Search

EP-3874577-B1 - ACTIVE FILTER FOR SINGLE PHASE CHARGING USING A SWITCH-MODE CONVERTER

EP3874577B1EP 3874577 B1EP3874577 B1EP 3874577B1EP-3874577-B1

Inventors

  • BROWN, ALAN WAYNE
  • JOHNSON, Philip Michael

Dates

Publication Date
20260513
Application Date
20191023

Claims (14)

  1. An on-board charger (10) for a vehicle comprising: a first switch-mode converter (16) being operable to convert a first rectified voltage into a first DC component; a second switch-mode converter (18) being operable to convert a second rectified voltage into a second DC component; a third switch-mode converter (20) being operable to convert a third rectified voltage into a third DC component, the third switch-mode converter (20) being bidirectional such that the third switch-mode converter (20) is operable as an active filter to remove harmonics from a DC output of the first (16) and second (18) switch-mode converters when coupled to a single-phase electrical grid, wherein the third switch mode converter (20) includes a primary-side full bridge, an isolation transformer, and a secondary-side full bridge; and a first rectifier (26), a second rectifier (28), and a third rectifier (30) electrically coupled in series with the first switch-mode converter (16), the second switch-mode converter (18), and the third switch-mode converter (20), respectively; and a filter capacitor (32) selectively coupled between the third rectifier (30) and the primary-side full bridge of the third switch-mode converter (20), wherein the filter capacitor (32) draws power from the DC output through the third switch-mode converter (20) if the DC output is greater than a power reference and supplies power to the DC output through the third switch-mode converter (20) if the DC output is less than the power reference.
  2. The on-board charger (10) of claim 1 wherein each of the first, second, and third switch-mode converters (16, 18, 20) includes a dual-active-bridge topology.
  3. The on-board charger (10) of claim 1 wherein the first rectifier (26), the second rectifier (28), and the third rectifier (30) each include a full bridge topology.
  4. The on-board charger (10) of claim 1 further including a relay (24) to alternatively couple the primary-side full bridge of the third switch-mode converter (20) to the third rectifier (30) and the filter capacitor (32).
  5. The on-board charger (10) of claim 4 further including a controller (14) to detect a single-phase AC input voltage and a three-phase AC input voltage and to control operation of the relay (24).
  6. The on-board charger (10) of claim 5 wherein each of the first, second, and third switch-mode converters (16, 18, 20) provide unity power factor when coupled to the three-phase AC input voltage.
  7. The on-board charger (10) of claim 5 wherein the third switch-mode converter (20) is operated 180° out of phase relative to the first and second switch-mode converters (16, 18) when the single-phase AC input voltage is detected by the controller (14).
  8. The on-board charger (10) of claim 5 further including a voltage sensor (34) across the filter capacitor (32), the voltage sensor (34) being coupled to the controller (14).
  9. The on-board charger (10) of claim 1 wherein the power reference is selected such that the third switch-mode converter (20) destructively interferes with the harmonics of the DC output.
  10. A method for converting an AC input voltage into a DC output voltage comprising: providing an on-board charger (10) including a first rectifier (26), a second rectifier (28), and a third rectifier (30) electrically coupled in series with a first switch-mode converter (16), a second switch-mode converter (18), and a third switch-mode converter (20), respectively, wherein the third switch mode converter (20) includes a primary-side full bridge, an isolation transformer, and a secondary-side full bridge, the on-board charger (10) further including a filter capacitor (32) selectively coupled between the third rectifier (30) and the primary-side full bridge of the third switch mode converter (20); in response to a three-phase AC input being detected at the on-board charger (10), operating the first rectifier (26) and the first switch-mode converter (16) to convert a first phase of the AC input into a first DC component, operating the second rectifier (28) and the second switch-mode converter (18) to convert a second phase of the AC input into a second DC component, and operating the third rectifier (30) and the third switch-mode converter (20) to convert a third phase of the AC input into a third DC component; and in response to a single-phase AC input being detected at the on-board charger (10), filtering a DC output of at least one of the first and second switch-mode converters (16, 18) through the third switch-mode converter (20) to reduce harmonics in the DC output, wherein filtering the DC output includes de-coupling the third switch-mode converter (20) from the third rectifier (30) and coupling the primary-side full bridge of the third switch-mode converter (20) to the filter capacitor (32), such that the filter capacitor (32) draws power from the DC output if the DC output is greater than a power reference and supplies power to the DC output if the DC output is less than the power reference.
  11. The method of claim 10 wherein the first rectifier (26), the second rectifier (28), and the third rectifier (30) each include a full bridge topology.
  12. The method of claim 10 wherein the first switch-mode converter (16), the second switch-mode converter (18), and the third switch-mode converter (20) each include a dual-active-bridge topology.
  13. The method of claim 10 wherein the filter capacitor (32) includes a capacitor bank, the capacitor bank being coupled to the third switch-mode converter (20) through a relay (24).
  14. The method of claim 10 further including: coupling the DC output of the on-board charger (10) to a vehicle battery (22); or coupling the filter capacitor (32) to a DC output of the on-board charger (10) through first and second switches (Sr5, Sr6) when a three-phase AC input is detected to reduce current ripple in the DC output of the on-board charger (10), optionally including decoupling the filter capacitor (32) from the DC output of the on-board charger (10) through the first and second switches (Sr5, Sr6) when a single-phase AC input is detected.

Description

FIELD OF THE INVENTION The present invention relates to an active filter using a bi-directional switch-mode converter for an electric vehicle on-board charger. BACKGROUND OF THE INVENTION Electric vehicles include a battery for powering an electric drive system. Plug-in electric vehicles are a category of electric vehicles having a rechargeable battery pack that can be recharged from the electrical grid. Because most electrical grids provide an AC voltage, and because most rechargeable battery packs require a DC voltage, power from the electrical grid must first be converted into a suitable DC voltage when recharging an electric vehicle. A variety of circuits exist for converting an AC voltage from an electrical grid into a DC voltage for a rechargeable battery. One known circuit includes a dual-active-bridge (DAB) converter. The DAB converter receives a DC voltage from a front end rectifier and outputs to a DC link capacitor. In operation, its DC input is inverted by a primary-side bridge and rectified by a secondary-side bridge. The DAB converter is typically operated by a controller to regulate the magnitude of the DC output in accordance with battery charging requirements. Reference may be made to US 9 729 066 B1 which relates to electric power conversion apparatus having single-phase and multi-phase operation modes. An AC/DC conversion apparatus includes first, second, and third AC/DC conversion modules operated by a controller in two modes of operation. In the first mode, the input AC signal is 3-phase and each of the three modules are enabled to handle a respective one of the input phases. In the second mode, the input AC signal is single phase and the first and second modules are enabled to deliver output power based on the single-phase AC input, while the controller actuates an H-bridge switches in the third module to which active filter circuitry is connected, to reduce an AC component in the output signal. The active filter circuitry can be selectively connected to the H-bridge switches when single-phase operation is desired. Reference may be made to MEHTA P ET AL: "SWITCHED - CAPACITOR FILTERS", 26 June 1989, PROCEEDINGS OF THE ANNUAL POWER ELECTRONICS SPECIALISTS CONFERENCE, MILWAUKEE, NEW YORK, IEE, US, PAGE(S) 392 - 399, which relates to an active filter using switched-capacitor circuits. It discloses a novel technique for building 'active filters' using switched-capacitor (s-c) circuits. The technique is used to control input current harmonics in a phase-controlled converter. Electrical grids exist as three-phase electrical grids or single-phase electrical grids, often changing between the two. While high-power charging is more ideally suited to a three-phase electrical grid than a single-phase electrical grid, the latter may be the only option available. It is therefore desirable to have an on-board charger that can support both grid types. In particular, it is desirable to have an on-board charger that removes second-order harmonics during single-phase charging to provide a purely DC output from a single-phase electrical grid. SUMMARY OF THE INVENTION The present invention is defined by the appended independent claims, to which reference should now be made. Specific embodiments are defined in the dependent claims. In one arrangement described herein, an on-board charger having a dual-purpose switch-mode converter for electrical connection to a three-phase electrical grid and a single-phase electrical grid is provided. When connected to a three-phase electrical grid, three switch-mode converters, for example three DAB converters, convert a rectified voltage to produce direct current at the output. When connected to a single-phase electrical grid, the third switch-mode converter is bi-directional such that it is operable to filter the power output of the first and second switch-mode converters and thereby maintain direct current at the output. The on-board charger includes a filter capacitor in electrical communication with the third switch-mode converter through a relay. The relay is responsive to a controller to couple the third switch-mode converter to the filter capacitor when the single-phase electrical grid is detected and to couple the third switch-mode converters to the third phase of the electrical grid when the three-phase electrical grid is detected. In one arrangement, the on-board charger includes a first DAB converter, a second DAB converter, and a third DAB converter, each being operable to convert a rectified voltage into a DC component when coupled to a three-phase electrical grid. When coupled to a single-phase electrical grid, however, the input stage of the third DAB converter is coupled to a filter capacitor as an active filter to remove harmonics from the DC output of one or both of the first and second DAB converters. In particular, the filter capacitor draws power from the DC output through the third DAB converter if the DC output is greater than a power reference and