Westinghouse Electric Corporation

Alberto Abbondanti

Michael B Brennen

Eric J Stacey

Robert S Gemp

Andress Kernick

Leonard J Kovalsky

A current source inverter for a load commutated induction motor drive is controlled in relation to the direct and quadrature components of the current vector as assigned in response to stator voltage, speed reference and actual speed. Control is on the inverter and the converter in relation to both components.

Load commutated inverter (LCI) induction motor drive

In a load commutated inverter induction motor drive a parallel capacitor bank is used in part to force-commutate the thyristors of the inverter as triggered by auxiliary thyristors and turned off by the other part of the capacitor bank.

Commutation circuit for load-commutated inverter induction motor drives

In a load commutated induction motor drive stability is achieved in a runaway situation by generating in response to the motor speed reference signal a signal representative of the desired power factor angle and in using such signal to delay by that much the gating pulses controlling the current-sourced inverter.

Current source inverter control system for load commutated induction

In order to maintain low telephone interference (IT factor) during its normal operation and to establish rapid-post-fault voltage support to preserve the integrity of electric power transmission lines in the presence of degraded system impedance and harmonic instability, amplitude detection in a transmission voltage regulator (static VAR generator, SVG) is provided based on real time conventional, or fast, Fourier analysis, data samples being used to establish the fundamental voltage amplitude and collected during a specific, frequency tracking sliding window that precedes the amplitude reading by one line voltage cycle of the transmission line. The number of samples in the window is an integer multiple of the line frequency and, in the case of conventional analysis, the pulse number of the switching power circuit is used in the SVG. The amplitude value is updated after each sampling by shifting (sliding) the one cycle sample data base in a first in - first out manner.

Transmission line voltage detector for static VAR generator

In a load commutated inverter (LCI) motor drive, the motor is started from a rotor rest position by modulating the rotor winding with a field current at a constant rate to induce stator voltages which are detected in terms of signs, so as to identify the rotor rest position. The induced stator voltages are used to select an initial pair of thyristors of the inverter to be turned on in the firing sequence for the chosen direction of rotation under normal operation of the drive.

Start-up system for a synchronous motor drive

In a load commutated inverter system, the recovery time of the outgoing static switch is extended by applying an auxiliary commutation voltage in series with the associated phase line. This action is triggered in response to the gating signal of the on-coming switch during a time interval initiated before the expiration of the overlap time interval. Its duration extends by a predetermined amount beyond the normal recovery time of the outgoing switch.

Load-commutated inverter and synchronous motor drive embodying the same

In an induction motor drive a signal representative of the torque T as derived by sensing only the stator armature current I, and the slip frequency f.sub.2 and by calculating instantaneously T=I.sub.1.sup.2 F, where F is a function of f.sub.2 /R.sub.2, where R.sub.2 is the rotor resistance of the motor. The value of R.sub.2 is adjusted to match temperature by generally two alternative methods: (1) measuring the stator temperature, relying on the change of resistance R.sub.1, known experimentally, and applying an equivalent change for the rotor resistance R.sub.2 ; (2) by running the motor at rated speed and determining experimentally R.sub.2 /f.sub.2 as a function of F.

Torque controller for an AC motor drive and AC motor drive embodying the

A timing reference generator for producing a multi-phase timing reference signal in synchronism with a multi-phase source voltage signal is disclosed. The timing reference generator uses an N stage array of series connected phase-locked loop (PLL) circuits to preserve the prefault condition of an input source signal by open circuiting at least the Nth stage prior to the propagation of the fault condition signal through the array. The open circuited stage acts like a flywheel to preserve the prefault condition of the source signal. This output can be used to replace the lost source signal until the fault condition has cleared. The output of the first PLL is used to provide the timing reference signals. This arrangement allows for sensing delays in establishing the occurrence of a fault and the consequent delay in activation of the flywheel. The first PLL comprises a positive sequence type phase detector and series connected band reject harmonic filters in order to eliminate phase errors caused by input voltage unbalance and input harmonic content. Subsequent PLL circuits are of the zero phase error type. Multiple faults are tolerated if two stages of the array are connected in parallel and alternately operated as flywheels. The flywheels are sequenced so that one is kept operating as a flywheel while the other one settles.

Line fault tolerant synchronous timing reference generator for static

A microprocessor-based solid state AC-DC converter system makes use of the microprocessor facility to implement sequential thyristor firing at selected delay angles. A first timer at the AC line fundamental frequency supplies to the microprocessor a numerical master ramp count, from which individual ramp counts are calculated which relate to the individual thyristors to be fired in sequence. From such an individual ramp count by comparison with a delay angle reference count the microprocessor calculates the number of units of time needed until zero count on the individual ramp. A second timer is preset at an initial count value equal to such calculated number of units of time and the second timer is run to count-down. The thyristor next to be fired is triggered when zero count occurs.

Apparatus for efficient use of a microprocessor to control thyristors

In a voltage-source inverter AC power supply, the AC currents are measured exclusively by sampling the DC current in the DC link between voltage-source and inverter. Each sample so derived is correlated to the status of the switches in the inverter at the instant of sampling, or before and after a change in the switching status of the inverter. This technique applies more generally to pulse-width modulation applications, but also to an adjustable voltage input (AVI) inverter motor drive.

Method and apparatus for sampling output AC currents in a voltage-fed

From the sensed input voltages and currents fed into a standard induction motor the stator resistance is known instantaneously through a direct and quadrature treatment of the sensed quantities from which are derived at least four of the following five quantities: the motor overall reactance, the motor overall real impedance, the air gap reactance, the parallel combination of stator and rotor leakage reactances and the stator leakage reactance. This derivation uses the motor intrinsic characteristics at rest, while those four quantities are used in ascertaining the stator resistance instantaneously and recurrently during motor operation, thus, without any sensing means on the motor itself. The load reactance is also determined with the above-stated five quantities. From the knowledge of the stator resistance and the load resistance, a simulated two-phase network is provided and used to ascertain any of the key process variables typically used in an induction motor drive, such as shaft speed, slip, flux, torque. The temperature and load of a standard induction motor are known without sensing and the motor can be remotely controlled for protection against overheating, or overload.

Apparatus and method for determining the operation of an induction motor

The invention provides a bilateral static isolator which is activated by 'soft' forced commutation. Between two points in the power line to be interrupted are connected two thyristors in series-opposition, thus cathode to cathode. In antiparallel with each thyristor is mounted a diode. Thus, the two diodes appear in series opposition between the two power line points. A resonant circuit is applied to the conducting thyristor in order to turn it off with a relatively small reverse voltage. This voltage is obtained by resonant discharge of a precharged capacitor C through an inductor L and a diode D connected in reverse with the thyristor. The forward voltage drop of the diodes appears in reverse across the thyristors from the instant the discharge current rises above the line current until the instant the discharge current drops below the level of the line current. It is during this interval that the thyristor is provided with 'soft' reverse bias. Subsequently the net current reverses again. With the thyristor now recovered, and the diode blocking, the current flows through the other diode and returns by the commutating branch associated therewith.

Force commutated static isolator circuit

A commutation circuit for thyristors alternately turned ON by pulse width modulation (PWM) for the generation of a fundamental sine wave is characterized by two separate primary windings associated with respective positive and negative thyristors with a common secondary winding at the output, and two commutating networks for the respective poles, each including an auxiliary thyristor for fixed-commutation and the resonant combination of a capacitor and an inductor. The thyristors, the commutating networks, the DC source, and the output transformer have a symmetrical disposition as well as symmetrical commutation steps.

Single-pole commutation circuit

Plug reversal of an induction motor supplied by an N-stage inverter system operating under harmonic neutralization technique is provided by reversing the polarity of the square-shaped voltages combined at .pi./N from each other and by reversing at the same time the sequence of the stages as well as the logic of dissection of the reference time wave. A mirror image of the time scale is effected at the instant of reversal. Digital means are used. Reversible ramp forming generators of the UP-DOWN type are associated in each stage with a phase shifter in order to create the mirror image of the logic controlling the inverter system. A reversible ring counter is used to reverse the sequence of the stages. A reversible pulse generator is used to accommodate an integer number of elementary time intervals in each ramp and between each ramp for the given number of stages.

Static controlled AC motor drive having plug reversal capability

Pulse width modulation is produced by digital means. Pulse width modulated waves are stored digitally in a memory and retrieved under control of a voltage signal in order to generate a pulse width modulated wave of predetermined pattern for any discrete value of successive desired output voltage levels. Optimal waveforms are selected and stored which extend only for one quadrant but an alteration of the addressing code based on symmetry yields the mirror image of the stored quadrant while sign modification provides symmetry about the abscissa axis. Also, only a single phase is stored and phase shifting by code alteration of the coded information provides the other phases after retrieval. The notches characterizing a particular pattern are stored in the form of a digital representation one level along several possible levels defining subdivisions of a given time interval which is itself a submultiple of the total duration of the stored quandrant. A comparator responsive to a series of ramp signals detects in real time the stored levels thereby to effect switching from one state to the other and define one edge of a notch. The notches may extend over several of the ramp signals. The invention provides, with substantially the same hardware, for a fixed pattern mode of operation in the normal frequency range, and for a free running triangulation mode for the lower frequency range. The invention applies to the field of induction motor drives with adjustable speed.

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Pittsburgh, PA, United States of America

Alberto Abbondanti