A multi-functional four-leg grid connected compensator

There has been a growing demand on using an active power filter (APF) for grid-connected converter systems based on non-conventional energy sources such as solar, wind and fuel-cells. In addition to power quality conditioning, the APF can also be used for bi-directional active power exchange with the three phase four wire grid and therefore acts as a multifunctional compensator. This paper presents a four-leg, shunt multi-functional grid-connected power quality compensator. The compensator reference currents are generated using the well known instantaneous p-q-r theory. A simple modification in the conventional theory to eliminate the neutral current from the three-phase four-wire power system is proposed. A digital controller is used to implement dead-beat current control. The outputs of the digital current controller are used as reference voltages for a 3D space-vector modulator (3D-SVM). A new approach for PWM waveform generation in 3D-SVM is proposed. The PWM is implemented on a floating point DSP. All the intermediate steps are discussed from the view point of implementation on DSP-FPGA platform. The multi-functional compensator is analysed and simulated for the most practical conditions at the power system and the simulation results are presented

Methods for multi-functional converter control in three-phase four-wire systems

An active rectifier-based shunt compensator plays a vital role in present-day static power compensation. This includes the conventional compensation features such as power factor improvements, harmonic compensation and neutral current elimination in a three-phase four-wire system. Recently, in addition to conventional compensation, the compensator has also been considered for bi-directional active power exchange, simultaneously, with grid-connected systems, when used with adjustable static drives or wind generators. The authors aim to investigate the appropriate control methods for this kind of multi-functional compensation to accurately generate the reference current signals in time domain. In this context, two prominent instantaneous power theories, namely p-q theory and p-q-r theory are compared from a multi-functional perspective. The compensation based on instantaneous p-q-r theory is analysed comprehensively for the proposed compensator. A new approach to eliminate the neutral current completely from four-wire systems with p-q-r theory is suggested. A control system for multi-functional compensation is designed based on instantaneous p-q-r theory. The control algorithm is verified through simulation and experimentation for both positive and negative active power exchange across the DC bus. The experimental results are shown to verify the effectiveness of the proposed controller

Vector Control of Two-motor Single-inverter Induction Machine Drives

Multi-machine single-inverter induction motor drives are attractive in situations in which all machines are of similar ratings and operate at approximately the same load torques. The advantages include their small size compared to multi-machine multi-inverter systems, lower weight, and overall cost. This article presents a consolidated study and comparison of vector control methods applied to multi-machine drives along with relevant simulation and experimental results. The mean control method and its modifications prove to be superior to the other control approaches

A multifunctional four-leg grid-connected compensator

There has been a growing demand for using active power filters (APFs) for grid-connected converter systems based on nonconventional energy sources such as solar, wind, and fuel cells. In addition to power quality conditioning, the APF can also be used for bidirectional active power exchange with the three-phase four-wire grid and, therefore, acts as a multifunctional compensator. This paper presents a four-leg shunt multifunctional grid-connected power quality compensator. The compensator reference currents are generated using the instantaneous p-q-r theory. This paper proposes a simple modification to the conventional theory to eliminate the source neutral current from the three-phase four-wire power system. A digital controller is used to implement dead-beat currents control. The outputs-of the digital current controller are used as reference voltages for a 3-D space vector modulator (3D-SVM). A new approach for pulse width modulation waveform generation in 3D-SVM is proposed. All the intermediate steps are discussed from the viewpoint of implementation on a digital signal processor field-programmable gate array platform. The multifunctional compensator is analyzed, simulated, and tested experimentally for the most practical conditions in the power system, and the results are presented

Two-motor single-inverter field-oriented induction machine drive dynamic performance

Multi-machine, single-inverter induction motor drives are attractive in situations in which all machines are of similar ratings, and operate at approximately the same load torques. The advantages include small size compared to multi-inverter system, lower weight and overall cost. However, field oriented control of such drives is a challenge since no two motors will have exactly the same operating conditions at any time. In general, at least some motors in the system will operate away from perfect field orientation. It is therefore important to analyse their torque dynamics carefully. This paper discusses existing multi-machine field-oriented control methods, and analyses and compares them from the viewpoint of dynamic performance. For this, an analytical framework based on small-signal analysis is developed to compare multi-machine control methods. This analysis is verified by simulations and experiments

Real-Time Electrical Load Emulator Using Optimal Feedback Control Technique

This paper presents a method of emulating electrical loads using power electronic converters. The loads include machines such as induction motors and their associated mechanical load and also more complex machine systems such as wind-driven generators. The load emulator is, effectively, a dynamically controllable source or sink which is capable of bidirectional power exchange with either a grid or another power electronic converter system. Using load emulation, the feasibility of connecting a particular machine to a grid under various load conditions can be examined without the need for any electromechanical machinery. This paper considers the case of a power electronic voltage source inverter (VSI) emulating a three-phase induction motor connected to a three-phase ac grid. The VSI is operated in a mode where the current drawn from the ac grid is controlled by closed-loop control. The consistency of the experimental results with the simulation results proves the ability of the emulator and the proposed testing approach

Modeling and Analysis of Stator Interturn Fault Location Effects on Induction Machines

Locating the stator interturn (SIT) fault on the motor winding structure adds an important feature in the fault diagnosis. This motivates to study the effects of SIT fault location on the induction machine. In this paper, a simple yet accurate stationary reference frame q - d - 0 model of SIT-faulted induction machine, including the fault location parameter, is developed. The fundamental components of winding functions (WFs) are used to calculate the machine inductances for the proposed model. These inductances in stationary reference frame q - d - 0 variables are rotor-position-independent expressions and functions of fault severity and fault location. The proposed model is as accurate as the multiple-coupled-circuit model for fault location study. It does not require the recalculation of machine inductances in each integration step to solve the model. The experimental validation of the model is presented. The steady-state analysis based on the proposed model indicates that the inclination of the current vector locus and the phase angle of the negative-sequence current phasor are the strong indicators of the SIT fault location

Design and implementation of FPGA-based phase modulation control for series resonant inverters

Owing to the tremendous advances in the digital technology, and improved reliability and performance of the digital control mechanisms, this paper focuses on design and implementation of digital controller using FPGA-based circuit design approach. The digital controller proposed is designed for series resonant inverter used in DC-DC converter applications. Phase modulation technique is proposed for the realization of digital controller on FPGA. The Series Resonant Converter (SRC) is considered in this paper as a preferred converter topology for high power, high voltage power supplies. This paper studies the implementation of phase shift modulation technique using FPGA. The inverter designed, is IGBT based, and Zero Voltage Switching (ZVS) technique is implemented due to reduced stresses on devices and increased efficiency. The phase modulated series resonant inverters (PM-SRC) promotes ZVS operation when its switching frequency is greater than resonant frequency. The designed PM controller is realized using FPGA on which control algorithm and other features of a controller are developed. The series resonant inverter is built and tested for full load under open loop and closed loop conditions at a switching frequency of 20 kHz. The results are presented under varying load conditions. The simulation and the experimental results were found to match closely