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Method of preventing condensation by heating the line filter inductors with additional current harmonics

IP.com Disclosure Number: IPCOM000241755D
Publication Date: 2015-May-28
Document File: 4 page(s) / 75K

Publishing Venue

The IP.com Prior Art Database

Related People

Juha Arminen: INVENTOR [+2]

Abstract

This document discloses a method for purposefully creating heat losses in line filter inductors of an outdoor inverter for condensation prevention. Additional losses are created by injecting current harmonics to the output of the inverter.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 44% of the total text.

Page 01 of 4

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1.Abstract

This document discloses a method for purposefully creating heat losses in line filter inductors of an outdoor inverter for condensation prevention. Additional losses are created by injecting current harmonics to the output of the inverter.


2.Background

Grid-tied power inverters (e.g. photovoltaic inverters) have line filter(s) in the AC output. Usually these filters comprise one or more capacitors and one or more inductors. Capacitive part filters the voltage distortion and inductive part filters the current distortion. Filtering causes power losses in the filtering components and for example in the utility-scale central inverters power losses of the line filter unit can be few kilowatts so additional cooling is needed.

Two commonly known control methods used in central inverter for line filter cooling are to rotate the fans at full speed always when the inverter is running or to control the cooling according to semiconductor's junction temperature. This means that in the evening when the sun is setting the line filter is cooled more than is actually needed.

Due to the fact that outdoor PV inverters are usually not operating at night time, moisture can condensate inside the inverter enclosure when the temperature changes, normally this happens when the ambient air temperature of the inverter starts to raise in the morning while the temperature inside the inverter enclosure remains cooler. Condensated moisture can cause malfunction for electric components and should therefore be avoided.


3.New solution

In this invention the temperature behavior of the line filters is utilized to keep the inverter cabinet warm longer and thus preventing the condensation. Line inductors are usually made of metal (copper, aluminum, steel) and weight can vary from few tens of kilograms up to couple of hundred kilograms which provides a substantial thermal storage capacity.

Line filter components are not ideal and they always include parasitic resistance which generates heat losses when current flows through the component. This resistance is dependent from frequency of the current. For example inductor's copper losses increase with increasing frequency due to phenomenon called skin effect which pushes the current to the surface of the conductor. Because of frequency dependency of the line filter heat losses, they can be increased by feeding plenty of current harmonics instead of fundamental frequency.

This invention broadens the inductor heating effect by feeding additional current harmonics which are used to heat up the line filter inductors of the PV central inverter before the inverter goes to standby mode in the evening or whenever it is reasonable.

In the evening generated power from the PV field is decreased so the inverter is not running at full power so also the losses are not at the maximum. This means that additional losses can be generated without risk of failures and this way maximizing the amount of stored heat.

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