Method for controlling power conversion device, and power conversion device

Abstract

A power conversion device (1, 1A) comprises a first main circuit (11), a transformer (10), a second main circuit (12), a third main circuit (13), and a control unit (14). The first main circuit (11) has a first H-bridge circuit (40) and converts a first DC voltage (V1) to a first AC voltage (Vt1). The transformer (10) has a primary winding (T1) to which the first AC voltage (Vt1) is input, a first secondary winding (T2), and a second secondary winding (T3). The second main circuit (12) has at least one diode (D1, D2), is connected to the first secondary winding (T2), and outputs a second DC voltage (V2). The third main circuit (13) has a second H-bridge circuit (50), is connected to the second secondary winding (T3), and outputs a third DC voltage (V3). The control unit (14) controls a second phase difference (θ13) of a switching pattern between the two H-bridge circuits (40, 50) within a range in which zero-voltage switching is established.

Description

Control method for power conversion device and power conversion device

[0001] The present invention relates to a control method for a power conversion device and a power conversion device.

[0002] Patent Document 1 describes a triple active bridge (TAB) power conversion device having one input and two outputs. This power conversion device includes an input conversion circuit that converts DC power into predetermined AC power, a transformer having a primary winding connected to the output of the input conversion circuit and two secondary windings that convert and output the voltage of the AC power supplied to the primary winding, and two output conversion circuits connected to the two secondary windings, respectively.

[0003] Special Publication No. 2008-543271

[0004] In Patent Document 1, the phase difference between the phases of the AC voltage of the input conversion circuit and the AC voltage of the first secondary winding, and the phase difference between the phases of the AC voltage of the input conversion circuit and the AC voltage of the second secondary winding are controlled. Therefore, the input conversion circuit and the two output conversion circuits each have a switch, and the number of control variables increases. This increases the cost of the switches and their driver circuits in the power conversion device, and makes it difficult to efficiently achieve zero voltage switching.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to reduce the number of switches and control variables in a power conversion device having one input and two outputs, and to efficiently realize zero voltage switching.

[0006] A power conversion device according to one aspect of the present invention includes a first main circuit, a transformer, a second main circuit, a third main circuit, and a control unit. The first main circuit has a first H-bridge circuit and converts a first DC voltage into a first AC voltage. The transformer has a primary winding to which the first AC voltage is input, a first secondary winding, and a second secondary winding. The second main circuit has at least one diode connected to the first secondary winding and outputs a second DC voltage. The third main circuit has a second H-bridge circuit connected to the second secondary winding and outputs a third DC voltage. The control unit controls a first phase difference in a switching pattern between two ribs of each H-bridge circuit and a second phase difference in a switching pattern between the first H-bridge circuit and the second H-bridge circuit so that the second DC voltage and the third DC voltage each have a predetermined value. The control unit also controls the second phase difference within a range that establishes zero voltage switching.

[0007] According to the present invention, the number of switches and control variables in a power conversion device having one input and two outputs can be reduced, and zero voltage switching can be efficiently achieved.

[0008] FIG. 1 is a circuit diagram showing the configuration of a power conversion device according to a first embodiment. FIG. 2 is a timing chart showing an example of a switching pattern of the first H-bridge circuit of the first main circuit and the second H-bridge circuit of the third main circuit, and the associated waveforms of the first AC voltage and the third AC voltage in the power conversion device according to the first embodiment. FIG. 3 is a graph showing an example of a relationship between the control of the first DC voltage and the third DC voltage command value according to the second phase difference θ31 in the power conversion device according to the first embodiment. FIG. 4 is a schematic diagram assuming a state in which the switch current of the fifth switch Q1 flows in the negative direction when the fifth switch Q1 and the eighth switch Q4 are on and the sixth switch Q2 and the seventh switch Q3 are off in the power conversion device according to the first embodiment. FIG. 5 is a schematic diagram illustrating the state of the switch current flowing through the fifth switch Q1 and the eighth switch Q4 when the fifth switch Q1 is turned off while the switch current of the fifth switch Q1 flows in the negative direction as shown in FIG. 4. Fig. 6 is a schematic diagram illustrating the state of the switch currents flowing through the fifth switch Q1 and the sixth switch Q2 when the sixth switch Q2 is turned on from the state shown in Fig. 5 . Fig. 7 is a timing chart illustrating an example of the switch current and switching pattern of the first switch S1 and the fourth switch S4 when the second phase difference θ31 is controlled so that the first DC voltage V1 and the third DC voltage V3 are equal. Fig. 8 is a timing chart illustrating an example of the switch current and switching pattern of the fifth switch Q1 and the eighth switch Q4 when the second phase difference θ31 is controlled so that the first DC voltage V1 and the third DC voltage V3 are equal. Fig. 9 is a graph illustrating an example of the upper and lower limits of the third DC voltage command value with respect to the first DC voltage. Fig. 10 is a diagram illustrating the relationship between the second phase difference θ31 at which zero voltage switching is possible and the ratio V3 / V1 of the third DC voltage to the first DC voltage. Fig. 11 is a circuit diagram showing the configuration of a power conversion device according to the second embodiment. Fig. 12 is a time chart showing the waveform of the third AC voltage and the waveform of the second AC current flowing through the second secondary winding when the third DC voltage V3 is changed by controlling the second phase difference θ31 in the power conversion device according to the second embodiment.

[0009] The embodiments will be described with reference to the drawings. In the description of the drawings, the same parts are designated by the same reference numerals and the description thereof will be omitted.

[0010] First Embodiment The configuration of a power conversion device 1 according to a first embodiment will be described with reference to Fig. 1 . The power conversion device 1 is mounted on a vehicle such as an electric vehicle. The power conversion device 1 converts DC power of a first DC voltage V1 input from a DC power source 2 into two DC powers of a second DC voltage V2 and a third DC voltage V3 and outputs the converted DC powers. The DC power of the second DC voltage V2 is supplied to a first load 3, and the DC power of the third DC voltage V3 is supplied to a second load 4.

[0011] The DC power supply 2 is, for example, a rechargeable lithium-ion battery, and the first DC voltage V1 has a rated voltage of, for example, 360 V. The value of the first DC voltage V1 varies depending on the charge / discharge status of the DC power supply 2. The first load 3 is, for example, an on-board auxiliary device or a battery, and the second DC voltage V2 has a rated voltage of, for example, 14 V.

[0012] 1 , the second load 4 is a DC / AC inverter circuit, and the third DC voltage V3 is, for example, 360 V, the same as the first DC voltage V1, or a value close to that. The DC / AC inverter circuit serving as the second load 4 supplies AC power having a frequency of 50 Hz or 60 Hz and an effective voltage of 100 V or 200 V to the third load 5. In addition to the DC / AC inverter circuit, the second load 4 may also be a load such as a power steering device that is driven at a rated voltage of 48 V.

[0013] The power conversion device 1 includes a transformer 10, a first main circuit 11 to which a first DC voltage V1 is input, a second main circuit 12 to which a second DC voltage V2 is output, a third main circuit 13 to which a third DC voltage V3 is output, a control unit 14, a first voltmeter 21, a second voltmeter 22, and a third voltmeter 23.

[0014] The transformer 10 is a high-frequency isolation transformer and includes a primary winding T1, a first secondary winding T2, and a second secondary winding T3. The primary winding T1, the first secondary winding T2, and the second secondary winding T3 are insulated from one another. In FIG. 1, the primary winding T1, the first secondary winding T2, and the second secondary winding T3 have the same polarity.

[0015] Assuming that the number of turns of the primary winding T1 is N1 and the number of turns of the first secondary winding T2 is N2, when the first secondary winding T2 is neutral-connected as shown in Figure 1, the first winding ratio n21 should be set to N2 / N1 = 2 x V2 / V1. Also, when the number of turns of the second secondary winding T3 is N3, the second winding ratio n31 should be set to N3 / N1 = V3 / V1. As in the first embodiment, when the third DC voltage V3 is, for example, 360 V, the same as the first DC voltage V1, or a voltage value close to that, the second winding ratio n31 should be set to 1.

[0016] The first main circuit 11 is a DC / AC inverter circuit that converts a first DC voltage V1 into a first AC voltage Vt1. The first main circuit 11 includes a first capacitor C1, a first H-bridge circuit 40, and a first inductor L1. The first capacitor C1 is connected in parallel to the DC power supply 2. The first H-bridge circuit 40 has a first leg 41 in which a first switch S1 and a second switch S2 are connected in series, and a second leg 42 in which a third switch S3 and a fourth switch S4 are connected in series, and the first leg 41 and the second leg 42 are connected in parallel.

[0017] In the first leg 41, a first main electrode of the first switch S1 is connected to the positive electrode of the DC power supply 2, and a second main electrode of the second switch S2 is connected to the negative electrode of the DC power supply 2. A connection point between the second main electrode of the first switch S1 and the first main electrode of the second switch S2 is connected to a first terminal of the primary winding T1 via a first inductor L1.

[0018] In the second leg 42, a first main electrode of the third switch S3 is connected to the positive electrode of the DC power supply 2, and a second main electrode of the fourth switch S4 is connected to the negative electrode of the DC power supply 2. A connection point between the second main electrode of the third switch S3 and the first main electrode of the fourth switch S4 is connected to the second terminal of the primary winding T1.

[0019] However, without being limited thereto, the connection point between the second main electrode of the first switch S1 and the first main electrode of the second switch S2 may be connected to the first terminal of the primary winding T1, and the connection point between the second main electrode of the third switch S3 and the first main electrode of the fourth switch S4 may be connected to the second terminal of the primary winding T1 via the first inductor L1.

[0020] Control electrodes of the first to fourth switches S1 to S4 are connected to the control unit 14. The first main circuit 11 converts the first DC voltage V1 into a first AC voltage Vt1 and outputs it to the primary winding T1 by controlling the switching patterns of the first to fourth switches S1 to S4 using the control unit 14. The switching frequency f of the switching pattern is a high frequency of, for example, about several tens of kHz to several tens of MHz, and in this embodiment, the switching frequency f=100 kHz.

[0021] In this embodiment, the first to fourth switches S1 to S4 are each configured with an N-channel MOSFET, but are not limited to this and may be configured with a semiconductor switching element such as an IGBT, etc. In this embodiment, the first main electrode of each of the first to fourth switches S1 to S4 is the drain, the second main electrode is the source, and the control electrode is the gate.

[0022] The second main circuit 12 is an AC / DC converter circuit that converts the first AC voltage Vt1 into a second AC voltage Vt2, which is output from the first secondary winding T2, under the control of the control unit 14. The second DC voltage V2 is output to the first load 3.

[0023] The second main circuit 12 includes a first diode D1, a second diode D2, a second inductor L2, and a second capacitor C2 that form a full-wave rectifier circuit. The cathode of the first diode D1 is connected to a first terminal of the first secondary winding T2. The cathode of the second diode D2 is connected to a second terminal of the first secondary winding T2. The neutral point of the first secondary winding T2 is connected to the positive terminal of the first load 3 via the second inductor L2. The anodes of the first diode D1 and the second diode D2 are connected to the negative terminal of the first load 3. The second capacitor C2 is connected in parallel with the first load 3. Note that the configuration of the second main circuit 12 is not limited thereto. For example, the second main circuit 12 may be configured to include a single first diode D1 that forms a half-wave rectifier circuit. Since rectifier circuits of this configuration are well known, detailed description thereof will be omitted.

[0024] The third main circuit 13 is an AC / DC converter circuit that converts the third AC voltage Vt3, which is converted from the first AC voltage Vt1 and output from the second secondary winding T3, into a third DC voltage V3 under the control of the control unit 14. The third DC voltage V3 is output to the second load 4.

[0025] The third main circuit 13 includes a third inductor L3, a second H-bridge circuit 50 serving as a full-wave rectifier circuit, and a third capacitor C3. The third capacitor C3 is connected in parallel with the second load 4. The second H-bridge circuit 50 includes a third leg 51 in which a fifth switch Q1 and a sixth switch Q2 are connected in series, and a fourth leg 52 in which a seventh switch Q3 and an eighth switch Q4 are connected in series, with the third leg 51 and the fourth leg 52 being connected in parallel.

[0026] In the third leg 51, a first main electrode of the fifth switch Q1 is connected to the positive input terminal of the second load 4, and a second main electrode of the sixth switch Q2 is connected to the negative input terminal of the second load 4. The connection point between the second main electrode of the fifth switch Q1 and the first main electrode of the sixth switch Q2 is connected to a first terminal of the second secondary winding T3 via a third inductor L3.

[0027] In the fourth leg 52, a first main electrode of the seventh switch Q3 is connected to the positive input terminal of the second load 4, and a second main electrode of the eighth switch Q4 is connected to the negative input terminal of the second load 4. The connection point between the second main electrode of the seventh switch Q3 and the first main electrode of the eighth switch Q4 is connected to the second terminal of the second secondary winding T3.

[0028] The control electrodes of the fifth to eighth switches Q1 to Q4 are connected to the control unit 14. The third main circuit 13 converts the third AC voltage Vt3 into the third DC voltage V3 by controlling the switching patterns of the fifth to eighth switches Q1 to Q4 using the control unit 14.

[0029] In this embodiment, the fifth to eighth switches Q1 to Q4 are each configured with an N-channel MOSFET, but are not limited to this and may be configured with a semiconductor switching element such as an IGBT, etc. In this embodiment, the first main electrode of each of the fifth to eighth switches Q1 to Q4 is the drain, the second main electrode is the source, and the control electrode is the gate.

[0030] The first voltmeter 21 measures the first DC voltage V1 input to the first main circuit 11, converts the measured value of the first DC voltage V1 into, for example, a digital signal, and sends it to the control unit 14. The second voltmeter 22 measures the second DC voltage V2 output by the second main circuit 12, converts the measured value of the second DC voltage V2 into, for example, a digital signal, and sends it to the control unit 14. The third voltmeter 23 measures the third DC voltage V3 output by the third main circuit 13, and converts the measured value of the third DC voltage V3 into, for example, a digital signal and sends it to the control unit 14.

[0031] 1 illustrates an example in which the second load 4 is a DC / AC inverter circuit that converts DC power of a third DC voltage V3 into AC power of a fourth AC voltage V4. The fourth AC voltage V4 has a frequency of 50 Hz or 60 Hz and an effective voltage of 100 V or 200 V, for example. The fourth AC voltage V4 is output to the third load 5.

[0032] The second load 4 includes a third H-bridge circuit 60, a fourth inductor L4, and a fourth capacitor C4. The fourth capacitor C4 is connected in parallel to the third load 5. The third H-bridge circuit 60 includes a fifth leg 61 in which a ninth switch P1 and a tenth switch P2 are connected in series, and a sixth leg 62 in which an eleventh switch P3 and a twelfth switch P4 are connected in series, and the fifth leg 61 and the sixth leg 62 are connected in parallel.

[0033] In the fifth leg 61, a first main electrode of the ninth switch P1 is connected to the positive input terminal of the second load 4, and a second main electrode of the tenth switch P2 is connected to the negative input terminal of the second load 4. The connection point between the second main electrode of the ninth switch P1 and the first main electrode of the tenth switch P2 is connected to the first terminal of the third load 5 via a fourth inductor L4.

[0034] In the sixth leg 62, the first main electrode of the eleventh switch P3 is connected to the positive input terminal of the second load 4, and the second main electrode of the twelfth switch P4 is connected to the negative input terminal of the second load 4. The connection point between the second main electrode of the eleventh switch P3 and the first main electrode of the twelfth switch P4 is connected to the second terminal of the third load 5.

[0035] The control electrodes of the ninth to twelfth switches P1 to P4 are connected to the control unit 14. The second load 4 converts the third DC voltage V3 into a fourth AC voltage V4 as an output AC voltage by controlling the switching patterns of the ninth to twelfth switches P1 to P4 by the control unit 14.

[0036] In this embodiment, the ninth to twelfth switches P1 to P4 are each configured with an N-channel MOSFET, but are not limited to this and may be configured with a semiconductor switching element such as an IGBT, etc. In this embodiment, the first main electrode of each of the ninth to twelfth switches P1 to P4 is the drain, the second main electrode is the source, and the control electrode is the gate.

[0037] In the power conversion device 1, the first main circuit 11 includes first to fourth switches S1 to S2, the third main circuit 13 includes fifth to eighth switches Q1 to Q4, and the second main circuit 12 does not include any switches. Therefore, in the power conversion device 1, the first to fourth switches S1 to S2 of the first main circuit 11 and the fifth to eighth switches Q1 to Q4 of the third main circuit 13 are controlled by the control unit 14.

[0038] The control unit 14 is a general-purpose computer equipped with a CPU (Central Processing Unit), a memory, and an input / output unit. A computer program (control program) is installed in the control unit 14. By executing the computer program, the control unit 14 performs various functions.

[0039] The control unit 14 observes the first DC voltage V1, the second DC voltage V2, and the third DC voltage V3, and controls the second DC voltage V2 and the third DC voltage V3 based on the observation results. The control unit 14 controls the first main circuit 11 and the third main circuit 13 so that the second DC voltage V2 and the third DC voltage V3 become predetermined second DC voltage command values ​​V2* and third DC voltage command values ​​V3*. The second DC voltage command value V2* and the third DC voltage command value V3* are controlled by the control unit 14 to become predetermined values. The control unit 14 controls the second DC voltage V2 and the third DC voltage V3 by controlling the switching patterns of the first to fourth switches S1 to S4 of the first main circuit 11 and the fifth to eighth switches Q1 to Q4 of the third main circuit 13. Furthermore, the control unit 14 controls the switching patterns of the ninth to twelfth switches P1 to P4 of the second load 4, thereby controlling the fourth AC voltage V4 of the second load 4.

[0040] When the second load 4 is a DC / AC inverter circuit, the control unit 14 can use a known method to control the fourth AC voltage V4, and therefore detailed description thereof will be omitted.

[0041] The control unit 14 controls the first phase difference θ1 and the second phase difference θ31 based on the observation results of the first DC voltage V1, the second DC voltage V2, and the third DC voltage V3 so that the second DC voltage V2 and the third DC voltage V3 become the second DC voltage command value V2* and the third DC voltage command value V3*. The first phase difference θ1 is the phase difference of the switching pattern between the first leg 41 and the second leg 42 of the first H-bridge circuit 40 and between the third leg 51 and the fourth leg 52 of the second H-bridge circuit 50. The second phase difference θ31 is the phase difference of the switching pattern between the first H-bridge circuit 40 and the second H-bridge circuit 50. More specifically, the control unit 14 controls the first phase difference θ1 and the second phase difference θ31 based on the measured values ​​of the first DC voltage V1, the second DC voltage V2, and the third DC voltage V3 so that the second DC voltage V2 and the third DC voltage V3 become predetermined values.

[0042] At the same time, the control unit 14 controls the second phase difference θ31 for the first to fourth switches S1 to S2 of the first main circuit 11 and the fifth to eighth switches Q1 to Q4 of the third main circuit 13 within a range that establishes zero voltage switching (ZVS).

[0043] With the above-described configuration, the power conversion device 1 can reduce the number of switches and control variables of a power conversion device having one input and two outputs, and can efficiently achieve ZVS.

[0044] Next, an example of a method for controlling the first phase difference θ1 and the second phase difference θ31 by the control unit 14 will be described with reference to Fig. 2. Fig. 2 shows an example of a switching pattern of the first to fourth switches S1 to S4 of the first main circuit 11 and the fifth to eighth switches Q1 to Q4 of the third main circuit 13 by the control unit 14, and an example of the waveforms of the first AC voltage Vt1 and the third AC voltage Vt3 generated at that time.

[0045] The first to fourth switches S1 to S4 and the fifth to eighth switches Q1 to Q4 are all controlled by a pulse wave generated by the control unit 14 with a switching frequency f of 100 kHz, i.e., a switching period T of 10 μs, and an on-duty of 50%. The on-duty is not limited to 50%, and may be changed depending on the usage status of the power conversion device 1. For example, the on-duty may be increased when the power consumption by the first load 3 and the second load 4 is large, and decreased when the power consumption is small. In either case, it is preferable that the first to fourth switches S1 to S4 and the fifth to eighth switches Q1 to Q4 be controlled by a switching pattern with the same on-duty.

[0046] 2, the switching period T=10 μs corresponds to a phase θ=360°=2π radians. For example, when two waveforms are compared, if the phases are the same, the phase difference is 0°=0 radians, and if the phases are shifted by ¼, the phase difference is 90°=π / 2 radians. As described below, the control unit 14 controls the second DC voltage V2 and the third DC voltage V3 by changing the first phase difference θ1 and the second phase difference θ31.

[0047] 2(1), in the first leg 41 of the first H-bridge circuit 40, when the first switch S1 is on, the second switch S2 is off, and when the first switch S1 is off, the second switch S2 is on. As shown in Fig. 2(2), in the second leg 42 of the first H-bridge circuit 40, when the fourth switch S4 is on, the third switch S3 is off, and when the fourth switch S4 is off, the third switch S3 is on.

[0048] The control unit 14 controls the first main circuit 11 to change a first phase difference θ1, which is the phase difference between the switching patterns of the first leg 41 and the second leg 42 of the first H-bridge circuit 40.

[0049] 2(3), in the third leg 51 of the second H-bridge circuit 50, when the fifth switch Q1 is on, the sixth switch Q2 is off, and when the fifth switch Q1 is off, the sixth switch Q2 is on. As shown in FIG. 2(4), in the fourth leg 52 of the second H-bridge circuit 50, when the eighth switch Q4 is on, the seventh switch Q3 is off, and when the eighth switch Q4 is off, the seventh switch Q3 is on.

[0050] The control unit 14 controls the phase difference between the switching patterns of the third leg 51 and the fourth leg 52 of the second H-bridge circuit 50 of the third main circuit 13 to change by the first phase difference θ1, similar to the first main circuit 11.

[0051] The control unit 14 also controls the first main circuit 11 and the third main circuit 13 to change a second phase difference θ31, which is the phase difference between the switching patterns of the first H-bridge circuit 40 and the second H-bridge circuit 50.

[0052] When the control unit 14 changes the first phase difference θ1, the first AC voltage Vt1 output to the primary winding T1 has a three-level waveform as shown in (5) of Fig. 2. Furthermore, when the control unit 14 changes the second phase difference θ31, the third AC voltage Vt3 output from the second secondary winding T3 has a three-level waveform whose phase difference with the first AC voltage Vt1 is the second phase difference θ31 as shown in (6) of Fig. 2.

[0053] The control unit 14 controls the first phase difference θ1 to vary within a range of, for example, 0° (0 radians) to 90° (π / 2 radians). Reducing the first phase difference θ1 increases the power transmitted from the first main circuit 11 to the second main circuit 12 and the third main circuit 13, and the second DC voltage V2 and the third DC voltage V3 also increase. Increasing the first phase difference θ1 decreases the power converted from the first main circuit 11 to the second main circuit 12 and the third main circuit 13, and the second DC voltage V2 and the third DC voltage V3 also decrease. When only the second main circuit 12 is operated and the third main circuit 13 is not operated, the control unit 14 only needs to control the first phase difference θ1 of the first main circuit 11 so that the second DC voltage V2 becomes a predetermined second DC voltage command value V2*.

[0054] The control unit 14 controls the second phase difference θ31 to vary within a range of, for example, 0° (0 radians) to 90° (π / 2 radians). Increasing the second phase difference θ31 increases the power transmitted from the first main circuit 11 to the third main circuit 13, and the third DC voltage V3 also increases. Increasing the second phase difference θ31 decreases the power converted from the first main circuit 11 to the third main circuit 13, and the third DC voltage V3 also decreases. When performing the integrated operation of the second main circuit 12 and the third main circuit 13, the control unit 14 controls the first phase difference θ1 and the second phase difference θ31 so that the second DC voltage V2 becomes a predetermined second DC voltage command value V2* and the third DC voltage V3 becomes a predetermined third DC voltage command value V3*.

[0055] Furthermore, by changing the second phase difference θ31, the control unit 14 can operate the switches S1 to S4 of the first main circuit 11 and the switches Q1 to Q4 of the third main circuit 13 at ZVS. When the control unit 14 controls both the first phase difference θ1 and the second phase difference θ31, achieving ZVS for the switches S1 to S4 and the switches Q1 to Q4 is desirable from the viewpoints of power conversion efficiency and element protection.

[0056] 3, the control unit 14 can establish ZVS for the switches S1 to S4 and the switches Q1 to Q4 by controlling the second phase difference θ31 so that the third DC voltage command value V3* becomes a predetermined value with respect to the first DC voltage V1. More specifically, when the second winding ratio n31=1, the second phase difference θ31 may be controlled so that the third DC voltage command value V3* becomes equal to the first DC voltage V1.

[0057] Furthermore, even when the second winding ratio n31≠1, the second phase difference θ31 may be controlled so that the third DC voltage command value V3* becomes a predetermined value with respect to the first DC voltage V1. More specifically, the second phase difference θ31 may be controlled so that the third DC voltage command value V3* becomes equal to the value obtained by multiplying the first DC voltage V1 by the second winding ratio n31, that is, so that V3*=n31×V1=(N3 / N1)×V1 is satisfied. This allows ZVS to be always established.

[0058] Next, the ZVS state will be explained in more detail using Figures 4 to 6. In the following, for the sake of simplicity, the case where the second winding ratio n31 = 1 will be explained, but if the second winding ratio n31 ≠ 1, the same can be considered as in the above example.

[0059] First, as shown in Fig. 4 , assume that in the third main circuit 13, the fifth switch Q1 and the eighth switch Q4 are on, the sixth switch Q2 and the seventh switch Q3 are off, and the switch current Id(Q1) flowing through the fifth switch Q1 is reversely flowing in the negative direction. Then, as shown in Fig. 5 , when only the fifth switch Q1 switches from on to off, the switch current Id(Q1) is commutated to the body diode of the fifth switch Q1. Then, as shown in Fig. 6 , when only the sixth switch Q2 switches from off to on, a recovery current (through current) flows through the body diode of the fifth switch Q1. This recovery current increases the loss in the power conversion device 1.

[0060] Therefore, the condition for achieving ZVS is that when the switch current Id is defined as the direction of the current flowing from the first main electrode (drain) to the second main electrode (source) of each switch is positive, the switch current Id immediately before each switch is switched from on to off is positive.

[0061] The conditions under which ZVS is established for the switch current Id(Q1) of the fifth switch Q1 and the switch current Id(Q4) of the eighth switch Q4, and for the switch currents Id(Q1) and Id(Q4) at the moment of switching from the state in Fig. 4 to the state in Fig. 5 are expressed as follows: Id(Q1) = (V3 - V1) (π - θ1) / (2πfL) ≥ 0 (1) Id(Q4) = (V3 - V1) (π - θ1) / (2πfL) + V1 × θ31 / (πfL) ≥ 0 (2) Here, f is the switching frequency, and L is the inductance of the third inductor L3. The units of the first phase difference θ1 and the second phase difference θ31 are radians.

[0062] Here, the first phase difference θ1 changes over time under the control of the control unit 14. Therefore, under the condition that V3≠V1, the switch current Id(Q1) in equation (1) and the switch current Id(Q4) in equation (2) change over time according to the first phase difference θ1. Therefore, the conditions for the third DC voltage V3 and the second phase difference θ31 that establish ZVS also change over time.

[0063] 3, under the condition of V3=V1, Id(Q1)=0 in equation (1) and Id(Q4)>0 in equation (2) are satisfied regardless of the conditions for the first phase difference θ1 and the second phase difference θ31, and it is clear that these are conditions under which ZVS is established. Therefore, ZVS can be established by the control unit 14 controlling the second phase difference θ31 so that V3=V1.

[0064] 7 and 8 show an example of the analysis results when the control unit 14 controls the second phase difference θ31 so that V3=V1.

[0065] 7, (1) indicates the switch current Id(S1) of the first switch S1, (2) indicates the switching pattern of the first switch S1, (3) indicates the switch current Id(S4) of the fourth switch S4, and (4) indicates the switching pattern of the fourth switch S4. As shown in FIG. 7, the first switch S1 switches from on to off at time t11 with Id(S1)>0, and the fourth switch S4 switches from on to off at time t12 with Id(S4)>0, which indicates that ZVS is established. Note that the second switch S2 operates in the same manner as the first switch S1, and the third switch S3 operates in the same manner as the fourth switch S4, and therefore, a description thereof will be omitted.

[0066] 8, (1) indicates the switch current Id(Q1) of the fifth switch Q1, (2) indicates the switching pattern of the fifth switch Q1, (3) indicates the switch current Id(Q4) of the eighth switch Q4, and (4) indicates the switching pattern of the eighth switch Q4. As shown in FIG. 8, the fifth switch Q1 switches from on to off at time t21 with Id(Q1)≧0, and the eighth switch Q4 switches from on to off at time t22 with Id(Q4)>0, which indicates that ZVS is established. Note that n operates in the same way as the fifth switch Q1, and the seventh switch Q3 operates in the same way as the eighth switch Q4, so a description thereof will be omitted.

[0067] The third DC voltage command value V3* does not necessarily have to be equal to the first DC voltage V1, and the third DC voltage command value V3* may have an upper limit and a lower limit with respect to the first DC voltage V1, as shown in Fig. 9. In this case, the upper limit and the lower limit of the third DC voltage command value V3* may be set within a range in which ZVS can be ensured, as shown in Fig. 10.

[0068] Furthermore, the lower limit value of the third DC voltage command value V3* is determined by the above-described formulas (1) and (2), and is therefore affected by the first phase difference θ1 and the second phase difference θ31. Therefore, by mapping in advance the characteristics of the region where ZVS is possible depending on the circuit status, it is possible to set appropriate upper and lower limit values ​​of the third DC voltage command value V3* for the first DC voltage V1.

[0069] When the third DC voltage V3 deviates from the upper limit or lower limit of the appropriate third DC voltage command value V3* for the first DC voltage V1, the control unit 14 changes the second phase difference θ31 so that the third DC voltage V3 is within the range between the upper limit and lower limit. By limiting the range of the third DC voltage V3 with respect to the first DC voltage V1 in advance, it becomes possible to control the second phase difference θ31 within a range where ZVS is possible, and the change range of the third DC voltage V3 can be widened.

[0070] It is preferable that the upper and lower limit values ​​of the appropriate third DC voltage command value V3* for the first DC voltage V1 are set by both the first phase difference θ1 and the second phase difference θ31. By setting the upper and lower limit values ​​by both the first phase difference θ1 and the second phase difference θ31, it is possible to widen the range in which the second phase difference θ31 can be changed so as to establish ZVS even when the first phase difference θ1 changes depending on the operating status of the power conversion device 1.

[0071] As described above, the power conversion device 1 according to the first embodiment can reduce the number of switches and control variables in a power conversion device having one input and two outputs, and can efficiently achieve ZVS.

[0072] Second Embodiment Fig. 11 shows a configuration example of a power conversion device 1A according to a second embodiment. The power conversion device 1A according to the second embodiment differs from the power conversion device 1 shown in Fig. 1 in that it includes a first ammeter 31 that measures a first AC current It1 flowing through the primary winding T1 and a second ammeter 33 that measures a second AC current It3 flowing through the second secondary winding T3. The other configuration of the power conversion device 1A according to the second embodiment is the same as that of the power conversion device 1 shown in Fig. 1, and therefore description thereof will be omitted.

[0073] The first ammeter 31 sends the measured value of the first AC current It1 to the control unit 14. By measuring the first AC current It1, it is possible to directly measure the switch currents immediately before the first to fourth switches S1 to S4 are switched from on to off.

[0074] When the first AC current It1 flows through the path including the first switch S1, the first inductor L1, the primary winding T1, and the fourth switch S4, the control unit 14 controls the second phase difference θ31 as follows. That is, when It1≧0, which is the condition under which the switch current is equal to or greater than zero, the control unit 14 controls the second phase difference θ31 so as to switch the first switch S1 and the fourth switch S4 from on to off. This enables ZVS to be achieved.

[0075] When the first AC current It1 flows through the path of the third switch S3, the primary winding T1, the first inductor L1, and the second switch S2, the control unit 14 controls the second phase difference θ31 as follows. That is, when the switch current is equal to or greater than zero (It1≦0 (−It1≧0)), the control unit 14 controls the second phase difference θ31 so as to switch the second switch S2 and the third switch S3 from on to off. This enables ZVS to be established.

[0076] The second ammeter 33 sends the measured value of the second AC current It3 to the control unit 14. By measuring the second AC current It3, it is possible to directly measure the switch currents immediately before the fifth to eighth switches Q1 to Q4 are switched from on to off.

[0077] When the second AC current It3 flows through the path including the fifth switch Q1, the third inductor L3, the second secondary winding T3, and the eighth switch Q4, the control unit 14 controls the second phase difference θ31 as follows. That is, when It3≧0, which is the condition under which the switch current is equal to or greater than 0, the control unit 14 controls the second phase difference θ31 so as to switch the fifth switch Q1 and the eighth switch Q4 from ON to OFF. This enables ZVS to be achieved.

[0078] When the second AC current It3 flows through the path including the seventh switch Q3, the second secondary winding T3, the third inductor L3, and the sixth switch Q2, the control unit 14 controls the second phase difference θ31 as follows. That is, when It3≦0 (−It3≧0), which is the condition under which the switch current is 0 or greater, the control unit 14 controls the second phase difference θ31 so as to switch the seventh switch Q3 and the sixth switch Q2 from on to off. This enables ZVS to be established.

[0079] In summary, the control unit 14 observes the value immediately before the switching pattern of at least one of the first AC current It1 of the primary winding T1 and the second AC current It3 of the second secondary winding T3 changes from on to off. Then, the control unit 14 may control the second phase difference θ31 based on the observed value of at least one of the first AC current It1 and the second AC current It3 to establish a range in which ZVS is established.

[0080] For example, the control unit 14 may observe the value of the first AC current It1, which has a predetermined direction flowing through the primary winding T1 as positive, immediately before the switching pattern of the first AC current It1 changes from on to off, and perform the following control: First, when the first AC current It1 is a predetermined value (e.g., 0 A) or more, it is determined that ZVS is established, and the second phase difference θ31 is maintained. Then, when the first AC current It1 is smaller than the predetermined value, it is determined that ZVS is not established, and the second phase difference θ31 is controlled so that the first AC current It1 becomes the predetermined value or more.

[0081] For example, the control unit 14 may observe the value of the second AC current It3, which has a predetermined direction flowing through the second secondary winding T3 as positive, immediately before the switching pattern of the second AC current It3 changes from on to off, and perform the following control: First, when the second AC current It3 is a predetermined value (e.g., 0 A) or more, it is determined that ZVS is established, and the second phase difference θ31 is maintained. Then, when the second AC current It3 is smaller than the predetermined value, it is determined that ZVS is not established, and the second phase difference θ31 is controlled so that the second AC current It3 becomes the predetermined value or more.

[0082] The control unit 14 can check whether ZVS is established from the measured value of at least one of the first AC current It1 and the second AC current It3, and can control the second phase difference θ31 to a range in which ZVS is established. Therefore, in the second embodiment, the control unit 14 can set the second phase difference θ31 to a range in which ZVS is established, without having to map the characteristics of the region in which ZVS is possible in advance.

[0083] This will be explained using the time chart of FIG. 12. In FIG. 12, (1) shows the third AC voltage Vt3, (2) shows the second AC current It3 when the third DC voltage V3 is 345 V, (3) shows the second AC current It3 when the third DC voltage V3 is 322 V, and (4) shows the second AC current It3 when the third DC voltage V3 is 300 V. The third DC voltage V3 can be reduced by increasing the second phase difference θ31. In FIG. 12, the fifth switch Q1 switches from on to off at time t31, and the eighth switch Q4 switches from on to off at time t32. Therefore, attention will be focused on the second AC current It3 from time t31 to t31.

[0084] In this case, the fifth switch Q1 and the eighth switch Q4 are switched from on to off when the second AC current It3 is greater than 0 in (2) and when the second AC current It3 is equal to 0 in (3), so ZVS is established. In contrast, in (4) of Fig. 12, the fifth switch Q1 and the eighth switch Q4 are switched from on to off when the second AC current It3 is less than 0, so ZVS is not established.

[0085] As described above, under the conditions of FIG. 12, if the control unit 14 changes the second phase difference θ31 so that the third DC voltage becomes 300 V or more, the second AC current It3 becomes 0 V or more in the range from time t31 to t31, and it can be seen that ZVS is established.

[0086] Moreover, in the second embodiment, by mapping in advance the characteristics of the region where ZVS is possible depending on the circuit state, it is possible to set appropriate upper and lower limit values ​​of the third DC voltage command value V3* for the first DC voltage V1 and the second AC current It3.

[0087] As described above, in the power conversion device 1A according to the second embodiment, as in the first embodiment, the number of switches and control variables of a power conversion device having one input and two outputs can be reduced, and ZVS can be efficiently realized.

[0088] Each of the functions described in the above embodiments may be implemented by one or more processing circuits, including programmed processors, electrical circuits, and even devices such as application specific integrated circuits (ASICs), or circuit components arranged to perform the described functions.

[0089] Although the embodiments of the present invention have been described above, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. Various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art from this disclosure.

[0090] 1, 1A Power conversion device 2 DC power supply 3 First load 4 Second load 5 Third load 10 Transformer 11 First main circuit 12 Second main circuit 13 Third main circuit 14 Control unit 21-23 First to third voltmeters 31 First ammeter 33 Second ammeter 40 First H-bridge circuit 41 First leg 42 Second leg 50 Second H-bridge circuit 51 Third leg 52 Fourth leg 60 Third H-bridge circuit 61 Fifth leg 62 Sixth leg C1-C4 First to fourth capacitors D1-D2 First and second diodes L1-L4 First to fourth inductors It1 First AC current It3 Second AC current P1-P4 Ninth to twelfth switches Q1-Q4 Fifth to eighth switches S1-S4 First to fourth switches T1 Primary winding T2 First secondary winding T3 Second secondary winding V1 First DC voltage V2 Second DC voltage V2* Second DC voltage command value V3 Third DC voltage V3* Third DC voltage command value V4 Fourth AC voltage Vt1 to Vt3 First to third AC voltages

Claims

1. A control method for a power conversion device comprising: a first main circuit having a first H-bridge circuit in which a first leg and a second leg are connected in parallel, and converting a first DC voltage into a first AC voltage; a transformer having a primary winding to which the first AC voltage is input, a first secondary winding, and a second secondary winding; a second main circuit having at least one diode, connected to the first secondary winding, and outputting a second DC voltage; a third main circuit having a second H-bridge circuit in which a third leg and a fourth leg are connected in parallel, and connected to the second secondary winding, and outputting a third DC voltage; and a control unit that controls a first phase difference of a switching pattern between the first leg and the second leg and a second phase difference of a switching pattern between the first H-bridge circuit and the second H-bridge circuit, a control method for a power conversion device, the control method comprising: controlling the second phase difference within a range that establishes zero voltage switching; 2. The control method for a power conversion device according to claim 1, wherein the control unit controls the second phase difference so that the third DC voltage has a predetermined value within a range in which the zero voltage switching is established, and the predetermined value is set based on the first DC voltage and a turns ratio between the second secondary winding and the primary winding.

3. The control method for a power conversion device according to claim 2, wherein the control unit controls the phase difference of the switching pattern between the third leg and the fourth leg to be equal to the first phase difference, and controls the second phase difference so that the third DC voltage becomes a value obtained by multiplying the first DC voltage by a turns ratio between the second secondary winding and the primary winding, within a range that establishes the zero voltage switching.

4. The control method for a power conversion device according to claim 2, wherein the control unit controls the second phase difference so that the third DC voltage has a predetermined value, and sets the value of the third DC voltage in consideration of the current of the second secondary winding.

5. The control method for a power conversion device according to claim 1, wherein the control unit sets an upper limit and a lower limit for the value of the third DC voltage relative to the first DC voltage as a range within which the zero voltage switching is established, and when the value of the third DC voltage deviates from the range between the upper limit and the lower limit, controls the second phase difference so that the value falls within the range between the upper limit and the lower limit.

6. The control method for a power conversion device according to claim 5, wherein the control unit sets the upper limit value and the lower limit value based on the first phase difference, the second phase difference, and the first DC voltage.

7. The control method for a power conversion device according to claim 6, wherein the control unit further sets the upper limit value and the lower limit value based on the current of the second secondary winding.

8. The control method for a power conversion device according to claim 1, wherein the control unit observes a value immediately before a switching pattern of at least one of the current in the primary winding and the current in the second secondary winding changes from on to off, and controls the second phase difference based on the observed current in the primary winding and / or the current in the second secondary winding as a range in which the zero voltage switching is established.

9. The control method for a power conversion device according to claim 8, wherein the control unit observes a value immediately before a switching pattern of a first current, the predetermined direction of which flows through the primary winding being positive, changes from on to off, and when the first current is at or above the predetermined value, determines that the zero voltage switching has been established and maintains the second phase difference, and when the first current is smaller than the predetermined value, determines that the zero voltage switching has not been established and controls the second phase difference so that the first current is at or above the predetermined value.

10. The control method for a power conversion device described in claim 8, wherein the control unit observes the value immediately before the switching pattern of the second current, which has a predetermined direction flowing through the second secondary winding as positive, changes from on to off, and when the second current is at or above the predetermined value, determines that the zero voltage switching has been established and maintains the second phase difference, and when the second current is smaller than the predetermined value, determines that the zero voltage switching has not been established and controls the second phase difference so that the second current is at or above the predetermined value.

11. A power supply comprising: a first main circuit having a first H-bridge circuit in which a first leg and a second leg are connected in parallel, and converting a first DC voltage into a first AC voltage; a transformer having a primary winding to which the first AC voltage is input, a first secondary winding, and a second secondary winding; a second main circuit having at least one diode, connected to the first secondary winding, and outputting a second DC voltage; a third main circuit having a second H-bridge circuit in which a third leg and a fourth leg are connected in parallel, and connected to the second secondary winding, and outputting a third DC voltage; and a control unit that controls a first phase difference of a switching pattern between the first leg and the second leg and a second phase difference of a switching pattern between the first H-bridge circuit and the second H-bridge circuit, wherein the control unit controls the first phase difference and the second phase difference based on measured values ​​of the second DC voltage and the third DC voltage so that the second DC voltage and the third DC voltage become predetermined values, and controls the second phase difference within a range that establishes zero voltage switching. Power conversion device.

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