K. Tan

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.

H APF harmonic mitigation technique for PMSG wind energy conversion system

This paper focuses on current harmonics mitigation at the permanent magnet synchronous generator (PMSG) wind turbine system using a variable frequency active power filter (VF-APF) harmonic mitigation technique. Mitigation of current harmonics in the PMSG reduces harmonic losses, thus reducing the heating effect on the PMSG cause by the current harmonic components and extends the lifespan of the PMSG. The current harmonics in the wind turbine system is mainly caused by non-linear loading effect from the AC-DC converter in the wind energy conversion system (WECS). Therefore, to filter current harmonics component in the PMSG, a conventional fixed frequency grid connected 3-phase-shunt APF is applied to compensate the current harmonics in the WECS PMSG generator. The conventional APF is coupled with a phase-lock-loop (PLL) synchronizer to facilitate variable frequency functionality. The simulation results shown in this paper is conducted at PMSG WECS maximum power point conditions. The demonstrated results show that the designed VF-APF successfully mitigates the PMSG current harmonic over a wide range of wind speed.

Mitigation of harmonics in wind turbine driven variable speed permanent magnet synchronous generators

Permanent magnet synchronous generators (PMSG) have been used more frequently as variable speed systems in wind energy conversion systems (WECS). Variable speed systems have several advantages such as yielding maximum power output while developing low amount of mechanical stress compared to constant speed systems. AC-DC converter such as six-pulse rectifier is used to convert variable voltage and variable frequency from the PMSG to DC voltage, thereby producing DC power. The DC link is converted back to AC at a fixed frequency that is appropriate for electrical utilizations in the grid. However, the use of six pulse rectifiers introduces high intensity of low frequency current harmonic content into the PMSG. The flow of these harmonic current induce further losses to the generator, thereby producing more heat in the generator. This leads to reduction in efficiency in WECS and also decreases the life span of the generator. This paper investigates and analyse the level of harmonic content of two different AC-DC converters operating at various wind speed. Mitigation techniques such as introducing passive filters are implemented and tested to the system. PSIMreg simulation package was used in developing generator models, AC-DC converters

Effect of loss modeling on optimum operation of wind turbine energy conversion systems

Permanent magnet synchronous generator (PMSG) wind energy converters system (WECS) with variable speed operation is being used more frequently in the wind turbine application. Variable speed systems have several advantages over the traditional method of operating wind turbines, such as the reduction of mechanical stress and increase in energy capture. To fully exploit the last mentioned advantage, this paper proposes a simple new sensor-less maximum power point tracking (MPPT) control scheme for PMSG WECS and show the optimum operating points of the PMSG for true maximum output power is not necessarily operating at maximum power coefficient (Cp) value. This is to propose a controller with minimal losses as well as optimum power extraction

Harmonics mitigation and reactive power compensation through a CC-VSI/APF WECS

The increasing interest to utilise wind energy as a power source prompted more researches to be dedicated to the efficient integration of this power source into the current grid. In this paper, one avenue to achieve this efficient utilisation, through the use of current- controlled voltage source inverter (CC-VSI) integrated with a permanent magnet synchronous generator (PMSG) wind energy conversion system (WECS) is presented. The system with the CC-VSI acting as an active power filter (APF) is capable of mitigating harmonics as well as providing reactive power support, which in turn increase the efficiency of the conversion system and correct power factor to unity. The proposed system increases the effectiveness of the utilisation of wind energy as one of the future energy source.

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.

Hybrid Passive Filter Design for Distribution Systems with Adjustable Speed Drives

Drive systems inject significant low order harmonics currents into distribution system and deteriorate the quality of electric power. This paper models variable frequency and PWM adjustable speed drives as harmonic current sources and performs power flow analysis before filtering to identify highly distorted buses and the spectrum of harmonic frequencies with unacceptable THD levels as specified by IEEE-519 standard. The IEEE 30-bus system with penetration of nonlinear adjustable speed drive loads is used to study the effectiveness of passive filters and to investigate the impact of their location and tuning frequencies on the quality of voltage and current waveforms. Simulation results before and after the installations of filters are presented, compared and analyzed for different nonlinear loading and filter configurations. It is shown that the number, locations and tuning frequencies of filters have major impacts on the overall quality of the distribution system.

Impact of harmonics on tripping time of overcurrent relays

Theoretical and experimental analyses are used to investigate the effects of harmonics on the operation of overcurrent relays. Two analytical approaches based on relay characteristics provided by the manufacturer and simulations using PSCAD software package are used to estimate tripping times under non-sinusoidal operating conditions. The tests were conducted such that the order and the magnitude of harmonics could be controlled by employing a computer-based single-phase harmonic source. Computed and measured tripping times are compared and suggestions on the application of overcurrent relays in harmonically polluted environments are provided.

VS-CCI and VS-CCI/APF configuration for PMSG wind energy conversion system

Recently, many efforts are dedicated to finding the most efficient way to utilise wind energy as a power source and integrate it to the grid. This paper presents a permanent magnet synchronous generator (PMSG) wind energy conversion system (WECS) with reactive power control. The WECS is implemented through a voltage source - current controlled inverter (VS-CCI). The implementation of WECS with reactive power control allows the system not only to supply renewable active power to the grid, but also reactive power to maintain the grid power factor at unity. The VS-CCI is capable of providing reactive power support and requires no additional components. A comparison of the reactive power configuration of the VS-CCI and the active power filter (VS-CCI/APF) configuration is also presented in this paper.

28 – 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.