Abstract: A voltage source inverter comprises a rectifier converting AC power to DC power at an output. An inverter receives DC power and converts the DC power to AC power. A link circuit is connected between the rectifier circuit and the inverter circuit and comprises a DC bus. A DC bus capacitor across the DC bus smoothes voltage ripple. An active filter circuit comprises a pair of filter capacitors in series across the first and second rails to create a midpoint. Bidirectional switches are connected between the rectifier input and the midpoint. A current sensor is connected between the bidirectional switches and the midpoint. An active switch controller controls a conduction angle of the bidirectional switches to maintain DC bus voltage at a desired reference level under a wide load range.

Abstract: A voltage source inverter comprises a rectifier having an input for receiving single-phase AC power from an AC source and converting the AC power to DC power on a DC bus. The DC bus has first and second rails to provide a relatively fixed DC voltage. A DC bus capacitor is across the first and second rails to smooth voltage ripple. An inverter receives DC power from the DC bus and converts the DC power to AC power. An active front end circuit comprises a pair of filter capacitors in series across the first and second rails to create a midpoint. A bidirectional switch is connected between the rectifier input and the midpoint. The bidirectional switch is controlled to inject current into the midpoint of the DC bus.

Abstract: A variable frequency motor drive comprises a converter including a rectifier having an input for connection to an AC power source and converting the AC power to DC power. A DC bus is connected to the rectifier circuit. At least one bus capacitor is across the DC bus. An inverter receives DC power from the DC bus and converts the DC power to AC power to drive a motor. A controller is operatively connected to the converter. The controller comprises a speed control controlling the inverter responsive to a speed command to maintain a desired motor speed. A speed foldback control measures DC bus ripple voltage and regulates the speed command responsive to the measured DC bus ripple voltage.

Abstract: A Variable Frequency Drive (VFD) supplies power to rotate a motor, controlling both the speed and direction. The method normally used for this power conversion by the VFD results in energy losses and line harmonics. When the motor is driven by the VFD to be rotating at the same speed and direction as if the motor was straight across the incoming AC power, a transfer in power supply to the motor can be made using contactors to bypass the VFD. When in this bypass mode, the energy losses of the VFD are greatly reduced, and the line harmonics due to the VFD are greatly reduced. When it is subsequently recognized that the speed reference has deviated from being the same speed and direction as if the motor was straight across the incoming AC power, a transfer in power supply can be made from using contactors to once again drive the motor from the VFD.

Abstract: As described herein, a drive circuit for a three phase AC motor comprises an AC/AC converter. The converter has an input for receiving multiphase AC power from an AC source and converting the AC power to variable voltage and variable frequency from the AC source for driving the AC motor. A filter circuit is connected to the AC/AC converter and comprises at least one inductor per phase and at least one capacitor per phase. The capacitors are connected in a broken wye configuration with one side connected to one of the inductors and an opposite side connected via a three phase diode bridge rectifier to a switch. The switch is controlled by a converter control to selectively open or short a neutral point of the broken wye capacitor configuration.

Abstract: An AC/DC converter system comprises an input circuit for connection to a three-phase AC source. An isolation transformer comprises a symmetrical core with a set of primary windings and first and second sets of secondary windings wound on the symmetrical core providing balanced flux in all three phases and magnetically coupling to the set of primary windings. The first and second sets of secondary windings are phase shifted by select amounts from the set of primary windings. The set of primary windings is connected to the input circuit. An AC/DC converter comprises first, second and third three-phase rectifiers, the first three-phase rectifier is powered by the first set of secondary windings, the second three-phase rectifier is powered by the second set of secondary windings, and the third three-phase rectifier is powered by the input circuit. An output circuit is connected between the AC/DC converter and a DC load.

Abstract: A voltage source inverter comprises a rectifier having an input for receiving single-phase AC power from an AC source and converting the AC power to DC power on a DC bus. The DC bus has first and second rails to provide a relatively fixed DC voltage. A DC bus capacitor is across the first and second rails to smooth voltage ripple. An inverter receives DC power from the DC bus and converts the DC power to AC power. An active front end circuit comprises a pair of filter capacitors in series across the first and second rails to create a midpoint. A bidirectional switch is connected between the rectifier input and the midpoint. The bidirectional switch is controlled to inject current into the midpoint of the DC bus.

Abstract: An AC/DC converter system comprises an input circuit for connection to a 3-phase AC source. An autotransformer is coupled to the input circuit for developing first and second phase shifted AC supplies. A first AC/DC converter has a first rectifier connected to the first phase shifted AC supply converting AC power to DC power across a first DC bus having a first DC bus capacitor. A second AC/DC converter has a second rectifier connected to the second phase shifted AC supply converting AC power to DC power across a second DC bus having a second DC bus capacitor. First and second sets of switches are connected between the respective first and second DC buses and a main DC bus having a main DC bus capacitor. The first and second sets of switches are controlled so that only one of the first and the second DC buses is connected to the main DC bus to charge the main DC bus capacitor.

Abstract: An AC/DC converter system comprises an input circuit for connection to a 3-phase AC source. An autotransformer is coupled to the input circuit for developing first and second phase shifted AC supplies. A first AC/DC converter has a first rectifier connected to the first phase shifted AC supply converting AC power to DC power across a first DC bus having a first DC bus capacitor. A second AC/DC converter has a second rectifier connected to the second phase shifted AC supply converting AC power to DC power across a second DC bus having a second DC bus capacitor. First and second sets of switches are connected between the respective first and second DC buses and a main DC bus having a main DC bus capacitor. The first and second sets of switches are controlled so that only one of the first and the second DC buses is connected to the main DC bus to charge the main DC bus capacitor.

Abstract: A resonant gate drive circuit for a power switching device, having a gate-emitter capacitance, is adapted for use with a high frequency power converter. The resonant gate drive circuit comprises a signal input source, a power supply and a resonant inductor. An electrical isolator is connected between the signal input source and a switching node. The electrical isolator is connected to the power supply. A first bidirectional switch is connected between the resonant inductor and the power switching device and includes a first switch control circuit connected to the node to be controlled by a signal from the signal input source. A second bidirectional switch is connected between the power supply and the power switching device and includes a second switch control circuit connected to the node to be controlled by the signal from the input source.

Abstract: An AC/DC converter system comprises an input circuit for connection to a three phase AC source. An isolation transformer comprises a set of primary windings and first and second sets of secondary windings magnetically coupled to the set of primary windings. The first and second sets of secondary windings are phase shifted by select amounts from the set of primary windings. The set of primary windings is connected to the input circuit. An AC/DC converter comprises first, second and third three phase rectifiers, the first three phase rectifier being powered by the first set of secondary windings, the second three phase rectifier being powered by the second set of secondary windings, and the third three phase rectifier being powered by the input circuit. An impedance matching inductor is electrically connected between the input circuit and the third three phase rectifier. An output circuit is connected between the AC/DC converter and a DC load.

Abstract: A variable frequency drive comprises a diode rectifier receiving multiphase AC power from a source and converting the AC power to DC power. An inverter receives DC power and converts the DC power to AC power to drive a load. A link circuit is connected between the diode rectifier and the inverter and comprises a DC bus to provide a relatively fixed DC voltage for the inverter. A bus capacitor is across the bus. A soft charge circuit limits inrush current to the bus capacitor. The soft charge circuit comprises an inductor connected between the source and the link circuit and a switch circuit in the link circuit for selectively providing a semiconverter configuration or a full bridge converter configuration to provide two stage charging of the bus capacitor.

Abstract: A variable frequency drive comprises a diode rectifier receiving multiphase AC power and converting the AC power to DC power. An inverter receives DC power and converts the DC power to AC power to drive a load. A link circuit is connected between the diode rectifier and the inverter and comprises a DC bus to provide a relatively fixed DC voltage for the inverter. A link capacitor is across the bus. A soft charge circuit limits in rush current to the link capacitor. The soft charge circuit comprises an inductor in the bus and a resistor assist circuit across the inductor along with an anti-parallel clamping thyristor reverse connected also across the inductor.

Abstract: An electrical enclosure assembly comprises an enclosure having walls defining an interior space for housing electrical components and having a front flange surrounding a front opening. A cover is hingedly mounted to the enclosure for selectively closing the front opening. The cover comprises a front wall larger than the front opening and a rearwardly extending peripheral rim. Cooling structure is integrally formed on an interior surface of the cover proximate the peripheral rim. The cooling structure comprises a plurality of spaced apart cooling ribs each having a shoulder engaging the enclosure front flange when the cover is in a closed position to provide an air flow path between the interior space and outside of the enclosure through spaces between the cooling ribs.