Common DC Link Capacitor Research Articles

The Design and Dynamic Control of a Unified Power Flow Controller with a Novel Algorithm for Obtaining the Least Harmonic Distortion

This study investigates the control and dynamic operation of the Unified Power Flow Controller made of shunt and series converters, a Static Synchronous Compensator, and a Static Synchronous Series Compensator, respectively, connected back-to-back through a common DC-link capacitor. The model of a 48-pulse Voltage Source Converter is constructed from a three-level Neutral Point Clamped converter, which allows the total harmonic distortion to be reduced. An optimal conduction angle tracking system of the three-level inverter is designed to minimize distortion by detecting proper harmonic component elimination. Starting from the six-step modulation strategy, the dq decoupled control schemes of both compensators in open and closed loops are presented. Finally, the MATLAB-Simulink model of the power flow controller is implemented and analyzed. The results show that the controller can track the power changes and apply a suitable voltage to the power system so that the power flow can be controlled. This way, the power flow controller dynamically improves the voltage and power quality across the power network while simultaneously improving the transient stability of the system. It can eliminate all system disturbances resulting from oscillations and harmonics in voltage and current within a very short time. The procedural approach used to model and simulate the Unified Power Flow Controller, as well as the new algorithm used to obtain the harmonic number that minimizes the total harmonic distortion, can be applied to any AC power system.

Common DC-Link Capacitor Lifetime Extension in Modular DC/DC Converters for Electric Vehicle Fast Chargers via Variable-Angle Interleaved Operation

The global shift towards the electrified transportation as a means of achieving decarbonized economy has led to an increase in the demand of electric vehicles. In order to enhance the transition, there is a need to develop fast and ultra-fast charging substations. Hence, power converters play an inherently vital role in the mass adoption of electric vehicles. However, the reliability and active maintenance scheduling of these converters are becoming prominent issues for manufacturers and operators. As a result, optimization of the operation of an interleaved dc/dc converter present in the charging poles plays a significant role. This paper proposes an alternative modulation technique for interleaved dc/dc power converters of fast chargers aiming to improve the harmonic performance of the common dc-link capacitor current. This technique leads to an extension of lifetime of the capacitor, which is one of the most critical component of the power system. Experimental results are shown in order to validate the effectiveness of the proposed method.

Common DC-Link Capacitor Harmonic Current Minimization for Cascaded Converters by Optimized Phase-Shift Modulation

This paper investigates the influence of a constant carrier phase shift on the DC-link capacitor harmonic current of cascaded converters used in fuel-cell and mild-hybrid electric vehicles. In these applications, a DC-DC converter can be adopted between the battery and the motor drive inverter in a cascaded structure, where the two converters share the same DC-link. Since the DC-link capacitor of such a system represents a critical component, the optimization of the converter operation to limit the current stress and extend the lifetime of the capacitor is an primary objective. This paper proposes the use of a carrier phase shift between the modulations of the two converters in order to minimize the harmonic current of the DC-link capacitor. By harmonic analysis, an optimal carrier phase shift can be derived depending on the converter configuration. Analytical results are presented and validated by hardware-in-the-loop experiments. The findings show that the pulse width modulation carrier phase shift between the interleaved boost converter and the voltage source motor drive inverter has a significant influence on the DC-link capacitor current and thus on its lifetime. A case study with two-cell and three-cell interleaved boost converters shows a possible DC-link capacitor lifetime extension of up to 390%.

Performance Analysis of Universal Power Quality Conditioner Systems Based on Seven-level NPC Inverter Using PD-SPWM with Fuzzy Control Scheme

This paper presents novel Unified Power Quality Conditioner (UPQC) system based on seven-level Neutral Point Clamped (NPC) inverter using combined PD-SPWM and fuzzy control scheme. The proposed UPQC is adopted to mitigate source current harmonics and compensate all voltage disturbances simultaneously. It is designed by the combination of series and shunt Active Filters (AFs) connected by a common DC link capacitor. The DC voltage at common DC bus is maintained constant using proportional integral voltage controller. The Synchronous Reference Frame (SRF) method is used to get the shunt APF reference signals and the power reactive theory (P-Q theory) for the series APF. Conventional control schemes require complex calculations, the use of intelligent systems help to reduce the control system size and the operation complexity. The shunt and series Active Power Filter (APF) reference signals derived from the control algorithm are injected in Fuzzy intelligent controllers to generate switching signals. The functionality of proposed UPQC system and its control system is evaluated using Matlab-Simulink software and SimPowerSystem Toolbox under various operation conditions in cases of most common power quality problems such as voltage sag, voltage swell, current harmonic compensation of nonlinear loads and unbalanced load. The simulation results show UPQC performances to improve the power quality in steady and transient conditions operation at the point of common coupling on power distribution under unbalanced and distorted voltage conditions.

Modeling and Control Strategy of Wind Energy Conversion System with Grid-Connected Doubly-Fed Induction Generator

The most prominent and rapidly increasing source of electrical power generation, wind energy conversion systems (WECS), can significantly improve the situation with regard to remote communities’ power supply. The main constituting elements of a WECS are a wind turbine, a mechanical transmission system, a doubly-fed induction generator (DFIG), a rotor side converter (RSC), a common DC-link capacitor, and a grid-side converter. Vector control is center for RSC and GSC control techniques. Because of direct and quadrature components, the active and reactive power can also be controller precisely. This study tracks the maximum power point (MPP) using a maximum power point tracking (MPPT) controller strategy. The MPPT technique provides a voltage reference to control the maximum power conversion at the turbine end. The performance and efficiency of the suggested control strategy are validated by WECS simulation under fluctuating wind speed. The MATLAB/Simulink environment using simpower system toolbox is used to simulate the proposed control strategy. The results reveal the effectiveness of the proposed control strategy under fluctuating wind speed and provides good dynamic performance. The total harmonic distortions are also within the IEEE 519 standard’s permissible limits which is also an advantage of the proposed control approach.

A dual-function SMES-based series-connected compensator of dynamic voltage restoration and fault current limitation for photovoltaic microgrid

A dual-function series-connected compensator based on superconducting magnetic energy storage (SMES-based SCC) is proposed for a photovoltaic microgrid. The SMES-based SCC can operate in two different modes: dynamic voltage restorer for voltage fluctuation and fault current limiter for short-circuit fault. The SMES provides/absorbs power to/from the common DC-link capacitor by a DC/DC converter under different modes with fast response speed. In order to achieve better tracking performance to reference voltage and overcome the drawback of the conventional control methods, a modified sliding mode controller based on SVPWM strategy (SMSVM) is proposed for control of the SCC. The performances of the SMES-based SCC under different operation modes are evaluated through a series of simulation results and its superiority is verified by comparing it to a battery energy storage-based SCC. Simulation and comparative analyses between the proposed SMSVM method and the conventional hysteresis control method are conducted to prove the validity and superiority of the SMSVM method.

Design of Common DC-Link Capacitor in Multiple-Drive System Based on Reduced DC-Link Current Harmonics Modulation

Many industrial applications are recently utilizing the advantages of a common dc-bus-based multiple-drive (multidrive) system, such as low installation cost, space savings as well as improved reliability, and flexibility. One of the main drawbacks of such systems is the requirement for a bulky dc capacitor due to the presence of large dc-link current ripples from the harmonic interaction between these multidrive and pulsewidth modulation (PWM) switching. This problem not only increases the cost and volume of the dc-link capacitors but also decreases its lifetime, which must be considered in the design from the industrial aspect. This article proposes a new dc-bus capacitor design method for a multidrive system, focused on the capacitor sizing, cost reduction, and lifetime improvements. First, an analytical model to obtain the dc-link capacitor current in a multidrive system is proposed, which would aid the designers to configure the dc-capacitor current in systems having numerous multiple drives. Next, using the developed analytical model, the dc-link current harmonics are reduced through optimal interleaving of the fundamental output currents in addition to the phase shifting of the carrier waves of the parallel connected inverters. Finally, new capacitor sizing/design is proposed considering the lifetime, power loss, cost, and volume of the dc-link capacitor bank. The proposed approach reduces the volume and cost of dc-cap bank by 50%, and increases the lifetime by four years ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 35 000 h), considering the worst-case scenarios. Experimental and analytical results are given for validation of the proposed method. The results could serve as a guideline for designing the dc-link capacitor in multidrive applications in a low-cost manner.

Performance Evaluation of BB-QZSI-Based DSTATCOMUnder Dynamic Load Condition

Abstract This paper presents the shunt compensation performance of quasi-Z-source inverter (QZSI) and back to back connected QZSIs (BB-QZSI) to address the power quality (PQ) issues in the three-phase three-wire power utility network (PUN). Generally, these PQ issues are poor voltage regulation, low power factor (PF), source current distortion, unbalanced voltage, etc. The proposed BBQZSI-based distribution static compensator (DSTATCOM) consists of two QZSIs with a common dc-link capacitor. Because the QZSI could achieve buck/boost conversion as well as DC to AC inversion in a single-stage and the back to back configuration decreases the system down time cost (if a fault occurs in one QZSI the other can continue the shunt compensation). Particularly, icos ϕ control algorithmcontrol algorithm is implemented to generate proper switching pulses for the switches of DSTATCOM. The effectiveness of the BB-QZSI is verified through simulation studies over QZSI using MATLAB/Simulink software satisfying the recommended grid code.

Perfprmance Analysis on Power Flow of a Three-Feeder/Multi-Bus Distribution System Using Gupqc

Power flow in any distribution system either it is multi-bus or three feeders explain by a Generalized Unified Power Quality Conditioner i.e. GUPQC.On the one side, that is DC side is connected with the common DC link capacitor which is also coupled consecutively through 3 voltage source converters. This is the simple block realization of GUPQC. This multi feeder is explained where one feeder is controlled by a parallel compensator and the next two feeders are controlled through the proposed series compensator. This technique i.e. GUPQC makes the feeder distribution free from harmonic and voltage-current compensation etc randomly. Also, it can improve the quality of supply power given to another consumer. A vast and huge study of Simulation is helped to how MATLAB/SIMULINK is used for making this type of GUPQC. Disrupted Voltage, current, and power quality issues can be easily improved in this technique.

Compensate Power Quality Related Problems by Mitigating Source Harmonics with Artificial Neural-Network controller

This paper deals with Unified Power Quality Conditioner (UPQC) which consists of series and shunt active filter sharing a common dc link capacitor. The series active filter reduces voltage source harmonics. Usually, the shunt active filter is designed to reduce harmonic current-components generated by the nonlinear loads. Thus with compensating effectively all the harmonics and reactive power improves power factor. The application of artificial intelligence is growing fast in the area of power electronics and power systems. The artificial neural network (ANN) is considered as a new device for the design of control circuitry for power-quality devices. Thus for optimal mitigation of voltage/current source harmonics, a neural network is proposed to control the UPQC. In this paper, ANN controller is designed for extracting the fundamental frequency components from non-sinusoidal and for controlling the current of the UPQC. An extensive simulation study has been carried out for investigating the performance of the ANN controller and the system performance has been verified by simulation analysis with Matlab/Simulink software.

Grid integration of Photovoltaic System Interfaced with Artificial Intelligence based Modified Universal Power Quality conditioning system

Unified Power Quality Compensators (UPQC) in load side utility system is not able to fully suppress harmonies in power grid and distortion in the interface system. To enhance the operation of the UPQC, a Fuzzy based Modified Universal power quality conditioning system (Fuzzy-MUPQCS) is developed. Modified Universal power quality conditioning system (MUPQCS) is a combination of two active filters in series and one active filter in shunt. A 3φ voltage source inverter is also used to maintain a common DC link capacitor voltage through Photo voltaic (PV) system connected to a utility grid. Highest Power Point Tracking (HPPT) algorithm is mainly used to pull out the maximum amount of power in the PV system. In this paper, Proportional integral controller based MUPQCS (PI- MUPQCS) and Fuzzy-MUPQCS are used to analyse the load voltage and load current distortion, THD analysis, power factor measurement, grid voltage and grid current distortion in the three phase system under nonlinear load conditions. The execution of the MUPQCS based 3φ system and the controllers are simulated using Matlab /Simulink model.

RETRACTED ARTICLE: Power flow control and power quality analysis in power distribution system using UPQC based cascaded multi-level inverter with predictive phase dispersion modulation method

Power quality is associated with the ability of utilities to provide electrical power without interruption. One of the major concerns in the electrical industry today is the issue of power quality over major loads. This work presents a Cascaded H-Bridge Multi-Level Inverter (CHBMLI) based unified power quality conditioner (UPQC) for the compensation of voltage sag/swell in the source side and current harmonics in the load side due to the non-linear loads. A predictive control based algorithm called as predictive phase dispersion modulation (PPDM) is used in the proposed system for the control of series and shunt active power filter of the UPQC. The shunt and series active power filter is connected back to back with a common DC link capacitor. The objectives of the proposed algorithm is to maintain a constant DC link voltage and to control the switching pulses of the CHBMLI according to the variations of the current in the load side and also the voltage unbalances in the source side. The performance of the UPQC is significantly improved with the proposed CHBMLI based UPQC than the conventional Voltage Source Inverters (VSI) based UPQC. The algorithm used in this work reduces the computational burden than the conventional model predictive controllers. The proposed CHBMLI based UPQC with PPDM technique is validated through simulation studies using MATLAB and a hardware prototype also realized and the results are investigated.

A survey of control strategies for grid connected wind energy conversion system based permanent magnet synchronous generator and fed by multi-level converters

In this study, two control strategies for speed and power control of three-level neutralpoint (3L-NPC) clamped back-to-back converters in wind energy conversion system (WECS) with permanent magnet synchronous generator (PMSG) are proposed. The system consists of generator side converters (GSCs) and grid side converter (GSC) which share a common DC-link capacitor. The proposed control laws combine sliding mode control (SMC) and vector oriented control (VOC) to maximise the generated power from wind turbine generators (WTGs). Considering the variation of wind speed, the GSC injects the generated power into the AC network, and regulates DC-link voltage. Also, it is employed to achieve unity power factor (UPC). The GSCs are employed to achieve maximum power point tracking (MPPT). To validate the proposed approaches, simulations are carried out with MATLAB/Simulink software. The simulation results demonstrate a good performance in various scenarios.

A survey of control strategies for grid connected wind energy conversion system based permanent magnet synchronous generator and fed by multi-level converters

In this study, two control strategies for speed and power control of three-level neutralpoint (3L-NPC) clamped back-to-back converters in wind energy conversion system (WECS) with permanent magnet synchronous generator (PMSG) are proposed. The system consists of generator side converters (GSCs) and grid side converter (GSC) which share a common DC-link capacitor. The proposed control laws combine sliding mode control (SMC) and vector oriented control (VOC) to maximise the generated power from wind turbine generators (WTGs). Considering the variation of wind speed, the GSC injects the generated power into the AC network, and regulates DC-link voltage. Also, it is employed to achieve unity power factor (UPC). The GSCs are employed to achieve maximum power point tracking (MPPT). To validate the proposed approaches, simulations are carried out with MATLAB/Simulink software. The simulation results demonstrate a good performance in various scenarios.

A non-linear controller design for UPQC in distribution systems

In this article, a new approach based on non-linear control scheme was proposed for unified power quality conditioner (UPQC). The combination of sliding mode control and instantaneous active and reactive power theories was used to design this controller. UPQC consisted of a series and a shunt active power filter (APF), which were back to back connected through a common dc link capacitor. Special features of the proposed controller were as follows: (1) fast dynamic response, (2) complete compensation of UPQC by the proposed controller for the sag/swell in supply voltage, (3) good performance in power system with extreme distortions, and (4) perfect performance in compensation for unbalance networks. UPQC with the sliding mode controller (SMC) was simulated in MATLAB/SIMULINK software. Simulation results under different loads and power system conditions showed that UPQC with the proposed controller could more effectively compensate for all voltage and current distortions than the conventional PI controller.

Performance of unified power quality conditioner (UPQC) based on fuzzy controller for attenuating of voltage and current harmonics

Power quality-related issues such as current and voltage distortions can adversely affect home and industrial appliances. Although several conventional techniques such as the use of passive and active filters have been developed to increase power quality standards, these methods have challenges and are inadequate due to the increasing number of applications. The Unified Power Quality Conditioner (UPQC) is a modern strategy towards correcting the imperfections of voltage and load current supply. A UPQC is a combination of both series and shunt active power filters in a back-to-back manner with a common DC link capacitor. The control of the voltage of the DC link capacitor is important in achieving a desired UPQC performance. In this paper, the UPQC with a Fuzzy logic controller (FLC) was used to precisely eliminate the imperfections of voltage and current harmonics. The results of the simulation studies using MATLAB/Simulink and Simpower system programming for R-L load associated through an uncontrolled bridge rectifier was used to assess the execution process. The UPQC with FLC was simulated for a system with distorted load current and a system with distorted source voltage and load current. The outcome of the comparison of %THD in the load current and source voltage before and after using UPQC for the two cases was presented.

Comparison of Dynamic Stability Response of A SMIB with PI and Fuzzy Controlled DPFC

Consumer utilities are non –linear in nature. This injects increased flow of current and reduced voltage with distortions which cause adverse effect on the stability of consumer utilities. To overcome this problem we are using a modern Flexible Alternating Current Transmission System controller i.e. distributed power flow controller (DPFC). This controller is similar to UPFC, which can be installed in a transmission line between the two electrical areas. In DPFC, instead of the common Dc link capacitor three single phase converters are used. In this paper we are concentrating on system stability (oscillation damping). For analyzing the stability of a single machine infinite bus system (SMIB) we have used PI controlled Distributed Power Flow Controller (DPFC) and Fuzzy controlled DPFC. All these models are simulated using MATLAB/SIMULINK. Simulation results shows Fuzzy controlled DPFC are better than PI controlled DPFC. The significance of the results are better stability and constant power supply.

Comparison of Dynamic Stability Response of A SMIB with PI and Fuzzy Controlled DPFC

Consumer utilities are non –linear in nature. This injects increased flow of current and reduced voltage with distortions which cause adverse effect on the stability of consumer utilities. To overcome this problem we are using a modern Flexible Alternating Current Transmission System controller i.e. distributed power flow controller (DPFC). This controller is similar to UPFC, which can be installed in a transmission line between the two electrical areas. In DPFC, instead of the common Dc link capacitor three single phase converters are used. In this paper we are concentrating on system stability (oscillation damping). For analyzing the stability of a single machine infinite bus system (SMIB) we have used PI controlled Distributed Power Flow Controller (DPFC) and Fuzzy controlled DPFC. All these models are simulated using MATLAB/SIMULINK. Simulation results shows Fuzzy controlled DPFC are better than PI controlled DPFC. The significance of the results are better stability and constant power supply.

ENGLISH

Power quality problems like voltage sag/swell, flickers, interruptions, voltage distortions and imbalance can have drastic effects on home appliances, industries, processing plants and other applications. In this paper, a novel multi-converter unified power quality conditioner (MC-UPQC) is proposed for simultaneous compensation of voltage and current in multibus/multifeeder distribution systems. A MC-UPQC is a combination of one shunt active power filter (APF) and two or more series APFs. MC-UPQC can be applied to adjacent feeders to compensate for supplyvoltage and load current imperfections on the main feeder and full compensation of supply voltage imperfections on the other feeders. In this paper, a two feeder MC-UPQC is used, which has one shunt APF and two series APFs. All APFs are connected back to back on the DC side and share a common DC link capacitor. As control of this DC link capacitor is very critical for the better performance of MC-UPQC, a novel hybrid fuzzy-PI controller is designed, which is more robust to parameter changes, is non-linear and has a fast dynamic response along with superior steady state response. Through simulation results, it is shown that the hybrid fuzzy-PI controller has performed very well and MC-UPQC is able to compensate supply voltage and load current imperfections on feeder1 and fully protect the sensitive/critical load on feeder2 against distortion, sag/swell, and interruption.

Single-Phase AC–AC Double-Star Chopper Cells (DSCC) Converter Without Common DC-Link Capacitor

This paper presents a single-phase ac–ac converter based on a modular multilevel cascade converter (MMCC) with double-star chopper cells (DSCC). The converter topology is composed of three DSCC legs, in which the middle leg is shared, and it does not present a common dc-link capacitor. It is suitable for nonregenerative or regenerative low-power and medium-power ac–ac conversions. A voltage-balancing control is presented for regulating the floating dc capacitor voltages. Furthermore, a grid current and load voltage control is presented to correct the input power factor and to ensure input/output sinusoidal waveforms. A phase-shifted carrier (PSC) pulsewidth modulation (PWM) commands submodules (SMs) using half of PSCs, preserving the characteristics of conventional modulation. Details about a downscaled prototype rated at 3.3 kW and 220 V are also presented. The experimental results allow validating the control strategies and the effectiveness of the proposed system.