Control of the Reactive Power Supplied by a WECS Based on an Induction Generator Fed by a Matrix Converter

In this paper, a new control system to regulate the reactive power supplied by a variable-speed wind energy conversion system (WECS), based on an induction generator fed by a matrix converter (MC), is presented. The control system discussed in this paper is based on an input current observer, implemented using an estimation of the modulation matrix, and a nonlinear control loop that regulates the displacement angle at the MC input. The reactive power capability of the proposed system is also investigated. The work presented in this paper demonstrates that, for the proposed WECS, the maximum reactive power supplied to the grid is about 40% of the nominal value. Experimental results obtained from an experimental prototype are presented in this paper. The performance of the system using a wind turbine emulator and typical wind profiles is discussed in this paper.      

FPGA-Based Real-Time Power Converter Failure Diagnosis for Wind Energy Conversion Systems

This paper discusses the design, implementation, experimental validation, and performances of a field-programmable gate array (FPGA)-based real-time power converter failure diagnosis for three-leg fault tolerant converter topologies used in wind energy conversion systems (WECSs). The developed approach minimizes the time interval between the fault occurrence and its diagnosis. We demonstrated the possibility to detect a faulty switch in less than 10 $muhbox{s}$ by using a diagnosis simultaneously based on a “time criterion” and a “voltage criterion.” To attain such a short detection time, an FPGA fully digital implementation is used. The performances of the proposed FPGA-based fault detection method are evaluated for a new fault tolerant back-to-back converter topology suited for WECS with doubly fed induction generator (DFIG). We examine the failure diagnosis method and the response of the WECS when one of the power switches of the fault tolerant back-to-back converter is faulty. The experimental failure diagnosis implementation based on “FPGA in the loop” hardware prototyping verifies the performances of the fault tolerant WECS with DFIG.      

NLCC controller for SEPIC-based micro-wind energy conversion system

The growth of the power industry is gaining greater momentum as the usage of the non-conventional energy sources that include fuel, solar, and wind energies, increases. Wind energy conversion systems (WECSs) are gaining more popularity and are expected to be able to control the power at the output. This paper describes the current control (CC), non-linear carrier charge control (NLCCC), and fuzzy logic control (FLC) applied to the single-ended primary inductor converter (SEPIC)-based WECS. The current controller has an inherent overcurrent protection with better line noise rejection. The pulses for the switch of the SEPIC are obtained by comparing the current flowing through it with the virtual current reference. FLC is also investigated for the micro-wind energy conversion system (μWECS), since it improves the damping characteristics of WECS over a wide range of operating points. This cannot attain the unity power factor rectification. In this paper, NLCCC is proposed for high-power factor rectifier-based SEPIC in continuous conduction mode (CCM) for μWECS. The proposed converter provides an output voltage with low input current ripple due to the presence of the inductor at the input side. By comparing the signal proportional to the integral of switch current with a periodic non-linear carrier wave, the duty ratio of the converter switch is determined for the NLCC controller. By selecting the shape of the periodic non-linear carrier wave the input-line current can be made to follow the input-line voltage. This work employs a parabolic carrier waveform generator. The output voltage is regulated for changes in the wind speed. The results obtained prove the effectiveness of the NLCC controller in improving the power factor.     

A novel ac-ac buck-boost voltage regulator with unity input power factor

This paper describes the design and control of a novel ac-ac buck-boost converter. In this new configuration, an ac-to-ac converter is connected between the ac mains and the load to provide regulated ac output voltage. Two topologies of the ac-to-ac converter are suggested and the current controller strategy is presented. The new regulator has nearly unity input power factor for a change in the load voltage from 10% to more than 200% of the supply voltage. The four-quadrant operation of the proposed controller enables it to accept reactive loads. Theoretical analysis and practical controller implementation using the DSP controller board are presented.     

An AC VRM topology for high frequency AC power distribution systems

In this paper, a series resonant converter with pulse-width modulation (PWM) control is presented as an ac voltage regulator module (VRM) for high frequency ac power distribution systems. The proposed topology has close-to-unity rated power factor, low total harmonic distortion in input current, zero voltage switching under all load conditions, low voltage stress of the active switch and high overall efficiency. Simulation and experimental results are presented to prove the performance of the proposed ac VRM converter.     

Reactive power capability of WECS based on matrix converter

The reactive power capability of a variable speed wind energy conversion system (WECS), based on an induction generator fed by a matrix converter is presented. A simplified analysis is performed neglecting the system losses. It is demonstrated that the maximum reactive power that can be supplied to the grid is ~40% of the nominal power. The results obtained in this work are experimentally validated using a 3 kW experimental prototype.     

Digital power-factor correction for a capacitor-charging power supply

The design and construction of a low-power low-cost power supply capable of charging an energy storage capacitor from a 120-V AC source and capable of power-factor correction (PFC) is presented. The load that is generally connected to a capacitor-charging power supply (CCPS) is a pulsed power load (i.e., laser, cardiac defibrillator, or flash lamp). A flyback converter was incorporated into the CCPS because it is capable of charging a capacitor while maintaining a high power factor. The control system of the CCPS uses peak current control to achieve PFC and is implemented using standard "off-the-shelf" digital logic components. A 300-V prototype has been constructed and tested. The experimental results show that a high power factor is obtained by the CCPS utilizing a flyback converter and the digital logic control system.     

Lagrangian modeling and passivity-based control of three-phase AC/DC voltage-source converters

In this paper, we investigate the dc-bus voltage regulation problem for a three-phase boost-type pulsewidth-modulated (PWM) ac/dc converter using passivity-based control theory of Euler-Lagrange (EL) systems. The three-phase PWM ac/dc converters modeled in the a-b-c reference frame are first shown to be EL systems whose EL parameters are explicitly identified. The energy-dissipative properties of this model are fully retained under the d-q-axis transformation. Based on the transformed d-q EL model, passivity-based controllers are then synthesized using the techniques of energy shaping and damping injection. Two possible passivity-based feedback designs are discussed, leading to a feasible dynamic current-loop controller. Motivated from the usual power electronics control schemes and the study of Lee, the internal dc-bus voltage dynamics are regulated via an outer loop proportional plus integral (PI) controller cascaded to the d-axis current loop. Nonlinear PI control results of Desoer and Lin are applied to theoretically validate the proposed outer loop control scheme. The PWM ac/dc converter controlled by the proposed passivity-based current control scheme with outer loop PI compensation has the features of enhanced robustness under model uncertainties, decoupled current-loop dynamics, guaranteed zero steady-state error, and asymptotic rejection of constant load disturbance. Experimental results on a 1.5-kVA PC-based controlled prototype provide verification of these salient features. The experimental responses of a classical linear PI scheme are also included for comparative study.     

Closed-Loop Control of a Three-Phase Neutral-Point-Clamped Inverter Using an Optimized Virtual-Vector-Based Pulsewidth Modulation

This paper presents a closed-loop control scheme for the three-level three-phase neutral-point-clamped dc-ac converter using the optimized nearest three virtual-space-vector pulsewidth modulation, which is a modulation that produces low output-voltage distortion with a significant reduction of the dc-link capacitance. A new specific loop modifying the modulating waveforms is proposed to rapidly control possible perturbations in the neutral-point voltage balance. An online estimation of the load displacement angle and load linear/nonlinear nature is introduced at no extra cost. The remaining part of the control is analogous to the control for a two-level converter with an appropriate interfacing to the selected modulation. The closed-loop control is designed for the case of a renewable-energy source connected to the ac mains, and its performance is analyzed through simulation and experiments.     

Analysis and Design of a Modular Three-Phase AC-to-DC Converter Using CUK Rectifier Module With Nearly Unity Power Factor and Fast Dynamic Response

In this paper, the analysis and design of a modular three-phase ac-to-dc converter using single-phase isolated CUK rectifier modules is discussed based on power balance control technique. This paper analyzes the operation of a modular converter as continuous-conduction-mode power factor correction (CCM-PFC). Design equations, as well as an average small-signal model of the proposed system to aid the control loop design are derived. It is used to obtain the inductor current compensator, thus the output impedance and audio susceptibility become zero, and therefore, the output voltage of the converter presented in this paper is independent of the variations of the dc load current and the utility voltage. The control strategy consists of a single output voltage loop and three-inductor current calculator. The main objective of the proposed system is to reduce the number of stages and improve dynamic response of dc bus voltage for distributed power system. The proposed scheme offers simple control strategy, flexibility in three-phase delta or star-connected, simpler design, fast transient response, good inductor current sharing, and power factor closed to unity. Both simulation and experimental results are presented. They are in agreement with the theoretical analysis and experimental work.      

Energy Management Fuzzy Logic Supervisory for Electric Vehicle Power Supplies System

This paper introduces an energy management strategy based on fuzzy logic supervisory for road electric vehicle, combining a fuel cell power source and two energy storage devices, i.e., batteries and ultracapacitors. The control strategy is designed to achieve the high-efficiency operation region of the individual power source and to regulate current and voltage at peak and average power demand, without compromising the performance and efficiency of the overall system. A multiple-input power electronic converter makes the interface among generator, energy storage devices, and the voltage dc-link bus. Classical regulators implement the control loops of each input of the converter. The supervisory system coordinates the power flows among the power sources and the load. The paper is mainly focused on the fuzzy logic supervisory for energy management of a specific power electronic converter control algorithm. Nevertheless, the proposed system can be easily adapted to other converters arrangements or to distributed generation applications. Simulation and experimental results on a 3-kW prototype prove that the fuzzy logic is a suitable energy management control strategy.     

Parallel processing inverter system

A novel method of instantaneous voltage and power balance control of a parallel processing inverter system is proposed. It consists of a high-speed switching PWM (pulsewidth modulated) inverter with an instantaneous current minor loop controller, a voltage major loop controller, and a power balance controller. This system realizes the following functions with only one inverter: constant AC output voltage control with reactive power control, active filtering to absorb load current harmonics, DC voltage and current control as AC-to-DC converter, and uninterruptible power supply (UPS) for stand-alone operation. This system covers a wide application range, including UPS systems, new energy systems, and active filters with voltage control functions     

Improved controller for power conditioner using high-temperature superconducting magnetic energy storage (HTS-SMES)

One of the most important functions in a superconducting magnetic energy storage (SMES) system when used for power conditioning, is the ability to charge the super-conducting coil as fast as possible to ensure that it is ready when it is next required. This paper describes a novel controller for a high-temperature SMES (HTS-SMES) that can ensure: 1) fast return of energy to the superconducting coil under constant-current mode and 2) a constant and sinusoidal input supply current irrespective of the varying load demand with and without harmonics. In the new HTS-SMES proposed, two hysteresis controllers are used, one to control the magnitude, phase and the waveform of the ac supply current, and the other is to control a dc chopper to regulate the SMES coil current. The first hysteresis controller ensures that as far as the power utility is concerned, the load appears to the utility system as a constant sinusoidal load with unity power factor irrespective whether the load is distorted or varying in nature. The second hysteresis controller has been designed to regulate the energy in and out of the superconducting coil. A special feature of this controller is its ability to smoothly charge the superconducting coil using constant current charging so that it can be ready for the next discharging operation as soon as possible. Analysis of the circuit operation under hysteresis control is presented in details. Simulation and experimental results are presented demonstrating the feasibility of the proposed power conditioning system.     

A Line-Interactive Single-Phase to Three-Phase Converter System

This paper describes a line-interactive single-phase to three-phase converter. A typical application is in rural areas supplied by a single-wire with earth return system. The traditional objective of feeding a three-phase induction motor is not anymore the main concern for such conversion. Due to the evolution of the farm technology, some of the local loads (as electronic power converters, computers, communication equipments, etc) require high power quality that is intended as sinusoidal, symmetrical, and balanced three-phase voltage. Additionally, to maximize the power from the feeder, the system provides a unity power factor to the grid. A three-phase voltage source inverter-pulsewidth modulation converter is used for this purpose. The power converter processes a fraction of the load power and the energy necessary to regulate the dc link voltage. As it does not need to supply active power, it is not necessary to have a source at the dc side. However, if island mode operation is needed, a dc source must be available at the dc link to supply the load. The control strategy, design criteria, and experimental results are presented     

Integrated photovoltaic maximum power point tracking converter

A low-power low-cost highly efficient maximum power point tracker (MPPT) to be integrated into a photovoltaic (PV) panel is proposed. This can result in a 25% energy enhancement compared to a standard photovoltaic panel, while performing functions like battery voltage regulation and matching of the PV array with the load. Instead of using an externally connected MPPT, it is proposed to use an integrated MPPT converter as part of the PV panel. It is proposed that this integrated MPPT uses a simple controller in order to be cost effective. Furthermore, the power converter has to be very efficient, in order to transfer more energy to the load than a directly-coupled system. This is achieved by using a simple soft-switched topology. A much higher conversion efficiency at lower cost will then result, making the MPPT an affordable solution for small PV energy systems     

Soft switching resonant converter with duty-cycle control in DC micro-grid system

Resonant converter has been widely used for the benefits of low switching losses and high circuit efficiency. However, the wide frequency variation is the main drawback of resonant converter. This paper studies a new modular resonant converter with duty-cycle control to overcome this problem and realise the advantages of low switching losses, no reverse recovery current loss, balance input split voltages and constant frequency operation for medium voltage direct currentgrid or system network. Series full-bridge (FB) converters are used in the studied circuit in order to reduce the voltage stresses and power rating on power semiconductors. Flying capacitor is used between two FB converters to balance input split voltages. Two circuit modules are paralleled on the secondary side to lessen the current rating of rectifier diodes and the size of magnetic components. The resonant tank is operated at inductive load circuit to help power switches to be turned on at zero voltage with wide load range. The pulse-width modulation scheme is used to regulate output voltage. Experimental verifications are provided to show the performance of the proposed circuit.     

Low cost fuel cell converter system for residential power generation

The high installation cost is the major obstacle of the commercialization of the solid oxide fuel cell for distributed power generation. This paper presents a new low cost 10-kW converter system to overcome this obstacle. The proposed system consists of an isolated dc-dc converter to boost the fuel cell voltage to 400 V dc and a pulse-width modulated inverter with filter to convert the dc voltage to two split-phase 120-V ac. The dc-dc converter uses phase shifting to control power flow through a transformer with a metal oxide semiconductor field effect transistor full bridge on the low voltage side and a voltage doubler on the high voltage side. One IPM is used to realize the voltage doubler and the dc-ac inverter. Compared to the existing fuel cell converter systems, the proposed circuit has low cost, less component count, smaller size, and reduced dc-dc converter peak current. Simulation and experimental results are demonstrated.     

A 1.5-MW Seven-Cell Series-Stacked Converter as an Active Power Filter and Regeneration Converter for a DC Traction Substation

A prototype 1.5 MW series-stacked converter system was built and installed at a dc traction substation. The converter inverts energy generated by slowing an electric train using regenerative braking. The regenerated energy is fed into the local ac network at the dc substation. A secondary function of the converter is to perform active power filtering (APF) while a train is drawing power from the substation. The system's control is based on the instantaneous reactive power theory. An interleaved switching scheme was used to switch the seven-cell series-stacked converter, thus exploiting the natural balancing properties of the series-stacked converter. Results obtained from tests done show that both the APF and regeneration functions of the system were successfully implemented.      

Voltage Unbalance Mitigation in Low Voltage Distribution Networks with Photovoltaic Systems

This paper proposes a technique to mitigate the voltage unbalance issue caused by the high penetration of photovoltaic(PV) systems into the low voltage distribution networks(LVDN) using a single phase energy storage system(ESS).The ESS comprises a bi-directional power flow inverter and a battery bank.The system is capable of absorbing the excess power and delivering power to the network in order to keep the voltage unbalance factor(VUF) below the statutory limit of 1%.Investigations are carried out in the experimental small-scale energy zone(SSEZ).The experimental results demonstrate that the ESS is capable of mitigating the VUF of the network.     

A digitally controlled switch mode power supply based on matrix converter

High power telecommunication power supply systems consist of a three-phase switch mode rectifier followed by a dc/dc converter to supply loads at -48 V dc. These rectifiers draw significant harmonic currents from the utility, resulting in poor input power factor with high total harmonic distortion (THD). In this paper, a digitally controlled three-phase switch mode power supply based on a matrix converter is proposed for telecommunication applications. In the proposed approach, the matrix converter directly converts the low frequency (50/60Hz, three-phase) input to a high frequency (10/20kHz, one-phase) ac output without a dc-link. The output of the matrix converter is then processed via a high frequency isolation transformer to produce -48V dc. Digital control of the system ensures that the output voltage is regulated and the input currents are of high quality under varying load conditions. Due to the absence of dc-link electrolytic capacitors, power density of the proposed rectifier is expected to be higher. Analysis, design example and experimental results are presented from a three-phase 208-V, 1.5-kW laboratory prototype converter.