Method for insulation monitoring of a converter-supplied power supply system

Patent metadata

Field	Value
Publication number	US-11391785-B2
Application number	US-201916564178-A
Country	US
Kind code	B2
Filing date	Sep 9, 2019
Priority date	Sep 10, 2018
Publication date	Jul 19, 2022
Grant date	Jul 19, 2022

Abstract

The present invention relates to a method for determining an insulation resistance and for locating insulation faults in a power supply system whose active parts are ungrounded and which is supplied via a converter operated grounded and equipped with controlled power semiconductor switches. A common-mode voltage against ground is generated at the output of the converter and is superimposed on the ungrounded network as an active measuring voltage in order to measure the insulation resistance. The direct integration of the generation of the common-mode measuring voltage in the converter allows cost-effective implementation including similarly comprehensive insulation monitoring functions as those possible in fully ungrounded power supply systems. Furthermore, the method for determining the insulation resistance can be expanded into a method for locating insulation faults and thus for locating faulty system branches.

First claim

The invention claimed is:

1. A method for determining an insulation resistance (R f ) of a power supply system ( 20 , 30 , 40 , 50 ) whose active parts are ungrounded and which is supplied via a converter ( 10 , 14 , 24 , 34 ) operated grounded and equipped with controlled power semiconductor switches (SW 10 , SW 20 , SW 30 , SW 40 , SW 50 , SW 60 ), the method comprising the following steps:
generating a common-mode voltage against ground at the output of the converter ( 10 , 14 , 24 , 34 ), wherein the common-mode voltage is generated by generating pulse patterns (sa, sb, sc) for controlling the power semiconductor switches (SW 10 , SW 20 , SW 30 , SW 40 , SW 50 , SW 60 ),
superimposing the common-mode voltage as a measuring voltage (U g ) for determining the insulation resistance (R f ) of the ungrounded power supply system ( 20 , 30 , 40 , 50 ),
detecting the measuring voltage (U g ) in the ungrounded power supply system ( 20 , 30 , 40 , 50 ),
detecting a measuring current (I g ) which is flowing in the ungrounded power supply system ( 20 , 30 , 40 , 50 ) via the insulation resistance (R f ) because of the measuring voltage (U g ), and
determining the insulation resistance (R f ) by assessing the measuring current (I g ).

2. The method according to claim 1 , wherein the pulse patterns (sa, sb, sc) are generated by a voltage displacement ( 12 ) of a reference voltage (U L1 , U L2 , U L3 ) for each phase (L 1 , L 2 , L 3 ) of the converter ( 10 , 14 , 24 , 34 ) using a bias voltage (U m ).

3. The method according to claim 2 , wherein the bias voltage (U m ) is set in such a manner that it has a square waveform with a fundamental frequency below a network frequency of the power supply system ( 20 , 30 , 40 , 50 ), resulting in a measuring frequency of the measuring voltage (U g ) at the level of the fundamental frequency of the bias voltage (U m ).

4. The method according to claim 1 , wherein an application in which the converter ( 10 , 14 , 24 , 34 ) is configured as an inverter ( 14 ) or as a rectifier ( 24 ) or as a frequency converter ( 34 ).

5. A method according to claim 1 , the method further comprising the steps of:
detecting a residual current (I x ) caused by the measuring voltage (U g ) in a system branch ( 41 , 42 , 51 , 52 ) to be monitored in the ungrounded power supply system ( 40 , 50 ) by means of a residual current measuring device ( 6 ),
assessing the residual current (I x ) to detect a system branch ( 41 , 51 ) exhibiting an insulation fault (R x ).

6. The method according to claim 5 , wherein determining a partial insulation resistance and/or a partial network leakage capacitance of the system branch ( 41 , 42 , 51 , 52 ) to be monitored.

Assignees

• Bender Gmbh & Co Kg

Inventors

• Hackl Dieter

Classifications

• G01R31/1263

  of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation · CPC title

• H02M7/04

  by static converters · CPC title

• G01R27/16

  Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line · CPC title

• G01R31/42 Primary

  AC power supplies · CPC title

• H02M5/44

  using discharge tubes or semiconductor devices to convert the intermediate DC into AC · CPC title