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This paper proposes a modified distribution static compensator (DSTATCOM) with the voltage controller. The modified DSTATCOM is incorporated in a three-phase four-wire distribution network. The design criteria of the modified DSTATCOM parameters is introduced. The Hysteresis Voltage Controller (HVC) is used to drive the Voltage Source Converter (VSC) and its reference voltage signal is generated based on the Instantaneous Symmetrical Components Theory (ISCT) to provide the proper compensation to stabilise the system voltage, improve the power factor and mitigate the harmonic distortion. Matlab/Simulink software is used to verify the performance of the modified DSTATCOM with the used controller under different load types and supply voltage conditions. The control algorithm ensures that the bus voltage is maintained at its rated value during different connected loads and supply conditions. Also, it compensates the non-linear and unbalanced supply currents and reducing the Total Harmonic Distortion (THD) of both current and voltage. The proposed modified DSTATCOM gives better results in comparison with the conventional DSTATCOM. [ABSTRACT FROM AUTHOR]

Wind turbine generators should be kept connected to a power grid, while supporting the voltage recovery in the case of a grid fault to meet low voltage ride-through requirement in some grid codes. This paper proposes a coordinated control scheme that prevents the increase in the DC-link voltage by reducing the active power in the machine side converter of permanent magnet synchronous generators (PMSGs) in proportion to the voltage dip at the terminal of PMSGs. The proposed scheme changes the current priorities from the active current to the reactive current to inject more reactive power for a severe fault depending on the voltage dip. In addition, the grid-side converter operates in a voltage control mode with the slope, which is the ratio of reactive current capability to the voltage tolerance around a rated value. Moreover, during the fault, the slope is changed depending on the voltage dip to inject more reactive current. The performance of the proposed scheme is validated for a wind power plant consisting of 20 units of 5-MW PMSGs using an EMTP-RV simulator. The results demonstrate that the scheme enables the PMSGs not only to survive during the fault, but also to provide a dynamic reactive power support. [ABSTRACT FROM AUTHOR]

This paper proposes a transient voltage control scheme of a doubly fed induction generator (DFIG)-based wind power plant (WPP) using a reactive current reduction loop to suppress the overvoltage at a point of interconnection (POI) and DFIG terminal after a fault clearance. The change of terminal voltage of a DFIG is monitored at every predefined time period to detect the fault clearance. If the voltage change exceeds a set value, then the reactive current reduction loop reduces the reactive current reference in the DFIG controller using the step function. The reactive current injection of DFIGs in a WPP is rapidly reduced, and a WPP can rapidly suppress the overvoltage at a fault clearance because the reactive current reference is reduced. Using an electromagnetic transients program–released version (EMTP–RV) simulator, the performance of the proposed scheme was validated for a model system comprising 20 units of a 5-MW DFIG considering various scenarios, such as fault and wind conditions. Test results show that the proposed scheme enables a WPP to suppress the overvoltage at the POI and DFIG terminal within a short time under grid fault conditions. [ABSTRACT FROM AUTHOR]

The presence of nonlinear loads like brushless DC (BLDC) motor drives in the distribution system leads to poor power quality (PQ) indices like low power factor, high total harmonic distortion and creates electromagnetic interference. Passive filters and Power factor correction converters are often inserted between the utility and BLDC motor drives to improve the PQ parameters. This paper proposes the shunt active power filter (SAF) for the PQ improvement of medium and high power BLDC motor drives. In this paper, the design steps and control of an SAF for a 20 kW BLDC motor drive are presented. The control of SAF is realized by applying the instantaneous "p–q" theory with the sinusoidal current control strategy. The current control is realized by a hysteresis controller. In contrast to normal electrical loads, the motor drive loads are subjected to continuous speed and load variations. This will result in fluctuations in the DC-link voltage of the SAF capacitor. Hence, the sliding mode controller is used for DC-link voltage control. The proposed methodology is validated in simulations and the experimental prototype. The enhancement of various PQ parameters is analysed for different loading conditions of the motor in the distorted and non-distorted distribution system voltage conditions. [ABSTRACT FROM AUTHOR]

In this paper, the authors propose a method of improvement of power quality by static synchronous compensators (STATCOMs) for low voltage system (single-phase STATCOMs) added the function of harmonic suppression. In the proposal method, the STATCOMs control the voltage of the distribution system within the proper range by compensating the reactive power. Additionally, they are operated as the filtering function and suppress harmonics of the voltage of the distribution system. The filtering gain is determined by PI controlling the error between the voltage total harmonic distortion of the point voltage at the installation of STATCOMs and the target value. In order to verify the validity of the proposal method, the numerical calculations are carried out by using an analytical model of distribution system which interconnected photovoltaic generation systems. Simulation results show the effect of improvement of power quality on both sides of voltage deviation and harmonics. [ABSTRACT FROM AUTHOR]

Fixed speed induction generator (FSIG)-based wind farms have poor low voltage ride through (LVRT) capacity and poor power quality and stability due to insufficient reactive power support during disturbances. Flexible AC transmission systems (FACTS) devices such as static synchronous compensator (STATCOM) can improve the LVRT capacity and power quality and stability of FSIG-based wind energy conversion system (WECS). Proportional and integral (PI) controllers are often used to control the operation of the STATCOM. However, since WECS is highly non-linear and subject to various disturbances, the PI-controlled STATCOM cannot provide optimal performance for different operating points. More robust controllers such as controllers based on fuzzy logic approach are required for the STATCOM to provide adequate dynamic voltage control and to improve power quality and stability of the WECS. This paper presents the design of fuzzy logic-based controller of a STATCOM for improving the power quality and stability of a WECS. Comparison study of PI-controlled and fuzzy logic-based STATCOM is carried out using SimPowerSystem in MATLAB/Simulink environment. The simulation results show that the fuzzy logic-based STATCOM controller provides better system dynamic response and hence improves power quality and stability for the WECS. [ABSTRACT FROM AUTHOR]

This paper proposes a method to determine the combined energy (kWh) and power (kW) capacity of a battery energy storage system and power conditioning system capacity (kVA) based on load leveling and voltage control performances. Through power flow calculations, a relationship between the capacity combination and the control performance is identified and evaluated. A tradeoff relationship between the capacity combination and control performance is confirmed, and the proper capacity combination for operation is determined based on the evaluated relationship. In addition, the control performance of the capacity combination is evaluated through the power flow calculation, confirming that the proposed method is effective for determining the optimized capacity combination. [ABSTRACT FROM AUTHOR]

A modified multilevel inverter with a configurable level generation is proposed in this paper. The MLI is composed of a modified boost converter at the front end followed by a level generation circuit and a H-bridge configuration. The front-end converter is biased with a PV source with a Hybrid boost resonant converter. The switches are triggered out of phase through a MPP tracker which uses Fractional INC MPPT. The secondary side of the circuit is composed of a derived voltage doubler along with the voltage regulator. The output of the doubler is regulated through a level converter which integrates a fuzzy controller and a phase shift controller. The modified multilevel inverter uses a low-voltage PV source as input and generates a variable-step multilevel output voltage with lower harmonic distortion and it is suitable for low-power PV applications. [ABSTRACT FROM AUTHOR]

This paper proposes backstepping technique for the direct-current bus voltage control in three-phase four-wire shunt active filter. The identification of reference currents is made by synchronous referential frame theory with self-tuning filter. The three-phase four-wire shunt active filter is implemented with DSPACE 1104 system to compensate harmonics generated by unbalanced system of non-linear loads. Four-leg topology is used for the inverter of shunt active filter and the switching patterns of the inverter are generated by analogue hysteresis card. The experimental results verify the good performance of the proposed shunt active filter in term of harmonic currents reduction and improvement of power quality. A comparison between backstepping controller and the conventional proportional-integral controller is illustrated, in steady state, the two controllers fixe direct-current bus voltage at its reference value, however, a clear advantage of the backstepping control in dynamic state can be observed. [ABSTRACT FROM AUTHOR]

To effectively utilize a photovoltaic (PV) system, reactive-power control methods for solar inverters have been considered. Among the various methods, the constant-voltage control outputs less reactive power compared with the other methods. We have developed a constant-voltage control to reduce the reactive-power output. However, the developed constant-voltage control still outputs unnecessary reactive power because the control parameter is constant in every waveform of the PV output. To reduce the reactive-power output, we propose a dynamic reactive-power control method with a PV output prediction. In the proposed method, the control parameter is varied according to the properties of the predicted PV waveform. In this study, we performed numerical simulations using a distribution system model, and we confirmed that the proposed method reduces the reactive-power output within the voltage constraint. [ABSTRACT FROM AUTHOR]

Secondary voltage control of islanded microgrid is one of the main needs of microgrid hierarchical control from one perspective and the realization of stable smart grids from another aspect. This article aims to achieve several goals simultaneously: First, it provides a decentralized structure for controlling and regulating the voltage of DGs, in which the effects of nonlinear terms on the dynamics of the microgrid system are considered without elimination or linearization. The fuzzy method has been used to approximate the uncertainties, the interactions of agents and nonlinear terms, and the adaptive method has been used to obtain the optimal fuzzy approximation gains. Sliding mode rules are also used to obtain a control signal and using Lyapunov's theory, the finite time and robust stability of the closed-loop control system is guaranteed. The finite time approach ensures the achievement of convergence in a finite and definite time, and the robust approach realizes the dynamic stability of the system against uncertainties and disturbances. The results of the microgrid system simulation show well the proposed controller capability in different operating conditions. [ABSTRACT FROM AUTHOR]

The aim of this paper is to find the non-linear behavior of a container ship roll motion by using fin-roll stabilizer and robust model predictive control (RMPC). To do so, numerical and analytical modeling has been introduced for the roll motion. Computational fluid dynamics method was employed to determine the hydrodynamic lift of the fin at various angles. RMPC was designed and used to control the non-linear roll motion in the presence of disturbances, uncertainties, which were caused by the irregular sea waves, and operational constraints of fin’s actuator. To boost the validity of our results, the performance of this controller was compared with a conventional PID (Proportional-Integral-Derivative) controller. Simulation results indicated the significant amount of reduction in roll amplitude and roll rate. [ABSTRACT FROM PUBLISHER]

Many photovoltaic (PV) systems have been installed in distribution systems. This installation complicates the maintenance of all voltages within the appropriate range in all low-voltage distribution systems (LVDSs) because the trends in voltage fluctuation differ in each LVDS. The installation of a low-voltage regulator (LVR) that can accordingly control the voltage in each LVDS has been studied as a solution to this problem. Voltage control in a medium-voltage distribution system must be considered to study the deployment of LVRs. In this study, we installed LVRs in the LVDSs in which the existing voltage-control scheme cannot prevent voltage deviation and performed a numerical simulation by using a distribution system model with PV to evaluate the deployment of the LVRs. [ABSTRACT FROM AUTHOR]