Power Quality Improvement at Distribution Level for Grid connected Renewable Energy Sources

Abstract—

Renewable energy resources (RES) are being increasingly connected in distribution systems utilizing power electronic converters. This paper presents a novel control strategy for achieving maximum benefits from these grid-interfacing inverters when installed in 3-phase 4-wire distribution systems. The inverter is controlled to perform as a multi-function device by incorporating active power filter functionality. The inverter can thus be utilized as: 1) power converter to inject power generated from RES to the grid, and 2) shunt APF to compensate current unbalance, load current harmonics, load reactive power demand and load neutral current. All of these functions may be accomplished either individually or simultaneously. With such a control, the combination of grid-interfacing inverter and the 3-phase 4-wire linear/non-linear unbalanced load at point of common coupling appears as balanced linear load to the grid. This new control concept is demonstrated with extensive MATLAB/Simulink simulation studies and results.

Power Quality Improvement Using New Control Algorithm Based Dynamic Voltage Restorer

Abstract:

Power quality is one of the major concerns in the present era. The problem of voltage sags and swells and its major impact on sensitive loads are well known. To solve this problem, custom power devices are used. One of those devices is the Dynamic Voltage Restorer (DVR), which is one of the most efficient and effective modern custom power devices used in power distribution networks. A new control algorithm for the DVR is proposed in this paper to regulate the load terminal voltage during sag, swell in the voltage at the point of common coupling (PCC). This new control algorithm is based on synchronous reference frame theory (SRF) along with PI controller is used for the generation of reference voltages for a dynamic voltage restorer (DVR). These voltages, when injected in series with a distribution feeder by a voltage source inverter (VSI) with PWM control, can regulate the voltage at the load terminals against any power quality problem in the source side. It first analyzes the power circuit of the system in order to come up with appropriate control limitations and control targets for the compensation voltage control through the DVR. The control of the DVR is implemented through derived reference load terminal voltages. The proposed control scheme is simple to design. Simulation results carried out by MATLAB with its Simulink and Sim Power System (SPS) toolboxes to verify the performance of the proposed method.

Simulation and Analysis of Zero Voltage Switching PWM Full Bridge Converter

Abstract—

In the conventional zero voltage switching full bridge converter the introduction of a resonant inductance and clamping diodes are introduced the voltage oscillation across the rectifier diodes is  eliminated and the load range for zero-voltage-switching (ZVS) achievement increases. When the clamping diode is conducting, the resonant inductance is shorted and its current keeps constant. So the clamping diode is hard turned-off, leading to reverse recovery loss if the output filter inductance is relatively larger. By introducing a reset winding in series with the resonant inductance to make the clamping diode current decay rapidly when it conducts this paper improves the full-bridge converter. The conduction losses are reduced by the use of reset winding. Also the clamping diodes naturally turn-off and avoids the reverse recovery. The proposed converter has been simulated for two different configurations and results have been compared. A 1 kW prototype converter is built to verify the operation principle and the experimental results are also demonstrated. 

Enhanced Power Quality Control Strategy for Single-Phase Inverters in Distributed Generation Systems

Abstract—

Power electronic converters are commonly used for interfacing distributed generation (DG) systems to the electrical power network. This paper deals with a single-phase inverter for DG systems requiring power quality features, such as harmonic and reactive power compensation for grid-connected operation. The idea is to integrate the DG unit functions with shunt active power filter capabilities. With this approach, the inverter controls the active power flow from the renewable energy source to the grid and also performs the nonlinear load current harmonic compensation by keeping the grid current almost sinusoidal. The control scheme employs a current reference generator based on sinusoidal signal integrator and instantaneous reactive power (IRP) theory together with a dedicated repetitive current controller. Experimental results obtained on a 4-kVA inverter prototype demonstrate the feasibility of the proposed solution.

Direct torque control of induction motor using discrete events of a hybrid system

Abstract—

In this paper, the direct torque control (DTC) is employed for fast and slow torque and flux control of induction motor coupled to an inverter (Inv-IM). This paper describes a combination of direct torque control (DTC) and space vector modulation (SVM) for an adjustable speed sensor-less induction motor (IM) drive. The motor drive is supplied by a two-level inverter. The inverter reference voltage is obtained based on input-output feedback control, using the IM model in the stator – axes reference frame with stator current and flux vectors components as state variables. We first model the DTC of Inv-IM as a hybrid system (HS). Then, we abstract the continuous dynamics of the HS in terms of discrete events. We thus obtain a discrete event model of the HS. And finally, we use Supervisory Control Theory of discrete event system (DES) to drive Inv-IM.

COMPENSATION OF SAGS AND SWELLS VOLTAGE USING DYNAMIC VOLTAGE RESTORER (DVR) DURING SINGLE LINE TO GROUND AND TREE-PHASE FAULTS

Abstract-

This paper deals with modeling and simulation technique of a Dynamic Voltage Restore (DVR). The DVR is a dynamic solution to protect sensitive loads against voltage sags and swells. The DVR can be implemented to protect a group of medium voltage or low voltage consumers. The new configuration of DVR has been proposed using improved d-q-0 controller technique.
This study presents compensation of sags and swells voltage during single line to ground (SLG) fault and three-phase fault. Simulation results carried out by Matlab/Simulink verify the performance of the proposed method.

A Novel Collaboration Compensation Strategy of Railway Power Conditioner for a High-Speed Railway Traction Power Supply System

Abstract—

High-speed train traction power supply system causes serious negative current problem. Railway power conditioner (RPC) is efficient in negative sequence compensation. A novel power quality collaboration compensation system and strategy based on RPC is proposed in this paper. The minimum capacity conducted is 1/3 smaller than traditional single station compensation. Simulation results have confirmed that the collaboration compensation system proposed can achieve a good performance at the negative sequence compensation with capacity and cost efficient.

Development of Combined Vector and Direct Torque Control Methods for Independent Two Induction Motor Drives

Abstract—

Many applications use two or more motors operating in parallel configuration by using one variable speed drive. This system is able to control these multiple motors at the same desired motor speed operation which provide advantages in terms of components and cost reduction. However, the system is not able to control each motor separately if it is desired to operate at different speeds and it also cannot withstand the load disturbance. To address this problem, the design of combined Vector Control-Direct Torque Control (DTC) methods is proposed and their performance is investigated for the case of independent controlled two induction motors fed by single Five Leg Inverter (FLI) method. Double Zero Sequence (DZS) Injection Method Space Vector Pulse Width Modulation (SVPWM) scheme is used for the FLI. Simulation results from the Simulink/Matlab that verify the validity of the method are also included. The results show the ability of the proposed method to control motor speed independently under forward-reverse step speed command and load disturbance condition.

Adaptive Fuzzy Logic Control of Permanent Magnet Synchronous Machines With Nonlinear Friction

Abstract—

In this paper, an adaptive fuzzy control scheme is introduced for permanent magnet synchronous machines (PMSMs). The adaptive control strategy consists of a Lyapunov stability-based fuzzy speed controller that capitalizes on the machine’s inverse model to achieve accurate tracking with unknown nonlinear system dynamics. As such, robustness to modeling and parametric uncertainties is achieved. Moreover, no explicit currents loop regulation is needed, which simplifies the control structure and unlike other control strategies, no apriori offline training, weights initialization, parameters knowledge, voltage, or current transducer is required. The system’s convergence and stability are proved by Lyapunov stability theory, which yields an improved performance. Simulation results for different situations highlight the performance of the proposed controller in transient, steady-state, and standstill conditions. Furthermore, the adaptive fuzzy systems inherent parallelism makes them a good candidate for implementation in real-time PMSM drive systems.