Three-phase Voltage Source Converter Research Articles

Fractional order sliding mode control for power quality improvement in the distribution system

This paper presents fractional order sliding mode control (FOSMC) based distribution system compensator (DSTATCOM) for power quality improvement in the distribution system. The three-phase two-level inverter-based voltage source converter (VSI) with DC-link capacitor is used as DSTACOM. In this paper, the FOSMC-based DSTATCOM improves supply current harmonics, load balancing, and reactive power and reduces THD. The sinusoidal pulse width modulation (SPWM) is generating gating pulses for VSI. The performance of the presented system is verified in MATLAB/Simulink software. The simulations are verified source voltage, current and load current as well as compensating current. The FOSMC has maintained a constant supply current when connecting non-linear load. The hardware results are also presented in the manuscript. The hardware results are supply current, voltage, compensating current, and load current.

DC-Link Capacitor Current Stress Minimization Strategy for Paralleled Three-Phase Voltage-Source Converters With Interleaving

DC-Link Capacitor Current Stress Minimization Strategy for Paralleled Three-Phase Voltage-Source Converters With Interleaving

Active decoupling control of the three-phase voltage source converter under nonlinear AC current

Active decoupling control of the three-phase voltage source converter under nonlinear AC current

A Robust Switching Control Strategy for Three-Phase Voltage Source Converters with Uncertain Circuit Parameters

This study proposes a novel double closed-loop robust control strategy based on a power switching affine model of three-phase voltage source converters (VSCs). The aim is to overcome the challenges posed by inaccurate mathematical models, complex controller configurations, indirect switching control, and performance degradation under circuit parameters uncertainty or load variation in conventional methods. These conventional methods rely on linearization models, duty ratio regulation, and pulse width modulation (PWM) technologies. The contributions of work are the following: (1) A two-dimensional (2D) power switching affine model is constructed without any approximation or averaging. (2) The proposed approach achieves direct switching control of three-phase VSCs, eliminating the need for complex rotation coordinate transformation, PWM, and phase locking loop (PLL), which are utilized in traditional control methods. (3) The rigor of the system stability analysis is enhanced based on the 2D power switching model compared to the existing three-dimensional (3D) current switching model. (4) A simple control structure with only two control parameters is employed to address circuit parameter uncertainties. The effectiveness and superiority of the proposed method is validated through simulation and experimental comparison results.

Nonlinear Optimal Control for a PMLSG-VSC Wave Energy Conversion Unit

This article aims to treat the nonlinear control problem for the complex dynamics of a wave energy unit (WEC) that consists of a Permanent Magnet Linear Synchronous Generator (PMLSG) and a Voltage Source Converter (VSC). The article has developed a globally stable nonlinear optimal control method for this wave power generation unit. The new method avoids complicated state-space model transformations and minimizes the energy dispersion by the control loop. A novel nonlinear optimal control method is proposed for the dynamic model of a wave energy conversion system, which includes a Permanent Magnet Linear Synchronous Generator (PMLSG) serially connected with an AC/DC three-phase voltage source converter (VSC). The dynamic model of this renewable energy system is formulated and differential flatness properties are proven about it. To apply the proposed nonlinear optimal control, the state-space model of the PMLSG-VSC wave energy conversion unit undergoes an approximate linearization process at each sampling instance. The linearization procedure relies on a first-order Taylor-series expansion and involves the computation of the system’s Jacobian matrices. It takes place at each sampling interval around a temporary operating point, which is defined by the present value of the wave energy conversion unit’s state vector and by the last sampled value of the control inputs vector. An H-infinity feedback controller is designed for the linearized model of the wave energy conversion unit. To compute the feedback gains of this controller, an algebraic Riccati equation is repetitively solved at each time step of the control algorithm. The global stability properties of the control scheme are proven through Lyapunov analysis.

Analysis of Distribution Static Compensator Control Strategies for Mitigating Voltage Dip Impact on Distribution Network

Voltage dip, over-voltage, load unbalanced, and current and voltage harmonics distortions are the key characteristics of poor power quality (PQ) issues on the power distribution network with a significant negative impact. The performance of a custom power device, distribution static compensator (D-STATCOM), in reducing current total harmonic distortion (THD) during the mitigation process of voltage dip with fault is investigated in this study. To control the load side voltage, the D-STATCOM utilizes a three-phase voltage source converter and is coupled at the point of common coupling (PCC). To mitigate voltage dip effects, this study implements and compares the effectiveness of the conventional PI controller with an intelligent optimization-based PI controller using the dynamic gravitational search algorithm (DGSA). The performance of these controllers is validated by the MATLAB/Simulink simulation results obtained. Analysis of the results demonstrates that D-STATCOM operates flawlessly with an intelligently optimized PI control strategy reducing the current THD from 11.68% to 3.74%.

A VSC-Based Isolated Matrix-Type AC/DC Converter Without Bidirectional Power Switches

In this paper, a three-phase voltage-source converter (VSC) based isolated matrix-type AC/DC converter is proposed for wind energy conversion system (WECS). The line-frequency transformer (LFT) is replaced by the high-frequency transformer (HFT), and there is no need for the intermediate electrolytic capacitors used in conventional two-stage power conversion system. Moreover, the bidirectional switches used for conventional matrix converter (MC) are eliminated in the proposed topology. Consequently, the complicated four-step commutation scheme is avoided and the additional conduction loss caused by serial connection of power switches can be eliminated. The proposed isolated matrix-type AC/DC can be regarded as the dual VSC circuit, where two VSCs alternately work during each switching cycle. Hence, the voltage vectors based space vector modulation (SVM) can be employed and the control schemes for non-isolated VSCs can be used for the proposed converter. For safe operation, the commutation strategy is proposed for the leakage-inductor current of HFT. Both simulations and experiments are conducted to verify the performance of the proposed converter.

Fuzzy MPPT operation-based model predictive flux control for linear induction motors

This research focuses on a methodology for connecting the linear induction machine (LIM) using model predictive flux control (MPFC) fed by Kyocera solar cells. Additionally, it incorporates a fuzzy logic regulator (FLR) for maximum power point tracking (MPPT) control. The boost converter's characteristics are regulated using MPPT, allowing it to achieve a voltage gain of up to twice the input voltage. The finite state-model predictive flux control (FS-MPFC) is employed to synthesize the three-phase voltage source converter switching states. The paper proposes an improved FS-MPFC strategy for LIMs, eliminating the cost function's need for a weighting parameter. This is achieved by unifying its terms of traditional control methods and reducing the number of calculation steps. The validity and effectiveness of the introduced system are confirmed by extensive simulation results. The findings revealed that the system can accurately extract maximum power from the Kyocera solar cells and track the preset speed values. In addition, it can enhance performance by minimizing the thrust and primary flux under varying speed and load conditions.

Analysis of an improved three-phase voltage source converter with high-performance operation under unbalanced conditions

The power system is rapidly transforming into a new large-scale distributed power generation model using renewable energy. Grid-connected converters, particularly voltage control compensators like STATCOM, will be crucial to the functioning of this new situation. Voltage source converter (VSC) is one of the most commonly used topologies in grid connection converters. As a distributed power-generating device, VSCs can be utilized as a means of connecting sustainable energy sources to the power grid. The three-phase voltage source currents or voltage ripples may appear in the DC chain. This study examines the enhanced three-phase VSC, pinpoints the factors that contribute to the great performance of VSCs, and looks at future trends in three-phase VSCs. VSC is a power electronic device capable of converting DC voltages to three-phase AC voltages and is commonly used in areas such as grid connection, reactive power compensation and harmonic suppression. In practical applications, various types of grid or load disturbances pose hidden dangers to the normal operation of the VSC. Due to the presence of unbalanced grids and loads, significant double frequency.

Space vector-based model predictive current controller for grid-connected converter under unbalanced and distorted grid without a phase-locked loop

This paper presents an improved current control strategy for a three-phase voltage source converter connected to distorted grid. The proposed controller can successfully compensate the induced harmonic currents, while suppressing possible active power ripple. To manage various objectives and deal with tough restrictions, model predictive control can offer a promising solution. However, a modified extended complex Kalman filter is introduced to estimate the positive and negative fundamental components of the grid voltages which are used with the real and reactive power references to generate pure sinusoidal reference currents without the need for a phase-locked loop (PLL), avoiding its challenges under abnormal grid conditions. An improved space vector-based model predictive control (SVM-MPC) is proposed to regulate the real and reactive power components. The main target of this controller is to maintain harmonic free grid currents, even in unbalanced and distorted grid conditions, with enhanced performance in terms of fast dynamic response and good steady-state behavior. The proposed SVM MPC uses Pythagoras theorem to determine duty factors, avoiding trigonometric functions, which improves the computational burden and implementation complexity. In addition, fixed switching frequency can be ensured. Simulation and experimental results are carried out to validate the effectiveness and the practical feasibility of the proposed controller under distorted grid conditions.

Modeling of a stand-alone solar photovoltaic water pumping system for irrigation

Solar photovoltaic water pumping systems have been research topics in recent decades. The purpose was to develop much more profitable and efficient systems to meet the needs of pumping water for livestock and irrigation. This paper describes the design of a stand-alone photovoltaic water pumping system. A Boost converter is used to apply the Maximum Power Point Tracking (MPPT) algorithm. Similarly, a three-phase voltage source converter (VSC) is used to supply the asynchronous motor. The installation must provide a continuous water flow during the irrigation interval. It has been verified that in adverse weather conditions (cloud transits or partly cloudy) it is necessary to incorporate a decentralized-hybrid energy storage system (based on batteries or ultracapacitors), or excessively oversize the standalone photovoltaic system, to supply the water pump. The model has been simulated in Matlab-Simulink. In this way, different simulations have been developed to verify the basic characteristics of the proposed system. The results of the simulated model and the conclusions obtained are also presented in this paper.

Hybrid Switching Control-Based DC to AC Inverter for Microgrid Using Renewable Energy Sources

Hybrid switching control-based direct current (DC) to alternating current (AC) inverter is a method of controlling the flow of power from DC sources such as solar panels or wind turbines to AC loads in a microgrid. In a microgrid, renewable energy sources are often used to supplement traditional sources of energy and improve overall energy efficiency. To simulate micro-grid systems, an effective three-legged IGBT inverter has been developed using Matlab R2016a/Simulink. The inverter switches are controlled by a pulse controller, which creates the switching gate pulses. This work models the output voltage and current waveforms of the three-phase 180° voltage source inverter that supplies nonlinear loads. To lower the total harmonic distortion (THD) of the current and voltage outputs of the three-phase voltage source converter (VSC), a filter circuit and a two-level pulse width modulation (PWM) generator have been presented. This pulse-width modulation generator compares the modulating signal and a high-frequency triangular carrier wave. Sinusoidal pulse width modulation (SPWM) is used for PWM control. Moreover, the hybrid switching control-based DC-to-AC inverter utilizes a combination of pulse width modulation (PWM) and hysteresis current control techniques to maintain a constant AC output voltage and frequency. PWM control is used to regulate the voltage, while hysteresis current control is used to regulate the current. Additionally, an inductor-capacitor-inductor (LCL) filter is used to improve the stability of the power converter by providing a damping effect on the system. Overall, the LCL filter is a versatile and effective tool for improving the performance of power inverters, especially in applications where high efficiency and low harmonic distortion are important. IUBAT Review—A Multidisciplinary Academic Journal, 6 (1): 25-46

Stability analysis of two-terminal HVDC transmission systems using SISO open-loop gains

The ports of a three-phase voltage source converter have multiple frequency electrical parameters, which makes HVDC systems with these converters present multiple input multiple output (MIMO) characteristics. The generalized Nyquist criterion of the MIMO model is often used to analyze the system stability. However, this model is more difficult to obtain than the single-input single-output (SISO) model, and the stability margin and the oscillation frequency band are difficult to capture. To solve these problems, this paper took the two-terminal HVDC transmission system as the research object to derive a SISO model that can be measured by a port. Moreover, this study also proposed a method for analyzing the system stability through envelope SISO open-loop gains. Finally, the key port and parameters affecting the system stability were analyzed according to the stability margin, which provided theoretical support for the design of the system parameters. The established model and the proposed analysis method were verified in a MATLAB/Simulink simulation model.

Lifetime Extension Method for Three-Phase Voltage Source Converters Using Discontinuous PWM Scheme with Hybrid Offset Voltage

This paper proposes a lifespan extension technique for three-phase voltage inverters using hybrid offset voltage. The proposed method lengthens the inverter lifetime by independently adjusting the switching frequency of the three phases in accordance with the aging degree. To reduce the switching operation of the phase with the shortest lifetime, the proposed technique injects the offset voltage for generalized discontinuous pulse-width modulation PWM (GDPWM) into the reference voltage in the region where the switching operation of the shortest lifespan phase can be stopped. When the switching operation does not need to be stopped, the offset voltage for space vector PWM (SVPWM) is injected into the reference voltage for high inverter load current quality. An offset voltage that varies according to the need to stop the switching operation is the proposed hybrid offset voltage. Using the proposed hybrid offset voltage, the switching frequencies of the three phases are independently controllable. In addition, since only the switching operation of the phase having the shortest lifespan is reduced, the load current quality in accordance with the switching operation reduction is good compared to the conventional method to simultaneously diminish all phase switching frequencies. The proposed method significantly increases the reliability of the three-phase voltage inverter, where the thermal stress of the phase having the shortest lifespan is decreased up to 55%, whereas the inverter lifetime can be increased by 10 times. The proposed technique was verified by simulations and experiments.

Development of Control Strategies for Operation of Cluster of Interconnected Hybrid Microgrids in Islanded Mode

This article presents the architecture and control techniques for interconnections of islanded hybrid smart microgrids (MGs, both dc and ac), for transferring the bidirectional power between different MGs. Three ring-type MGs, i.e., one ac microgrid (acMG) and two dc microgrids (dcMGs) operating at different voltages are interconnected to form a power park. A bidirectional dc–dc converter has been used to interconnect two dcMGs, and bidirectional three-phase voltage source converter (VSC) is used to interconnect the dcMG and acMG. The control techniques of these bidirectional VSCs are also proposed to control the operation of interconnected MGs system. The feedforward and feedback control signals are suggested in the proposed control techniques. The objectives of the proposed control techniques are to control the bidirectional power flow between the interconnected MGs, and to establish the constant rated voltages of all MGs, under islanded mode, for various operating scenarios. To check the effectiveness and robustness of the developed interconnected MGs system and proposed control techniques, the simulations have been carried out for the different operating conditions, in the real-time digital simulator environment.

Power quality improvement adopting DSTATCOM using immune feedback control algorithm

This work presents a three-phase distribution static compensator (DSTATCOM) immune feedback control technique. A three-phase voltage source converter (VSC) that is adequately managed as a shunt compensator to carry out these functions is the basis for a configuration that was selected for DSTATCOM. Immune feedback uses adaptive control to estimate fundamental reference grid currents from nonlinear load currents. This DSTATCOM control method has been shown to maintain a power factor of unity, balance the load, and reduce supply current harmonics. To compensate for nonlinear loads, this application puts the proposed control method for a DSTATCOM into operation. MATLAB/SIMULINK served as the platform upon which the simulations were carried out.

Quasi newton least mean fourth control for multifunctional grid tied solar photovoltaic system

The quality of power delivered has significantly decreased as distributed energy resources are increasingly incorporated into the current electricity grid. Three-phase voltage source converters with strong and stable control capability are essential for grid-connected solar energy systems. The application of a quasi-newton least mean fourth-based adaptive control strategy for producing the reference grid currents is described in this article. The presented control scheme provides the seamless flow of active and reactive power from the solar system to the grid along with the redressal of significant power quality issues such as harmonic generation at the grid, worsening of power factor, and load unbalancing. The proposed quasi-newton least-mean fourth algorithm aids in effectively filtering the significant lower-order harmonic components. The system is tested under various conditions such as constant irradiance, varying irradiance, and balanced and unbalanced load patterns to demonstrate the robustness and stability of the quasi-newton least-mean fourth algorithm. The simulation results are also presented to illustrate the control strategy's capabilities. dSPACE 1202 controller is utilized for the software-in-loop implementation, and the empirical assessment is verified for both steady-state and dynamic loadconditions.

Self-tuning methodology for adaptive controllers based on genetic algorithms applied for grid-tied power converters

The performance and stability of adaptive controllers is highly dependent on its parameter initialization. For non-expert designers, the parametrization of these controllers can be highly time consuming and an exhausting task. In order to improve the response of adaptive controllers without needing more specialized knowledge, this work proposes a procedure for self-tuning (optimal parametrization) of direct type adaptive controllers using a genetic algorithm. The proposal does not harm any property of stability and convergence of the adaptive strategy, only adding an off-line stage of parameter selection, which is carried out in a reasonable computational time. As a case study, this self-tuning procedure is applied for initialization of nine parameters of a Robust Model Reference Adaptive Controller and Adaptive Super-Twisting Sliding Mode, a known adaptive structure from the literature, suitable for current regulation of three-phase voltage source converters operating under grid impedance variations. For comparison with the proposed self-tuning, a similar procedure using fmincon and simulated annealing algorithms are also tested. The experimental results show that the proposed procedure using Genetic Algorithm can provide lower tracking error, faster regulation dynamics and reduced settling time, leading to better performance than the same controller with parameters initialized empirically.

Fault Analysis of a Small PV/Wind Farm Hybrid System Connected to the Grid

The dynamic modeling, control, and simulation of renewable energy sources connected to the electrical grid are investigated in this study. Photovoltaic (PV) systems and wind systems connected to the power grid via the point of common connection (PCC) were the only two systems included in our study. Simulation and control methodologies are provided. For both PV arrays, the method of extracting maximum power point tracking (MPPT) is utilized to obtain the highest power under standard test conditions (STC: 1000 W/m2, 25 °C). A power electronics converter that can transform DC voltage into three-phase AC voltage is required to connect a PV system to the grid. Insulated gate bipolar transistors (IGBTs) are utilized in a three-level voltage source converter (VSC). The distribution network is connected to this three-phase VSC by way of a step-up transformer and filter. During synchronous rotation in the d−q reference frame, the suggested control for the three-level solar power system that is connected to the grid is constructed. To obtain a power factor as near to one as possible, the phase-locked loop (PLL) is employed to align the angle of the power grid voltage with the angle of the current coming from the inverter. Squirrel-cage induction generators (SCIGs), which are utilized as fixed speed generators and are linked directly to the power network, are the foundation of the wind system. Additionally, a pitch angle control approach is suggested to keep the wind turbine’s rotor speed stable. MATLAB/Simulink software is utilized to model and simulate the suggested hybrid system. Under fault scenarios such as the line to line to line to ground fault (LLLG fault), the suggested hybrid system’s dynamic performance is examined. The simulation results prove the ability to manage the small hybrid system that combines solar and wind power, as well as its dynamic performance.

A Switching Predictive Control Method of Three Phase VSCs Based on Switching Affine Model

The working process of three-phase voltage source converters (VSCs) can be treated as the switching between the different subsystems, which is a typical switched system. The switching control strategies based on the switching model achieve satisfactory control performance of three-phase VSCs with very simple control structure and less control parameters. However, two drawbacks restrict the flexible applications of the present switching control strategies, i.e. the unfixed switching frequency problem and the unstable subsystem switching problem caused by the system delay. In this paper, a current switching predictive control (CSPC) method based on the current switching affine error model is proposed to the three-phase VSCs. The proposed method, by remaining the advantages of traditional switching control methods, realizes the fixed switching frequency of three-phase VSCs in the framework of switched system and achieves desired performance under system delay conditions. The simulation and experiment results verify the effectiveness of the proposed methodology.