# US 5,710,698 A · Delta connected resonant snubber circuit

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- Number: US 5,710,698 A
- Document ID: US5710698A
- Status: Granted
- Kind: A
- Application number: 08/540,302
- Filed: 1995-10-06
- Granted: 1998-01-20
- Earliest claimed: 1994-09-30
- Assignees: Lockheed Martin Energy Systems, Inc.
- Inventors: Jih-Sheng Lai; Fang Zheng Peng; Robert W. Young, Sr.; George W. Ott, Jr.
- Web page: https://patentgrep.com/patent/US5710698A

## CPC

- H02M 7/5387: in a bridge configuration
- H02M 1/34: Snubber circuits
- H03K 17/08148: {in composite switches}
- H02M 1/342: {Active non-dissipative snubbers}
- H03K 2217/0036: Means reducing energy consumption
- Y02B 70/10: Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS

## Abstract

A delta connected, resonant snubber-based, soft switching, inverter circuit achieves lossless switching during dc-to-ac power conversion and power conditioning with minimum component count and size. Current is supplied to the resonant snubber branches solely by the dc supply voltage through the main inverter switches and the auxiliary switches. Component count and size are reduced by use of a single semiconductor switch in the resonant snubber branches. Component count is also reduced by maximizing the use of stray capacitances of the main switches as parallel resonant capacitors. Resonance charging and discharging of the parallel capacitances allows lossless, zero voltage switching. In one embodiment, circuit component size and count are minimized while achieving lossless, zero voltage switching within a three-phase inverter.

## Claims

### Claim 1

A resonant snubber inverter circuit comprising:
a main inverter circuit having a plurality of main switches; and
one or more snubber branches connected in a delta configuration to said main circuit for selectively conducting a resonant current that produces a zero voltage across predetermined ones of said main switches.

### Claim 2 (depends on 1)

The inverter circuit as described in claim 1, wherein each of said snubber branches includes an inductor connected in series with a semiconductor switch.

### Claim 3 (depends on 2)

The inverter circuit as described in claim 2, wherein said semiconductor switch is a power MOSFET device.

### Claim 4 (depends on 1)

The inverter circuit as described in claim 1, wherein each of said snubber branches comprises:
an inductor;
a diode in series connection with said inductor; and
a semiconductor switch in series connection with said inductor and said diode.

### Claim 5 (depends on 1)

The inverter circuit as described in claim 1, further comprising sources of capacitance connected in parallel with each of said main switches, wherein said main switches supply current to said snubber branches to produce resonant current, said resonant current producing zero voltage across said main switches by repetitively charging and discharging said sources of capacitance to enable zero voltage turn-on of said inverter circuit main switches.

### Claim 6 (depends on 1)

The inverter circuit as described in claim 1, wherein each of said resonant branches comprises a bi-directional switched, resonant branch.

### Claim 7 (depends on 6)

The inverter circuit as described in claim 6, where each of said bi-directional switched, resonant branches comprises:
an inductor; and
a bi-directional switch connected in series with said inductor.

### Claim 8

A resonant snubber-based, soft switching, multi-phase, inverter circuit for achieving lossless switching of circuit components, comprising:
a main inverter circuit having a plurality of main switches and sources of capacitance in parallel with said main switches, said main circuit producing a plurality of current phases;
an auxiliary resonant snubber circuit connected to said inverter circuit in a delta configuration and having a plurality of resonant snubber branches for repetitively producing zero voltage across each of said main switches and sources of capacitance, each of said snubber branches comprising an inductor and an auxiliary switch connected in series with said inductor; and
a controller for controlling said main and auxiliary switches to achieve lossless switching by switching said auxiliary switches to produce zero voltage conditions across said main switches and by switching said main switches during said zero voltage conditions.

### Claim 9 (depends on 8)

The inverter circuit as described in claim 8, wherein said sources of capacitance further comprise capacitance in parallel with each of said main switches, said capacitance being charged and discharged by a resonant current in said snubber branches.

### Claim 10 (depends on 8)

The inverter circuit as described in claim 8, said main inverter circuit further comprising for each current phase:
an upper semiconductor switch and a lower semiconductor switch, each having a source, gate, and drain;
means for connecting the source of the upper semiconductor switch to the drain of the lower semiconductor switch; and
a free-wheeling diode antiparalleled against each of said semiconductor switches;
wherein the alternating current for each phase is produced at the source-drain junction of the two semiconductor switches for each phase.

### Claim 11 (depends on 8)

The inverter circuit as described in claim 8, wherein each of said resonant branches comprises a bi-directional switched, resonant branch.

### Claim 12 (depends on 11)

The inverter circuit as described in claim 11, wherein each of said bi-directional switched, resonant branches comprises:
an inductor; and
a bi-directional switch connected in series with said inductor.

### Claim 13

A resonant snubber-based, soft switching, single-phase, inverter circuit for achieving lossless switching of circuit components, comprising:
a main inverter circuit having a plurality of main switches and sources of capacitance connected to said main switches, said main circuit producing a single phase output current;
an auxiliary resonant snubber circuit connected to said inverter circuit in a delta configuration and having one resonant snubber branch for repetitively producing zero voltage across each of said main switches and sources of capacitance, said snubber branch comprising an inductor and one bi-directional, auxiliary switch connected in series with said inductor; and
a controller for controlling said main and auxiliary switches to achieve lossless switching by switching said auxiliary switch to produce zero voltage conditions across said main switches and by switching said main switches during said zero voltage conditions.

### Claim 14 (depends on 13)

The inverter circuit as described in claim 13, wherein said sources of capacitance further comprise capacitance in parallel with each of said main switches, said capacitance being charged and discharged by a resonant current in said snubber branch.

### Claim 15

A resonant snubber-based, soft switching, single-phase, inverter circuit for achieving lossless switching of circuit components, comprising:
a main inverter circuit having a plurality of main switches and sources of capacitance connected to said main switches, said main circuit producing a single phase output current;
an auxiliary resonant snubber circuit connected to said inverter circuit in a delta configuration and having two resonant snubber branches for repetitively producing zero voltage across each of said main switches and sources of capacitance, each of said snubber branches comprising an inductor and one auxiliary switch connected in series with said inductor; and
a controller for controlling said main and auxiliary switches to achieve lossless switching by switching said auxiliary switches to produce zero voltage conditions across said main switches and by switching said main switches during said zero voltage conditions.

### Claim 16 (depends on 15)

The inverter circuit as described in claim 15, wherein said sources of capacitance further comprise capacitance in parallel with each of said main switches, said capacitance being charged and discharged by a resonant current in said snubber branches.

### Claim 17 (depends on 15)

The inverter circuit of claim 15, wherein each of said resonant snubber branches further comprises a diode, said resonant branches are connected in parallel and said diodes of said branches are oppositely oriented.

### Claim 18

A method for achieving lossless resonant snubbing during switching of an inverter circuit having a first upper main switch and a first lower main switch connected in series, and a second upper main switch and a second lower main switch connected in series, each of the main switches having a parallel capacitance associated with the switch, the method comprising the steps of:
turning on the first lower main switch and second upper main switch so that the first lower and second upper main switches conduct current;
providing one or more resonant snubber branches, each of said snubber branches being connected in a delta configuration at junctions between said upper and lower main switches;
turning on a predetermined auxiliary switch located within a resonant snubber branch to produce increasing current flows in said resonant snubber branch and decreasing voltage across said first lower and second upper main switches;
turning off said first lower and second upper main switches when the voltage across said first lower and second upper switches is zero, thereby initiating resonant discharge of the capacitances located in parallel with the first upper main switch and the second lower main switch to produce a zero voltage condition across said first upper and second lower main switches; and
turning on said first upper and second lower main switches at said zero voltage condition.

### Claim 19

A method for achieving lossless resonant snubbing during transition cycle switching of an inverter circuit having a first upper main switch and a first lower main switch connected in series, a second upper main switch and a second lower main switch connected in series, and a load that is drawing a load current, said first upper and second lower switches in an initially off state with substantially zero current flow, said second upper and first lower switches in an initially on state with positive current flow, each of the main switches having a parallel capacitance associated with the switch, for one transition switching cycle the method comprising the steps of:
providing a first resonant snubber branch comprising:
a first inductor;
a first diode in series connection with said first inductor; and
a first auxiliary semiconductor switch in series connection with said first inductor and said first diode;
providing a second resonant snubber branch comprising:
a second inductor;
a second diode in series connection with said second inductor; and
a second auxiliary semiconductor switch in series connection with said second inductor and said second diode;
turning on the second auxiliary semiconductor switch to substantially linearly increase current flow through the second inductor and reduce the current flow through the second upper and first lower main switches to zero when the second inductor current equals the load current;
turning off the second upper and first lower main switches when the second inductor current is sufficient to charge and discharge said sources of capacitance, thereby charging the parallel capacitances associated with the second upper and first lower main switches until the second upper and first lower capacitances conduct current and discharging to zero voltage the parallel capacitances associated with the first upper and second lower main switches, producing zero voltage across said first upper and second lower main switches;
turning on the first upper and second lower main switches at zero voltage;
diverting the load current to antiparalleled diodes associated with the first upper and second lower main switches as the second inductor current decreases linearly;
diverting current from the antiparalleled diodes associated with the first upper and second lower main switches to the first upper and second lower main switches when the second inductor current equals the load current, producing linearly increasing current flow through the first upper and second lower main switches; and
turning off the second auxiliary semiconductor switch when the second inductor current equals zero.