# US 12,113,456 B2 · Apparatus and method for controlling delta-connected cascaded multilevel converter

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- Number: US 12,113,456 B2
- Document ID: US12113456B2
- Status: Granted
- Kind: B2
- Application number: 17/753,860
- Filed: 2020-02-28
- Published: 2022-12-22
- Granted: 2024-10-08
- Earliest claimed: 2020-02-28
- Assignees: ABB Schweiz AG
- Applicants: ABB Schweiz AG
- Inventors: Xing Huang; Hailian Xie; Guangming Pei; Hua Wei; Min Li
- Web page: https://patentgrep.com/patent/US12113456B2

## CPC

- H02M 7/49: Combination of the output voltage waveforms of a plurality of converters
- H02M 1/12: Arrangements for reducing harmonics from AC input or output
- H02M 1/15: using active elements
- H02J 3/01: Arrangements for reducing harmonics or ripples
- H02M 1/0003: {Details of control, feedback or regulation circuits}
- H02M 1/0025: {Arrangements for modifying reference values, feedback values or error values in the control loop of a converter}
- H02M 5/458: using semiconductor devices only
- 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)
- H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY

## Abstract

Embodiments of present disclosure relate to an apparatus and a method for controlling a delta-connected cascaded multilevel converter. The apparatus (100) for controlling a delta-connected cascaded multilevel converter (110) comprises: a converter controller (102) configured to: receive current signals indicating phase currents flowing through respective phase arms of the converter (110); determine a harmonic current signal indicating a circulating current of the converter (110) from the current signals; and generate, based on the determined harmonic current signal and a reference current signal, a harmonic voltage signal to cause an amplitude of the circulating current flowing through the phase arms of the converter (110) to be a predetermined amplitude.

## Claims

### Claim 1

An apparatus for controlling a delta-connected cascaded multilevel converter, comprising:
a converter controller configured to:
receive current signals indicating phase currents flowing through respective phase arms of the converter;
determine a harmonic current signal indicating a circulating current of the converter from the current signals;
generate, based on the determined harmonic current signal and a reference current signal, a harmonic voltage signal to cause an amplitude of the circulating current flowing through the phase arms of the converter to be a predetermined amplitude;
receive a phase voltage reference signal associated with a load electrically coupled to the converter; and
generate, by combining the harmonic voltage signal with the phase voltage reference signal, a control signal for controlling the converter to cause a peak amplitude of the phase currents to be a first amplitude,
wherein the first amplitude is associated with a second amplitude of the circulating current in the phase currents.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein the converter controller is configured to:
determine the harmonic current signal indicating a third order harmonic circulating current of the converter from the current signals; and
generate the harmonic voltage signal to cause the amplitude of the third order harmonic circulating current to be 0.167 times of the amplitude of the rated current of the converter.

### Claim 3 (depends on 1)

The apparatus of claim 1, wherein the converter controller is configured to generate the harmonic voltage signal based on a comparison of the harmonic current signal and the reference current signal.

### Claim 4 (depends on 3)

The apparatus of claim 3, wherein the converter controller is configured to:
determine a first DC component of the harmonic current signal from the current signals;
compare the first DC component with a first reference DC component of the reference current signal to generate a first DC difference;
determine a second DC component of the harmonic current signal from the current signals;
compare the second DC component with a second reference DC component of the reference current signal to generate a second DC difference; and
generate the harmonic voltage signal based on the first DC difference and the second DC difference.

### Claim 5 (depends on 4)

The apparatus of claim 4, wherein the first reference DC component of the reference current is set to be 0.167 times of an amplitude of a rated current of the converter, and the second reference DC component of the reference current is set to be zero.

### Claim 6 (depends on 3)

The apparatus of claim 3, wherein the converter controller is configured to:
determine a first AC component of the harmonic current signal from the current signals;
compare the first AC component with a first reference AC component of the reference current signal to generate a first AC difference;
determine a second AC component of the harmonic current signal from the current signals;
compare the second AC component with a second reference AC component of the reference current signal to generate a second AC difference; and
generate the harmonic voltage signal based on the first AC difference and the second AC difference.

### Claim 7 (depends on 1)

The apparatus of claim 1, further comprising:
a cell controller configured to control, based on a cell control signal generated from the control signal, one of a plurality of converter cells in the phase arm to cause the amplitude of the circulating current to be the predetermined amplitude.

### Claim 8 (depends on 7)

The apparatus of claim 7, wherein the cell controller is further configured to:
receive a DC voltage value indicating a DC voltage across a capacitor in the one of the plurality of converter cells;
compare the DC voltage value with a nominal value to generate a compensation factor; and
control the one of the plurality of converter cells based on the generated compensation factor and the cell control signal.

### Claim 9 (depends on 8)

The apparatus of claim 8, wherein the cell controller is configured to generate the compensation factor by dividing the DC voltage value by the nominal value.

### Claim 10 (depends on 9)

The apparatus of claim 9, wherein the cell controller is configured to:
determine a compensated control signal by dividing a level of the cell control signal by the compensation factor; and
control the one of the plurality of converter cells based on the compensated control signal.

### Claim 11 (depends on 1)

A system for controlling a delta-connected cascaded multilevel converter, comprising:
the apparatus of claim 1;
a first controller configured to generate a phase voltage reference signal based on a load electrically coupled to the converter; and
a second controller configured to generate a plurality of cell control signals for the plurality of converter cells based on the harmonic voltage signal.

### Claim 12

A method for controlling a delta-connected cascaded multilevel converter, comprising:
receiving current signals indicating phase currents flowing through respective phase arms of the converter;
determining a harmonic current signal indicating a circulating current of the converter from the current signals;
generating, based on the determined harmonic current signal and a reference current signal, a harmonic voltage signal to cause an amplitude of the circulating current flowing through the phase arms of the converter to be a predetermined amplitude;
receiving a phase voltage reference signal associated with a load electrically coupled to the converter; and
generating, by combining the harmonic voltage signal with the phase voltage reference signal, a control signal for controlling the converter to cause a peak amplitude of the phase currents to be a first amplitude,
wherein the first amplitude is associated with a second amplitude of the circulating current in the phase currents.

### Claim 13 (depends on 12)

The method of claim 12, wherein determining the harmonic current signal indicating the circulating current comprises determining the harmonic current signal indicating a third order harmonic circulating current, and
wherein generating the harmonic voltage signal to cause the amplitude of the circulating current to be the predetermined amplitude comprises generating the harmonic voltage signal to cause the amplitude of the third order harmonic circulating current to be 0.167 times of the amplitude of the rated current of the converter.

### Claim 14 (depends on 12)

The method of claim 12, wherein generating the harmonic voltage signal comprises generating the harmonic voltage signal based on a comparison of the harmonic current signal and the reference current signal.

### Claim 15 (depends on 14)

The method of claim 14, wherein generating the harmonic voltage signal based on the comparison comprises:
determining a first DC component of the harmonic current signal from the current signals;
comparing the first DC component with a first reference DC component of the reference current signal to generate a first DC difference;
determining a second DC component of the harmonic current signal from the current signals;
comparing the second DC component with a second reference DC component of the reference current signal to generate a second DC difference; and
generating the harmonic voltage signal based on the first DC difference and the second DC difference.

### Claim 16 (depends on 15)

The method of claim 15, wherein comparing the first DC component with the first reference DC component comprises comparing the first DC component with an amplitude of 0.167 times of a rated current of the converter, and
wherein comparing the second DC component with the second reference DC component comprises comparing the second DC component with zero.

### Claim 17 (depends on 14)

The method of claim 14, wherein generating the harmonic voltage signal based on the comparison comprises:
determining a first AC component of the harmonic current signal from the current signals;
comparing the first AC component with a first reference AC component of the reference current signal to generate a first AC difference;
determining a second AC component of the harmonic current signal from the current signals;
comparing the second AC component with a second reference AC component of the reference current signal to generate a second AC difference; and
generating the harmonic voltage signal based on the first AC difference and the second AC difference.

### Claim 18 (depends on 12)

The method of claim 12, further comprising:
controlling, based on a cell control signal generated from the control signal, one of a plurality of converter cells in the phase arm to cause the amplitude of the circulating current to be the predetermined amplitude.

### Claim 19 (depends on 18)

The method of claim 18, further comprising:
receiving a DC voltage value indicating a DC voltage across a capacitor in the one of the plurality of converter cells;
comparing the DC voltage value with a nominal value to generate a compensation factor; and
controlling the one of the plurality of converter cells based on the generated compensation factor and the cell control signal.

### Claim 20 (depends on 19)

The method of claim 19, wherein generating the compensation factor comprises generating the compensation factor by dividing the DC voltage value by the nominal value.

### Claim 21 (depends on 20)

The method of claim 20, wherein controlling the one of the plurality of converter cells comprises:
determining a compensated control signal by dividing a level of the cell control signal by the compensation factor; and
controlling the one of the plurality of converter cells based on the compensated control signal.

### Claim 22 (depends on 12)

A non-transitory computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, causing the at least one processor to carry out the method of claim 12.

### Claim 23

An apparatus for controlling a delta-connected cascaded multilevel converter, comprising:
a converter controller configured to:
receive current signals indicating phase currents flowing through respective phase arms of the converter;
determine a harmonic current signal indicating a circulating current of the converter from the current signals;
generate, based on the determined harmonic current signal and a reference current signal, a harmonic voltage signal to cause an amplitude of the circulating current flowing through the phase arms of the converter to be a predetermined amplitude;
determine a first DC component of the harmonic current signal from the current signals;
compare the first DC component with a first reference DC component of the reference current signal to generate a first DC difference;
determine a second DC component of the harmonic current signal from the current signals;
compare the second DC component with a second reference DC component of the reference current signal to generate a second DC difference; and
generate the harmonic voltage signal based on the first DC difference and the second DC difference,
wherein the converter controller is configured to generate the harmonic voltage signal based on a comparison of the harmonic current signal and the reference current signal.

### Claim 24

A method for controlling a delta-connected cascaded multilevel converter, comprising:
receiving current signals indicating phase currents flowing through respective phase arms of the converter;
determining a harmonic current signal indicating a circulating current of the converter from the current signals;
generating, based on the determined harmonic current signal and a reference current signal, a harmonic voltage signal to cause an amplitude of the circulating current flowing through the phase arms of the converter to be a predetermined amplitude;
controlling, based on a cell control signal generated from the control signal, one of a plurality of converter cells in the phase arm to cause the amplitude of the circulating current to be the predetermined amplitude;
receiving a DC voltage value indicating a DC voltage across a capacitor in the one of the plurality of converter cells;
comparing the DC voltage value with a nominal value to generate a compensation factor; and
controlling the one of the plurality of converter cells based on the generated compensation factor and the cell control signal,
wherein generating the compensation factor comprises generating the compensation factor by dividing the DC voltage value by the nominal value.