Sinusoidal Output Voltage Research Articles

Single-phase three-wire transformerless inverter

A single-phase inverter providing three wire two-voltage (generally 110/220 V) power is designed and implemented. Instead of using a full-bridge inverter and an output transformer with centre-tapped winding, a three-leg inverter is used to yield a single-phase three-wire circuit. In performing the switching control, the proposed inverter system is decoupled into differential-mode and common-mode subsystems. The controllers of the differential mode are designed mainly to shape and regulate the main output voltage (220 V). As to the common-mode subsystem, its controllers are arranged to compensate the imbalance between two suboutputs (110 V). Each subsystem has an inner current loop as well as an outer voltage loop. In addition, the feedforward control is augmented to the feedback control to yield sinusoidal output voltage with good regulating control performance. Furthermore, the output impedance of the proposed inverter can be significantly reduced and the voltage ratio of the two suboutputs can be programmable. The effectiveness of the proposed method is confirmed by simulation and experimental results.

Small battery energy storage system

A small battery energy storage (BES) system is proposed. The power circuit of this BES system is simple, since only one current-forced subharmonic PWM switching converter is used. The precise current control is achieved by applying feedforward control. If the utility power is off, the BES system operates in the inverter mode to supply power to the load. A sinusoidal output voltage with low distortion and good regulation is obtained by using instantaneous voltage control and average voltage control techniques. When the utility power recovers, the BES system minimises the power from the utility to the load in the peak load period. Conversely, the power from the BES system is minimised in the medium load period. During the off-peak load period, the utility supplies power to the load and also charges the battery bank. In addition to real power conditioning, the BES system can also compensate the load reactive and harmonic powers. Thus the current waveform and the power factor on the utility grid are much improved. The modelling, design and implementation of the proposed controllers are described and some experimental results are given to show the performance of this BES system.

An AC voltage switching regulator with instantaneous output voltage control

This is the first attempt to control the instantaneous output of an ac/ac direct power converter. The ac chopper-type regulator has the potential ability of quick response to the control command. However, detecting the mean or effective value of the ac output voltage, as is commonly done in the conventional closed-loop ac regulators, greatly degrades the inherent fast response capability of the chopper circuit. The proposed ac switching regulator adopts the Cuk converter for the main circuit and an instantaneous voltage control technique. A practical state feedback scheme together with the integral control was devised to stabilize the system and also minimize the steady-state error. The response speed is so fast (about 300 μs with resistive load) that the converter can produce a sinusoidal output voltage even from a distorted source voltage. The four-quadrant operation can handle any kind of ac load. A complete analytical description and relevant design data of this new regulator are provided with some experimental results.

A current source PWM inverter with instantaneous current control capability

A new approach for the control of a current source pulse width modulated (PWM) inverter is proposed to achieve instantaneous current control capability. The proposed scheme provides instantaneous current response in the AC motor by altering the modulation index of the current source PWM patterns. In order to achieve this task, optimum programmed PWM patterns with selective elimination of lower order harmonics in the motor line currents are used. Output filter capacitors are provided to bypass the current harmonics in the inverter output and allow for the instantaneous changes in the line currents. This method of control provides sinusoidal output voltages and sinusoidal currents in the AC motor. The proposed scheme guarantees fast response characteristics combined with high-performance steady-state behavior. A design procedure for the current source PWM and selection of programmed PWM current patterns for a variable-speed situation is illustrated. Selected results are verified experimentally. >

Output voltage control method for PWM-controlled cycloconverters.

The forced commutated cycloconverters (PWM-controlled cycloconverters) have no energy storage components except for small ac filters for elimination of switching ripples. Therefore, the PWM-controlled cycloconverters can be made compact and highly reliable compared with the conventional rectifier-inverter systems. The PWM-controlled cycloconverters, however, directly connect the input terminals to the output terminals by the switching devices. Therefore, if the source voltages contain asymmetrical and/or harmonic components, the influences directly appear on the output terminals. This problem may be a major obstacle for the PWM-controlled cycloconverters to be used in place of the conventional converter-inverter systems. We have already reported a real time control method based on a coordinate transformation. The method realizes sinusoidal output voltages and sinusoidal input currents with controllable input displacement factors regardless of the load power factors. But the control functions of this control method need complex calculations to compensate the distortion of the input source voltages and are difficult to comprehend physically.In this paper, we propose a novel control method using a new control function with a clear physical meaning. By this control method, the compensation of the asymmetrical and harmonic components of the input source voltages is easily realized. Feasibility of the proposed control method is confirmed by simulations and experiments.

Polarized film resolver for the control of permanent magnet synchronous machines

The design of a three-phase sinusoidal output electrooptic resolver is presented. This resolver utilizes polarized films to provide variable attenuation of a light source. It generates a sinusoidal output voltage which is a function of the angular position of its shaft. A prototype of the sensor has been constructed and tested. It can be used to control an inverter to drive a permanent magnet synchronous machine. Uses include electric cars, industrial machine drives, and controllers for wind turbine systems. >

Digital control of three-phase PWM inverter with LC filter

A digital control algorithm for the three-phase sinusoidal voltage inverter with an output LC filter has been developed. To take the transient of the LC filter during the discretization time into consideration, a fourth-order matrix state equation of the current and the voltage on the d-q frame is discretized. Precise discrete equations for the inverter are introduced. Using these equations, a deadbeat controller consisting of a d-g current minor loop and a d-q voltage major loop, with precise decoupling of the d-q components, was developed. The voltage major loop controller assures the sinusoidal output voltage and stabilizes the system. A deadbeat controller is used because both the current minor loop and the voltage major loop can used one sampling response. The validity of these techniques is confirmed by simulation studies. This method is expected to be useful for direct digital control of large-capacity sinusoidal voltage inverters using low-switching-frequency devices. >

A 2.5-kW cascaded Schwarz converter for 20-kHz power distribution

The cascaded Schwarz converter, which provides a relatively simple method for driving 20 kHz power systems, is discussed. The cascaded Schwarz is compared with other 20 kHz converters, showing that the circuit is relatively easy to protect and provides a predictable trapezoidal voltage waveform. Because it avoids the high currents in a parallel loaded capacitor, the cascaded Schwarz should offer better component utilization than converters with sinusoidal output voltages. Operation has been verified on a 2.5 kW circuit that uses input and output voltages in the same range as those anticipated for certain future spacecraft power systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An AC voltage switching regulator with instantaneous output voltage control.

This is the first attempt of controlling the instantaneous output voltage of an AC/AC direct power converter. The AC chopper-type regulator has the potential ability of quick response to the control command. However, detecting the mean or effective value of the AC output voltage, as is commonly done in the conventional closed-loop AC regulators, greatly ruins the inherent fast response capability of the chopper circuit.The proposed AC switching regulator adopts the _??_uk converter for the main circuit and an instantaneous voltage control technique. A practical state feedback scheme together with the integral control was devised to stabilize the system and also minimize the steady state error. The response speed is so fast (about 300μs with resistive load) that the converter can produce a sinusoidal output voltage even from a distorted source voltage. The four quadrant operation can handle any kind of AC load. A complete analytical description and relevant design data of this new regulator are provided with some experimental results.

A three-phase to three-phase series-resonant power converter with optimal input current waveforms. II. Applications and results

For pt.I see ibid., vol.35, no.2, p.263-8 (1988). A 15 kW three-phase prototype series-resonant power converter is constructed. The converter features sinusoidal output voltage and sinusoidal input currents. The control concepts and necessary electronics, as well as the layout of the power circuit, are discussed. Low distortion levels are achieved for both the output voltages and the input currents, and measurements show the very fast (milliseconds) reaction capabilities of this type of equipment.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Waveform compensation of PWM inverter with cyclic fluctuating loads

A repetitive voltage compensation technique that generates a high-quality sinusoidal output voltage from a single-phase pulse width modulation (PWM) inverter used for uninterruptible power supplies is described. A repetitive control technique eliminates the steady-state error in the distorted output voltage caused by cyclic loads. The proposed PWM inverter system uses microprocessor-based closed-loop digital feedback with a sinusoidal reference. The PWM pattern is determined at every sampling instant by the proposed algorithm, implemented by a microprocessor using a set of detected output voltages and the reference signals through one cycle. The system has low distortion and very fast response for AC phase-controlled loads.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dead Beat Microprocessor Control of PWM Inverter for Sinusoidal Output Waveform Synthesis

A new control technique based on dead beat control theory to obtain a nearly sinusoidal PWM inverter output voltage is described. The closed-loop digital feedback system measures the output and controls the inverter switches to generate the required pulsewidth-modulated (PWM) pattern to produce low total harmonic distortion (THD) sinusoidal output voltage. This scheme inherently provides very good voltage regulation, phase positioning, and compensation for load disturbances and nonlinear loads. A theoretical analysis, computer simulation, and experimental results for a single-phase bridge inverter controlled by an Intel 8086 microprocessor-based system is presented.

Sinusoidal response of dc SQUIDs for rf power measurements

Current, power, and attenuation measurements with rf SQUIDs are based on the fact that the voltage from the microwave readout circuit can be made a nearly sinusoidal function of the magnetic flux threading the SQUID. We point out here that an asymmetric dc SQUID with sufficiently low inductance can achieve a very sinusoidal output voltage with good modulation depth. The spectral purity of the sinusoid can be substantially better than that obtained with rf SQUID systems. The purity improves with increasing asymmetry of the junction critical currents, and decreasing values of the LIc product, where L is the SQUID inductance and Ic is the smaller of the critical currents. Results of several calculations are presented. Substantial improvement in SQUID methods of rf current, power, or attenuation measurement may thus be possible with use of such dc SQUIDs.

EXPERIMENTAL INVESTIGATION OF SIMPLE CONSTRUCTION SINGLE TO THREE PHASE CONVERTER

This paper shows the behaviour of three phase transformer to work as a single phase to three phase converter. The converter is to supply the three phase load by a three phase sinusoidal wave form voltage. The converter consists of an ordinary three phase transformer and a capacitor. One coil is connected to the single phase main supply. Another coil on another limb is connected to the capacitor. Three coils, with one coil at each limb, are to supply the load by the three phase voltages. The hybrid connections of the converter coils and capacitor are to give the 120 degrees shift between the phases, sinusoidal wave form output voltage and symmetrical values of output voltages. The value of the capacitor is chosen to give the 120 degrees shift and the sinusoidal wave form. The number of turns for each of the three output coils are also chosen to give the symmetrical values of output voltages. The simple construction and good operating characteristics of this converter, enables it to work in light or heavy currents utilization.

High-Performance PWM Frequency Changers

Besides the ability to change the frequency and amplitude of output voltages a high-performance frequency changer (FC) should produce sinusoidal output voltages and sinusoidal in-phase input currents and allow bidirectional power flow. The Venturini FC meets all these requirements but has some deficiencies which affect its practicality. Three kinds of improved FC's?a new direct FC and its special applications, a current source FC, and a voltage source indirect FC?which retain all good features of Venturini's FC and overcome its deficiencies are investigated. Their principles, features, and problems are discussed. New control laws and control circuits are proposed.

A New Current Source GTO Inverter with Sinusoidal Output Voltage and Current

A new current source inverter with sinusoidal output voltage and current is presented. Gate turn-off thyristors (GTO's) and pulsewidth modulation (PWM) control techniques are used in the current source inverter to produce the sinusoidal output voltage and current. Three capacitors are connected to the ac output terminals to absorb overvoltages which occur when the GTO current is cut off and to provide a filter function for reducing harmonics in the output current. Voltage spikes, which have been a serious problem in the practical application of this inverter, are suppressed by adding gate pulses which force the inverter into a state of shoot-through. Moreover, this inverter permits the capacitance of an ac output terminal capacitor for absorbing overvoltages to be reduced to one-tenth or less of that of a commutating capacitor in a conventional thyristor type current source inverter. A 3.7-kW induction motor is driven by the inverter. The motor efficiency and noise level are measured and compared with those obtained when the motor is driven by a conventional voltage source PWM inverter. An operating efficiency five or six percent higher and noise level 10 dB lower are obtained for the former. Therefore, this current source GTO inverter is very suitable for ac motor variable speed drives.

A New Approach to the Design of Asymmetrically Loaded Three Phase Sinusoidal Inverters

A new type of three phase inverters powered from a current source is presented. The inverter consists of only three thyristors, successively fired in equal time intervals. A three phase magnetic circuit, with windings for phase coupling and for returning surplus energy into the d-c circuit, combines with capacitors to produce: (1) a sinusoidal output voltage and (2) a symmetrical voltage system in both amplitudeand phase. The three phase system, due to its nature and the way it is constructed, tends to sustain a symmetrical and sinus oid three phase voltage oscillation. The basic idea of the new design is to feed the oscillations of the system using static switches.

Static DC to sinusoidal AC inverter using techniques of high-frequency pulse-width modulation

A dc to sinusoidal ac inverter is described in which high-frequency pulse-width modulation is used to provide a low-frequency sine-wave output without the need for either a low-frequency power transformer or for low-frequency filter components. The inverter is physically simple and has low weight and small size. From a practical viewpoint the usefulness of this inverter is further enhanced by its self-regulating property. An analysis of this circuit and its output waveform is also given which provides the mathematical basis for the experimentally observed test results. In addition to the proof of the self-regulating property, it is further proven analytically that the amplitudes of the harmonics of the sinusoidal output voltage are very small with respect to the amplitude of the fundamental voltage.

Optimization of Rotor Tooth Shape of Aerospace Homopolar Alternators

In the first part of the optimization process, the width and depth of the rotor tooth are incrementally varied for two airgap radial lengths and two field excitations. In the second part the tooth shape that would yield a sinusoidal voltage is investigated. The numerical results are represented by curves for the no-load radial flux density in a 95 KVA, 120/208 v 3,400 cps alternator. The results show that the fundamental airgap flux density depends on the length of the airgap and on the rotor tooth width. It depends only slightly on the rotor tooth depth and excitation. A more sinusoidal output voltage can be obtained by flaring the tips of the rotor tooth and widening the rotor tooth.

Design considerations of junction-transistor oscillators for the conversion of power from direct to alternating current

Resonant oscillators using transistors provide a suitable means for the conversion of d.c. into a.c. power, in particular where a reasonably sinusoidal output voltage is required.For the design of such oscillators, the current-amplification factor, the fraction of the cycle during which collector current is permitted to flow and the feedback conditions have to be considered. The maintenance equation correlating these factors is derived, and an angle-of-flow chart is described, by means of which sets of values of the amplitude of oscillation, the current amplification of the transistor, the amount of feedback and the fraction of the cycle (flow angle) during which collector current is flowing, simultaneously fulfilling the maintenance equation, can be readily determined. Practical oscillator design must take into account the non-linearity of the transistor circuit which has to be incurred in order to ensure correct amplitude limiting of the oscillator. Deviations from sinusoidal operation resulting from this as well as from other causes are considered in some detail, and graphical methods are described for the quantitive assessment of oscillator performance. These methods are based on Lienard&apos;s construction which, suitably extended, provides a convenient means of predicting the amplitude, output waveform, frequency and other performance data of the oscillator.The design of a Class B oscillator is described in detail and illustrated by means of a practical numerical example. Calculated data agreed well with practical measurements.