Bi-directional switch for neutral point clamped PWM inverter
First Claim
1. A bi-directional switch for use in a neutral point clamped PWM inverter which develops alternating output current and voltage comprising alternating first and second voltage and current half-cycles, the inverter having a pair of series-connected main power switches which are coupled across first and second voltages developed by first and second series-connected DC power sources, the first main power switch being intermittently operated in only the first half-cycles of the output voltage to develop a first series of pulses at an output junction between the main power switches and the second main power switch being intermittently operated in only the second half-cycles of the output voltage to develop a second series of pulses at the junction, comprising:
- a clamping switch having main current path electrodes coupled between the main power switches and a neutral voltage developed at a junction between the first and second power sources and further including a control electrode;
means coupled to the control electrode of the clamping switch for operating the clamping switch between pulses in the first and second series of pulses to intermittently connect the inverter output to the junction between the first and second power sources so that load current flows between such junction and the load; and
means coupled to the clamping switch for providing a high impedance path between the first voltage and the neutral voltage and between the second voltage and the neutral voltage so that shorting of the power sources is avoided even when one of the main power switches and the clamping switch are both in an on state.
1 Assignment
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Accused Products
Abstract
Bi-directional switches for use with neutral point clamped PWM inverters have utilized clamping switches which are operated alternately with main power switches in the inverter to periodically connect an output terminal of the inverter to a neutral voltage. However, a delay period is typically interposed between turn-off of a main power switch and turn-on of the clamping switch to minimize the possibility of a potentially destructive shoot-through condition. This delay adversely affects the quality of the power developed by the inverter and leads to an undesired increase in the size of snubber circuits coupled across the power switches. In order to overcome these problems, a bi-directional switch according to the present invention includes circuitry for providing a high impedance path in series circuits including the main power switches and the clamping switch so that shoot-through currents are blocked even when one of the main power switches and the clamping switch are simultaneously on. The delays between turn-off of a main power switch and turn-on of the clamping switch can thereby be reduced or eliminated, thereby resulting in improved quality of the output power of the inverter and a reduction in the size of snubber circuits used therein.
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Citations
23 Claims
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1. A bi-directional switch for use in a neutral point clamped PWM inverter which develops alternating output current and voltage comprising alternating first and second voltage and current half-cycles, the inverter having a pair of series-connected main power switches which are coupled across first and second voltages developed by first and second series-connected DC power sources, the first main power switch being intermittently operated in only the first half-cycles of the output voltage to develop a first series of pulses at an output junction between the main power switches and the second main power switch being intermittently operated in only the second half-cycles of the output voltage to develop a second series of pulses at the junction, comprising:
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a clamping switch having main current path electrodes coupled between the main power switches and a neutral voltage developed at a junction between the first and second power sources and further including a control electrode; means coupled to the control electrode of the clamping switch for operating the clamping switch between pulses in the first and second series of pulses to intermittently connect the inverter output to the junction between the first and second power sources so that load current flows between such junction and the load; and means coupled to the clamping switch for providing a high impedance path between the first voltage and the neutral voltage and between the second voltage and the neutral voltage so that shorting of the power sources is avoided even when one of the main power switches and the clamping switch are both in an on state. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A bi-directional switch for use in a neutral point clamped PWM inverter having a pair of series-connected main power switches which are coupled across a power supply and which are operated to produce an output at a junction therebetween, comprising:
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a bridge including first and second diodes in first and second arms of the bridge and first and second controlled switches in third and fourth arms of the bridge, the bridge further including first through fourth vertices at the junctions between arms, the first vertex between the first and third arms being coupled to a neutral voltage and the second vertex between the second and fourth arms being coupled to the junction between the main power switches; a clamping switch having main current path electrodes coupled between the third and fourth vertices of the bridge; and means for controlling the first and second controlled switches and the clamping switch alternately with the main power switches to prevent shorting of the power supply. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A bi-directional switch for use in a neutral point clamped PWM inverter which develops alternating output current and voltage comprising alternating first and second voltage and current half-cycles, the inverter having a pair of series-connected main power switches which are coupled across first and second voltages developed by first and second series-connected DC power sources, the first main power switch being intermittently operated in only the first half-cycles of the output voltage to develop a first series of pulses at an output junction between the main power switches and the second main power switch being intermittently operated in only the second half-cycles of the output voltage to develop a second series of pulses at the junction, comprising:
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a bridge including first and second diodes in first and second arms of the bridge and first and second SCR'"'"'s in third and fourth arms of the bridge, the bridge further including first through fourth vertices at the junctions between arms, the first vertex at the junction between the cathode of the first SCR and the anode of the first diode being coupled to a neutral voltage at the junction between the power sources, the second vertex at the junction between the cathode of the second SCR and the anode of the second diode being coupled to the junction between the main power switches; a clamping transistor having a first main current path electrode coupled to the third vertex at the junction between the cathodes of the first and second diodes, a second main current path electrode coupled to the fourth vertex at the junction between the anodes of the first and second SCR'"'"'s and a control electrode; and means coupled to the control electrode of the clamping transistor and to the SCR'"'"'s for controlling the clamping transistor and the SCR'"'"'s such that the clamping switch and the second SCR are turned on between pulses during each first half-cycle of the output current and the first SCR is maintained in an off condition during such half-cycles and the clamping switch and the first SCR are turned on between pulses during each second half-cycle of the output current and the second SCR is maintained in an off condition during such half-cycles. - View Dependent Claims (20)
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21. A bi-directional switch for use in a neutral point clamped PWM inverter having a pair of series-connected main power switches which are coupled across a power supply and which are operated to produce an output at a junction therebetween, comprising:
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a bridge including first and second diodes in first and second arms of the bridge and first and second transistors in third and fourth arms of the bridge, the bridge further including first and second vertices at the junctions between arms, the first vertex between the first and third arms being coupled to a neutral voltage and the second vertex between the second and fourth arms being coupled to the junction between the main power switches; and means for controlling the first and second controlled switches alternately with the main power switches to prevent shorting of the power supply. - View Dependent Claims (22, 23)
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Specification