Unified Power Quality Conditioner Topology Research Articles

Two-stage robust optimization of unified power quality conditioner (UPQC) siting and sizing in active distribution networks considering uncertainty of loads and renewable generators

This paper proposes a robust optimization siting and sizing strategy for the unified power quality conditioner (UPQC) in the active distribution network (ADN) integrated with renewable energy generators. The optimization objectives including investment cost, line loss, and voltage deviation are integrated into an overall cost for both the planning and operating stages. A novel UPQC equivalent power injection model is proposed based on the auxiliary branch method. A set of linear and second-order conic (SOC) constraints are employed to accurately describe the steady-state operation of UPQC. An improved branch current flow model is developed to incorporate radial distribution networks with UPQCs. The UPQC siting and sizing planning is formulated as a mixed integer second-order conic programming (MISOCP) problem. Accounting for the uncertainty in loads and distributed generators, a two-stage robust optimization model is established to address worst-case operational scenarios. A solving strategy is developed based on the strong duality theory and the column-and-constraint generation (C&CG) algorithm, and then commercial solvers can solve the problem accurately and efficiently. Case studies on an IEEE 33-node distribution network demonstrate this strategy's robustness in dealing with loads and renewable energy uncertainties, making it applicable across different UPQC topologies and operation modes. The proposed method has superior performance over the representative meta-heuristic approaches in terms of global optimality as well as an over 7.5 times faster computation speed. This work has significance in enhancing the quality and efficiency of modern power systems highly integrated with renewable energy.

Improved Single-Phase UPQC With Integrating Auxiliary Capacitor for Power Rating Reduction

Unified Power Quality Conditioner (UPQC) can well achieve comprehensive control for power quality. However, the power rating reductions of the series side and parallel side of the back-to-back connected converters in UPQC are hard to be achieved simultaneously, and they even restrict each other. In this paper, a new topology of UPQC is proposed. It has an LC filter coupled with an external capacitor at the series part. Besides, a comprehensive coordination strategy is proposed to operate the improved UPQC (iUPQC) at reactive power compensation (RPC) mode and voltage fluctuation compensation (VC). Specifically, to achieve the low power rating, the proposed control strategy makes the series part undertakes partial reactive power that needs to be compensated at the parallel side in RPC mode. At the same time, it makes the parallel side coordinates the series side to expand the optimal operation range in VC mode. Compared with the conventional UPQCs, the iUPQC can well reduce the power rating of back-to-back connected converters from both parallel and series sides. Moreover, the optimal parameters design method is also provided. Finally, the effectiveness of the proposed topology and control method is validated by both simulation and experimental results.

The Full Load Voltage Compensation Strategy in Capacity Configuration of燯PQC Integrated PV-BESS

Unified power quality conditioner (UPQC) with energy storage is commonly based on conventional capacity configuration strategy with power angle control. It has problems such as phase jumping before and after compensation. DC-link cannot continuously emit active power externally. Therefore, this paper presents the compensation strategy of full load voltage magnitude and phase in capacity configuration of UPQC. The topology of UPQC is integrated a series active power filter (SAPF), a shunt active power filter (PAPF) and a photovoltaic-battery energy storage system (PV-BESS). The principle of full load voltage compensation is analyzed based on the PV-BESS-UPQC topology. The magnitude constant of load voltage is maintained by controlling the appropriate shunt compensation current. Then the UPQC capacity configuration is carried out using the full load voltage compensation strategy. The compensation capacity of UPQC series and shunt units are reduced. Finally, the simulation results show that the proposed compensation strategy reduces the capacity configuration by 5.11 kVA (36.4%) compared to the conventional compensation strategy. The proposed strategy can achieve full compensation of the load voltage, which can effectively reduce the capacity allocation and improve the economy of UPQC. It also has the PV-BESS units' ability of providing active power and can stabilize the DC-link voltage.

Three-Phase Unified Power Quality Conditioner Based on High-Frequency Link

In this article, a unified power quality conditioner (UPQC) that does not employ line-frequency transformers (LFTs) is proposed. In the proposed UPQC, the dc links of the series H-bridge cells are fed from the dc link of the three-phase shunt cell with a unidirectional dc–dc converter isolated with a multiwinding high-frequency transformer (HFT). The three-phase shunt cell is able to compensate reactive power, current harmonics, and unbalances from the load, while the H-bridge series cells compensate voltage disturbances such as sags and swells. A control strategy of the dc-link voltages of the series cells is proposed to allow the compensation of unbalanced disturbances, and strategies to extend the operation of the converter to also compensate voltage swells are discussed. Compared with the UPQC topologies available in the literature, the proposed one does not require LFTs and does not present the operational problems of the transformerless solutions such as limitations of series compensation and balancing issues. Also, it requires fewer controlled switches than the HFT-based solutions in the literature and does not require control in the dc–dc converter. Converter model is presented as well as pulsewidth modulation, control strategy, and experimental results for validation.

Cascade PI-Fuzzy Based Position Optimization of Nonal Switched UPQC with DG for Power Quality Enhancement in IEEE 14 Bus System

An Unified Power Quality Conditioner (UPQC), owning the composition of shunt and series Active Power Filter (APF), has become a standard accepted solution in the area of current and voltage harmonics mitigation of a power system network. This paper furnishes a novel approach of nonal switched UPQC topology, supported with Distributed Generation (DG), aiming at the power quality enhancement and position optimization, placed at different locations in a standard IEEE 14 bus system. In addition to this, behaviour of the proposed topology is analysed using novel Cascade Proportional Integral (PI) - Fuzzy and Space Vector Pulse Width Modulation (SVPWM) as control algorithms and the outcomes are compared with the historical twelve switch UPQC topology. Simulation results of the proposal modelled in MATLAB/SIMULINK reveals the superiority of nonal switched UPQC and the optimal position of the proposed conditioner, for mitigating the harmonic issues in the standard IEEE 14 bus system.

3P4SW and 3P9SW Based UPQC Topologies to Improve the Power Quality in Medium Voltage Distribution System

Background: The undesirable effect of power quality issues on distribution system due to power electronics based controllers; it is highly desired to design a novel power quality conditioner with a minimum number of switches. The proposed configuration reduces the switching loss and also effectively alleviates the power quality issues. This paper introduces the configuration of 3P4SW (Three Phase Four Switch) UPQC (Unified Power Quality Conditioner) for both shunt and series APF (Active Power Filter) as well as 3P9SW (Three Phase Nine Switch) UPQC topologies, which can be implemented in medium voltage power grid. The major challenge of phase balance with only four switches in UPQC is accomplished by adaptive Self-tuning PID using neuro-fuzzy logic control and adaptive reference current generation scheme. This controller improves sag and swells compensation with better angle control via shunt and series converter performance and passive components design. The efficacy of proposed topology is tested on MATLAB/Simulink software and results are compared with the existing three phase six switch configuration (3P6SW). Methods: The main objective of this work is to identify the most suitable configuration of UPQC to mitigate the power quality issues in power distribution system. to achieve this goal a Synchronous reference frame theory is used to generate the pulses in the back to back connected VSI in UPQC. Results: The suggested topologies should not compromise with the nominal functions of the controller; hence from the simulation analysis it clear that the 3P4SW UPQC, as well as 3P9SW UPQC topologies, will fulfill the given constraints and also it maintains the magnitude of the load voltage as per the standard values. Also, the THD percentage is maintained well within the IEEE standard. Conclusion: The proposed topologies can be implemented for medium voltage distributed system with improved power quality.

Optimal Placement of Fuzzy Based Nonal Switched UPQC Topology with Distributed Generation for the Power Quality Enhancement in IEEE 14 Bus System

An Unified Power Quality Conditioner (UPQC), owning the integration of shunt and series Active Power Filter (APF), has become a standard accepted solution in the area of current and voltage harmonics mitigation of a power system network. This paper furnishes a novel approach of nonal switched UPQC topology, supported with Distributed Generation (DG), aiming at the power quality enhancement and position optimization, placed at different locations in a standard IEEE 14 bus system. In addition to this, the behaviour of the proposed topology is analysed using Fuzzy Logic and Space Vector Pulse Width Modulation (SVPWM) as control algorithms and the outcomes are compared with the historical twelve switch UPQC topology. Simulation results of the proposal modelled in MATLAB/SIMULINK reveals the superiority of nonal switch UPQC and the optimal position of the proposed conditioner, for mitigating the harmonic issues in the standard IEEE 14 bus system.

A comparative study among UPQC models with and without real power injection to improve energy efficiency of radial distribution networks

This paper presents a comparative study among different models of unified power quality conditioner (UPQC) designed to improve the energy efficiency of the radial distribution networks. An UPQC consists of two voltage-sourced inverters, i.e., series and shunt inverters. In connected UPQC topology, these two are connected with a DC link. In open UPQC (UPQC-O), these two are not physically connected. But, they share a common communication link. Four models are formulated. They are: (1) UPQC without real power injection, (2) UPQC with real power injection, (3) UPQC-O without real power injection, and (4) UPQC-O with real power injection. A planning optimization model is formulated to determine the optimal locations for the series and shunt inverters for these four models. The objective function consists of the investment and maintenance cost of the inverters and battery, and the cost of energy loss. The energy loss comprises of line losses, inverter losses, and transformer loss. The planning optimization is constrained to ensure a desired power quality level of the network. Particle swarm optimization is chosen as the solution tool. The results show that the placement of UPQC-O provides higher energy efficiency as compared to the connected UPQC topology.

Photovoltaic tied unified power quality conditioner topology based on a novel notch filter utilized control algorithm for power quality improvement

Nonlinear loads and grid side disturbances in the power distribution network cause harmonic rich currents and voltage perturbations such as voltage harmonics, voltage sags and voltage swells. The unified power quality conditioner (UPQC) with shunt inverter and series inverter are usually employed for elimination of current and voltage related power quality issues. However, elimination of voltage and current quality issues in a grid connected Photovoltaic (PV) system is essential. Therefore, PV integrated UPQC topology is proposed in this paper with a novel controller for power quality improvement. The control algorithm based on notch filter Phase Locked Loop (PLL) is utilized for proper phase detection and elimination of voltage and current disturbances. PV tied UPQC controller based on notch filter PLL has the capability to avoid multiple zero crossing during highly distorted grid voltage condition. Conventional control algorithms such as synchronous reference frame theory, unit vector controller based on traditional PLL are also analyzed for the control of PV tied UPQC. The proposed system is developed in Matlab/Simulink and the results obtained are evaluated to measure the performance. A real-time hardware prototype is developed using dSPACE processor. The obtained experimental results validate the efficiency of the proposed controller for PV tied UPQC.

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.

An Advanced Synchronous Reference Frame Control on Reduced Switch Unified Power Quality Conditioner for Harmonics Reduction for Distribution Load

This paper is presented a reduced switch count - parallel and series converter is presented in Unified Power Quality Conditioner (UPQC) system. The topology of UPQC is designed with Four-switch in three phase three wire system with series and parallel injection converter connected back to back converter through DC-Link capacitor. Reduced switch count is introduced on both parallel and series converter i.e three phase series and parallel injection converter designed under three phase circuit having 4 switches for two legs of converter and third leg is replaced by capacitor elements. Reduced switch count topology is introduced in the reason for minimizing cost, maintenance, harmonics problems and so improving efficiency of system. The nature of switch replacement by capacitor is an important task to balancing of three phase of each phase voltages. So an ANFIS based synchronous reference frame controller is introduced to balancing of both reduced switch converter and also used to maintained power quality and harmonics minimization. Present controller of ANFIS is combined application of Fuzzy logic and neural network controller so this is used to extract harmonics, disturbances and controlled accurately.

Power Quality Improvement of Novel PWM Based 15 Level Inverter for Modified Unified Power Quality Conditioner (UPQC)

The unified power quality conditioner (UPQC) is a traditional power device, which mitigates the voltage and current related PQ problems in the power distribution systems. In this paper describes the UPQC topology for an application with non-stiff source is proposed. The proposed topology enables UPQC to have a reduced harmonics. Here, the unified power quality conditioner (UPQC) deals with a solution to compensate the voltage sags and swells and to protect sensitive loads. In order to apply the MLI consists of fifteen levels inverter in the distribution systems with voltage in range of kilovolt, series converter as one of the important component of UPQC should be implemented based on the multilevel converter which have the capability to handle voltage in the range of kilovolts and power of several megawatts. Hence, the proposed configuration of UPQC based on asymmetrical cascade Multicell converters for power quality analysis. The main property of this asymmetrical CM converter is to increase the number of output voltage level with reduced number of switches. Also, in order to achieve the pre-sag compensation strategy and the voltage sag/swell detection with verified the simulation results under Matlab/Simulink platform.

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.

A Novel Hybrid Unified Power Quality Conditioner (UPQC) for Medium-Voltage Power Grid

This paper proposed a three-phase three wire UPQC (hybrid UPQC). The topology is novel which consists of a series and a hybrid shunt filters. The unique topology can reduce the capacity of power devices in the hybrid UPQC when compensating source harmonic currents. In this paper a detailed design about the main circuit is presented. Finally a simulation study of the proposed hybrid UPQC has been carried out by using MATLAB/Simulink. The results verified the effectiveness of the UPQC topology.

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.

Performance Evaluation of R-UPQC and L-UPQC Based on a Novel Voltage Imperfections Detection Algorithm

This paper proposes a new method to detect voltage imperfections, such as balanced/unbalanced voltage sag/swell, voltage flicker and voltage disturbance in both single and three-phase electrical distribution systems with excellent performance characteristics. The proposed method is based on the single-phase synchronous d-q reference frame transformation (SPSRF). In contrast to the previous detection methods which need a measurement of the three-phase voltage for sag detection and fails to detect the voltage sag lower than a definite depth, the proposed method employs the series compensator of the unified power quality conditioner (UPQC) to inject a compensation voltage in-phase/out of phase with the source current during voltage sag/swell. The performance of the two structures of the UPQC, the right-shunt UPQC (R-UPQC) and the left-shunt UPQC (L-UPQC,) were tested under different operating conditions based on the proposed controller to improve the power quality of the single feeder distribution system. The simulation analysis and compensation performance of both UPQC topologies was implemented on a PSCAD/EMTDC platform

3P-3W UPQC with zig-zag transformer for 3P-4W Distribution System

In this paper, a new topology is developed for a three-phase four-wire (3P4W) distribution system utilizing a zig-zag transformer along with three-phase three- wire (3P3W) Unified Power Quality Conditioner (UPQC).In this proposed topology the neutral point of the star connected transformer, used for the connection of series active power filter (APF) of 3P3W UPQC, is utilized as a fourth wire for 3P4W distribution system. The zig-zag transformer is connected near the load to compensate the neutral current that may flow toward the neutral point of the series transformer of series APF. The series and shunt APF of 3P-3W UPQC are realized by readily available three-leg voltage source inverters (VSIs). For the mitigation of different power quality problems a control technique based on synchronous reference frame (SRF) theory is used for the control of UPQC. In this control scheme of UPQC, the current/voltage control is applied over the fundamental supply currents/voltages instead of fast changing APFs currents/voltages, there by reducing the computational delay and the required sensors. The performance of the proposed topology of UPQC is analyzed through simulations results using MATLAB software with its Simulink and Power System Block set toolboxes.