A ZVS Grid-Connected Three-Phase Inverter

Abstract-

A six-switch three-phase inverter is widely used in a high-power grid-connected system. However, the antiparallel diodes in the topology operate in the hard-switching state under the traditional control method causing severe switch loss and high electromagnetic interference problems. In order to solve the problem, this paper proposes a topology of the traditional six-switch three-phase inverter but with an additional switch and gave a new space vector modulation (SVM) scheme. In this way, the inverter can realize zero-voltage switching (ZVS) operation in all switching devices and suppress the reverse recovery current in all antiparallel diodes very well. And all the switches can operate at a fixed frequency with the new SVM scheme and have the same voltage stress as the dc-link voltage. In grid-connected application, the inverter can achieve ZVS in all the switches under the load with unity power factor or less. The aforementioned theory is verified in a 30-kW inverter prototype.

Vector-Controlled Voltage-Source-Converter-Based Transmission Under Grid Disturbances

Abstract-

Voltage-source converter (VSC)-based transmission systems have attractive potential features in terms of power flow control and stability of the network. Although relatively low switching frequency operation of high-power converters (9-15 times the line frequency) is desirable, it makes them sensitive to power network imbalances when they may be needed the most. This paper specifically proposes a control structure to improve the performance of high-power vector-controlled back-to-back VSC systems for conventional and emerging utility applications. The main improvement is to suppress the possible dc-link voltage fluctuations under power line faults and unbalanced conditions. The proposed controller structure is designed based on regulating the converter system's states locally in dq synchronous reference frame without sequence components extraction or resonant notch compensator. RTDS results verify the validity of the proposed control architecture during normal and unbalanced power system conditions.

Direct Power Control of Series Converter of Unified Power-Flow Controller With Three-Level Neutral Point Clamped Converter

Abstract-

A unified power-flow controller (UPFC) can enforce unnatural power flows in a transmission grid, to maximize the power flow while maintaining stability. Theoretically, active and reactive power flow can be controlled without overshoot or cross coupling. This paper develops direct power control, based on instantaneous power theory, to apply the full potential of the power converter. Simulation and experimental results of a full three-phase model with nonideal transformers, series multilevel converter, and load confirm minimal control delay, no overshoot nor cross coupling. A comparison with other controllers demonstrates better response under balanced and unbalanced conditions. Direct power control is a valuable control technique for a UPFC, and the presented controller can be used with any topology of voltage-source converters. In this paper, the direct power control is demonstrated in detail for a third-level neutral point clamped converter.

Integration of Distributed Generating Units into Distribution Networks

Abstract- 

This paper discusses the technical aspects of distributed generation (DG) unit’s integration into distribution systems. The paper objectives are: selection of the site and size of DG unit/s to be investigated to the system and to check the system performance as follows: reduce the power losses, increase the stability limit as well as improve the protection devices settings. A matlab simulink model of the system is done at different operating conditions to check the feasibility of DG units'
implementation into distribution systems. Simulation results based on one real power distributor system of Egyptian network of voltage level 11 kV are efficiently presented.

Predictive current control implementation in the sensorless induction motor drive

Abstract-

A speed sensorless control system for an induction motor with predictive current controller is presented. The whole control does not require measurements of the motor speed and motor flux. A closed loop observer system with robustness against parameters variation is used for the control approach. The proposed observer computes the required state variables correctly in wide frequency range. In the system predictive current controller based on the computation of back electromagnetic force by the observer is implemented. In case of motor choke use, the choke parameters are added to predictive current controller algorithm. It is shown that the choke inductance has to be taken into account in predictive controller. The whole proposed control idea makes the system practically insensitive to the changes of motor parameters, even at very low frequency. It is proved that the drive system is applicable to the high dynamic performance and wide range of rotor speed. The description of test bench is included. The obtained simulation and experimental results confirm the good properties of the proposed speed sensorless induction motor drive.

A single sensor based PFC Zeta converter Fed BLDC motor drive for fan applications

Abstract-

A novel PFC (Power Factor Corrected) Converter using Zeta DC-DC converter feeding a BLDC (Brush Less DC) motor drive using a single voltage sensor is proposed for fan applications. A single phase supply followed by an uncontrolled bridge rectifier and a Zeta DC-DC converter is used to control the voltage of a DC link capacitor which is lying between the Zeta converter and a VSI (Voltage Source Inverter). Voltage of a DC link capacitor of Zeta converter is controlled to achieve the speed control of BLDC motor. The Zeta converter is working as a front end converter operating in DICM (Discontinuous Inductor Current Mode) and thus using a voltage follower approach. The DC link capacitor of the Zeta converter is followed by a VSI which is feeding a BLDC motor. A sensorless control of BLDC motor is used to eliminate the requirement of Hall Effect position sensors. A MATLAB/Simulink environment is used to simulate the developed model to achieve a wide range of speed control with high PF (power Factor) and improved PQ (Power Quality) at the supply.