Four-wire Unified Power Quality Conditioner Research Articles

Balance control of grid currents for UPQC under unbalanced loads based on matching-ratio compensation algorithm

In three-phase four-wire systems, unbalanced loads can cause grid currents to be unbalanced, and this may cause the neutral point potential on the grid side to shift. The neutral point potential shift will worsen the control precision as well as the performance of the three-phase four-wire unified power quality conditioner (UPQC), and it also leads to unbalanced three-phase output voltage, even causing damage to electric equipment. To deal with unbalanced loads, this paper proposes a matching-ratio compensation algorithm (MCA) for the fundamental active component of load currents, and by employing this MCA, balanced three-phase grid currents can be realized under 100% unbalanced loads. The steady-state fluctuation and the transient drop of the DC bus voltage can also be restrained. This paper establishes the mathematical model of the UPQC, analyzes the mechanism of the DC bus voltage fluctuations, and elaborates the interaction between unbalanced grid currents and DC bus voltage fluctuations; two control strategies of UPQC under three-phase stationary coordinate based on the MCA are given, and finally, the feasibility and effectiveness of the proposed control strategy are verified by experiment results.

Novel Three-phase Four-wire UPQC Topology Using Adaptive-network-based Fuzzy Inference System for Voltage Sag Compensation

This Study Proposes the novel four wire UPQC topology for Non-linear load and three-phase fault compensation. The electrical power quality is affected by many factors like harmonic pollution due to non-linear loads such as large thyristor power converters, rectifiers and the voltage/current flickering due to arc furnaces and also the sag and swell creation due to the switching of the loads. To overcome the above mentioned problems use of a combined system of shunt and active series filters like Unified Power Quality Conditioner (UPQC) topology. This device contains the integration of a shunt active filter together with a series active filter in a back to back configuration to simultaneously compensate the supply voltage and the load current. Also, it is used to mitigate any type of voltage and current fluctuations and power factor correction in a power distribution network. In this study a novel design of UPQC proposed for voltage sag compensation by using Adaptive Network based fuzzy inference system (ANFIS). This proposed controller has been provided the dynamic control of shunt and series converter operation. It has the combined operations of FL and Artificial Neural Network (ANN) relative advantages and also a powerful processing tool with both advantages can be obtained by combining them together. The simulation results have verified by using MATLAB/SIMULINK environment.

Generation of Reference Compensator to Isolate the Load Current Harmonics by a Customized Three-Phase Four-Wire UPQC System

The Unified Power Quality Conditioner (UPQC) is a customer adjust device, which deals with the Power-Quality issues in the power distribution system. In the proposed topology allows UPQC to have a lower dc-link voltage without limiting its compensation capability. This topology also allows to maintain the dc-link voltage need of the series and shunt active filters of the UPQC. A simulation study of the suggested topology has been performed using Matlab/Simulink. In the extension for the proposed topology added with a multilevel inverter and the compensated DVR voltages. The load voltages after settlement are shown in the same determine. This clearly reveals the customized topology with multilevel inverter efficiency is better than the suggested topology with a less dc-link volts, decrease in switching function, and regular monitoring of referrals compensator voltages.

Extended Reference Signal Generation Scheme for Integration of Unified Power Quality Conditioner in Grid-connected Photovoltaic System

—This article proposes an extended reference signal generation scheme for the integration of a three-phase four-wire unified power quality conditioner in a grid-connected photovoltaic system. The photovoltaic–unified power quality conditioner provides compensation against voltage harmonics, current harmonics, and voltage interruption for the whole day. It also transmits the power generated in the photovoltaic system to the load. The proposed topology utilizes the green energy source with an energy storage unit to address the DC-link voltage requirement of the shunt and series active power filters of the unified power quality conditioner. The high-selectivity filter is used in the shunt inverter control scheme for reference current generations. The series inverter in the unified power quality conditioner is used for supplying a part of reactive power required by the load and for compensation of sag/swell, supply voltage unbalance, and distortions. This is achieved by controlling the phase angle and magnitude of series-injected voltage called the power angle control method. The simulation and experimental studies are carried out to validate the effectiveness of the proposed photovoltaic-based three-phase four-wire unified power quality conditioner.

Performance Evaluation of UPQC for Interconnecting Photovoltaic Systems to the Electric Grid

This paper proposes the efficient operation of a unified power-quality conditioner (UPQC) for interconnecting the photovoltaic (PV) systems to the utility grid. An extended reference signal generation scheme is proposed based on a modified version of the p-q theory using a high selectivity filter (HSF) and power angle control method. The proposed topology provides PV power generation, as well as the function of the UPQC. The shunt active power filter (SAPF) is used to extract the power from the PV power-generating system along with compensating the current harmonics and reactive power. The series active power filter (APF) in the UPQC is used for supplying a part of reactive power required by the load, along with the compensation of the voltage sag/swell, voltage unbalance, and voltage harmonics. This is achieved by controlling the phase angle and magnitude of series injected voltage called the power angle control method. The proposed topology utilizes the renewable energy source with an energy storage unit to meet the dc-link voltage requirement of the shunt and series APF of the UPQC. The shunt inverter control scheme is based on the use of HSF for reference-current generations. In addition, the fuzzy-logic controller is implemented for better current control accuracy of the shunt active filter. The simulation and experimental studies are carried out to validate the effectiveness of the proposed PV-based three-phase, four-wire UPQC.

Photovoltaic interfaced three-phase four-wire unified power quality conditioner with extended reference current generation scheme

This paper proposes an extended reference current calculation method for the photovoltaic (PV) and battery interfaced three-phase four-wire unified power quality conditioner (UPQC). The proposed PV-UPQC provides compensation against the voltage harmonics, current harmonics and voltage interruption for the whole day. Besides, it exports the power generated in the PV system to the load. The proposed topology utilises the green energy source with an energy storage unit to meet the DC-link voltage requirement of the shunt and series active power filters of the UPQC. The shunt inverter control scheme is based on the use of high selectivity filter for reference current generations. In addition the fuzzy logic controller is implemented for better current control accuracy of shunt active filter. The simulation and experimental studies are carried out to validate the effectiveness of the proposed PV-based three-phase four-wire UPQC.

Improving the performance of UPQC under unbalanced and distortional load conditions: A new control method

This paper presents a new control method for a three-phase four-wire Unified Power Quality Conditioner (UPQC) to deal with the problems of power quality under distortional and unbalanced load conditions. The proposed control approach is the combination of instantaneous power theory and Synchronous Reference Frame (SRF) theory which is optimized by using a self-tuning filter (STF) and without using load or filter currents measurement. In this approach, load and source voltages are used to generate the reference voltages of series active power filter (APF) and source currents are used to generate the reference currents of shunt APF. Therefore, the number of current measurements is reduced and system performance is improved. The performance of proposed control system is tested for cases of power factor correction, reducing source neutral current, load balancing and current and voltage harmonics in a three-phase four-wire system for distortional and unbalanced loads. Results obtained through MATLAB/SIMULINK software show the effectiveness of proposed control technique in comparison to the conventional p-q method.

Three-Phase Four-Wire UPQC Topology with Reduced DC-Link Voltage Rating Using Z-Source

The unified power quality conditioner (UPQC) is a custom power device, which mitigates voltage and current-related PQ issues in the power distribution systems. In this paper, the Z-source is combined with UPQC topology for application with non-stiff source is proposed. The existing topology enables UPQC to have a reduced dc-link voltage without compromising its compensation capability. This proposed topology also helps to match the dc-link voltage requirement of the shunt and series active filters of the UPQC. The topology uses a Z-source is connected between the series and the shunt active filter, and the system neutral is connected to the negative terminal of the dc-link voltage to avoid the requirement of the fourth leg in the voltage source inverter (VSI) of the shunt active filter. The average switching frequency of the switches in the VSI also reduces, consequently the switching losses in the inverters reduce. Detailed design aspects of the series capacitor and VSI parameters have been discussed in the Project.

Enhanced PLL based SRF control method for UPQC with fault protection under unbalanced load conditions

This paper presents novel control strategy of a three-phase four-wire unified power quality conditioner (UPQC). It is used to improve power quality in distribution system. The UPQC is realized by the integration of series and parallel active power filter (SAPF and PAPF) sharing a common dc bus capacitor. The realization of parallel APF and series APF are carried out using a three-phase, three legs voltage source inverter (VSI) with split capacitor. In both APFs the fundamental source voltages and currents are extracted by synchronous reference frame technique. SAPF connected with the supply by series transformer. The secondary of series transformer is affected by load side short circuits. This paper also explains the control circuit for protection of series transformer against over voltage and over current. PAPF connected with the system by series inductance. The performance of the applied control algorithm of shunt active filter with series active filter is evaluated in terms of power-factor correction, load balancing, and mitigation of voltage and current harmonics in a three-phase four-wire distribution system for non-linear load, unbalanced supply and load conditions . Sinusoidal PWM current controller, modulated hysteresis current controller are used for generation of switching pulses to series and parallel APFs. The two control algorithm is simulated by use of MATLAB/Simulink-based environment and the obtained results validated through experimental study with the UPQC hardware prototype.

A Modified Three-Phase Four-Wire UPQC Topology With Reduced DC-Link Voltage Rating

The unified power quality conditioner (UPQC) is a custom power device, which mitigates voltage and current-related PQ issues in the power distribution systems. In this paper, a UPQC topology for applications with non-stiff source is proposed. The proposed topology enables UPQC to have a reduced dc-link voltage without compromising its compensation capability. This proposed topology also helps to match the dc-link voltage requirement of the shunt and series active filters of the UPQC. The topology uses a capacitor in series with the interfacing inductor of the shunt active filter, and the system neutral is connected to the negative terminal of the dc-link voltage to avoid the requirement of the fourth leg in the voltage source inverter (VSI) of the shunt active filter. The average switching frequency of the switches in the VSI also reduces, consequently the switching losses in the inverters reduce. Detailed design aspects of the series capacitor and VSI parameters have been discussed in the paper. A simulation study of the proposed topology has been carried out using PSCAD simulator, and the results are presented. Experimental studies are carried out on three-phase UPQC prototype to verify the proposed topology.

A comparative analysis of different magnetics supported three-phase four-wire unified power quality conditioners – A simulation study

In this paper Scott-transformer supported three-phase four-wire unified power quality conditioner (3P-4W UPQC) is proposed and compared with different magnetics supported 3P-4W UPQC. Moreover, these magnetic supported 3P-4W UPQCs are also compared with the most commonly used four-leg VSI based 3P-4W UPQC in terms of% total harmonics distortions (THD) of source current and load voltage. A comparative analysis of required hardware and KAV rating of different magnetics is also given to choose the best option. A control strategy based on synchronous reference frame (SRF) with in-direct approach is used for the control of 3P-4W UPQCs. In this in-direct approach, the current/voltage control is applied over the fundamental supply currents/voltages instead of fast changing APFs currents/voltages, thereby reducing the effect of computational delay and required numbers of current sensors. The performances of the proposed topologies of UPQC are analyzed through simulations using MATLAB software with its Simulink and Power System Block set toolboxes.

A New Control Algorithm for Three-Phase, Four-Wire Unified Power Quality Conditioner (UPQC) in Distributing Systems

This paper presents the new control algorithm for three-phase, four-wire distributing system using unified power quality conditioner (UPQC). The UPQC, a combination of series and shunt active filter (AF) with common dc link, is one of the best solution towards the compensation of voltage sag, swell problems and also compensate voltage flicker/imbalance, reactive power, negative sequence current and maintain zero voltage regulation (ZVR) at the point of common coupling (PCC) on distribution system. The series AF is seen by using a three-phase, three leg voltage source inverter (VSI) and the shunt AF is of a three-phase, four leg voltage source inverter (VSI). The proposed model of the UPQC is developed in the MATLAB/SIMULINK environment and the simulation results prove the power quality improvement in the system.

Control Strategy for Selective Compensation of Power Quality Problems through Three-Phase Four-Wire UPQC

This paper presents a novel control strategy for selective compensation of power quality (PQ) problems, depending upon the limited rating of voltage source inverters (VSIs), through a unified power quality conditioner (UPQC) in a three-phase four-wire distribution system. The UPQC is realized by the integration of series and shunt active power filters (APFs) sharing a common dc bus capacitor. The shunt APF is realized using a three-phase, four-leg voltage source inverter (VSI), while a three-leg VSI is employed for the series APF of the three-phase four-wire UPQC. The proposed control scheme for the shunt APF, decomposes the load current into harmonic components generated by consumer and distorted utility. In addition to this, the positive and negative sequence fundamental frequency active components, the reactive components and harmonic components of load currents are decomposed in synchronous reference frame (SRF). The control scheme of the shunt APF performs with priority based schemes, which respects the limited rating of the VSI. For voltage harmonic mitigation, a control scheme based on SRF theory is employed for the series APF of the UPQC. The performance of the proposed control scheme of the UPQC is validated through simulations using MATLAB software with its Simulink and Power System Block set toolboxes.

A Simplified Control Algorithm for Three-Phase, Four-Wire Unified Power Quality Conditioner

In this paper, a simplified control algorithm for a three-phase, four-wire unified power quality conditioner (UPQC) is presented to compensate for supply voltage distortions/unbalance, supply current harmonics, the supply neutral current, the reactive power and the load unbalance as well as to maintain zero voltage regulation (ZVR) at the point of common coupling (PCC). The UPQC is realized by the integration of series and shunt active filters (AFs) sharing a common dc bus capacitor. The shunt AF is realized using a three-phase, four leg voltage source inverter (VSI) and the series AF is realized using a three-phase, three leg VSI. A dynamic model of the UPQC is developed in the MATLAB/SIMULINK environment and the simulation results demonstrating the power quality improvement in the system are presented for different supply and load conditions.