Mustafa Inci

A New Control Approach for Shunt Hybrid Active Power Filter to Compensate Harmonics and Dynamic Reactive Power with Grid Interconnection

The grid interconnection of renewable energy source is a popular issue in the electric utilities. Different types of converter topology in grid interconnection have been improved by researchers to improve power quality and efficiency of the electrical system. The main contribution of this paper is that shunt hybrid active power filter (SHAPF) with a DC-DC converter at dc link is to provide interconnection between renewable source and grid with linear dynamic loads. The other contribution of this paper is to present a novel control strategy for reactive power compensation and harmonics elimination in industrial networks using a hybrid active power filter as a combination of a three phase, two level voltage source converter connected in parallel with single tuned LC passive filter. In proposed control method, reactive power compensation is achieved successfully with perceptible amount. Besides, the performance results of harmonic compensation are satisfactory. Theoretical analyses and simulation results are obtained from an actual industrial network model in PSCAD. The simulation results are presented for proposed system in order to demonstrate that the harmonic compensation performance meets the IEEE-519 standard.

Performance evaluation of LLCL filter for active power filter

Active Power Filter (APF) is an inverter based device that compensates the harmonic currents generated by nonlinear loads. Inverters release high frequency switching ripple harmonics. In early studies, APFs have been generally interfaced to the grid via a single L filter to reduce these harmonics. However, high order filters like LCL and LLCL filters have been recently used with APFs instead of L filter due to insufficient mitigation of L filter. LCL and LLCL filters have better attenuation of switching ripple harmonics at high frequencies. Attenuation performance of LLCL filter at switching frequency is superior to LCL filter. Since LLCL filter has resonance problem, a simple resistor is connected in series with parallel LC branch. The purpose of this paper is to evaluate the performance of LLCL filter for different damping resistor values when used with APF. In order to examine the performance of the LLCL filter, a simulation model is developed in Simulink/MATLAB.

The Analysis and Performance Results of Bidirectional DC-DC Converter Based Dynamic Voltage Restorer under Voltage Sag/Swell Conditions

This paper presents Dynamic Voltage Restorer (DVR) based on bidirectional full-bridge dc-dc converter to compensate severe voltage sag/swell problems in medium voltage system. Voltage swell causes the continuous rise at dc-link voltage of DVR which may damage the dc-link capacitors and solid-state devices, and increase the power losses. Unidirectional dc-dc converters based DVRs do not allow power flow from dc link of inverter to battery. This condition may damage the dc-link capacitors and solid-state devices, and increase the power losses. The main contribution of this study is that bidirectional dc-dc converter permits the DVR to prevent voltage rise at DC link capacitor under severe voltage swell conditions. In this topology, power can flow both from battery to multilevel inverter and vice versa. For this propose, a control algorithm based on Proportional-Integrator (PI) control is developed for bidirectional dc-dc converter. This algorithm can keep the DC link voltage constant during voltage sag/swell. The performance results of proposed topology and control method is verified with PSCAD/EMDTC.

EPLL based controller for voltage harmonic mitigation in grid connected wind systems

Voltage harmonics are very important voltage disturbances which induce overheating of transformer/generator, connection loss and rise of current rating in grid connected wind energy systems. In this paper, Enhanced Phase Locked Loop (EPLL) based controller method is proposed to generate reference signals of voltage harmonics at grid-side voltages. In order to achieve the harmonic compensation, EPLL based controller method is tested to compensate voltage harmonics for balanced and unbalanced conditions in Dynamic Voltage Restorer (DVR) tied grid-connected wind energy systems. The performance results of EPLL based controller demonstrate that it is a very effective technique for harmonic compensation under steady-state and transient conditions.

Survey of inverter topologies implemented in dynamic voltage restorers

Voltage disturbances which affect the stability of electrical networks are the most important power quality problems. The most known voltage disturbances are voltage sag and swell in distribution systems. Dynamic Voltage Restorer (DVR) is the most effective device to compensate these voltage disturbances among the custom power devices. The basic structure of a conventional DVR consists of an inverter, dc link capacitor, injection transformer and filter. The major component in DVR is inverter that generates controlled voltage to compensate voltage sag/swell and other problems such as flicker, interruption and harmonics. Each inverter implemented in DVR has individual properties such as voltage level, unbalanced compensation capability and/or dc link capacitor requirement. This paper aims a comprehensive review on different inverter topologies according to the number of phases, size, voltage level and structure of DVR. In addition, individual properties of inverters are presented in this study.

A notch filter based active damping of llcl filter in shunt active power filter

Shunt Active Power Filter (APF) is a custom power device applied in electric grid system in order to compensate harmonic currents generated by nonlinear loads. Shunt APF operates by firing power electronic devices of voltage source inverter (VSI) to produce the compensation currents. The VSI also generates high frequency switching ripple harmonics that distorts the source current. High order filters, such as LCL and LLCL, have been recently used with shunt APF to decrease the ripple harmonics and to couple shunt APF with the grid. Compared with LCL filter, LLCL filter has more effective attenuation performance at switching frequency because of demonstrating nearly zero impedance. As other high order filters, LLCL filter has resonance problem that leads the system to unstable condition. Passive damping or active damping method is exploited to mitigate the resonance impact and make the system stable. AD methods have more widespread applications and research due to no damping power losses. AD is fulfilled through making improvment in the control system. The objective of this paper is to point out notch filter based AD for shunt APF with output LLCL filter. The proposed system is constructed in Matlab/Simulink and the performance of the proposed system is investigated through simulation cases.

FFT based reference signal generation to compensate simultaneous voltage sag/swell and voltage harmonics

The most severe power quality problems are known as voltage sag, swell and harmonics. Series connected custom power device called as dynamic voltage restorer (DVR) is the most effective device used in electrical systems to compensate these power quality problems. Traditional DVR compensates only voltage sag/swell in electrical grids. The main contribution of this paper is that FFT based a novel reference generation method is used in DVR to compensate unbalanced voltage sag/swell and unbalanced voltage harmonics, simultaneously. In this study, FFT achieves both voltage sag/swell detection and voltage harmonics extraction at the same time. FFT controlled DVR compensates voltage sag/swell within 5 ms while unbalanced selective voltage harmonics (5th, 7th, 11th and 13th) are compensated in the system, simultaneously. The system is analyzed for various case studies. The performance of proposed controller method is presented and confirmed through simulation results using PSCAD/EMTDC.

A novel low cost sag/swell generator

This study presents a new Sag Swell Generator (SSG) topology to generate several power quality problems such as sag, swell and interruption. In this paper, bridge type bidirectional switch based SSG is presented to generate different fault conditions. The main contribution of proposed topology is to provide low-cost and simple solution compared to conventional transformer based SSG topologies. The experimental results show that the proposed SSG is a novel topology for low-cost laboratory applications.

Performance investigation of shunt hybrid active power filter with a synchronous reference frame based controller

This paper presents a novel synchronous reference frame based (SRF) control strategy for shunt hybrid active power filter (SHAPF). The control strategy includes a direct current control (DCC) and an indirect current control (ICC) strategy. SHAPF can achieve harmonic compensation and dynamic reactive power compensation with the proposed controller. In this proposed method, as distinct from studies in literature, dynamic reactive power compensation and dc link voltage control is realized with ICC and harmonic current compensation is realized with DCC. Also, the proposed controller provides a variable SHAPF dc link voltage which is adjusted according to the reactive power compensation requirements in order to decrease the switching losses of converter and achieve power savings. The performance of proposed controller is verified with experimental results.

Performance evaluation of a new hybrid unified power quality conditioner (HUPQC)

In this paper, a new hybrid unified power quality conditioner (HUPQC) is proposed to improve current and voltage imperfections in distribution systems. The proposed HUPQC is comprised of the shunt hybrid active power filter (SHAPF), the dynamic voltage restorer (DVR) and the isolated bi-directional DC-DC converter. The main contribution of the study is a new HUPQC topology that enables the reduction in the voltage rating of the DC link capacitor by the help of the SHAPF. The cost and size of the DC link are reduced and switching losses of the voltage source inverter (VSI) is reduced with the low voltage DC link advantage of SHAPF. The DC-DC converter provides isolation and bi-directional power flow between the DVR and the SHAPF during voltage sag and swell. The performance of the proposed HUPQC is evaluated through extensive simulations for mitigating unbalanced voltage sag/swell and compensating current harmonics by using PSCAD/EMTDC simulation tool.