Soft switching three-level inverter
First Claim
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1. A three-level neutral point clamped inverter leg for providing soft switching of power devices, the inverter leg comprising:
- series coupled first, second, third, and fourth main switches connected between positive and negative rails of a DC supply, the first main switch connected between the positive rail and a first node, the second main switch connected between the first node and an output node, the third main switch connected between the output node and a second node, and the fourth main switch connected between the second node and the negative DC rail, the output node also connectable to a load for providing a load current, the DC supply including two DC sources arranged in series, a first DC source connected between the positive DC rail and a neutral node and the second DC source connected between the neutral node and the negative DC rail;
a current provider for providing a boost current source or boost current sink at either the first or second nodes;
first, second, third, and fourth diodes coupled in antiparallel relationship with the first, second, third, and fourth main switches respectively;
first and fourth capacitors coupled in parallel with the first and fourth main switches respectively; and
a first clamping diode and a first clamping capacitor connected between the first and neutral nodes and a second clamping diode and a second clamping capacitor connected between the neutral and second nodes, the first clamping diode arranged to pass current from the neutral node to the first node when forward biased and the second clamping diode arranged to pass current from the second node to the neutral node when forward biased.
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Abstract
A three-level NPC inverter topology including two auxiliary resonant commutation circuits which are controlled to clamp the voltage across each main inverter switch to zero voltage prior to altering the state of the switch in order to achieve soft switching of all main inverter switches while reducing output voltage harmonics and gradients.
86 Citations
25 Claims
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1. A three-level neutral point clamped inverter leg for providing soft switching of power devices, the inverter leg comprising:
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series coupled first, second, third, and fourth main switches connected between positive and negative rails of a DC supply, the first main switch connected between the positive rail and a first node, the second main switch connected between the first node and an output node, the third main switch connected between the output node and a second node, and the fourth main switch connected between the second node and the negative DC rail, the output node also connectable to a load for providing a load current, the DC supply including two DC sources arranged in series, a first DC source connected between the positive DC rail and a neutral node and the second DC source connected between the neutral node and the negative DC rail; a current provider for providing a boost current source or boost current sink at either the first or second nodes; first, second, third, and fourth diodes coupled in antiparallel relationship with the first, second, third, and fourth main switches respectively; first and fourth capacitors coupled in parallel with the first and fourth main switches respectively; and a first clamping diode and a first clamping capacitor connected between the first and neutral nodes and a second clamping diode and a second clamping capacitor connected between the neutral and second nodes, the first clamping diode arranged to pass current from the neutral node to the first node when forward biased and the second clamping diode arranged to pass current from the second node to the neutral node when forward biased. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method for controlling a three-level neutral point clamped inverter leg to provide soft switching of power devices, each inverter leg including a plurality of main switches and an output node which is connected to a load providing a line current thereat and a current means for providing a current source or sink, the leg also including at least one capacitor in parallel with each of the main switches, the inverter controlled so that turn-on delay periods are provided between each time one main switch is turned off and another main switch is turned on, the method comprising the steps of:
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during each turn-on delay period, prior to turning on a main switch wherein the main switch to be turned on is a next-on switch; (a) providing a discharge current including a boost current which, together with said line current, fully discharges all capacitors which are in parallel with said next-on switch so there is substantially zero potential across the next-on switch; at the end of each turn-on delay period; (b) turning on said next-on switch; and (c) eliminating said source or sink current. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. An n-level neutral point clamped inverter leg for providing soft switching of power devices where n is greater than two, the inverter leg comprising:
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a DC supply providing n different potential rails including a zero potential rail, and at least one maximum positive potential rail and one maximum negative potential rail; a plurality of series coupled switches connected between the maximum positive and negative potential rails, the switches arranged in (n-1) pairs, switches in each pair connected at intraswitch nodes and adjacent switch pairs connected at interswitch nodes, a first switch connected to the maximum positive potential rail and a (2n-2) switch connected to the maximum negative potential rail, each of the interswitch nodes uniquely connected to a different one of said potential rails, one of the interswitch nodes connected to an output line which is connectable to a load; a plurality of capacitors, at least one of said capacitors arranged in parallel with each of said switches; a plurality of diodes, a different one of said diodes coupled in antiparallel relationship with each of said switches; a current provider for providing a discharging current source or sink at any of the intraswitch nodes; and a controller for controlling the current provider and the switches; whereby, the controller controls the switches and the current provider so that, prior to changing the state of a switch, the current provider provides a current source or a current sink to at least one of said intraswitch nodes to discharge all capacitors in parallel with said switch so that at least one diode in parallel with said switch clamps zero voltage across said switch. - View Dependent Claims (21, 22, 23, 24, 25)
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Specification