Showing papers on "Inverter published in 1989"

The resonant DC link converter-a new concept in static power conversion

Abstract: A novel approach to realizing efficient high-performance power converters is presented. The concept of a resonant DC link inverter has been proposed and realized with the addition of only one small inductor and capacitor to a conventional voltage source inverter circuit. The proposed technology is capable of switching almost an order of magnitude faster than state-of-the-art voltage source inverters at significantly improved efficiencies using the same family of devices. The topology is especially suitable for high-power applications using gate turn-off devices. A 4.5 kW inverter has been fabricated and tested extensively in the laboratory, and the superior characteristics of the resonant DC link topology have been verified. >

High-performance direct torque control of an induction motor

Abstract: A novel direct torque control method for an induction motor is presented which is quite different from field-oriented control. Improving the torque response of a large-capacity induction motor using two sets of three-phase inverters and an open-data induction motor is of special concern. Instantaneous voltage vectors applied by an inverter have redundancy characteristics which provide some flexibility for selecting the inverter switching modes. By using this switching freedom, control is achieved according to the following priorities: (1) high-speed torque control; (2) regulation of the primary flux; (3) decreasing the zero phase sequence current; and (4) minimization of the inverter switching frequency. Simulations and experiments have been carried out to verify the feasibility of this priority control, accompanied by comparisons with another control scheme. Torque frequency-response corner frequencies above 2000 Hz have been experimentally measured, and time constants of 4 ms have been achieved for rotor-speed step responses from -500 to 500 r/min. The peak transient torque during the step change is about 20 times the rate torque. >

Switching converter with pseudo-resonant DC link

Abstract: A pseudo-resonant DC link for coupling direct current from a DC source to an inverter includes a plurality of switches which are controlled so as to minimize switching loss in the DC link and in the inverter. The DC link includes a capacitor and an inductor coupled through controllable switches in a manner that momentarily reduces to zero the input voltage to the inverter each time that a switch in the inverter is commutated. The controllable switches in the DC link function to allow the capacitor to resonate through the inductor and then be recharged at the end of a commutation interval. The controllable switches in the DC link are timed to that switching generally occurs under conditions of zero current.

Zero-switching-loss inverters for high-power applications

Abstract: The development of zero switching loss inverters has attracted much interest for industrial applications. Two topologies for realizing zero switching losses in high-power converters are proposed. The actively clamped resonant DC link inverter uses the concept of a lossless active clamp to restrict voltage stresses to only 1.3-1.5 supply voltage. For applications demanding substantially better spectral performance, the resonant pole inverter (RPI), also called the quasi-resonant current mode inverter, is proposed as a viable topology. Using only six devices rated at supply voltage, this circuit transfers the resonant components to the AC side of each phase and thus requires additional inductor and capacitor (LC) components. On the other hand, the RPI is capable of true pulsewidth modulation (PWM) operation at high frequency as opposed to discrete pulse modulation operation found in resonant DC link invertors. >

Novel space vector based current controllers for PWM-inverters

Abstract: Two novel, simple control strategies for current-controlled pulse-width modulated (PWM) transistor inverters are presented. Both methods are based on the three-level hysteresis comparators which select appropriate inverter output voltage vectors via a switching electrically programmable read-only memory (EPROM) table. The first controller works with current components represented in a stationary coordinate system (AC components) and the second with components represented in a rotated (field-oriented) coordinate system (DC components). The theoretical principles of these methods are discussed. The results of a comparative study, which illustrates the performance of the proposed controller in comparison to the most popular scheme (based on three independent two-level hysteresis comparators), are presented. >

Control strategies for direct torque control using discrete pulse modulation

Abstract: A scheme for direct torque control of AC machines using discrete pulse modulated inverters, such as the resonant DC link inverter, is presented. A unique feature of the control method presented is that only one current sensor in the DC link is required. Excellent control of torque, stator flux and motor current waveshapes is obtained without affecting the high dynamic performance associated with the direct self-control of machines. A control that does not use the zero voltage vector is defined, and an observer is proposed for estimation of the motor current using only one current sensor in the DC link. A direct bang-bang (sliding mode) torque controller is then derived on the basis of this current observer. Experimental verification of simulation results on a resonant DC link inverter drive with a switching frequency of 27 kHz is included. The inverter switching scheme is implemented using a real-time Motorola DSP56000 digital signal processor-based controller. >

Design aspects of synchronous PWM rectifier-inverter systems under unbalanced input voltage conditions

Abstract: A complete analysis of a synchronous front-end PWM rectifier-inverter system under unbalanced input voltage conditions is presented. The analysis includes the harmonic assessment of input/output current and voltage waveforms. It is shown both theoretically and experimentally that input voltage unbalance generates uncharacteristic low-frequency harmonic components in the input and output currents. Special emphasis is given to the generation of a DC component in the inverter output voltage in the case in which the output frequency is twice the input frequency. System design curves for different degrees of unbalance for all major system components are reported. Key predicted results are confirmed experimentally. >

Combined low-cost, high-efficient inverter, peak power tracker and regulator for PV applications

Abstract: A novel compound power converter that serves as a DC-to-AC inverter, maximum power point tracker (MPPT), and battery charger for stand-alone photovoltaic (PV) power systems is introduced. A theoretical analysis of the proposed converter is performed, and the results are compared with experimental results obtained from a 1.5 kW prototype. The overall cost of PV systems can thus be reduced by using load management control and efficiency-optimization techniques. Power flow through the converter is controlled by means of a combination of duty cycle and output frequency control. With load management, large domestic loads, such as single phase induction motors for water pumping, hold-over refrigerators, and freezers, can be driven by day at a much higher energy efficiency. This is due to the high efficiency of the inverter with high insolation, and because the inverter uses the energy directly from the solar array. The battery loss component is thus reduced. >

Resonant DC/DC converter with class-E inverter and class-E rectifier

Abstract: A new type of high-frequency high-efficiency resonant DC/DC converter is proposed, analyzed, and verified experimentally. It is called a class-E converter because it consists of a class-E inverter and a class-E rectifier. The class-E rectifier acts as an impedance inverter and is compatible with the class-E inverter. Consequently, the converter can operate with load resistances from a full load to infinity while maintaining zero-voltage switching of the transistor in the inverter and the diode in the rectifier. It operates safely with a short circuit at the output. Because of a high value of the load quality factor Q/sub 1/, a narrow frequency range suffices to regulate the DC output voltage over the whole load range. The measured relative bandwidth was delta f/f/sub min/=42.2% as the load resistance was varied from 70 Omega to open circuit. The measured efficiency at the full load was 89% with a 9 W output power at 1 MHz. A family of class-E/sup 2/ resonant DC/DC power converters is given. The possibility of reduction of class-E/sup 2/ converters to lower-order resonant and pulse-width-modulation converters is shown. >

Derivation of motor line-current waveforms from the DC-link current of an inverter

Abstract: A technique for reconstructing squirrel cage motor line currents using information from a single current transducer in the DC-link of an inverter is presented. All the instantaneous motor line currents can be reconstructed with a bandwidth limited to half the inverter switching frequency. These waveforms are used to produce a high-bandwidth signal, proportional to the scalar magnitude of the line current, and which is suitable for motor control purposes. A simple, low-cost implementation of the scheme demonstrates accurate results in a practical motor drive.

BOLD: The Boulder Optimal Logic Design system

Abstract: The BOLD (Boulder-Optimal Logic Design) system is a set of software tools that optimally transform an arbitrary combinational logic description into a standard cell, gate array, or complex CMOS gate technology. The design philosophy and structure of BOLD are summarized, and the various software tools and algorithms that comprise the BOLD system are described. The input to BOLD is either a behavioral circuit description or a Logical Interchange Format (LIF) file. The output is a netlist consisting of gates from a user supplied library or a netlist of CMOS complex gates. The philosophy of BOLD is contrasted with that of other available synthesis programs (most notably MIS and YLE), and the output of each is compared on a small set of examples. >

PWM-CSI inverter for induction motor drives

Abstract: The authors discuss a number of issues involved in designing a current source inverter system for a large induction motor drive. Using two modulation techniques-selected harmonic elimination in the upper frequency range and trapezoidal modulation in the lower frequency range-control of voltage, current, and torque harmonics is achieved while limiting the GTO switching frequency to 180 Hz. Each modulation range is divided into a number of subranges to exploit the available switching capacity and to avoid harmonic resonances involving the capacitor and the motor inductance. In addition to the development of basic principles, the authors include simulation waveforms and test results from a laboratory experimental system. >

Parallel resonant DC link circuit-a novel zero switching loss topology with minimum voltage stresses

Abstract: A parallel-resonant DC link (PRDCL) circuit topology is presented as a way to realizing zero-switching-loss, DC-AC high switching frequency power conversion. The circuit is used as an interface between DC voltage supply and the voltage-source PWM (pulse-width-modulated) inverter. It provides a short zero-voltage period in the DC link of the inverter to allow zero-voltage switching to take place in the PWM inverter. The peak voltage stress on the PWM inverter switches is limited to the DC supply voltage. Another significant advantage of the proposed circuit is that the inverter can be controlled by the conventional PWM strategy. The circuit is systematically analyzed, and its operation principle is explained in detail. Design considerations and formulae are also presented. A complete zero-voltage-switching DC-AC converter system consisting of the proposed circuit and the PWM inverter is simulated on computer. >

Control of a switched-reluctance aircraft engine starter-generator over a very wide speed range

Abstract: An electric direct-drive gearless starter-generator has been designed and built for an aircraft-engine application. The system is based on a switched reluctance motor, which was chosen for its simplicity, ruggedness, high-speed capability, and efficiency. A description is given of motor control system algorithms and hardware, which are used to control the motor over its operating speed range from standstill to 48000 RPM in both monitoring and generating modes. Novel features of the starter-generator control system are a closed-loop regulator which controls the amount of firing angle advance to maintain optimum torque production at high speed, and a hardware-based digital commutation controller which generates phase firing pulses for the inverter on the basis of machine rotor angle, pulse width, and pulse advance. >

Discrete pulse modulation strategies for high-frequency inverter systems

Abstract: High-performance, high-frequency inverter systems for UPS (uninterruptible power system) applications cannot be easily realized using conventional hard-switched PWM inverter topologies. Adoption of typical soft-switched inverters such as the resonant DC link inverter, require the use of discrete pulse modulation strategies. New controller structures are necessary to cope with stringent voltage regulation and distortion constraints in the presence of unbalanced and nonlinear loads. A controller that utilizes a load current feedforward strategy with a cost function current regulator to achieve excellent transient performance characteristics is presented. Voltage regulation is ensured using a synchronous frame regulator. Detailed simulation and experimental results verifying the concepts are presented. Although this work focuses on soft-switching inverters, the control concepts can be applied to conventional hard-switching inverters as well. >

Innovative Remedial Strategies for Inverter Faults in IPM Synchronous Motor Drives

Abstract: Interior permanent magnet (IPM) synchronous motors are used extensively in many industrial drives, and the development of fault-tolerant control techniques may extend their use to applications where high reliability, also in the flux-weakening region, is a key-feature. This paper proposes some innovative fault-remedial control strategies for failures occurring in the drive voltage inverter.

Ultrafast all-optical logic gates based on soliton trapping in fibers

Abstract: Ultrafast all-optical soliton-trapping logic gates, including an inverter, exclusive OR, and AND, are experimentally demonstrated in birefringent fibers The soliton-trapping logic gates are three terminal devices with orthogonally polarized inputs, phase-insensitive nonlinear operation, and switching energies of ~42 pJ Using a 02-THz bandpass filter, the contrast ratio for the exclusive-OR gate is ~8:1, but the output pulses are ~10 times broader than the input pulse width By widening the filter bandpass to 058 THz, an inverter is demonstrated with an ~4:1 contrast ratio and output pulses that can propagate as solitons in a fiber Numerical simulations show that the output from the inverter can be cascaded to other trapping gates

Modeling and Dynamic Performance of a Line-Commutated Photovoltaic Inverter System

Abstract: Interest in utility-interactive photovoltaic (PV) inverter systems has increased over the past decade and numerous central-station PV systems have been installed. It is anticipated that as PV system costs decrease, residential systems will be installed in increased numbers. Although a substantial amount of literature is available concerning the design, protection, safety, economics, and operating experience of residential and central-station PV systems, little information is available regarding their dynamic electrical characteristics and the computer modeling of these systems. Moreover, most of the available literature concerning modeling and/or dynamic performance focuses either upon the long-term dynamic behavior as it affects power system scheduling or upon the steady-state harmonic characteristics. In recent work, highly detailed computer models of a representative set of PV systems have been developed and several of these models have been verified by comparison with system measurements [1, 2]. However, the models described in [1, 2] are more complex than necessary for large-scale power system studies in which the fast switching transients associated with the dc-to-ac inverter are of little concern and only the slower cycle-to-cycle behavior of the PV system is of interest. In fact, it is not possible to incorporate these detailed models into conventional transient stability programs due, in part, to the very small time-step requirements associated with these models. In this paper, a three-phase self-commutated utility-interactive photovoltaic inverter system is described including its associated control system. A schematic diagram of the selected PV inverter system is depicted in Fig. 1.

A synchronized resonant DC link converter for soft-switched PWM

Abstract: A resonant DC link scheme for soft-switched inverters, where the link oscillation can be synchronized with inverter modulation, is proposed. The scheme is able to operate with reduced commutation losses at a high switching frequency. Synchronization capability allows development of suitable modulation techniques that ensure improved waveform accuracy. The system performance and control strategies were verified by simulation and by experimental tests, and the interesting features of the proposed scheme were confirmed. >

Ultrafast compact 32-bit CMOS adders in multiple-output domino logic

Abstract: A dynamic CMOS logic style, called multioutput domino logic (MODL), has been developed. In this logic style, single logic gates produce multiple functions, and a circuit's device count can be reduced by a factor of more than 2, depending on the degree of recurrence in the circuit. In addition, MODL circuits are, by construction, considerably more stable than other dynamic circuits including conventional domino. A 32-bit carry lookahead (CLA) structure which reduces the adder's worst-case path by two logic stages has also been devised. This CLA structure has been developed to effectively utilize the advantages of MODL. Taken together, these developments have resulted in two 32-bit CMOS adders, providing area and speed improvements of 1.5* and 1.7* over the combination of the domino and conventional CLA techniques. Both adders have been fabricated in a standard 0.9- mu m two-level metal CMOS technology, and measured results show that the straight adder has achieved 32-bit addition times of less than 3.1 ns at 25 degrees C with V/sub DD/+5.0 V. >

Power conversion system with bi-directional power converter having prime mover start capability

Abstract: A power conversion system utilizes a brushless generator driven by a prime mover when operating in a generating mode and drives the prime mover when operating in a starting mode. The system includes first and second bidirectional converter/inverter units, each of the bidirectional units being operable as either an AC to DC converter or a DC to AC inverter. A DC link couples the first and second bidirectional units. A transformer is connected to the second unit and the first unit is further connected to the armature windings, the transformer further being connected to the external power source. A control unit is connected to the first and second bidirectional units and causes the first bidirectional unit to operate as a converter and the second bidirectional unit to operate as an inverter when operating in the generating mode, and for causing the first bidirectional unit to operate as an inverter and the second bidirectional unit to operate as a converter when operating in the starting mode.

Low-voltage CMOS output buffer

Abstract: A CMOS push-pull output buffer is powered by a low-voltage (e.g., +3.3 V) supply, but is able to withstand elevation of its output node to higher voltage without sinking large currents into the low-voltage supply. Thus, this buffer is able to operate tied to a bus that has various higher-voltage sources also operating on the bus. The P-channel pull-up transistor (11) of this buffer has another P-channel transistor (23) connecting its gate to the output node so that this gate will follow the voltage of the output node and thus keep the pull-up (11) transistor from conducting from the output node to the power supply (V DD3 ). The inverter (15) which drives this gate of the P-channel pull-up transistor (11) is also protected from reverse current into its low-voltage power supply by a series N-channel transistor (12) which will exhibit body effect and is sized to present a significant resistance.

Power conversion system having prime mover start capability

Abstract: A power conversion system utilizes a brushless generator driven by a prime mover when operating in a generating mode and drives the prime mover when operating in a starting mode. The system includes an AC/DC power rectifier and an inverter coupled to the AC/DC power rectifier for developing at least one AC voltage. Contactors are provided for coupling, when in the generating mode, the generator to the rectifier input and the inverter output to an AC load during operation in the generating mode, and for coupling an external power source to the rectifier input and the inverter output to the generator during operation in the starting mode. Transformers are provided for adjusting system voltages so that the generator windings need not be modified to accomplish starting of the prime mover.

Optimal power control strategies for neutral point clamped (NPC) inverter topology

Abstract: A programmed pulsewidth modulation (PWM) technique for selectively eliminating several lower-order harmonics at the output of a neutral point clamped (NPC) inverter topology is investigated. The switching function approach is utilized to derive relevant analytical expressions for input/output variables. A thorough evaluation of the NPC inverter topology based on the switching function approach is described. Optimal power control strategies for an NPC inverter employing programmed PWM patterns are proposed. For a constant-frequency variable-voltage NPC inverter power supply, the proposed strategy is to maintain a minimum specified total harmonic distortion employing a low-output impedance filter. In the case of an NPC inverter powering an AC motor drive, the proposed strategy is to maintain a minimum specified harmonic current factor. The proposed power control strategies are achieved without substantial increase in inverter switching frequency and are therefore suitable for high-power applications employing gate-turn-off-thyristor (GTO) type devices. >

Multi-inverter UPS system with redundant load sharing control

Abstract: The concept of a redundant multi-inverter UPS (uninterruptible power supply) system includes extended monitoring of the status and the operating conditions of all power electronic equipment. Each block of the UPS system is monitored by two independent microcomputers that process the same data. The microcomputers are part of a redundant distributed monitoring system, being separately interlinked by two serial data buses through which they communicate. They establish a hierarchy among the participating blocks, defining one of the healthy inverter blocks as the master. The actual master runs the central synchronizing unit for the entire system, while the slave units perform the control of equal active and reactive load sharing. Operation and fault detection are experimentally exemplified in a dual inverter system having a rating of 10 kVA of redundant power. >

An accurate and efficient delay time modeling for MOS logic circuits using polynomial approximation

Abstract: A delay model for multiple delay simulation for NMOS and CMOS logic circuits is proposed. For the simple inverter the rise or fall delay time is approximated by a product of polynomials of the input waveform slope, the output loading capacitance, and the device configuration ratio, with the polynomial coefficients determined so as to best fit the SPICE simulation results for a given fabrication process. This approach can easily be extended to the case of multiple-input transitions. The simulation results show that the proposed modes can predict the delay times within 5% error and with a speedup of three orders of magnitude for several circuits tested as compared with the SPICE simulation. >

Transputer-based harmonic-elimination PWM control of inverter drives

Abstract: Harmonic elimination PWM strategies for voltage source inverter and current source inverter (VSI and CSI) drives have been developed using modified regular sampling techniques. These strategies can be generated online in real time using a simple microprocessor software algorithm and can be used over the complete voltage/frequency range of the drive up to and including the transition from PWM to quasi-square wave (QSW) operation. The implementation and generation of these techniques using the parallel processing INMOS transputer are discussed, and the concurrency programming ability of the transputer for PWM generation is emphasized. The implementation of the new PWM strategy can also be performed on any standard 8 or 16 b microprocessor using 4 or 1 timer implementations. Results from an experimental transputer-controlled PWM inverter drive are presented to demonstrate and confirm the special features of the new regular sampled harmonic elimination PWM control strategies. >

Electro-mechanical analysis of the audible noise of an inverter-fed squirrel-cage induction motor

Abstract: The audible noise emitted by a three-phase squirrel cage induction motor fed by a frequency inverter is determined by the electromagnetic and mechanical behavior of the components of the drive. A computerized analysis method is described that uses theoretical and experimental data for predicting the audible noise spectrum components. Starting from the inverter voltage and the motor data, the electromagnetic forces are predicted and analyzed. The mechanical natural frequencies are considered, either in a theoretical (finite element calculation) or in an experimental (modal analysis) methodology, to predict the vibrational behavior of the machine. The scheme contains the following steps: analysis of the frequency spectrum of the inverter used; synthesis of the magnetic force spectrum accounting for the motor data: calculation or measurement of the resonant data of the stator assembly; and comparison of the force spectrum and the resonant data. These various steps are discussed. >

Simulation studies of islanded behavior of grid-connected photovoltaic systems

Abstract: Simplified computer models are presented for predicting the run-on time of self-commutated inverters operating in a utility interactive mode. The inverter receives DC power from a photovoltaic (PV) array and delivers AC power to a local load or the utility lines. The models represent the dynamics of a phase-locked loop control circuit that is designed to destabilize the inverter operation and shut down the power-conditioning subsystem when a phase discrepancy between the line and some reference signal is detected. The sustained isolated operation (or islanding) of the PV system poses a possible safety concern to utility personnel and potential damage to utility-connected equipment. Two computer models, the TESLACO model and the APCC model, were implemented on an IBM PC using Pascal. They provide results compatible with experimental evidence and more elaborate computer modeling techniques. >

Experimental results and their simplified analysis on instability problems in PWM inverter induction motor drives

Abstract: The instability problems often experienced in PWM (pulsewidth modulation) inverter induction motor drive systems are discussed. Experimental results are presented on how the unstable regions and oscillating frequencies are dependent on dead time. It is noted that the experimental results can clarify the physical description of sources of the instability phenomena. It is shown that a switching-type inverter necessarily includes regenerative intervals. Its existence is the main source of unstable phenomena. It is also shown that a stable region can be determined by applying analytical results to a self-excited induction generator. >