Showing papers on "Voltage regulation published in 2009"
TL;DR: In this article, two types of pulsewidth-modulated modular multilevel converters (PWM-MMCs) with focus on their circuit configurations and voltage balancing control are investigated.
Abstract: A modular multilevel converter (MMC) is one of the next-generation multilevel converters intended for high- or medium-voltage power conversion without transformers. The MMC is based on cascade connection of multiple bidirectional chopper-cells per leg, thus requiring voltage-balancing control of the multiple floating DC capacitors. However, no paper has made an explicit discussion on voltage-balancing control with theoretical and experimental verifications. This paper deals with two types of pulsewidth-modulated modular multilevel converters (PWM- MMCs) with focus on their circuit configurations and voltage-balancing control. Combination of averaging and balancing controls enables the PWM-MMCs to achieve voltage balancing without any external circuit. The viability of the PWM-MMCs, as well as the effectiveness of the voltage-balancing control, is confirmed by simulation and experiment.
1,506 citations
TL;DR: Experimental results in a laboratory authenticate that energy-storage devices can assist the FC to meet the vehicle power demand and help achieve better performance, as well as to substantiate the excellent control schemes during motor-drive cycles.
Abstract: This paper studies the impact of fuel-cell (FC) performance and control strategies on the benefits of hybridization. One of the main weak points of the FC is slow dynamics dominated by a temperature and fuel-delivery system (pumps, valves, and, in some cases, a hydrogen reformer). As a result, fast load demand will cause a high voltage drop in a short time, which is recognized as a fuel-starvation phenomenon. Therefore, to employ an FC in vehicle applications, the electrical system must have at least an auxiliary power source to improve system performance when electrical loads demand high energy in a short time. The possibilities of using a supercapacitor or a battery bank as an auxiliary source with an FC main source are presented in detail. The studies of two hybrid power systems for vehicle applications, i.e., FC/battery and FC/supercapacitor hybrid power sources, are explained. Experimental results with small-scale devices (a polymer electrolyte membrane FC of 500 W, 40 A, and 13 V; a lead-acid battery module of 33 Ah and 48 V; and a supercapacitor module of 292 F, 500 A, and 30 V) in a laboratory authenticate that energy-storage devices can assist the FC to meet the vehicle power demand and help achieve better performance, as well as to substantiate the excellent control schemes during motor-drive cycles.
285 citations
TL;DR: A control method is proposed to lock the switching frequency at just above the load insensitive frequency for optimized efficiency at heavy loads and a prototype transcutaneous power regulator is built and found to to perform excellently with high efficiency and tight regulation under variations of the alignment or gap of the trans cutaneous transformer, load and input voltage.
Abstract: Based on a generic transcutaneous transformer model, a remote power supply using a resonant topology for use in artificial hearts is analyzed and designed for easy controllability and high efficiency. The primary and secondary windings of the transcutaneous transformer are positioned outside and inside the human body, respectively. In such a transformer, the alignment and gap may change with external positioning. As a result, the coupling coefficient of the transcutaneous transformer is also varying, and so are the two large leakage inductances and the mutual inductance. Resonant-tank circuits with varying resonant-frequency are formed from the transformer inductors and external capacitors. For a given range of coupling coefficients, an operating frequency corresponding to a particular coupling coefficient can be found, for which the voltage transfer function is insensitive to load. Prior works have used frequency modulation to regulate the output voltage under varying load and transformer coupling. The use of frequency modulation may require a wide control frequency range which may extend well above the load insensitive frequency. In this paper, study of the input-to-output voltage transfer function is carried out, and a control method is proposed to lock the switching frequency at just above the load insensitive frequency for optimized efficiency at heavy loads. Specifically, operation at above resonant of the resonant circuits is maintained under varying coupling-coefficient. Using a digital-phase-lock-loop (PLL), zero-voltage switching is achieved in a full-bridge converter which is also programmed to provide output voltage regulation via pulsewidth modulation (PWM). A prototype transcutaneous power regulator is built and found to to perform excellently with high efficiency and tight regulation under variations of the alignment or gap of the transcutaneous transformer, load and input voltage.
221 citations
TL;DR: In this article, the authors investigated a permanent-magnet wind generator with a full power voltage-source converter in weak-grid mode, where the DC-link voltage needs to be controlled from the generator side instead of the grid side.
Abstract: When the wind power accounts for a large portion of the grid power, it may need to help the grid voltage and frequency regulation. This paper investigates a permanent-magnet wind generator with a full power voltage-source converter in weak-grid mode, where the DC-link voltage needs to be controlled from the generator side instead of the grid side. The energy relationship of the wind generator, DC-link energy storage, and load is established. An intrinsic right-half-plane zero, together with the wind power characteristics, the mechanical system inertia, and the DC-link energy storage, is identified as the physical limitations for the control. With the understanding of the system energy relationship and limitations, a hybrid adaptive control algorithm is proposed that searches for the optimal generator acceleration to achieve the maximum wind generator power change rate to match the load power variation. The proposed control scheme is verified through simulation of a 1.5-MW wind system as well as through the experiment of a scaled 1-kW, DSP-/field-programmable-gate-array-controlled, permanent-magnet-generator-based test bed. The results show that it is feasible to regulate DC link by the generator-side converter through the generator speed control. Some important applications issues are also investigated, including the DC-link energy storage requirement, wind speed change impact, and control transition between the weak-grid and strong-grid modes.
205 citations
01 Jan 2009
TL;DR: In this paper, the static synchronous compensator (STATCOM) is used to regulate the point of common coupling voltage during nighttime when the solar farm is not producing any active power.
Abstract: This letter presents a novel concept of utilizing pho- tovoltaic (PV) solar farm (SF) as a flexible ac transmission systems controller—static synchronous compensator, to regulate the point of common coupling voltage during nighttime when the SF is not producing any active power. This concept, although general, is pre- sented for the scenario of a distribution feeder, which has both PV solar and wind farms connected to it. The proposed control will en- able increased connections of renewable energy sources in the grid. A MATLAB/Simulink-based simulation study is presented under variable wind power generation and fault condition to validate the proposed concept. Index Terms—Distributed generation, flexible ac transmission systems (FACTS), solar energy, static synchronous compensator (STATCOM), voltage regulation, wind energy.
198 citations
TL;DR: The relationship between input voltage sharing (IVS) and output current sharing of the constituent modules of the ISOP converter is revealed and a novel IVS control strategy, which is decoupled with the output voltage regulation, is proposed.
Abstract: The input-series-output-parallel (ISOP) converter, which consists of multiple dc-dc converter modules connected in series at the input and in parallel at the output, is an attractive solution for high input voltage and high power applications. This paper reveals the relationship between input voltage sharing (IVS) and output current sharing of the constituent modules of the ISOP converter. A novel IVS control strategy, which is decoupled with the output voltage regulation, is proposed. This control allows IVS and output voltage regulation to be designed independently. An ISOP converter, which uses the phase-shifted full-bridge (PS-FB) converter as the basic module, is considered. Based on the proposed control strategy, this ISOP converter together with the control circuit can be decoupled from several independent single-input and single-output systems. An ISOP converter consisting of three PS-FB modules is used to illustrate the design procedure, and a 3-kW experimental prototype is fabricated and tested.
193 citations
TL;DR: In this paper, a control system based on a repetitive controller to compensate for key power-quality disturbances, namely voltage sags, harmonic voltages, and voltage imbalances, using a dynamic voltage restorer (DVR), is presented.
Abstract: This paper presents a control system based on a repetitive controller to compensate for key power-quality disturbances, namely voltage sags, harmonic voltages, and voltage imbalances, using a dynamic voltage restorer (DVR). The control scheme deals with all three disturbances simultaneously within a bandwidth. The control structure is quite simple and yet very robust; it contains a feedforward term to improve the transient response and a feedback term to enable zero error in steady state. The well-developed graphical facilities available in PSCAD/EMTDC are used to carry out all modeling aspects of the repetitive controller and test system. Simulation results show that the control approach performs very effectively and yields excellent voltage regulation.
180 citations
TL;DR: A multi-power-port topology which is capable of handling multiple power sources and still maintains simplicity and features like obtaining high gain, wide load variations, lower output-current ripple, and capability of parallel-battery energy due to the modular structure is proposed.
Abstract: For hybrid electric vehicles, the batteries and the drive dc link may be at different voltages. The batteries are at low voltage to obtain higher volumetric efficiencies, and the dc link is at higher voltage to have higher efficiency on the motor side. Therefore, a power interface between the batteries and the drive's dc link is essential. This power interface should handle power flow from battery to motor, motor to battery, external genset to battery, and grid to battery. This paper proposes a multi-power-port topology which is capable of handling multiple power sources and still maintains simplicity and features like obtaining high gain, wide load variations, lower output-current ripple, and capability of parallel-battery energy due to the modular structure. The scheme incorporates a transformer winding technique which drastically reduces the leakage inductance of the coupled inductor. The development and testing of a bidirectional flyback dc-dc converter for hybrid electric vehicle is described in this paper. Simple hysteresis voltage control is used for dc-link voltage regulation. The experimental results are presented to show the working of the proposed converter.
170 citations
TL;DR: In this article, a novel concept of utilizing photovoltaic (PV) solar farm (SF) as a flexible ac transmission system controller-static synchronous compensator, to regulate the point of common coupling voltage during nighttime when the SF is not producing any active power.
Abstract: This letter presents a novel concept of utilizing photovoltaic (PV) solar farm (SF) as a flexible ac transmission systems controller-static synchronous compensator, to regulate the point of common coupling voltage during nighttime when the SF is not producing any active power. This concept, although general, is presented for the scenario of a distribution feeder, which has both PV solar and wind farms connected to it. The proposed control will enable increased connections of renewable energy sources in the grid. A MATLAB/Simulink-based simulation study is presented under variable wind power generation and fault condition to validate the proposed concept.
169 citations
TL;DR: In this paper, a control approach applied on a doubly fed induction generator (DFIG) to provide both voltage and frequency regulation capabilities, and hence, an improvement in the dynamic behavior of a microgrid system.
Abstract: This paper describes a control approach applied on a doubly fed induction generator (DFIG) to provide both voltage and frequency regulation capabilities, and hence, an improvement in the dynamic behavior of a microgrid system. The microgrid system is assumed to be a portion of a medium voltage distribution feeder and is supplied by two distributed generation (DG) units, i.e., a gas-turbine synchronous generator and a variable-speed wind turbine with DFIG. A control approach algorithm is proposed for the DFIG unit to improve both voltage and primary frequency controls. Two distinct operation modes, i.e., grid-connected and islanding mode, are used in the proposed approach for proper transfer from normal to islanding operation. Case studies are simulated based on both planned and unplanned islanding scenarios to evaluate the performance of the control approach. The study results show that the proposed control approach for DGs in the microgrid increase the microgrid system's dynamic performance, reduce frequency changes, and improve bus voltages regulation during islanding and autonomous operations.
155 citations
TL;DR: In this paper, the authors present an analysis of the voltage balancing dynamics of a three-phase flying capacitor converter when supplying an induction motor, using a least squares minimization method.
Abstract: This paper presents an analysis of the natural voltage balancing dynamics of a three-phase flying capacitor converter when supplying an induction motor. The approach substitutes double Fourier harmonic series for the pulsewidth modulation switching waveforms and the frequency response of the motor, to create a linear state-space model of this type of load. The model requires the mid-frequency response (500 Hz-20 kHz) of the induction motor impedance to be identified, and takes skin and proximity effects into account by adding parallel R-L networks to a standard motor model. Model parameters were measured by applying FFT analysis to variable frequency square waves injected into the motor terminals, and fitting parameter values to these measurements using a least squares minimization method. From the analysis, it was found that the converter voltage balancing behavior degrades substantially at low motor speeds, and that a balance booster filter, as previously proposed, considerably improves the dynamic response. Experimental verification results using a scaled-down flying capacitor converter drive are included in the paper.
TL;DR: A reactive power controller design for doubly fed induction generator drives that enables the control of reactive power independently of the active power flow using both rotor and mains-side inverters and can be used to enhance the drive efficiency.
Abstract: The high penetration level of wind power generation in an interconnected electrical network carries new technical challenges regarding system stability. Despite the stochastic nature of the wind, grid reliability has to be guaranteed. In compliance with power companies' new requirements on wind turbines as regards contribution to voltage regulation, this paper proposes a reactive power controller design for doubly fed induction generator drives. This drive topology enables the control of reactive power independently of the active power flow using both rotor and mains-side inverters. This degree of freedom is used in order to share the reactive powers circulating in the drive system and resulting from the reactive power required in the network. The controllers are designed using well-known linear control techniques in order to present the same dynamics. Furthermore, the proper reactive power share can be used to enhance the drive efficiency. Experimental results show the performance of the proposed reactive power control.
06 Nov 2009
TL;DR: In this article, the authors present the structure and capabilities of a small, grid-interactive distributed energy resource system comprised of a photovoltaic source, plug-in hybrid electric vehicle, and various local loads.
Abstract: This paper presents the structure and capabilities of a small, grid-interactive distributed energy resource system comprised of a photovoltaic source, plug-in hybrid electric vehicle, and various local loads. Implemented at the residential level, this system, with a plug-in hybrid electrical vehicle, has the ability to isolate a house from the utility grid (intentionally due to a fault or other abnormal grid conditions), work in the standalone mode, synchronize and reconnect to the utility grid, without load power interruptions. Plug-in hybrid electrical vehicles, with a built-in bidirectional power converter, present the opportunity for demand-response operation in the grid connected mode, whereas in the islanded mode, it can perform frequency and voltage regulation of the power bus. In this paper, system structure and modes of operation are described, and measured results are presented for two main modes of operation and mode transitions.
TL;DR: A transformerless hybrid active filter integrated into the 6.6-kV, 1MW adjustable-speed motor drive having a three-phase diode rectifier at the front end is discussed in this paper.
Abstract: This paper discusses a transformerless hybrid active filter integrated into the 6.6-kV, 1-MW adjustable-speed motor drive having a three-phase diode rectifier at the front end. The hybrid filter consists of an active filter using a three-level diode-clamped pulsewidth modulator converter rated at 60 kVA, and a 250-kVA passive filter tuned to the seventh harmonic frequency. They are directly connected in series without a transformer. This circuit configuration enables one to use 1.2-kV insulated gate bipolar transistors because the dc voltage of the three-level converter is 1.32 kV (20% of 6.6 kV). Voltage balancing control characterized by superimposing a sixth harmonic zero-sequence voltage on the active filter voltage reference in each phase is introduced to the three-level converter with triangle carrier modulation. Experimental waveforms obtained from a 400-V, 15-kW downscaled system verify the viability and effectiveness of the proposed hybrid filter, keeping the two dc capacitor voltages well-balanced.
TL;DR: This paper presents a 64 kb reconfigurable SRAM fabricated in 65 nm low-power CMOS process operating from 250 mV to 1.2 V, enabled by a combination of circuits optimized for both subthreshold and above-threshold regimes and by employing hardware reconfigurability.
Abstract: In modern ICs, the trend of integrating more on-chip memories on a die has led SRAMs to account for a large fraction of total area and energy of a chip. Therefore, designing memories with dynamic voltage scaling (DVS) capability is important since significant active as well as leakage power savings can be achieved by voltage scaling. However, optimizing circuit operation over a large voltage range is not trivial due to conflicting trade-offs of low-voltage (moderate and weak inversion) and high-voltage (strong inversion) transistor characteristics. Specifically, low-voltage operation requires various assist circuits for functionality which might severely impact high-voltage performance. Reconfigurable assist circuits provide the necessary adaptability for circuits to adjust themselves to the requirements of the voltage range that they are operating in. This paper presents a 64 kb reconfigurable SRAM fabricated in 65 nm low-power CMOS process operating from 250 mV to 1.2 V. This wide supply range was enabled by a combination of circuits optimized for both subthreshold and above-threshold regimes and by employing hardware reconfigurability. Three different write-assist schemes can be selectively enabled to provide write functionality down to very low voltage levels while preventing excessive power overhead. Two different sense-amplifiers are implemented to minimize sensing delay over a large voltage range. A prototype test chip is tested to be operational at 20 kHz with 250 mV supply and 200 MHz with 1.2 V supply. Over this range leakage power scales by more than 50 X and a minimum energy point is achieved at 0.4 V with less than 0.1 pJ/bit/access.
TL;DR: In this paper, a 6.6-kV adjustable-speed motor drive for pumps and blowers without transformer is described, which consists of a front-end diode rectifier, a five-level diode-clamped pulsewidth modulation (PWM) inverter with a voltage balancing circuit, and a hybrid active filter for harmonic-current mitigation of the rectifier.
Abstract: This paper describes a 6.6-kV adjustable-speed motor drive for pumps and blowers without transformer. The power conversion system consists of a front-end diode rectifier, a five-level diode-clamped pulsewidth modulation (PWM) inverter with a voltage balancing circuit, and a hybrid active filter for harmonic-current mitigation of the diode rectifier. The control of the inverter is characterized by superimposing a third-harmonic zero-sequence voltage on each of the three-phase reference voltages to achieve the so-called overmodulation and reduce the switching stress of insulated gate bipolar transistors (IGBTs). A 200-V 5.5-kW downscale model is designed, constructed, and tested with focus on the five-level PWM inverter and the voltage balancing circuit. Experimental results obtained from the 200-V downscale model verify the viability and effectiveness of the 6.6-kV adjustable-speed motor drive, showing that the four split dc capacitor voltages are well balanced in all the operating conditions and that the switching stress of the IGBTs is reduced at low modulation indexes.
TL;DR: In this article, a fast-acting dc-link voltage controller based on the energy of a DC-link capacitor is proposed to achieve fast transient response of distribution static compensator (DSTATCOM).
Abstract: The transient response of the distribution static compensator (DSTATCOM) is very important while compensating rapidly varying unbalanced and nonlinear loads. Any change in the load affects the dc-link voltage directly. The sudden removal of load would result in an increase in the dc-link voltage above the reference value, whereas a sudden increase in load would reduce the dc-link voltage below its reference value. The proper operation of DSTATCOM requires variation of the dc-link voltage within the prescribed limits. Conventionally, a proportional-integral (PI) controller is used to maintain the dc-link voltage to the reference value. It uses deviation of the capacitor voltage from its reference value as its input. However, the transient response of the conventional PI dc-link voltage controller is slow. In this paper, a fast-acting dc-link voltage controller based on the energy of a dc-link capacitor is proposed. Mathematical equations are given to compute the gains of the conventional controller based on fast-acting dc-link voltage controllers to achieve similar fast transient response. The detailed simulation and experimental studies are carried out to validate the proposed controller.
TL;DR: In this article, the authors present a control system based on the so-called repetitive control for a five-level flying-capacitor dynamic voltage restorer (DVR).
Abstract: This paper presents the control system based on the so-called repetitive control for a five-level flying-capacitor dynamic voltage restorer (DVR). This DVR multilevel topology is suitable for medium-voltage applications and operated by the control scheme developed in this paper. It is able to mitigate power-quality disturbances, such as voltage sags, harmonic voltages, and voltage imbalances simultaneously within a bandwidth. The control structure has been divided into three subsystems; the first one improves the transient response of the filter used to eliminate the modulation high-frequency harmonics, the second one deals with the load voltage; and the third is charged with maintaining balanced voltages in the flying capacitors. The well-developed graphical facilities available in PSCAD/EMTDC are used to carry out all modelling aspects of the repetitive controller and test system. Simulation results show that the control approach performs very effectively and yields excellent voltage regulation.
TL;DR: In this paper, a highly efficient and novel control strategy for improving the transients in the output voltage of a DC-DC positive buck-boost converter, required for low-power portable electronic applications, is presented.
Abstract: A highly efficient and novel control strategy for improving the transients in the output voltage of a DC-DC positive buck-boost converter, required for low-power portable electronic applications, is presented in this paper. The proposed control technique can regulate the output voltage for variable input voltage, which is higher, lower, or equal to the output voltage. There are several existing solutions to these problems, and selecting the best approach involves a tradeoff among cost, efficiency, and output noise or ripple. In the proposed method, instead of instantaneous transition from buck to boost mode, intermediate combination modes consisting of several buck modes followed by several boost modes are utilized to distribute the voltage transients. This is unique of its kind from the point of view of improving the efficiency and ripple content in the output voltage. Theoretical considerations are presented. Simulation and experimental results are shown to prove the proposed theory.
06 Nov 2009
TL;DR: In this paper, the authors proposed a dc-link voltage stabilization algorithm using active damping to achieve load/source independent stabilization, and the source state estimator which estimates both source voltage and current is also proposed.
Abstract: A PMW inverter with reduced dc-link capacitor has a problem that the dc-link voltage is less stable compared to the conventional inverter because of the lack of energy storage capability. The proposed dc-link voltage stabilization algorithm using active damping gives a solution to this problem. To achieve load/source independent stabilization, the source state estimator which estimates both source voltage and current is also proposed. The proposed methods are evaluated by experimental results. While the inverter with a small DC link capacitor tripped due to dc-link overvoltage fault at step load change, the fluctuation of dc-link voltage of the inverter is suppressed under the tolerance range with the proposed method at the same step load change.
Patent•
29 Jan 2009
TL;DR: In this article, a system, device and method for regulating the voltage at a customer premises that is supplied power via a first medium voltage power line is provided, which includes determining medium voltage (MV) data comprising data of the voltage supplied to the first medium-voltage power line at a plurality of times.
Abstract: A system, device and method for regulating the voltage at a customer premises that is supplied power via a first medium voltage power line is provided. In one embodiment, the method of using a computer system comprises determining medium voltage (MV) data comprising data of the voltage supplied to the first medium voltage power line at a plurality of times, storing the MV data for each of the plurality of times in a memory, determining current data comprising data of a current supplied to the medium voltage power line at the plurality of times, storing the current data at each of the plurality of times in memory in association with the voltage data of the same time. In addition, the method includes receiving low voltage data comprising data of a voltage measurement of a low voltage power line conductor at the customer premises at a plurality of times, storing at least some of the low voltage data in memory in association with MV data that corresponds to the voltage supplied to the first medium voltage power line during the voltage measurement of the low voltage power line conductor, and determining a supply voltage to be supplied to the first medium voltage power line based on the current data stored in memory, MV data stored in memory, and the low voltage data stored in memory.
TL;DR: Several flatness-based current controllers for three-phase three-wire boost rectifiers are compared, and the flatness of a rectifier model is shown, and a trajectory planning algorithm that nominally achieves voltage regulation in finite time is given.
Abstract: Several flatness-based current controllers for three-phase three-wire boost rectifiers are compared. For this purpose, the flatness of a rectifier model is shown, and a trajectory planning algorithm that nominally achieves voltage regulation in finite time is given. The main focus lies on the inner loop current controllers. On one hand, linearization-based controllers using exact feedback linearization, exact feedforward linearization, and input-output linearization are discussed. On the other hand, two passivity-based approaches are compared. The first one is the energy shaping and damping injection method, and the other one uses exact tracking error dynamics passive output feedback. Furthermore, a reduced-order load observer is given, and a method that allows the prevention of invalid switching patterns is presented. The presented control algorithms are tested by simulations on a switched model.
Patent•
28 Apr 2009TL;DR: In this paper, a hysteretic voltage regulator consisting of an inductor having a first end and a second end is connected to an output capacitor in shunt with a load.
Abstract: A hysteretic voltage regulator is disclosed comprising an inductor having a first end and a second end, wherein the second end is connected to an output capacitor in shunt with a load. A switch connects the first end of the inductor to a supply voltage when an output voltage across the load falls below a reference voltage, and disconnects the first end of the inductor from the supply voltage when a current flowing through the output capacitor rises above a reference current.
TL;DR: In this article, a digital control approach for time-optimal load step response of DC-DC synchronous buck converters intended for point-of-load (PoL) applications and employing low-equivalent series resistance ceramic output capacitors is investigated.
Abstract: In this paper, a digital control approach is investigated for time-optimal load step response of DC-DC synchronous buck converters intended for point-of-load (PoL) applications and employing low-equivalent series resistance ceramic output capacitors. Unlike previously reported approaches, the proposed technique is insensitive to converter parametric variations and design uncertainties, as its operation does not rely on the knowledge of the output filter inductance or capacitance. The time-optimal response is achieved through a single on/off switching action undertaken as soon as a load transient is detected. In its most general formulation, the proposed technique automatically incorporates adaptive voltage positioning (AVP) regulation, according to the typical droop design guidelines for powering modern microprocessors. A simpler version, suitable for voltage-mode controlled PoL converters not requiring AVP positioning, is also presented. The technique employs an asynchronous A/D conversion scheme, which quantizes the converter state variables and triggers a nonlinear, event-based digital controller whenever a quantization level transition is detected. Additional sensing requirements are not needed, since the time-optimal transient is achieved through the measurement of the output voltage and, whenever AVP regulation is needed, of the phase currents. Effectiveness and properties of the proposed robust time-optimal approach are validated through both computer simulations and experimental tests on a synchronous buck converter prototype and a VHDL implementation of the control algorithm on an field programmable gate array device.
TL;DR: In this paper, a reduced-rating voltage-source converter with a zig-zag transformer as a distribution static compensator is proposed for power-quality improvement in the three-phase four-wire distribution system.
Abstract: A detailed investigation is made into the causes, standards, and remedies of the excessive neutral current. A reduced-rating voltage-source converter with a zig-zag transformer as a distribution static compensator is proposed for power-quality improvement in the three-phase four-wire distribution system. The proposed DSTATCOM is employed for the compensation of reactive power, harmonics currents, neutral current, load balancing and the voltage regulation at the point of common coupling. The zig-zag transformer is used for providing a path to the zero-sequence current. The performance of the DSTATCOM is validated through extensive simulations using MATLAB software with its Simulink and power system blockset toolboxes.
TL;DR: In this article, a split-link inverter with an active balancing circuit (also eight switches) is used to modulate the DC busbar offset voltage to make better use of the available DC-link voltage.
Abstract: Three-phase four-wire inverters, with either three-leg or four-leg topology, are useful for interfacing distributed generation to networks of unbalanced loads, but neither of the available circuit topologies is ideal. The split-link three-leg topology (with six switches) suffers from poor DC voltage utilization compared with the four-leg topology (with eight switches). The four-leg topology has an electromagnetic compatibility (EMC) difficulty because it imposes large-amplitude high-frequency voltages between the DC-link busbars and ground. To obtain both good dc voltage utilization and good EMC performance, it is proposed to use a split-link inverter with an active balancing circuit (also eight switches). The balancing circuit is used to modulate the DC busbar offset voltage to make better use of the available DC-link voltage. The optimum voltage term is established to be a third harmonic term, and the DC voltage utilization is improved. A deadbeat controller supplemented with a repetitive controller is designed to give good tracking and good disturbance rejection for the busbar offset voltage. System performance is studied through an experimental test rig.
TL;DR: In this article, the instantaneous active and reactive powers, directly controlled by selecting the optimum state of the converter, are used as the PWM control variables instead of the phase line currents being used.
TL;DR: In this article, a multimode control strategy for a doubly fed induction generator-based wind-power unit, which enables operation in the islanded (autonomous) mode as well as the grid-connected mode, is proposed.
Abstract: This paper proposes a multimode control strategy for a doubly fed induction generator-based wind-power unit, which enables operation in the islanded (autonomous) mode as well as the grid-connected mode. The configuration can be an option for electricity generation in remote communities with favorable wind conditions, but limited or unreliable connection to the grid. In the grid-connected mode, the proposed control enables the wind power unit to operate with or without battery energy storage, as desired. In case that the wind-power unit is augmented with battery energy storage, in the islanded mode, the proposed control strategy enables voltage and frequency regulation for the network, and parallel operation with constant-speed wind-power units, induction motor loads, and passive loads. The proposed control strategy employs a unified controller for all of the foregoing modes of operation and, therefore, relieves the need for switching between different controllers or reconfiguration of the hardware. The effectiveness and robustness of the proposed control strategy are demonstrated for faulted as well as normal operating conditions through simulation studies carried out on a detailed switched model of the system in the PSCAD/EMTDC software environment.
TL;DR: In this paper, a novel current mode control scheme for the tristate boost converter circuit is proposed, which eliminates the zero in the right-half plane (RHP) and improves the dynamic performance.
Abstract: A novel current mode control scheme for the tristate boost converter circuit is proposed, which eliminates the zero in the right-half plane (RHP), and improves the dynamic performance. The tristate boost converter contains an additional switch across the inductor. Within a clock cycle, the inductor current first rises during the on interval of the main switch, then falls during the off or capacitor charging interval, and finally, remains almost constant during the freewheeling interval when the additional switch is turned on. In the proposed controller, the peak value of the inductor current is controlled by peak current mode control using an outer voltage feedback loop, whereas the freewheeling current is controlled by the input voltage and the reference voltage feedforward path. Applying both feedback as well as feedforward control on the inductor current significantly improves the output voltage regulation, audio susceptibility, and transient responses. We show that the RHP zero is completely eliminated from the closed-loop control-to-output transfer function. This results in a very large bandwidth, and hence a superior dynamic performance. The latter is established by comparison with the voltage-mode- and current-mode-controlled classical boost converters that suffer from the RHP zero problem, as well as with other tristate boost converter control techniques like the constant charging interval and dual mode control, recently proposed in the literature. Significant superiority of the proposed scheme is established both through simulation and experimentation.
TL;DR: In this paper, a flywheel energy storage system (FESS) is connected to a wind generator at the DC bus in order to evaluate its capacity to participate to the ancillary services.