Electric power conversion systems – Current conversion – Including automatic or integral protection means
Reexamination Certificate
1995-09-29
2001-07-24
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Including automatic or integral protection means
C363S037000
Reexamination Certificate
active
06266258
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the art of electrical power substrates. More particularly, the invention relates to an advantageous arrangement of switching devices and diodes in an inverting circuit of the type used in power substrates.
In the art of power electronics, numerous applications are known for switch-mode inverter circuits. Such circuits typically include a pair of solid state switching devices, such as semiconductor controlled rectifiers (SCR's), power transistors, insulated gate bipolar transistors (IGBT's) or the like, coupled in series across a direct current (DC) power bus. A flyback diode is coupled in parallel with each switching device. Input DC power is commonly applied to the inverter circuit via a direct current bus from a rectifying and filtering circuit coupled to a source of alternating current (AC) power. By controlled operation of the switching devices, such as by pulse-width-modulation, AC power output is obtained in an output line between the switching devices at desired frequency and voltage. The circuits may be configured for single or three phase applications, such as in AC motor drives.
During controlled switching of such inverter circuits, voltage spikes are commonly encountered due to parasitic inductance, particularly between the switching devices and the output line. In particular, due to the topology of known inverter circuits, parasitic inductance is problematic during transient turnoff periods due to the length of current carrying paths between each switching device and the opposing diode, as well as to the close proximity of the flyback diodes to their corresponding switching devices, and the proximity of current paths between the output line and the diodes. The adverse effects of such parasitic inductance is especially troublesome in applications where controlled switching is extremely rapid, such as in pulse-width-modulation techniques used to generate AC output having desired waveforms.
Thus, there is a need for an improved inverter topology which reduces or eliminates such parasitic inductance and thereby improves the characteristics of the output power waveforms. In particular, there is a need for an improved circuit topology of this type that can be employed in a rather straightforward manner in both single phase and three phase inverter arrangements, such as in power substrates for devices such as variable frequency motor drives.
SUMMARY OF THE INVENTION
The present invention features a novel topology for inverter circuits of the type incorporated in power substrates and similar devices. The topology employs placement of the switching devices and flyback diodes that advantageously cancels or reduces parasitic inductance during transient switching phases of operation. In particular, the topology permits current carrying paths between switching devices and their opposing diodes to be shortened considerably as compared to existing inverter circuitry. The topology also judiciously places each switching device physically adjacent to the opposing diode and permits current carrying paths between the diodes and switching devices to be physically routed so as to contribute to inductance cancelling effects. The technique is applicable both to single phase inverter circuits as well as to three phase circuits.
Thus, in accordance with one aspect of the invention, an inverter circuit for converting direct current power from a direct current bus to controlled alternating current power includes a high side switching device, a low side switching device, and a pair of flyback diodes. The high side switching device is coupled between a high side of the bus and an output line, while the low side switching device coupled between a low side of the bus and the output line. A first of the flyback diodes is electrically coupled in parallel with the high side switching device and disposed adjacent to the low side switching device. The second flyback diode is electrically coupled in parallel with the low side switching device and disposed adjacent to the high side switching device.
In accordance with another aspect of the invention, a three phase inverter circuit for converting direct current electrical power from a direct current bus to alternating current power includes first, second and third phase inverters. Each inverter includes high and low side switching devices and a pair of flyback diodes. The high side switching device of each inverter is coupled between a high side of the bus and a respective output line, while the low side switching device is coupled between a low side of the bus and the output line. A first of the flyback diodes in each inverter is electrically coupled in parallel with the high side switching device of the inverter and is disposed adjacent to the low side switching device. The second flyback diode of each inverter is electrically coupled in parallel with the low side switching device of the inverter and disposed adjacent to the high side switching device.
In accordance with another aspect of the invention, a power substrate for converting alternating current power from a source to controlled frequency alternating current power includes a rectifier circuit, a direct current bus and an inverter circuit. The rectifier circuit is configured for converting alternating current power from the source to direct current power. The direct current bus is coupled to the rectifier circuit for conducting direct current power from the rectifier circuit and includes a high side bus and a low side bus. The inverter circuit includes high and low side switching devices and first and second flyback diodes. The high side switching device is coupled between the high side bus and an output line. The low side switching device is coupled between the low side bus and the output line. The first flyback diode is electrically coupled between the high side bus and the output line and is disposed adjacent to the low side switching device, while the second flyback diode is electrically coupled between the low side bus and the output line and is disposed adjacent to the high side switching device.
REFERENCES:
patent: 5055990 (1991-10-01), Miki et al.
patent: 5123746 (1992-06-01), Okado
Gerasimow A. M.
Rockwell Technologies LLC
Vu Bao Q.
Wong Peter S.
Yoder Patrick S.
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