Abstract: A control method and apparatus to reduce current through a DC capacitor linking two converters causes the value of the DC-side current output of the first converter to approach the value of the DC-side input current into the second converter, thus minimizing the DC capacitor current which is equal to the difference between the output current from the first converter and the input current into the second converter.

Abstract: A hybrid tap-changer for delivering AC power to a load in which a high-power tap-changing transformer with full range of adjustment but limited resolution is combined with a low-power electronic converter of limited range but high resolution to provide a tap-changing transformer with high resolution.

Abstract: A device and control method to produce braking torque counter to motor rotation. A converter supplies multiple frequency AC power to the motor. A first frequency is supplied at the normal operating frequency/speed. A second frequency, different from the normal operating frequency, is supplied to produce braking torque. The level of braking can be controlled to generally consume some or all of the braking in the device or motor. More than one braking frequency may be utilized. In addition, the relationship between the normal and braking frequency(s) can be maintained to limit motor pulsation.

Abstract: This invention is an improvement to a multi-level, multi-phase power supply. Typically, in such power supplies, each of the phases has one or more power cells providing a pulse width modulated output. In such a configuration, when the transition of the pulse width modulated outputs of corresponding power cells in different phases occurs simultaneously, a double step in voltage is observed on the output of the power cell. This invention is an improvement over the prior art wherein the transitions of the outputs of the power cells are controlled to avoid simultaneous transitions.

Abstract: An electric drive apparatus and method for controlling AC motors wherein the motor output is a function of the AC input power to the electric drive. Means are provided for detecting the voltage being supplied by the source of AC power to a drive circuit, and for controlling the output to the multi-phase AC load based on the detected power level. A controller monitors the motor voltage, current, and speed or frequency while also receiving a command for torque or torque-producing current. The method provides for the operation of the drive circuit in the event of either a partial or complete loss of AC input power. During such an occurrence, the controller will cause the circuit to generate sufficient negative torque to cause a power flow from the motor to the drive circuit to substantially equal the inherent losses in the drive and motor to avoid loss of energy from the DC filter of the drive circuit. Motor torque and speed can be quickly restored when the input power is re-established.

Abstract: An improvement in a power drive is disclosed that allows four quadrant operation with reduced harmonics. The power drive has a multiphase, non phase shifted transformer with a single common input connected inductive reactance. Multiple series connected power cells are utilized, each configured for four quadrant operation and having a multiphase input and a single phase output, each controllable to reduce harmonics in both the input source line and the output line. Each power cell includes a three phase input converter, a smoothing filter, and a single phase output converter. A method for operating the power drive includes the steps of selectively controlling switching events at the input and output of each power cell such that switching events in respective power cells are spaced apart in time thereby reducing harmonic components. The method can be implemented using pulse width modulation control based upon interdigitated carrier signals which control the input and output of each power cell.

Abstract: A device and control method to produce braking torque counter to motor rotation. A converter supplies multiple frequency AC power to the motor. A first frequency is supplied at the normal operating frequency/speed. A second frequency, different from the normal operating frequency, is supplied to produce braking torque. The level of braking can be controlled to generally consume some or all of the braking in the device or motor. More than one braking frequency may be utilized. In addition, the relationship between the normal and braking frequency(s) can be maintained to limit motor pulsation.

Abstract: An adjustable frequency multiphase power supply providing low harmonics to the line and load. The power supply having a plurality of power cells in each phase output thereof, each cell having an input side, and an output side. The input side is capable of converting single-phase AC into DC and for converting DC into AC to said source. The output side is capable of converting DC into a controlled AC output and for converting AC from said load to feed said DC bus. The respective outputs and respective inputs of the cells are series connected. Each cell can have a single-phase transformer connected either to the input side or the output side. The output side of each cell can be controlled to limit the harmonic content of the output AC to the load, and the input side of each cell can be controllable to limit harmonic content of the AC power feed to the source.

Abstract: A high output level is maintained in power supplies having multiple cells in each leg. Failed cells in any leg are bypassed to provide a current path through the respective leg. All of the unfailed cells are utilized while maintaining equal magnitude between phases and a balance phase relationship in the line-to-line output voltage. The invention may be utilized in conjunction with a peak voltage reduction circuit, and a by-pass switch.

Abstract: An electric drive apparatus and method for controlling medium-voltage alternating current motors wherein a multi-phase power transformer having multiple secondary windings provides multi-phase power to multiple power cells which provide four quadrant operation. Each power cell has a single-phase output and is controllable by a modulation controller. The power cells are connected in series thus permitting the maximum output voltage for each cell to be less than the maximum line-to-line voltage. Each power cell can have a rectifier portion to convert input AC-to-DC, capacitors, an output DC-to-AC inverter, a regenerative bridge converter connected in parallel with the rectifier portion and a local modulation controller connected to a master controller.

Abstract: A three-phase transformer having a variable output utilizes an auxiliary winding to minimize the number of switches or taps required to provide a plurality of output voltages. At least two output windings or coils each have a plurality of taps corresponding to varying percentages of output voltages. Although each output winding has at least one tap at the same voltage level, one of the output windings has an additional tap corresponding to a different output voltage level. The auxiliary winding, which preferably has a number of coil turns equal to that corresponding to the spacing between the different voltage levels on the output winding, permits one output winding to be set at a different voltage level than the other output winding. The auxiliary winding includes a pair of terminals which are alternately operable to balance the level and phase of the overall output voltage of the three-phase transformer.

Abstract: An electrical power converter for an incoming AC transformer connected to a multiphase power source and having multiple secondary windings. Each secondary winding is connected to multiple switching cells, each of which functions like a matrix converter. The secondary windings can be either single or multi-phase and more than one transformer can be provided such that the multiple secondary windings can be distributed among individual transformers. The output of at least two of the switching cells are connected in series. The switching cells can be either bi-directional or unidirectional and can also have a three-phase input. A combination of IGBTs and diodes can form the switching cells.

Abstract: A high output level is maintained in power supplies having multiple cells in each leg. Failed cells in any leg are bypassed to provide a current path through the respective leg. All of the unfailed cells are utilized while maintaining equal magnitude between phases and a balance phase relationship in the line-to-line output voltage. The invention may be utilized in conjunction with a peak voltage reduction circuit, and a by-pass switch.

Abstract: A common mode reactor between a DC converter and an AC converter to reduce common mode voltage from current source drives. Smoothing reactors are also placed in the DC current path. Additionally, a combined DC smoothing inductor and common mode reactor can be built on a common core. The single core can be a three legged core having two coils.

Abstract: The invention provides for an autotransformer for converting three-phase AC power to nine-phase AC power. The autotransformer includes three coils each having a plurality of serial windings and a plurality of stub windings. The serial windings form a delta and the stub windings are magnetically coupled with the serial windings from the same coil. Three terminals are provided at the apices of the delta and the three-phase AC source may be directly connected to the respective apex terminals. A plurality of direct outputs are interposed between respective serial windings and a plurality of indirect outputs are electrically connected with the second ends of the stub windings. The voltage magnitude of each of the direct outputs is preferably equal to the voltage magnitude of each of the indirect outputs. The voltages of the direct outputs and indirect outputs are out of phase with the voltages at the apex terminals.

Abstract: An electric arc furnace control system is provided for positioning the furnace electrodes in accordance with the resistance of the arc. This is accomplished by balancing the arc current signal against a voltage signal multiplied by a signal representing the arc circuit power factor to provide an error signal. An analog command signal is then derived from the error signal to control the direction and speed of the electrode hoist drive motor.

Abstract: An adjustable voltage alternating current power supply is provided which is especially suitable for supplying loads of variable resistance. The power supply consists of a transformer having two secondary windings with solid-state switches for alternatively connecting the secondary windings in either parallel or series, and with a firing control circuit for changing the connection of the windings from parallel to series at a predetermined point in each half-cycle of the voltage to adjust the effective output voltage so that constant output power can be maintained, or the output power can be varied in any desired manner.