Auxiliary Thyristors Research Articles

Classification of Thyristor Commutation Methods

A classification of thyristor commutation methods is presented. The classification is based on whether the commutation pulse is a voltage pulse or current pulse, whether it is connected in parallel or in series with the thyristor to be commutated, whether the pulse is applied with the help of a main or an auxiliary thyristor, and whether the commutation circuit is charged from the main source or from an auxiliary source. Inverters are further classified according to the location of the commutation pulses.

Microprocessor Controller for a Thyristor Converter with an Improved Power Factor

A microprocessor-based algorithm for steady-state and dynamic control of a modified six-pulse converter with two neutral-connected auxiliary thyristors is described. The algorithm which is applicable to the standard six-thyristor bridge is experimentally verified and is found to give a very fast, precise, and equidistant control of the thyristor triggerings. This paper describes the operation of the modified bridge, the control algorithm and the microprocessor implementation, and gives the bridge transfer function and dynamic response.

The Performance of an Inverter Having AC Switched Commutation

A voltage-fed thyristor inverter in which the commutating circuit contains a pair of auxiliary thyristors in an ac switch connection is presented. Operation of the circuit is investigated by computer-aided analysis and performance calculation, leading to selection of design conditions. The results are compared with another type of commutating circuit. Overall, the features of this circuit may or may not be advantageous, depending on the particular application.

An Economical Auxiliary Commutated Thyristor Three-Phase Inverter Suitable for Pulse Frequency Modulation

A new economical auxiliary impulse commutated thyristor inverter is described that is capable of providing a wide range of output ac voltage and output frequency which is useful in variable speed ac drive applications. Output voltage control is provided by a pulse frequency modulation technique, and input dc voltage to the inverter is constant and can be provided by a diode rectifier bridge. The parameters for the various circuit elements, such as commutating inductances and capacitances, di/dt limiting series thyristor inductances, and dv/dt limiting RC snubber circuits are all calculated from a dynamic simulation of a single-phase version of the inverter circuit using a software named ATOSEC I developed at the Universitedu Quebec for a CDC 6400/IBM-370 computer. Experimental results obtained on a practical single-phase inverter are compared with those predicted from computer simulation and performance characteristics obtained in the case of a practical three-phase pulse frequency modulated inverter providing variable output voltage and variable output frequency are reported.

Characteristics of a Two-Phase Double-Superimposed Auxiliary Impulse Commutated Chopper

Circuit configurations, operations, characteristics, and evaluations of a two-phase auxiliary impulse commutated chopper are dealt with. The auxiliary impulse commutated chopper is composed of at least two main thyristors which alternately repeat turn on and turn off during each cycle operation. A commutating capacitor is commonly combined with the main thyristors to supply a commutating current for them in a reverse direction. A plurality of auxiliary thyristors is set for charging the capacitor in alternative polarities and selectively discharging through the main conducting thyristors. Since the first trial operation in 1968 of dc electric trains using the auxiliary impulse commutated chopper, this type of chopper cannot be disregarded for chopper electric trains.

Characteristics of a Current-Fed Inverter with Commutation Applied Through Load Neutral Point

A current-fed inverter which is commutated by an auxiliary commutating circuit acting through the load neutral point is investigated. The auxiliary commutation circuit consists of a single commutating capacitor and two auxiliary thyristors which are used to sequentially commutate the main thyristors. The properties of the inverter are considered for the case of an ac machine load, although the results are general and can be easily applied to cases where the inverter is interconnected with an ac power system. A ``voltage behind subtransient reactance'' model results in a good prediction of the inverter operating modes for either a synchronous or an induction machine. It is shown that if conventional simple-sequential gating is used, the inverter can only operate in the motoring region, while a commutation failure will result in the generating region. This negative feature is overcome by introducing a ``delayed gating'' scheme for the thyristor, which allows the peak commutating capacitor voltage to be actively controlled; thus, commutation for various inverter conditions is maintained. A scheme of parallel commutation circuits is introduced which allows the value of commutating capacitance to be actively selected as a function of load condition. While the main thyristors are subjected to approximately 50 percent more applied voltage compared to the more conventional auto-sequential type of inverter in present use, the thyristors may be rectifier grade since a substantial di/dt inductance is naturally provided by the motor leakage inductance: a fact which means that negligible snubber components are needed compared to the auto-sequential circuit.

Analysis of a Novel Forced-Commutation Starting Scheme for a Load-Commutated Synchronous Motor Drive

A load-commutated inverter synchronous motor drive system employing a simple auxiliary commutation circuit for machine startup analyzed, and results hybrid computer simulation are presented. The commutation circuit employs a single commutation capacitor connected to the neutral of the machine and two auxiliary thyristors, which are used only during machine starting. A practical operating scheme is developed for the forced commutated inverter, which insures commutation over all load currents by actively allowing the commutation capacitor to charge to a voltage proportional to load, current. Results of key computer runs are given including inverter waveforms, transient waveforms during transition from forced to load commutation, as well as the effect of forced commutation and load commutation on pulsating torque. The forced-commutation circuit is used only for synchronous machine startup. However, due to its simplicity it also is an attractive alternative to be considered for other types of current-fed inverter ac drives.

Thyristor Commutation in DC Choppers - A Comparative Study

The typical dc chopper motor controller consists of two thyristors, two or three diode rectifiers, a commutating capacitor, and one or more commutating inductances. The major art in circuit design is selecting the most suitable configuration for the given application, particularly the location of the inductances. It is desirable to minimize the inductance in certain loops and to carefully choose the inductance in other loops. A computer-aided analysis and optimization technique has been applied to several attractive chopper circuits. It appears that inductance in series with the auxiliary thyristor favors turn-off of the main thyristor at the expense of the auxiliary thyristor and vice versa. The best arrangement has most of the commutating inductance in a path that is common to both thyristors. Where one of the thyristors has a diode connected directly across it, there is generally an optimum value of inductance which yields maximum turn-off time. If no such diode is used, the maximum turn-off time is obtained when the inductance is zero.

A Comparative Investigation of High Power Pulsewidth Modulated Inverter Circuits

Publisher Summary The maglov drive at the maximum speed of 500 km/h and a traction force of 100 KN requires a converter power of 14 to 20 MW. A linear synchronous motor with extended primary winding drive involves relatively low stator currents to keep reduced active and reactive losses in the train winding. In all the circuits being examined, the load current is commutated from the main thyristor, through which the load current was flowing, to the auxiliary thyristor. The rate of rise of the commutating current is limited in the first time interval by means of the commutating inductance. McMurray circuit represents a PWM type inverter that can be constructed with relatively few semiconductors and therefore, it seems to be suitable for very high power loads. The condition for the subsequent extinguishing of this thyristor is a positive capacitor voltage.

High-voltage high-power gate-assisted turn-off thyristor for high-frequency use

The fast switching thyristor with an integrated rectifier-diode connected in antiparallel to the cathode-emitter junction of auxiliary thyristor has been made. This thyristor has the ratings of blocking voltage 1200 V, average current 400 A. The turn-off time of less than 6 µs can be obtained by applying -10 V gate bias. It has the interdigitated gate structure and the high-frequency current rating more than 500 A at 10 kHz.

Optimum Design of Commutation Circuit in a Thyristor Chopper for DC Motor Control

This paper deduces the expressions for the commutating capacitor voltage and current during the commutation period of the main and auxiliary thyristor in a chopper for a dc motor control system. After a successful commutation, a certain amount of energy is ``stored'' in the circuit components, and for best component utilization this stored energy has to be minimized. The procedure of minimum stored energy in the commutation circuit has resulted in the selection of optimum values of commutating capacitors and inductors, and the values so obtained are more precisely defined than those indicated by early workers.

A New and Simple Three-Phase Thyristor Inverter for Variable Frequency Operation

A new three-phase inverter circuit is described and analyzed for the condition of an inductive load. The circuit does not require an auxiliary supply or any auxiliary thyristors to assist commutation. All commutation capacitors are placed across the dc side but are used in the same way as capacitors that are normally used for ac side commutation. The output voltage of the inverter is a quasi sine wave controlled by a simple firing circuit. The author was a visiting Research Fellow with the Department of Electrical Engineering and Electronics, the University of Manchester Institute of Science and Technology, Manchester, England.

A thyristor protected against di/dt failure at breakover turn-on

The principle and the operation of a thyristor that can be turned on by exceeding its breakover voltage are described. The principle uses the concept of an auxiliary thyristor amplifying the small breakover current to a large gate current for the main thyristor. In this arrangement the breakover turn-on has to occur first in the auxiliary thyristor. This is ensured by a doping of the n-base of the auxiliary thyristor which is higher than that of the n-base of the main thyristor. Time resolved infrared photographs of the breakover turn-on are presented. Also, infrared photographs of the breakdown radiation from p- n- p structures are used to give a survey on the starting silicon which already contains the inhomogeneous doping.

A Brushless DC Motor With Armature Induced Voltage Commutation

The brushless dc motor described in this article is composed of six thyristors and of a single synchronous motor with an auxiliary position sensor. On the field poles of this motor compensating windings are provided. These windings are connected in series with dc supply as is the case with a dc motor. However, in the motor described in this article the commutation is performed by the armature induced voltage, therefore commutating devices such as capacitors, reactors and auxiliary thyristors are not required.

Adjustable Speed Drive with a Brushless DC Motor

The brushless dc motor described consists of a synchronous motor with a rotor position sensor and a three-phase bridge inverter. The commutation in the inverter circuit is performed by the induced voltage of the armature windings. In this situation, since auxiliary commutation devices such as capacitors, inductors, and auxiliary thyristors are not required, the simplest inverter circuit is obtained. However, the commutation ability decreases at low speed and starting difficulty results. A novel starting procedure is described whereby the chopping of the rectifier output voltage is accomplished by control of the delay angle. In order to obtain a rapid interruption of the main circuit current, an auxiliary thyristor antiparalleled to the smoothing reactor is used. Finally, a new method of speed sensing that eliminates the need of a tachogenerator is proposed. Speed stabilization with an accuracy about 5 percent in a speed range of 10:1 is perforned with this new control system.

Analysis of thyristor DC chopper power converters including nonlinear commutating reactors

Dc chopper power converters are used to control the power supplied to a dc load from a dc source. In a battery-powered vehicle, for example, a dc chopper can control the dc series traction motor. Thyristors are favored for the switching element in high power applications. The particular circuit described here can be used as a voltage step-down converter or a voltage step-up converter and uses two auxiliary thyristors to turn off the main power thyristor. The behavior of the step-up circuit is described by exactly the same equations as the step-down circuit when the input voltage is replaced by the load voltage and the load current is replaced by the input current. The analysis treats the general case where saturating reactors are used to soften the commutation of current in the power semiconductors. The nonlinear characteristics of these reactors are approximated by two linear segments when molybdenum-Permalloy powder cores are used. Linear or square-loop cores are included by the theory as special cases. A design synthesis based on the analytical equations is best performed with the aid of a computer.