltage. • There is constant switching frequency (easy design of the EMI filter) by SVM application. • Advanced SVM strategies for reduction of switching losses can be implemented [6]. ACKNOWLEDGMENT The authors thank Prof. F. Harashima, the former Editor-in Chief of the IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, for selecting this paper for publication.

[1] J. L. Duarte, A. Van Zwam, C. Wijnands, and A. Vandenput, “Reference frames fit for controlling PWM rectifiers,” IEEE Trans. Ind. Electron., vol. 46, pp. 628–630, June 1999. [2] S. Hansen, M. Malinowski, F. Blaabjerg, and M. P. Kazmierkowski, “Control strategies for PWM rectifiers without line voltage sensors,” in Proc. IEEE APEC, vol. 2, 2000, pp. 832–839. [3] M. P. Kazmierkowski and L. Malesani, “Current control techniques for three-phase voltage-source PWM converters: A survey,” IEEE Trans. Ind. Electron., vol. 45, pp. 691–703, Oct. 1998. [4] B. H. Kwon, J. H. Youm, and J. W. Lim, “A line-voltage-sensorless synchronous rectifier,” IEEE Trans. Power Electron., vol. 14, pp. 966–972, Sept. 1999. [5] M. Malinowski, M. P. Kaz´ mierkowski, S. Hansen, F Blaabjerg, and G. D Marques, “Virtual flux based direct power control of three-phase PWM rectifiers,” IEEE Trans. Ind. Applicat., vol. 37, pp. 1019–1027, July/Aug. 2001. [6] M. Malinowski, “Adaptive modulator for three-phase PWM rectifier/inverter,” in Proc. EPE-PEMC Conf., 2000, pp. 1.35–1.41. [7] , “Sensorless control strategies for three-phase PWM rectifiers,” Ph.D. dissertation, Inst. Control Ind. Electron., Warsaw Univ. Technol., Warsaw, Poland, 2001. [8] T. Noguchi, H. Tomiki, S. Kondo, and I. Takahashi, “Direct power control of PWM converter without power-source voltage sensors,” IEEE Trans. Ind. Applicat., vol. 34, pp. 473–479, May/June 1998. [9] T. Ohnishi, “Three-phase PWM converter/inverter by means of instantaneous active and reactive power control,” in Proc. IEEE IECON’91, 1991, pp. 819–824. [10] B. T. Ooi, J. W. Dixon, A. B. Kulkarni, and M. Nishimoto, “An integrated AC drive system using a controlled current PWM rectifier/inverter link,” in Proc. IEEE PESC’86, 1986, pp. 494–501. [11] M. Weinhold, “A new control scheme for optimal operation of a threephase voltage dc link PWM converter,” in Proc. PCIM Conf., 1991, pp. 371–3833. [12] ACS 600 Catalogue 2000 (EN 29.2.2000), ABB Automotion Group Ltd., 2000. [13] Vector Control Simovert Masterdrives VC Catalog DA 65.10 2003/2004, Siemens AG, Munich, Germany, 2000.

Mariusz Malinowski (S’99–M’03) received the M.Sc.E.E. and Ph.D. degrees in electrical engineering (with awards) from the Institute of Control and Industrial Electronics, Warsaw University of Technology (WUT), Warsaw, Poland, in 1997 and 2001, respectively. He is currently with the Institute of Control and Industrial Electronics, WUT. He was a Visiting Scholar at Aalborg University, Denmark, and at the University of Nevada, Reno. He is an author of two patents and 40 technical papers, and coauthor of two book chapters in Control in Power Electronics (New York: Academic, 2002). His current research activities include control of PWM rectifiers, modulation techniques, and DSP applications. Dr. Malinowski received the Siemens Prize for his Ph.D. dissertation, a WUTPresident Prize, a Paper Award at the IEEE IECON 2000, and a Polish Minister of Education Award. He is also a Scholar of the Foundation for Polish Science.

Marek Jasinski (S’00) was born in Warsaw, Poland, in 1976. He received the M.Sc.E.E. degree with distinction in electrical engineering from the Institute of Control and Industrial Electronics, Warsaw University of Technology (WUT), Warsaw, Poland, in 2000. He is currently with the Institute of Control and Industrial Electronics, WUT. His current research activity deals with control of ac–dc–ac converters. He was at Aalborg University, Denmark, as a secondment of the NorFa Program, in 2001. Mr. Jasinski won the First Prize for the Best M.Sc. Thesis from the Faculty of Electrical Engineering of WUT and the Second Prize for the Best M.Sc. Thesis from the Polish Faculties of Electrical Engineering from SEP and the IEEE Poland Section.

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Marian P. Kazmierkowski (M’89–SM’91–F’98) received the M.S., Ph.D., and Dr. Sci. degrees in electrical engineering from the Institute of Control and Industrial Electronics (ICIE), Warsaw University of Technology, Warsaw, Poland, in 1968, 1972, and 1981, respectively. From 1967 to 1969, he was with the Industrial Institute of Electrical Engineering, WarsawMiedzylesie, Poland, and from 1969 to 1980, he was an Assistant Professor at ICIE. From 1980 to 1983, he was with RWTH Aachen, West Germany, as an Alexander von Humboldt Fellow. From 1986 to 1987, he was a Visiting Professor at NTH Trondheim, Norway. Since 1987, he has been a Professor and Director of ICIE. He was a Visiting Professor at the University of Minnesota, Minneapolis, in 1990, at Aalborg University, Denmark, in 1990 and 1995, and at the University of Padova, Italy, in 1993. He was a Coordinating Professor of the International Danfoss Professor Program from 1997 to 2000 at Aalborg University. Since 1996, he has served as an elected member of the State Committee for Scientific Research in Poland. At present, he is also Director of the Centre of Excellence in Power Electronics and Intelligent Control for Energy Conservation (European Framework Program V) at ICIE. He is engaged in experimental research and theoretical work on electric drives and industrial electronics. He is the author or coauthor of over 200 technical papers and reports, as well as 13 books and textbooks. He coauthored Automatic Control of Converter-Fed Drives (Amsterdam, The Netherlands: Elsevier, 1994). Recently, he coedited (with R. Krishnan and F. Blaabjerg) and coauthored the book Control in Power Electronics (San Diego, CA: Academic, 2002). Dr. Kazmierkowski was Chairman of the 1996 IEEE International Symposium on Industrial Electronics held in Warsaw, Poland. He was Vice-President, Publications, of the IEEE Industrial Electronics Society from 1999 to 2001, as well as an Associate Editor of the IEEE TRANSACTION ON INDUSTRIAL ELECTRONICS. He has served on several IEEE committees and conference organizing committees. He is Chairman of the IEEE Poland Section.