WO2012055869A2 - Series resonant dc/dc converter - Google Patents

Series resonant dc/dc converter Download PDF

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Publication number
WO2012055869A2
WO2012055869A2 PCT/EP2011/068663 EP2011068663W WO2012055869A2 WO 2012055869 A2 WO2012055869 A2 WO 2012055869A2 EP 2011068663 W EP2011068663 W EP 2011068663W WO 2012055869 A2 WO2012055869 A2 WO 2012055869A2
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WO
WIPO (PCT)
Prior art keywords
switch
switches
terminals
terminal
circuit
Prior art date
Application number
PCT/EP2011/068663
Other languages
French (fr)
Other versions
WO2012055869A3 (en
Inventor
Roberto Rojas
Nils BÄCKMAN
Original Assignee
Eltek Valere As
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Eltek Valere As filed Critical Eltek Valere As
Publication of WO2012055869A2 publication Critical patent/WO2012055869A2/en
Publication of WO2012055869A3 publication Critical patent/WO2012055869A3/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J9/00—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting
    • H02J9/04—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source
    • H02J9/06—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems
    • H02J9/062—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems for AC powered loads
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33584—Bidirectional converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Definitions

  • the present invention relates to a series resonant DC/DC converter.
  • a typical uninterruptable power supply (UPS) system is shown in fig. 1.
  • the UPS system comprises an input converter for converting electric power from an AC or DC power source.
  • a typical UPS has an input power stage that converts the commercial AC mains or a renewable energy AC or DC source, to a DC voltage.
  • the DC voltage is then converted by means of a converter to a controlled AC or DC voltage thus forming a power supply to electrical loads such as computers, refrigerators etc that need uninterrupted power supply.
  • a regulated DC bus is provided between the input converter and the output converter.
  • the DC bus is ideally suited to be connected to a DC battery.
  • a bidirectional DC/DC converter is needed if the battery voltage differs from the DC voltage on the DC-bus.
  • a typical AC-UPS can handle a power failure in the AC mains, by using a battery to supply DC power to the DC bus via a DC/DC converter, so the power supplied to the AC load is not interrupted.
  • power from the AC mains can be used to recharge the battery and supply energy to the load.
  • one DC/DC converter is used for supplying power from the battery to the DC bus and a separate converter is used to charge the battery.
  • the battery charging converter can either be an AC/DC converter supplied with power from the AC mains, or a separate DC/DC converter supplied with power from the DC bus.
  • the input may also be a DC source, for example a renewable electrical energy source such as solar cells.
  • the object of the present invention is to provide a series resonant DC/DC converter with improved efficiency.
  • the obj ect is also to provide a series resonant DC/DC converter which can be controlled to be bidirectional.
  • the series resonant DC/DC converter can be used both for supplying power from the battery to the DC bus during power failures and for supplying power from the DC bus to recharge the battery after a power failure. This reduces the number of components, and hence costs/space can be saved.
  • the present invention relates to a series resonant DC/DC converter comprising: first DC terminals;
  • first switching circuit connected between the first DC terminals and the inductor device where the first switching circuit comprises a first set of switches and a second set of switches;
  • the second switching circuit comprises a first set of switches and a second set of switches
  • control circuit for controlling the first and second sets of switches of the first and second switching circuits to provide that power may be transferred from the first DC terminals to the second DC terminals, where the control circuit is configured to control the relation between the voltage between the first DC terminals of the series resonant DC/DC converter and the voltage between the second DC terminals of the series resonant DC/DC converter by varying the length of the switching period.
  • a voltage Vin between the first DC terminals can be smaller than a voltage Vout between the second DC terminals.
  • a load is connected between the second DC terminals.
  • the load is a rechargeable battery.
  • control circuit is configured to control the direction of the power flow through the series resonant DC/DC converter by varying the length of the switching period.
  • the first switching circuit is a bridge circuit.
  • the first switching circuit is a full bridge circuit or a half bridge circuit.
  • the second switching circuit is a bridge circuit.
  • the second switching circuit is a full bridge circuit or a half bridge circuit.
  • the resonant circuit is a multi-element resonant circuit.
  • control circuit is controlling the current and/or voltage at the first DC-terminals or controlling current and/or voltage at the second DC- terminals, depending on a status flag signal.
  • Fig. 1 illustrates a typical application for bidirectional DC/DC converters
  • Fig. 2 illustrates a first embodiment of the DC/DC converter
  • Fig. 3 illustrates a second embodiment of the DC/DC converter
  • Fig. 4 illustrates a third embodiment of the DC/DC converter
  • Fig. 5 illustrates a fourth embodiment of the DC/DC converter
  • Fig. 6 illustrates a fifth embodiment of the DC/DC converter
  • Fig. 7 illustrates a fifth embodiment of the DC/DC converter; this embodiment does not have a transformer device;
  • Fig. 8 shows waveforms of voltages and currents of the second embodiment at full load
  • Fig. 9 shows details of fig. 9
  • Fig. 10 shows waveforms of voltages and currents of the second embodiment at no load;
  • Fig. 1 1 shows details of fig. 10;
  • Fig. 12 shows the variation of output voltage Vout for different switching frequencies and different loads
  • Fig. 13 shows the efficiency curve as a function of the output power for the embodiment in fig. 3.
  • series resonant DC/DC converter series it is meant different types of series resonant LC DC/DC converters and different types of series resonant LLC DC/DC converters.
  • the series resonant DC/DC converter may also be a bidirectional DC/DC converter.
  • the DC/DC converter comprises first DC terminals TIP, TIN and second DC terminals T2P, T2N.
  • the first DC terminals comprise a first positive DC terminal TIP and a first negative DC terminal TIN.
  • the second DC terminals comprise a second positive DC terminal T2P and a second negative DC terminal T2N.
  • the DC/DC converter further comprises an inductor device, either in the form of a single inductor device ID (as in the embodiment of fig. 7) or in the form of a transformer device TD (as in the embodiments of figs. 2 - 6).
  • the single inductor device ID may comprise a single inductor Lm, or may comprise several inductors, but does not provide a galvanic isolation.
  • the transformer device TD may comprise a first winding and a second winding.
  • the transformer device provides galvanic isolation between the first DC terminals and the second DC terminals.
  • the transformer also comprises a magnetizing inductance, which forms a parallel resonance circuit together with the resonant capacitor(s).
  • the transformer ratio of the transformer device is 1 : 1 in the present
  • transformer ratios are also possible and can be designed in order to meet requirements for input output voltage and current ratios.
  • a first switching circuit SCI (illustrated by a dashed box) is connected between the first DC terminals TIP, TIN and the inductor device (either the single inductor device ID or the transformer device TD).
  • the first switching circuit SCI comprises a first set of switches and a second set of switches.
  • the first set and the second set of switches may each comprise one, two or several switches.
  • the first switching circuit SC I is arranged to be controlled in three different switching states.
  • the first state allows a current to flow through the inductor device from the first positive DC terminal TIP to the negative DC terminal TIN by commanding the first set of switches to be ON.
  • the second state allows a current to flow through the inductor device from the first negative DC terminal TIN to the first positive DC terminal TIP by commanding the second set of switches to be ON.
  • the third switching state is characterized by commanding both sets of switches to be OFF
  • a second switching circuit SC2 (illustrated by a dashed box) and a resonant circuit RC (illustrated by a dashed box) are connected between the second DC terminals T2P, T2N and the inductor device (either the single inductor device ID or the transformer device TD).
  • the second switching circuit SC2 comprises a first set of switches and a second set of switches.
  • the first set and the second set of switches may each comprise one, two or several switches. It can be seen that the second switching circuit SC2 and a resonant circuit RC are connected in series with the inductor device (the single inductor device ID or the transformer device TD) between the second DC-terminals T2P and T2N.
  • the series combination of the resonant circuit RC and the inductor device is connected to the second switching circuit SC2.
  • the second switching circuit, SC2 is arranged to be controlled in three different switching states.
  • the first state allows a resonant current to flow through the series combination of the resonant circuit RC and the inductor device from the second positive DC terminal T2P to the second negative DC terminal T2N by commanding the first set of switches to be ON.
  • the second state allows a resonant current to flow through the series combination of RC and the inductor device from the second negative DC terminal T2N to the second positive DC terminal T2P by commanding the second set of switches to be ON.
  • the third switching state is characterized by
  • the first switching circuit SCI may be a push pull circuit or a bridge circuit, such as a full bridge circuit or a half bridge circuit.
  • the second switching circuit SC2 may also be a bridge circuit, such as a full bridge circuit or a half bridge circuit.
  • the resonant circuit RC is often referred to as a resonant tank and comprises at least one capacitor or at least one inductor in a suitable configuration together with the inductor device, either the single inductor device ID or the second winding of the transformer device T, where the inductance of the at least one capacitor and/or at least one inductor together with the inductance of the single inductor device ID or the second winding of the transformer device T defines a resonance frequency so that the DC/DC converter exhibits zero voltage turn on switching on all active switches of SC I and SC2.
  • the resonant circuit RC may also be a multi-element resonant circuit comprising several capacitors and inductors in a LC network. Hence, the converter can be considered as a series resonant LLC DC/DC converter.
  • the DC/DC converter comprises a control circuit for controlling the first and second sets of switches of the first and second switching circuits SC I, SC2.
  • the control circuit is configured to control the first and second sets of switches of the first and second switching circuits SCI, SC2 and can then determine the desired direction of power flow and control the direction of current at the first and second DC-terminals and thus make the converter supply energy either to the load connected to the first DC-terminals or the load connected to the second DC-terminals.
  • the switches are MOSFET switches.
  • the switches may be switches with intrinsic diodes or switches connected in parallel with anti- parallel diodes, such as IGBTs with anti-parallel diodes.
  • the first switching circuit SC I is a half bridge circuit comprising a first switch S l scl and a second switch S2scl .
  • the first set of switches of the first switching circuit SCI here comprises the first switch S l scl and the second set of switches of the first switching circuit SC I comprises the second switch S2scl .
  • the first switch S l scl is connected between the first negative DC terminal TIN and a first terminal of the first winding.
  • the source of the switch is connected to the first negative DC terminal TIN.
  • the second switch S2scl is connected between the first negative DC terminal TIN and a second terminal of the first winding.
  • the source of the switch is connected to the first negative DC terminal TIN.
  • the first winding of the transformer device T comprises a third terminal connected to the first positive DC terminal TIP.
  • the third terminal of the second winding is provided between the first terminal and the second terminal of the second winding.
  • the number of turns between the first and third terminals and the number of turns between the second and third terminals is equal to the total number of turns for the second winding.
  • the number of turns between the first and third terminals and the number of turns between the second and third terminals is equal to each other.
  • a first capacitor C I is connected between the first positive DC terminal TIP and the first negative DC terminal TIN.
  • the second switching circuit SC2 is a half bridge circuit comprising a first switch S l sc2 and a second switch S2sc2.
  • the first set of switches of the second switching circuit SC2 here comprises the first switch S l sc2 and the second set of switches of the second switching circuit SC2 comprises the second switch S2sc2
  • the first switch S l sc2 is connected between a first node 10 and the second positive DC terminal T2P.
  • the second switch S2sc2 is connected between the second negative DC terminal T2N and the second node 10.
  • the source of the first switch S l sc2 is connected to the second negative DC terminal T2N and the source of the second switch S2sc2 is connected to the first node 10.
  • the first node 10 is also connected to a first terminal of the second winding of the transformer device T.
  • the resonant circuit RC comprises a resonant inductor Lrc, a first resonant capacitor C lrc and a second resonant capacitor C2rc.
  • the resonant inductor Lrc is connected between a second terminal of the second winding of the transformer T and a second node 12.
  • the first resonant capacitor C lrc is connected between the second node 12 and the second positive DC terminal T2P.
  • the second resonant capacitor C2rc is connected between the second node 12 and the second negative DC terminal T2N.
  • the first switching circuit SC I is a full bridge circuit comprising a first switch S l scl, a second switch S2scl, a third switch S3scl and a fourth switch S4scl .
  • the first set of switches of the first switching circuit SC I here comprises the first switch S l scl and the fourth switch S4scl .
  • the second set of switches of the first switching circuit SC I comprises the second switch S2scl and the third switch S3scl .
  • the first switch S l scl is connected between the first positive DC terminal TIP and a first node 20.
  • the source of the switch is connected to the first node 20.
  • the second switch S2scl is connected between the first negative DC terminal TIN and the first node 20.
  • the source of the switch is connected to the first negative DC terminal TIN.
  • the third witch S3scl is connected between the first positive DC terminal TIP and a second node 22.
  • the source of the switch is connected to the second node 22.
  • the fourth switch S4scl is connected between the first negative DC terminal TIN and the second node 22.
  • the source of the switch is connected to the first negative DC terminal TIN.
  • the first node 20 is connected to the first terminal of the first winding of the transformer device T.
  • the second node 22 is connected to the second terminal of the first winding of the transformer device T.
  • a first capacitor C I is connected between the first positive DC terminal TIP and the first negative DC terminal TIN.
  • the second switching circuit SC2 is here a half bridge circuit comprising a first switch S l sc2 and a second switch S2sc2.
  • the first set of switches of the second switching circuit SC2 here comprises the first switch S l sc2 and the second set of switches of the second switching circuit SC2 comprises the second switch S2sc2.
  • the first switch S l sc2 is connected between a first node 10 and the second positive DC terminal T2P.
  • the second switch S2sc2 is connected between the second negative DC terminal T2N and the second node 10.
  • the source of the first switch S l sc2 is connected to the node 10 and the source of the second switch S2sc2 is connected to the second negative DC terminal T2N.
  • the first node 10 is also connected to a first terminal of the second winding of the transformer device T.
  • the resonant circuit RC comprises a resonant inductor Lrc, a first resonant capacitor C lrc and a second resonant capacitor C2rc.
  • the resonant inductor Lrc is connected between a second terminal of the second winding of the transformer T and a second node 12.
  • the first resonant capacitor C lrc is connected between the second node 12 and the second positive DC terminal T2P.
  • the second resonant capacitor C2rc is connected between the second node 12 and the second negative DC terminal T2N.
  • a second capacitor C2 is connected between the second positive DC terminal T2P and the second negative DC terminal T2N.
  • the first winding of the transformer device TD is denoted as Tp
  • the second winding of the transformer device TD is denoted as Ts.
  • the current through the first winding is denoted as Ip
  • the current through the second winding is denoted as Is.
  • a voltage source with input voltage Vin is connected between the first negative DC terminal and the first positive DC terminal TIP, TIN.
  • a load denoted with "load” is connected between the second negative DC terminal and the second positive DC terminal T2P, T2N.
  • the first switching circuit SC I is a full bridge circuit comprising a first switch S l scl, a second switch S2scl, a third switch S3scl and a fourth switch S4scl .
  • the first set of switches of the first switching circuit SC I here comprises the first switch S l scl and the fourth switch S4scl .
  • the second set of switches of the first switching circuit SC I comprises the second switch S2scl and the third switch S3scl .
  • the first switch S l scl is connected between the first positive DC terminal TIP and a first node 20.
  • the source of the switch is connected to the first node 20.
  • the second switch S2scl is connected between the first negative DC terminal TIN and the first node 20.
  • the source of the switch is connected to the first negative DC terminal TIN.
  • the third witch S3scl is connected between the first positive DC terminal TIP and a second node 22.
  • the source of the switch is connected to the second node 22.
  • the fourth switch S4scl is connected between the first negative DC terminal TIN and the second node 22.
  • the source of the switch is connected to the first negative DC terminal TIN.
  • the first node 20 is connected to the first terminal of the first winding of the transformer device T.
  • the second node 22 is connected to the second terminal of the first winding of the transformer device T.
  • a first capacitor C I is connected between the first positive DC terminal TIP and the first negative DC terminal TIN.
  • the second switching circuit SC2 is a full bridge circuit comprising a first switch S l sc2, a second switch S2sc2, a third switch S3sc2 and a fourth switch S4sc2.
  • the first set of switches of the second switching circuit SC2 here comprises the first switch S l sc2 and the fourth switch S4sc2.
  • the second set of switches of the second switching circuit SC2 comprises the second switch S2sc2 and the third switch S3sc2.
  • the first switch S l sc2 is connected between the second positive DC terminal T2P and a first node 10.
  • the source of the first switch S l sc2 is connected to the first node 10.
  • the second switch S2sc2 is connected between the second negative DC terminal TIN and the first node 10.
  • the source of the switch is connected to the second negative DC terminal T2N.
  • the third switch S3sc2 is connected between the second positive DC terminal T2P and a second node 12.
  • the source of the switch is connected to the second node 12.
  • the fourth switch S4sc2 is connected between the second negative DC terminal T2N and the second node 12.
  • the source of the switch is connected to the second negative DC terminal T2N.
  • the second node 12 of the second switching circuit SC2 is also connected to a first terminal of the second winding of the transformer device T.
  • the resonant circuit RC comprises a resonant inductor Lrc and a resonant capacitor Crc connected in series between a second terminal of the second winding of the transformer device T and the first node 10.
  • a second capacitor C2 is connected between the second positive DC terminal T2P and the second negative DC terminal T2N.
  • the first switching circuit SC I is a half bridge circuit comprising a first switch S l scl and a second switch S2scl .
  • the first set of switches of the first switching circuit SC I here comprises the first switch S l scl and the second set of switches of the first switching circuit SC I comprises the second switch S2scl .
  • the first switch S l scl is connected between the first negative DC terminal TIN and a first terminal of the first winding.
  • the source of the switch is connected to the first negative DC terminal TIN.
  • the second switch S2scl is connected between the first negative DC terminal TIN and a second terminal of the first winding.
  • the source of the switch is connected to the first negative DC terminal TIN.
  • the first winding of the transformer device T comprises a third terminal connected to the first positive DC terminal TIP.
  • the third terminal of the second winding is provided between the first terminal and the second terminal of the second winding.
  • the number of turns between the first and third terminals and the number of turns between the second and third terminals is equal to the total number of turns for the second winding.
  • the number of turns between the first and third terminals and the number of turns between the second and third terminals is equal to each other.
  • a first capacitor C I is connected between the first positive DC terminal TIP and the first negative DC terminal TIN.
  • the second switching circuit SC2 is a full bridge circuit comprising a first switch S l sc2, a second switch S2sc2, a third switch S3sc2 and a fourth switch S4sc2.
  • the first set of switches of the second switching circuit SC2 here comprises the first switch S l sc2 and the fourth switch S4sc2.
  • the second set of switches of the second switching circuit SC2 comprises the second switch S2sc2 and the third switch S3sc2.
  • the first switch S l sc2 is connected between the second positive DC terminal T2P and a first node 10.
  • the source of the first switch S l sc2 is connected to the first node 10.
  • the second switch S2sc2 is connected between the second negative DC terminal TIN and the first node 10.
  • the source of the switch is connected to the second negative DC terminal T2N.
  • the third switch S3sc2 is connected between the second positive DC terminal T2P and a second node 12.
  • the source of the switch is connected to the second node 12.
  • the fourth switch S4sc2 is connected between the second negative DC terminal T2N and the second node 12.
  • the source of the switch is connected to the second negative DC terminal T2N.
  • the second node 12 of the second switching circuit SC2 is also connected to a first terminal of the second winding of the transformer device T.
  • the resonant circuit RC comprises a resonant inductor Lrc and a resonant capacitor Crc connected in series between a second terminal of the second winding of the transformer device T and the first node 10.
  • a second capacitor C2 is connected between the second positive DC terminal T2P and the second negative DC terminal T2N.
  • the first switching circuit SC I is a voltage doubler circuit comprising a first switch S l scl and a second switch S2scl .
  • the first set of switches of the first switching circuit SC I here comprises the first switch S l scl and the second set of switches of the first switching circuit SC I comprises the second switch S2scl .
  • the first switch S l scl is connected between the first positive DC terminal TIP and a first terminal of the first winding of the transformer device TD.
  • the source of the switch is connected to the first terminal of the first winding of the transformer device TD.
  • the second switch S2scl is connected between the first negative DC terminal TIN and a second terminal of the first winding of the transformer device TD.
  • the source of the switch is connected to the second terminal of the first winding of the transformer device TD.
  • a first capacitor C I is connected between the first positive DC terminal TIP and a node 20.
  • a second capacitor C2 is connected between the node 20 and the first negative DC terminal TIN.
  • the node 20 is connected to a third terminal of the first winding of the transformer device TD.
  • the third terminal of the second winding is provided between the first terminal and the second terminal of the second winding.
  • the number of turns between the first and third terminals and the number of turns between the second and third terminals is equal to the total number of turns for the second winding.
  • the number of turns between the first and third terminals and the number of turns between the second and third terminals is equal to each other.
  • the second switching circuit SC2 is here a half bridge circuit comprising a first switch S l sc2 and a second switch S2sc2.
  • the first set of switches of the second switching circuit SC2 here comprises the first switch S l sc2 and the second set of switches of the second switching circuit SC2 comprises the second switch S2sc2.
  • the first switch S l sc2 is connected between a first node 10 and the second positive DC terminal T2P.
  • the second switch S2sc2 is connected between the second negative DC terminal T2N and the second node 10.
  • the source of the first switch S l sc2 is connected to the node 10.
  • the source of the second switch S2sc2 is connected to the second negative DC terminal T2N.
  • the first node 10 is also connected to a first terminal of the second winding of the transformer device T.
  • the resonant circuit RC comprises a resonant inductor Lrc, a first resonant capacitor C lrc and a second resonant capacitor C2rc.
  • the resonant inductor Lrc is connected between a second terminal of the second winding of the transformer T and a second node 12.
  • the first resonant capacitor C lrc is connected between the second node 12 and the second positive DC terminal T2P.
  • the second resonant capacitor C2rc is connected between the second node 12 and the second negative DC terminal T2N.
  • the first switching circuit SC I is a full bridge circuit comprising a first switch S l scl, a second switch S2scl, a third switch S3scl and a fourth switch S4scl .
  • the first set of switches of the first switching circuit SC I here comprises the first switch S l scl and the fourth switch S4scl .
  • the second set of switches of the first switching circuit SC I comprises the second switch S2scl and the third switch S3scl .
  • the first switch S l scl is connected between the first positive DC terminal TIP and a first node 20.
  • the source of the switch is connected to the first node 20.
  • the second switch S2scl is connected between the first negative DC terminal TIN and the first node 20.
  • the source of the switch is connected to the first negative DC terminal TIN.
  • the third switch S3scl is connected between the first positive DC terminal TIP and a second node 22.
  • the source of the switch is connected to the second node 22.
  • the fourth switch S4scl is connected between the first negative DC terminal TIN and the second node 22.
  • the source of the switch is connected to the first negative DC terminal TIN.
  • an inductor device ID in the form of a magnetizing inductor Lm is provided.
  • the first node 20 is connected to the first terminal of the magnetizing inductor Lm.
  • the second node 22 is connected to the second terminal of the magnetizing inductor Lm.
  • a first capacitor C I is connected between the first positive DC terminal TIP and the first negative DC terminal TIN.
  • the second switching circuit SC2 is here a half bridge circuit comprising a first switch S l sc2 and a second switch S2sc2.
  • the first set of switches of the second switching circuit SC2 here comprises the first switch S l sc2 and the second set of switches of the second switching circuit SC2 comprises the second switch S2sc2.
  • the first switch S l sc2 is connected between a first node 10 and the second positive DC terminal T2P.
  • the second switch S2sc2 is connected between the second negative DC terminal T2N and the second node 10.
  • the source of the first switch S l sc2 is connected to the node 10 and the source of the second switch S2sc2 is connected to the second negative DC terminal T2N.
  • the first node 10 is also connected to the second terminal of the magnetizing inductor Lm.
  • the resonant circuit RC comprises a resonant inductor Lrc, a first resonant capacitor C lrc and a second resonant capacitor C2rc.
  • the resonant inductor Lrc is connected between the first terminal of the magnetizing inductor Lm and a second node 12.
  • the first resonant capacitor C lrc is connected between the second node 12 and the second positive DC terminal T2P.
  • the second resonant capacitor C2rc is connected between the second node 12 and the second negative DC terminal T2N.
  • a second capacitor C2 is connected between the second positive DC terminal T2P and the second negative DC terminal T2N.
  • a control circuit is provided for controlling the switches of the first and second switching circuits SCI and SC2 to be ON and OFF.
  • the control circuit may be implemented as a software program executed by a digital signal processor (DSP) or it may be implemented as an analogue circuit.
  • DSP digital signal processor
  • All switches are uni-polar, meaning that the switches can only block conduction in one direction.
  • An example of a uni-polar switch is the MOSFET switch comprising an anti-parallel diode.
  • Another example is the IGBT switch with an anti-parallel diode connected from emitter to drain.
  • the control method for controlling the series resonant DC/DC converter will now be described in detail below with reference to figs. 8 - 12.
  • the control signals and resulting voltages and/or currents are shown for the embodiment shown in fig. 3.
  • the input voltage Vin was set to 50 VDC, and an output voltage was regulated to 350 VDC.
  • the switching frequency is approximately 1 10kHz.
  • a switching period TP is defined from time Tstart to time Tend for the series resonant DC/DC converter.
  • the switching period TP comprises a first half period TA from time Tstart to time Tcenter and a second half period TB from time Tcenter to time Tend.
  • a next switching period after the switching period TP is denoted as a subsequent switching period TP+1.
  • the series resonant DC/DC converter has a resonance frequency defined by the properties of the inductor device (ID or TD) and the elements (capacitors and inductors) of the resonance circuit RC.
  • the switching period TP and hence the switching frequency, can be controlled by the control circuit to be be higher than, equal to, or lower than the resonance frequency. Hence, the switching period TP is not dependant of the resonance frequency.
  • Time T8 is the start (i.e. time T0(TP+1)) of the subsequent switching period TP+1.
  • Time T4 is here equal to Tcenter, but the length of the time intervals TO - Tl, Tl - T2, T2 - T3, T3 - T4, T4 - T5, T5 - T6, T6 - T7, T7 - T8 are not all equal to each other.
  • the duty cycle of all set of switches are essentially 50%, meaning that the switches have a control signal demanding the switch to be in a conducting state, ON, during nearly half of the switching period and having the control signal demanding the switch to be in a non-conducting state, OFF, during nearly half of the switching period.
  • the set of switches are controlled independently to have different delays and yet synchronized.
  • the first set S l scl ; S l scl, S4scl of switches of the first switching circuit SC I is controlled to be ON from the beginning Tstart of the first half period TA minus a time interval ⁇ 1, where the time interval ⁇ 1 is provided at the end of the first half period TA.
  • the first set S l scl ; S l scl, S4scl of switches of the first switching circuit SC I is controlled to be OFF in the second half period TB.
  • the time interval ⁇ 1 in the present embodiment is starting at time T3 and is ending at time T4.
  • the second set S2scl ; S2scl , S3 scl of switches of the first switching circuit SC I is controlled to be ON from the beginning Tcenter of the second half period TB minus a time interval ⁇ 1 , where the time interval ⁇ 1 is provided at the end of the second half period TB.
  • the second set S2scl ; S2scl , S3 scl of switches of the first switching circuit SC I is controlled to be OFF in the first half period TA.
  • the time interval ⁇ 1 is in the present embodiment starting at time T7 and is ending at time T8.
  • the first set S l scl ; S l scl, S4scl and the second set S2scl ; S2scl, S3scl of switches of the first switching circuit SCI is controlled to be OFF in the time interval ⁇ 1 and the time interval ⁇ 1.
  • the time interval ⁇ 1 forms a first time interval Tscloffl wherein the first and second sets of switches of the first switching circuit SCI are OFF.
  • the time interval ⁇ forms a second time interval Tscloff2 wherein the first and second sets of switches of the first switching circuit SCI are OFF.
  • the first set S l sc2; S l sc2, S4sc2 of switches of the second switching circuit SC2 is controlled to be ON in the first half period TA minus a time interval ATAS l and minus a time interval ⁇ 2, where the time interval ATAS l is provided at the beginning of the first half period TA and where the time interval ⁇ 2 is provided at the end of the first half period TA.
  • the first set S l sc2; S l sc2, S4sc2 of switches of the second switching circuit SC is controlled to be OFF in the second half period TB.
  • the time interval ATAS l in the present embodiment is starting at time TO and is ending at time Tl .
  • the time interval ⁇ 2 in the present embodiment is starting at time T2 and is ending at T4.
  • the second set S2sc2; S2sc2, S3 sc2 of switches of the second switching circuit SC2 is controlled to be ON in the second half period TB minus time interval ATBS l and minus time interval ⁇ 2, where the time interval ATBS l is provided at the beginning of the second half period TB and where the time interval ⁇ 2 is provided in the end of the second half period TB.
  • the second set S2sc2; S2sc2, S3sc2 of switches of the second switching circuit SC2 is controlled to be OFF in the first half period TA.
  • the time interval ATBS l in the present embodiment is starting at time T4 and is ending at time T5.
  • the time interval ⁇ 2 in the present embodiment is starting at T6 and is ending at T8.
  • the first set S l sc2; S l sc2, S4sc2 and the second set S2sc2; S2sc2, S3 sc2 of switches of the second switching circuit SC2 are controlled to be OFF in the time intervals ATAS l, ⁇ 2, ATBS l and ⁇ 2.
  • the time intervals ⁇ 2 and ATBS l form a continuous time interval Tsc2offl from time T2 to time T5 where the first and second sets of switches of the second switching circuit (SC2) are OFF.
  • the time intervals ⁇ 2 and ATAS 1(TP+1) (that is, the time interval ATAS l of a subsequent switching period TP+1) form a continuous time interval Tsc2off2 from time T6 to time T1(TP+1) (that is, the time instance Tl of a subsequent switching period TP+1) where the first and second sets of switches of the second switching circuit (SC2) are OFF.
  • Table 1 shows the states for the first and second set of switches for the first switching circuit SC I for the switching period TP. The start time and end time of each interval are also given.
  • Table 1 ON/OFF states for first and second set of switches of the first switching circuit SCI .
  • Table 2 shows the states for the first and second set of switches for the second switching circuit SC2 for the switching period TP. The start time and end time of each interval are also given.
  • Table 2 ON/OFF states for first and second set of switches of the second switching circuit SC2.
  • the time interval Tscloffl and the time interval Tsc2offl are at least partially overlapping, i.e. the time interval Tscloffl starts before the time interval Tsc2offl ends or the time interval Tsc2offl starts before the time interval Tscloffl ends.
  • the time interval Tscloff2 and the time interval Tsc2off2 are at least partially overlapping, i.e. the time interval Tscloff2 starts before the time interval Tsc2off2 ends or the time interval Tsc2off2 starts before the time interval Tscl off2 ends.
  • the length of time interval Tsc2offl is equal to the length of time interval Tsc2off2
  • the length of time interval Tsc l offl is equal to the length of time interval Tsc l off2.
  • the time intervals Tsc2offl and Tsc2off2 are longer than the time intervals Tscl offl and Tscl off2. However, they could have the same duration, or the time interval Tscl off could be longer than the period Tsc2off. This depends on the required time for achieving Zero Voltage Switching (ZVS) in the switching circuits and may also depend on the voltage between the first positive and negative DC terminals and the voltage between the second positive and negative DC terminals.
  • ZVS Zero Voltage Switching
  • the centre of time interval Tsc l offl is controlled to be close to or equal to the centre of time interval Tsc2offl and the centre of time interval Tsc l off2 is controlled to be close to or equal to the centre of time interval Tsc2off2 .
  • the first set S l sc2 of switches in the second switching circuit SC2 is turned off at time instance T2. At the time instance when current Is becomes positive it is capable of bringing the voltage at node 10 from high to low by discharging the output capacitances in both the first and second set of switches of the second switching circuit.
  • the second set of switches S2sc2 of the second switching circuit is commanded to be ON at T5, and are thus turned on with a voltage close to zero without any significant switching losses, so called Zero Voltage
  • first set of switches S l sc l and S4sc l at T3 results in a rapid change of voltage at node 20 from high to low and voltage at node 22 from low to high, caused by the discharging/charging of the output capacitances in the first and second sets of switches S l sc l , S3 scl and S2scl , S4sc l of the first switching circuit.
  • the second set of switches S2scl and S3 sc l of the first switching circuit SC I are commanded to be ON at T4, and are thus turned on with a voltage close to zero without any significant switching losses, so called ZVS.
  • the time interval T2 to T5 between turning off S l sc2 and turning on S2sc2 is longer then the time interval T3 to T4 for turning off S l scl, S4scl and turning on S2scl, S3scl since it will take longer time for the voltage Vout of 350 V of the second switching circuit SC2 to commutate than for the voltage Vin of 50 V of the first switching circuit SCI .
  • the switch S l sc2 is turned off at time instance T2.
  • the current Is is positive and is therefore capable of bringing V10 from high to low by discharging the output capacitances in the switches S l sc2 and S2sc2.
  • the current Is is decaying due to the changed voltage over resonant inductor, L R C , during the time period T2 to T3.
  • the magnetizing current I LM in winding Ls is still increasing and is therefore reflected to primary winding, L P; and causes the current I P to increase. Since Ip is increasing and positive, turning off switches S l scl and S4scl results in a rapid change of voltage V20 at node 20 from high to low and voltage V22 at node 22 from low to high, caused by the discharging/charging of the output capacitances in the switches S l scl , S3 scl and S2scl, S4scl .
  • the output voltage Vout may be controlled by changing the switching frequency. This is illustrated in fig. 12, where it is shown that the output voltage Vout may be varied for different loads and different switching frequencies.
  • the ZVS operation of all switches is controlled by proper delays , i.e. the time intervals Tscloffl, Tscl off2, Tsc2offl and Tsc2off2, between switching instances as described in the text and in figure 8 and table 2 and table 3.
  • the relation between the voltage between first DC terminals TIP, TIN of the series resonant DC/DC converter and the voltage between second DC terminals T2P, T2N of the series resonant DC/DC converter can be controlled by varying the length of the switching period TP.
  • the direction of the power flow through the series resonant DC/DC converter can be controlled by varying length of the switching period TP.
  • the series resonant DC/DC converter can be controlled to be a bidirectional series resonant DC/DC converter.
  • the switches of the first and second switching circuit SC I, SC2 are controlled to provide zero voltage switching ZVS at switch turn on and to provide nearly zero current switching ZCS at switch turn off by controlling the first and second switching circuit to have a fixed switching frequency close to the series resonant frequency.
  • the switches of the first and second switching circuit SCI , SC2 can be controlled by switching at an operating point at or near the series resonant frequency for all voltages over the first DC terminals which are inside a specified operating range.
  • the switches of the first and second switching circuit SCI , SC2 can be controlled by switching at an operating point at or near the series resonant frequency for all load conditions at the second DC terminals.
  • the common control circuit can for example comprise a status flag signal as an indicator for the direction of the power flow through the UPS system
  • control circuit comprises sensors for sensing the current and/or the voltage at the first DC terminals TIP, TIN and the second DC terminals T2P, T2N.
  • the status flag signal indicates that the power should flow from the first DC terminals TIP, TIN to the second DC terminals T2P, T2N.
  • the control circuit is controlling the current and/or voltage of the second DC terminals T2P, T2N based on a predetermined reference signal for the first mode of operation.
  • the status flag signal indicates that the power should flow from the second DC terminals T2P, T2N to the first DC terminals TIP, TIN.
  • the control circuit is controlling the current and/or voltage of the first DC terminals TIP, TIN based on a predetermined reference signal for the second mode of operation.
  • the series resonant DC/DC converter may be used as a DC/DC converter for an UPS system, as shown in fig. 1, where its first DC terminals TIP, TIN are connected to the battery and its second DC terminals T2P, T2N connected to a DC bus (not shown).
  • the status flag signal may be switched to the first mode of operation when a failure in the AC mains is detected. In such a situation power should be transferred from the battery connected to the first DC terminals to the DC bus connected to the second DC terminals.
  • the control circuit is controlling the voltage and/or current at the second DC terminals T2P, T2N at a predetermined level suitable as input to the DC/AC converter as long as the battery power supply allows it.
  • the status flag signal may be switched to the second mode of operation when the AC mains is working again, then supplying power from the DC bus to the battery for recharging the battery.
  • the control circuit is controlling the voltage and/or current at the first DC terminals TIP, TIN at a predetermined level suitable as input to the battery.
  • the status flag signal may have a third mode of operation for indicating that no power should be transferred through the bidirectional DC/DC converter. In this mode of operation, all switches should be switched off. In this mode of operation there is no failure in the AC mains, and the battery is fully charged.
  • Another application for the series resonant DC/DC converter is for re-use of energy stored in battery storages.
  • Fig. 12 shows the results of the testing. In the testing, two efficiency curves are illustrated, the first curve shows the efficiency as a function of output power for a circuit having an input voltage Vin of 50V and the second curve shows the efficiency as a function of output power for a circuit having an input voltage Vin of 48V.
  • the output voltage Vout was controlled to be 355V.
  • the efficiency is above 96% in the power output range from ca 400W to 2200W.
  • the maximum power efficiency is above 97.5%. This is a considerable improvement over the prior art DC/DC converters mentioned in the introduction, which showed efficiencies of ca 92%.

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Abstract

The invention relates to a series resonant DC/DC converter comprising:first DC terminals (T1P, T1N); second DC terminals (T2P, T2N); an inductor device (ID; TD); and a first switching circuit (SC1) connected between the first DC terminals (T1P, T1N) and the inductor device (ID; TD). The first switching circuit (SC1) comprises a first set (S1sc1; S1sc1, S4sc1) of switches and a second set (S2sc1; S2sc1, S3sc1) of switches. A second switching circuit (SC2) and a resonant circuit (RC) are connected between the second DC terminals (T2P, T2N) and the inductor device (ID; TD), where the second switching circuit (SC2) comprises a first set (S1sc2; S1sc2, S4sc2) of switches and a second set (S2sc2; S2sc2, S3sc2) of switches. A control circuit for controlling the set of switches of the first and second switching circuits (SC1, SC2) to control the current and/or voltage at either the first DC terminals (T1P, T1N) or the second DC terminals (T2P, T2N).

Description

SERIES RESONANT DC/DC CONVERTER
FIELD OF THE INVENTION
The present invention relates to a series resonant DC/DC converter. BACKGROUND OF THE INVENTION
A typical uninterruptable power supply (UPS) system is shown in fig. 1. The UPS system comprises an input converter for converting electric power from an AC or DC power source. A typical UPS has an input power stage that converts the commercial AC mains or a renewable energy AC or DC source, to a DC voltage. The DC voltage is then converted by means of a converter to a controlled AC or DC voltage thus forming a power supply to electrical loads such as computers, refrigerators etc that need uninterrupted power supply.
Typically, a regulated DC bus is provided between the input converter and the output converter. The DC bus is ideally suited to be connected to a DC battery. A bidirectional DC/DC converter is needed if the battery voltage differs from the DC voltage on the DC-bus.
A typical AC-UPS can handle a power failure in the AC mains, by using a battery to supply DC power to the DC bus via a DC/DC converter, so the power supplied to the AC load is not interrupted. When the AC mains is operable again, power from the AC mains can be used to recharge the battery and supply energy to the load.
In many UPS systems, one DC/DC converter is used for supplying power from the battery to the DC bus and a separate converter is used to charge the battery. The battery charging converter can either be an AC/DC converter supplied with power from the AC mains, or a separate DC/DC converter supplied with power from the DC bus.
In some applications, the input may also be a DC source, for example a renewable electrical energy source such as solar cells.
There exist many proposed circuits for one-directional and bi-directional DC/DC converters for improved efficiency such as in "Performance optimization of a High Current Dual Active Bridge with Wide operating Voltage Range ", by Krismer, Round, Kolar" published in Power Electronics Specialists Conference, 2006, "A new HE ZVZCS Bidirectional DC/DC converter for HEV 42V Power Systems ", by Kim, Han, Park, Moon published in Journal of Power Electronics, Vol. 6, No. 3, July 2006, "Bidirectional DC/DC Power Conversion using Quasi- Resonant Topology ", by Ray, published in Power Electronics Specialists
Conference, 1992, "A Bidirectional DC DC converter for renewable energy systems ", by Jalbrzykowski, Citko, published in Bulletin of the Polish Academy of Technical Sciences Vol. 57, No. 4, 2009. All of these are operated at fixed frequency and controlled by either phase-shifting gate pulses or duty cycle modulation. All of these circuits have the drawback of limited operating ranges for high efficiency operation, such as zero voltage switching ( ZVS) of main switches for only a limited load range etc.
The object of the present invention is to provide a series resonant DC/DC converter with improved efficiency. The obj ect is also to provide a series resonant DC/DC converter which can be controlled to be bidirectional. Hence, the series resonant DC/DC converter can be used both for supplying power from the battery to the DC bus during power failures and for supplying power from the DC bus to recharge the battery after a power failure. This reduces the number of components, and hence costs/space can be saved.
SUMMARY OF THE INVENTION
The present invention relates to a series resonant DC/DC converter comprising: first DC terminals;
second DC terminals;
an inductor device;
a first switching circuit connected between the first DC terminals and the inductor device where the first switching circuit comprises a first set of switches and a second set of switches;
a second switching circuit and a resonant circuit connected between the second DC terminals and the inductor device, where the second switching circuit comprises a first set of switches and a second set of switches;
a control circuit for controlling the first and second sets of switches of the first and second switching circuits to provide that power may be transferred from the first DC terminals to the second DC terminals, where the control circuit is configured to control the relation between the voltage between the first DC terminals of the series resonant DC/DC converter and the voltage between the second DC terminals of the series resonant DC/DC converter by varying the length of the switching period.
In one aspect, a voltage Vin between the first DC terminals can be smaller than a voltage Vout between the second DC terminals.
In one aspect, a load is connected between the second DC terminals. In one aspect, the load is a rechargeable battery.
In one aspect, the control circuit is configured to control the direction of the power flow through the series resonant DC/DC converter by varying the length of the switching period.
In one aspect, the first switching circuit is a bridge circuit.
In one aspect, the first switching circuit is a full bridge circuit or a half bridge circuit.
In one aspect, the second switching circuit is a bridge circuit.
In one aspect, the second switching circuit is a full bridge circuit or a half bridge circuit.
In one aspect, the resonant circuit is a multi-element resonant circuit.
In one aspect, the control circuit is controlling the current and/or voltage at the first DC-terminals or controlling current and/or voltage at the second DC- terminals, depending on a status flag signal.
DETAILED DESCRIPTION
Embodiments of the present invention will be described in detail in the following with reference to the enclosed drawings, where:
Fig. 1 illustrates a a typical application for bidirectional DC/DC converters;
Fig. 2 illustrates a first embodiment of the DC/DC converter;
Fig. 3 illustrates a second embodiment of the DC/DC converter;
Fig. 4 illustrates a third embodiment of the DC/DC converter;
Fig. 5 illustrates a fourth embodiment of the DC/DC converter;
Fig. 6 illustrates a fifth embodiment of the DC/DC converter;
Fig. 7 illustrates a fifth embodiment of the DC/DC converter; this embodiment does not have a transformer device;
Fig. 8 shows waveforms of voltages and currents of the second embodiment at full load;
Fig. 9 shows details of fig. 9;
Fig. 10 shows waveforms of voltages and currents of the second embodiment at no load; Fig. 1 1 shows details of fig. 10;
Fig. 12 shows the variation of output voltage Vout for different switching frequencies and different loads;
Fig. 13 shows the efficiency curve as a function of the output power for the embodiment in fig. 3.
It is now referred to fig. 2 - 7, illustrating embodiments of the series resonant DC/DC converter. It should be noted that by the term "series resonant DC/DC converter series" it is meant different types of series resonant LC DC/DC converters and different types of series resonant LLC DC/DC converters. The series resonant DC/DC converter may also be a bidirectional DC/DC converter.
The DC/DC converter comprises first DC terminals TIP, TIN and second DC terminals T2P, T2N. The first DC terminals comprise a first positive DC terminal TIP and a first negative DC terminal TIN. The second DC terminals comprise a second positive DC terminal T2P and a second negative DC terminal T2N.
The DC/DC converter further comprises an inductor device, either in the form of a single inductor device ID (as in the embodiment of fig. 7) or in the form of a transformer device TD (as in the embodiments of figs. 2 - 6).
The single inductor device ID may comprise a single inductor Lm, or may comprise several inductors, but does not provide a galvanic isolation.
The transformer device TD may comprise a first winding and a second winding. The transformer device provides galvanic isolation between the first DC terminals and the second DC terminals. The transformer also comprises a magnetizing inductance, which forms a parallel resonance circuit together with the resonant capacitor(s).
The transformer ratio of the transformer device is 1 : 1 in the present
embodiments; however, other transformer ratios are also possible and can be designed in order to meet requirements for input output voltage and current ratios.
A first switching circuit SCI (illustrated by a dashed box) is connected between the first DC terminals TIP, TIN and the inductor device (either the single inductor device ID or the transformer device TD). The first switching circuit SCI comprises a first set of switches and a second set of switches. The first set and the second set of switches may each comprise one, two or several switches.
The first switching circuit SC I is arranged to be controlled in three different switching states. The first state allows a current to flow through the inductor device from the first positive DC terminal TIP to the negative DC terminal TIN by commanding the first set of switches to be ON. The second state allows a current to flow through the inductor device from the first negative DC terminal TIN to the first positive DC terminal TIP by commanding the second set of switches to be ON. The third switching state is characterized by commanding both sets of switches to be OFF
A second switching circuit SC2 (illustrated by a dashed box) and a resonant circuit RC (illustrated by a dashed box) are connected between the second DC terminals T2P, T2N and the inductor device (either the single inductor device ID or the transformer device TD). The second switching circuit SC2 comprises a first set of switches and a second set of switches. The first set and the second set of switches may each comprise one, two or several switches. It can be seen that the second switching circuit SC2 and a resonant circuit RC are connected in series with the inductor device (the single inductor device ID or the transformer device TD) between the second DC-terminals T2P and T2N. The series combination of the resonant circuit RC and the inductor device is connected to the second switching circuit SC2. The second switching circuit, SC2, is arranged to be controlled in three different switching states. The first state allows a resonant current to flow through the series combination of the resonant circuit RC and the inductor device from the second positive DC terminal T2P to the second negative DC terminal T2N by commanding the first set of switches to be ON. The second state allows a resonant current to flow through the series combination of RC and the inductor device from the second negative DC terminal T2N to the second positive DC terminal T2P by commanding the second set of switches to be ON. The third switching state is characterized by
commanding both sets of switches to be OFF.
The first switching circuit SCI may be a push pull circuit or a bridge circuit, such as a full bridge circuit or a half bridge circuit.
The second switching circuit SC2 may also be a bridge circuit, such as a full bridge circuit or a half bridge circuit.
The resonant circuit RC is often referred to as a resonant tank and comprises at least one capacitor or at least one inductor in a suitable configuration together with the inductor device, either the single inductor device ID or the second winding of the transformer device T, where the inductance of the at least one capacitor and/or at least one inductor together with the inductance of the single inductor device ID or the second winding of the transformer device T defines a resonance frequency so that the DC/DC converter exhibits zero voltage turn on switching on all active switches of SC I and SC2. The resonant circuit RC may also be a multi-element resonant circuit comprising several capacitors and inductors in a LC network. Hence, the converter can be considered as a series resonant LLC DC/DC converter.
In addition, the DC/DC converter comprises a control circuit for controlling the first and second sets of switches of the first and second switching circuits SC I, SC2. Hence the control circuit is configured to control the first and second sets of switches of the first and second switching circuits SCI, SC2 and can then determine the desired direction of power flow and control the direction of current at the first and second DC-terminals and thus make the converter supply energy either to the load connected to the first DC-terminals or the load connected to the second DC-terminals.
In the following, several embodiments will be described. In all these
embodiments, the switches are MOSFET switches. Alternatively, the switches may be switches with intrinsic diodes or switches connected in parallel with anti- parallel diodes, such as IGBTs with anti-parallel diodes.
First embodiment
It is now referred to fig. 2. Here the first switching circuit SC I is a half bridge circuit comprising a first switch S l scl and a second switch S2scl . The first set of switches of the first switching circuit SCI here comprises the first switch S l scl and the second set of switches of the first switching circuit SC I comprises the second switch S2scl .
The first switch S l scl is connected between the first negative DC terminal TIN and a first terminal of the first winding. The source of the switch is connected to the first negative DC terminal TIN.
The second switch S2scl is connected between the first negative DC terminal TIN and a second terminal of the first winding. The source of the switch is connected to the first negative DC terminal TIN.
The first winding of the transformer device T comprises a third terminal connected to the first positive DC terminal TIP. The third terminal of the second winding is provided between the first terminal and the second terminal of the second winding. Hence, the number of turns between the first and third terminals and the number of turns between the second and third terminals is equal to the total number of turns for the second winding. In the present embodiment, the number of turns between the first and third terminals and the number of turns between the second and third terminals is equal to each other. A first capacitor C I is connected between the first positive DC terminal TIP and the first negative DC terminal TIN.
The second switching circuit SC2 is a half bridge circuit comprising a first switch S l sc2 and a second switch S2sc2. The first set of switches of the second switching circuit SC2 here comprises the first switch S l sc2 and the second set of switches of the second switching circuit SC2 comprises the second switch S2sc2
The first switch S l sc2 is connected between a first node 10 and the second positive DC terminal T2P. The second switch S2sc2 is connected between the second negative DC terminal T2N and the second node 10. The source of the first switch S l sc2 is connected to the second negative DC terminal T2N and the source of the second switch S2sc2 is connected to the first node 10. The first node 10 is also connected to a first terminal of the second winding of the transformer device T.
The resonant circuit RC comprises a resonant inductor Lrc, a first resonant capacitor C lrc and a second resonant capacitor C2rc. The resonant inductor Lrc is connected between a second terminal of the second winding of the transformer T and a second node 12. The first resonant capacitor C lrc is connected between the second node 12 and the second positive DC terminal T2P. The second resonant capacitor C2rc is connected between the second node 12 and the second negative DC terminal T2N.
Second embodiment
It is now referred to fig. 3.
The first switching circuit SC I is a full bridge circuit comprising a first switch S l scl, a second switch S2scl, a third switch S3scl and a fourth switch S4scl .
The first set of switches of the first switching circuit SC I here comprises the first switch S l scl and the fourth switch S4scl . The second set of switches of the first switching circuit SC I comprises the second switch S2scl and the third switch S3scl .
The first switch S l scl is connected between the first positive DC terminal TIP and a first node 20. The source of the switch is connected to the first node 20.
The second switch S2scl is connected between the first negative DC terminal TIN and the first node 20. The source of the switch is connected to the first negative DC terminal TIN. The third witch S3scl is connected between the first positive DC terminal TIP and a second node 22. The source of the switch is connected to the second node 22.
The fourth switch S4scl is connected between the first negative DC terminal TIN and the second node 22. The source of the switch is connected to the first negative DC terminal TIN.
The first node 20 is connected to the first terminal of the first winding of the transformer device T. The second node 22 is connected to the second terminal of the first winding of the transformer device T.
A first capacitor C I is connected between the first positive DC terminal TIP and the first negative DC terminal TIN.
The second switching circuit SC2 is here a half bridge circuit comprising a first switch S l sc2 and a second switch S2sc2.
The first set of switches of the second switching circuit SC2 here comprises the first switch S l sc2 and the second set of switches of the second switching circuit SC2 comprises the second switch S2sc2.The first switch S l sc2 is connected between a first node 10 and the second positive DC terminal T2P. The second switch S2sc2 is connected between the second negative DC terminal T2N and the second node 10. The source of the first switch S l sc2 is connected to the node 10 and the source of the second switch S2sc2 is connected to the second negative DC terminal T2N. The first node 10 is also connected to a first terminal of the second winding of the transformer device T.
The resonant circuit RC comprises a resonant inductor Lrc, a first resonant capacitor C lrc and a second resonant capacitor C2rc. The resonant inductor Lrc is connected between a second terminal of the second winding of the transformer T and a second node 12. The first resonant capacitor C lrc is connected between the second node 12 and the second positive DC terminal T2P. The second resonant capacitor C2rc is connected between the second node 12 and the second negative DC terminal T2N.
A second capacitor C2 is connected between the second positive DC terminal T2P and the second negative DC terminal T2N.
In fig. 3, the first winding of the transformer device TD is denoted as Tp, the second winding of the transformer device TD is denoted as Ts. The current through the first winding is denoted as Ip, the current through the second winding is denoted as Is. As shown in fig. 3, a voltage source with input voltage Vin is connected between the first negative DC terminal and the first positive DC terminal TIP, TIN. A load denoted with "load" is connected between the second negative DC terminal and the second positive DC terminal T2P, T2N.
Third embodiment
It is now referred to fig. 4.
The first switching circuit SC I is a full bridge circuit comprising a first switch S l scl, a second switch S2scl, a third switch S3scl and a fourth switch S4scl .
The first set of switches of the first switching circuit SC I here comprises the first switch S l scl and the fourth switch S4scl . The second set of switches of the first switching circuit SC I comprises the second switch S2scl and the third switch S3scl . The first switch S l scl is connected between the first positive DC terminal TIP and a first node 20. The source of the switch is connected to the first node 20.
The second switch S2scl is connected between the first negative DC terminal TIN and the first node 20. The source of the switch is connected to the first negative DC terminal TIN.
The third witch S3scl is connected between the first positive DC terminal TIP and a second node 22. The source of the switch is connected to the second node 22.
The fourth switch S4scl is connected between the first negative DC terminal TIN and the second node 22. The source of the switch is connected to the first negative DC terminal TIN.
The first node 20 is connected to the first terminal of the first winding of the transformer device T. The second node 22 is connected to the second terminal of the first winding of the transformer device T.
A first capacitor C I is connected between the first positive DC terminal TIP and the first negative DC terminal TIN.
The second switching circuit SC2 is a full bridge circuit comprising a first switch S l sc2, a second switch S2sc2, a third switch S3sc2 and a fourth switch S4sc2.
The first set of switches of the second switching circuit SC2 here comprises the first switch S l sc2 and the fourth switch S4sc2. The second set of switches of the second switching circuit SC2 comprises the second switch S2sc2 and the third switch S3sc2. The first switch S l sc2 is connected between the second positive DC terminal T2P and a first node 10. The source of the first switch S l sc2 is connected to the first node 10.
The second switch S2sc2 is connected between the second negative DC terminal TIN and the first node 10. The source of the switch is connected to the second negative DC terminal T2N.
The third switch S3sc2 is connected between the second positive DC terminal T2P and a second node 12. The source of the switch is connected to the second node 12.
The fourth switch S4sc2 is connected between the second negative DC terminal T2N and the second node 12. The source of the switch is connected to the second negative DC terminal T2N.
The second node 12 of the second switching circuit SC2 is also connected to a first terminal of the second winding of the transformer device T.
The resonant circuit RC comprises a resonant inductor Lrc and a resonant capacitor Crc connected in series between a second terminal of the second winding of the transformer device T and the first node 10.
A second capacitor C2 is connected between the second positive DC terminal T2P and the second negative DC terminal T2N.
Fourth embodiment
It is now referred to fig. 5.
Here, the first switching circuit SC I is a half bridge circuit comprising a first switch S l scl and a second switch S2scl . The first set of switches of the first switching circuit SC I here comprises the first switch S l scl and the second set of switches of the first switching circuit SC I comprises the second switch S2scl . The first switch S l scl is connected between the first negative DC terminal TIN and a first terminal of the first winding. The source of the switch is connected to the first negative DC terminal TIN.
The second switch S2scl is connected between the first negative DC terminal TIN and a second terminal of the first winding. The source of the switch is connected to the first negative DC terminal TIN.
The first winding of the transformer device T comprises a third terminal connected to the first positive DC terminal TIP. The third terminal of the second winding is provided between the first terminal and the second terminal of the second winding. Hence, the number of turns between the first and third terminals and the number of turns between the second and third terminals is equal to the total number of turns for the second winding. In the present embodiment, the number of turns between the first and third terminals and the number of turns between the second and third terminals is equal to each other.
A first capacitor C I is connected between the first positive DC terminal TIP and the first negative DC terminal TIN.
The second switching circuit SC2 is a full bridge circuit comprising a first switch S l sc2, a second switch S2sc2, a third switch S3sc2 and a fourth switch S4sc2.
The first set of switches of the second switching circuit SC2 here comprises the first switch S l sc2 and the fourth switch S4sc2. The second set of switches of the second switching circuit SC2 comprises the second switch S2sc2 and the third switch S3sc2.
The first switch S l sc2 is connected between the second positive DC terminal T2P and a first node 10. The source of the first switch S l sc2 is connected to the first node 10.
The second switch S2sc2 is connected between the second negative DC terminal TIN and the first node 10. The source of the switch is connected to the second negative DC terminal T2N.
The third switch S3sc2 is connected between the second positive DC terminal T2P and a second node 12. The source of the switch is connected to the second node 12.
The fourth switch S4sc2 is connected between the second negative DC terminal T2N and the second node 12. The source of the switch is connected to the second negative DC terminal T2N.
The second node 12 of the second switching circuit SC2 is also connected to a first terminal of the second winding of the transformer device T.
The resonant circuit RC comprises a resonant inductor Lrc and a resonant capacitor Crc connected in series between a second terminal of the second winding of the transformer device T and the first node 10.
A second capacitor C2 is connected between the second positive DC terminal T2P and the second negative DC terminal T2N.
Fifth embodiment It is now referred to fig. 6.
Here, the first switching circuit SC I is a voltage doubler circuit comprising a first switch S l scl and a second switch S2scl . The first set of switches of the first switching circuit SC I here comprises the first switch S l scl and the second set of switches of the first switching circuit SC I comprises the second switch S2scl .
The first switch S l scl is connected between the first positive DC terminal TIP and a first terminal of the first winding of the transformer device TD. The source of the switch is connected to the first terminal of the first winding of the transformer device TD.
The second switch S2scl is connected between the first negative DC terminal TIN and a second terminal of the first winding of the transformer device TD. The source of the switch is connected to the second terminal of the first winding of the transformer device TD.
A first capacitor C I is connected between the first positive DC terminal TIP and a node 20. A second capacitor C2 is connected between the node 20 and the first negative DC terminal TIN. The node 20 is connected to a third terminal of the first winding of the transformer device TD.
The third terminal of the second winding is provided between the first terminal and the second terminal of the second winding. Hence, the number of turns between the first and third terminals and the number of turns between the second and third terminals is equal to the total number of turns for the second winding. In the present embodiment, the number of turns between the first and third terminals and the number of turns between the second and third terminals is equal to each other.
The second switching circuit SC2 is here a half bridge circuit comprising a first switch S l sc2 and a second switch S2sc2.
The first set of switches of the second switching circuit SC2 here comprises the first switch S l sc2 and the second set of switches of the second switching circuit SC2 comprises the second switch S2sc2.
The first switch S l sc2 is connected between a first node 10 and the second positive DC terminal T2P. The second switch S2sc2 is connected between the second negative DC terminal T2N and the second node 10.
The source of the first switch S l sc2 is connected to the node 10. The source of the second switch S2sc2 is connected to the second negative DC terminal T2N. The first node 10 is also connected to a first terminal of the second winding of the transformer device T. The resonant circuit RC comprises a resonant inductor Lrc, a first resonant capacitor C lrc and a second resonant capacitor C2rc. The resonant inductor Lrc is connected between a second terminal of the second winding of the transformer T and a second node 12. The first resonant capacitor C lrc is connected between the second node 12 and the second positive DC terminal T2P. The second resonant capacitor C2rc is connected between the second node 12 and the second negative DC terminal T2N.
Sixth embodiment
It is now referred to fig. 7.
The first switching circuit SC I is a full bridge circuit comprising a first switch S l scl, a second switch S2scl, a third switch S3scl and a fourth switch S4scl .
The first set of switches of the first switching circuit SC I here comprises the first switch S l scl and the fourth switch S4scl . The second set of switches of the first switching circuit SC I comprises the second switch S2scl and the third switch S3scl .
The first switch S l scl is connected between the first positive DC terminal TIP and a first node 20. The source of the switch is connected to the first node 20.
The second switch S2scl is connected between the first negative DC terminal TIN and the first node 20. The source of the switch is connected to the first negative DC terminal TIN.
The third switch S3scl is connected between the first positive DC terminal TIP and a second node 22. The source of the switch is connected to the second node 22.
The fourth switch S4scl is connected between the first negative DC terminal TIN and the second node 22. The source of the switch is connected to the first negative DC terminal TIN.
As mentioned above, there is no transformer device TD in the present
embodiment. Instead, an inductor device ID in the form of a magnetizing inductor Lm is provided.
The first node 20 is connected to the first terminal of the magnetizing inductor Lm. The second node 22 is connected to the second terminal of the magnetizing inductor Lm.
A first capacitor C I is connected between the first positive DC terminal TIP and the first negative DC terminal TIN. The second switching circuit SC2 is here a half bridge circuit comprising a first switch S l sc2 and a second switch S2sc2.
The first set of switches of the second switching circuit SC2 here comprises the first switch S l sc2 and the second set of switches of the second switching circuit SC2 comprises the second switch S2sc2.
The first switch S l sc2 is connected between a first node 10 and the second positive DC terminal T2P. The second switch S2sc2 is connected between the second negative DC terminal T2N and the second node 10. The source of the first switch S l sc2 is connected to the node 10 and the source of the second switch S2sc2 is connected to the second negative DC terminal T2N. The first node 10 is also connected to the second terminal of the magnetizing inductor Lm.
The resonant circuit RC comprises a resonant inductor Lrc, a first resonant capacitor C lrc and a second resonant capacitor C2rc. The resonant inductor Lrc is connected between the first terminal of the magnetizing inductor Lm and a second node 12. The first resonant capacitor C lrc is connected between the second node 12 and the second positive DC terminal T2P. The second resonant capacitor C2rc is connected between the second node 12 and the second negative DC terminal T2N.
A second capacitor C2 is connected between the second positive DC terminal T2P and the second negative DC terminal T2N.
Control circuit
A control circuit is provided for controlling the switches of the first and second switching circuits SCI and SC2 to be ON and OFF. The control circuit may be implemented as a software program executed by a digital signal processor (DSP) or it may be implemented as an analogue circuit.
All switches are uni-polar, meaning that the switches can only block conduction in one direction. An example of a uni-polar switch is the MOSFET switch comprising an anti-parallel diode. Another example is the IGBT switch with an anti-parallel diode connected from emitter to drain.
The control method for controlling the series resonant DC/DC converter will now be described in detail below with reference to figs. 8 - 12. Here, the control signals and resulting voltages and/or currents are shown for the embodiment shown in fig. 3. The input voltage Vin was set to 50 VDC, and an output voltage was regulated to 350 VDC. The switching frequency is approximately 1 10kHz.
It is now referred to fig. 8. In a first step a switching period TP is defined from time Tstart to time Tend for the series resonant DC/DC converter. The switching period TP comprises a first half period TA from time Tstart to time Tcenter and a second half period TB from time Tcenter to time Tend. A next switching period after the switching period TP is denoted as a subsequent switching period TP+1.
As is described above, the series resonant DC/DC converter has a resonance frequency defined by the properties of the inductor device (ID or TD) and the elements (capacitors and inductors) of the resonance circuit RC.
The switching period TP, and hence the switching frequency, can be controlled by the control circuit to be be higher than, equal to, or lower than the resonance frequency. Hence, the switching period TP is not dependant of the resonance frequency.
In fig. 8, relevant times TO (equal to Tstart) to T8 (equal to Tend) for the first switching period TP are indicated by dashed lines, and several time intervals are also defined, as will be apparent from the description below. Time T8 (equal to Tend) is the start (i.e. time T0(TP+1)) of the subsequent switching period TP+1. Time T4 is here equal to Tcenter, but the length of the time intervals TO - Tl, Tl - T2, T2 - T3, T3 - T4, T4 - T5, T5 - T6, T6 - T7, T7 - T8 are not all equal to each other.
The duty cycle of all set of switches are essentially 50%, meaning that the switches have a control signal demanding the switch to be in a conducting state, ON, during nearly half of the switching period and having the control signal demanding the switch to be in a non-conducting state, OFF, during nearly half of the switching period. The set of switches are controlled independently to have different delays and yet synchronized.
The first set S l scl ; S l scl, S4scl of switches of the first switching circuit SC I is controlled to be ON from the beginning Tstart of the first half period TA minus a time interval ΔΤΑΕ1, where the time interval ΔΤΑΕ1 is provided at the end of the first half period TA. The first set S l scl ; S l scl, S4scl of switches of the first switching circuit SC I is controlled to be OFF in the second half period TB. The time interval ΔΤΑΕ1 in the present embodiment is starting at time T3 and is ending at time T4.
The second set S2scl ; S2scl , S3 scl of switches of the first switching circuit SC I is controlled to be ON from the beginning Tcenter of the second half period TB minus a time interval ΔΤΒΕ1 , where the time interval ΔΤΒΕ1 is provided at the end of the second half period TB. The second set S2scl ; S2scl , S3 scl of switches of the first switching circuit SC I is controlled to be OFF in the first half period TA. The time interval ΔΤΒΕ1 is in the present embodiment starting at time T7 and is ending at time T8.
The first set S l scl ; S l scl, S4scl and the second set S2scl ; S2scl, S3scl of switches of the first switching circuit SCI is controlled to be OFF in the time interval ΔΤΑΕ1 and the time interval ΔΤΒΕ1.
The time interval ΔΤΑΕ1 forms a first time interval Tscloffl wherein the first and second sets of switches of the first switching circuit SCI are OFF. The time interval ΔΤΒΕ forms a second time interval Tscloff2 wherein the first and second sets of switches of the first switching circuit SCI are OFF.
The first set S l sc2; S l sc2, S4sc2 of switches of the second switching circuit SC2 is controlled to be ON in the first half period TA minus a time interval ATAS l and minus a time interval ΔΤΑΕ2, where the time interval ATAS l is provided at the beginning of the first half period TA and where the time interval ΔΤΑΕ2 is provided at the end of the first half period TA. The first set S l sc2; S l sc2, S4sc2 of switches of the second switching circuit SC is controlled to be OFF in the second half period TB. The time interval ATAS l in the present embodiment is starting at time TO and is ending at time Tl . The time interval ΔΤΑΕ2 in the present embodiment is starting at time T2 and is ending at T4.
The second set S2sc2; S2sc2, S3 sc2 of switches of the second switching circuit SC2 is controlled to be ON in the second half period TB minus time interval ATBS l and minus time interval ΔΤΒΕ2, where the time interval ATBS l is provided at the beginning of the second half period TB and where the time interval ΔΤΒΕ2 is provided in the end of the second half period TB. The second set S2sc2; S2sc2, S3sc2 of switches of the second switching circuit SC2 is controlled to be OFF in the first half period TA. The time interval ATBS l in the present embodiment is starting at time T4 and is ending at time T5. The time interval ΔΤΒΕ2 in the present embodiment is starting at T6 and is ending at T8.
The first set S l sc2; S l sc2, S4sc2 and the second set S2sc2; S2sc2, S3 sc2 of switches of the second switching circuit SC2 are controlled to be OFF in the time intervals ATAS l, ΔΤΑΕ2, ATBS l and ΔΤΒΕ2.
The time intervals ΔΤΑΕ2 and ATBS l form a continuous time interval Tsc2offl from time T2 to time T5 where the first and second sets of switches of the second switching circuit (SC2) are OFF. The time intervals ΔΤΒΕ2 and ATAS 1(TP+1) (that is, the time interval ATAS l of a subsequent switching period TP+1) form a continuous time interval Tsc2off2 from time T6 to time T1(TP+1) (that is, the time instance Tl of a subsequent switching period TP+1) where the first and second sets of switches of the second switching circuit (SC2) are OFF. Table 1 below shows the states for the first and second set of switches for the first switching circuit SC I for the switching period TP. The start time and end time of each interval are also given.
Figure imgf000018_0001
Table 1 : ON/OFF states for first and second set of switches of the first switching circuit SCI .
Table 2 below shows the states for the first and second set of switches for the second switching circuit SC2 for the switching period TP. The start time and end time of each interval are also given.
Figure imgf000018_0002
Table 2: ON/OFF states for first and second set of switches of the second switching circuit SC2.
The time interval Tscloffl and the time interval Tsc2offl are at least partially overlapping, i.e. the time interval Tscloffl starts before the time interval Tsc2offl ends or the time interval Tsc2offl starts before the time interval Tscloffl ends. Moreover, the time interval Tscloff2 and the time interval Tsc2off2 are at least partially overlapping, i.e. the time interval Tscloff2 starts before the time interval Tsc2off2 ends or the time interval Tsc2off2 starts before the time interval Tscl off2 ends. In this way the switches of the first switching circuit SC I and switches of the second switching circuit SC2 are synchronized.
In the present embodiment, the length of time interval Tsc2offl is equal to the length of time interval Tsc2off2, and the length of time interval Tsc l offl is equal to the length of time interval Tsc l off2.
In the embodiment above, the time intervals Tsc2offl and Tsc2off2 are longer than the time intervals Tscl offl and Tscl off2. However, they could have the same duration, or the time interval Tscl off could be longer than the period Tsc2off. This depends on the required time for achieving Zero Voltage Switching (ZVS) in the switching circuits and may also depend on the voltage between the first positive and negative DC terminals and the voltage between the second positive and negative DC terminals.
In the embodiment above, the centre of time interval Tsc l offl is controlled to be close to or equal to the centre of time interval Tsc2offl and the centre of time interval Tsc l off2 is controlled to be close to or equal to the centre of time interval Tsc2off2 .
Zero Voltage Switching is maintained for all switches at turn ON at high to full load as is illustrated in 8.
In fig. 9, voltage VI 0 at node 10 and voltage V20 at node 20 are both high before time instance T2, thus switches S l sc l , S4sc l (first set of SC I) and S l sc2 (first set of SC I ) are all conducting and the switches S2scl , S3 scl (second set of SC I) and S2sc2 (second set of SC2) are all non-conducting.
The first set S l sc2 of switches in the second switching circuit SC2 is turned off at time instance T2. At the time instance when current Is becomes positive it is capable of bringing the voltage at node 10 from high to low by discharging the output capacitances in both the first and second set of switches of the second switching circuit. The second set of switches S2sc2 of the second switching circuit is commanded to be ON at T5, and are thus turned on with a voltage close to zero without any significant switching losses, so called Zero Voltage
Switching (ZVS).
Since Ip is positive, turning off first set of switches S l sc l and S4sc l at T3 results in a rapid change of voltage at node 20 from high to low and voltage at node 22 from low to high, caused by the discharging/charging of the output capacitances in the first and second sets of switches S l sc l , S3 scl and S2scl , S4sc l of the first switching circuit. The second set of switches S2scl and S3 sc l of the first switching circuit SC I are commanded to be ON at T4, and are thus turned on with a voltage close to zero without any significant switching losses, so called ZVS.
Note that in the present embodiment, the time interval T2 to T5, between turning off S l sc2 and turning on S2sc2 is longer then the time interval T3 to T4 for turning off S l scl, S4scl and turning on S2scl, S3scl since it will take longer time for the voltage Vout of 350 V of the second switching circuit SC2 to commutate than for the voltage Vin of 50 V of the first switching circuit SCI .
ZVS is also maintained for all switches at turn on even at low to no load which is illustrated in figure 10. We are now referring to figure 1 1.
Voltage V10 at node 10 and the voltage V20 at node 20 are both high before time instance T2, thus switches S l scl, S4scl, and S l sc2 are all conducting.
The switch S l sc2 is turned off at time instance T2. The current Is is positive and is therefore capable of bringing V10 from high to low by discharging the output capacitances in the switches S l sc2 and S2sc2.
The current Is is decaying due to the changed voltage over resonant inductor, LRC, during the time period T2 to T3. However the magnetizing current ILM in winding Ls, is still increasing and is therefore reflected to primary winding, LP; and causes the current IP to increase. Since Ip is increasing and positive, turning off switches S l scl and S4scl results in a rapid change of voltage V20 at node 20 from high to low and voltage V22 at node 22 from low to high, caused by the discharging/charging of the output capacitances in the switches S l scl , S3 scl and S2scl, S4scl .
The output voltage Vout may be controlled by changing the switching frequency. This is illustrated in fig. 12, where it is shown that the output voltage Vout may be varied for different loads and different switching frequencies. The ZVS operation of all switches is controlled by proper delays , i.e. the time intervals Tscloffl, Tscl off2, Tsc2offl and Tsc2off2, between switching instances as described in the text and in figure 8 and table 2 and table 3.
The relation between the voltage between first DC terminals TIP, TIN of the series resonant DC/DC converter and the voltage between second DC terminals T2P, T2N of the series resonant DC/DC converter can be controlled by varying the length of the switching period TP.
The direction of the power flow through the series resonant DC/DC converter can be controlled by varying length of the switching period TP. Hence, the series resonant DC/DC converter can be controlled to be a bidirectional series resonant DC/DC converter.
The switches of the first and second switching circuit SC I, SC2 are controlled to provide zero voltage switching ZVS at switch turn on and to provide nearly zero current switching ZCS at switch turn off by controlling the first and second switching circuit to have a fixed switching frequency close to the series resonant frequency.
The switches of the first and second switching circuit SCI , SC2 can be controlled by switching at an operating point at or near the series resonant frequency for all voltages over the first DC terminals which are inside a specified operating range.
The switches of the first and second switching circuit SCI , SC2 can be controlled by switching at an operating point at or near the series resonant frequency for all load conditions at the second DC terminals.
UPS system with series resonant DC/DC converter
In the introduction above, the typical uses of a series resonant DC/DC converter was described. In a typical UPS system there will be one common control system for all the components of the UPS system, including the series resonant DC/DC converter. The common control circuit can for example comprise a status flag signal as an indicator for the direction of the power flow through the
bidirectional DC/DC converter.
Moreover, the control circuit comprises sensors for sensing the current and/or the voltage at the first DC terminals TIP, TIN and the second DC terminals T2P, T2N.
In a first mode of operation the status flag signal indicates that the power should flow from the first DC terminals TIP, TIN to the second DC terminals T2P, T2N. Here, the control circuit is controlling the current and/or voltage of the second DC terminals T2P, T2N based on a predetermined reference signal for the first mode of operation.
In a second mode of operation the status flag signal indicates that the power should flow from the second DC terminals T2P, T2N to the first DC terminals TIP, TIN. Here, the control circuit is controlling the current and/or voltage of the first DC terminals TIP, TIN based on a predetermined reference signal for the second mode of operation. As mentioned above, the series resonant DC/DC converter may be used as a DC/DC converter for an UPS system, as shown in fig. 1, where its first DC terminals TIP, TIN are connected to the battery and its second DC terminals T2P, T2N connected to a DC bus (not shown).
The status flag signal may be switched to the first mode of operation when a failure in the AC mains is detected. In such a situation power should be transferred from the battery connected to the first DC terminals to the DC bus connected to the second DC terminals. Here, the control circuit is controlling the voltage and/or current at the second DC terminals T2P, T2N at a predetermined level suitable as input to the DC/AC converter as long as the battery power supply allows it.
The status flag signal may be switched to the second mode of operation when the AC mains is working again, then supplying power from the DC bus to the battery for recharging the battery. Here, the control circuit is controlling the voltage and/or current at the first DC terminals TIP, TIN at a predetermined level suitable as input to the battery.
The status flag signal may have a third mode of operation for indicating that no power should be transferred through the bidirectional DC/DC converter. In this mode of operation, all switches should be switched off. In this mode of operation there is no failure in the AC mains, and the battery is fully charged.
Another application for the series resonant DC/DC converter is for re-use of energy stored in battery storages.
Results
The efficiency of the series resonant DC/DC converter according to fig. 3 of has been tested. Fig. 12 shows the results of the testing. In the testing, two efficiency curves are illustrated, the first curve shows the efficiency as a function of output power for a circuit having an input voltage Vin of 50V and the second curve shows the efficiency as a function of output power for a circuit having an input voltage Vin of 48V. The output voltage Vout was controlled to be 355V.
As seen, the efficiency is above 96% in the power output range from ca 400W to 2200W. The maximum power efficiency is above 97.5%. This is a considerable improvement over the prior art DC/DC converters mentioned in the introduction, which showed efficiencies of ca 92%.

Claims

1. Series resonant DC/DC converter comprising:
first DC terminals (TIP, TIN);
second DC terminals (T2P, T2N);
an inductor device (ID; TD);
- a first switching circuit (SCI) connected between the first DC terminals (TIP, TIN) and the inductor device (ID; TD), where the first switching circuit (SC I) comprises a first set (S l scl ; S l scl, S4scl) of switches and a second set (S2scl ; S2scl, S3scl) of switches;
a second switching circuit (SC2) and a resonant circuit (RC) connected between the second DC terminals (T2P, T2N) and the inductor device (ID; TD), where the second switching circuit (SC2) comprises a first set (S l sc2; S l sc2, S4sc2) of switches and a second set (S2sc2; S2sc2, S3 sc2) of switches;
a control circuit configured to control the first and second sets of switches of the first and second switching circuits (SC I, SC2) to provide that power may be transferred from the first DC terminals (TIP, TIN) to the second DC terminals
(T2P, T2N), where the control circuit is configured to control the relation between the voltage between the first DC terminals (TIP, TIN) of the series resonant DC/DC converter and the voltage between the second DC terminals (T2P, T2N) of the series resonant DC/DC converter by varying the length of the switching period (TP).
2. Series resonant DC/DC converter according to claim 1, where a voltage Vin between the first DC terminals (TIP, TIN) can be smaller than a voltage Vout between the second DC terminals (T2P, T2N).
3. Series resonant DC/DC converter according to claim 1 or 2, where a load (load) is connected between the second DC terminals (T2P, T2N).
4. Series resonant DC/DC converter according to one of claims 1 - 3, where the load is a rechargeable battery.
5. Series resonant DC/DC converter according to claim 1, where the control circuit is configured to control the direction of the power flow through the series resonant DC/DC converter by varying the length of the switching period (TP).
6. Series resonant DC/DC converter according to claim 1, where the first switching circuit (SC I) is a bridge circuit.
7. Series resonant DC/DC converter according to claim 2, where the first switching circuit (SC I) is a full bridge circuit or a half bridge circuit.
8. Series resonant DC/DC converter according to claim 1 , where the second switching circuit (SC2) is a bridge circuit.
9. Series resonant DC/DC converter according to claim 4, where the second switching circuit (SC2) is a full bridge circuit or a half bridge circuit.
10. Series resonant DC/DC converter according to claim 1 , where the resonant circuit (RC) is a multi-element resonant circuit.
1 1. Series resonant DC/DC converter according to claim 1, where the control circuit is controlling the current and/or voltage at the first DC-terminals (TIP, TIN) or controlling current and/or voltage at the second DC-terminals (T2P, T2N), depending on a status flag signal.
PCT/EP2011/068663 2010-10-28 2011-10-25 Series resonant dc/dc converter WO2012055869A2 (en)

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