Abstract: A single-phase variable-frequency power supply with two output voltages drives a single-phase AC motor that has a start circuit and main winding. For permanent split-capacitor motors, the power supply maintains a constant voltage to the start winding while it reduces the voltage to the main winding at lower frequencies. The power supply can similarly control the speed of capacitor-start and split-phase motors. For fans and pumps and other variable-torque applications, the power supply maintains approximately a constant ratio of main-winding voltage to the square of frequency. The power supply is preferably an electronic pulse-width modulated inverter.

Abstract: A driver circuit for a semiconductor power switch. The driver circuit supplies a high voltage pulse to the gate of an IGBT. The driver circuit also monitors the voltage on the collector of the IGBT with respect to the emitter. If the voltage at the collector of the IGBT does not drop when the IQBT is turned on, the IGBT driver circuit detects a short circuit and triggers a linear integrator within the driver circuit. The linear integrator gently ramps down the voltage on the gate of the IGBT.

Abstract: A motor starter circuit for minimizing the amount of current drawn by the motor from a power source during starting of the motor through current transformation achieved by selectively controlling actuation of a plurality of high speed switches. The circuit is for use with a alternating current power source that provides positive and negative voltage alternations, and an alternating current motor. The motor starter circuit comprises a first bidirectional switch through which line current from the power source is provided to the motor, and a pair of switch-diode combinations electrically configured to carry the current in the motor when the bidirectional switch, which is controlled to cycle between an open and a closed position, is in an open position. Actuation of the pair of switch-diode combinations is controlled based on the polarity of the motor current alternation.

Abstract: A refrigeration system includes a temperature sensor in a freezing compartment, a temperature sensor in a cooling compartment, an adjustable damper controlling the flow of cooled air from the freezing compartment to the cooling compartment and variable speed drives for fan motors and a compressor motor. The desired set point temperatures for the compartment are compared with the actual sensed temperatures through a controller that controls the speed of the compressor and fan motors, to achieve the desired temperature in a fast and efficient manner. When excessive ice is detected on freezing compartment coils, the controller reverses the heat transfer cycle of the refrigerant to defrost the freezing compartment coils.

Abstract: A refrigeration system includes a temperature sensor in a freezing compartment, a temperature sensor in a cooling compartment, an adjustable damper controlling the flow of cooled air from the freezing compartment to the cooling compartment and variable speed drives for fan motors and a compressor motor. The desired set point temperatures for the compartment are compared with the actual sensed temperatures through a controller that controls the speed of the compressor and fan motors, to achieve the desired temperature in a fast and efficient manner. When excessive ice is detected on freezing compartment coils, the controller reverses the heat transfer cycle of the refrigerant to defrost the freezing compartment coils.

Abstract: By employing a single phase pulse width modulated inverter system, a-c power line voltage may be effectively converted to single phase, variable amplitude and frequency sinusoidal voltage for driving a single phase a-c induction motor at an adjustable speed. The motor may be driven directly in response to the power line voltage (such as during start-up or when it is desired to run the motor at the power line frequency) by bypassing the inverter system and connecting the motor across the power line. Reduced energy consumption may be obtained by operating the motor in response to a reduced inverter output frequency. Switching the motor from the power line to the inverter, and vice versa, is accomplished without interruption. Immediately prior to each, switchover the inverter output voltage is synchronized to the power line voltage to minimize any electrical disturbance during the switching transition.

Abstract: A motor drive system for driving a conventional single phase PSC motor from a two-phase power source which allows for convenient motor direction reversal. In one embodiment, the PSC motor is supplied from a three-phase inverter that is controlled to generate two-phase power. In another embodiment, the PSC motor is connectable through a double-pole double-throw switch to either a single phase source including a run capacitor or a two-phase inverter source.

Abstract: A motor drive system for driving a single-phase PSC motor, in which the two motor windings are conductively isolated from each other, from a two phase power source. In one embodiment, the PSC motor is supplied from a two phase inverter circuit. The PSC motor is also connectable through a four-pole double-throw switch to either a single phase source including a run capacitor or the two phase inverter circuit.

Abstract: A motor drive system for driving a conventional single phase PSC motor from a two-phase power source. In one embodiment, the PSC motor is supplied from a three-phase inverter that is controlled to generate two-phase power. In another embodiment, the PSC motor is connectable through a double-pole double-throw switch to either a single phase source including a run capacitor or a two-phase inverter source.

Abstract: A snubber circuit for use with a power seimconductor switching device of a power converting circuit. The snubber circuit includes a snubber capacitor, coupled across the switching device for charging with current bypassing the switching device when the switching device is turned off. The snubber circuit also includes a transformer having a primary winding coupled in series with the snubber capacitor to conduct the flow of current discharged by the snubber capacitor when the switching device is turned on. The snubber circuit further includes an inductor, coupled in series with a secondary winding of the transformer, for regulating the flow of discharged current from the capacitor. The snubber circuit is coupled to return the energy discharged from the snubber capacitor to a power source to which the power converting circuit is coupled.

Abstract: A control circuit for generating gating signals to drive the SCRs of an AC switch coupled between a three phase AC source and a three phase load. A reference voltage signal is derived from the source and, after filtering, is applied to a squaring amplifier. The amplifier output is applied to a phase-locked loop (PLL). The output signal of the voltage controlled oscillator (VCO) of the PLL is fed back to the phase comparator thereof via two dividing counters. The output of one counter is applied to a logic block for generating a ramp reset signal in phase with a selected source phase-to-neutral voltage. The ramp reset signal is applied to a ramp forming circuit the output of which is applied to a first input of a comparator. The comparator receives a DC control voltage on its second input and provides on its output a gating signal corresponding to the source selected phase.

Abstract: A substantially perfect single phase sinusoidal shaped voltage waveform may be generated for driving a single phase a-c induction motor by employing a sinusoidally weighted pulse width modulated signal to switch a pair of solid state power switches on and off in alternation in order to connect the motor alternately across positive and negative power supplies. A low pass filter is effectively connected in series with the single phase motor to filter out all of the signal components except the fundamental of the sine wave modulating frequency. In this way, only a sinusoidal voltage is applied to the motor. By making the switching frequency very high relative to the sine wave modulation component, the filter size and cost are minimized and it is unnecessary to correlate or synchronize the sine wave modulation and switching frequencies.

Abstract: A sinusoidally weighted pulse width modulated switching signal may be developed, for operating an inverter to apply sinusoidal voltage to a single phase a-c induction motor, by comparing a triangular voltage waveform of fixed frequency with a variable frequency sine wave voltage, the switching signal varying between its high and low states whenever the triangular waveform and modulating sine wave intercept one another. A constant ratio of the amplitude of the sinusoidal motor voltage relative to the voltage's frequency, and thus motor speed, may be obtained simply by translating the sinusoidal modulating waveform through a high pass filter before it is compared with the triangular wave. By setting the filter cut-off frequency above the operating frequency range (preferably from about 12 to 60 hertz) of the sine wave generator, the sine wave voltage will be attenuated by the filter in an amount inversely proportional to the sine wave frequency.

Abstract: The power delivered from a three-phase A-C power source and through a network of SCR's (connected, for example, to form a full wave rectifier bridge or to provide an A-C switch) to a load circuit is adjusted by controlling the conduction angles of the SCR's. The control is achieved by developing, from only one of the three alternating phase voltages provided by the A-C power supply, a reference square wave signal of the same frequency and whose amplitude excursions are precisely synchronized or keyed to the zero voltage crossings of the selected phase voltage, even though that phase voltage may include undesired harmonics, noise, transients or other distortion components.

Abstract: A control system is disclosed for connecting the primary windings of a three-phase AC inducton motor in a delta-connection at heavy loads and for automatically reconnecting the windings in a wye-connection at light loads to effect energy savings. Power sensing means produces a control signal which is directly proportional to the power applied to the induction motor. Differential comparator means respond to the control signal and to an adjustable reference signal, representing a preselected power input level, for generating an actuating signal for switching a wye-delta starter between two conditions, one of which effects the wye connection and the other the delta connection. When the power input is below the preselected level the wye-connection is established, whereas the delta-connection is made when the power input is above the preselected level.

Abstract: An input rectifier supplies d-c energy for an auxiliary-commutated inverter. A logic circuit provides gating signals for the semiconductor switches in the input rectifier circuit and in the inverter circuit. A pre-charge circuit provides an independent path to charge the commutating capacitor in the inverter when the system is energized. The gating signals to the input rectifier are delayed by a predetermined time interval, allowing the commutating capacitor in the inverter to be charged and thus ensure effective commutation when the inverter commences operation.

Abstract: A diagnostic system is provided for apparatus including a heat pump, a thermostat and a logic module intercoupled to regulate operation of the heat pump electro-mechanical units. The normal control and operating circuits for the heat pump are completed over a wiring harness plugged into an electrical connector on the logic module, which also receives a plurality of sensor information inputs. To check the system, the diagnostic system has a first cable terminating in an interconnector, inserted between the electrical connector on the module and the harness plug. The sensor inputs are disconnected, and additional connectors, carried in a second cable of the diagnostic system, are coupled to the sensor input connections on the logic module. When thus connected, the diagnostic system monitors operation of the thermostat, even though the module is removed at a considerable distance from the thermostat, and also actuates the heat pump units to check their operation.

Abstract: The phases of a three-phase AC power supply are applied to a three-phase load, such as a motor, by respective ones of three triacs. Three alternating voltages, phase-displaced by 120.degree., appear across the triacs. When each alternating voltage is in its half cycles of one polarity, for example when the main terminal T.sub.2 is negative relative to the main terminal T.sub.1 of the triac to which the voltage is applied, the triac conducts continuously. During the half cycles of the opposite polarity, however, the conduction angle or time of each triac is varied in response to a control effect. In this way, the magnitude of the phase voltages applied to the load are varied to control the operation of the load, such as to vary the speed of the motor. No neutral point exists for the load currents so a triac, during the negative excursion of its main terminal T.sub.2, cannot conduct unless the terminals T.sub.2 of the other two triacs are in a positive excursion and have been triggered into conduction.

Abstract: Constant condenser pressure is maintained in a refrigeration system by modulating the speed of at least one fan motor of an air-cooled condenser coil in response to the temperature of the refrigerant in the condenser coil, the speed varying directly with temperature. Motor speed variations are achieved by controlling the conduction time of a triac which couples the fan motor to a source of alternating voltage. The triac is triggered into conduction at a phase angle, following the beginning of each half cycle of the alternating voltage, determined by the charging rate of a timing capacitor which charges through a photosensitive transistor optically coupled to an LED. Variation of the refrigerant temperature in the condenser coil changes the light emission of the LED and this in turn varies the charging current translated to the capacitor. The greater the temperature, the greater the charging current and the faster the triac conducts following the start of each half cycle.