A PROPOSED REFERENCE CURRENT SIGNAL GENERATION TECHNIQUE FOR SHUNT ACTIVE POWER FILTER

Journal of Engineering Science and Technology Vol. 13, No. 6 (2018) 1834 - 1849 © School of Engineering, Taylor’s University A PROPOSED REFERENCE CURRENT SIGNAL GENERATION TECHNIQUE FOR SHUNT ACTIVE POWER FILTER B. NAYAK, B. MISRA*, A. MOHAPATRA School of Electrical Engineering, KIIT University, Bhubaneswar-24, India *Corresponding Author: Abstract This paper presents a new control technique for reference current generation for shunt active power filter to eliminate harmonics and to compensate the reactive power required by non-linear load using adaptive hysteresis band control. Twophase lock loop (PLL) controllers are utilised here to extract the phase angles of distorted load side current and source voltage. The normalisation and delaysignal cancellation techniques are utilized to extract the positive sequence of distorted signals, which is necessary to get the accurate information of phase angle. The peak current magnitude and the phase angle information of signals are used to generate the appropriate signals for the reference current. The adaptive hysteresis band controller, proposed in the literature is adopted here to generate the constant frequency switching pulses for the firing of 6-active switches of the inverter. The capacitor voltage is maintained constant through a voltage feedback utilising PI controller. The performance of the new active power filter (APF) is evaluated in MATLAB/Simulink power system toolbox. Simulation study provides quite satisfactory results for the elimination of harmonics and compensation of reactive power of the utility grid current under different load conditions. The total harmonic distortion (THD) is found effective to meet IEEE 519 standard recommendation on the harmonic level. Keywords: Adaptive hysteresis band current controller, Compensation reference current signal, Phase lock loop control, Shunt active power filter, Total harmonic distortion. 1. Introduction The rapid increase of industrial infrastructure, which utilizes power electronic devices, increases the non-linear load in power supply network. Various threephase loads which are nonlinear in nature such as variable frequency drives, thyristor converters, arc furnaces, etc., are accountable for creating the voltage and 1834 A Proposed Reference Current Signal Generation Technique for Shunt . . . .1835 Nomenclatures C fc Ica I*c,a i La ia, ib, ic idc M n Vss v vsa Capacitance of DC link voltage, µF Average switching frequency, kHz Actual current of phase A, amp Current command in phase A, amp Instantaneous load current of phase A, amp Compensating current references for all three phases, amp d-axis compensating current, amp Slope of the command current wave Harmonic order The voltage stabilization feedback Dc link voltage, volt Instantaneous phase voltage of grid side bus, volt Greek Symbols 𝜃1 , 𝜃2 𝜃̂ 𝜑 Phase angle information of voltage and current from the respective PLLs, deg Output of voltage control oscillator (VCO) Phase angle difference between the output current and voltage, deg Abbreviations ANN APF DSC EMI PCC PID PLL PWM SRF-PLL THD VCO VSI Artificial neural networks Active power filters Delay signal cancellation Electromagnetic Interference Point of common coupling Proportional-Integral-Derivative Phase-Locked Loops Pulse width modulation Synchronous-Reference-Frame Phase Locked Loop Total harmonic distortion Voltage control oscillator Voltage source inverter current harmonics in power distribution system and draws large amount of reactive power. Power quality can be improved by suppressing the harmonic pollution and performing reactive power compensation. A great deal of attention has been focused to mitigate it as they overload the utility, cause reliability problems on the equipment such as higher line losses, transformer overheating, machine vibration and a waste of energy [1-3]. The voltage profile of the grid is also distorted because current harmonics in power networks leads to voltage harmonics [3]. The passive harmonic filter has been widely used in industries because of low cost and ease of interfacing. However, with a change in load current the current filtering effect changes and it also leads to series and parallel resonance in the utility network [46]. Alternatively, active power filters (APFs) are considered as an effective solution for the above-mentioned problems though they are critical to design and costly in nature [7, 8]. Journal of Engineering Science and Technology June 2018, Vol. 13(6) 1836 B. Nayak et al. Many research works incorporated active power filters APF, for the elimination of harmonic pollutions and compensation of reactive power in the utility grid [911]. The main categories of three-phase, three-wire active power filters are the shunt, series, and hybrid configurations. Their merits and demerits are discussed in [12]. There are many research papers [13, 14] on series APF where a transformer is connected in series to the transmission line to inject the required voltage to filter out the harmonic current. The main disadvantage of series APF is being costly due to the presence of transformer. Series hybrid APF approach proposed by different researchers has the potential for harmonic compensation in high voltage grid with lower APF rating [15]. The instantaneous reactive power theory proposed [16] has been applied earlier for the control of shunt APFs to remove harmonic pollution of grid side current loaded by non-linear load [17]. Artificial neural networks (ANNs) have been applied to various power system problems for extracting the harmonic current to eliminate the harmonics [18-20]. This technique has been successfully applied for making the current perfectly sinusoidal in active power filters and replaces the conventional Proportional-Integral-Derivative (PID) controllers. Hybrid active filter proposed by Peng and Adams, [15] is a combination of active filters and passive filters, to solve the distortion of utility current of power network [21]. The above researches are based on only three-phase balanced voltage with nonlinear load. However, in practical application load and source may be unbalanced in nature. For unbalanced condition, if negative sequence current is not extracted, it will be included in reference current command and affect the information of phase angle. This raises the question of the robustness of APFs. Some researchers [22, 23] have used the hysteresis band controller to generate the pulses to trigger the active switches of voltage source inverter which is the heart of APFs. The main drawback of hysteresis band controller is the variable switching frequency, which affects the reliability of operation of voltage source inverter. Adaptive hysteresis band controller proposed in [24, 25] has been successfully used in APFs to make the switching frequency constant. This paper proposes a new control technique, which takes care of both unbalanced grids and loads side voltage. It also ke (...truncated)