Proposed DC Link Research Articles

Efficient Power Management and Control Strategy of Hybrid Renewable Energy System in Microgrid

Currently, the use of renewable energy has gradually increased due to the environmental problems present nowadays. The intermittency of distributed renewable generation poses significant challenges for the operation and integration of microgrids. Unlike the main power grid, where load balancing resources, in general, are abundant, the balancing of generation and load in a microgrid must be done by small gas turbines, diesel generators, or energy storage devices with very limited capacity and at much higher costs. Consequently, the proposed methodology seeks a model for minimizing the Energy Cost (EC) and enhancing the power supply for rural areas by designing and analyzing four different hybrid system configurations based on integrating a biomass system with a photovoltaic (PV), wind turbine (WT) and battery system. To ensure the desired power demand with minimum production cost, the research proposed an energy-efficient Hybrid DC/AC microgrid using four renewable energy sources. Lithium-ion batteries were chosen for this study due to their high energy density, long life cycle, and high efficiency. The existence of both AC and DC microgrids has led to a new concept of hybrid AC/DC microgrids which consists of both AC and DC grids tied by an Interlinking Converter (ILC). It comprises a DC grid and AC grid interlinked by a bidirectional DC/AC converter. Such a hybrid AC/DC microgrid has the advantages of both AC and DC with increased efficiency and less cost. To provide higher voltages, the Multi-Input Booster (MIB) DC-DC converters are used as a power converter in between load and source to enforce and increase the PV depending on the voltage output signal. Further extract maximum power from the solar PV system, perturb and observe algorithm-based power point tracking control mechanism is proposed DC link voltage of ILC is regulated usually by DC side control in load sharing among sources in the DC microgrid. In addition, to overcome the load fluctuation problem in a microgrid, the research introduced a Mamdani type 2 PID-fuzzy controller. Performance index parameters of the transient response characteristics are also improved by using the proposed control approach. The time-domain dynamic responses reveal that the proposed type-II fuzzy PID controller can balance the power generation and demand properly and control both system frequency and tie-line power effectively.

Control DC link of single-phase dynamic voltage restorer

This paper is aimed to illustrate and expose the performance of single-phase voltage dynamic voltage restorer (DVR) control connected to the electrical distribution grid. This performance is easily expressed by compensating for the sags and the swells voltages, and regulating the voltage across the load by injecting a voltage component in series with the source voltage increased or decreased with respect to the source voltage the load-side waveforms are purely sinusoidal. The integration of serial and chopper converters makes the DVR capable of bidirectional power flow. The key to this topology is its ability to compensate for sagging and swelling of the voltage in the long run. The modeling of the DVR and the design of its controller is included in this document. Effectiveness of control systems and start-up sequence of DVR operation is verified by detailed simulation studies. The control method used in this work is based on the use of a booster chopper and two cascade loops to generate the PWM command to control the chopper. The effectiveness of the suggested method is confirmed by the MATLAB/SIMULINK® simulation results and some prototype experiments. These results show the capacity of the proposed DC link control.

Droop characteristics based damping and inertia emulation of DC link in a hybrid microgrid

In this study, a proportionate power sharing among the parallel inverters operating in an islanded microgrid is achieved using droop and virtual inductance control. The same droop coefficients are used to achieve the frequency regulation as well. The frequency changes which are inevitable in droop control are measured and used to emulate the behaviour of damping and inertia to the DC link voltage using hybrid energy storage system consisting of battery and supercapacitor units. The proposed DC link voltage regulator restores the DC link voltage quickly by providing power corresponding to the rate of change of frequency and frequency deviation. This reduces the impact of voltage variations on the DC-load and keeps modulation index within the linear range for voltage source inverter. The design aspects of DC link voltage regulator, damping and inertia constants, selection of battery and supercapacitor units based on rating of the DC link voltage are discussed. The proposed decentralised droop control and DC link voltage restoration methods are validated through detailed simulation and experimental studies.

PV integrated single-phase dynamic voltage restorer for sag voltage, voltage fluctuations and harmonics compensation

<span>This document proposes a photovoltaic (PV) based single-phase dynamic voltage restoration (DVR) device, it eliminates both sag and swell voltage and compensates for power. The proposed system requires a power source to compensate for the sag/swell voltage. This system has found a simple topology for the DVR that uses PV with two DC-DC boosts converters as the DC power source for the dynamic voltage conservator. The DC/DC boost converter powered by the PV generator is used to increase the voltage to meet the DC bus voltage requirements of the single-branch voltage source inverter (VSI). This system uses renewable energy; saves energy accordingly and supplies power to critical/sensitive loads. The control method used in this work is a Sliding Mode Control (SMC) method and relies on a phase locked loop (PLL) used to control the active filter. The effectiveness of the suggested method is confirmed by the MATLAB/Simulink® simulation results and some prototype experiments. These results show the capacity of the proposed DC link control.</span>

The Voltage Control Strategy of a DC-Link Bus Integrated Photovoltaic Charging Module in a Unified Power Quality Conditioner

In order to improve the functionality and efficiency of a unified power quality conditioner (UPQC), a DC-link bus integrated photovoltaic charging module is proposed in a UPQC. It can generate power for essential loads apart from providing energy to a DC-link bus. A conventional proportional integral (PI) controller fails to run smoothly in dynamic conditions of the micro-grid, since it has poor capabilities in determining suitable values of proportional gain and integral gain. So, the optimization algorithm for a PI controller based on chaos particle swarm optimization based on a multi-agent system (CPSO-MAS) algorithm was developed in this paper to overcome properties such as intermittent instability in the micro-grid. Through verification by simulation and experiment of UPQC harmonic compensation, it showed that the proposed DC link bus voltage control strategy can be effectively applied to UPQC towards various conditions related to voltage and current distortion. In addition, it proved that the proposed strategy has faster convergence than other algorithms, which enhances the stability of DC-link bus voltage. Hence, the contribution presented in this paper is to provide a novel approach for the power quality improvement of UPQC.

Performance Testing of an Active Multiport DC Link for Grid-Connected PMG-Based WECSs

This paper presents the development, implementation, and performance evaluation of a new active dc link for permanent magnet generator (PMG)-based wind energy conversion systems (WECSs). The proposed dc link is developed based on the multiport converter (MPC) topology with two dc–dc power electronic converters (PECs) that have separate inputs and parallel-connected outputs. The first dc–dc PEC is designed as a boost converter, while the second dc–dc PEC is designed as a flyback converter. Each dc–dc PEC is operated and controlled independently to facilitate processing continuous and/or discontinuous input dc voltages. The performance of the MPC active dc-link is experimentally evaluated using a grid-connected 7.5-kW PMG-based WECS, when operated under different wind speeds and/or levels of power delivery to the host grid. Test results show that the proposed dc link can produce a high-quality-regulated dc output voltage over a wide range of wind speeds and levels of power delivery to the host grid. Performance results also demonstrate that the operation of the MPC active dc link has minor impacts on the operation and control of the generator-side and grid-side PECs.

Damping tie-line power oscillations by modulation feedback of wind generators

This paper uses the power modulation capability of wind generators for damping tie-line power oscillations. The type of wind generator investigated is the permanent magnet synchronous generator (PMSG) connected to the power grid through a dc link. First, the paper develops a small-signal aggregate model for the wind generator. Subsequently, three modulation signals are investigated in order to provide effective power modulation: the PMSG speed reference, the rotor blade pitch angle and the dc link voltage. The latter is a novel approach that utilizes the energy stored in the dc link capacitors in order to modulate the power injected into the grid. The paper investigates the relation between the wind turbine and PMSG dynamics and the ability of each modulation loop to provide effective damping. A design method of the feedback loops based on the damping torque concept is demonstrated in the paper. Analytical results on a two-area power system show that wind generation can enhance the system dynamic stability by damping tie-line power oscillations. The analytical results are verified through time-domain simulations of a detailed 3-phase model of the system. The proposed dc link voltage modulation is shown to be a very effective means to provide power modulation in dynamic conditions.

DC Link Active Power Filter for Three-Phase Diode Rectifier

In this paper, a dc link active power filter (APF) for three-phase diode rectifier is proposed. The proposed dc link APF, which is composed of two series-connected bidirectional boost converters, intends to eliminate the input current harmonics. It is paralleled at the dc link of the diode rectifier and is coupled to the ac input with three line-frequency switches. Compared with the full power processed power factor correction (PFC) solution, the dc link APF is partially power processed in that it only compensates for the harmonic current component at the dc link. Thus, it features with lower power processing. Moreover, it exhibits better total harmonic distortion of the ac line current when compared with the traditional ac side shunt APF. Voltage and current loop models are developed for average current control, and the selection of the current loop bandwidth is presented. Switching stresses of the ac APF, the dc link APF, and the six-switch PFC are also calculated and analyzed. Experimental and simulation results demonstrate the effectiveness of this dc link APF.