Current Controlled Voltage Source Converter Research Articles

Hybrid Control Strategy for Variable Speed Wind Turbine Power Converters

This article employs a hybrid control strategy for variable speed wind turbine power converters. A voltage-controlled voltage source converter algorithm was used in the machine or rotor side of the variable speed wind turbine system. For the grid or stator side of the variable speed wind turbine, a current-controlled voltage source converter method was used. The effectiveness of the hybrid converter system was compared with those using only voltage or current controlled power converters for the variable speed wind turbine in a standard laboratory power simulation package of the Manitoba Research Centre in Canada (PSCAD/EMTDC). It is palpable and discernable from the results that the hybrid control strategy improves the performance of the variable speed wind turbine stability during transient compared to when only the voltage-controlled algorithm was used for the power converters. However, when the current-controlled method is applied for the variable speed wind turbine power converters, the transient stability of the variable speed wind turbine was slightly improved compared to the hybrid converter system.

A new control strategy for active power line conditioner (APLC) using adaptive notch filter

This paper proposes a new adaptive control algorithm for a three-phase current-source shunt active power-line conditioner (APLC) operating under unbalanced and distorted network conditions. This control scheme aims at compensation of network’s reactive power, elimination of active power’s oscillating components, compensation of network current and voltage harmonic contents resulting in sinusoidal waveforms, and equilibrating the drawn power from the source evenly between the three-phases. Unlike many of the existing methods, the proposed strategy does not require any coordinate transformations or complicated calculations. The reference signals for the hysteresis-band current controlled voltage-source converter (HBCC-VSC) are generated by passing the measured current and voltage signals through two layers of modified adaptive notch filters (ANFs). To ensure superb performance and minimum total harmonic distortion (THD) level of the power system, parameters of the HBCC-VSC are obtained using differential evolution (DE) optimization algorithm. The proposed strategy is simple, easily implementable, and robust against uncertainty or variations of power system parameters and loads. The effectiveness of the proposed control scheme is validated by simulation results of a selected network under various load and power system conditions.

Effectiveness of Current-controlled Voltage Source Converter Excited Doubly Fed Induction Generator for Wind Farm Stabilization

In this article, stabilization methods of wind farms composed of fixed-speed wind turbines and variable-speed wind turbines are analyzed. A current-controlled voltage source converter scheme for a variable-speed wind turbine driving doubly fed induction generator is proposed. The proposed scheme is then compared with two other doubly fed induction generator control schemes to show the effectiveness of the proposed controller. Different types of symmetrical and unsymmetrical faults are analyzed considering wind farm recent grid codes. Though all of the schemes are able to stabilize the wind farms during transient conditions, the proposed current-controlled voltage source converter scheme offers the advantage of less intricacy of controller design, better performance during grid fault, and omission of DC-link protection scheme, which can reduce the overall cost of the system. Moreover, extensive simulation analyses by using PSCAD/EMTDC (Manitoba HVDC Research Center, Manitoba, Canada) are performed to determine the optimum amount of the fixed-speed wind turbine system that can be stabilized by variable-speed wind turbine system.

Wind Farm Stabilization by using DFIG with Current Controlled Voltage Source Converters Taking Grid Codes into Consideration

Recent wind farm grid codes require wind generators to ride through voltage sags, which means that normal power production should be re-initiated once the nominal grid voltage is recovered. However, fixed speed wind turbine generator system using induction generator (IG) has the stability problem similar to the step-out phenomenon of a synchronous generator. On the other hand, doubly fed induction generator (DFIG) can control its real and reactive powers independently while being operated in variable speed mode. This paper proposes a new control strategy using DFIGs for stabilizing a wind farm composed of DFIGs and IGs, without incorporating additional FACTS devices. A new current controlled voltage source converter (CC-VSC) scheme is proposed to control the converters of DFIG and the performance is verified by comparing the results with those of voltage controlled voltage source converter (VC-VSC) scheme. Another salient feature of this study is to reduce the number of proportionate integral (PI) controllers used in the rotor side converter without degrading dynamic and transient performances. Moreover, DC-link protection scheme during grid fault can be omitted in the proposed scheme which reduces overall cost of the system. Extensive simulation analyses by using PSCAD/EMTDC are carried out to clarify the effectiveness of the proposed CC-VSC based control scheme of DFIGs.

Neural-Network-Based Integrated Electronic Load Controller for Isolated Asynchronous Generators in Small Hydro Generation

This paper deals with a neural-network (NN)-based integrated electronic load controller (IELC) for an isolated asynchronous generator (IAG) driven by a constant-power small hydro uncontrolled turbine feeding three-phase four-wire loads. The proposed IELC utilizes an NN based on the least mean-square algorithm known as adaptive linear element to extract the fundamental component of load currents to control the voltage and the frequency of an IAG with load balancing in an integrated manner. The IELC is realized using zigzag/three single-phase transformers and a six-leg insulated-gate bipolar-transistor-based current-controlled voltage-source converter, a chopper switch, and an auxiliary load on its dc bus. The proposed IELC, with the generating system, is modeled and simulated in MATLAB environment using Simulink and Simpower System toolboxes. The simulated results are validated with test results on a developed prototype to demonstrate the effectiveness of IELC for the control of an IAG feeding three-phase four-wire linear/nonlinear balanced/unbalanced loads with neutral-current compensation.

Decoupled Electronic Load Controller for Offgrid Induction Generators in Small Hydro Power Generation

The control of voltage and frequency is one of the prime concerns in small off-grid hydroelectric power plants located in remote and inaccessible places. Induction generators are prime contenders for such applications which are robust, require less maintenance and have low cost. This paper deals with an implementation of a decoupled electronic load controller (DELC) for a three-phase induction generator (IG) system in standalone applications. The DELC is a combination of a static synchronous compensator (STATCOM) and conventional electronic load controller (ELC). The STATCOM consists of three-phase insulated gate bipolar transistor (IGBT) based current controlled voltage source converter (CC-VSC) with a dc bus capacitor and an ELC consists of an IGBT based chopper and an auxiliary load on the dc bus of the diode bridge rectifier. An Icos? based control algorithm is used in DELC to regulate terminal voltage and frequency, suppress harmonics and to provide load balancing. Test results are presented under balanced/unbalanced nonlinear loads to demonstrate the effectiveness of the DELC for an induction generator system.

Instantaneous Symmetrical Component Theory Based Voltage and Frequency Controller for Isolated Small Hydropower Generation

This article deals with the design and implementation of an instantaneous sequence component theory based integrated voltage and frequency controller for an isolated asynchronous generator, which is used in constant power small hydropower generation for feeding three-phase four-wire consumer loads. The proposed integrated voltage and frequency controller is used to control the voltage and frequency of an isolated asynchronous generator in the integrated manner. This integrated voltage and frequency controller is realized using a zigzag/star transformer and a three-leg insulated-gate bipolar transistor based current-controlled voltage source converter, a capacitor, a chopper switch, and an auxiliary load on its DC bus. The proposed integrated voltage and frequency controller with an isolated generating system is modeled and simulated in MATLAB along with Simulink and simpower system (SPS) toolboxes (The MathWorks, Natick, Massachusetts, USA). The simulated results are validated with test results of a developed prototype using a 3.7-kW, 230-V asynchronous generator to demonstrate its performance for feeding three-phase four-wire consumer loads with the neutral current compensation.

VSC with a T-connected transformer-based electronic load controller for an isolated asynchronous generator feeding three-phase four-wire loads in a micro hydro system

This paper deals with a novel solid state controller (NSSC) for isolated asynchronous generator (IAG) feeding three-phase four-wire loads driven by constant power prime movers, such as uncontrolled micro hydro turbines. AC capacitor banks are used to meet the reactive power requirement of the asynchronous generator. The proposed NSSC is realised using a set of IGBTs (insulated gate bipolar junction transistors) based current controlled voltage source converter (CC-VSC) and a DC chopper at its DC bus, which keeps the generated voltage and frequency constant in spite of changes in consumer loads. The neutral point of the load is created using a T-configuration of the transformers. The IAG system is modelled in MATLAB along with Simulink and PSB (power system block set) toolboxes. The simulated results are presented to demonstrate the capability of isolated generating system consisting of NSSC and IAG driven by uncontrolled micro hydro turbine and feeding three-phase four-wire loads.

Decoupled Solid State Controller for Asynchronous Generator in Pico-hydro Power Generation

This paper deals with a decoupled solid state controller (DSSC) for an isolated asynchronous generator (IAG), used in constant power pico-hydro power generation for feeding three-phase four-wire loads. The proposed DSSC is used to control the voltage and frequency of the IAG in the decoupled manner. This DSSC is a combination of a voltage regulator (VR) for regulating the voltage and a conventional electronic load controller (ELC) for controlling the active power to regulate the frequency. The VR is realized using a zigzag/three-single-phase transformer and six-leg insulated gate bipolar transistors (IGBTs)-based current controlled voltage source converter (VSC) with a capacitor on its DC bus and an ELC is a combination of a three-phase diode bridge rectifier with a chopper switch and an auxiliary load. The proposed DSSC with an isolated generating system is modeled and simulated in MATLAB along with Simulink and power system blockset (PSB) toolboxes. The simulated results of the IAG-DSSC system are presented to demonstrate its performance for feeding three-phase four-wire linear/nonlinear (balanced/unbalanced) loads with the neutral current compensation.

Harmonic elimination, voltage control and load balancing in an isolated power generation

This paper deals with an implementation of a voltage controller for an isolated power generating system employing an asynchronous generator. In such standalone system, an asynchronous generator is driven by a constant speed prime mover such as diesel, bio-gas and a gasoline engine etc. and it is isolated from the grid. A three-phase insulated gate bipolar junction transistor (IGBT) based current controlled voltage source converter (CC-VSC) with a dc bus capacitor is used to regulate the magnitude of the generated voltage along-with its functioning as a harmonic eliminator and a load balancer. The proposed controller for an isolated generating system is developed using dSPACE–DS1104 DSP controller and extensive tests are conducted with non-linear and unbalanced loads to demonstrate its capability. Copyright © 2009 John Wiley & Sons, Ltd.

Incorporation of a Redox Flow Battery in a Wind-Diesel Power System for Simultaneous Frequency and Voltage Control

Energy storage devices are required for power quality maintenance in stand alone power systems like wind-diesel ones. A redox flow battery system has many virtues which make its integration with a wind-diesel power system attractive. This paper proposes the integration of a redox flow battery system with a typical multi-machine wind-diesel power system for simultaneous voltage and frequency regulation. The redox flow battery is connected to wind park bus through a current controlled voltage source converter based on hysterisis current control. Keeping in view the non-linear and time varying nature of the hybrid wind-diesel-redox flow battery system, neuro-adaptive control is proposed for active/reactive power modulation of the redox flow battery.

A Novel Solid State Controller for Parallel Operated Isolated Asynchronous Generators in Pico Hydro Systems

This paper deals with a novel solid state controller (NSSC) for parallel operated isolated asynchronous generators (IAG) feeding 3-pbase 4-wire loads in constant power applications, such as uncontrolled pico hydro turbines. AC capacitor banks are used to meet the reactive power requirement of asynchronous generators. The proposed NSSC is realized using a set of IGBTs (Insulated gate bipolar junction transistors) based current controlled 4-leg voltage source converter (CC-VSC) and a DC chopper at its DC bus, which keeps the generated voltage and frequency constant in spite of changes in consumer loads. The complete system is modeled in MATLAB along with simulink and PSB (power system block set) toolboxes. The simulated results are presented to demonstrate the capability of isolated generating system consisting of NSSC and parallel operated asynchronous generators driven by uncontrolled pico hydro turbines and feeding 3-phase 4-wire loads.

Analysis of Subsynchronous Torsional Interaction With Power Electronic Converters

This paper extends previously proposed methods for frequency-domain analysis of subsynchronous oscillation phenomena in synchronous machines. Particular attention is given to the case where a current-controlled voltage-source converter is located electrically nearby. It is shown that the converter can contribute with significant positive electrical damping. Negative electrical damping is normally contributed only in the frequency region where the converter acts as a negative resistance. This region can be reduced or eliminated by proper design of the current controller

Series equivalence/operation of current-controlled boost-type single-phase voltage source converters for bidirectional power flow

Single-phase voltage source power converters (VSCs) under consideration are AC-DC current-controlled boost-type power converters with bidirectional power-handling capability. Equivalence between two series-connected two-level power converters and a single three-level power converter is considered here. Further considered is the series operation of three-level power converters. Simulation results and experimental verification for both are provided. Economical configurations of three-level power converters leading to multilevel waveforms are presented thereafter.

Current-controlled boost-type single-phase voltage source converters for bidirectional power flow

A consolidation of existing as well as new configurations of voltage source power converters (VSCs) using gate turn-offs (GTOs) or a combination of GTOs and thyristors is considered. These VSCs are single-phase AC-DC current-controlled boost-type power converters with bidirectional power-handling capability. Both two-level and three-level power converters are presented along with a definitive classification. Experimental results are provided on a selective basis, confirming a 360/spl deg/ power angle range of the power converters.