Toshiba International Corporation

Takashi Morishita

Mike Daskalos

John David Kleinecke

Yoichi Morishima

Toshiaki Oka

An inverter system for driving electrical loads such as multi-phase induction motors is disclosed utilizing five single-phase inverter cells configured in a wye configuration. Inverter cells such as neutral-point-clamp inverter cells are configured to generate a voltage waveform between two output terminals and further configured with a terminal providing a neutral voltage reference point with respect to each of the two output terminals. The inverter cells may be configured with the neutral voltage reference points connected together and with one output terminal from each inverter cells connected together to provide three outputs of the inverter system at different voltage phases and with the common neutral reference point as the wye connection of the three outputs. The other three single phase inverter cells may be added to each of the three outputs to boost the output voltage of the inverter system and decrease the maximum voltage requirements on each inverter cell.

Medium voltage inverter system

An 18n-pulse rectifier for AC drive systems having a separate DC bus for each output phase is provided, where n=any positive integer. The rectifier uses three separate phase rectifiers, one for each output phase of a transformer, each comprised of 2n six-pulse diode bridges connected in series or parallel. Each phase rectifier may be supplied with n unique sets of phase inputs from a transformer secondary winding. In some configurations, the n sets of inputs provided to each rectifier are separated by 60/n degrees of phase (when n is greater than 1), while the corresponding inputs to neighboring rectifiers are separated by 20/n degrees of phase. In a 36-pulse example, the phase offsets for the inputs provided to the rectifiers may be &#x2212;25&#xb0; and +5&#xb0; from the transformer primary winding (for the first rectifier), &#x2212;15&#xb0; and +15&#xb0; from the primary winding (for the second rectifier) and &#x2212;5&#xb0; and +25&#xb0; from the primary winding (for the third rectifier). Each set of inputs may include three lines of in-phase current, and may be coupled to one of the six-pulse diode bridges. In some configurations, two identically-wound transformers may be used to supply output voltages to the rectifiers. The transformers may each supply the same phase offsets to each rectifier, in accordance with the methodology above, which may support higher-capacity applications.

Multi-pulse rectifier for AC drive systems having separate DC bus per output phase and multiple isolation transformers

An uninterruptible power supply having a controllable leakage current is disclosed. The leakage current is controlled by adjusting a switching speed (i.e., dV/dt rate) of switches in the output inverter (i.e. DC-AC converter stage). Leakage current can be reduced by reducing the switching speed (dV/dt rate) of the output inverter switches. In one embodiment, leakage current is held constant or moderated as output power decreases by reducing the switching speed (responsive to leakage current) as output power decreases. The switching speed can be adjusted by adjusting the gate resistance or gate voltage. Increasing the gate resistance or decreasing the gate voltage will cause a reduction in the switching speed, and increase in leakage current. Conversely, reducing the gate resistance, or decreasing the gate voltage will cause an increase in switching speed, and increase in leakage current. The present invention is applicable to any uninterruptible power supply having output inverter switches.

Uninterruptible power supply with low leakage current

A medium or high voltage multi-inverter system is described, in which multiple inverter cells are included in a phase line to increase the voltage level supported by the system, and support higher voltage loads such as AC three-phase motors. In one configuration, five cells are used: two each in two phase lines, and one in a third phase line. In one of the phase lines having two cells, a second cell is series connected in reverse polarity, generates a phase matching the phase of the third line, while the other cell in the phase line generates an output with a different phase. One or more failure switches may be included to allow for short-circuiting of the output poles of one or more of the cells, so that in case of cell failure, the system can continue operation. For example, switches may be employed for the second cells in the two phase lines having two cells, and those cells may be available as spare cells in case of a cell failure.

Systems and methods are provided for dynamically changing configurations of multi-inverter drive systems. By changing configurations during operation, a multi-inverter system of the present invention can provide greater than half of full output power during failure of a power cell and can provide efficient braking torque during regeneration. The inverter drive system includes a plurality of single pole inverter cells and a configuration switch system connecting the single pole inverter cells in a star configuration and for changing the connection configuration of the single pole inverter cells. In one embodiment, the configuration switch system is adapted to dynamically change the star configuration of the inverter system to a mesh configuration during operation of the load. In another embodiment, the configuration switch system is adapted to dynamically change the star configuration of the single pole inverter cells to form a polyphase inverter.

Inverter drive system

A method and apparatus for conducting regenerative braking for a motor load is disclosed wherein the load is driven by a plurality of power cells on each phase-line to the load, the plurality of power inverters comprising at least one single phase power inverter and at least one 3-phase inverter wherein the 3-phase inverter is connected across 3-phase lines. First, it is detected when the motor load is regenerating a motor load voltage. Then, each single phase inverter in each phase line is shorted out after detecting the motor load regeneration. The motor load voltage is then supplied to the 3-phase inverter. Finally, the load motor voltage is lowered by conducting regenerative braking through the 3-phase inverter.

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Houston, TX, United States of America

Takashi Morishita