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HYBRID ACTIVE FILTER

IP.com Disclosure Number: IPCOM000257178D
Publication Date: 2019-Jan-18
Document File: 13 page(s) / 1M

Publishing Venue

The IP.com Prior Art Database

Related People

Rohr Eduardo: AUTHOR [+1]

Abstract

The disclosure is related to a filter arrangement that may be used in connection with electric drives and power converter devices. A solution is suggested that combines advantages of a passive LC filter and an active filter cell. The solution may include a main power stage operating at a low switching frequency, a main LC filter tuned at a high resonance frequency, and an additional converter that provides damping of the main LC filter and inject current harmonics not damped by the main LC filter. The additional converter can operate with much reduced voltages and currents, but with higher switching frequency. The additional converter and LC filter are not subject to neither the main converter voltage nor the main converter current.

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This is the abbreviated version, containing approximately 18% of the total text.

Page 1 of 13  P17806

© Copyright [2019] ABB. All rights reserved.

HYBRID ACTIVE FILTER

This disclosure generally relates to filters that may be used in connection with electric drives

and power converter devices.

In MV drives / MV converters, for example, the converter losses may impose a limitation

on the maximum switching frequency of a few hundreds of Hertz. As a consequence, the

output voltage/current may have a relatively high Total Harmonic Distortion (THD) and its

effects may need to be mitigated by either designing a machine that is compatible with

high losses or having bulky passive filters.

One option to improve the quality of the converter’s output waveform is to use an LC filter

(or sine filter) in the output of the converter. However such a LC filter is bulky and

expensive.

In this disclosure a Hybrid Active Filter (HAF) is proposed that combines the advantages

of the passive LC filter and an active filter cell. The idea is to have a main power stage

operating at a low switching frequency, a main LC filter tuned at a high resonance

frequency, and an additional converter that provides damping of the main LC filter and

inject the current harmonics not damped by the main LC filter. The additional converter

can operate with much reduced voltages and currents, but with higher switching

frequency. The additional converter and LC filter are not subject to neither the main

converter voltage nor the main converter current. Figure 1 shows an exemplary system.

Figure 1. An example of a power converter system.

Page 2 of 13  P17806

© Copyright [2019] ABB. All rights reserved.

One of the main design considerations in power converters is the tradeoff between

converter losses and output voltage/current quality. This tradeoff may affect the choice of

switching frequency and the design of passive filters. Typically, in e.g. MV drives the

converter losses may impose a limitation on the maximum switching frequency of a few

hundereds of Hertz. As a consequence, the output voltage/current have a relatively high

Total Harmonic Distortion (THD) and its effects must be mitigating by either desiging a

machine that is compatible with high losses or having bulky passive filters.

One option to improve the quality of a converter’s output waveform is to use an LC filter

(or sine filter, for instance) in the output of the converter. In this case, the converter output

voltage is much smoother, which reduces issues caused by wave reflections in long

cables, and a machine rated for direct online connection may be used. Also, it is possible

to design a grounding scheme that eliminates common mode voltages seen by the load,

which in turn reduce problems caused by bearing currents. However, the use of LC filters

may also have some drawbacks:

- A damping mechanism may need to be designed. Passive damping often results in

unacceptable losses. Active damping schemes may pose limitations on the maximum

resonance frequency and can also increase the switching frequen...

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