Three-phase resonant DC-DC converter

Abstract

A three-phase resonant DC-DC converter for converting a first DC voltage between two first terminals into a second DC voltage between two second terminals is described. The converter includes a transformer device having three primary windings and three secondary windings, a switching circuit, a rectifying circuit, a resonant cavity device, a secondary capacitor, and a control circuit. The resonant cavity device has a primary side resonant cavity device with three resonant inductors and three resonant capacitors connected to a primary winding. The converter further includes three clamping diodes between each second primary terminal of the primary winding and the first positive terminal, and another three clamping diodes between the first negative terminal and each second primary terminal of the primary winding.

Description

Technical Field

[0001] The present invention relates to a three-phase resonant DC-DC converter for converting a first DC voltage into a second DC voltage. Background Art

[0002] Resonant converters are typically used to convert an uncontrolled DC (direct current) voltage (the uncontrolled DC voltage is typically the output of an AC (alternative current)-DC converter) into a controlled DC voltage as required by a load (the load is typically a data center, telecommunication equipment, etc.).

[0003] In Chapter 5 of Yang Bo's "Topology Research on Front-End DC-DC Power Conversion in Distributed Power Systems", published on September 12, 2003, single-phase LLC resonant converters are discussed. Different types of overload / short-circuit protection are discussed in Chapter 5.2. This protection can be implemented in the control software, such as increasing the switching frequency (Chapter 5.2.1) or through a hybrid control of PWM (pulse width modulation) and variable frequency control (Chapter 5.2.2). This protection can also be implemented in hardware by using clamping diodes (Chapter 5.2.2). Figure 1a A single-phase full-bridge LLC resonant converter with a clamping diode Dclamp is shown.

[0004] Three-phase LLC resonant converters or so-called interleaved LLC resonant converters are also known. These resonant converters have some advantages, such as smaller output capacitors. However, they also have some disadvantages, such as an additional transformer that increases the size, mass and cost of the converter.

[0005] The prior art three-phase LLC resonant DC-DC converter is as follows Figure 1b shown.

[0006] An object of the present invention is to improve the prior art. More specifically, an object of the present invention is to provide a three-phase LLC resonant DC-DC converter in which software-based short-circuit protection can be avoided. Summary of the invention

[0007] The present invention relates to a three-phase resonant DC-DC converter for converting a first DC voltage into a second DC voltage, wherein the converter comprises:

[0008] a transformer apparatus comprising three primary windings and three secondary windings, each primary winding comprising a first primary terminal and a second primary terminal, and each secondary winding comprising a first secondary terminal and a second secondary terminal;

[0009] a switching circuit SC having a first side and a second side, the first side comprising a first positive terminal and a first negative terminal forming a first terminal of the converter, the second side comprising a first SC-node, a second SC-node and a third SC-node respectively connected to the primary winding of the transformer device;

[0010] a rectifier circuit RC having a first side and a second side, the first side of the rectifier circuit comprising RC nodes respectively connected to the secondary winding of the transformer device, the second side of the rectifier circuit comprising a second positive terminal and a second negative terminal forming a second terminal of the converter;

[0011] a resonant cavity device comprising a primary side resonant cavity device connected between the first SC node, the second SC node and the third SC node of the switching circuit and primary terminals of three primary windings of the transformer device;

[0012] a secondary capacitor connected between the second positive terminal and the second negative terminal;

[0013] A control circuit, which is used to control the switch circuit;

[0014] wherein the first DC voltage is defined as a voltage between the first positive terminal and the first negative terminal;

[0015] wherein the second DC voltage is defined as a voltage between the second positive terminal and the second negative terminal;

[0016] The primary-side resonant cavity device comprises a first resonant inductor, a second resonant inductor and a third resonant inductor, wherein the first resonant inductor is connected between the first SC node of the switch circuit and the first primary terminal of the first primary winding, the second resonant inductor is connected between the second SC node of the switch circuit and the first primary terminal of the second primary winding, and the third resonant inductor is connected between the third SC node of the switch circuit and the first primary terminal of the third primary winding;

[0017] The primary-side resonant cavity device comprises a first resonant capacitor, a second resonant capacitor and a third resonant capacitor, wherein the first resonant capacitor is connected between the resonant cavity node and the second-first primary terminal of the first primary winding, the second resonant capacitor is connected between the resonant cavity node and the second-second primary terminal of the second primary winding, and the third resonant capacitor is connected between the resonant cavity node and the second-third primary terminal of the third primary winding;

[0018] The converter comprises three clamping diodes between each second primary terminal of the primary winding and the first positive terminal;

[0019] The converter comprises three further clamping diodes between the first negative terminal and each second primary terminal of the primary winding.

[0020] The first positive terminal and the first negative terminal are often referred to as input terminals of the converter. The second positive terminal and the second negative terminal are often referred to as output terminals of the converter.

[0021] The load is typically connected between the second positive terminal and the second negative terminal. Therefore, the second DC voltage may represent the load voltage.

[0022] The three clamping diodes between each second primary terminal of the primary winding and the first positive terminal may include:

[0023] a first clamping diode having an anode connected to the second-first primary terminal of the first primary winding and a cathode connected to the first positive terminal;

[0024] a second clamping diode having an anode connected to the second second primary terminal of the second primary winding and a cathode connected to the first positive terminal;

[0025] a third clamping diode having an anode connected to the second third primary terminal of the third primary winding and a cathode connected to the first positive terminal; and

[0026] wherein the other three clamping diodes between the first negative terminal and each second primary terminal of the primary winding include:

[0027] a fourth diode having an anode connected to the first negative terminal and a cathode connected to the second-first primary terminal of the first primary winding;

[0028] a fifth diode having an anode connected to the first negative terminal and a cathode connected to the second second primary terminal of the second primary winding;

[0029] A sixth diode has an anode connected to the first negative terminal and a cathode connected to the second third primary terminal of the third primary winding.

[0030] The resonant cavity node may be a floating neutral point of the primary side resonant cavity device.

[0031] The converter may include a capacitor circuit connected between the resonant cavity node and the first negative terminal.

[0032] The transformer device may include:

[0033] a first transformer core, on which the first primary winding and the first secondary winding may be wound;

[0034] a second transformer core on which the second primary winding and the second secondary winding may be wound;

[0035] The third transformer core may be wound with the third primary winding and the third secondary winding.

[0036] The first transformer core, the second transformer core, and the third transformer core may be electromagnetically independent of one another.

[0037] As used herein, the term "electromagnetic independence" means that the electromagnetic flux in one of the transformer cores leaks to the other transformer cores at a rate of less than 10%, preferably less than 5%.

[0038] Therefore, the electromagnetic flux generated by the first primary winding or the first secondary winding in the first transformer core will not generate substantial electromagnetic flux in the second transformer core or the third transformer core. Similarly, the electromagnetic flux generated by the second primary winding or the second secondary winding in the second transformer core will not generate substantial electromagnetic flux in the first transformer core or the third transformer core. Similarly, the electromagnetic flux generated by the third primary winding or the third secondary winding in the third transformer core will not generate substantial electromagnetic flux in the first transformer core or the second transformer core.

[0039] The first transformer core, the second transformer core, and the third transformer core may be separate cores. The separate cores may be located a distance from each other. The first transformer core, the second transformer core, and the third transformer core may be core portions of the same core, wherein an air gap or other electromagnetic insulating material prevents magnetic flux from being shared between the core portions.

[0040] The switch circuit may include:

[0041] a first switch having a source terminal connected to the first SC node and a drain terminal connected to the first positive terminal;

[0042] a second switch having a source terminal connected to the first negative terminal and a drain terminal connected to the first SC node;

[0043] a third switch having a source terminal connected to the second SC node and a drain terminal connected to the first positive terminal;

[0044] a fourth switch having a source terminal connected to the first negative terminal and a drain terminal connected to the second SC node;

[0045] a fifth switch having a source terminal connected to the third SC node and a drain terminal connected to the first positive terminal;

[0046] A sixth switch has a source terminal connected to the first negative terminal and a drain terminal connected to the third SC node.

[0047] The rectifier circuit may be a diode rectifier. The diode rectifier may include six diodes or twelve diodes. Alternatively, the rectifier circuit may include switches controlled by a control circuit. These switches may also be MOSFET switches, GaN switches, etc.

[0048] The rectifier circuit RC may include:

[0049] a first switch connected between the first RC node and the second positive terminal;

[0050] a second switch connected between the second negative terminal and the first RC node;

[0051] a third switch connected between the second RC node and the second positive terminal;

[0052] a fourth switch connected between the second negative terminal and the second RC node;

[0053] a fifth switch connected between the third RC node and the second positive terminal;

[0054] a sixth switch connected between the second negative terminal and the third RC node;

[0055] a seventh switch connected between the fourth RC node and the second positive terminal;

[0056] an eighth switch connected between the second negative terminal and the fourth RC node;

[0057] a ninth switch connected between the fifth RC node and the second positive terminal;

[0058] a tenth switch connected between the second negative terminal and the fifth RC node;

[0059] an eleventh switch connected between the sixth RC node and the second positive terminal;

[0060] A twelfth switch is connected between the second negative terminal and the sixth RC node.

[0061] The first RC node of the rectifier circuit can be directly connected to the first secondary terminal of the first secondary winding, the second RC node of the rectifier circuit can be directly connected to the second secondary terminal of the first secondary winding, the third RC node of the rectifier circuit can be directly connected to the first secondary terminal of the second secondary winding, the fourth RC node of the rectifier circuit can be directly connected to the second secondary terminal of the second secondary winding, the fifth RC node of the rectifier circuit can be directly connected to the first secondary terminal of the third secondary winding, and the sixth RC node of the rectifier circuit can be directly connected to the second secondary terminal of the third secondary winding.

[0062] In an embodiment, the resonant cavity device may include a secondary side resonant cavity device on a secondary side of the transformer device.

[0063] In an embodiment, the secondary side resonant cavity device may include a fourth resonant capacitor, a fifth resonant capacitor, and a sixth resonant capacitor, and may also include a fourth resonant inductor, a fifth resonant inductor, and a sixth resonant inductor.

[0064] The fourth resonant capacitor and the fourth resonant inductor may be connected in series between the first secondary terminal of the first secondary winding and the first RC node of the rectifier circuit;

[0065] The fifth resonant capacitor and the fifth resonant inductor may be connected in series between the first secondary terminal of the second secondary winding and a third RC node of the rectifier circuit;

[0066] The sixth resonant capacitor and the sixth resonant inductor may be connected in series between the first secondary terminal of the third secondary winding and a fifth RC node of the rectifier circuit.

[0067] In one embodiment, the fourth resonant inductor may be connected between the first secondary terminal of the first secondary winding and the first RC node of the rectifier circuit;

[0068] The fourth resonant capacitor may be connected between the second secondary terminal of the first secondary winding and the second resonant cavity node;

[0069] The fifth resonant inductor may be connected between the first secondary terminal of the second secondary winding and the second RC node of the rectifier circuit;

[0070] The fifth resonant capacitor may be connected between the second secondary terminal of the second secondary winding and the second resonant cavity node;

[0071] The sixth resonant inductor may be connected between the first secondary terminal of the third secondary winding and a third RC node of the rectifier circuit;

[0072] The sixth resonant capacitor may be connected between the second secondary terminal of the third secondary winding and the second resonant cavity node.

[0073] In an embodiment, the converter may include a clamping diode also on the secondary side of the transformer device.

[0074] In an embodiment, the converter may include three clamping diodes between each second secondary terminal of the secondary winding and the second positive terminal; and another three clamping diodes between the second negative terminal and each second secondary terminal of the secondary winding.

[0075] In one embodiment, the three clamping diodes between each second secondary terminal of the secondary winding and the second positive terminal include:

[0076] a seventh clamping diode having an anode connected to the second secondary terminal of the first secondary winding and a cathode connected to the second positive terminal;

[0077] an eighth clamping diode having an anode connected to the second secondary terminal of the second secondary winding and a cathode connected to the second positive terminal;

[0078] a ninth clamping diode having an anode connected to the second secondary terminal of the third secondary winding and a cathode connected to the second positive terminal; and

[0079] Wherein, the other three clamping diodes between the second negative terminal and each second secondary terminal of the secondary winding include:

[0080] a tenth diode having an anode connected to the second negative terminal and a cathode connected to the second secondary terminal of the first secondary winding;

[0081] an eleventh diode having an anode connected to the second negative terminal and a cathode connected to the second secondary terminal of the second secondary winding;

[0082] A twelfth diode has an anode connected to the second negative terminal and a cathode connected to the second secondary terminal of the third secondary winding.

[0083] In an embodiment, the control circuit may be configured to increase the current flowing from the second positive terminal for a period of time in response to a short circuit condition detectable by the control circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Hereinafter, detailed embodiments of the present invention will be described with reference to the accompanying drawings, in which:

[0085] Figure 1aA prior art single-phase LLC resonant DC-DC converter with a clamping diode is shown;

[0086] Figure 1b A prior art three-phase LLC resonant DC-DC converter is shown;

[0087] Figure 2 A first embodiment of a three-phase LLC resonant DC-DC converter with protection diodes is shown;

[0088] Figure 3 is a circuit with an additional capacitor Figure 2 A magnified view of the resonant cavity device and the transformer device;

[0089] Figure 4 A second embodiment in the form of a three-phase CLLC resonant DC-DC converter with protection diodes is shown;

[0090] Figure 5 A third embodiment in the form of a three-phase CLLC resonant DC-DC converter with dual sets of protection diodes is shown;

[0091] Figure 6 Is a circuit with additional capacitors Figure 5 A magnified view of the transformer device and the second resonant circuit;

[0092] Figure 7 Shows Figure 2 Transformer equipment in;

[0093] Figure 8 A power supply system of multiple three-phase LLC resonant DC-DC converters with clamping diodes is shown;

[0094] Figure 9a shows the short circuit current of the converter with clamping diodes;

[0095] Figure 9b shows the short-circuit current of the converter without the clamping diode;

[0096] Fig.9c The switching frequency of the control circuit before, during and after the short circuit current is shown. DETAILED DESCRIPTION

[0097] First embodiment

[0098] Reference now Figure 2, which shows a first embodiment of a three-phase resonant DC-DC converter 1. In addition to other electrical components that will be described below, the converter 1 includes a switching circuit SC (indicated by a dotted box), a resonant cavity device RTD (also indicated by a dotted box), a transformer device TD (also indicated by a dotted box) and a rectifier circuit RC (also indicated by a dotted box).

[0099] Switching Circuit SC (Switching Circuit) of the First Embodiment

[0100] The switch circuit SC has a first side ( Figure 2 The left side of the switching circuit SC in the middle) has a first positive terminal P1 and a first negative terminal N1. The first positive terminal P1 and the first negative terminal N1 are first terminals or input terminals of the converter 1, and the converter 1 is defined as having a first DC voltage U1 between the first positive terminal P1 and the first negative terminal N1. A DC voltage source is usually connected between the first positive terminal P1 and the first negative terminal N1.

[0101] The switch circuit SC has a second side ( Figure 2 The right side of the middle switch circuit SC includes a first SC node SCN1, a second SC node SCN2 and a third SC node SCN3.

[0102] The switch circuit SC has six switches connected between the first positive terminal P1, the first negative terminal N1, the first SC node SCN1, the second SC node SCN2 and the third SC node SCN3. These switches may be referred to as primary side switches. These switches are:

[0103] A first switch S11 having a source terminal connected to the first SC node SCN1 and a drain terminal connected to the first positive terminal P1;

[0104] a second switch S12 having a source terminal connected to the first negative terminal N1 and a drain terminal connected to the first SC node SCN1;

[0105] a third switch S13 having a source terminal connected to the second SC node SCN2 and a drain terminal connected to the first positive terminal P1;

[0106] a fourth switch S14 having a source terminal connected to the first negative terminal N1 and a drain terminal connected to the second SC node SCN2;

[0107] a fifth switch S15 having a source terminal connected to the third SC node SCN3 and a drain terminal connected to the first positive terminal P1;

[0108] The sixth switch S16 has its source terminal connected to the first negative terminal N1 and its drain terminal connected to the third SC node SCN3.

[0109] The switch may be a MOSFET switch, a GaN switch or other types of switches.

[0110] Rectifying Circuit RC (rectifying circuit) of the first embodiment

[0111] The rectifier circuit RC has a first side ( Figure 2 The left side of the rectifier circuit RC) and the second side ( Figure 2 The right side of the rectifying circuit RC in the middle), the first side of the rectifying circuit includes RC nodes RCN1, RCN2, RCN3, RCN4, RCN5, RCN6, and the second side of the rectifying circuit includes a second positive terminal P2 and a second negative terminal N2.

[0112] The RC nodes RCN1, RCN2, RCN3, RCN4, RCN5, RCN6 may be referred to as a first RC node RCN1, a second RC node RCN2, a third RC node RCN3, a fourth RC node RCN4, a fifth RC node RCN5, and a sixth RC node RCN6 of the rectifier circuit RC.

[0113] The second positive terminal P2 and the second negative terminal N2 are second terminals or output terminals of the converter 1, and the converter 1 is defined as having a second DC voltage U2 between the second positive terminal P2 and the second negative terminal N2. The load is usually connected between the second positive terminal P2 and the second negative terminal N2. Therefore, the second DC voltage U2 can represent a load voltage.

[0114] The rectifier circuit RC includes twelve switches connected between RC nodes RCN1, RCN2, RCN3, RCN4, RCN5, RCN6, the second positive terminal P2 and the second negative terminal N2. These switches may be referred to as secondary side switches. These switches are:

[0115] a first switch S21 having a source terminal connected to the first RC node RCN1 and a drain terminal connected to the second positive terminal P2;

[0116] a second switch S22 having a source terminal connected to the second negative terminal N2 and a drain terminal connected to the first RC node RCN1;

[0117] a third switch S23 having a source terminal connected to the second RC node RCN2 and a drain terminal connected to the second positive terminal P2;

[0118] a fourth switch S24 having a source terminal connected to the second negative terminal N2 and a drain terminal connected to the second RC node RCN2;

[0119] a fifth switch S25 having a source terminal connected to the third RC node RCN3 and a drain terminal connected to the second positive terminal P2;

[0120] a sixth switch S26 having a source terminal connected to the second negative terminal N2 and a drain terminal connected to the third RC node RCN3;

[0121] a seventh switch S27 having a source terminal connected to the fourth RC node RCN4 and a drain terminal connected to the second positive terminal P2;

[0122] an eighth switch S28 having a source terminal connected to the second negative terminal N2 and a drain terminal connected to the fourth RC node RCN4;

[0123] a ninth switch S29 having a source terminal connected to the fifth RC node RCN5 and a drain terminal connected to the second positive terminal P2;

[0124] a tenth switch S30 having a source terminal connected to the second negative terminal N2 and a drain terminal connected to the fifth RC node RCN5;

[0125] an eleventh switch S31 having a source terminal connected to the sixth RC node RCN6 and a drain terminal connected to the second positive terminal P2;

[0126] The twelfth switch S32 has its source terminal connected to the second negative terminal N2 and its drain terminal connected to the sixth RC node RCN6.

[0127] The switch may be a MOSFET switch, a GaN switch or other types of switches.

[0128] Transformer device of the first embodiment

[0129] The transformer device TD comprises three primary windings PW1, PW2, PW3 ( Figure 2 The left side of the transformer device TD) and three secondary windings SW1, SW2, SW3 ( Figure 2 on the right side of the transformer device TD).

[0130] The first primary winding PW1 has a first primary terminal 40 and a second primary terminal 41. The second primary winding PW2 has a first primary terminal 42 and a second primary terminal 43. The third primary winding PW3 has a first primary terminal 44 and a second primary terminal 45.

[0131] The first secondary winding SW1 has a first secondary terminal 70 and a second secondary terminal 71. The second secondary winding SW2 has a first secondary terminal 72 and a second secondary terminal 73. The third secondary winding SW3 has a first secondary terminal 74 and a second secondary terminal 75.

[0132] Reference now Figure 7 Here it is shown that the transformer device TD comprises a first transformer core TC1 , a second transformer core TC2 and a third transformer core TC3 .

[0133] The first primary winding PW1 and the first secondary winding SW1 are wound on the first core TC1. The second primary winding PW2 and the second secondary winding SW2 are wound on the second core TC2. The third primary winding PW3 and the third secondary winding SW3 are wound on the third core TC3.

[0134] like Figure 7 As shown, the transformer cores TC1, TC2, TC3 are separated from each other and are at a certain distance from each other. In this way, the first transformer core TC1, the second transformer core TC2 and the third transformer core TC3 are electromagnetically independent from each other.

[0135] As used herein, the term "electromagnetic independence" means that the electromagnetic flux in one of the transformer cores leaks to the other transformer cores at a rate of less than 10%, preferably less than 5%.

[0136] Resonant tank device RTD (resonant tank device) of the first embodiment

[0137] Now refer to it again Figure 2 Here it is shown that the resonant cavity device RTD comprises a primary side resonant cavity RTD1 connected between first SC node SCN1, second SC node SCN2, third SC node SCN3 of the switching circuit SC and primary terminals 40, 41, 42, 43, 44, 45 of three primary windings PW1, PW2, PW3 of the transformer device TD.

[0138] The primary side resonant cavity device RTD1 further comprises a resonant cavity node RTDN.

[0139] The primary side resonant cavity device RTD1 includes a first resonant inductor Lr1 connected between the first SC node SCN1 of the switching circuit SC and the first primary terminal 40 of the first primary winding PW1, a second resonant inductor Lr2 connected between the second SC node SCN2 of the switching circuit SC and the first primary terminal 42 of the second primary winding PW2, and a third resonant inductor Lr3 connected between the third SC node SCN3 of the switching circuit SC and the first primary terminal 44 of the third primary winding PW3.

[0140] In addition, the primary side resonant cavity device RTD1 includes a first resonant capacitor Cr1 connected between the resonant cavity node RTDN and the second primary terminal 41 of the first primary winding PW1, a second resonant capacitor Cr2 connected between the resonant cavity node RTDN and the second primary terminal 43 of the second primary winding PW2, and a third resonant capacitor Cr3 connected between the resonant cavity node RTDN and the second primary terminal 45 of the third primary winding PW3. The resonant capacitors Cr1, Cr2, Cr3 here form a star connection.

[0141] In this embodiment, the resonant cavity node RTDN is regarded as a floating neutral point of the primary side resonant cavity device RTD1.

[0142] Additional Information About the First Embodiment

[0143] In this embodiment, the first RC node RCN1 of the rectifier circuit RC is directly connected to the first secondary terminal 70 of the first secondary winding SW1, the second RC node RCN2 of the rectifier circuit RC is directly connected to the second secondary terminal 71 of the first secondary winding SW1, the third RC node RCN3 of the rectifier circuit RC is directly connected to the first secondary terminal 72 of the second secondary winding SW2, the fourth RC node RCN4 of the rectifier circuit CR is directly connected to the second secondary terminal 73 of the second secondary winding SW2, the fifth RC node RCN5 of the rectifier circuit RCRC is directly connected to the first secondary terminal 74 of the third secondary winding SW3, and the sixth RC node RCN6 of the rectifier circuit RC is directly connected to the second secondary terminal 75 of the third secondary winding SW3.

[0144] The converter 1 further comprises a capacitor CS connected between the second positive terminal P2 and the second negative terminal N2. Since this capacitor CS is connected on the secondary side with respect to the transformer device TD, it is hereby referred to as secondary capacitor CS.

[0145] The converter 1 further comprises a control circuit 50 for controlling switches of the switching circuit SC and for controlling switches of the rectifier circuit RC. Typically, the control circuit 50 comprises a digital signal processor and software, which is controlled to switch on / off the switches based on signals from sensors such as signals measuring parameters representing the first voltage U1, the second voltage U2, the first current I1 flowing into the first positive terminal P1 and / or the second current I2 flowing out of the second positive terminal P2.

[0146] Finally, converter 1 includes six clamping diodes D1, D2, D3, D4, D5, D6. These six clamping diodes are:

[0147] a first clamping diode D1 having an anode connected to the second first primary terminal 41 of the first primary winding PW1 and a cathode connected to the first positive terminal P1;

[0148] a second clamping diode D2 having an anode connected to the second second primary terminal 43 of the second primary winding PW2 and a cathode connected to the first positive terminal P1;

[0149] a third clamping diode D3 having an anode connected to the second third primary terminal 45 of the third primary winding PW3 and a cathode connected to the first positive terminal P1 ; and

[0150] a fourth diode D4 having an anode connected to the first negative terminal N1 and a cathode connected to the second first primary terminal 41 of the first primary winding PW1;

[0151] a fifth diode D5 having an anode connected to the first negative terminal N1 and a cathode connected to the second second primary terminal 43 of the second primary winding PW2; and

[0152] A sixth diode D6 has its anode connected to the first negative terminal N1 and its cathode connected to the second third primary terminal 45 of the third primary winding PW3 .

[0153] The control circuit 50 is configured to control the switch by a PWM control method.

[0154] Second embodiment

[0155] Will refer to Figure 3 A second embodiment of the converter 1 is described. The converter 1 of the second embodiment is similar to the converter 1 of the first embodiment. Various differences between the second embodiment and the first embodiment will be described here.

[0156] In the second embodiment, the resonant cavity node RTDN is not a floating neutral point. Instead, the converter 1 comprises a capacitor circuit 60 connected between the resonant cavity node RTDN and the first negative terminal N1. The capacitor circuit 60 may comprise one or more capacitors.

[0157] The purpose of capacitor circuit 60 is to reduce electromagnetic interference of the circuit under at least some operating conditions.

[0158] Third embodiment

[0159] Will refer to Figure 4 A third embodiment of the converter 1 is described. The converter 1 of the third embodiment is similar to the converter 1 of the first embodiment. Various differences between the third embodiment and the first embodiment will be described here.

[0160] In the present embodiment, the resonant cavity device RTD further comprises, in addition to the primary-side resonant cavity device RTD1, a secondary-side resonant cavity device RTD2 on the secondary side of the transformer device TD.

[0161] The secondary side resonant cavity device RTD2 includes a fourth resonant capacitor Cr4, a fifth resonant capacitor Cr1, and a sixth resonant capacitor Cr2, and further includes a fourth resonant inductor Lr4, a fifth resonant inductor Lr5, and a sixth resonant inductor Lr6.

[0162] like Figure 4 As shown, the fourth resonant capacitor Cr4 and the fourth resonant inductor Lr4 are connected in series between the first secondary terminal 70 of the first secondary winding SW1 and the first RC node RCN1 of the rectifier circuit RC. The fifth resonant capacitor Cr5 and the fifth resonant inductor Lr5 are connected in series between the first secondary terminal 72 of the second secondary winding SW2 and the third RC node RCN3 of the rectifier circuit RC. The sixth resonant capacitor Cr6 and the sixth resonant inductor Lr6 are connected in series between the first secondary terminal 74 of the third secondary winding SW3 and the fifth RC node RCN5 of the rectifier circuit RC.

[0163] It should be noted that in an alternative to the third embodiment, the primary side resonant cavity device RTD1 comprises a capacitor circuit 60 connected between the resonant cavity node RTDN and the first negative terminal N1, i.e. similar to the above Figure 3 The second embodiment of the present invention.

[0164] This embodiment is generally referred to as a three-phase CLLC resonant converter. The clamping diodes here also protect the primary side resonant capacitors Cr1 , Cr2 , Cr3 from overvoltages and the primary side switches from overcurrents.

[0165] Fourth embodiment

[0166] Will refer to Figure 5 A fourth embodiment of the converter 1 is described. The converter 1 of the fourth embodiment is similar to the converter 1 of the third embodiment. Various differences between the fourth embodiment and the third embodiment will be described here.

[0167] Also here, the resonant cavity device RTD includes a primary side resonant cavity device RTD1 and a secondary side resonant cavity device RTD2.

[0168] The secondary side resonant cavity device RTD2 here also includes three resonant inductors Lr4, Lr5, Lr6 and three resonant capacitors Cr4, Cr5, Cr6. However, the secondary side resonant cavity device RTD2 here includes a second resonant cavity node RTDN2. Therefore, Figure 5 As shown, the resonant cavity node of the first resonant cavity device RTD1 is represented as a first resonant cavity node RTDN1.

[0169] like Figure 5As shown, the fourth resonant inductor Lr4 is connected between the first secondary terminal 70 of the first secondary winding SW1 and the first RC node RCN1 of the rectifier circuit RC. The fourth resonant capacitor Cr4 is connected between the second secondary terminal 71 of the first secondary winding SW1 and the second resonant cavity node RTDN2. The fifth resonant inductor Lr5 is connected between the first secondary terminal 72 of the second secondary winding SW2 and the second RC node RCN2 of the rectifier circuit RC. The fifth resonant capacitor Cr5 is connected between the second secondary terminal 73 of the second secondary winding SW2 and the second resonant cavity node RTDN2. The sixth resonant inductor Lr6 is connected between the first secondary terminal 73 of the third secondary winding SW3 and the third RC node RCN3 of the rectifier circuit RC. The sixth resonant capacitor Cr6 is connected between the second secondary terminal 75 of the third secondary winding SW3 and the second resonant cavity node RTDN2.

[0170] In this embodiment, the second resonant cavity node RTDN2 is a floating neutral point.

[0171] The fourth embodiment of the converter 1 further comprises six clamping diodes on the secondary side of the transformer device TD. These clamping diodes are:

[0172] a seventh clamping diode D7 having an anode connected to the second secondary terminal 71 of the first secondary winding SW1 and a cathode connected to the second positive terminal P2;

[0173] an eighth clamping diode D8 having an anode connected to the second secondary terminal 73 of the second secondary winding SW2 and a cathode connected to the second positive terminal P2;

[0174] a ninth clamping diode D9 having an anode connected to the second secondary terminal 73 of the third secondary winding SW3 and a cathode connected to the second positive terminal P2; and

[0175] a tenth diode D10 having an anode connected to the second negative terminal N2 and a cathode connected to the second secondary terminal 71 of the first secondary winding SW1;

[0176] an eleventh diode D11 having an anode connected to the second negative terminal N2 and a cathode connected to the second secondary terminal 73 of the second secondary winding SW2;

[0177] The twelfth diode D12 has its anode connected to the second negative terminal N2 and its cathode connected to the second secondary terminal 75 of the third secondary winding SW3.

[0178] The fourth embodiment is also referred to as a three-phase CLLC resonant converter. The clamping diodes on the secondary side will protect the resonant capacitors Cr4, Cr5, Cr6 from overvoltage.

[0179] Fifth embodiment

[0180] Will refer to Figure 6 A fifth embodiment of the converter 1 is described. The converter 1 of the fifth embodiment is similar to Figure 5 Various differences between the fifth embodiment and the fourth embodiment will be described here.

[0181] In the fifth embodiment, the second resonant cavity node RTDN2 is not a floating neutral point. Instead, the converter 1 comprises a capacitor circuit 61 connected between the second resonant cavity node RTDN2 and the second negative terminal N2.

[0182] The purpose of the capacitor circuit 61 is to reduce the electromagnetic interference of the circuit.

[0183] Operation of the Second Embodiment

[0184] Reference now Figure 8 . Here is shown a power supply system having one or more AC-DC converters that convert alternating current from a main line to an intermediate DC bus. One or more three-phase resonant DC-DC converters 1 of the second embodiment described above have their first terminals P1, N2 connected to the intermediate DC bus, and their second terminals P2, N2 connected to a DC load bus to which one or more DC loads are connected. It is further shown that each converter 1 has a fuse F between its second terminals P2, N2 and the DC load bus.

[0185] The resonant frequency is defined in particular by the characteristics of the resonant inductors Lr1, Lr2, Lr3 and the resonant capacitors Cr1, Cr2, Cr3, and possibly also together with the characteristics of the primary windings PW1, PW2, PW3. When the switching frequency from the control circuit 50 is at or close to the resonant frequency of the first resonant cavity device RTD1, the current in the primary side switches S11, S12, S13, S14, S15, S16 may reach very high levels (e.g. during circuit startup, overload or short circuit of the LLC output terminals P2, N2), which may damage the switches of the converter 1. In addition, the voltage level of the resonant capacitors Cr1, Cr2, Cr3 may reach very high levels.

[0186] By means of the clamping diode, the voltage of the resonant capacitor is clamped to the voltage level of the first voltage U1, which, as described above, generally represents the intermediate DC bus voltage between the AC-DC converter and the DC-DC converter. In addition, when the voltage of the resonant capacitor reaches the DC link voltage, the current through the switch of the switching circuit SC is clamped and freewheeling.

[0187] The short circuit condition of converter 1 is as follows Figure 9aHere it is shown that the short circuit current (blue line) is quickly clamped to a constant current (time scale is 500μs / div) due to the clamping diode. It should be noted that the current level after the short circuit is higher than before the short circuit.

[0188] This is caused by the control software, which, after detecting a short circuit, changes the frequency to increase the output current, causing fuse F to blow. Fig.9c Here, the switching frequency changes within the period p1. Therefore, when the fuse F is blown, the operator of the power supply system can check whether maintenance is required, such as disconnecting the device causing the short circuit from the power supply system.

[0189] It should be noted that control software is usually slow compared to a short circuit. Therefore, within the first microsecond, or even the first millisecond, of a short circuit situation, the control software will not be able to change anything. This can be seen from Fig.9c As can be seen in Figure 1, there is a short period of time between the occurrence of a short circuit and the start of the tp1 period when the control software is actually able to detect and take action. However, during the first stages of a short circuit condition, the clamping diodes will provide protection for both the converter itself and the load.

[0190] exist Figure 9b In FIG. 1 , the results of a corresponding short circuit situation of a corresponding converter without a clamping diode are shown. Instead, control software is used to reduce the destructive effects of the short circuit current. Figure 9b As shown, the current can be much higher for a short time (due to the lack of clamping diodes) before the control software manages to close all switches. Even if the current is short-lived, it may be enough to damage the converter's components. What's more, due to the short duration, fuse F will most likely not blow. Therefore, the load is also susceptible to short-circuit current.

[0191] exist Figure 9b In Figure 1, the subsequent current peak is shown. This peak is the result of the control software trying to restart the converter. However, since the short circuit still exists, the control software closes the switch again.

[0192] Thus, as described above, one of the advantages of the converter 1 is that it provides protection from the time a short circuit condition occurs until the control software is able to detect the condition and take action. Furthermore, it is achieved that the time and complexity of testing the control software under all operating conditions can be avoided.

[0193] Alternative Embodiments

[0194] In the above-described embodiment, the first transformer core TC1 , the second transformer core TC2 , and the third transformer core TC3 are separated from each other to prevent or at least significantly reduce the magnetic flux generated in one core from generating magnetic flux in other cores.

[0195] In an alternative embodiment, the first transformer core TC1 , the second transformer core TC2 and the third transformer core TC3 are cores of a single core, wherein an air gap or other electromagnetic insulating material prevents or at least significantly reduces magnetic flux sharing between the various cores.

[0196] In an alternative embodiment, the rectifying circuit RC is a diode rectifier. The diode rectifier may include six diodes or twelve diodes instead of the twelve or six switches of the above embodiments.

Claims

1. A three-phase resonant DC-DC converter (1) for converting a first DC voltage (U1) into a second DC voltage (U2), wherein the converter (1) comprises: A transformer device (TD) comprising three primary windings (PW1, PW2, PW3) and three secondary windings (SW1, SW2, SW3), each primary winding (PW1, PW3, PW2) comprising a first primary terminal (40, 42, 44) and a second primary terminal (41, 43, 45), and each secondary winding (SW1, SW2, SW3) comprising a first secondary terminal (70, 72, 74) and a second secondary terminal (71, 73, 75); a switching circuit (SC) having a first side and a second side, the first side of the switching circuit comprising a first positive terminal (P1) and a first negative terminal (N1) forming a first terminal of the converter (1), the second side of the switching circuit comprising a first SC node (SCN1), a second SC node (SCN2) and a third SC node (SCN3) respectively connected to the primary winding (PW1, PW2, PW3) of the transformer device (TD); a rectifier circuit (RC) having a first side and a second side, the first side of the rectifier circuit comprising RC nodes (RCN1, RCN2, RCN3, RCN4, RCN5, RCN6) respectively connected to the secondary windings (SW1, SW2, SW3) of the transformer device (TD), the second side of the rectifier circuit comprising a second positive terminal (P2) and a second negative terminal (N2) forming a second terminal of the converter (1); a resonant cavity device (RTD) comprising a primary side resonant cavity device (RTD1) connected between the first SC node (SCN1), the second SC node (SCN2) and the third SC node (SCN3) of the switching circuit (SC) and primary terminals (40, 41, 42, 43, 44, 45) of three primary windings (PW1, PW2, PW3) of the transformer device (TD); a secondary capacitor (CS) connected between the second positive terminal (P2) and the second negative terminal (N2); A control circuit (50) for controlling the switch circuit (SC); wherein the first DC voltage (U1) is defined as a voltage between the first positive terminal (P1) and the first negative terminal (N1); wherein the second DC voltage (U2) is defined as a voltage between the second positive terminal (P2) and the second negative terminal (N2); wherein the primary-side resonant cavity device (RTD1) comprises a first resonant inductor (Lr1), a second resonant inductor (Lr2) and a third resonant inductor (Lr3), wherein the first resonant inductor (Lr1) is connected between a first SC node (SCN1) of the switch circuit (SC) and a first primary terminal (40) of the first primary winding (PW1), the second resonant inductor (Lr2) is connected between a second SC node (SCN2) of the switch circuit (SC) and a first primary terminal (42) of the second primary winding (PW2), and the third resonant inductor (Lr3) is connected between a third SC node (SCN3) of the switch circuit (SC) and a first primary terminal (44) of the third primary winding (PW3); wherein the primary side resonant cavity device (RTD1) comprises a first resonant capacitor (Cr1), a second resonant capacitor (Cr2) and a third resonant capacitor (Cr3), wherein the first resonant capacitor (Cr1) is connected between a resonant cavity node (RTDN) and a second primary terminal (41) of the first primary winding (PW1), the second resonant capacitor (Cr2) is connected between the resonant cavity node (RTDN) and a second primary terminal (43) of the second primary winding (PW2), and the third resonant capacitor (Cr3) is connected between the resonant cavity node (RTDN) and a second primary terminal (45) of the third primary winding (PW3); wherein the converter (1) comprises three clamping diodes (D1, D2, D3) between each second primary terminal (41, 43, 45) of the primary winding (PW1, PW2, PW3) and the first positive terminal (P1); The converter (1) comprises three further clamping diodes (D4, D5, D6) between the first negative terminal (N1) and each second primary terminal (41, 43, 45) of the primary windings (PW1, PW2, PW3).

2. The three-phase resonant DC-DC converter (1) according to claim 1, wherein: Three clamping diodes (D1, D2, D3) between each second primary terminal (41, 43, 45) of the primary winding (PW1, PW2, PW3) and the first positive terminal (P1) include: a first clamping diode (D1) having an anode connected to a second first primary terminal (41) of the first primary winding (PW1) and a cathode connected to the first positive terminal (P1); a second clamping diode (D2) having an anode connected to a second primary terminal (43) of the second primary winding (PW2) and a cathode connected to the first positive terminal (P1); a third clamping diode (D3) having an anode connected to the second third primary terminal (45) of the third primary winding (PW3) and a cathode connected to the first positive terminal (P1); and The other three clamping diodes (D4, D5, D6) between the first negative terminal (N1) and each second primary terminal (41, 43, 45) of the primary winding (PW1, PW2, PW3) include: a fourth diode (D4) having an anode connected to the first negative terminal (N1) and a cathode connected to the second primary terminal (41) of the first primary winding (PW1); a fifth diode (D5) having an anode connected to the first negative terminal (N1) and a cathode connected to the second primary terminal (43) of the second primary winding (PW2); A sixth diode (D6) having an anode connected to the first negative terminal (N1) and a cathode connected to the second primary terminal (45) of the third primary winding (PW3).

3. The three-phase resonant DC-DC converter (1) according to claim 1 or 2, wherein: The converter (1) comprises a capacitor circuit (60) connected between the resonant cavity node (RTDN) and the first negative terminal (N1).

4. A three-phase resonant DC-DC converter (1) according to any one of the preceding claims, wherein: The transformer device (TD) comprises: a first transformer core (TC1) on which the first primary winding (PW1) and the first secondary winding (SW1) are wound; a second transformer core (TC2) on which the second primary winding (PW2) and the second secondary winding (SW2) are wound; A third transformer core (TC3) is wound with the third primary winding (PW3) and the third secondary winding (SW3).

5. The three-phase resonant DC-DC converter (1) according to claim 4, wherein: The first transformer core (TC1), the second transformer core (TC2) and the third transformer core (TC3) are electromagnetically independent from each other.

6. A three-phase resonant DC-DC converter (1) according to any one of the preceding claims, wherein: The switching circuit (SC) comprises: a first switch (S11) having a source terminal connected to the first SC node (SCN1) and a drain terminal connected to the first positive terminal (P1); a second switch (S12) having a source terminal connected to the first negative terminal (N1) and a drain terminal connected to the first SC node (SCN1); a third switch (S13) having a source terminal connected to the second SC node (SCN2) and a drain terminal connected to the first positive terminal (P1); a fourth switch (S14), having a source terminal connected to the first negative terminal (N1) and a drain terminal connected to the second SC node (SCN2); a fifth switch (S15) having a source terminal connected to the third SC node (SCN3) and a drain terminal connected to the first positive terminal (P1); A sixth switch (S16) has a source terminal connected to the first negative terminal (N1) and a drain terminal connected to the third SC node (SCN3).

7. A three-phase resonant DC-DC converter (1) according to any one of the preceding claims, wherein: The rectifier circuit (RC) comprises: a first switch (S21) connected between the first RC node (RCN1) and the second positive terminal (P2); a second switch (S22) connected between the second negative terminal (N2) and the first RC node (RCN1); a third switch (S23) connected between the second RC node (RCN2) and the second positive terminal (P2); a fourth switch (S24) connected between the second negative terminal (N2) and the second RC node (RCN2); a fifth switch (S25) connected between the third RC node (RCN3) and the second positive terminal (P2); a sixth switch (S26) connected between the second negative terminal (N2) and the third RC node (RCN3); a seventh switch (S27) connected between the fourth RC node (RCN4) and the second positive terminal (P2); an eighth switch (S28) connected between the second negative terminal (N2) and the fourth RC node (RCN4); a ninth switch (S29) connected between the fifth RC node (RCN5) and the second positive terminal (P2); a tenth switch (S30) connected between the second negative terminal (N2) and the fifth RC node (RCN5); an eleventh switch (S31) connected between the sixth RC node (RCN6) and the second positive terminal (P2); A twelfth switch (S32) is connected between the second negative terminal (N2) and the sixth RC node (RCN6).

8. The three-phase resonant DC-DC converter (1) according to claim 7, characterized in that: The first RC node (RCN1) of the rectifier circuit (RC) is directly connected to the first secondary terminal (70) of the first secondary winding (SW1), the second RC node (RCN2) of the rectifier circuit (RC) is directly connected to the second secondary terminal (71) of the first secondary winding (SW1), the third RC node (RCN3) of the rectifier circuit (RC) is directly connected to the first secondary terminal (72) of the second secondary winding (SW2), the fourth RC node (RCN4) of the rectifier circuit (RC) is directly connected to the second secondary terminal (73) of the second secondary winding (SW2), the fifth RC node (RCN5) of the rectifier circuit (RC) is directly connected to the first secondary terminal (74) of the third secondary winding (SW3), and the sixth RC node (RCN6) of the rectifier circuit (RC) is directly connected to the second secondary terminal (75) of the third secondary winding (SW3).

9. A three-phase resonant DC-DC converter (1) according to any one of the preceding claims, wherein: The resonant cavity device (RTD) further comprises a secondary side resonant cavity device (RTD2) on a secondary side of the transformer device (TD).

10. The three-phase resonant DC-DC converter (1) according to claim 9, wherein: The secondary side resonant cavity device (RTD2) includes a fourth resonant capacitor (Cr4), a fifth resonant capacitor (Cr5) and a sixth resonant capacitor (Cr6), and also includes a fourth resonant inductor (Lr4), a fifth resonant inductor (Lr5) and a sixth resonant inductor (Lr6).

11. The three-phase resonant DC-DC converter (1) according to claim 10, wherein: The fourth resonant capacitor (Cr4) and the fourth resonant inductor (Lr4) are connected in series between the first secondary terminal (70) of the first secondary winding (SW1) and the first RC node (RCN1) of the rectifier circuit (RC); The fifth resonant capacitor (Cr5) and the fifth resonant inductor (Lr5) are connected in series between the first secondary terminal (72) of the second secondary winding (SW2) and the third RC node (RCN3) of the rectifier circuit (RC); The sixth resonant capacitor (Cr6) and the sixth resonant inductor (Lr6) are connected in series between the first secondary terminal (74) of the third secondary winding (SW3) and a fifth RC node (RCN5) of the rectifier circuit (RC).

12. The three-phase resonant DC-DC converter (1) according to claim 10, wherein: The fourth resonant inductor (Lr4) is connected between the first secondary terminal (70) of the first secondary winding (SW1) and the first RC node (RCN1) of the rectifier circuit (RC); The fourth resonant capacitor (Cr4) is connected between the second secondary terminal (71) of the first secondary winding (SW1) and the second resonant cavity node (RTDN2); The fifth resonant inductor (Lr5) is connected between the first secondary terminal (72) of the second secondary winding (SW2) and the second RC node (RCN2) of the rectifier circuit (RC); The fifth resonant capacitor (Cr5) is connected between the second secondary terminal (73) of the second secondary winding (SW2) and the second resonant cavity node (RTDN2); The sixth resonant inductor (Lr6) is connected between the first secondary terminal (73) of the third secondary winding (SW3) and the third RC node (RCN3) of the rectifier circuit (RC); The sixth resonant capacitor (Cr6) is connected between the second secondary terminal (75) of the third secondary winding (SW3) and the second resonant cavity node (RTDN2).

13. The three-phase resonant DC-DC converter (1) according to claim 12, wherein: The converter (1) comprises three clamping diodes (D7, D8, D9) between each second secondary terminal (71, 73, 75) of the secondary winding (SW1, SW2, SW3) and the second positive terminal (P2); and another three clamping diodes (D10, D11, D12) between the second negative terminal (N2) and each second secondary terminal (71, 73, 75) of the secondary winding (SW1, SW2, SW3).

14. The three-phase resonant DC-DC converter (1) according to claim 13, wherein: Three clamping diodes (D7, D8, D9) between each second secondary terminal (71, 73, 75) of the secondary winding (SW1, SW2, SW3) and the second positive terminal (P2) include: a seventh clamping diode (D7), an anode of which is connected to the second secondary terminal (71) of the first secondary winding (SW1) and a cathode of which is connected to the second positive terminal (P2); an eighth clamping diode (D8), an anode of which is connected to the second secondary terminal (73) of the second secondary winding (SW2) and a cathode of which is connected to the second positive terminal (P2); a ninth clamping diode (D9) having an anode connected to the second secondary terminal (75) of the third secondary winding (SW3) and a cathode connected to the second positive terminal (P2); and The other three clamping diodes (D10, D11, D12) between the second negative terminal (N2) and each second secondary terminal (71, 73, 75) of the secondary winding (SW1, SW2, SW3) include: a tenth diode (D10) having an anode connected to the second negative terminal (N2) and a cathode connected to the second secondary terminal (71) of the first secondary winding (SW1); an eleventh diode (D11), an anode of which is connected to the second negative terminal (N2) and a cathode of which is connected to the second secondary terminal (73) of the second secondary winding (SW2); A twelfth diode (D12) has an anode connected to the second negative terminal (N2) and a cathode connected to the second secondary terminal (75) of the third secondary winding (SW3).

15. A three-phase resonant DC-DC converter (1) according to any one of the preceding claims, wherein: The control circuit (50) is configured to increase the current (I2) flowing from the second positive terminal (P2) for a period of time (tp1) in response to a short circuit condition detected by the control circuit (50).

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