Power converter for transferring power between an AC side and a DC side, and power supply method

Patent metadata

Field	Value
Publication number	US-12500512-B2
Application number	US-202318316286-A
Country	US
Kind code	B2
Filing date	May 12, 2023
Priority date	Nov 12, 2020
Publication date	Dec 16, 2025
Grant date	Dec 16, 2025

Abstract

A power converter between an AC side and DC of the power converter is disclosed. The AC side is connected to an AC supply grid and the DC side is connected to a DC grid. The power converter includes a bridge circuit connected to the AC side of the power converter via AC switches and connected to the DC side of the power converter via circuit breakers, wherein a DC link circuit of the power converter is chargeable from the AC supply grid via an AC precharging circuit. The power converter has an insulation monitor to measure the insulation resistance of the DC side when the AC precharging circuit is connected to the DC link circuit. The disclosure also includes a related method.

First claim

What is claimed is:

1 . A power converter for transferring power between an AC side of the power converter and a DC side of the power converter, wherein the AC side of the power converter is connected to a grounded three-phase AC supply grid and the DC side of the power converter is connected to an ungrounded DC grid, wherein the power converter comprises a bridge circuit having AC terminals connected to the AC side of the power converter via AC switches and the bridge circuit having DC terminals connected to the DC side of the power converter via circuit breakers,
wherein a DC link circuit of the power converter is configured to be charged from the grounded three-phase AC supply grid via a galvanically isolating AC precharging circuit, and wherein the power converter has an insulation monitor that is configured to measure an insulation resistance of the DC side of the power converter when the galvanically isolating AC precharging circuit is connected to the DC link circuit.

2 . The power converter as claimed in claim 1 , wherein the AC terminals and the DC terminals of the bridge circuit are galvanically coupled and a power transfer path between the AC side and the DC side of the power converter is configured to be transformerless.

3 . The power converter as claimed in claim 1 , wherein the insulation monitor is arranged between the AC side of the power converter and the AC terminals of the bridge circuit.

4 . The power converter as claimed in claim 3 , wherein the insulation monitor comprises a grounding resistor that connects a potential, which lies between switching elements of a half-bridge circuit, of the bridge circuit to ground potential via a grounding switch.

5 . The power converter as claimed in claim 4 , wherein at least one of the AC switches serves as the grounding switch.

6 . The power converter as claimed in claim 1 , wherein at least one circuit breaker with an additionally connected precharging resistor is present for each DC terminal.

7 . The power converter as claimed in claim 1 , wherein at least one circuit breaker with an additionally connected precharging resistor is present for solely one of the DC terminals.

8 . The power converter as claimed in claim 1 , further comprising an insulation monitoring device configured to perform a fault current measurement on the AC terminals.

9 . The power converter as claimed in claim 1 , further comprising a control circuit configured to:
precharge the DC link circuit through the galvanically isolating AC precharging circuit when the AC switches are open, connect the DC terminals to the ungrounded DC grid by closing the circuit breakers, measure the insulation resistance of the ungrounded DC grid with the insulation monitor, and when the insulation resistance is higher than a predetermined value: close the AC switches and set a voltage of the DC grid using the power converter.

10 . The power converter as claimed in claim 9 , wherein the control circuit is configured to charge the DC link circuit with a power that is significantly lower than a rated power of the power converter.

11 . The power converter as claimed in claim 9 , wherein the power converter is configured to set the voltage of the DC side while the DC side is connected to the DC terminals without an interposition of precharging resistors.

12 . A method for supplying power to an ungrounded DC grid from a grounded three-phase AC supply grid using a transformerless power converter comprising a bridge circuit DC terminals of which are connected to the DC grid by way of circuit breakers and AC terminals of which are connected to the AC supply grid via AC switches, and comprising a galvanically isolating AC precharging circuit configured to precharge a DC link circuit of the transformerless power converter from the AC supply grid, wherein the method comprises:
precharging the DC link circuit through the galvanically isolating AC precharging circuit when the AC switches are open, connecting the bridge circuit DC terminals to the DC grid by closing the circuit breakers, measuring an insulation resistance of the DC grid with an insulation monitor, and when the insulation resistance is above a predetermined level: closing the AC switches, and setting a voltage of the DC grid using the power converter.

13 . The method as claimed in claim 12 , wherein at least one DC terminal is connected to the DC grid via a precharging resistor.

14 . The method as claimed in claim 13 , wherein measuring the insulation resistance comprises connecting a first DC terminal to the DC grid via a first precharging resistor, and connecting a second DC terminal, different from the first DC terminal, to the DC grid via a second precharging resistor, wherein the insulation resistance is measured from measured values acquired while only the first DC terminal and while both DC terminals are connected.

15 . The method as claimed in claim 12 , further comprising setting the voltage of the DC grid by the power converter while the DC grid is connected to the bridge circuit DC terminals without an interposition of precharging resistors.

16 . The method as claimed in claim 12 , wherein at least one DC terminal is connected to the DC grid via a precharging resistor when the AC switches are closed.

17 . The method as claimed in claim 12 , further comprising:
in an event of failure of the AC supply grid, opening the AC switches and continuing to operate the DC grid via an energy source connected to the DC grid, wherein the insulation resistance of the DC grid is continuously or repeatedly measured using the insulation monitor during continued operation.

18 . The method as claimed in claim 12 , wherein, after the AC switches have been closed, performing insulation monitoring of the DC grid by way of a fault current measurement on the AC terminals.

Assignees

• Sma Solar Technology Ag

Inventors

• Unru Alexander
• Kratochvil Marcel
• Müller Burkard

Classifications

• H02M7/04

  by static converters · CPC title

• H02J1/00

  Circuit arrangements for DC mains or DC distribution networks · CPC title

• H02M1/0009

  Devices or circuits for detecting current in a converter · CPC title

• H02H11/005

  in case of too low isolation resistance, too high load, short-circuit; earth fault · CPC title

• H02H3/16

  responsive to fault current to earth, frame or mass (with balanced or differential arrangement H02H3/26 {; monitoring earth connection H02H5/105}) · CPC title