Showing papers on "Inverter published in 2004"

Cascaded DC-DC converter connection of photovoltaic modules

Abstract: New residential scale photovoltaic (PV) arrays are commonly connected to the grid by a single dc-ac inverter connected to a series string of pv panels, or many small dc-ac inverters which connect one or two panels directly to the ac grid. This paper proposes an alternative topology of nonisolated per-panel dc-dc converters connected in series to create a high voltage string connected to a simplified dc-ac inverter. This offers the advantages of a "converter-per-panel" approach without the cost or efficiency penalties of individual dc-ac grid connected inverters. Buck, boost, buck-boost, and Cu/spl acute/k converters are considered as possible dc-dc converters that can be cascaded. Matlab simulations are used to compare the efficiency of each topology as well as evaluating the benefits of increasing cost and complexity. The buck and then boost converters are shown to be the most efficient topologies for a given cost, with the buck best suited for long strings and the boost for short strings. While flexible in voltage ranges, buck-boost, and Cu/spl acute/k converters are always at an efficiency or alternatively cost disadvantage.

A dual two-level inverter scheme with common mode voltage elimination for an induction motor drive

Abstract: Pulse-width modulated (PWM) inverters are known to generate common mode voltages which cause motor bearing currents in the induction motor drives. They also result in leakage currents which act as sources of conducted electromagnetic interference in the drive system. The common mode voltage generated by a conventional three-level inverter can be eliminated by switching only the voltage space vectors which do not produce the common mode voltage. This paper presents a PWM switching strategy to eliminate common mode voltage using the open-end winding configuration for the induction motor. The switching strategy presented in this paper, does not generate any alternating common mode voltages in the drive system and hence the electrostatic coupling of the common mode voltage, which results in the bearing currents and the leakage currents, is avoided. The proposed scheme is devoid of neutral point voltage fluctuations and does not require neutral point clamping diodes, when compared to the common mode elimination scheme based on the conventional three-level inverter topology. Also, the present scheme uses a single dc-link with half the voltage compared to the conventional three-level inverter based scheme.

The nearest three virtual space vector PWM - a modulation for the comprehensive neutral-point balancing in the three-level NPC inverter

Abstract: This letter presents a new modulation approach for the complete control of the neutral-point voltage in the three-level three-phase neutral-point-clamped voltage source inverter. The new modulation approach, based on the virtual space vector concept, guarantees the balancing of the neutral-point voltage for any load (linear or nonlinear) over the full range of converter output voltage and for all load power factors, the only requirement being that the addition of the output three-phase currents equals zero. The implementation of the proposed modulation is simple according to the phase duty-ratio expressions presented. These expressions are only dependent on the modulation index and reference vector angle. The performance of this modulation approach and its benefits over other previously proposed solutions are verified experimentally.

A new control structure for grid-connected LCL PV inverters with zero steady-state error and selective harmonic compensation

Abstract: The PI current control of a single-phase inverter has well known drawbacks: steady-state magnitude and phase error and limited disturbance rejection capability. When the current controlled inverter is connected to the grid, the phase error results in a power factor decrement and the limited disturbance rejection capability leads to the need of grid feed-forward compensation. However the imperfect compensation action of the feed-forward control results in high harmonic distortion of the current and consequently noncompliance with international standards. In this paper a new control strategy aimed to mitigate these problems is proposed. Stationary-frame generalized integrators are used to control the fundamental current and to compensate the grid harmonics providing disturbance rejection capability without the need of feed-forward grid compensation. Moreover the use of a grid LCL-filter is investigated with the proposed controller. The current control strategy has been experimentally tested with success on a 3 kW PV inverter.

Multilevel DC link inverter

Abstract: This paper presents a new class of multilevel inverters based on a multilevel dc link (MLDCL) and a bridge inverter to reduce the number of switches, clamping diodes, or capacitors. An MLDCL can be a diode-clamped phase leg, a flying-capacitor phase leg, or cascaded half-bridge cells with each cell having its own dc source. A multilevel voltage-source inverter can be formed by connecting one of the MLDCLs with a single-phase bridge inverter. The MLDCL provides a dc voltage with the shape of a staircase approximating the rectified shape of a commanded sinusoidal wave, with or without pulsewidth modulation, to the bridge inverter, which in turn alternates the polarity to produce an ac voltage. Compared with the cascaded H-bridge, diode-clamped, and flying-capacitor multilevel inverters, the MLDCL inverters can significantly reduce the switch count as well as the number of gate drivers as the number of voltage levels increases. For a given number of voltage levels m, the required number of active switches is 2/spl times/(m-1) for the existing multilevel inverters but is m+3 for the MLDCL inverters. Simulation and experimental results are included to verify the operating principles of the MLDCL inverters.

Adaptive inductive power supply

Abstract: A contactless power supply has a dynamically configurable tank circuit powered by an inverter. The contactless power supply is inductively coupled to one or more loads. The inverter is connected to a DC power source. When loads are added or removed from the system, the contactless power supply is capable of modifying the resonant frequency of the tank circuit, the inverter frequency, the inverter duty cycle or the rail voltage of the DC power source.

Microgrid power quality enhancement using a three-phase four-wire grid-interfacing compensator

Abstract: This paper presents a three-phase four-wire grid-interfacing power quality compensator for microgrid applications. The compensator is proposed for use with each individual distributed generation (DG) system in the microgrid and consists of two four-phase-leg inverters (a shunt and a series), optimally controlled to achieve an enhancement of both the quality of power within the microgrid and the quality of currents flowing between the microgrid and the utility system. During utility grid voltage unbalance, the four-phase-leg compensator can compensate for all the unwanted positive-, negative-, and zero-sequence voltage-current components found within the unbalanced utility. Specifically, the shunt four-leg inverter is controlled to ensure balanced voltages within the microgrid and to regulate power sharing among the parallel-connected DG systems. The series inverter is controlled complementarily to inject negative- and zero-sequence voltages in series to balance the line currents, while generating zero real and reactive power. During utility voltage sags, the series inverter can also be controlled using a newly proposed flux-charge current-limiting algorithm to limit the flow of large fault currents between the micro- and utility grids. The performance of the proposed compensator has been verified in simulations and experimentally using a laboratory prototype.

Comparison of traditional inverters and Z-source inverter for fuel cell vehicles

Abstract: In This work, three different inverters: traditional PWM inverter, DC/DC boosted PWM inverter, and Z-source inverter for fuel cell vehicles were investigated. Total switching device power of each of these inverters was calculated. For purposes of comparison, an example of the total switching device power, requirement of passive components, efficiency, and the constant power speed ratio of the different inverters powered by the same fuel cell and loaded by the same motor were conducted. This comparison shows that the Z-source inverter is very promising for fuel cell vehicles.

Predictive current control of voltage-source inverters

Abstract: A new predictive current controller for a voltage-source inverter is presented in this paper. Practical aspects of realizing the new controller in a system with a digital signal processor (DSP) are considered. Delays introduced by measurements are considered and an improved algorithm with one-period prediction of current is presented. The controller was realized in an experimental system with DSP and field-programmable gate array circuits. Results of the simulations and experiments are presented.

A novel concept of a multiphase, multimotor vector controlled drive system supplied from a single voltage source inverter

Abstract: Since variable speed electric drive systems are supplied from power electronic converters, it is possible to utilize ac machines with a phase number higher than three. It is shown in the paper, using general theory of electrical machines, that an increase of the stator phase number to at least five (or more) enables completely independent vector control of two (or more) multiphase machines that are supplied from a single current-controlled voltage source inverter. In order to achieve such an independent control it is necessary to connect multiphase stator windings of the machines in series and perform an appropriate phase sequence transposition. The concept is equally applicable to any multiphase ac machine type and its major advantage, compared to an equivalent multimotor three-phase drive system, is the saving of a certain number of inverter legs. The actual saving depends on the number of phases. The concept is introduced using an n-phase induction machine as the starting point and further analysis is restricted to an odd number of phases, for the reason explained in the paper. Classification of all the possible cases that may arise is given, followed by presentation of connection diagrams for selected phase numbers. Detailed verification of the proposed concept is provided by simulating the operation of a seven-phase three-motor drive system, controlled using indirect rotor flux oriented control principles. Some preliminary experimental results, which confirm the feasibility of a two-motor series-connected drive system, are included as well. The main advantages and drawbacks of the concept, when compared with an equivalent three-phase multimotor drive system, are finally addressed.

Z-source inverter for motor drives

Abstract: This paper presents a Z-Source inverter system and control for general-purpose motor drives. The Z-source inverter system employs a unique LC network in the DC link and a small capacitor on the AC side of the diode front end. By controlling the shoot-through duty cycle, the Z-source can produce any desired output AC voltage, even greater than the line voltage. As a result, the new Z-source inverter system provides ride-through capability under voltage sags, reduces line harmonics, improves power factor and reliability, and extends output voltage range. Analysis, simulation, and experimental results will be presented to demonstrate these new features.

Maximum constant boost control of the Z-source inverter

Abstract: This paper proposes two maximum constant boost control methods for the Z-source inverter, which can obtain maximum voltage gain at any given modulation index without producing any low-frequency ripple that is related to the output frequency. Thus the Z-network requirement will be independent of the output frequency and determined only by the switching frequency. The relationship of voltage gain to modulation index is analyzed in detail and verified by simulation and experiment.

Investigating an LCL load resonant inverter for inductive power transfer applications

Abstract: A inductor/capacitor/inductor load resonant inverter is investigated for inductive power transfer applications. The inverter uses a variable frequency controller and operates in discontinuous current mode. The steady state operation of this system is determined by a power flow balance between the inverter and the resonant tank. The results are used to design a system to achieve maximum power transfer.

Design and performance of a passive EMI filter for use with a voltage-source PWM inverter having sinusoidal output voltage and zero common-mode voltage

Abstract: This paper deals with integrating a small-sized passive electromagnetic interference (EMI) filter with a voltage-source pulse-width modulated (PWM) inverter. The purpose of the filter is to eliminate both high-frequency common-mode and normal-mode voltages from the three-phase output voltages of the inverter. A laboratory system consisting of a 5-kVA inverter, a 3.7-kW induction motor, and a specially-designed passive EMI filter was constructed to verify the viability and effectiveness of the filter. As a result, both line-to-line and line-to-neutral output voltages look purely sinusoidal as if the inverter were an ideal three-phase variable-voltage, variable-frequency power supply when viewed from the motor terminals. This results in a complete solution to serious EMI issues related to high-frequency common-mode and normal-mode voltages produced by the PWM inverter.

Optimal common-mode Voltage reduction PWM technique for inverter control with consideration of the dead-time effects-part I: basic development

Abstract: The objective of this paper is to investigate the optimal common-mode voltage reduction pulsewidth modulation (PWM) technique when dead-time effect is taken into account. The effect of dead time on common-mode voltage for inverter control and the associated solution are discussed. Based upon these results, an optimal common-mode voltage reduction PWM technique, which requires no extra voltage/current sensors and compensation mechanism while not being affected by the dead time, is recommended. The common-mode voltage can be reduced to one-third for the inverter with diode front end, which is widely used in industry. Intensive measured results are presented to fully support the claims.

Development of a novel wind turbine simulator for wind energy conversion systems using an inverter-controlled induction motor

Abstract: A wind turbine simulator for wind energy conversion systems has been developed with a view to design, evaluate, and test of actual wind turbine drive trains including generators, transmissions, power-electronic converters and controllers. The simulator consists of a 10-hp induction motor (IM) which drives a generator and is driven by a 10-kW variable speed drive inverter and real-time control software. In this simulator, a microcontroller, a PC interfaced to LAB Windows I/O board, and an IGBT inverter-controlled induction motor are used instead of a real wind turbine to supply shaft torque. A control program based on C language is developed that obtains wind profiles and, by using turbine characteristics and rotation speed of IM, calculates the theoretical shaft torque of a real wind turbine. Comparing with this torque value, the shaft torque of the IM is regulated accordingly by controlling stator current demand and frequency demand of the inverter. In this way, the inverter driven induction motor acts like a real wind turbine to the energy conversion system. The drive is controlled using the measured shaft torque directly, instead of estimating it as conventional drives do. The experimental results of the proposed simulator show that this scheme is viable and accurate. This paper reports the operating principles, theoretical analyses, and test results of this wind turbine simulator.

Calculation of circulating bearing currents in machines of inverter-based drive systems

Abstract: The high-frequency circulating bearing current that may occur in machines of inverter-based drive systems can be described by an eddy-current model. The parameters of an equivalent circuit are derived from the model. The ratio between bearing current and common-mode current amplitudes for different machines is calculated. The theoretical maximum ratio is about 0.35. Copper loops applied for bearing current measurement may decrease the circulating bearing currents up to almost 40%

Inverter apparatus connected to a plurality of direct current power sources and dispersed-power-source system having inverter apparatus linked to commercial power system to operate

Abstract: An inverter apparatus (4) includes a plurality of converters (5A-5D) each receiving a direct current power from respective plurality of solar cell arrays (2A-2D) having different output voltage ranges, and an inverter (6) transforming the direct current power from the plurality of converters (5A-5D) into an alternating current power and allowing the alternating current power to reversely flow into a commercial power system (10). The plurality of converters (5A-5D) have different voltage input ranges corresponding to the output voltage ranges of the plurality of solar cell arrays (2A-2D), and each control, based on a pulse frequency modulation control signal received from a corresponding converter control unit, an output voltage of corresponding one of the plurality of solar cell arrays (2A-2D), so that an output power from corresponding one of the plurality of solar cell arrays (2A-2D) becomes maximum.

Motor driving apparatus

Abstract: A motor driving apparatus comprises an inverter circuit for converting an output voltage of a power supply into a three-phase AC and outputting the same to the brushless motor; a rotor position estimation unit for estimating a rotor position of the brushless motor; and an inverter control unit for controlling the inverter circuit so that the brushless motor is driven by a current based on the estimated rotor position. The inverter control unit determines an advance angle of the current supplied to the brushless motor with respect to the estimated rotor position so as to minimize a deviation between a command rpm and an actual rpm. Therefore, it is possible to perform stable weak field control for the brushless motor, independently from the input voltage of the inverter circuit, without using predetermined control variables such as table values.

Power quality from multiple grid-connected single-phase inverters

Abstract: This paper reports on a study into the aggregate power quality from multiple grid connected inverters. Measurements are presented for individual single-phase inverters generating into the low voltage network under a range of operational conditions, and for groups of similar converters connected at the same point on the network. Some results from the modeling of multiple inverter interaction are also presented. Particular attention is given to power factor, the harmonic content of the generated currents, and dc injection.

Organic complementary-like inverters employing methanofullerene-based ambipolar field-effect transistors

Abstract: We demonstrate a complementary-like inverter comprised of two identical ambipolar field-effect transistors based on the solution processable methanofullerene [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The transistors are capable of operating in both the p- and n-channel regimes depending upon the bias conditions. However, in the p-channel regime transistor operation is severely contact limited. We attribute this to the presence of a large injection barrier for holes at the Au∕PCBM interface. Despite this barrier the inverter operates in both the first and third quadrant of the voltage output versus voltage input plot exhibiting a maximum gain in the order of 20. Since the inverter represents the basic building block of most logic circuits we anticipate that other complementary-like circuits can be realized by this approach.

A novel hybrid isolated generating system based on PV fed inverter-assisted wind-driven induction Generators

Abstract: Isolated renewable energy systems based on hybrid wind-solar sources are considered as feasible and reliable options instead of wind-diesel systems. An isolated hybrid scheme employing a simple three-phase square-wave inverter to integrate a photovoltaic array with a wind-driven induction generator has been proposed for the first time. A dynamic mathematical model of the hybrid scheme with variables expressed in d-q synchronous reference frame has been developed. The model is implemented in the power system blockset platform and a comparison has been made between transients simulated and transients obtained in an experimental prototype. Close agreement between experimental and the simulated waveforms has been observed, which validates the model.

Matrix converters

Abstract: This paper deals with the vector-controlled MCT matrix converter induction motor drive with minimized commutation time and enchanced waveform quality. It also deals with the design, construction, and testing of a 10-kVA three-phase to three-phase matrix converter induction motor drive. The converter has been built using discrete 65 A metal-oxide-semiconductor (MOS) controlled thyristors (MCTs). The commutation time has been minimized to avoid any unnecessary waveform distortion, particularly at low demanded output voltages. This minimization gives the matrix converter superior waveform quality in comparison to a conventional inverter and maximizes the available converter output voltage before over modulation is required. The converter is vector controlled and has been tested using a 12-hp induction motor. Full results of these tests are presented.

Dual-inverter control strategy for high-speed operation of EV induction motors

Abstract: An integrated starter/alternator (ISA) is normally designed to have high pole structure (10-14 poles) for high starting torque. However, its back electromotive force (EMF) at the peak revolutions per minute should be less than its battery voltage for the power flow control. For example, the back-EMF of a 12-pole ISA should be 42 V at 6000 r/min. These types of conflicting requirements lead to a nonclassical motor design that has extremely large field-weakening range (8:1/spl sim/10:1). In this paper, we are considering the use of an induction machine instead of a permanent synchronous machine. As an idea for solving the voltage limit problem, two inverters are utilized with an objective of sharing the required voltage. The secondary inverter only takes care of the reactive voltage component that grows very fast in high-speed operation. Therefore, an extra voltage source is not required for the secondary inverter. Only a capacitor bank suffices for the secondary inverter.

Inverter control methodology for distributed generation sources connected to a utility grid

Abstract: The present invention provides an improved control methodology for maximum power point tracking (MPPT), anti-islanding, and output current regulation for distributed generation sources connected to a utility grid The control includes enhancements for MPPT and regulating the inverter output-current that is sourced into the utility grid In addition, the functions associated with MPPT, anti-islanding detection and output current regulation are integrated together; the MPPT algorithm operates in conjunction with the anti-islanding detection, and the output current regulation operates in conjunction with the MPPT algorithm

Performance of diagnosis methods for IGBT open circuit faults in voltage source active rectifiers

Abstract: Fault diagnosis of electrical drives is becoming more and more important today, since variable speed drives have become industrial standard in many applications. As an integral part of the drive, many faults occur within the inverter. One possible fault within the inverter is an open circuit transistor fault, whose diagnosis is subject of this paper. The practical performances of several open-circuit fault diagnostic methods are tested in simulation and experiment. An overview of the different strategies is given, including the algorithms used to localize the open transistor. Simulation results are presented and show different capabilities of each diagnostic strategy in terms of effectivity and false alarm resistivity for a voltage source inverter used as an active rectifier. The existing methods are further developed and adapted to a closed loop controlled active rectifier. An experimental setup in the laboratory is used to validate simulation results. Typical detection results are presented including time-to-detection measurements.

Performance representation of variable-speed compressor for inverter air conditioners based on experimental data

Abstract: Variable speed control of compressors is one of the best methods to regulate the capacity of heat pumps and air conditioners. An analysis is conducted for modeling the variable speed compressor for simulation of inverter air conditioner and heat pump. Having scattered the real operation performance of inverter compressor into infinite operation performance of constant speed compressor, the map-based method is utilized to fit the performance curves of inverter compressor. The model is built at the basic frequency and the map condition as the second-order function of condensation temperature and evaporation temperature. Then it is corrected by the compressor frequency as the second-order function of frequency and by the actual operating condition as the actual specific volume of the suction gas. This method is used to set up simulation models of three different compressors. Compared with the data provided by the compressor manufacturers, the average relative errors are less than 2, 3 and 4% for refrigerant mass flow rate, compressor power input and coefficient of performance (COP), respectively. This model of variable speed compressor is suitable for the simulation of inverter air conditioner and heat pump systems. Based on the experimental data and simulation model, the frequency at zero mass flow rate and power input at zero frequency are discussed and the relation between COP and compressor frequency is analyzed.

Development of a low cost fuel cell inverter system with DSP control

Abstract: In this paper, the development of a low cost fuel cell inverter system is detailed. The approach consists of a three-terminal push-pull dc-dc converter to boost the fuel cell voltage (48V) to /spl plusmn/200 VDC. A four switch [insulated gate bipolar transistor (IGBT)] inverter is employed to produce 120-V/240-V, 60-Hz ac outputs. High performance, easy manufacturability, lower component count, safety and cost are addressed. Protection and diagnostic features form an important part of the design. Another highlight of the proposed design is the control strategy, which allows the inverter to adapt to the requirements of the load as well as the power source (fuel cell). A unique aspect of the design is the use of the TMS320LF2407 DSP to control the inverter. Two sets of lead-acid batteries are provided on the high voltage dc bus to supply sudden load demands. Efficient and smooth control of the power drawn from the fuel cell and the high voltage battery is achieved by controlling the front end dc-dc converter in current mode. The paper details extensive experimental results of the proposed design on Department of Energy (DoE) National Energy Technology Laboratory (NETL) fuel cell.

Bearing Currents in Inverter-fed AC-motors

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Predictive current control of a voltage source inverter

Abstract: This work presents the application of predictive current control in a voltage source inverter. The method uses a discrete-time model of the system to predict the future value of the load current for all possible voltage vectors generated by the inverter. The voltage vector which minimizes the current error at the next sampling time is selected. The performance of the proposed predictive control method is compared with hysteresis and PWM control. The results show that the predictive method controls very effectively the load current and compares very well with the classical solutions.