Power-Management Strategies for a Grid-Connected PV-FC Hybrid System

Abstract—

This paper presents a method to operate a grid connected hybrid system. The hybrid system composed of a Photovoltaic (PV) array and a Proton exchange membrane fuel cell (PEMFC) is considered. The PV array normally uses a maximum power point tracking (MPPT) technique to continuously deliver the highest power to the load when variations in irradiation and temperature occur, which make it become an uncontrollable source. In coordination with PEMFC, the hybrid system output power becomes controllable. Two operation modes, the unit-power control (UPC) mode and the feeder-flow control (FFC) mode, can be applied to the hybrid system. The coordination of two control modes, the coordination of the PV array and the PEMFC in the hybrid system, and the determination of reference parameters are presented. The proposed operating strategy with a flexible operation mode change always operates the PV array at maximum output power and the PEMFC in its high efficiency performance band, thus improving the performance of system operation, enhancing system stability, and decreasing the number of operating mode changes.

A combined protection and control strategy to enhance the LVRT capability of a wind turbine driven by DFIG

Abstract—

 In order to enhance the low voltage ride-through (LVRT) capability of a wind turbine driven doubly
fed induction generator (DFIG)， this paper proposes a combined protection and control strategy including the Active Crowbar and Battery Energy Storage System. The conventional crowbar is activated to protect the rotor side converter during the fault interval, premature removal the crowbar will not achieve good purpose of protection for the converter, too late removal will make the motor absorption the reactive power too much from the grid. This problem can be improved by using a control scheme which is auto-switching the crowbar according to the size of rotor current .Furthermore, under fault condition the voltage will ripple in the DC link side, a battery energy storage system (BESS) connected to the DC bus is proposed which is controlled to attenuate the DC voltage ripple via absorbing the redundant power stored in the DC link capacitor. Simulation results show the effectiveness of this combined protection and control strategy.

Application of UPFC Based on Improved Double-loop Decoupling PI Control in Photovoltaic Systems

Abstract—

The mutation of solar irradiance can cause the output power of photovoltaic power plant to mutate, and it takes great changes to active power and reactive power which feed into the power grid. When the system security constraint is exceeded, the photovoltaic power plant will stop running. In this paper, the structure and the mathematical model of large grid-connected photovoltaic power plant are introduced; then an improved double loop PI decoupling control system is proposed based on the d-q model of UPFC parallel converter. On the basis of traditional PI control, DC load current is directly used as feed-forward control in the control system of capacitor voltage. It is not only easy to get feedback, but also conducive to design and operate the series controller and the parallel controller independently. Finally, this paper sets up a Simulink model of UPFC in the environment of Matlab/Simulink after analyzing its principle. And then, this model was applied into a three-phase system to observe its influences to power quality. The simulation results show that this control system based on the UPFC can effectively control the voltage and the power flow, maintain bus voltage and reduce reactive exchange. It can also improve the active photovoltaic power transmission, as well as maintaining the stability of the system. 

Effects of Common-Mode Active Filtering in Induction Motor Drives for Electric Vehicles

Abstract—

This paper deals with the active common-mode (CM) voltage compensation in an induction motor drive where the inverter is supplied by a dc source, which is typical of vehicle applications. The CM voltage at motor terminals, creating a shaft voltage through the motor air gap with possible rise in bearing current, can endanger motor reliability and reduce its lifetime. Therefore, CM voltage filtering is desirable. On the other hand, the operation of an active filter has an impact on drive efficiency due to its specific losses and can affect the electromagnetic interference (EMI) emissions that are generated by the drive. Such effects are investigated in this paper. A detailed description of a CM active filter (CMAF) is presented. An analysis of the CM voltage and current on the motor ground connection before and after the introduction of the CMAF is performed. The power losses due to the CMAF operation are analyzed and experimentally evaluated. Furthermore, the EMI toward the vehicle dc power supply line is investigated. All phenomena are studied by simulation and experimentally. The simulated results “are obtained developing” a high-frequency circuit model of the drive system, including the CMAF, which is implemented using the PSpice software. To accurately perform the experimental tests, a new dedicated high voltage dual dc line impedance stabilization network (LISN) is designed and set up on purpose. The CMAF is found to be an effective solution for the increase in motor reliability and drive electromagnetic compatibility, and its operation does not significantly reduce drive efficiency. Moreover, the CMAF does not worsen the EMI toward the dc supply line. Therefore, its presence does not imply the need for additional filters with respect to the case where no CMAF is used. Simulated results are in good agreement with the experimental ones, confirming the validity of the proposed modeling of the drive system.

Proof-of-Concept of a Smart Fault Current Controller With a Superconducting Coil for the Smart Grid

Abstract—

The power grid, especially distribution grid, has been more complicated due to distributed generations (DGs) with renewable energy sources and the smart grid. The complexity changes two things in terms of a fault; higher prospective fault current and the temporal variation of sources and loads. To correspond to those remarkable changes, we propose a fault current controller (FCC) named “smart FCC.” The smart FCC consists of a superconducting coil with a freewheeling diode if necessary, four thyristors, and a control unit. Smart FCC can not only limit but also control the current when a fault occurs. The smart grid technology can provide so enough information that it is possible to estimate which level of limited current should be the best in the real-time situation of the grid. Based on a real-time calculation of optimal fault current using the smart grid monitoring technologies, this new device is always ready to adjust the fault current. In this paper, we introduce a concept of the smart FCC and prove the concept. Various topologies have been proposed and simulated. Finally, a case study on a distribution class of 22.9 kV smart FCC has been conducted based on a conceptional system design.

DESIGN PROCEDURE OF A PUSH PULL CURRENT-FED DC-DC CONVERTER

Abstract—

Some of the major drawbacks of Voltage-fed converter can be resolved by its Current-fed counterpart with its certain practical advantages. The recent increase in interest and use of current-fed converters calls for establishing a systematic design methodology. While some papers have provided useful insights to these converters, elaborate design steps are not available in literature. This paper presents complete design process of a push-pull current-fed converter. 

Buck Converter Design

PHOTOVOLTAIC-GRID INTEGRATED SYSTEM

This paper proposed solution for directly energizing of ac load throughout  Photovoltaic Solar Array during the daytime by applying so called variable voltage tracking system (VVT). The main function of VVT is to maintain the average output chopped voltage at fixed value irrespective of solar radiation rate, in turn the chopped voltage is converted into ac voltage suitable for grid-connected loads. This solution is realized by integrating both complementary buck-boost chopper and dc to ac converter. The ac-grid contributes to the load in two cases, first when there is a power shortage during the daytime due to weak irradiation rates, and second during the night time. The power estimator unit is used to determine the grid contribution intervals. 
This solution excludes the use of battery bank which is the main obstacle in massive use of solar energy due to their weight, short life time, maintenance and cost. Matlab/Simulink is used to simulate the proposed model, where the obtained simulation results confirm and justify the proposed approach for further study and looking for optimized solutions for cost reduction and energy savings.