C.V. Nayar

Application of voltage- and current-controlled voltage source inverters for distributed generation systems

Voltage source inverters (VSI) have been widely used in uninterruptible power supplies, unified power flow controllers or unified power quality conditioners, and distributed generation systems (DGS). VSIs are inherently efficient, compact, and economical devices used to control power flow and provide quality supply. VSIs can be classified as voltage-controlled VSIs (VCVSIs) and current-controlled VSIs (CCVSIs), depending on their control mechanism. In this paper, a detailed comparison of VCVSIs and CCVSIs for DGS applications is presented. This paper examines the advantages and limitations of each control technique in a single-phase DGS, without incorporating additional hardware and/or extra complex control techniques. Discussions on the concepts, hypotheses, and computer simulations of different VSIs in the presence of different loads and conditions are presented. The experimental results confirm the validity of the analysis and simulations outlined. The paper provides design recommendations for the use of VCVSIs and CCVSIs in various applications

A grid-interactive photovoltaic uninterruptible power supply system using battery storage and a back up diesel generator

This paper presents a practical implementation of a grid interactive photovoltaic uninterruptible power supply (UPS) system using battery storage and a back up diesel generator. The system incorporates 2.5 kWp of photovoltaic arrays, a 10 kVA power conditioning unit capable of operating in both inverting and charging modes, and a 300-Ah battery bank. Two such systems were installed in two Indian cities. The project was implemented using soft loans available in India through a World Bank Loan for photovoltaic market development. The system has been working satisfactorily since May 1997 and has demonstrated the capability of the system to provide uninterrupted power, demand side management function and load voltage stabilization in a grid which experiences frequent blackouts and under/over voltage problems. Some results from the field installation are also included in this paper.

Zero average current error controlled power flow for AC-DC power converters

Unity and controlled power factor AC-DC power converters require a current control technique with zero average current error (ZACE) in each switching period. Acting on the current error signal alone, a ZACE controlled converter offers complete real and reactive power flow control with negligible low order current harmonics, a narrow switching frequency band, and relative immunity to DC link or AC line voltage harmonics. Slope-generated hysteresis, a new ZACE current control method is introduced. Simulation and experimental results in a three phase converter are presented. >

Development and testing of a 20-kW grid interactive photovoltaic power conditioning system in Western Australia

A prototype current-controlled power conditioning system has been developed and tested on a weak rural feeder line at Kalbarri, about 600 km northwest of Perth in Western Australia. This system sources 20 kW of power from a photovoltaic array with maximum power point tracking control. In addition, it provides voltage support for the power grid at Kalbarri by varying its reactive power in response to the measured voltage at the point of connection. This paper describes the development and testing of the power conditioning system.

Optimum operation strategy and economic analysis of a photovoltaic-diesel-battery-mains hybrid uninterruptible power supply

This paper presents the optimum operation strategy and economic analysis of a photovoltaic-diesel-battery-mains hybrid uninterruptible power supply (UPS). The system involves a photovoltaic, battery and bi-directional inverter that is connected in parallel to the grid. A diesel generator is required when the grid is not available for a longer time. The optimum operation strategy of the system is proposed for the diesel-connected mode (when the grid fails for several hours), while the economic analysis is evaluated for the grid-connected mode. The optimum strategy determines the ‘set point’ value for starting and stopping the diesel generator, resulting in a lower system operation cost within its lifetime. The optimum value is obtained by comparing the cost of the diesel fuel consumption and the battery wear. The economic analysis includes the system operation as UPS and demand side management. The system will reduce the power flow from the mains by increasing the power from the inverter to the load when the tariff is high. However, when the grid tariff is low, the power from the mains is used to charge the battery and to meet the load simultaneously.

Power electronics for renewable energy sources

Publisher Summary This chapter focuses on solar photovoltaic and wind power. Stand-alone PV energy system requires storage to meet the energy demand during periods of low solar irradiation and nighttime. Blocking diodes in series with PV modules are used to prevent the batteries from being discharged through the PV cells at night when there is no sun available to generate energy. Two of the main factors that have been identified as limiting criteria for the cycle life of batteries in PV power systems are incomplete charging and prolonged operation at a low state-of-charge (SOC). The power output of the PV array is sampled at an every definite sampling period and compared with the previous value. Voltage source inverters are usually used in stand-alone applications. They can be single phase or three phase. There are three switching techniques commonly used: square wave, quasi-square wave, and pulse width modulation. Centrifugal pumps are used for low-head applications especially if they are directly interfaced with the solar panels. Centrifugal pumps are designed for fixed-head applications and the pressure difference generated increases in relation to the speed of pump.

Development and testing of a 20 kW grid interactive photovoltaic power conditioning system in Western Australia

A prototype current controlled power conditioning system has been developed and is being tested on a weak rural feeder line at Kalbarri, about 600 kilometers north-west of Perth in Western Australia. This system sources 20 kW of power from three photovoltaic arrays with a maximum power point tracking control. In addition, it provides voltage support for the grid at Kalbarri by varying its reactive power in response to the measured voltage at the point of connection. This paper describes the development and testing of the power conditioning system.

A grid current-controlling shunt active power filter

In this paper, the implementation of a three-phase shunt active power filter is presented. The filter is essentially three independent single-phase current-controlled voltage source inverters (CC-VSI) with a common DC bus. The CC- VSI is operated to directly control the AC grid current to be sinusoidal and in phase with the grid voltage. The APF consists of a current control loop, which uses polarized ramptime current control and a voltage control loop, which employs a simple Proportional Integral control. The experimental results indicate that the active filter is able to handle predominantly the harmonics, as well as the unbalance and reactive power, so that the grid currents are sinusoidal, in phase with the grid voltages and symmetrical.

Variable speed constant frequency diesel power conversion system using doubly fed induction generator (DFIG)

Most of the diesel generators (DG) set used in remote areas runs at constant speed to produce ac output power with constant voltage and constant frequency. In remote areas the peak demand typically occurs only for a few hours in the evening. Therefore the DG set has to be heavily over-sized in relation to the prevalent load conditions. However prolonged light load operation results in poor fuel efficiency and excessive maintenance problems. In this paper, a variable speed diesel power generation system using a DFIG is presented. The control strategy for the diesel engine enables it to operate below and above the synchronous speed according to load demand. Simulation results of the dynamic system and preliminary experimental results based on a 15 kW prototype are included.

Analysis and design of a solar charge controller using cuk converter

This paper presents a scheme for transferring power from the photovoltaic (PV) modules to a battery using a solar charge controller based on a Cuk dc/dc converter. The converter is configured in parallel power transfer mode (PPT) to achieve higher efficiency. PWM control with maximum power point tracking algorithm is used to extract maximum power from the PV modules. Mathematical modelling and field test results using multi crystalline photovoltaic modules have been carried out to verify the effectiveness of the device.