Showing papers on "Inverter published in 1993"

Disturbance free operation of a multiphase current regulated motor drive with an opened phase

Abstract: An improved induction motor control strategy is proposed incorporating a multiphase machine which allows for continuous, disturbance free operation of the drive even with complete loss of one (or more) legs of the inverter or motor phase. A complete analysis of both even phase and odd phase machines utilizing this control and circuit concept is presented. By using a five-phase or a seven-phase machine, it is possible to take advantage of the additional degrees of freedom as a result of more phases. It is shown that when one phase is open circuited, with appropriate control, the zero sequence current is no longer a necessary component as in a three-phase machine. That is, one can eliminate the need for a neutral line and the machine can still be controlled so as to produce a smooth nonpulsating torque. It has also been determined that the ratings of motor and inverter will both benefit by the use of extra phases. >

On continuous control of PWM inverters in the overmodulation range including the six-step mode

Abstract: The power output and the dynamic performance of PWM (pulse width modulated) controlled AC motor drives can be improved by increasing the inverter output voltage through overmodulation. Two different solutions are proposed to increase the output voltage in a continuously controllable fashion up to maximum possible value, which is reached in the six-step mode. The solutions differ in their approaches. A space vector strategy is used for high dynamic performance, high switching frequency drives, while a field-oriented PWM method is used for low switching frequency, high power inverters. Experimental results are presented. >

Electronic ballast for fluorescent lamps

Abstract: A frequency-domain analysis is given for a Class D voltage-switching power inverter with a load resistance connected in parallel with a resonant capacitor Using the fundamental component approximation, design equations are derived to provide easy-to-use design tools The inverter is inherently short-circuit-proof, but cannot operate safely with an open circuit at the resonant frequency Safe operation with an open circuit can be achieved if the operating frequency is sufficiently lower or higher than the resonant frequency Experimental results are given for two F40 fluorescent lamps connected in series, using MTP5N40 MOSFETs The operating frequency was 50 kHz at full power and 70 kHz at 20% of full power At full power, the efficiency of the Class D inverter was 956% and the efficiency of the power factor corrector was 93% The overall efficiency of the ballast was 894% at full power >

Five-level GTO inverters for large induction motor drives

Abstract: The development of large induction motor drives with low torque ripple and fast dynamic response for new or retrofit applications has been limited by the device ratings and problems of series connections. This paper investigates the use of a five-level GTO voltage-sourced inverter for large induction motor drives. The advantages of such a drive are that single GTO thyristors may be used at each level, thereby avoiding the need for series connection of the thyristors. The thyristors are well protected from overvoltages by the clamping action of the DC supply capacitors. The disadvantages are that each DC level requires a separate supply, four in the case of the five-level inverter, and that the devices are not equally loaded. This paper reviews the basic operation of the five-level inverter and possible PWM voltage/frequency control techniques for the specific application of induction motor drives. The simulation results clearly show the unequal loading of the devices and the need for independent voltage supplies for the five levels. It is shown that a combination of several PWM techniques offers the best solution for the drives application. The conclusions indicate that large induction motors with ratings up to 22 MVA, 7.46 kV may be supplied by the five-level inverter using available 4.5 kV, 3.0 kA GTO thyristors. The recommended supply for such an inverter with full regenerative operation over the complete speed range is four, four-quadrant converters in a quasi-24-pulse configuration. >

Analysis of variation of neutral point potential in neutral-point-clamped voltage source PWM inverters

Abstract: The authors present the analysis of the neutral-point potential variation of the neutral-point-clamped voltage source PWM (pulse-width-modulation) inverter (NPC-VSI) for AC motor drives and static VAr compensators (SVC). The potential variation is analyzed with the focus on the current flowing out of or into the neutral point of the DC link. The theoretical minimum capacity of the DC link capacitors is discussed for its application to both a vector-controlled induction motor system of 2.2 kW and a SVC system of 10 MVA, 6.6 kV, 60 Hz. It is shown that the proposed control scheme makes it possible to suppress the neutral-point potential variation within a few percent, so that the total capacity of the DC link capacitors in the NPC-VSI is almost the same as that in the conventional voltage source inverter. >

A rule-based fuzzy logic controller for a PWM inverter in a stand alone wind energy conversion scheme

Abstract: The paper presents a rule-based fuzzy logic controller to control the output power of a pulse width modulated (PWM) inverter used in a stand-alone wind energy conversion scheme (SAWECS). The self-excited induction generator used in SAWECS has the inherent problem of fluctuations in the magnitude and frequency of its terminal voltage with changes in wind velocity and load. To overcome this drawback the variable magnitude, variable frequency voltage at the generator terminals is rectified and the DC power is transferred to the load through a PWM inverter. The objective is to track and extract maximum power from the wind energy system and transfer this power to the local isolated load, This is achieved by using the fuzzy logic controller which regulates the modulation index of the PWM inverter based on the input signals: the power error; and its rate of change. These input signals are fuzzified, that is defined by a set of linguistic labels characterized by their membership functions predefined for each class. Using a set of 49 rules which relate the fuzzified input signals to the fuzzy controller output, fuzzy set theory and associated fuzzy logic operations, the fuzzy controller's output is obtained. The fuzzy set describing the controller's output (in terms of linguistic labels) is defuzzified to obtain the actual analog (numerical) output signal which is then used to control the PWM inverter and ensure complete utilization of the available wind energy. The proposed rule-based fuzzy logic controller is simulated and the results are experimentally verified on a scaled down laboratory prototype of the SAWECS.

A simple, novel method for variable-hysteresis-band current control of a three phase inverter with constant switching frequency

Abstract: A novel method for implementing a variable hysteresis band current controller is described which achieves constant switching frequency without requiring a precise knowledge of the motor parameters. The controller works by using feedback and feedback variables to create a variable hysteresis band envelope, and then compensating for the interaction between phase back-EMFs that occurs when the neutral of a three-phase motor is left floating. The controller has good dynamic and steady-state response, and its performance is substantially immune to variations in the inverter DC supply voltage and motor parameters. It can be readily implemented in hardware, and only requires a few additional components compared to a conventional hysteresis current controller. Analytical, hardware implementation, simulation, FFT (fast Fourier transform) analysis, and experimental results are presented. >

Electric system for electric vehicle

Abstract: An electric system for an electric vehicle includes a voltage type inverter that receives dc input voltage from a dc input circuit, and generates variable ac voltage of a variable frequency, and an ac motor including a plurality of windings each of which has one end connected to an ac output terminal of the voltage type inverter, the other ends of the windings being connected together to provide a neutral point of motor windings. A variable-voltage energy storage element is connected between the neutral point and a connecting point provided in the dc input circuit, and an on-vehicle dc power supply is connected to the opposite ends of the energy storage element or input terminals of the dc input circuit. The inverter performs switching operations in a zero-voltage vector mode, to operate as a chopper, so that power is transferred between the variable-voltage energy storage element, and the dc input side of the inverter.

Analysis and average-value modeling of line-commutated converter-synchronous machine systems

Abstract: Analytical relationships are established which can be used to predict the steady-state characteristics of line-commutated AC-DC-converter-synchronous machine systems. In particular, basic relationships are established in which the average DC voltage and the average electromagnetic torque are related to the converter firing delay angle. It is shown that these average-value relationships predict the steady-state performance with significantly higher accuracy than the classical converter average-value equations in which the d-axis subtransient reactance is used as the commutating reactance. >

A pulsewidth-modulated inverter with parallel connected transistors using current-sharing reactors

Abstract: A technique for parallel connection of transistors by using current-sharing reactors for the pulse-width-modulated (PWM) transistor inverter is reported. The technique not only increases current capacity, but also decreases the output harmonic contents. The output voltage waveforms of the proposed inverter have certain voltage levels during their half cycles, and thus it is anticipated that it will be difficult to analyze the output harmonics. For such waveforms, a frequency analysis approach is described, and its results are verified by experiments. >

A New Resonant Tunneling Logic Gate Employing Monostable-Bistable Transition

Abstract: This letter describes a new resonant tunneling logic gate. The concept of the proposed gate has two features: 1) to employ the monostable-to-bistable transition of a circuit consisting of two N-type negative differential resistance (NDR) devices connected serially, and 2) to drive the logic gate by oscillating the bias voltage to produce the transition. This mode of operation has a significant advantage in that a large number of fanouts is possible without sacrificing the high-speed operation. Serially connected resonant tunneling field effect transistors having p+-junction gates were fabricated to test the above operation principle. The inverter operation of the proposed logic gate has been successfully achieved at room temperature.

A super high speed PM motor drive system by a quasi-current source inverter

Abstract: The authors describe a surface-mounted PM (permanent magnet) motor with the ratings of 5 kW and 180000 RPM for super-high-speed drive applications such as machine tools. A much larger air gap, compared with that of the existing PM motors, is used to reduce the slot ripples and hence the resultant eddy current loss in the metallic sleeve that retains the permanent magnets; otherwise, this loss would be objectionable at such high speeds. The motor is supplied from a quasi-current source inverter with the DC current controlled by a chopper and operated at a near-unity power factor by the use of a simple position sensorless control, to improve the motor efficiency. Analytic results are presented showing the slot ripple reducing effect of increasing the air gap length. To investigate the losses of the sleeve, several motors with different sleeves were manufactured and tested. Typical experimental results on these prototypes are given, which show that a motor efficiency of higher than 90% can be realized at the rated torque over a wide speed range. >

Electro-thermal simulation of an IGBT PWM inverter

Abstract: A recently developed electro-thermal network simulation methodology is used to analyze the behavior of a full-bridge, pulse-width-modulated (PWM), voltage-source inverter which uses insulated gate bipolar transistors (IGBTs) as the switching devices. The electro-thermal simulations are performed using the Saber circuit simulator and include the control logic circuitry, the IGBT gate drivers, the physics-based IGBT electro-thermal model, and the thermal network component models for the power device silicon chips, packages, and heat sinks. It is shown that the thermal response of the silicon chip determines the IGBT temperature rise during the device switching cycle. The thermal response of the device TO247 package and silicon chip determines the device temperature rise during a single phase of the 60-Hz sinusoidal output. Also, the thermal response of the heat sink determines the device temperature rise during the system start-up and after load impedance changes. It is also shown that the full electro-thermal analysis is required to accurately describe the power losses and circuit efficiency. >

Power spectra of a PWM inverter with randomized pulse position

Abstract: Random pulse width modulation in static power converters results in the partial transfer of power from the discrete spectrum of the output voltage to the continuous spectrum, with advantageous effects on the operation of the supplied electromechanical systems. In this paper, a random PWM technique with randomized pulse position for three-phase voltage-controlled inverters is analyzed. Closed-form equations for the discrete and continuous power spectra of the line-to-line and line-to-neutral voltages of the inverter have been derived and confirmed by experiments. Presented theory opens the way to numerical optimization of the voltage spectra of randomly modulated inverters. >

Space vector PWM technique with minimum switching losses and a variable pulse rate

Abstract: A novel PWM technique for three-phase voltage-controlled power inverters, based on the concept of voltage space vectors, is described. The minimum-loss, variable pulse rate (MLVPR) strategy, employing an implicit asymmetrical modulating function, results in the switching losses in the inverter reduced by half in comparison with the classic space vector PWM method. The pulse rate is varied from one 60/spl deg/ sector of the vector space to another, which produces spread, partly continuous spectra of the output voltage of the inverter. Theoretical analysis and results of experimental investigation of a prototype modulator are presented. >

Combined motor drive and battery recharge system

Abstract: A combined battery recharge and motor drive system employs an essentially conventional polyphase pulse width modulated (PWM) inverter and a polyphase motor which may be reconnected to operate in a battery recharge mode. Single phase or three-phase AC power from an external source is applied across the reconfigured circuit, and the inverter switches are then controlled to operate as a boost switching regulator. Electrostatic (Faraday) shielding techniques and construction allow extremely small ground currents for improved safety an GFI outlet compatibility.

Simple structure and control method for a neutral-point-clamped PWM inverter

Abstract: A new configuration for a neutral point clamped PWM inverter and its control strategy is proposed. The proposed configuration consists of an auxiliary circuit with four switching devices and a single full-bridge inverter. The control method is based on closed-loop regulation of the instantaneous line-to-line output voltages. The proposed scheme is simple, has fast response, and is effective for reducing the size of the DC-link capacitors. The performance of the system is verified by computer simulation and by experiment. >

Electric vehicle control system

Abstract: An electric vehicle control system for driving a battery powered motor with use of power inverters. First and second inverters are connected with the respective three-phase primary windings of an induction motor. If one of the inverters fails, failure detection circuits detect it, and a control unit stops the failed inverter and allows the other normal inverter to drive the induction motor to move the electric vehicle. Driving the single motor with a plurality of power inverters allows the electric vehicle to move and run even if one of the power inverters fails.

Controlled AC drives with ride-through capability at power interruption

Abstract: General-purpose PWM (pulse width modulated) inverter drives are equipped with an undervoltage protection mechanism, causing the system to shut down within a few milliseconds after a power interruption in the mains. This may entail loss or damage of material in such critical applications as the production of textile fibers on paper, or with extruder drives. The proposed solution to this problem is to recover some of the mechanical energy stored in the rotating masses. When a power interruption occurs, a sequence of fast feedforwarded commands is applied to force an immediate transition into the regeneration mode. During the interrupt interval, the drive system continues to operate at almost zero torque, just regenerating a minor amount of power to cover the electrical losses in the inverter. The method is implemented in an additional software package to be used with general-purpose inverter drives of limited dynamic performance. Experimental results are presented. >

A new zero-voltage transition, three-phase PWM rectifier/inverter circuit

Abstract: A switching rectifier/inverter technique that combines the conventional three-phase, six-stepped pulse-width modulated (PWM) rectifier/inverter with a simple commutation circuit to provide zero-voltage turn-on for the switches and soft turn-off for the diodes is presented. The commutation circuit is active only during a short period of the switching cycle, thus it consumes minimum power and does not impair the normal constant frequency PWM control. The addition of the commutation circuit does not result in increased component current and voltage stresses compared to the conventional PWM converter. >

Design of a 10 kW, 500 kHz phase-shift controlled series-resonant inverter for induction heating

Abstract: A phase-shift-controlled series-resonant inverter is used as power supply for a 10 kW, 500 kHz induction heating system. Analysis of the system for power regulation with zero voltage switching is presented, including the effect of MOSFET output capacitance. A control scheme is proposed to ensure switch turn-on with zero-voltage for all load conditions. The switching frequency is kept as close as possible to resonance to maintain near-minimal circulating energy. A prototype power supply was built and tested at 10 kW. >

Closed loop pulse width modulator inverter with volt-seconds feedback control

Abstract: A closed loop pulse width modulator (PWM) inverter (50) corrects for variations and distortion in the ouput AC voltage (52) waveform caused by non-linearities of the switching devices (S1-S6) or changes in the DC link voltage (3). A signal is generated that is a volt-seconds representation of the voltage error between a voltage command signal (25) and the actual AC output voltage (52) of the PWM inverter (50). The volt-seconds error signal becomes a controlling signal means in the closed loop of the PWM inverter (50) to regulate the output AC voltage (52) of the PWM inverter (50). Another signal that represents changes in the DC link voltage (3) also modifies the voltage command signal (25). The system will compensate for the non-linear behavior of the PWM inverter (50) due to deadtime, minimum on-times and off-times, and DC link voltage (3) variations and voltage drops across the switching devices (S1-S6), and will also allow the operation of the inverter (50) in a linear fashion for the region of operation when one or more of its phases are saturated, i.e., either fully on or fully off.

Commutation strategies for brushless DC motors: influence on instant torque

Abstract: A solution to obtaining torque smoothness of a brushless DC drive within a wide speed range is presented. The voltage between the neural point of the inverter and the neutral point of the machine is not always zero. This voltage disturbs the phase currents during commutation. Since, in the case of real EMFs, the limited loop bandwidths of the current controller does not allow the currents to follow the adapted reference, a compensative and a predictive term have been added to the controller output. The robustness of the concept in the case of parameter variations is studied. >

Electrical power inverter

Abstract: An electrical power inverter having an output voltage waveform that closely corresponds to a reference waveform under a wide range of load conditions is disclosed. The present invention allows for excess energy present at the output port of the electrical power inverter to be coupled back to the input port to maintain the correspondence of the output voltage waveform with the reference waveform when the inverter is providing power to inductive or light resistive loads. The electrical power inverter comprises an input port for receiving a unipolar input voltage and an output port for providing electrical energy to a load, a circuit for generating a reference waveform, a power converter for generating an output voltage at the output port having a waveform that approximately corresponds to the reference waveform, an energy return circuit for selectively coupling energy from the output port to the input port, and a controller for enabling said energy return circuit to selectively couple excess energy from the output port such that the output voltage waveform more closely corresponds to the reference waveform under a wide range of load conditions.

Current-sourcing push-pull parallel-resonance inverter (CS-PPRI): theory and application as a fluorescent lamp driver

Abstract: A novel topology, current-sourcing push-pull parallel-resonance inverter (CS-PPRI), is investigated theoretically and experimentally. The proposed power stage is built around a current fed push-pull inverter. The main features of the proposed inverter are a load-independent output current and zero voltage switching (ZVS). It is suggested that the proposed CS-PPRI is a viable alternative for realizing electronic ballasts for low and high intensity discharge lamps. >

Voltage controlled oscillator operating with digital controlled loads in a phase lock loop

Abstract: A phase lock loop (16) operates independent of temperature and process variation by digitally loading a VCO (22) until reaching the desired operating frequency. The VCO reaches a high output frequency even under worst case processing by controlling multiple current mirrors (162-166, 174-180, 182-188) to increase inverter switching current without slowing the response of the VCO to changes in loop node voltage. An Initialize-to-VDD circuit (32) sets the loop node voltage to V DD so that the load control circuit need only increase loading to slow down the VCO to the desired operating frequency. A frequency range detector (34) monitors the output frequency of the VCO and passes control signals to a load control circuit to (36) activate digital loads (38) and slow down the VCO to the desired operating frequency.

Inverter apparatus and uinterruptible power supply using the same

Abstract: In a uninterruptible power supply in which a plurality of inverters are operated in parallel, a current control loop is provided which responds to the magnitude of an output current of each inverter brought into parallel running to change a command value for a voltage waveform control circuit associated with each inverter, and the gain of the current control loop is made to be variable, whereby currents shared by the inverters can be set desirably to effectively suppress a cross current flowing between the inverters upon establishment of parallel running.

Method of formation of transistor and logic gates

Abstract: A transistor (10) has a substrate (12) and a diffusion (14). A gate conductive layer (18) overlies the substrate (12) and has a sidewall formed by an opening that exposes the substrate (12). A sidewall dielectric layer (22) formed laterally adjacent the conductive layer (18) sidewall functions as a gate dielectric for the transistor (10). A conductive region is formed within the opening. The conductive region has a first current electrode region (28) and a second control electrode region (34) and a channel region (30) laterally adjacent the sidewall dielectric layer (22). A plurality of transistors, each in accordance with transistor (10), can be stacked in a vertical manner to form logic gates such as NMOS or PMOS NAND, NOR, and inverter gates, and/or CMOS NAND, NOR, and inverter gates with multiple inputs.

Application of fuzzy logic in the speed control of AC servo system and an intelligent inverter

Abstract: A fuzzy logic controller for use in the fully digital speed control of AC servomotor systems is presented. An intelligent inverter is also proposed to reduce the switching loss and the current harmonics in induction motors. A 16 bit single-chip microprocessor is used to reduce the number of circuit components for cost reduction and reliability enhancement. In order to facilitate the instantaneous control of motor torque, indirect field orientation is adopted along with a current-regulated pulse-width-modulation voltage-source inverter. A computer simulation for assessing the feasibility of the system proposed is described. Circuit design and software development are then undertaken. Simulation results are verified experimentally. >