Single-phase Unified Power Quality Conditioner Research Articles

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.

A new six‐switch converter based unified power quality conditioner for improving power quality in single‐phase system

This study encapsulates a unique six-switch converter (SSC) based unified power quality conditioner (UPQC) for a single-phase system. SSC based UPQC has a 25% less switch count than conventional single-phase back-to-back (B2B) UPQC. An SSC based UPQC is a single-phase dual output converter, with one output for series compensation and the other output for shunt compensation. A detailed analysis of SSC and its operating principle is also discussed. Control signals for series and shunt compensation are developed using the unit vector template method. It is found that the SSC based single-phase UPQC system effectively compensates the supply side voltage sag, swell, and distortions at the load end as well as compensate the load reactive power and current harmonics at the source end. Real-time simulation results using OPAL-RT (OP4510) validate the efficacy of the proposed SSC based UPQC system.

Control Strategy of Single-Phase UPQC for Suppressing the Influences of Low-Frequency DC-Link Voltage Ripple

The single-phase unified power quality conditioner (UPQC) is widely used to improve power quality for sensitive end-users. However, the inherent instantaneous power difference between parallel and series converter will generate significant low-frequency dc-link voltage ripple and degrade the compensation performance of UPQC. The mechanism of dc-link voltage ripple generation and its influences on compensation voltage and current are analyzed in this article. To suppress the influence, a control strategy is proposed for the single-phase UPQC. For parallel converter, a notch filter is introduced in the outer voltage loop to prevent the voltage ripple entering the control loop, the specific order harmonics compensation is proposed in the inner-current loop to reduce the grid current harmonics. For the series converter, the dc-link voltage feedback is adopted to suppress the influence of voltage ripple on the compensation performance. Simulation and experimental results show that the grid current total harmonic distortion (THD) can be reduced effectively with the fixed dc-link capacitance compared with the traditional control strategy. More than half of the load voltage THD are also decreased by the dc-link voltage feedback control. Moreover, with the smaller dc-link capacitance, single-phase UPQC can maintain the better performance under the proposed control strategy.

A new space vector pulse width modulated transformer less single-phase unified power quality conditioner

Emergence of solid-state switching devices, like thyristors, GTO's, IGBT's and etc, are widely used for controlling electric power in power electronic equipment for various purpose such as HVDC systems, computers etc. These devices draw disturbance in voltages and currents of both source side and distribution ends due to its non-linearity. This induce harmonics, reactive power, and excess neutral current cause the system to have less efficiency and reduction in power factor. In this paper transformer less single-phase unified power quality conditioner has been implemented to reduce the voltage and current distortions. The operation and control of single-phase transformer less three leg Unified power quality conditioner is investigated with the implementation of a new pulse width modulation method for solving the coupling problem introduced by common leg switches.

Power quality enhancement in solar power with grid connected system using UPQC

The need to generate pollution free energy has triggered the effect towards the usage of solar energy interconnection with the grid. Consequently, the Photovoltaic (PV) panel interfaced with the grid causes the power quality problems such as a voltage harmonics and voltage distortion etc., Active power filters are the powerful tool for mitigation of harmonics. This work involves the use of single-phase Unified Power Quality Conditioner (UPQC) based on a unit vector template control algorithm for its functions with grid integration of photovoltaic, such as voltage sags/ swell, unit power factor correction, voltage and current harmonic cancelation. The unit vector template control algorithm includes a phase-locked loop (PLL) mechanism that is responsible for avoiding multiple zero crossings during highly distorted grid voltage detection. A unit vector template control with a PLL-based control algorithm is applied to the shunt and series inverters of PV grid connected UPQC. In addition to normalizing voltage and current disturbances, the proposed controller has the functions of phase detection and perfect grid synchronization. It is proposed that the system performance is fully verified by MATLAB simulation with the response of load variation, transient response, THD, voltage swell and sag. The Total Harmonic Distortions (THDs) of proposed grid integration of photovoltaic systems through single-phase unified power quality conditioner (UPQC) obtain the range of IEEE standard.

Comparative analysis involving PI and state-feedback multi-resonant controllers applied to the grid voltage disturbances rejection of a unified power quality conditioner

This paper presents a detailed evaluation of the grid voltage disturbance rejection capability using three kinds of controllers inserted into the current control loop of the series converter that composes a single-phase unified power quality conditioner (UPQC). The mentioned controllers are evaluated and compared to each other to give subsidies to the designer in choosing the one that performs better, since static behaviour of the UPQC is directly affected with the presence of grid voltage disturbances. Firstly, the classical proportional-integral (PI) controller is discussed. After that, in order to improve the performance of the conventional PI controller, multi-resonant (MR) terms are added resulting in the PI-MR controller. Finally, a state-feedback controller composed of an error integrator and multi-resonant terms, named SF-MR controller is employed, where the state-feedback controller gains are calculated using an increased model of the controlled system. Independent of the three current controllers implemented in the series converter, the parallel converter of the UPQC will always be controlled to operate using the SF-MR controller. Mathematical models, stability and sensitivity analyses are presented and discussed in detail. Furthermore, experimental results are presented to comparatively evaluate the static UPQC performance involving the PI-MR and SF-MR controllers, as well as the well-known conventional PI controller.

A unified power quality conditioner for power quality improvement in distributed generation network using adaptive distributed power balanced control (ADPBC)

Power quality improvement is one of the central and critical needs in all types of power-driven industries for perfect utilization of sources. However, fundamental inconveniences in power quality have been recognized, for instance, sags, swells, harmonic distortions and different blocks. Among those, sags and swells are overwhelmingly uncovered, and each influences the electrical gadgets or electrical machines and this requires to be compensated with an advancement to ensure any mal-operation or disappointment. To settle these troubles, custom power gadgets are used like unified power quality conditioner (UPQC), dynamic voltage restorer (DVR) and Distributed Static Compensator (DSTATCOM). This work aims to update the power quality in both single-phase and three-phase system using UPQC. The capacity of UPQC to mitigate voltage sag, voltage swell, responsive power remuneration, load balancing, zero voltage direction, and power factor redress and Total Harmonics Distortion (THD) in the appropriation framework is done by utilizing adaptive distributed power balanced control (ADPBC) method. This investigation works on the single-phase UPQC design to utilize two H-connect setups with eight switches and the three-phase UPQC arrangement to use four legs and three-phase four wire course of action. The overall function of the UPQC with distributed generation (DG) system will be able to compensate for the offset voltage and current disturbances with all the compensated data being collected and verified in Internet of Things (IoT) based on conditional Random Fields (CRFs).

Adaptive shunt filtering control of UPQC for increased nonlinear loads

In a distribution system, to compensate for the effect of voltage sag/swell and mitigate harmonic currents, a unified power quality conditioner (UPQC) is used. Conventionally, the power rating of UPQC is determined based on the expected sag/swell, linear and nonlinear loads. However, with the shift towards usage of electronic loads and electrical drives, the composition of nonlinear loads is increasing. Hence, the UPQC deployed earlier may not be capable of handling increased harmonic currents due to its limited current rating. While trying to compensate for both harmonic currents and voltage sag/swell, the shunt converter (of UPQC) may reach its current limit and would result in undesirable behaviour. To address this issue, a technique to prioritise sag/swell compensation over active filtering is proposed in this study. The remaining power capacity of UPQC (after sag/swell compensation) is utilised for harmonic filtering. Adaptive determination of harmonic compensation current also allows prioritising the various harmonics to be compensated. This helps in case passive tuned filters are installed for some harmonic frequencies for which UPQC need not respond. Detailed simulation studies are performed on MATLAB/SIMULINK platform and results are included in this study. A laboratory prototype of single phase UPQC is developed to validate the performance of the proposed scheme.

Design and Modeling of Single-Phase PV-UPQC Scheme for Power Quality Improvement Utilizing a Novel Notch Filter-Based Control Algorithm: An Experimental Approach

This paper deals with grid integration of photovoltaic systems through single-phase unified power quality conditioner (PV-1UPQC) based on notch filter novel control algorithm for its function such as better phase detection, voltage sag/swell, voltage unbalance, voltage and current harmonics eliminations. A notch filter-based control algorithm includes a phase-locked loop (PLL) mechanism which is responsible to avoid multiple zero crossing at the time of highly distorted grid voltage detection. Notch filter PLL-based control algorithm is applied to both series and shunt inverters of PV-tied UPQC. In addition to normalizing voltage and current perturbations, proposed controller has feature of phase detection and perfect grid synchronization. Synchronous reference d-q frame controller and unit vector control algorithm with conventional PLL is also studied, utilized and evaluated for control of PV-1UPQC. Hardware setup is developed in laboratory using DS1103 dSPACE processor. Performance and efficiency of PV-1UPQC are analyzed through simulation and experimentation for various operating conditions.

Analysis and Control of M3C-Based UPQC for Power Quality Improvement in Medium/High-Voltage Power Grid

To enhance the power quality in the medium/high-voltage distribution power systems, a single-phase unified power quality conditioner (UPQC) based on the modular multilevel matrix converter (M3C) is presented in this paper. The M3C-UPQC is comprised of four identical multilevel converter arms and associated filtering inductors. According to the established equivalent circuit of M3C-UPQC, its operation principle and power balance of each arm are analyzed theoretically, and the parameters’ design for the arm inductance as well as submodule capacitance is studied. Then, an integrated control method for M3C-UPQC in which the dc circulating current is used to balance the instantaneous active power of each arm is proposed to prevent the capacitor voltages from divergence inter- and intra-arms, so as to achieve voltages balance of M3C-UPQC. Finally, the effectiveness of the proposed control method is verified by a prototype rated at 8 kVA.

Flexible Control of Single-phase Unified Power Quality Conditioner Using Frequency-domain Approach

Power conditioning devices are generally designed for full compensation of power quality problems irrespective of the requirements of the consumers. In this article, flexible control of a single-phase unified power quality conditioner is proposed, which attributes the responsibility of the consumer and the utility. For the flexible control of a single-phase unified power quality conditioner, an approach based on Fourier analysis is used. The performance of a single-phase unified power quality conditioner is evaluated for the mitigation of customer-generated harmonics, total current harmonics, reactive power, voltage harmonics, and their combinations, depending on the requirements. In this proposed control strategy, an indirect approach is used in which control is made over the fundamental supply current and fundamental supply voltage instead of the fast changing active power filter current and voltage, thereby reducing the effect of computational delay. A dynamic model of the unified power quality conditioner is developed in MATLAB/SIMULINK (The MathWorks, Natick, Massachusetts, USA), and simulation results demonstrating power quality improvement in the system are presented for a distorted supply and a combination of linear and non-linear loads.

Power quality enhancement utilising single-phase unified power quality conditioner: digital signal processor-based experimental validation

This study is based on a single-phase unified power quality conditioner (UPQC) to enhance power quality problem in single-phase systems. A simple control approach is implemented and validated through simulation as well as experimental studies. A laboratory prototype of UPQC is designed and developed using a digital signal processor. The performance of UPQC is validated experimentally under several operating conditions. It is found that the UPQC in single-phase system effectively compensates the important power quality issues, such as the load reactive power, load current harmonics, voltage harmonics, voltage sag, voltage swell and voltage flicker. Under distorted source voltage having total harmonics distortion (THD) of 14.1% with a non-linear load producing a distorted current (THD of 30.98%), the UPQC simultaneously compensates these harmonics resulting sinusoidal source current (THD of 3.77%) and load voltage (THD of 2.54%).

Double Integration Control for Single-Phase Unified Power Quality Conditioner Based on A Neuron Adaptive Harmonic Detection

AbstractThis paper proposes a neuron adaptive harmonic detection algorithm which can adaptively, rapidly and precisely calculate the voltage and current reference signals in presence of the system frequency variation, according to which, a Double Integration Control (DIC) strategy is applied in Unified Power Quality Conditioner (UPQC) as an interface between the hybrid power system and the load.Generally, the UPQC consists of a shunt inverter, a series inverter and a DC-link capacitor, where DIC strategy is used separately in the shunt inverter and series inverter to force the output voltage of Voltage-Source Inverter (VSI) to track the reference value with high precision. The reference value for the shunt inverter is obtained based on the Recursive Least Squares (RLS). Simulation results demonstrate the effectiveness and reliability of the proposed detection algorithm and control strategy.

Output Feedback Control of Single-Phase UPQC Based on a Novel Model

The single-phase unified power-quality conditioner can be treated as a typical switched linear system due to its typical switching dynamic characteristics. However, because the switched model is difficult for controller design, we first transform it to an equivalent discrete system model (EDSM) in light of the pulsewidth-modulation principle. The EDSM is further transformed to a linear equivalent discrete system model (LEDSM) by states reconstruction and linearization at some neighborhood of the equilibrium manifold. The LEDSM, where the pulsewidths are adopted as the controller variables, is a periodical discrete linear system with the constrained control. Since some states cannot be available, the output feedback periodical-switched controller is designed to meet suboptimal performance and stabilize the closed-loop system. Compared with the proportional-integral controller, the output feedback control strategy features better characteristics. The voltage reference for the series inverter is obtained by using an adaptive voltage detection method. Simultaneously based on the detected phase of the system voltage, the instantaneous reactive power theory is adopted to calculate the reference current for the shunt inverter. Additionally, the power flow and power consumption are described and analyzed. Simulation results demonstrate the effectiveness and reliability of the proposed control strategy.

Experimental Investigation of a Single-Phase UPQC With Minimum VA Loading

The paper deals with an optimized unified power-quality conditioner (UPQC), which aims at the integration of series active and shunt active power filters with minimum volt-ampere (VA) loading of the UPQC. The series active filter is a dynamic voltage restorer (DVR), which regulates the voltage at the load end with minimum VA loading of the overall UPQC by injecting the voltage at an optimum angle. The proposed scheme is validated by an experimental prototype in the laboratory. Selected experimental results are reported along with analytical findings, which show the effectiveness of the proposed UPQC