Power converter, control method of power converter, charger, and vehicle

Abstract

To provide a power converter capable of expanding an output range of an output voltage with respect to an operation frequency rage, without providing a change-over switch on an output side.SOLUTION: A power converter 1 comprises a plurality of full-bridge LLC converters. The full-bridge LLC converters each convert a DC voltage Vin into an output voltage Vo by switching operations of a first switching leg and a second switching leg. Secondary windings N2 of transformers T in the plurality of full-bridge LLC converters are connected in series to each other, in the power converter 1. The plurality of full-bridge LLC converters each comprise a control part 30 driven by switching a plurality of drive modes whose output characteristics are different from each other, according to a voltage command value Vcom, in the power converter 1.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a power converter that converts a DC voltage into a desired output voltage. [Background technology]

[0002] Charging devices that charge storage batteries installed in electric vehicles and the like are increasingly adopting efficient LLC circuits (resonant circuits) (see, for example, Patent Document 1). LLC circuits have an input / output range where they are efficient, but outside of that range, their efficiency deteriorates significantly. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-249375 Summary of the Invention [Problem to be solved by the invention]

[0004] By providing multiple LLC circuits and switching between parallel and series connection of the outputs, an efficient input / output range can be obtained. The power converter 100 shown in Fig. 13 includes two half-bridge LLC converters (hereinafter referred to as LLC circuits 200) and a selector switch SW. The selector switch SW switches between series connection and parallel connection of the outputs of the two LLC circuits 200. In Fig. 13, (a) shows a state in which the outputs of the two LLC circuits 200 are connected in parallel, and (b) shows a state in which the outputs of the two LLC circuits 200 are connected in series.

[0005] The output voltage Vo of the LLC circuit 200 changes according to the switching frequency. FIG. 14 shows an example of the output characteristics between the switching frequency and the output voltage Vo. At low voltage outputs, the frequency increases significantly. The output characteristics of the two LLC circuits 200 are different between the case of parallel connection and the case of series connection. When the operating range of the switching frequency (hereinafter referred to as the operating frequency range) is X11 to X12 (X11 < X12), the output range of the output voltage Vo is V1 to V2 (V1 > V2) for series connection and V2 to V3 (V2 > V3) for parallel connection. By switching between parallel connection and series connection with the switching switch SW at the output voltage Vo = V2, the output range of the output voltage Vo can be expanded to V1 to V3 for the operating frequency range X1 to X2.

[0006] However, since the switching switch SW needs to be provided on the output side of the LLC circuit 200 to which the battery is connected, a surge current having a large amount of energy such as a battery short circuit due to a circuit failure may occur. Therefore, the switching switch SW needs to use a mechanical relay and cannot use a semiconductor switch. The mechanical relay is expensive and large-sized and cannot be replaced with a cheap and small-sized semiconductor switch.

[0007] One aspect of the present invention is to provide a power converter, a control method for the power converter, a charging device, and a vehicle that can expand the output range of the output voltage with respect to the operating frequency range without providing a switching switch on the output side.

Means for Solving the Problems

[0008] A power converter according to one aspect of the present invention converts a DC voltage into an output voltage using a full-bridge LLC converter. The full-bridge LLC converter has a first switching leg and a second switching leg, each including an upper switch element and a lower switch element connected in series. The full-bridge LLC converter has the first switching leg and the second switching leg connected between a positive pole and a negative pole of the DC voltage. The full-bridge LLC converter has a series resonant circuit, including a resonant inductor, a primary winding of a transformer, and a resonant capacitor, connected between an output point of the first switching leg and an output point of the second switching leg. The full-bridge LLC converter converts the DC voltage into an output voltage by switching operations of the first switching leg and the second switching leg. The power converter includes a plurality of full-bridge LLC converters. The power converter has secondary windings of the transformers of the plurality of full-bridge LLC converters connected in series. The power converter includes a control unit that drives the plurality of full-bridge LLC converters by switching between a plurality of drive modes with different output characteristics in accordance with an output voltage command value. A control method for a power converter according to one aspect of the present invention is a control method for a power converter using a full-bridge LLC converter. The full-bridge LLC converter has a first switching leg and a second switching leg, each including an upper switch element and a lower switch element connected in series. The full-bridge LLC converter has the first switching leg and the second switching leg connected between a positive pole and a negative pole of a DC voltage. In the full-bridge LLC converter, a series resonant circuit including a resonant inductor, a primary winding of a transformer, and a resonant capacitor is connected between an output point of the first switching leg and an output point of the second switching leg. The full-bridge LLC converter converts a DC voltage into an output voltage by switching operations of the first switching leg and the second switching leg. The power converter includes a plurality of full-bridge LLC converters. The power converter has secondary windings of the transformers of the plurality of full-bridge LLC converters connected in series. A control unit drives the plurality of full-bridge LLC converters by switching between a plurality of drive modes with different output characteristics in accordance with an output voltage command value. [Effects of the Invention]

[0009] According to one aspect of the present invention, the range of output voltages that can be output within the operating frequency range can be widened without providing a selector switch on the output side. The operating frequency range can be set to a narrow range around the resonant frequency, thereby improving conversion efficiency. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 10 is a diagram illustrating an example of use of a power converter as a charging device. [Figure 2] FIG. 1 is a diagram illustrating a configuration example of a power converter. [Figure 3] 5A and 5B are diagrams illustrating examples of drive modes of a control unit. [Figure 4] FIG. 1 is a diagram illustrating a normal operation of an LLC circuit. [Figure 5] FIG. 10 is a diagram illustrating PDM operation of an LLC circuit. [Figure 6] FIG. 10 is a diagram illustrating the always-on operation of the LLC circuit. [Figure 7] FIG. 1 is a diagram illustrating a power converter in standalone operation. [Figure 8] FIG. 10 is a diagram showing changes in impedance. [Figure 9] 5A and 5B are diagrams illustrating examples of output characteristics in each drive mode. [Figure 10] FIG. 2 is a diagram illustrating a configuration example of a gate signal generating circuit. [Figure 11] FIG. 1 is a diagram illustrating an example of the configuration of a power converter having an N-stage configuration. [Figure 12] FIG. 1 is a diagram illustrating an example of the configuration of an LLC circuit compatible with HVDC input. [Figure 13] FIG. 1 is a diagram illustrating an example of the configuration of a conventional power converter. [Figure 14] FIG. 1 is a diagram illustrating an example of output characteristics of a conventional power converter. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following embodiments, components having similar functions will be given the same reference numerals and descriptions thereof will be omitted as appropriate.

[0012] Referring to FIG. 1, a power converter 1 according to this embodiment is used as a charging device for charging a storage battery 3 (battery) mounted on a vehicle 2 such as an electric car.

[0013] 1(a), when the power supplied to the vehicle 2 from outside the vehicle is an alternating current (AC) voltage such as a commercial power supply, the power converter 1 is mounted on the vehicle 2 together with a power factor correction (PFC) circuit 4. The PFC 4 converts the AC voltage supplied to the vehicle 2 into a direct current (DC) voltage, and the power converter 1 converts the DC voltage converted by the PFC 4 into a desired output voltage to charge the storage battery 3.

[0014] 1(b), when the power supplied from outside the vehicle to the vehicle 2 is a DC voltage, the power converter 1 is installed in a facility outside the vehicle 2, such as a charging station, together with a power factor correction (PFC) circuit 4. The PFC 4 converts the AC voltage supplied from a commercial power source or the like into a direct current (DC) voltage, and the power converter 1 converts the DC voltage converted by the PFC 4 into a desired DC voltage and supplies it to the vehicle 2 to charge the storage battery 3.

[0015] Referring to FIG. 2, the power converter 1 includes two full-bridge LLC converters (hereinafter referred to as LLC circuits 10). N ) and includes a rectifier 20 and a control unit 30.

[0016] LLC circuit 10 N The first switching leg (upper switch element QH N1 and lower switch element QL N1 ) and the second switching leg (upper switch element QH N2 and lower switch element QL N2 ) are connected in parallel. The subscript N indicates the number of stages (1 to 2). In the following description, when there is no distinction to be made based on the number of stages or switching legs, the subscript will be omitted as appropriate.

[0017] The upper switch element QH and the lower switch element QL are configured, for example, by field-effect transistors (MOSFETs: metal-oxide-semiconductor field-effect transistors). The upper switch element QH and the lower switch element QL have a body diode between the source and drain. The upper switch element QH and the lower switch element QL may be switching elements such as IGBTs (insulated gate bipolar transistors), GaN (gallium nitride), and SiC (silicon carbide) devices.

[0018] The upper switch element QH connected to the positive terminal of the DC voltage Vin is the upper arm of the switching leg, and the lower switch element QL connected to the negative terminal of the DC voltage Vin is the lower arm of the switching leg.

[0019] LLC circuit 10 N is the output point of the first switching leg (upper switch element QH N1 and lower switch element QL N1 The LLC circuit 10 includes a resonant inductor Lr having one end connected to the output point of the second switching leg (the connection point of the upper switch element QH N2 and lower switch element QL N2 The resistors are connected in series between the resistors (connection point with the resistor).

[0020] The secondary winding N2 is connected in series to the transformer T of each of the two LLC circuits 101 and 102. Hereinafter, when distinguishing between the two LLC circuits 101 and 102, in which the secondary winding N2 of the transformer T is connected in series, they will be referred to as the first-stage LLC circuit 101 and the second-stage LLC circuit 102.

[0021] The rectifier 20 rectifies the AC current output from the series-connected secondary winding N2 and outputs it from the high-potential output terminal and the low-potential output terminal. The rectifier 20 can employ circuit methods such as center-tap rectification, bridge rectification, voltage-doubler rectification, or Cock-Walton rectification. The rectifier 20 can also employ synchronous rectification using FETs instead of diodes. The rectifier 20 may also include an output capacitor connected between the high-potential output terminal and the low-potential output terminal. In this case, the rectifier 20, together with the output capacitor Co, constitutes a rectifying and smoothing circuit.

[0022] The control unit 30 is a semiconductor device integrated on a substrate. N The drive signal SH that drives N1 , S.L. N1 , SHN2 , S.L. N2 Generates a drive signal SH N1 and drive signal SL N1 is the upper switch element QH of the first switching leg. N1 and lower switch element QL N1 The drive signal SH is a pulse signal (gate signal) that drives each of the N2 and drive signal SL N2 is the upper switch element QH of the second switching leg. N2 and lower switch element QL N2 are signals that drive the respective

[0023] As shown in FIG. 3, the control unit 30 drives the first-stage LLC circuit 101 and the second-stage LLC circuit 102 in a plurality of different drive modes (modes A to E) according to the output voltage command value Vcom.

[0024] A full-bridge LLC converter can halve the current flowing through the primary side of the transformer T compared to a half-bridge LLC converter, assuming the same power, but the voltage applied to the primary side of the transformer T is doubled. As a result, the frequency rises to lower the output voltage Vo, making it impossible to output a low output voltage Vo within the operating frequency range. Therefore, the control unit 30 switches the drive mode according to the output voltage command value Vcom, thereby expanding the output range of the output voltage Vo that can be output within the operating frequency range (in the direction of lower output voltage Vo).

[0025] When the output voltage command value Vcom is equal to or greater than the first threshold voltage Vth1, the control unit 30 operates in the A mode, and drives both the first-stage LLC circuit 101 and the second-stage LLC circuit 102 in normal operation.

[0026] In normal operation, as shown in FIG. 4(a), the drive signal SH N1 , S.L. N2 and drive signal SL N1 , SH N2 and are complementary signals with a duty cycle of 50%. In normal operation, the upper switch element QH of the first switching leg N1and the lower switch element QL of the second switching leg N2 and the lower switching element QL of the first switching leg N1 and the upper switch element QH of the second switching leg N2 The power converter 1 operates in a series connection manner with the first stage LLC circuit 101 and the second stage LLC circuit 102 both switching in normal operation. Figure 4(b) shows the operation of each switch element (QH N1 , Q.L. N1 QH N2 , Q.L. N2 ) is the current waveform flowing through

[0027] In normal operation, the control unit 30 controls the frequency of the drive signal SH N1 , S.L. N1 , SH N2 , S.L. N2 By increasing the switching frequency, the output voltage Vo is decreased, and by decreasing the switching frequency, the output voltage Vo is increased.

[0028] When the output voltage command value Vcom is equal to or greater than the second threshold voltage Vth2 and less than the first threshold voltage Vth1, the control unit 30 operates in mode B, driving the first-stage LLC circuit 101 in normal operation and the second-stage LLC circuit 102 in PDM (pulse density modulation) operation. In mode B, the first-stage LLC circuit 101 may be operated in PDM operation and the second-stage LLC circuit 102 in normal operation.

[0029] The PDM operation is performed by applying the drive signal SH N1 and drive signal SL N1 and are complementary signals with a duty of 25%:75%, and the drive signal SH N2 and drive signal SL N2 and are complementary signals with a phase difference of 180° and a duty cycle of 25%:75%. In PDM operation, one cycle is twice that of normal operation, and the switching per unit time is half that of normal operation. In PDM operation, the upper switch element QH of the first switching leg N1 and lower switch element QLN1 The lower switching element QL of the second switching leg operates in a complementary manner with a duty of 25%:75%. N2 and upper switch element QH N2 The power converter 1 operates in a series connection, with the first stage LLC circuit 101 in normal operation and the second stage LLC circuit 102 in PDM operation, performing complementary operation with a phase difference of 180 deg and a duty of 25%:75%. Figure 5(b) shows the operation of each switch element (QH N1 , Q.L. N1 , Q.H. N2 , Q.L. N2 ) is the current waveform flowing through

[0030] In the PDM operation, the control unit 30 controls the frequency of the drive signal SH N1 , S.L. N1 , SH N2 , S.L. N2 By increasing the switching frequency, the output voltage Vo is decreased, and by decreasing the switching frequency, the output voltage Vo is increased.

[0031] As mentioned above, in PDM operation, the switching is half that of normal operation. Therefore, when driven at the same switching frequency, the output voltage Vo in B mode will be lower than the output voltage Vo in A mode.

[0032] When the output voltage command value Vcom is equal to or greater than the third threshold voltage Vth3 and less than the second threshold voltage Vth2, the control unit 30 operates in mode C, driving the first-stage LLC circuit 101 in normal operation and the second-stage LLC circuit 102 in always-on operation. In mode C, the first-stage LLC circuit 101 may be operated in always-on operation and the second-stage LLC circuit 102 in normal operation.

[0033] The always-on operation is performed by driving the drive signal SH N1 and drive signal SH N2 and are always at a low level, and the drive signal SL N1 and drive signal SL N2As shown in FIG. 7(a), the upper switch element QH N1 and the upper switching element QH of the second switching leg N2 The lower switch element QL of the first switching leg is always in the OFF state. N1 and the lower switching element QL of the second switching leg N2 The power converter 1 operates independently, with only the first-stage LLC circuit 101 switching in normal operation. FIG. 6(b) shows the state of each switch element (QH N1 , Q.L. N1 QH N2 , Q.L. N2 ) is the current waveform flowing through

[0034] The normally-on operation is achieved by the upper switch element QH of the first switching leg. N1 and the upper switching element QH of the second switching leg N2 and the lower switch element QL of the first switching leg is always in the ON state. N1 and the lower switching element QL of the second switching leg N2 However, in this case, the upper switch element QH of the first switching leg may be always in the OFF state. N1 and the upper switching element QH of the second switching leg N2 A separate voltage must be provided to keep the transistors in a constantly on state.

[0035] Lower switch element QL of the first switching leg N1 and the lower switching element QL of the second switching leg N2 By keeping these in a constantly on state, a series resonant circuit of resonant inductor Lr and resonant capacitor Cr is formed in second-stage LLC circuit 102, as shown in Fig. 7(b). The impedance Z of the series resonant circuit of resonant inductor Lr and resonant capacitor Cr is given by the following equation (1). In equation (1), ω is an angular frequency, and is expressed as ω=2πf using frequency f.

[0036]

number

[0037] When the angular frequency ω is ωr shown in the following equation (2), the impedance Z becomes zero as shown in the following equation (3).

[0038]

number

[0039]

number

[0040] The angular frequency ωr at which the impedance Z becomes zero is called the resonant angular frequency, and the resonant frequency fr is fr = ωr / 2π. As shown in Figure 8, the impedance Z becomes larger as the switching frequency moves away from the resonant frequency fr.

[0041] Since the impedance Z changes with frequency, the impedance also changes when viewed from the secondary side of the transformer T, and as shown in Figure 7(c), the second-stage transformer T can be represented as an equivalent circuit with variable impedance.

[0042] In particular, at the resonant frequency fr where the impedance Z becomes zero, the second-stage transformer T is short-circuited on the primary side, and the impedance on the secondary side also becomes zero, as shown in Figure 7(d). In other words, the second-stage transformer T is equivalent to the secondary winding N2 being short-circuited.

[0043] Therefore, the first-stage LLC circuit 101 performs switching operation near the most efficient resonant frequency fr, and the second-stage LLC circuit 102 forms a series resonant circuit with a resonant inductor Lr and a resonant capacitor Cr. Then, as shown in Fig. 7(d), the second stage can be regarded as short-circuited, and the power converter 1 can be regarded as consisting only of the first-stage LLC circuit 101. In other words, it is possible to switch between a series-connected operation in which the first-stage LLC circuit 101 and the second-stage LLC circuit 102 perform switching operation, and an independent operation in which only the first-stage LLC circuit 101 performs switching operation, without providing a selector switch on the secondary side.

[0044] As described above, the C mode is a standalone operation in which only the first-stage LLC circuit 101 performs switching operation. Therefore, when driven at the same switching frequency, the output voltage Vo in the C mode is lower than the output voltage Vo in the B mode.

[0045] When the output voltage command value Vcom is equal to or greater than the fourth threshold voltage Vth4 and less than the third threshold voltage Vth3, the control unit 30 operates in the D mode, and drives both the first-stage LLC circuit 101 and the second-stage LLC circuit 102 in PDM operation. When driven at the same switching frequency, the output voltage Vo in the D mode is lower than the output voltage Vo in the C mode.

[0046] When the output voltage command value Vcom is less than the fourth threshold voltage Vth4, the control unit 30 drives the first-stage LLC circuit 101 in PDM operation and the second-stage LLC circuit 102 in always-on operation as the E mode. In the E mode, the first-stage LLC circuit 101 may be driven in always-on operation and the second-stage LLC circuit 102 in PDM operation. When driven at the same switching frequency, the output voltage Vo in the E mode is lower than the output voltage Vo in the D mode.

[0047] FIG. 9 shows an example of output characteristics between the switching frequency and the output voltage Vo in each driving mode (A mode to E mode). Referring to FIG. 9, the output voltage Vo at the same frequency decreases in the order from A mode to E mode. In the example shown in FIG. 9, when X1 to X2 (X1 < X2) sandwiching the resonance frequency fr are set as the operating frequency range of the switching frequency, the A mode cannot output an output voltage Vo lower than the first threshold voltage Vth1. By switching the driving mode, the power converter 1 can widen the output voltage Vo that can be output in the same operating frequency range to the lower voltage side than the first threshold voltage Vth1.

[0048] FIG. 10 shows a configuration example of the control unit 30 using the LLC-IC41. The control unit 30 includes a control circuit 40, a first-stage gate circuit 501, and a second-stage gate circuit 502.

[0049] The control circuit 40 includes an LLC-IC41, a shift register 42, a first selection circuit 43, a second selection circuit 44, and OR circuits OR1 to OR3. The LLC-IC41 is an existing integrated circuit that drives a half-bridge LLC converter and generates signals Ho and Lo corresponding to the driving signals SH N1 , SL N1 according to the output voltage command value Vcom. The signals Ho and Lo are input as clock signals CLK to the shift register 42 via the OR circuit OR1.

[0050] The shift register 42 outputs pulse signals Q0 to Q3 that sequentially become Hi level each time the clock signal CLK rises. The pulse signal Q0 is output from the control circuit 40 as a signal A1 corresponding to the driving signal SH N1 during PDM operation. The pulse signal Q2 is output from the control circuit 4 as a signal A2 corresponding to the driving signal SL N2 during PDM operation. The pulse signals Q1, Q2, and Q3 are output from the control circuit 40 as a signal A3 corresponding to the driving signal SL N1 during PDM operation via the OR circuit OR2. The pulse signals Q0, Q1, and Q3 are output from the control circuit 40 as a signal A3 corresponding to the driving signal SH N2is output from the control circuit 40 as a signal A4 corresponding to the above.

[0051] The first selection circuit 43 and the second selection circuit 44 are circuits that select a drive mode according to the output voltage command value Vcom. N When the first selector circuit 43 is driven in normal operation, the first selector circuit 43 outputs a high-level signal A5 N The second selection circuit 44 outputs a low-level signal A6 N The Nth stage LLC circuit 10 outputs N When the PDM operation is performed, the first selection circuit 43 selects a low-level signal A5 N The second selection circuit 44 outputs a low-level signal A6 N The Nth stage LLC circuit 10 outputs N When the first selection circuit 43 is driven in a constantly ON operation, the second selection circuit 44 outputs a high-level signal A6 N Output.

[0052] Gate circuit 50 N comprises OR circuits OR4 to OR7, AND circuits AND1 to AND6, NAND circuits NAND1 and NAND2, and NOT circuits NOT1 and NOT2.

[0053] Signal A6 N The output is the drive signal SH through the NOT circuit NOT1. N1 The output is input to one input terminal of the AND circuit AND5, and is output via the NOT circuit NOT2 as the drive signal SH N2 The signal A6 is input to one input terminal of the AND circuit AND6. N The output is the drive signal SL N1 The signal is input to one input terminal of the OR circuit OR6, and the output is the drive signal SL N2 The signal A6 is input to one input terminal of the OR circuit OR7. N When the driving signal SH is at a high level, as shown in FIG. N1 , SH N2 is always at a low level, and the drive signal SL N1 , S.L.N2 is always at Hi level, and always-on operation is selected.

[0054] The signal A1 is input to one input terminal of the OR circuit OR4, and the output of the OR circuit OR4 is the drive signal SH. N1 The other input terminal of the OR circuit OR4 receives the signals A2 and A5. N The output of the AND circuit AND1, which receives the inputs 1 and 2, is input.

[0055] The signal A2 is input to one input terminal of the OR circuit OR5, and the output of the OR circuit OR5 is the drive signal SL N2 The other input terminal of the OR circuit OR5 receives the signals A1 and A5. N The output of an AND circuit AND4, which receives as inputs the above signals, is input.

[0056] The signal A3 is input to one input terminal of the AND circuit AND4, and the output of the AND circuit AND4 is the drive signal SL N1 The other input terminal of the AND circuit AND3 receives the signals A4 and A5. N The output of the NAND circuit NAND1, which receives the inputs 1 and 2, is input.

[0057] The signal A4 is input to one input terminal of the AND circuit AND3, and the output of the AND circuit AND3 is the drive signal SH N2 The other input terminal of the AND circuit AND3 receives the signals A4 and A5. N The output of the NAND circuit NAND1, which receives the inputs 1 and 2, is input.

[0058] Therefore, signal A5 N is at Hi level and signal A6 N When is at a low level, the normal operation drive signal SH N1 , S.L. N2 , S.L. N1 , SH N2is output, and normal operation is selected. Signal A5 N is at a low level, and signal A6 N When is at a low level, the drive signal SH of the PDM operation, as shown in Fig. 5(a), N1 , S.L. N2 , S.L. N1 , SH N2 is output and PDM operation is selected.

[0059] As described above, the power converter 1 is configured to switch between five drive modes with different output characteristics, but some of the drive modes may be omitted. For example, by setting the third threshold voltage Vth3 and the fourth threshold voltage Vth4 to the same value, the D mode can be omitted.

[0060] As shown in FIG. 11, the LLC circuit 10 N The number of stages N may be 3 or more. For example, the LLC circuit 10 N When there are three stages, up to nine drive modes with different output characteristics can be set by combining normal operation, PDM operation, and always-on operation.

[0061] LLC circuit 10 N As shown in FIG. 12, an LLC circuit 10a compatible with HVDC (High Voltage Direct Current) input is N LLC circuit 10a N The first switching leg (upper switch element QH N1 and lower switch element QL N1 ) and the second switching leg (upper switch element QH N2 and lower switch element QL N2 ) are connected in series. Capacitors Cin1 and Cin2 are connected in series between the positive and negative poles of a DC voltage Vin. The first switching leg is connected in parallel with capacitor Cin1, and the second switching leg is connected in parallel with capacitor Cin2.

[0062] (summary) (1) The power converters 1 and 1a according to the embodiments of the present invention are full-bridge LLC converters (LLC circuits 10 N ) to convert a DC voltage Vin into an output voltage Vo. The full-bridge LLC converter has a first switching leg and a second switching leg, each including an upper switch element QH and a lower switch element QL connected in series. The full-bridge LLC converter has the first switching leg and the second switching leg connected between the positive and negative poles of the DC voltage Vin. The full-bridge LLC converter has a series resonant circuit including a resonant inductor Lr, a primary winding N1 of a transformer T, and a resonant capacitor Cr connected to the output point of the first switching leg (upper switch element QH N1 and lower switch element QL N1 ) and the output point of the second switching leg (upper switch element QH N2 and lower switch element QL N2 The full-bridge LLC converter converts a DC voltage Vin into an output voltage Vo through the switching operations of a first switching leg and a second switching leg. The power converter 1, 1a includes a plurality of full-bridge LLC converters. The power converter 1, 1a includes a plurality of full-bridge LLC converters, with secondary windings N2 of the transformers T of the full-bridge LLC converters connected in series. The power converter 1, 1a includes a control unit 30 that drives each of the plurality of full-bridge LLC converters by switching between a plurality of drive modes with different output characteristics in accordance with an output voltage command value Vcom.

[0063] According to the power converters 1, 1a, 1b, 1c, and 1d described in (1) above, the range of output voltage Vo that can be output within the operating frequency range can be widened without providing a changeover switch on the output side, so that the operating frequency range can be set to a narrow range near the resonant frequency, thereby improving the conversion efficiency.

[0064] (2) In the power converter 1, 1a described in (1) above, the control unit 30 has a first operation (normal operation) and a second operation (always-on operation) as driving operations for driving the full-bridge LLC converter. The first operation is performed by turning on the upper switching element QH of the first switching leg.N1 and the lower switch element QL of the second switching leg N2 and the lower switching element QL of the first switching leg N1 and the upper switch element QH of the second switching leg N2 The second operation is to operate the upper switching element QH of the first switching leg and the upper switching element QH of the second switching leg in a complementary manner with a duty of 50%. N1 , Q.H. N2 and the lower switching element QL of the first switching leg and the second switching leg. N1 , Q.L. N2 One of the full-bridge LLC converters is always on, and the other is always off. The multiple drive modes include a first mode (A mode) in which all of the multiple full-bridge LLC converters are driven in a first operation. The multiple drive modes include a second mode (C mode, E mode) in which one or more of the multiple full-bridge LLC converters are driven in a second operation.

[0065] According to the power converters 1 and 1a described in (2) above, the operating frequency at low voltage output can be suppressed by switching from the first mode to the second mode.

[0066] (3) In the power converter 1, 1a described in (1) or (2) above, the control unit 30 has a first operation (normal operation) and a third operation (PDM operation) as driving operations for driving the full-bridge LLC converter. The first operation is a first operation (normal operation) and a third operation (PDM operation) as driving operations for driving the upper switching element QH of the first switching leg. N1 and the lower switch element QL of the second switching leg N2 and the lower switching element QL of the first switching leg N1 and the upper switch element QH of the second switching leg N2 The third operation is to operate the upper switch element QH of the first switching leg in a complementary manner with a duty of 50%. N1 and lower switch element QL N1 and operate complementary with a duty of 25%:75%, and the lower switch element QL of the second switching leg N2 and upper switch element QH N2and operate in a complementary manner with a phase difference of 180 deg and a duty of 25%:75%. The multiple drive modes include a first mode (mode A) in which all of the multiple full-bridge LLC converters are driven in a first operation. The multiple drive modes include a third mode (mode B, mode D, mode E) in which one or more of the multiple full-bridge LLC converters are driven in a third operation.

[0067] According to the power converters 1 and 1a described in (3) above, the operating frequency at low voltage output can be suppressed by switching from the first mode to the third mode.

[0068] (4) In the power converters 1 and 1a described in (1) to (3) above, the control unit 30 has three drive operations for driving the full-bridge LLC converter: a first operation (normal operation), a second operation (always-on operation), and a third operation (PDM operation). The first operation is performed by switching the upper switching element QH of the first switching leg to the ON state. N1 and the lower switch element QL of the second switching leg N2 and the lower switching element QL of the first switching leg N1 and the upper switch element QH of the second switching leg N2 The second operation is to operate the upper switching element QH of the first switching leg and the upper switching element QH of the second switching leg in a complementary manner with a duty of 50%. N1 , Q.H. N2 and the lower switching element QL of the first switching leg and the second switching leg. N1 , Q.L. N2 The third operation is to keep one of the upper switch element QH of the first switching leg in a normally ON state and the other in a normally OFF state. N1 and lower switch element QL N1 and operate complementary with a duty of 25%:75%, and the lower switch element QL of the second switching leg N2 and upper switch element QH N2and operate in a complementary manner with a phase difference of 180 deg and a duty of 25%:75%. The multiple drive modes include a first mode (A mode) in which all of the multiple full-bridge LLC converters are driven in a first operation. The multiple drive modes include a second mode (C mode, E mode) in which one or more of the multiple full-bridge LLC converters are driven in a second operation. The multiple drive modes include a third mode (B mode, D mode, E mode) in which one or more of the multiple full-bridge LLC converters are driven in a third operation.

[0069] According to the power converters 1 and 1a described in (4) above, the operating frequency at low voltage output can be suppressed by switching from the first mode to the second mode or the third mode.

[0070] (5) The control method of the power converter 1, 1a according to each embodiment of the present invention is a full-bridge LLC converter (LLC circuit 10 N The full-bridge LLC converter has a first switching leg and a second switching leg, each including an upper switching element QH and a lower switching element QL connected in series. The full-bridge LLC converter has the first switching leg and the second switching leg connected between the positive and negative poles of a DC voltage Vin. The full-bridge LLC converter has a series resonant circuit including a resonant inductor Lr, a primary winding N1 of a transformer T, and a resonant capacitor Cr, which is connected to the output point of the first switching leg (upper switching element QH N1 and lower switch element QL N1 ) and the output point of the second switching leg (upper switch element QH N2 and lower switch element QL N2The full-bridge LLC converter converts a DC voltage Vin into an output voltage Vo through the switching operations of a first switching leg and a second switching leg. The power converter 1, 1a includes a plurality of full-bridge LLC converters. The power converter 1, 1a has secondary windings N2 of the transformers T of the plurality of full-bridge LLC converters connected in series. The control unit 30 drives each of the plurality of full-bridge LLC converters by switching between a plurality of drive modes with different output characteristics in accordance with an output voltage command value Vcom.

[0071] According to the control method of the power converters 1, 1a described in (5) above, the range of output voltage Vo that can be output within the operating frequency range can be widened without providing a changeover switch on the output side, so that the operating frequency range can be set to a narrow range near the resonant frequency, thereby improving the conversion efficiency.

[0072] (6) A charging device for charging the storage battery 3, which charges the storage battery 3 with the output voltage Vo of the power converters 1 and 1a described above in (1) to (4).

[0073] According to the charging device described in (6) above, the range of the output voltage Vo that can be output within the operating frequency range can be widened, so that the operating frequency range can be set to a narrow range near the resonance frequency, and the storage battery 3 can be charged efficiently.

[0074] (7) A vehicle (2) equipped with a storage battery (3) includes the power converters (1, 1a, 1b, 1c, 1d) described above in (1) to (4) that convert externally supplied power into an output voltage Vo that charges the storage battery (3).

[0075] According to the vehicle 2 described in (7) above, the range of the output voltage Vo that can be output within the operating frequency range can be widened, so that the operating frequency range can be set to a narrow range near the resonant frequency, and the on-board storage battery 3 can be efficiently charged.

[0076] Although the present invention has been described above with reference to specific embodiments, it goes without saying that the above embodiments are merely examples and can be modified and implemented without departing from the spirit of the present invention. [Explanation of symbols]

[0077] 1, 1a power converter 2 vehicles 3. Storage battery 10, 10c LLC 20 rectifier 30 Control Unit 40 Control circuit 41 LLC-IC 42 Shift Register 43 First selection circuit 44 Second selection circuit 50 N Gate circuit Cr Resonant Capacitor Lr Resonant inductor QH, QH N1 , Q.H. N2 Upper switch element QL, QL N1 , Q.L. N2 Lower switch element T transformer

Claims

1. a power converter including a first switching leg and a second switching leg each including an upper switch element and a lower switch element connected in series, the first switching leg and the second switching leg being connected between a positive pole and a negative pole of a DC voltage, and a series resonant circuit including a resonant inductor, a primary winding of a transformer, and a resonant capacitor being connected between an output point of the first switching leg and an output point of the second switching leg, the power converter converting the DC voltage into an output voltage by switching operations of the first switching leg and the second switching leg; a plurality of the full-bridge LLC converters; secondary windings of the transformers of the plurality of full-bridge LLC converters are connected in series; a control unit that drives each of the plurality of full-bridge LLC converters by switching between a plurality of drive modes with different output characteristics in accordance with an output voltage command value.

2. The control unit performs a driving operation to drive the full-bridge LLC converter by: a first operation of causing the upper switch element of the first switching leg and the lower switch element of the second switching leg, and the lower switch element of the first switching leg and the upper switch element of the second switching leg to perform complementary operations at a duty of 50%; a second operation of always keeping one of the upper switch elements of the first switching leg and the second switching leg and the lower switch elements of the first switching leg and the second switching leg in an on state and always keeping the other in an off state, The plurality of driving modes include a first mode in which all of the plurality of full-bridge LLC converters are driven in the first operation mode; a second mode in which one or more of the plurality of full-bridge LLC converters are driven in a second operation mode.

3. The control unit performs a driving operation to drive the full-bridge LLC converter by: a first operation of causing the upper switch element of the first switching leg and the lower switch element of the second switching leg, and the lower switch element of the first switching leg and the upper switch element of the second switching leg to perform complementary operations at a duty of 50%; a third operation of causing the upper switch element and the lower switch element of the first switching leg to perform a complementary operation with a duty of 25%:75% and causing the lower switch element and the upper switch element of the second switching leg to perform a complementary operation with a duty of 25%:75% with a phase difference of 180 deg, The plurality of driving modes include a first mode in which all of the plurality of full-bridge LLC converters are driven in the first operation mode; a third mode in which one or more of the plurality of full-bridge LLC converters are driven in a third operation mode.

4. The control unit performs a driving operation to drive the full-bridge LLC converter by: a first operation of causing the upper switch element of the first switching leg and the lower switch element of the second switching leg, and the lower switch element of the first switching leg and the upper switch element of the second switching leg to perform complementary operations at a duty of 50%; a second operation of always keeping one of the upper switch elements of the first switching leg and the second switching leg and the lower switch elements of the first switching leg and the second switching leg in an on state and always keeping the other in an off state; a third operation of causing the upper switch element and the lower switch element of the first switching leg to perform a complementary operation with a duty of 25%:75% and causing the lower switch element and the upper switch element of the second switching leg to perform a complementary operation with a duty of 25%:75% with a phase difference of 180 deg, The plurality of driving modes include a first mode in which all of the plurality of full-bridge LLC converters are driven in the first operation mode; a second mode in which one or more of the plurality of full-bridge LLC converters are driven in a second operation mode; a third mode in which one or more of the plurality of full-bridge LLC converters are driven in a third operation mode.

5. a control method for a power converter that converts a DC voltage into an output voltage by switching operations of the first switching leg and the second switching leg using a full-bridge LLC converter, the full-bridge LLC converter having a first switching leg and a second switching leg each including an upper switch element and a lower switch element connected in series, the first switching leg and the second switching leg being connected between a positive pole and a negative pole of a DC voltage, and a series resonant circuit including a resonant inductor, a primary winding of a transformer, and a resonant capacitor being connected between an output point of the first switching leg and an output point of the second switching leg, the method comprising: a plurality of the full-bridge LLC converters; secondary windings of the transformers of the plurality of full-bridge LLC converters are connected in series; A control method for a power converter, which drives each of the plurality of full-bridge LLC converters by switching between a plurality of drive modes with different output characteristics in accordance with an output voltage command value.

6. A charging device for charging a storage battery, A charging device comprising the power converter according to claim 1 , wherein the DC voltage is converted into the output voltage for charging the storage battery.

7. A vehicle equipped with a storage battery, A vehicle comprising the power converter according to claim 1 , wherein the power converter converts power supplied from outside the vehicle into the output voltage for charging the storage battery.

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