# US 12,119,741 B2 · Modular multilevel converter system and voltage detection method and open-circuit fault diagnosis method thereof

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- Number: US 12,119,741 B2
- Document ID: US12119741B2
- Status: Granted
- Kind: B2
- Application number: 17/232,110
- Filed: 2021-04-15
- Published: 2021-12-09
- Granted: 2024-10-15
- Earliest claimed: 2020-06-03
- Assignees: Delta Electronics (Shanghai) Co., Ltd.
- Applicants: Delta Electronics (Shanghai) Co., Ltd.
- Inventors: Peng Xiao; Ming Wang; Yi Zhang; Teng Liu; Jianping Ying
- Web page: https://patentgrep.com/patent/US12119741B2

## CPC

- G01R 31/3275: {Fault detection or status indication}
- H02M 1/32: Means for protecting converters other than automatic disconnection
- G01R 31/3004: {Current or voltage test}
- H02M 7/483: Converters with outputs that each can have more than two voltages levels
- H02M 7/4835: {comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- 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)

## Abstract

A modular multilevel converter system, and a voltage detection method and an open-circuit fault diagnosis method thereof are disclosed. The modular multilevel converter system includes: N sub-modules sequentially cascaded, where N is an integer greater than or equal to 2, each of the sub-modules comprising at least one bridge arm and a capacitor connected in parallel to the bridge arm, the capacitor having a positive terminal and a negative terminal; and a voltage detection unit for detecting a voltage between at least two adjacent sub-modules in the N sub-modules, the voltage detection unit being connected between the positive terminal of the capacitor of the first sub-module and the negative terminal of the capacitor of the last sub-module in the at least two sub-modules.

## Claims

### Claim 1

A modular multilevel converter system, comprising:
N sub-modules sequentially cascaded, where N is an integer greater than or equal to 2, each of the sub-modules comprising at least one bridge arm and a capacitor connected in parallel to the bridge arm, the capacitor having a positive terminal and a negative terminal; and
a voltage detection unit for detecting a voltage between at least two adjacent sub-modules in the N sub-modules, the voltage detection unit being connected in parallel between the positive terminal of the capacitor of the first sub-module and the negative terminal of the capacitor of the last sub-module in the at least two sub-modules.

### Claim 2 (depends on 1)

The modular multilevel converter system according to claim 1, wherein the voltage detection unit is a voltage sensor.

### Claim 3 (depends on 1)

The modular multilevel converter system according to claim 1, wherein the voltage detection unit detects the voltage between two adjacent sub-modules, the two sub-modules comprising a first sub-module and a second sub-module sequentially cascaded, wherein, during normal operation,
when the two sub-modules are in a switch-on state, a detection result from the voltage detection unit is a sum of capacitor voltages of the two sub-modules;
when the two sub-modules are in a switch-off state, a detection result from the voltage detection unit is a capacitor voltage of the first sub-module;
when the two sub-modules are in a blocked state and current flows from an output terminal of the first sub-module to an output terminal of the second sub-module, a detection result from the voltage detection unit is the sum of capacitor voltages of the two sub-modules;
when the two sub-modules are in the blocked state and current flows from the output terminal of the second sub-module to the output terminal of the first sub-module, a detection result from the voltage detection unit is the capacitor voltage of the first sub-module.

### Claim 4 (depends on 3)

The modular multilevel converter system according to claim 3, wherein a capacitor voltage of the second sub-module is estimated by subtracting the capacitor voltage of the first sub-module from the sum of capacitor voltages of the two sub-modules.

### Claim 5

A voltage detection method of a modular multilevel converter system, comprising:
configuring N sub-modules sequentially cascaded, where N is an integer greater than or equal to 2, each of the sub-modules comprising at least one bridge arm and a capacitor connected in parallel to the bridge arm, the capacitor having a positive terminal and a negative terminal; and
configuring a voltage detection unit for detecting a voltage between at least two adjacent sub-modules in the N sub-modules and connected in parallel between the positive terminal of the capacitor of the first sub-module and the negative terminal of the capacitor of the last sub-module in the at least two sub-modules.

### Claim 6 (depends on 5)

The voltage detection method according to claim 5, wherein the voltage detection unit is a voltage sensor.

### Claim 7 (depends on 6)

The voltage detection method according to claim 6, wherein the voltage detection unit detects the voltage between two adjacent sub-modules, the two sub-modules comprising a first sub-module and a second sub-module sequentially cascaded, wherein, during normal operation,
when the two sub-modules are in a switch-on state, a detection result from the voltage detection unit is a sum of capacitor voltages of the two sub-modules;
when the two sub-modules are in a switch-off state, a detection result from the voltage detection unit is a capacitor voltage of the first sub-module;
when the two sub-modules are in a blocked state and current flows from an output terminal of the first sub-module to an output terminal of the second sub-module, a detection result from the voltage detection unit is the sum of capacitor voltages of the two sub-modules;
when the two sub-modules are in the blocked state and current flows from the output terminal of the second sub-module to the output terminal of the first sub-module, a detection result from the voltage detection unit is the capacitor voltage of the first sub-module.

### Claim 8 (depends on 7)

The voltage detection method according to claim 7, further comprising:
estimating a capacitor voltage of the second sub-module by subtracting the capacitor voltage of the first sub-module from the sum of capacitor voltages of the two sub-modules.

### Claim 9

An open-circuit fault diagnosis method of a modular multilevel converter system, wherein the modular multilevel converter system comprises a plurality of sub-modules sequentially cascaded, each of the sub-modules comprising at least one bridge arm and a capacitor connected in parallel to the bridge arm, the capacitor having a positive terminal and a negative terminal, and a voltage detection unit for detecting a voltage between a first sub-module and a second sub-module connected adjacent in the plurality of sub-modules, the voltage detection unit being connected in parallel between the positive terminal of the capacitor of the first sub-module and the negative terminal of the capacitor of the second sub-module in the two sub-modules, comprising:
detecting the voltages between the two sub-modules in a switch-on state and a switch-off state by the voltage detection unit;
determining the sub-module with an open-circuit fault in the two sub-modules according to the detected result.

### Claim 10 (depends on 9)

The open-circuit fault diagnosis method according to claim 9, wherein the sub-modules are in a half-bridge structure, the first sub-module comprises a first switch and a second switch connected in series, and the second sub-module comprises a third switch and a fourth switch connected in series.

### Claim 11 (depends on 10)

The open-circuit fault diagnosis method according to claim 10, further comprising:
when the first sub-module and the second sub-module are in the switch-on state, a detection result from the voltage detection unit being a sum of capacitor voltages of the two sub-modules;
when the first sub-module and the second sub-module are in the switch-off state, a detection result from the voltage detection unit being a capacitor voltage of the first sub-module; and,
when the detected capacitor voltage of the first sub-module has a DC bias and the DC bias exceeds a first preset threshold, determining that the open-circuit fault occurs on the first switch of the first sub-module.

### Claim 12 (depends on 10)

The open-circuit fault diagnosis method according to claim 10, further comprising:
when the first sub-module and the second sub-module are in the switch-on state, a detection result from the voltage detection unit being a sum of capacitor voltages of the two sub-modules;
when the first sub-module and the second sub-module are in the switch-off state, a detection result from the voltage detection unit being a capacitor voltage of the first sub-module; and,
when current flows from an output terminal of the first sub-module to an output terminal of the second sub-module and a sum of several voltage variations of the first sub-module is greater than a second preset threshold, determining that the open-circuit fault occurs on the second switch of the first sub-module.

### Claim 13 (depends on 10)

The open-circuit fault diagnosis method according to claim 10, further comprising:
when the first sub-module and the second sub-module are in the switch-on state, if a detection result from the voltage detection unit is a capacitor voltage of the first sub-module, determining that the open-circuit fault occurs on the third switch of the second sub-module.

### Claim 14 (depends on 10)

The open-circuit fault diagnosis method according to claim 10, further comprising:
when the first sub-module and the second sub-module are in the switch-off state, if a detection result from the voltage detection unit is a sum of capacitor voltages of the two sub-modules, determining that the open-circuit fault occurs on the fourth switch of the second sub-module.

### Claim 15 (depends on 9)

The open-circuit fault diagnosis method according to claim 9, wherein each of the sub-modules is in an H bridge structure comprising a first bridge arm and a second bridge arm connected in parallel to the first bridge arm, wherein the first bridge arm comprises a first switch and a second switch connected in series, the second bridge arm comprises a third switch and a fourth switch connected in series; the capacitor is connected in parallel between the first bridge arm and the second bridge, when each of the sub-modules is in the switch-on state, the first switch and the fourth switch are turned on, and when each of the sub-modules is in the switch-off state, the second switch and the fourth switch are turned on.

### Claim 16 (depends on 15)

The open-circuit fault diagnosis method according to claim 15, further comprising:
when the first sub-module and the second sub-module are in the switch-on state, a detection result from the voltage detection unit being a sum of capacitor voltages of the two sub-modules, when the first sub-module and the second sub-module are in the switch-off state, a detection result from the voltage detection unit being a capacitor voltage of the first sub-module, and
when the detected capacitor voltage of the first sub-module has a DC bias and the DC bias exceeds a first preset threshold, determining that the open-circuit fault occurs on the first switch of the first sub-module.

### Claim 17 (depends on 15)

The open-circuit fault diagnosis method according to claim 15, further comprising:
when the first sub-module and the second sub-module are in the switch-on state, a detection result from the voltage detection unit being a sum of capacitor voltages of the two sub-modules, when the first sub-module and the second sub-module are in the switch-off state, a detection result from the voltage detection unit being a capacitor voltage of the first sub-module, and
when current flows from an output terminal of the first sub-module to an output terminal of the second sub-module and a sum of several voltage variations of the first sub-module is greater than a second preset threshold, determining that the open-circuit fault occurs on the second switch of the first sub-module.

### Claim 18 (depends on 15)

The open-circuit fault diagnosis method according to claim 15, further comprising:
when the first sub-module and the second sub-module are in the switch-on state, a detection result from the voltage detection unit being a sum of capacitor voltages of the two sub-modules, when the first sub-module and the second sub-module are in the switch-off state, a detection result from the voltage detection unit being a capacitor voltage of the first sub-module, and
when the detected capacitor voltage of the first sub-module has a DC bias exceeding a first preset threshold, and a sum of several voltage variations of the first sub-module is greater than a second preset threshold when current flows from an output terminal of the second sub-module to an output terminal of the first sub-module, determining that the open-circuit fault occurs on the fourth switch of the first sub-module.

### Claim 19 (depends on 15)

The open-circuit fault diagnosis method according to claim 15, further comprising:
when the first sub-module and the second sub-module are in the switch-on state, if a detection result from the voltage detection unit is a capacitor voltage of the first sub-module, determining that the open-circuit fault occurs on the first switch of the second sub-module.

### Claim 20 (depends on 15)

The open-circuit fault diagnosis method according to claim 15, further comprising:
when the first sub-module and the second sub-module are in the switch-off state, if a detection result from the voltage detection unit is a sum of capacitor voltages of the two sub-modules, determining that the open-circuit fault occurs on the second switch of the second sub-module.

### Claim 21 (depends on 15)

The open-circuit fault diagnosis method according to claim 15, further comprising:
when the first sub-module and the second sub-module are in the switch-on state, a detection result from the voltage detection unit being a sum of capacitor voltages of the two sub-modules, when the first sub-module and the second sub-module are in the switch-off state, a detection result from the voltage detection unit being a capacitor voltage of the first sub-module, and
when a capacitor voltage of the second sub-module has a DC bias exceeding a first preset threshold, and a sum of several voltage variations of the second sub-module is greater than a second preset threshold when current flows from an output terminal of the second sub-module to an output terminal of the first sub-module, determining that the open-circuit fault occurs on the fourth switch of the second sub-module.