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A naturally commutated six-pulse cycloconverter working in the inverting mode is used to feed power to a single phase AC motor at 400 Hz. The motor is connected at the input side of the cycloconverter while the three-phase mains is connected at its output. Three-phase mains feeds power to the input side of the cycloconverter which is arranged as a tuned load at 400 Hz. The effect of the single-phase induction motor on system performance is discussed. The principle of voltage and frequency control for proper operation of the induction motor is presented. The results are experimentally verified. [ABSTRACT FROM AUTHOR]

Describes an AC-AC cycloconverter frequency changer for induction heating. Operation and timing mechanism; Details of control circuits; Experimental results; Potential commercial applications.

Investigates the use of a naturally commutated cycloconverter between an induction heating load and the mains supply to effect the necessary transfer of power. Requirements of the commutation of converter thyristors; Process of transient build-up of the tank voltage.

Investigates the use of cycloconverter for induction heating. Application as a link between the high frequency induction load and the AC mains; Effect of the naturally commutated converter on the tank and AC mains.

A new LC commutation circuit configuration is proposed for two-pulse bridge converters. It is suitable for motoring and regenerative operations of DC motors. Initial charging of the commutation capacitors is natural. The system has no starting problems. It does not require supporting capacitors. The commutation circuit has been analysed and experimentally verified. The commutation period is almost halved as compared to the schemes where the armature current is diverted through the commutating capacitor during the commutation process. [ABSTRACT FROM AUTHOR]

In order to reduce the commutation period, a new L—C commutation circuit configuration is proposed. The commutation circuit is useful both for motoring and regenerative operations of the motor. A supporting capacitor has been used to restrict the voltage of the commutating capacitor to E[sub m]. The supporting capacitor can be electrolytic. The commutation process has been analysed and experimentally verified. Theoretical and experimental results are in close agreement. [ABSTRACT FROM AUTHOR]

Forced commutation schemes have been used in two-pulse convertors in order to improve the power factor. Such a scheme also increases the regenerative power. A bridge converter with transformer-coupled force-commutation circuit is proposed in this paper. The commutation process is analysed and normalized turn-off time curves are presented. The effect of load current on the commutation process is discussed. The proposed converter configuration is useful for both motoring and regenerative operations of series as well as separatively excited DC motors. The results are experimentally verified. [ABSTRACT FROM AUTHOR]

In a current source inverter-fed induction motor drive system, the effect of pulsating torques can be overcome by eliminating the lower-order harmonic components in the stator current. Stepped current wave current source inverters with transformer connections have been proposed to achieve this result. Such an inverter system has only (12n ± 1)f harmonic components. Hence, the lowest predominant pulsating torque is the 12th harmonic. The proposed schemes are superior to existing dual inverter systems. The results have been experimentally verified. [ABSTRACT FROM AUTHOR]

Three sub-units of series-parallel compensated voltage fed inverters can be used to realize time-sharing and increase the circuit turn-off time by more than one period of the output cycle. The operation of the circuit is possible only if the parallel compensated tank load is inductive. Thus, time-sharing imposes severe restrictions on the circuit parameters. These restrictions are analysed and discussed. Choice of circuit parameters for reliable operation of the circuit is presented. Feed-back control scheme for automatic variation of triggering frequency is given. The analytical results are experimentally verified. [ABSTRACT FROM AUTHOR]

A direct a.c. to a.c. static frequency changer is analysed taking into account induction heating load. Closed-form expressions for the line current harmonic components and the input power factor are derived. For output to input frequency ratio of 21 or more, the displacement angle is less than 2° and the line side harmonic frequency spectrum is shifted towards the higher order frequencies. Hence, it is possible to achieve almost unity power factor by using a simple low-pass filter. The control circuit is presented and the experimental results are discussed. [ABSTRACT FROM AUTHOR]

A voltage-fed high-frequency inverter circuit with a parallel compensated load is analysed. The inverter circuit works on the principle of natural commutation. Circuit conditions for reliable operation of the inverter are derived. The design criteria for the choice of circuit components and their effect on steady-state circuit operation are discussed. [ABSTRACT FROM AUTHOR]

A voltage-fed high-frequency inverter circuit with series-parallel compensated load is analysed. The inverter circuit works on the principle of natural commutation. Necessary conditions for reliable operation of the inverter circuit are derived and the resulting improved operating characteristics of the series-parallel compensated inverter are discussed. It is shown that the circuit operation with a capacitive tuned load is preferable. The range of circuit parameters for reliable operation of the circuit is specified. [ABSTRACT FROM AUTHOR]

In this paper it is shown that Moschytz's active filter incurs large passive Q sensitivity if high-Q's are to be realized. A modified circuit is proposed where passive Q sensitivity is reduced by Q times. The new circuit retains all the advantages of Moschytz's high-Q filter. It is also compared with Saha's high-Q active filter to evaluate its superior performance. [ABSTRACT FROM AUTHOR]

The paper describes a simple high-Q insensitive active band-pass filter having relatively few passive components and active elements with low closed-loop gains, using positive feedback Q enhancement scheme. The proposed filter has minimum dependence on the bandwidth of the operational amplifiers and is capable of operating over a wide frequency range with relatively stable Q and resonant frequency. [ABSTRACT FROM AUTHOR]

A current fed thyristor inverter circuit useful for ultrasonic frequency cleaning and welding is analysed. The design criteria for the choice of circuit components and their effect on circuit operation are discussed. Experimental results are presented.
For high power ultrasonic applications such as cleaning and welding, a frequency range of 20 to 50 kHz is used. Transistor inverter circuits are generally used as ultrasonic sources. A number of transistors are connected in parallel to obtain the required power output. In high power applications thyristors can be used with advantage. With the advent of fast acting gate turn-off thyristors (Raderecht 1974), the thyristor circuits are likely to become more economical and the system more compact.
Voltage fed inverters (Fry 1960, Mapham 1967, Revankar and Karande 1974) can be used as ultrasonic sources. These circuits essentially consist of a series inverter configuration. The ultrasonic inverters proposed by Mapham have a better circuit turn-off time, but they suffer from high dv/dt. Nowadays the current fed inverters (Pelly 1970, Revankar and Gadag 1973, 1974) are being widely used for high frequency induction heating systems with a tuned compensated load because of their distinct advantages. These circuits work on the principle of forced commutation. They have high di/dt and starting problems. The principle of time-sharing (Thompson 1963, Akodis et al. 1965, Pelly 1970, Berkovich et al. 1973, Revankar and Patwardhan 1974) can be applied to increase the frequency range of such inverters. In this paper a current fed inverter described by Berkovich is studied in greater detail and its suitability for ultrasonic applications is discussed. [ABSTRACT FROM AUTHOR]

A simple type of d.c. chopper circuit with triacs is presented. The circuit is analyzed and the design criteria for the reliable operation of the circuit are evolved. Certain circuit modifications are suggested and their effects are discussed.
The triac (RCA manual 1971, GE SCR manual 1972) is basically a controlled bidirectional switch and can be used to replace the combination of a thyristor and an inverse-parallel connected diode used in chopper circuits. In an earlier work the concept of forced commutation in triac circuits (Revankar and Trasi 1975 a) is evolved and the necessary conditions are derived. Use of triacs in chopper circuits (Revankar and Trasi 1975 b) is investigated and a simple chopper circuit with a commutating L-C circuit directly across the main triac is presented. In this paper a triac chopper circuit, where the commutating circuit appears directly across the load circuit, is discussed. [ABSTRACT FROM AUTHOR]

The flow-charts for an SCR. logic variable S(j) and the phase angle for use in digital computation of the output voltage harmonic components in a three-pulse cyclo-converter circuit are discussed. A simple mathematical expression for the digital computation of the components is derived in terms of Fourier series and computed results are presented. [ABSTRACT FROM AUTHOR]

A McMurray commutation circuit with a (di/dt) inductor in series with the main thyristors is analysed. Analysis shows that advanced firing on the commutation current ring is necessary in order to avoid the commutation failure in case of sudden loading of the inverter. Advanced firing boosts the commutation capacitor voltage. Hence, the operating conditions should be adjusted so as to control the commutation capacitor voltage in a narrow range from no-load to full-load conditions. At the same time, the commutation energy corresponding to these conditions should not deviate much from the minimum commutation energy. [ABSTRACT FROM AUTHOR]

This paper presents a multistage pulse-width modulated system for generating three-phase controlled stepped voltage waveforms. A four stage system is discussed. Voltage control is achieved by pulse-width modulation. Harmonics are eliminated by suitable transformer connections. In the four-stage system the eleventh and thirteenth harmonics predominate in its three-phase output voltage waveforms. The advantages of the proposed system are discussed. The results are experimentally verified and compared with the conventional systems. [ABSTRACT FROM AUTHOR]

A voltage control scheme for a magnetically coupled dual bridge inverter with a single star-delta-star three.phase transformer has been investigated. The output waveform is devoid of all harmonic components up to the eleventh. The scheme has the advantage that there are only two commutations for each inverter arm per half cycle and the transformer requires a single core. However, the transformer utilization factor is poor. The control scheme has been experimentally verified. [ABSTRACT FROM AUTHOR]

Proposes a method for synthesizing stepped current waveform. Diagram showing the synthesis of stepped current waveform; Diagram of proposed inverter configuration; Commutation circuit limitations.

A number of voltage-control schemes in 3-phase bridge inverters are investigated. These control schemes are applied to dual 3-phase cascaded bridge inverters with fifth- and seventh-harmonic neutralization to realize pulse-width and amplitude controlled waveforms. kVA ratings of filter components are calculated to realize a total harmonic distortion of 5% in the output waveform. The control scheme with two pulses per half cycle spaced 60° apart in individual inverters gives the lowest total harmonic distortion and requires the lowest filter kVA rating. The theoretical results are experimentally verified and are in close agreement. [ABSTRACT FROM AUTHOR]

Various attempts have been made for the selective reduction of harmonies in the output of AC/AC converters. However, when some harmonics are reduced other harmonic amplitudes increase. Thus, to reduce the harmful effects of these harmonics on other equipment operating on the same line, it may be necessary to use filters. A suitable type of filter depending on the line inductance for such cases is suggested in this paper. Experimental results are also presented. [ABSTRACT FROM AUTHOR]

The paper presents a three-thyristor inverter circuit for generating a three-level output voltage waveform. The operation of the circuit is described. Analysis of the commutation circuit is carried out to evolve optimum values of the commutation elements. Trapped energy problems are discussed. Experimental results on a 5 kVA prototype inverter are presented. [ABSTRACT FROM AUTHOR]

The paper presents an improved method of generating a three-phase stepped-voltage waveform using ten thyristor power switches. In the proposed method, it is possible to generate one step for every 20° of the voltage waveform on all the phases. The waveform has a total harmonic distortion of about 10% and the predominant harmonics are the 17th and 19th. This is possible by a unique method of magnetic coupling between a 120° conduction three-phase bridge inverter and a triple frequency single-phase bridge inverter. The theoretical results are in close agreement with experimental results. [ABSTRACT FROM AUTHOR]

Discusses the simultaneous elimination of undesirable harmonics and output voltage variation in a pulse-width modulated inverter. Advantages of the sinusoidal modulation technique and the Patel-Hoft method; Relationship between the actual load voltage waveform and phase shift angle; Causes of variation in phase shift between the triggering signals applied to the half-bridge inverters.

Whenever the required load voltage variation is over a limited range, it is preferable to use tap-changers to supply power to the resistive loads. This improves the power factor over the conventional phase-control method. However, when phase control is used in conjunction with a tap-hanger, the resulting voltage waveform will have a sufficient amount of harmonics. Thus, a method of reducing any one unwanted line harmonic to a low value is proposed in this investigation. A power circuit to implement the proposed scheme is also suggested. [ABSTRACT FROM AUTHOR]

The paper describes three methods that can be used for controlling the power of resistive loads. One of the methods described here aims at reducing any one unwanted harmonic to a very small value in the case of an a.c./a.c, phase-controlled converter feeding a resistive load. All three methods discussed are compared with the method suggested by Bland (1975) with regard to harmonics, power factor and practical realization of the power circuit. The power circuit and the control circuitry are described. Design criteria for choosing the components in the power circuit are also discussed. [ABSTRACT FROM AUTHOR]

The paper describes a scheme of a frequency multiplier that can be used for multiplying the frequency by n times. By connecting such m circuits in sequence it is possible to achieve frequency multiplication of mn. [ABSTRACT FROM AUTHOR]