IMPLEMENTATION OF A SHUNT ACTIVE FILTER USING THE THEORY OF GENERALIZED

INSTANTANEOUS POWER

Paulo Vitor Silva1, Ricardo Ferreira Pinheiro2, Marcos V. Aguiar3 Luciano P. Júnior4, Andrés Ortiz Salazar5 e Caio D. Cunha6

Universidade Federal do Rio Grande do Norte - UFRN - Campus Universitário, s/nº - 59072-970 - Natal – RN – Brasil 1paulo.silva@ifrn.edu.br; 2ricpinh@ufrnet.br;3 marcosmilfont@yahoo.com.br; 4luciano.junior@ifsertao-pe.edu.br;

5andres@dca.ufrn.br; 6dorneles@ufrnet.br;

Abstract – This paper describes the implementation of a strategy to obtain the currents reference of a shunt filter active using the method of the Theory of Generalized Instantaneous Power applied to the control of a generator Induction of feeding a nonlinear load. The objectives are to establish control of generator excitation and reduce harmonic distortion caused by nonlinear load. It is made a comparison with other method for obtaining the reference currents, the dq synchronous reference. First, they are simulations using the Borland C++. The control and communications necessary for the supervisory stage were implemented via DSP - TMS320F2812.

Keywords - shunt filter active, harmonic distortion,

instantaneous power, DSP.

I. INTRODUCTION

The electrical systems have presented several problems due to increased nonlinear loads connected, affecting power quality. Examples of such loads are rectifiers, inverters, devices, machinery drives, arc furnaces, fluorescent lamps, switching power supply and saturated magnetic devices [1]. Due to the growing use of these burdens in Brazil, utilities power distribution deal with problems like harmonics, power factor control, voltage fluctuations, etc., problems that in many settings, such as the use of induction generators can be minimized through active filters. These harmonics significantly alter the waves of current waveform and stretch, causing excessive losses engines due to heating, the dielectric breakdown, capacitor banks, voltage, electromagnetic interference, mechanical vibrations of induction machines and synchronous.

Akagi et al [5] proposed the Generalized Theory of Instantaneous Power for almost 30 years, several researchers around the world contributed to the evolution this theory, and applied it in several cases [3] and [4]. In 1999, Akagi [6] reviewed the theory by considering the case more general application in the four-wire systems.

The development of power electronics has expanded the possibility of using new equipment systems industry, especially with the development of devices switching capable of operating at higher frequencies. Through the use of digital control strategies and PWM digital drive many applications has become possible in improving the performance of active filters (FA) enabling the use of many

disturbing loads than before were not viable in industrial systems.

The shunt active filter is one of the most used in combating the problems of power quality caused by harmonic currents. In this type of filter, is injected a current which, added to the supply current, gives rise to the cancellation of current harmonics, resulting only the fundamental component of current to supply the system. This topology is used to eliminate harmonics current, reactive compensation and balancing unbalanced currents [2] [3].

This work makes a comparative study of efficiency in obtaining the reference currents of active filter through Generalized Theory of Instantaneous Power by comparing with the method of synchronous reference dq. Therefore, it was used an experimental setup, shown in Fig. 4, involving: an induction generator, a shunt active filter, nonlinear load and control system that was implemented digitally by DSP - TMS320F2812, which provided reference signals to drive the electronic filter. Finally, simulations and experimental results are presented in order to demonstrate the performance, performing a comparison between the two methods evaluated.

II. SYNCHRONISM AND CONTROL STRATEGIES

A. Generalized Theory of Instantaneous Power Now well known in the literature, several papers in the

area of active filtering using the Generalized Theory of Instantaneous Power. In studies that followed this theory, in addition to applications in control filters can also be used in applied problems using systems unbalanced or not, presenting distortions [4].

The Clarke Transformation is used to transform the traditional abc coordinates into the alfa-beta-zero coordinates. From the three-phase voltages generated and line currents of the load, one can determine the power instantaneous active [5].

00)( ivivivtp ++= ββαα (1)

Where: vα,vβ e v0 are the voltages in the coordinates αβ0; iα,iβ e i0 are the currents in the coordinates αβ0;

782978-1-4577-1646-1/11/$26.00 ©2011 IEEE

Different the calculation of active power, the instantaneous reactive power arises from the multiplication vector [6].

Components axis zero only come into being, if the circuit presents the neutral wire and its load imbalances present, which is not the case of the system studied in this work, which reduces the equations, resulting in:

ββαα ivivp += (2)

αββα ivivq −= (3) The block diagram of Fig. 1 represents the obtained

the instantaneous power from three phase system.

Fig. 1. Active power filter control circuit.

Where:

p - instantaneous real power. p~ - instantaneous real power oscillating. p - instantaneous real power constant. q - instantaneous imaginary power Thus, after algebraic manipulations, obtain the matrix

general to obtain the currents αβ0 reference filter active, represented by:

⎥⎦

⎤⎢⎣

⎡

⎥⎥⎦

⎤

⎢⎢⎣

⎡ −=

⎥⎥⎦

⎤

⎢⎢⎣

⎡

qp

vvvvvv

vvii ~

..12

2

2*

*

βαβ

ββα

ββ

α (4)

Where:

( )222βα vvv += (5)

B. Synchronous dq reference The obtaining of the current reference it, this method

consists of, from reading the three-phase load currents, transform the signal obtained in a biphasic system with axes stationary Clarke transformation and then in a system biphasic rotating axes (transform Park).

The currents in the dq format, takes place a filtering these currents, resulting only in harmonic currents, represented by *

dhi e *qhi and that will be the current

reference for the active filter.

The diagram in Fig. 2 represents the obtaining of these

currents.

Fig. 2. Park transformation and harmonic current injection circuit.

C. Scheme General Mount The diagram of Fig. 3 represents, in general, as form

currents involved in the assembly. The aim of work is, from the harmonic load current IL, using control strategies presented earlier to obtain a current reference for active filter in order to from injection of IF into the system, minimize the harmonics the supply current, IS.

Fig. 3. Basic structure of a shunt AF

A more detailed schematic diagram of the assembly is shown in Fig. 4. As can be observed, are used a DC source and a DC motor to drive the generator induction. The DC motor is directly coupled to the generator induction. It uses a capacitor bank connected to induction generator to supply the reactive power and perform his excitement. A photograph of the assembled system is shown in Fig. 5.

Fig. 4. Basic compensation scheme.

V123

I123

Calculation of active and reactive powers

ClarkeTransformation

a-b-0

Measurementsload currents

Measurementsthree-phase

system voltages

p q

HPFFiltering

V

I

p- p~

Measurementsload currents

iLaiLbiLc

ClarkeTransformation

a-b-0

iLςiLς

Park Transformationd-q-0

iLd iLq

HPFFiltering

idh* iqh

*

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Fig. 5. Photograph of the mount in the laboratory.

D. Synchronism Method Will be used the methods proposed in [7], known

as Modified Synchronous Reference Frames - Low-Pass Filter Based (MSRF - LPF-B). In it, the angle of synchronization or the synchronization normalized vector is obtained directly readings of voltage from the grid. The method uses filters low-pass, with the aimed at alleviating the components harmonic voltages from the grid

With the Clarke transform of input voltages (V) is possible to get the module from voltages as (6) and then we obtain the (sin(θ) cos(θ)) as (7), which are used to obtain an angle of reference that allows synchronize the output variables of the drive with voltages supply of the system.

( )22βααβ VVV += (6)

Where:

αβ

α

αβ

β

θ

θ

VV

VV

sen

=

=

)cos(

)(

(7)

Fig. 6 represents, respectively, the sine signal cosine and the resulting timing method used, implemented by DSP TMS320F2812.

Fig. 6. Sine and cosine graphs obtained from the use of the method

of proposed synchronization - Experimental result.

III. RESULTS

A. Simulation Results In this step, were applied to the system, three-phase

voltages with constant peak value of 311 V and the other data used in the simulation are:

• Frequency: 60 Hz; • Filter resistance: 50mΩ; • Filter inductance: 2 mH; • Reference Capacitor Voltage: 800 V; • Capacitor: 10 mF.

In both tests, the nonlinear load used is the same and a graph of load current of phase A is shown in Fig. 7. The THD of load current, and hence the source is of 42.79% and its spectrum is shown in Fig. 8.

Fig. 7. Load current used in simulation

Fig. 8. Graph of Frequency Spectrum - Load Current.

1) Reference by Instantaneous Power: The analysis were initiated from the instantaneous power

obtained by the system. The instantaneous active and reactive powers are shown below, respectively, in Fig. 9 and 10.

Then, through filtering, the plots were obtained oscillating active and real constant, both shown respectively in: Figures 11 and 12. After the performance of active filter, we get the current source shown in Fig. 13 with THD of 1.87%.

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Fig. 9. Active power instant used in simulation

Fig. 10. Reactive power used in simulation

Fig. 11. Active power oscillating used in simulation

Fig. 12. Active power real used in simulation

Fig. 13. Source current waveform used in simulation - Phase A

2) Synchronous dq reference: The following is the result for the second method: a

current source power, Fig. 14 showing a THD of 7.67%.

Fig. 14. Graphic source current - Phase A

B. Experimental Results For the stage of experimental tests were applied to two

systems proposed the same condition of input voltages generated by the induction generator and the same non-linear load. Figures presented below was obtained through Tektronix oscilloscope (TPS 2024).

Fig. 15 represents the three-phase input voltages entry. As can be seen in the figure, the tension has a peak value of 130V and a frequency of about 27 Hz.

The phase currents of nonlinear load are shown in Fig. 16, with a THD of 31.11% and its spectrum is shown in Fig. 17.

Fig. 18 represents the voltage and current Source, both Phase A.

Fig. 15. Mains voltages

Fig. 16. Nonlinear currents waveform

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Fig. 17. Graph of Frequency Spectrum - Load Current.

1) Reference by Instantaneous Power: Using the method of instantaneous power there were the

following results after operation of filter: Fig. 19 shows graphs of voltage and current source, both for phase A. Then it is seen in Fig. 20 the graph of voltage source, current source, as corrected and the load current, all of phase A. Finally, Fig. 21 shows a graph of the spectrum frequency of current source, which was calculated at 5.47 THD%.

The summary of results: • Voltage in DC bus of inverter: 750V; • Peak Voltage Generator: 60V; • System Frequency: 29 Hz; • Voltage DC Resistive Load: 115V; • DC current of resistive load: 3.5 A; • Load Power: 400W; • THD - Supply current: 5.47%.

Fig. 18. Graph of Current and Voltage Supply - Phase A.

Fig. 19. Graph of Current and Voltage Supply - Phase A (after

correction)

Fig. 20. Graphics: power supply voltage / Current source / Current

load - Phase A.

Fig. 21. Graph of Frequency Spectrum - Supply current – 1st

Method.

2) Synchronous dq reference: After functioning the filter, one can observe the following

results: Fig. 22 show the voltage source and the source, both in phase A. Next up is shown in Fig. 23 the voltage source, current source, as amended, and load current, all of Phase A. Finally, the graph of the frequency spectrum of the supply current is shown in Fig. 24, with a THD of 9.36%.

The summary of results: • Voltage in DC bus of inverter: 720V; • Peak Voltage Generator: 60V; • System Frequency: 29 Hz; • Voltage DC Resistive Load: 110V; • DC current of resistive load: 3.6 A; • Load Power: 400W; • THD - Supply current: 9.36%.

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Fig. 22. Graph of Current and Voltage Supply - Phase A (after

correction).

Fig. 23. Graphics: Power Supply Voltage / Current Source /

Current Load - Phase A.

Fig. 24. Graph of Frequency Spectrum - Supply current – 2nd

Method.

IV. CONCLUSION

This article was mounted to a bench check efficiency of a parallel active filter currents in control harmonics coming from a non-linear load fed by an induction generator.

The filtering of harmonics, the simulations presented reductions of 42.79% THD to 7.67% (Synchronous dq Refence) and 42.79% to 1.87% (Instantaneous Power).

In experimental tests, the results were respectively 31.11% to 9.36% and 31.11% to 5.47% Synchronous dq reference

and instantaneous power. The two control methods have been successfully implemented.

There was a better performance of the method of instantaneous power to obtain the current reference the active filter. It also can be highlighted: the acquisition of technological mastery in digital PWM drive active filters using DSP, the assembly of the stand able to perform various experimental works, undertaking tests using the control strategy of the powers instant, easy to implement via the DSP and the good results demonstrate the potential of instantaneous power at lower levels of THD.

REFERENCES

[1] L. H. Tey, P. L. So, and Y. C. Chu “Improvement of Power Quality Using Adaptive Shunt Active Filter”, IEEE Trans. on Power Delivery, vol. 20, no. 2, April 2005, pp.1558-1568.

[2] Rafael Cardoner, Robert Grino, Ramon Costa-Castelló, and Enric Fossas, “Digital Repetitive Control of a Three-Phase Four-Wire Shunt Active Filter”, IEEE Trans. Ind. Electron, vol. 54, no. 3, Jun 2007, pp 1495-1503.

[3] Maurício Aredes, Jurgen H¨afner, and Klemens Heumann, “Three-Phase Four-Wire Shunt Active Filter Control Strategies”, IEEE Trans. on Power Eletronics, vol. 12, no. 2, Mar 1997, pp 311-318.

[4] Edson H. Watanabe, Maurício Aredes, “Teoria da Potência Ativa e Reativa Instantânea e Aplicações- Filtros Ativos e FACTS ”.

[5] Akagi, H., Kanazawa, Y., and Nabae, A. “Generalized Theory of the Instantaneous Reactive Power in Three-Phase Circuits”, Proceedings of the IPEC’83, 1983, pp.1375-1386.

[6] Hirofumi Akagi, Satoshi Ogasawara, and Hyosung Kim, “The Theory of Instantaneous Power in Three-Phase Four-Wire System: A comprehensive Approach”, 1999, pp.1-9.

[7] CAMARGO et al (2005) Robinson F. de Camargo, Marcelo Hey Duarte, Fernando Botterón, Humberto Pinheiro, and Jéferson Marques, “Análise e Implementação de Retificadores PWM Trifásicos com Resposta de Tempo Mínimo Utilizando Desacoplamento por Retroação de Estados”, Revista Controle Automação vol. 16, no. 4, Dec. 2005, pp.503-513.

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