Power converter, method for controlling power converter, charging device, and vehicle

Abstract

In a power converter (1), secondary windings (N2) of transformers (T) of a plurality of full-bridge LLC converters are connected in series. In the power converter (1), each of the plurality of full-bridge LLC converters is provided with a control unit (30) that switches and drives a plurality of drive modes having different output characteristics in accordance with an output voltage command value (Vcom).

Description

Power converter, power converter control method, charging device, and vehicle

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

[0002] Charging devices for charging storage batteries mounted on 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 in which they are efficient, but outside of that range, their efficiency deteriorates significantly.

[0003] JP 2012-249375 A

[0004] By providing multiple LLC circuits and switching between parallel and series connection of their 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 varies depending on the switching frequency. FIG. 14 shows an example of the output characteristics of the switching frequency and the output voltage Vo, with the frequency increasing significantly at low voltage outputs. The output characteristics of two LLC circuits 200 differ when connected in parallel and when connected in series. If 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) when connected in series, and V2 to V3 (V2 > V3) when connected in parallel. By using a selector switch SW to switch between parallel and series connection when 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 of X1 to X2.

[0006] However, because the selector switch SW must be installed on the output side of the LLC circuit 200 to which the storage battery is connected, a surge current with a large amount of energy may be generated due to a circuit failure, such as a short circuit of the storage battery. Therefore, the selector switch SW must be a mechanical relay, and a semiconductor switch cannot be used. Mechanical relays are expensive and large, and cannot be replaced with inexpensive, small semiconductor switches.

[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 for the operating frequency range without providing a switching switch on the output side.

[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. 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 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.

[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.

[0010] 1 is a diagram showing an example of use of a power converter as a charging device; FIG. 2 is a diagram showing an example of the configuration of a power converter; FIG. 3 is a diagram showing an example of a drive mode of a control unit; FIG. 4 is a diagram showing normal operation of an LLC circuit; FIG. 5 is a diagram showing PDM operation of an LLC circuit; FIG. 6 is a diagram showing always-on operation of an LLC circuit; FIG. 7 is a diagram showing a power converter in standalone operation; FIG. 8 is a diagram showing changes in impedance; FIG. 9 is a diagram showing example output characteristics of each drive mode; FIG. 10 is a diagram showing an example of the configuration of a gate signal generation circuit; FIG. 11 is a diagram showing an example of the configuration of a power converter with an N-stage configuration; FIG. 12 is a diagram showing an example of the configuration of an LLC circuit compatible with HVDC input; FIG. 13 is a diagram showing an example of the configuration of a conventional power converter; FIG. 14 is a diagram showing example output characteristics of a conventional power converter.

[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 mounted on a vehicle 2 such as an electric vehicle.

[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, a power converter 1 is mounted on the vehicle 2 together with a power factor correction circuit (PFC) 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 PFC (power factor correction circuit) 4. The PFC 4 converts 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 the lower switch element QL Ｎ１ ) and the second switching leg (upper switch element QH Ｎ２ and the 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), or SiC (silicon carbide) devices.

[0018] The upper switch element QH connected to the positive electrode of the DC voltage Vin is the upper arm of the switching leg, and the lower switch element QL connected to the negative electrode 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 the lower switch element QL Ｎ１ The LLC circuit 10 includes a resonant inductor Lr having one end connected to a connection point of the upper switch element QH and the other end of the resonant inductor Lr. The LLC circuit 10 includes a transformer T and a resonant capacitor Cr. The primary winding N1 of the transformer T and the resonant capacitor Cr are connected to the other end of the resonant inductor Lr and the output point of the second switching leg (the connection point of the upper switch element QH). Ｎ２ and the lower switch element QL Ｎ２ The inverter is connected in series between the inverter and the connection point.

[0020] Two LLC circuits 10 １ , 10 ２ The secondary windings N2 of the transformers T are connected in series. １ , 10 ２ When distinguishing, the first stage LLC circuit 10 １ , second stage LLC circuit 10 ２ It is called.

[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 a circuit method 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 Ｎ１ , S.L. Ｎ１ , S.H. Ｎ２ , S.L. Ｎ２ The drive signal SH Ｎ１ and drive signal SL Ｎ１is the upper switch element QH of the first switching leg Ｎ１ and the lower switch element QL Ｎ１ The driving 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 the lower switch element QL Ｎ２ are signals that drive the respective

[0023] As shown in FIG. 3, the control unit 30 controls the first-stage LLC circuit 10 in a plurality of different drive modes (modes A to E) according to the output voltage command value Vcom. １ and the second stage LLC circuit 10 ２ Drives.

[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, and a low output voltage Vo cannot be output 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 sets the A mode and controls the first-stage LLC circuit 10 １ and the second stage LLC circuit 10 ２ Both of these operate in normal operation.

[0026] In normal operation, as shown in FIG. Ｎ１ , S.L. Ｎ２ and drive signal SL Ｎ１ , S.H. Ｎ２ and are complementary signals with a duty cycle of 50%. In normal operation, the upper switch element QH of the first switching leg Ｎ１ and the lower switch element QL of the second switching leg Ｎ２ and the lower switch element QL of the first switching leg. Ｎ１and the upper switch element QH of the second switching leg Ｎ２ The power converter 1 includes a first stage LLC circuit 10 １ and the second stage LLC circuit 10 ２ In normal operation, all of these are switched in series connection. 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 , S.H. 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 sets the first stage LLC circuit 10 in the B mode. １ In normal operation, the second stage LLC circuit 10 ２ In B mode, the first stage LLC circuit 10 １ In PDM operation, the second stage LLC circuit 10 ２ may be driven in normal operation.

[0029] As shown in FIG. 5(a), the PDM operation is performed by driving 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 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 the lower switch element QL Ｎ１The lower switching element QL of the second switching leg operates in a complementary manner with a duty ratio of 25%:75%. Ｎ２ and upper switch element QH Ｎ２ The power converter 1 operates in a complementary manner with a phase difference of 180 deg and a duty of 25%:75%. １ is normal operation, and the second stage LLC circuit 10 ２ In PDM operation, 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 , S.H. 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 described 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 is 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 sets the first stage LLC circuit 10 in the C mode. １ In normal operation, the second stage LLC circuit 10 ２ In the C mode, the first stage LLC circuit 10 １ is always on, and the second stage LLC circuit 10 ２ may be driven 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. 7A, the upper switch element QH of the first switching leg is always at a high level. Ｎ１ and the upper switch 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 switch element QL of the second switching leg Ｎ２ The power converter 1 includes a first-stage LLC circuit 10 １ In the LLC circuit 10, only the １ is normal operation, LLC circuit 10 ２ In always-on operation, LLC circuit 10 ２ 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 performed by the upper switch element QH of the first switching leg. Ｎ１ and the upper switch element QH of the second switching leg Ｎ２ and the lower switch element QL of the first switching leg are always in the ON state. Ｎ１ and the lower switch 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 switch 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 switch element QL of the second switching leg Ｎ２ By keeping the second stage LLC circuit 10 in a constantly on state, ２ 7B, a series resonant circuit of a resonant inductor Lr and a resonant capacitor Cr is formed. The impedance Z of the series resonant circuit of the resonant inductor Lr and the resonant capacitor Cr is expressed by the following equation (1). In equation (1), ω is an angular frequency, and is expressed as ω=2πf using frequency f.

[0036]

[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]

[0039]

[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 FIG. 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 is 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 Fig. 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 10 １ The second stage LLC circuit 10 is switched at the most efficient resonant frequency fr. ２ 7D, the second stage is considered to be short-circuited, and the power converter 1 operates in the first stage LLC circuit 10. １ That is, the first stage LLC circuit 10 １ and the second stage LLC circuit 10 ２ and a series connection operation for switching the first stage LLC circuit 10 １ This allows switching between a single operation in which only the first and second inverters are switched on and off without providing a changeover switch on the secondary side.

[0044] In the C mode, as described above, the first stage LLC circuit 10 １ 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 sets the D mode and controls the first-stage LLC circuit 10 １ and the second stage LLC circuit 10 ２ 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 sets the E mode and controls the first-stage LLC circuit 10 １ In PDM operation, the second stage LLC circuit 10 ２ In the E mode, the first stage LLC circuit 10 １ is always on, and the second stage LLC circuit 10 ２ 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 drive mode (mode A to mode E). Referring to FIG. 9, the output voltage Vo at the same frequency decreases in the order from mode A to mode E. In the example shown in FIG. 9, when the operating frequency range of the switching frequency is set to X1 to X2 (X1<X2) sandwiching the resonant frequency fr, mode A cannot output an output voltage Vo lower than the first threshold voltage Vth1. By switching the drive mode, the power converter 1 can output an output voltage Vo within the same operating frequency range to a lower voltage side than the first threshold voltage Vth1.

[0048] 10 shows an example of the configuration of the control unit 30 using the LLC-IC 41. The control unit 30 includes a control circuit 40 and a first-stage gate circuit 50. １and the second stage gate circuit 50 ２ And, it is equipped with.

[0049] The control circuit 40 includes an LLC-IC 41, a shift register 42, a first selection circuit 43, a second selection circuit 44, and OR circuits OR1 to OR3. The LLC-IC 41 is an existing integrated circuit that drives a half-bridge LLC converter, and generates a drive signal SH for normal operation in response to an output voltage command value Vcom. Ｎ１ , S.L. Ｎ１ The signals Ho and Lo are input as a clock signal CLK to the shift register 42 via an OR circuit OR1.

[0050] The shift register 42 outputs pulse signals Q0 to Q3 that sequentially go to a high level at each rising edge of the clock signal CLK. The pulse signal Q0 is a driving signal SH during PDM operation. Ｎ１ The pulse signal Q2 is output from the control circuit 40 as a signal A1 corresponding to the drive signal SL during PDM operation. Ｎ２ The pulse signals Q1, Q2, and Q3 are output from the control circuit 40 as a signal A2 corresponding to the drive signal SL during PDM operation via an OR circuit OR2. Ｎ１ The pulse signals Q0, Q1, and Q3 are output from the control circuit 40 as a signal A3 corresponding to the drive signal SH during PDM operation via an OR circuit OR3. Ｎ２ is output from the control circuit 40 as a signal A4 corresponding to

[0051] The first selection circuit 43 and the second selection circuit 44 are circuits that select a drive mode in accordance with the output voltage command value Vcom. Ｎ When the first selector circuit 43 is driven in normal operation, the first selector circuit 43 selects 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 ＮWhen the first selection circuit 43 is driven in a constantly ON state, 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 is output as the drive signal SH via the NOT circuit NOT1. Ｎ１ The signal is input to one input terminal of the AND circuit AND5, and the output 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 , S.H. 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 an AND circuit AND1, which receives the above and the above inputs, 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 the above and 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 a NAND circuit NAND1 having the inputs of

[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 a NAND circuit NAND1 having the inputs of

[0058] Therefore, signal A5 Ｎ is at a high level, and signal A6 Ｎ When the signal S is at a low level, the normal operation drive signal SH Ｎ１ , S.L. Ｎ２ , S.L. Ｎ１ , S.H. Ｎ２ is output, and normal operation is selected. Ｎ is at a low level, and signal A6 Ｎ When the driving signal SH of the PDM operation is at a low level, as shown in FIG. Ｎ１ , S.L. Ｎ２ , S.L. Ｎ１ , S.H. 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 three or more. For example, ＮWhen the number of stages is three, a maximum of nine driving 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 is the first switching leg (upper switch element QH Ｎ１ and the lower switch element QL Ｎ１ ) and the second switching leg (upper switch element QH Ｎ２ and the 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 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 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 (the upper switching element QH Ｎ１ and the lower switch element QL Ｎ１ ) and the output point of the second switching leg (upper switch element QH Ｎ２ and the lower switch element QL Ｎ２The full-bridge LLC converter converts a DC voltage Vin into an output voltage Vo through switching operations of a first switching leg and a second switching leg. The power converter 1, 1a includes multiple full-bridge LLC converters. The power converter 1, 1a includes a control unit 30 that drives each of the multiple full-bridge LLC converters by switching between multiple 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 switch 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 switch 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 (mode A) in which all of the multiple full-bridge LLC converters are driven in a first operation. The multiple drive modes include a second mode (mode C, mode E) 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 or 1a described in (1) or (2) above, the control unit 30 includes a first operation (normal operation) and a third operation (PDM operation) as drive operations for driving the full-bridge LLC converter. The first operation is a PDM operation 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 switch 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 the lower switch element QL Ｎ１ and the lower switch element QL of the second switching leg are operated in a complementary manner with a duty of 25%:75%. Ｎ２ and upper switch element QH Ｎ２ and are operated in a complementary manner with a phase difference of 180° and a duty cycle 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 a first operation (normal operation), a second operation (always-on operation), and a third operation (PDM operation) as driving operations for driving the full-bridge LLC converter. 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 switch element QL of the first switching leg. Ｎ１and 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 switch element QL of the first switching leg and the second switching leg. Ｎ１ , Q.L. Ｎ２ The third operation is to turn on one of the upper switch elements QH of the first switching leg and turn off the other. Ｎ１ and the lower switch element QL Ｎ１ and the lower switch element QL of the second switching leg are operated in a complementary manner with a duty of 25%:75%. Ｎ２ and upper switch element QH Ｎ２ and operate in a complementary manner with a phase difference of 180° and a duty cycle 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 second mode (mode C, mode E) 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 (mode B, mode D, mode E) 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 ＮThe 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 connected to the output point of the first switching leg (the upper switching element QH Ｎ１ and the lower switch element QL Ｎ１ ) and the output point of the second switching leg (upper switch element QH Ｎ２ and the lower switch element QL Ｎ２ The full-bridge LLC converter converts a DC voltage Vin into an output voltage Vo through switching operations of a first switching leg and a second switching leg. The power converter 1, 1a includes multiple full-bridge LLC converters. The power converter 1, 1a has secondary windings N2 of the transformers T of the multiple full-bridge LLC converters connected in series. The control unit 30 drives each of the multiple full-bridge LLC converters by switching between multiple 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 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 storage battery 3 can be charged efficiently.

[0074] (7) A vehicle (2) equipped with a storage battery (3) and including 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 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.

[0077] REFERENCE SIGNS LIST 1, 1a Power converter 2 Vehicle 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 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 the positive and negative poles 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, the power converter comprising: a plurality of the full-bridge LLC converters; secondary windings of the transformers of the plurality of full-bridge LLC converters being connected in series; and 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 power converter according to claim 1, wherein the control unit is provided with, as drive operations for driving the full-bridge LLC converter, a first operation in which 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, are caused to perform complementary operation at a duty of 50%, and a second operation in which 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 is always in an ON state and the other is always in an OFF state, and the plurality of drive modes include a first mode in which all of the plurality of full-bridge LLC converters are driven by the first operation, and a second mode in which one or more of the plurality of full-bridge LLC converters are driven by the second operation.

3. The power converter according to claim 1, wherein the control unit, as drive operations for driving the full-bridge LLC converter, comprises: a first operation in which 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, perform complementary operation at a duty of 50%; and a third operation in which the upper switch element and the lower switch element of the first switching leg perform complementary operation at a duty of 25%:75%, and the lower switch element and the upper switch element of the second switching leg perform complementary operation at a duty of 25%:75% with a phase difference of 180°, and wherein the plurality of drive modes include a first mode in which all of the plurality of full-bridge LLC converters are driven by the first operation, and a third mode in which one or more of the plurality of full-bridge LLC converters are driven by the third operation.

4. The control unit, as driving operations for driving the full-bridge LLC converter, comprises: 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 operate complementarily at a duty of 50%; a second operation of causing either the upper switch elements of the first switching leg and the second switching leg, or the lower switch elements of the first switching leg and the second switching leg, to be always in an on state and the other to be always in an off state; and a third operation of causing the upper switch element and the lower switch element of the first switching leg to operate complementarily at a duty of 25%:75%, and causing the lower switch element and the upper switch element of the second switching leg to operate complementarily at a duty of 25%:75% with a phase difference of 180 degrees, 2. The power converter according to claim 1, wherein the plurality of drive modes include: a first mode in which all of the plurality of full-bridge LLC converters are driven in the first operation; a second mode in which one or more of the plurality of full-bridge LLC converters are driven in the second operation; and a third mode in which one or more of the plurality of full-bridge LLC converters are driven in a third operation.

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 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 the positive and negative poles 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 control method for a power converter that converts the DC voltage into an output voltage by switching operations of the first switching leg and the second switching leg, the control method comprising: a plurality of the full-bridge LLC converters; secondary windings of the transformers of the plurality of full-bridge LLC converters being connected in series; and driving 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, comprising the power converter according to claim 1, which converts the DC voltage into the output voltage for charging the storage battery.

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

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