# US 10,122,165 B2 · Apparatus and method for reducing harmonics

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- Number: US 10,122,165 B2
- Document ID: US10122165B2
- Status: Granted
- Kind: B2
- Application number: 14/916,219
- Filed: 2014-09-29
- Published: 2016-07-07
- Granted: 2018-11-06
- Earliest claimed: 2013-10-14
- Assignees: Danfoss Power Electronics A/S
- Applicants: Danfoss Power Electronics A/S
- Inventors: Firuz Zare
- Web page: https://patentgrep.com/patent/US10122165B2

## CPC

- H02M 1/4225: {using a non-isolated boost converter}
- H02J 3/00: Circuit arrangements for AC mains or AC distribution networks
- H02J 3/01: Arrangements for reducing harmonics or ripples
- H02M 1/12: Arrangements for reducing harmonics from AC input or output
- H02M 1/4216: {operating from a three-phase input voltage (H02M1/4233 takes precedence)}
- H02M 5/458: using semiconductor devices only
- 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
- Y02E 40/40: Arrangements for reducing harmonics
- 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
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

The present invention provides systems and methods for reducing harmonics, for example when using an AC to AC converter to drive a load such as a motor drive. In a first embodiment, a plurality of load driving circuits is provided, each drawing current from a 3-phase AC supply and driving an AC load, wherein each of said load driving circuit includes a 3-phase rectifier, with the rectifiers of the load driving circuits being controlled such that the rectification of the AC supply by the load driving circuits is staggered. In a second embodiment, a load driving circuit comprises an electronic inductor configured to control the DC link voltage and/or current such that the current drawn from the AC supply by the load driving circuit has a stepped profile. The first and second embodiments may be combined.

## Claims

### Claim 1

A load driving circuit comprising:
a 3-phase rectifier having an input coupled to a 3-phase AC supply;
a DC link stage;
an inverter having an input coupled to an output of the DC link stage and an output coupled to a load, wherein the inverter converts an output voltage of the DC link stage into a signal for driving the load; and
an electronic inductor configured to control the output voltage and/or output current of the DC link stage such that the current drawn from the AC supply by the load driving circuit has a stepped profile;
wherein said stepped profile is mathematically equivalent to the sum of a first, second and third pulses having first, second and third phase offsets respectively;
wherein said stepped profile is given by:
4
⁢
I
dc
⁢
⁢
1
⁢
cos
⁡
(
n
⁢
⁢
30
)
n
⁢
⁢
π
+
4
⁢
I
dc
⁢
⁢
2
⁢
cos
⁡
(
n
⁢
⁢
α1
)
n
⁢
⁢
π
-
4
⁢
I
dc
⁢
⁢
2
⁢
cos
⁡
(
n
⁢
⁢
α2
)
n
⁢
⁢
π
,
wherein Idc1, Idc2 and −Idc2 are the amplitudes of the first, second and third pulses.

### Claim 2 (depends on 1)

The load driving circuit as claimed in claim 1, wherein 30, α1 and α2are the said first, second and third offsets respectively.

### Claim 3 (depends on 1)

The load driving circuit as claimed in claim 1, wherein the stepped profile is shaped such that, in a three-phase system, the sum of the stepped profile for each of the three phases is symmetrical.

### Claim 4 (depends on 1)

The load driving circuit as claimed in claim 1, wherein the stepped profile has a first portion and a second portion, the first and second portions being symmetrical, the first portion comprising a first projection and a second projection, wherein each projection has a duration θ, the first projection starting at a time β after the start of the pulse, the time between the first and second projections being 2β, and the time from the end of the second projection to the end of the portion of the pulse being given by β.

### Claim 5 (depends on 4)

The load driving circuit as claimed in claim 4, wherein the first and second portions of the pulse each have a duration of 120 degrees such that 2β+θ=60.

### Claim 6 (depends on 1)

The load driving circuit as claimed in claim 1, wherein the electronic inductor is configured such that at least one harmonic of the current drawn from the AC supply is eliminated.

### Claim 7

A system comprising a plurality of load driving circuits, each of the load driving circuits drawing current from a 3-phase AC supply and driving an AC load, wherein each of said load driving circuit comprises:
a 3-phase rectifier having an input coupled to the AC supply;
a DC link stage having an input coupled to the output of the rectifier; and
an inverter having an input coupled to an output of the DC link stage and an output coupled to the respective load, wherein the inverter converts a DC link voltage into a signal for driving the respective AC load,
wherein:
each DC link stage includes an electronic inductor configured to control the output voltage and/or output current of the DC link stage; and
the rectifiers of the load driving circuits are arranged such that the rectification of at least some of the load driving circuits is staggered.

### Claim 8 (depends on 7)

The system as claimed in claim 7, wherein each of the plurality of inverters drives a different load.

### Claim 9 (depends on 7)

The system as claimed in claim 7, wherein each electronic inductor is controlled such that substantially square wave current pulses are drawn from the AC supply by the respective load driving circuit.

### Claim 10 (depends on 7)

The system as claimed in claim 7, wherein the rectifiers of at least some of the plurality of load driving circuits are thyristor-based rectifiers in which the thyristors are controlled in order to provide said staggered rectification.

### Claim 11 (depends on 7)

The system as claimed in claim 7, further comprising a control module for controlling the electronic inductors.

### Claim 12 (depends on 7)

The system as claimed in claim 7, wherein at least some of the electronic inductors are in communication with other electronic inductors.

### Claim 13 (depends on 7)

The system as claimed in claim 7, wherein each of said load driving circuits is a load driving circuit.

### Claim 14

A method comprising controlling an electronic inductor provided between a 3-phase rectifier and a DC link stage of a load driving circuit such that the output voltage and/or output current of the DC link stage is controlled such that the current drawn from a 3-phase AC supply by the load driving circuit has a stepped profile,
wherein said stepped profile is mathematically equivalent to the sum of a first, second and third pulses having first, second and third phase offsets respectively;
wherein said stepped profile is given by:
4
⁢
I
dc
⁢
⁢
1
⁢
cos
⁡
(
n
⁢
⁢
30
)
n
⁢
⁢
π
+
4
⁢
I
dc
⁢
⁢
2
⁢
cos
⁡
(
n
⁢
⁢
α1
)
n
⁢
⁢
π
-
4
⁢
I
dc
⁢
⁢
2
⁢
cos
⁡
(
n
⁢
⁢
α2
)
n
⁢
⁢
π
,
wherein Idc1, Idc2 and −Idc2 are the amplitudes of the first, second and third pulses.

### Claim 15

A method comprising controlling rectifiers of a plurality of load driving circuits arranged in parallel such that the rectification of at least some of the load driving circuits are staggered, wherein each of said load driving circuits comprises: a 3-phase rectifier, a DC link stage, an inverter and an electronic inductor, the electronic inductor being configured to control the output voltage and/or output current of the DC link stage.

### Claim 16 (depends on 15)

The method as claimed in claim 15, further comprising controlling the electronic inductor of each of the parallel load driving circuits such that substantially square wave current pulses are drawn from the AC supply by the respective load driving circuit.

### Claim 17 (depends on 15)

The method as claimed in claim 15, further comprising controlling the electronic inductor of each of the parallel load driving circuits such that the current drawn by that load driving circuit from a 3-phase AC supply has a stepped profile.