Three-phase four-wire shunt hybrid active power filter model with model predictive control in imbalance distribution networks

This paper presents a harmonic reduction and load imbalance model in a three-phase four-wire distribution network. This model uses a hybrid active power filter, a passive inductor and capacitor filter, and an active power filter in the form of a three-phase, four-leg connected grid inverter. The switching of the voltage source converter on this filter uses finite control set model predictive control (FCS-MPC). Control of this hybrid active power filter uses model predictive control (MPC) with a cost function, comparing the reference current and prediction current with mathematical modelling of the circuit. The reference current is taken from the load current by extracting dq, and the predicted current is obtained from the iteration of the voltage source converter (VSC) switching pattern. Each combination is compared with the reference current in the cost function to get the smallest error used as a power switching signal. Modelling was validated by using MATLAB Simulink. The simulation results prove a decrease in harmonics at a balanced load from 22.16% to 4.2% and at an unbalanced load, reducing the average harmonics to 4.74%. The simulation also decreases the load current imbalance in the distribution network. Reducing the current in the neutral wire from 62.01%-0.42% and 11.29-0.3 A

Control System Design, Analysis, and Simulation of a Photovoltaic Inverter for Unbalanced Load Compensation in a Microgrid

This thesis presents a control scheme for a single-stage three-phase Photovoltaic (PV) converter with negative sequence load current compensation. In this thesis a dual virtual impedance active damping technique for an LCL filter is proposed to address the issue of LCL filter resonance. Both inverter-side current and the capacitor current are used in the feedback loop. Using both signals provides higher DC rejection than using capacitor current alone. The proposed active damping scheme results in a faster transient response and higher damping ratio than can be obtained using inverter-side current alone. The feedback gains can be calculated to achieve a specified damping level. A method of determining the gains of the Proportional and Resonant current controller based on frequency response characteristics is presented. For a specified set of gain and phase margins, the controller gains can be calculated explicitly. Furthermore, a modification is proposed to prevent windup in the resonator. A numerically compensated Half-Cycle Discrete Fourier Transform (HCDFT) method is developed to calculate the negative sequence component of the load current. The numerical compensation allows the HCDFT to accurately estimate the fundamental component of the load current under off-nominal frequency conditions. The proposed HCDFT method is shown to have a quick settling time that is comparable to that obtained with conventional sequence compensation techniques as well as immunity to harmonics in the input signal. The effect of unbalance compensation on the PV power output depending on the irradiance and the operational region on the power-voltage curve is examined. Analysis of the DC link voltage ripple shows the region of operation on the P-V curve affects the amplitude of the DC link voltage ripple during negative sequence compensation. The proposed control scheme is validated by simulation in the Matlab/Simulink® environment. The proposed control scheme is tested in the presence of excessive current imbalance, unbalanced feeder impedances, and non-linear loads. The results have shown that the proposed control scheme can improve power quality in a hybrid PV-diesel microgrid by reducing both voltage and current imbalance while simultaneously converting real power from a PV array

New topology of shunt hybrid power filter for harmonic mitigation and re-utilization of harmonic filter current as useful power

Power electronic appliances are recently used widely in industrial, commercial, and home sectors; these appliances include diode and thyristor rectifiers, and variable speed drive systems. When these appliances are connected to the grid, they generate harmonics in the current and voltage waveform which contributes to the degradation of the system efficiency and deterioration of the overall system performance due to an increase of effective peak value and also the rms current in some devices. Conventional passive power filters (PPF) for harmonic mitigation have inherent problems, while purely active power filters (APF) have the disadvantages of higher costs and ratings. Hybrid active filters (HPF) inherit the efficiency of PPFs and the improved performance of APFs, and thus, constitute a viable improved approach for harmonic compensation. An eight different HPF topology is composed of one APF and PPF in series or shunt or combination. Nevertheless, among the existing mitigation HPFs, the shunt LC HPF is the most effective against current harmonics problems due to its feasibility for harmonic current compensation. However, it cannot perform satisfactory dynamic reactive power compensation because reactive power varies from time to time. Furthermore, to have low impedances at high frequencies, the capacitor of this filter needs to be large which will be influenced seriously by the source inductor. In this study, a new topology of shunt RLC-HPF is introduced to improve the efficiency of current harmonic reduction and perform power factor (PF) correction through reactive power compensation via the provision of a low impedance path through the inductor (for low frequencies) and low impedance through the capacitor (for high frequencies).. The effectiveness of HPF is strictly dependent on how quickly and accurately the detection of reference harmonic current, DC-link capacitor voltage regulation, and current control is achieved. The shunt HPF was designed based on synchronous reference frame strategy (SRF) and self-tuning filter (STF) to develop the operation of the filter under non-ideal (unbalanced and/or distorted) source voltage conditions. As for its controller, switching signals to drive the voltage source inverter (VSI) of the shunt APF adaptive hysteresis current controller (AHCC) are used. Also, proportional-integral (PI) and back propagation neural network (BPNN) controllers are developed to maintain a constant voltage across the DC-link capacitor so that the shunt APF can precisely inject the desired referred currents back into the harmonic power system. The shunt HPF performance is validated for all possible conditions of source and load by simulation using MATLAB/ Simulink environment. The simulation results obtained by the STF -SRF strategy with BPNN controller showed excellent achievement when compared to SRF with PI controller in the mitigation of current harmonics, PF enhancement, and DC voltage regulation. As a result, the minimum total harmonic distortion (THD) values of the source current recorded clear advantages of the STF-SRF strategy (1.8 %) over the existing SRF strategy (10 %), especially in dealing with non-ideal source voltage conditions. Furthermore, the encouraging findings have led to the correction of the PF to 0.999 using STF-SRF in contrast to 0.842 with the SRF strategy. Moreover, the DC-link capacitor voltage was properly regulated and maintained at the respective desired values under all cases with the BPNN controller, while the PI controller failed to be regulated. Ultimately, the main aim of the new HPF topology is the improvement of PF and reducing harmonic current, as well as re-utilization of the extracted harmonic filter current via conversion to useful power to feed the RL load within the limitation of the IEEE-519-2014 standards

A Comprehensive Survey on Different Control Strategies and Applications of Active Power Filters for Power Quality Improvement

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).Power quality (PQ) has become an important topic in today’s power system scenario. PQ issues are raised not only in normal three-phase systems but also with the incorporation of different distributed generations (DGs), including renewable energy sources, storage systems, and other systems like diesel generators, fuel cells, etc. The prevalence of these issues comes from the non-linear features and rapid changing of power electronics devices, such as switch-mode converters for adjustable speed drives and diode or thyristor rectifiers. The wide use of these fast switching devices in the utility system leads to an increase in disturbances associated with harmonics and reactive power. The occurrence of PQ disturbances in turn creates several unwanted effects on the utility system. Therefore, many researchers are working on the enhancement of PQ using different custom power devices (CPDs). In this work, the authors highlight the significance of the PQ in the utility network, its effect, and its solution, using different CPDs, such as passive, active, and hybrid filters. Further, the authors point out several compensation strategies, including reference signal generation and gating signal strategies. In addition, this paper also presents the role of the active power filter (APF) in different DG systems. Some technical and economic considerations and future developments are also discussed in this literature. For easy reference, a volume of journals of more than 140 publications on this particular subject is reported. The effectiveness of this research work will boost researchers’ ability to select proper control methodology and compensation strategy for various applications of APFs for improving PQ.publishedVersio

Distributed static series compensator in 11kV networks

PhD ThesisSeries compensation techniques can be very effective when applied in an electrical network to increase the power transfer capacity of existing power lines. Distributed Static Series Compensation (DSSC) is a power electronics based series compensation scheme in which a DSSC device comprises of a single-phase H-bridge voltage source converter, a dc link capacitor and a low pass filter suspended from the power line via a single turn transformer. The application of DSSC in the 11kV distribution network is investigated in this thesis. This is followed by a study of existing control strategies employed in DSSC and Static Synchronies Series Compensation (SSSC) schemes. Most of these controllers are based on dq transformation methods in which balanced conditions are assumed and zero sequence currents are assumed to be negligible. While this might be a reasonable assumption at transmission level voltages, but it can be argued that in the presence of unbalanced loads and currents (a common feature of lower voltage distribution networks) these strategies can be inaccurate, leading to the wrong amount of compensation being injected. In addition some of the studied controllers are based on the 90° phase shift of line current. Practically, the injection angle must be slightly different in order to compensate the internal losses of the DSSC. The need for the diversion from the 90° can change over the time and this can threaten the stability of the system. A new single-phase control strategy based on the instantaneous power exchange between the DSSC devices and each of the three phase conductors is proposed in this thesis to address this issue. The new control method does not employ a dq transformation and is immune from the probable errors resulting from the presence of unbalanced network conditions. In the same time the injection angle is not fixed and it is adjusted by the controller. The operation of DSSC can be categorized in two modes and transfer function of system is obtained based on these two modes. The transfer function is used in the design of controller. This is followed by analyzing immunity of the designed controller against change of system parameters. The proposed scheme is simulated (using PSCAD software) to examine the operation of the new control method and the resulting impact on the 11kV distribution feeder, including the ability to divert power from one line to another and the ability to improve network voltage profiles. Performance of DSSC using the proposed controller is compared with performance of DSSC when the traditional controllers are employed

Power Quality Improvement Using Unified Power Quality Conditioner (UPQC)

The advance use of power electronic devices introduces harmonics in the supply system which creates a problem in the quality of power delivered. Good Power Quality is very much important for our day to day use of appliances in both industrial and domestic sectors. Researchers have tried and implemented many useful technology for removing all the voltage and current related harmonic occurrence problems which in turn improves the quality of power delivered to the power system. The prime focus of this thesis is the implementation of control strategies like SRF theory and instantaneous power (p-q) for the operation of Unified Power Quality Conditioner (UPQC) which is one of the recent technology that includes both series and shunt active power filter operating at the same time and thereby improves all the current and voltage related problem like voltage sag/swell, flicker, etc. at the same time and helps in reduction of Total Harmonic Distortion (THD). In this thesis it is shown via MATLAB simulation how UPQC model can be used to decrease the % THD in source voltage, source current and load voltage waveforms created due to non-linear/ sensitive loads usage

POWER QUALITY CONTROL AND COMMON-MODE NOISE MITIGATION FOR INVERTERS IN ELECTRIC VEHICLES

Inverters are widely utilized in electric vehicle (EV) applications as a major voltage/current source for onboard battery chargers (OBC) and motor drive systems. The inverter performance is critical to the efficiency of EV system energy conversion and electronics system electro-magnetic interference (EMI) design. However, for AC systems, the bandwidth requirement is usually low compared with DC systems, and the control impact on the inverter differential-mode (DM) and common-mode (CM) performance are not well investigated. With the wide-band gap (WBG) device era, the switching capability of power electronics devices drastically improved. The DM/CM impact that was brought by the WBG device-based inverter becomes more serious and has not been completely understood. This thesis provides an in-depth analysis of on-board inverter control strategies and the corresponding DM/CM impact on the EV system. The OBC inverter control under vehicle-to-load (V2L) mode will be documented first. A virtual resistance damping method minimizes the nonlinear load harmonics, and a neutral balancing method regulates the unbalanced load impact through the fourth leg. In the motor drive system, a generalized CM voltage analytical model and a current ripple prediction model are built for understanding the system CM and DM stress with respect to different modulation methods, covering both 2-level and 3-level topologies. A novel CM EMI damping modulation scheme is proposed for 6-phase inverter applications. The performance comparison between the proposed methods and the conventional solution is carried out. Each topic is supported by the corresponding hardware platform and experimental validation

Mitigation of Power Quality Problems Using Custom Power Devices: A Review

Electrical power quality (EPQ) in distribution systems is a critical issue for commercial, industrial and residential applications. The new concept of advanced power electronic based Custom Power Devices (CPDs) mainly distributed static synchronous compensator (D-STATCOM), dynamic voltage restorer (DVR) and unified power quality conditioner (UPQC) have been developed due to lacking the performance of traditional compensating devices to minimize power quality disturbances. This paper presents a comprehensive review on D-STATCOM, DVR and UPQC to solve the electrical power quality problems of the distribution networks. This is intended to present a broad overview of the various possible DSTATCOM, DVR and UPQC configurations for single-phase (two wire) and three-phase (three-wire and four-wire) networks and control strategies for the compensation of various power quality disturbances. Apart from this, comprehensive explanation, comparison, and discussion on D-STATCOM, DVR, and UPQC are presented. This paper is aimed to explore a broad prospective on the status of D-STATCOMs, DVRs, and UPQCs to researchers, engineers and the community dealing with the power quality enhancement. A classified list of some latest research publications on the topic is also appended for a quick reference

Novi pristup za poboljšanje karakteristika UPQC-a tijekom nesimetričnih i distorzijskih uvjeta tereta temeljen na teoriji trenutne snage

In order to deal with power quality problems under distortional and unbalanced load conditions, this paper presents a new control method for a four-wire three-phase unified power quality conditioner (UPQC) which is based on instantaneous power p-q theory. The proposed control approach is based on instantaneous power and is optimized by using a self-tuning filter (STF), without using any low-pass filters (LPFs) or phase locked loop (PLL), and without measuring load or filter currents. In this approach, the load and source voltages are used to generate the reference voltages of a series active power filter (APF) and source currents are used to generate the reference currents of a shunt APF. Therefore, the number of times that current is measured is reduced and system performance is improved. The performance of the proposed control approach is evaluated in terms of power factor correction, source neutral current mitigation, load balancing and mitigation of the current and voltage harmonics of distortional and unbalanced loads in a three-phase four-wire system. The results obtained by MATLAB/SIMULINK software show the effectiveness of the proposed control technique in comparison to the conventional p-q method.U ovom radu prikazana je nova metoda upravljanja za trofazni četverožični UPQC (engl. unified power quality conditioner) temeljena na teoriji trenutne vrijednosti snage koja je prikladna za upravljanje tijekom distorzijskih i nesimetričnih uvjeta na teretu. Predloženo upravljanje temelji se na teoriji o trenutnoj radnoj i jalovoj snazi i optimirano je korištenjem samopodešavajućeg fitera, bez korištenja niskopropusnih filtera ili PLL-a i bez mjerenja struje tereta i filtra. Korišteni su naponi na teretu i napon izvora kako bi se generirala referentna vrijednost napona aktivnog filtra, a struje izvora koriste se za generiranje referentne vrijednosti struje aktivnog filtra. Na taj način smanjen je broj mjerenja struje i sustav ima bolje značajke. Uz predloženi sustav upravljanja testire su mogućnosti korekcije faktora snage, smanjenja neutralne struje izvora, balansiranja tereta, smanjenje harmonika u struji i naponu. Rezultati dobiveni pomoću MATLAB/SIMULINK-a pokazuju učinkovitost predloženog sustava upravljanja