Showing papers on "Inverter published in 2003"

Fault tolerant three-phase AC motor drive topologies; a comparison of features, cost, and limitations

Abstract: This paper compares the many fault tolerant three-phase ac motor drive topologies that have been proposed to provide output capacity for the inverter faults of switch short or open-circuits, phase-leg short-circuits, and single-phase open-circuits. Also included is a review of the respective control methods for fault tolerant inverters including two-phase and unipolar control methods. The output voltage and current space in terms of dq components is identified for each topology and fault. These quantities are then used to normalize the power capacity of each system during a fault to a standard inverter during normal operation. A silicon overrating cost factor is adopted as a metric to compare the relative switching device costs of the topologies compared to a standard three-phase inverter.

Direct repetitive control of SPWM inverter for UPS purpose

Abstract: A novel repetitive controller directly combined with an open loop SPWM inverter is presented in this paper. To cope with the high-resonant peak of the open loop inverter that may cause instability, a zero-phase-shift notch filter other than the inverse transfer function of the inverter or a conventional second-order filter is incorporated in the controller. The proposed method has good harmonic rejection and large tolerance to parameter variations. To further reduce the steady-state error, a low-pass-filter Q(z) algorithm is applied. The DC bias problem is also taken into consideration and solved with the repetitive controller itself. The method is implemented with a digital signal processor and achieves low THD% (1.4%-1.7%) with nonlinear loads and fast error convergence (3-5 fundamental periods). It proves to be a cost-effective solution for common UPS products where high-quality output voltage is more stressed than fast dynamic response.

A novel high-performance utility-interactive photovoltaic inverter system

Abstract: This paper presents a novel photovoltaic inverter that cannot only synchronize a sinusoidal AC output current with a utility line voltage, but also control the power generation of each photovoltaic module in an array. The proposed inverter system is composed of a half-bridge inverter at the utility interface and a novel generation control circuit which compensates for reductions in the output power of the system that are attributable to variations in the generation conditions of respective photovoltaic modules. The generation control circuit allows each photovoltaic module to operate independently at peak capacity, simply by detecting the output power of the system. Furthermore, the generation control circuit attenuates low-frequency ripple voltage, which is caused by the half-bridge inverter, across the photovoltaic modules. Consequently, the output power of the system is increased due to the increase in average power generated by the photovoltaic modules. The effectiveness of the proposed inverter system is confirmed experimentally and by means of simulation.

Output filter design for a grid-interconnected three-phase inverter

Abstract: Traditionally, LC filter is used for an inverter power supply. A grid-interconnected inverter, however, has some unique requirements that an LC filter may not be sufficient. This paper comprehensively discusses the design considerations of the output filter for the grid-interconnected inverter. Different passive damping filter solutions are compared and the optimized design guidelines are also proposed. Simulation results are provided to validate the design.

Control of a hybrid asymmetric multi-level inverter for competitive medium-voltage industrial drives

Abstract: In symmetric multilevel inverters, there is a tradeoff between the output quality and the reliability and efficiency of the converter. New asymmetric and hybrid solutions, using different voltages and devices in various parts of the inverter, promise significant improvements for medium-voltage industrial drives. This paper investigates such a hybrid asymmetric nine-level inverter. It consists of a three-phase three-level integrated gate-commutated thyristor inverter (main inverter), with a two-level insulated-gate bipolar transistor H-bridge (subinverter) in series with each phase. To keep the power part simple and the efficiency high, the subinverters have no feeding from the net and can only supply reactive power. This is a very interesting solution in terms of power quality, efficiency, reliability, and cost. But the nonsupplied intermediate-circuit capacitors form an unstable system. This paper proposes a control method to stabilize their voltages. Power balancing is guaranteed by varying the common-mode voltage, using an online nonlinear model-predictive controller. The controller predicts the system evolution as a function of the control inputs. A cost function of system and control quantities is iteratively minimized in real time, to find the optimal control to apply to the system. Simulations and measurements demonstrate stable behavior in steady state and during transients. Precharging of the nonsupplied capacitors is also an issue to consider. This paper proposes a startup method that charges them in parallel with the supplied ones, without any additional equipment. Measurements show its successful application in the proposed drive system.

A new single-phase five-level PWM inverter employing a deadbeat control scheme

Abstract: A single-phase five-level PWM inverter is presented to alleviate harmonic components of the output voltage and the load current. Operational principles with switching functions are analyzed. To keep the output voltage sinusoidal and to have the high dynamic performances even in the cases of load variations and the partial magnetization in filter inductor, the deadbeat controller is designed and implemented on a prototype. The validity of the proposed inverter is verified through simulation and experiments. To assess the proposed inverter, it is compared with the conventional single-phase three-level PWM inverter under the conditions of identical supply DC voltage and switching frequency. In addition, it is compared with the five-level cascaded PWM inverter.

Z-source inverter for adjustable speed drives

Abstract: This paper presents a Z-source inverter system and control for adjustable speed drives (ASD). The Z-source inverter employs a unique LC network to couple the inverter main circuit to 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 results, the new Z-source inverter system provides ride-through capability under voltage sags, reduces line harmonics, and extends output voltage range. Simulation results are presented to demonstrate the new features.

A discrete-time predictive current control for PMSM

Abstract: In this paper, a new predictive current controller for a permanent magnet synchronous motor (PMSM) considering delays is presented. In a full digital current control system for a PMSM, there are inevitable delays in calculating and applying the inverter output voltages to the motor terminals. A predictive current controller implemented in a full digital system has serious problems such as the oscillation and large overshoot. A discussion of compensation methods to cope with the nonlinearities of the real system is also presented. The proposed current controller has been analyzed, and the experimental results are shown to prove the feasibility and effectiveness of the proposed predictive current controller using a prototype 750 W PMSM servo drive system.

Sensorless speed and position control of synchronous machines using alternating carrier injection

Abstract: High frequency carrier injection is a promising approach solving high performance sensorless drive demands. Position control at low and zero speed is only possible using anisotropic effects considered in high-frequency models. The usually open loop carrier signal injection is impacted by nonlinear inverter properties like the dead-time effect. This paper discusses the influence of the dead time effect on the carrier signal excitation comparing alternating and revolving injection principles. To overcome disturbing effects an alternating injection procedure is proposed using a predefined injection angle. The approach reduces the effects of the inverter distortion voltages. As a result it is possible to track even small saliencies typical for surface mounted permanent magnet synchronous machines. For processing the high frequency current for position estimation, there is no additional hardware necessary within a standard drives with field oriented control. The paper presents theoretical analysis and experimental results.

Modeling, analysis, and implementation of parallel multi-inverter systems with instantaneous average-current-sharing scheme

Abstract: Parallel multi-inverter systems can be designed to have the advantages of expandable output power, improved reliability, and easy N+X redundancy operation. However, a current-sharing control scheme has to be employed to enable the inverters to share the load current equally. A multi-inverter system with instantaneous average-current-sharing scheme is presented in this paper. By introducing a disturbance source to represent all the sources that may cause current unbalances, a model of the system can be built. Some key issues are discussed based on the model, including stability of the current-sharing controller, impedance characteristics and voltage regulation. Three experimental 110 VAC/1.1 kVA inverters are built and paralleled to verify the theoretical predictions.

Control of cascaded multi-level inverters

Abstract: A new type of multilevel inverter is introduced which is created by cascading two three-phase three-level inverters using the load connection, but requires only one dc voltage source. This new inverter can operate as a seven-level inverter and naturally splits the power conversion into a higher-voltage lower-frequency inverter and a lower-voltage higher-frequency inverter. This type of system presents particular advantages to Naval ship propulsion systems which rely on high power quality, survivable drives. New control methods are described involving both joint and separate control of the individual three-level inverters. Simulation results demonstrate the effectiveness of both controls. A laboratory set-up at the Naval Surface Warfare Center power electronics laboratory was used to validate the proposed joint-inverter control. Due to the effect of compounding levels in the cascaded inverter, a high number of levels are available resulting in a voltage THD of 9% (without filtering).

Design optimization of a single phase inverter for photovoltaic applications

Abstract: The objective for this paper is to present a novel inverter topology for photovoltaic (PV) applications, in particular for the AC-module. A modified version of the inverter proposed by Shimizu et al. solves a major problem within the original topology; regeneration of transformer leakage energy. Also presented is a decomposition of the currents and voltages inside the inverter. The decomposition is used to derive the stress and power losses, and hereby developing a tool for optimizing the inverter in terms of efficiency and ratings. Finally, the developed tool is used to design an inverter. The annual European efficiency is calculated to 81.8% for a 160 W inverter, which is regarded as high for an inverter for AC-module applications, as long the cost can be kept low.

Analysis for the Effect of Inverter Ripple Current on Fuel Cell Operating Condition

Abstract: The effect of inverter ripple current on fuel cell stack performance and stack lifetime remains uncertain. This paper provides a first attempt to examine the impact of inverter load dynamics on the fuel cell. Since reactant utilization is known to impact the mechanical nature of a fuel cell, it is suggested that the varying reactant conditions surrounding the cell govern. at least in part the lifetime of the cells. This paper investigates these conditions through the use of a dynamic model for the bulk conditions within the stack, as well as a one-dimensional model for the detailed mass transport occurring within the electrode of a cell. These two independent modeling approaches are used to verify their respective numerical procedures. in this work, the inverter load is imposed as a boundary condition to the models. Results show the transient behavior of the reactant concentrations within the stack, and of the mass diffusion within the electrode under inverter loads with frequencies between 30 Hz and 1250 Hz.

Voltage balancing control of diode-clamped multilevel rectifier/inverter systems

Abstract: This paper presents a new voltage balancing control for the diode-clamped multilevel rectifier/inverter system. A complete analysis of the voltage balance theory for a 5-level back-to-back system is given. The analysis is based on fundamental frequency switching control and then extended to pulse-width modulation. The method involves obtaining optimal switching angles; a process which is described in detail in this paper. The proposed control strategy regulates the DC bus voltage, balances the capacitors, and decreases the harmonic components of the voltage and current. Simulation and experimental results demonstrate the validity of the optimizing method and control theory.

A fixed-frequency quasi-sliding control algorithm: application to power inverters design by means of FPGA implementation

Abstract: In this paper, a fixed-frequency quasi-sliding control algorithm based on switching surface zero averaged dynamics (ZAD) is reported. This algorithm is applied to the design of a buck-based inverter, and implemented in a laboratory prototype by means of a field programmable gate array (FPGA), taking into account processing speed versus computational complexity trade-off. Three control laws, namely sliding control (SC), fixed-frequency quasi-sliding ZAD and PWM-based control have been experimentally tested to highlight the features of the proposed algorithm. According to the experimental results presented in the paper, the ZAD algorithm fulfills the requirement of fixed switching frequency and exhibits similar robustness properties in the presence of perturbations to those of sliding control mode.

Dynamic NBTI of PMOS transistors and its impact on device lifetime

Abstract: We report a new NBTI phenomenon for p-MOSFETs with ultra thin gate oxides. We demonstrate that in a CMOS inverter circuit, the interface traps generated under NBTI stressing in a p-MOSFET (corresponding to the "high" output state of the inverter) are subsequently passivated when the gate to drain voltage switches to positive (corresponding to the "low" output state of the inverter). As a result, it was found that this "Dynamic" NBTI (DNBTI) operating in a CMOS inverter circuit prolongs significantly the device lifetime while the conventional "static" NBTI (SNBTI) underestimates the device lifetime. Furthermore, the DNBTI effect is dependent on temperature and gate oxide thickness, but independent of operation frequency. A physical model is proposed for DNBTI that involves the interaction between hydrogen and silicon dangling bonds. This finding has significant impact on the determination of maximum operation voltage as well as lifetime projection for future scaling of CMOS devices.

A general space vector PWM control algorithm for multilevel inverters

Abstract: To solve the problem of computational complexity in multilevel inverters due to the large number of space vectors and redundant switching states, a simple and general space vector PWM algorithm is proposed. Based on this algorithm, the location of the reference voltage vector can be easily determined and the calculation of dwell times becomes very simple. More importantly, the proposed algorithm is general and can be directly applied to the cascaded H-bridge inverter of any voltage levels. In addition, a new switching sequence, large-small alternation (LSA), is proposed for the minimization of total harmonic distortion. To verify the algorithms, a 7-level cascaded H-bridge inverter drive system was constructed and experimental results are provided.

Inverter nonlinearity effects in high frequency signal injection-based, sensorless control methods

Abstract: An analysis of pulsewidth-modulation inverter nonlinearities influencing high-frequency carrier-signal voltage injection for saliency-tracking-based rotor/flux position estimation is presented in this paper. Distortion of the injected carrier voltage caused by the nonlinear behavior of the inverter has been reported to cause errors in the estimated rotor/flux position. Though a number of techniques have been developed to compensate for inverter nonlinearities, they have not been proven to be effective when a high-frequency low-magnitude voltage needs to be generated. Both the origins of the distortion as well as the requirements for compensation methods to be effective when producing such high-frequency voltages will be established in this paper.

Control of small distributed energy resources

Abstract: A method of controlling the output inverter of a microsource in a distributed energy resource system is disclosed. Embodiments of the invention include using unit or zone power controllers that reduce the operating frequency of the inverter to increase its unit output power. Preferred embodiments includes methods wherein the inverter reaches maximum output power and minimum operating frequency at the same time, and further comprising using a voltage controller implementing a voltage vs. reactive current droop. Other aspects of this embodiment relate to an inverter that implements such methods, and a microsource containing such an inverter. These methods can be extended to control inverters in a plurality of microsources, organized in a single zone or in a plurality of zones.

Space vector PWM techniques for dual three-phase AC machine: analysis, performance evaluation and DSP implementation

Abstract: The major drawback of dual three-phase ac machines (6phiM), when supplied by a voltage-source inverter (VSI), is the occurrence of extra harmonic currents. These extra currents circulate only in the stator windings and cause additional losses. One solution to reduce their amplitude is to act on the supply side using dedicated pulsewidth modulation (PWM) control strategies. The aim of this paper is to investigate new space-vector PWM (SVPWM) techniques suitable for 6phiM and to perform a detailed analysis and a performance evaluation. The proposed performance criteria, specific to VSI-fed 6phiM, lead to analytical formulas and graphics, which aid the design of high-performance PWM techniques and demonstrate the superiority of the proposed SVPWM techniques. Experimental results carried out on a 15-kW prototype machine and using a low-cost fixed-point TMS320F240 digital signal processor are given and discussed

Reduced common-mode modulation strategies for cascaded multilevel inverters

Abstract: This paper presents modulation strategies for cascaded multilevel inverters that substantially eliminate common-mode voltage on the output phases. The paper begins by developing generic multilevel inverter reference waveforms that use only "allowed" space vectors to achieve reduced common-mode voltage. A graphical technique is then proposed that allows various carrier disposition modulation strategies for a diode-clamped inverter to be converted to equivalent modulation of a cascaded inverter for any fundamental reference waveform. This graphical technique is confirmed for both alternative phase opposition disposition and phase disposition equivalent modulation of a cascaded inverter, and is then used to create reduced common-mode modulation strategies for cascaded inverters from their equivalent counterparts for diode-clamped inverters under both continuous and discontinuous switching conditions. The strategies have been confirmed by both simulation and experimental results obtained using a cascaded five-level inverter.

An approach to eliminating high-frequency shaft voltage and ground leakage current from an inverter-driven motor

Abstract: This paper proposes a small-sized passive electromagnetic interference (EMI) filter for the purpose of eliminating high-frequency shaft voltage and ground leakage current from an ac motor driven by a voltage-source pulsewidth-modulation inverter. The filter requires access to the neutral point of the motor. A common-mode inductor is connected between the inverter and the motor. The neutral point of the motor is connected to the dc-bus midpoint via a resistor. The dc-bus midpoint is created by using two capacitors in series across the dc positive and negative buses. This unique circuit configuration makes the common-mode inductor effective in reducing the common-mode voltage appearing at the motor terminals. The validity and effectiveness of the EMI filter is verified by experimental results obtained from a 5-kVA laboratory system.

Space vector pulse width modulation of three-level inverter extending operation into overmodulation region

Abstract: Multilevel voltage-fed inverters with space vector pulse width modulation have established their importance in high power high performance industrial drive applications. The paper proposes an overmodulation strategy of space vector PWM of a three-level inverter with linear transfer characteristic that easily extends from the undermodulation strategy previously developed by the authors for neural network implementation. The overmodulation strategy is very complex because of large number of inverter switching states, and hybrid in nature, that incorporates both undermodulation and overmodulation algorithms. The paper describes systematically the algorithm development, system analysis, DSP based implementation, and extensive evaluation study to validate the modulator performance. The modulator takes the command voltage and angle information at the input and generates symmetrical PWM waves for the three phases of an IGBT inverter that operates at 1.0 kHz switching frequency. The switching states are distributed such that the neutral point voltage always remains balanced. An open loop volts/Hz controlled induction motor drive has been evaluated extensively by smoothly varying the voltage and frequency in the whole speed range that covers both undermodulation and overmodulation (nearest to square-wave) regions, and performance was found to be excellent. The PWM algorithm can be easily extended to vector-controlled drive. The algorithm development is again fully compatible for implementation by a neural network.

Molecular-junction-nanowire-crossbar-based inverter, latch, and flip-flop circuits, and more complex circuits composed, in part, from molecular-junction-nanowire-crossbar-based inverter, latch, and flip-flop circuits

Abstract: Methods for implementing familiar electronic circuits at nanoscale sizes using molecular-junction-nanowire crossbars, and nanoscale electronic circuits produced by the methods. In one embodiment of the present invention, a 3-state inverter is implemented. In a second embodiment of the present invention, two 3-state inverter circuits are combined to produce a transparent latch. The 3-state inverter circuit and transparent-latch circuit can then be used as a basis for constructing additional circuitry, including master/slave flip-flops, a transparent latch with asynchronous preset, a transparent latch with asynchronous clear, and a master/slave flip-flop with asynchronous preset. 3-state inverters can thus be used to compose latches and flip-flops, and latches and flip-flops can be used, along with additional Boolean circuitry, to compose a wide variety of useful, state-maintaining circuits, all implementable within molecular-junction-nanowire crossbars by selectively configuring junctions within the molecular-junction-nanowire crossbars.

Monopolar DC to bipolar DC to AC converter

Abstract: This invention improves the performance and lowers the cost of DC to AC inverters and the systems where these inverters are used. The performance enhancements are most valuable in renewable and distributed energy applications where high power conversion efficiencies are critical. The invention allows a variety of DC sources to provide power thru the inverter to the utility grid without a transformer and at very high power conversion efficiencies. The enabling technology is a novel inverter circuit topology where the DC source is connected directly to the positive bus of the DC to AC converter and where a negative bus is generated from the positive bus with a flyback converter. The inverter power topology does include or require a transformer. The AC inverter output configuration can be either single-phase or three-phase. The AC inverter output can be either utility interactive or directly supply loads.

A new active common-mode EMI filter for PWM inverter

Abstract: This paper presents a new active common-mode electromagnetic interference (EMI) filter for the pulse-width modulation (PWM) inverter application. The proposed filter is based on the current sensing and compensation circuit and it utilizes a fast transistor amplifier for the current compensation. The amplifier utilizes an isolated low-voltage DC power supply for its biasing and it is possible to construct the active filter independent of the source voltage of the equipment. Thus the proposed active filter can be used in any application regardless of its working voltage. The effectiveness of the proposed circuit has been verified by experimental results.

Dc to ac inverter with single-switch bipolar boost circuit

Abstract: This invention improves the performance and lowers the cost of DC to AC inverters and the systems where these inverters are used. The performance enhancements are most valuable in renewable and distributed energy applications where high power conversion efficiencies are critical. The invention allows a variety of DC sources to provide power thru the inverter to the utility grid or directly to loads without a transformer and at very high power conversion efficiencies. The enabling technology is a novel boost converter stage that regulates the voltage for a following DC to AC converter stage and uses a single semiconductor switching device. The AC inverter output configuration is either single-phase or three-phase.

High-fidelity PWM inverter for digital audio amplification: Spectral analysis, real-time DSP implementation, and results

Abstract: A complete digital audio amplifier has been developed, implemented and tested. The process is entirely computational, and the output load and filter are the only analog components in the system. The process makes use of digital signal processing and a switching power stage to provide both high fidelity and high efficiency, beginning with a digital audio data stream. The advantages of naturally-sampled pulse-width modulation (PWM) are discussed in depth, including spectral analysis and comparisons to uniformly-sampled PWM. It is shown that natural PWM does not introduce audible distortion at switching frequencies consistent with power electronics practice. Interpolation methods for sample data conversion to natural PWM are discussed, and error analysis is presented based on Lagrange's Expansion Theorem. Noise-shaping processes are used to support high fidelity with practical values of time resolution. A counter conversion process enforces switching dead time in the inverter gate signals. The experimental full-bridge inverter implementation demonstrates that miniaturization is possible. A complete test system delivered more than 50 W into an 8 /spl Omega/ load with an efficiency of 80% and total harmonic distortion plus noise of 0.02%.

Three-level inverter configuration cascading two two-level inverters

Abstract: A power circuit configuration to realise three-level inversion is proposed. Three-level inversion is realised by connecting two two-level inverters in cascade, in the proposed configuration. An isolated DC power supply is used to supply each inverter in this power circuit. Each DC-link voltage is equal to half of the DC-link voltage in a conventional NPC (neutral point clamped) three-level inverter topology. Neutral point fluctuations are absent, and fast recovery neutral clamping diodes are not needed. The proposed inverter scheme produces 64 space-vector combinations distributed over 19 space-vector locations as compared to 27 combinations in a conventional three-level topology. The present power circuit can be operated as a two-level inverter in the range of lower modulation, by clamping one inverter to a zero state and by switching the other inverter. When compared to the H-bridge topology, this circuit needs one power supply less. A space vector based PWM scheme is used for the experimental verification of the proposed topology.

Bi-directional multi-port inverter with high frequency link transformer

Abstract: This invention is a multi-port power converter where all ports are coupled through different windings of a high frequency transformer. Two or more, and typically all, ports have synchronized switching elements to allow the use of a high frequency transformer. This concept and type of converter is known. This invention mitigates a number of limitations in the present art and adds new capabilities that will allow applications to be served that would otherwise not have been practical. A novel circuit topology for a four-quadrant AC port is disclosed. A novel circuit topology for a unidirectional DC port with voltage boost capabilities is disclosed. A novel circuit topology for a unidirectional DC port with voltage buck capabilities is disclosed. A novel circuit for a high efficiency, high frequency, bi-directional, AC semiconductor switch is also disclosed.