Power conversion device control method and power conversion system

Abstract

This power conversion device is provided with: a transformer comprising a first circuit having a first switch for converting input power, a first coil to which the power converted by the first circuit is input, a second coil for converting a voltage input to the first coil and outputting the resulting voltage, and a third coil for converting the voltage input to the first coil and outputting the resulting voltage; a second circuit having a rectifier circuit for converting the power output from the second coil; and a third circuit having a second switch for converting the power output from the third coil. When the value of the power input into the first circuit is less than a reference value, the control unit controls the second switch so that the value of the voltage converted by the second switch is equal to or less than a value obtained by multiplying the value of the voltage input into the first circuit by the ratio of the number of turns of the third coil to the number of turns of the first coil.

Description

Control method for power conversion device and power conversion system

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

[0002] Patent Document 1 discloses a switching power supply device that reduces the installation space of the entire power supply device by integrating a DC / DC converter and a DC / AC inverter mounted on an electric vehicle.

[0003] JP 2008-109754 A

[0004] However, when the power supplied to the load by the integrated power supply device is small, that is, when the load is light, the soft switching of the DC / DC converter fails, resulting in an increase in switching loss.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to realize soft switching even under light load conditions.

[0006] One aspect of the present invention is a method for controlling a power conversion device using a control unit. The power conversion device includes: a first circuit having a first switch that converts input power; a first coil that receives the power converted by the first circuit; a transformer that includes a second coil that converts and outputs a voltage input to the first coil; and a third coil that converts and outputs the voltage input to the first coil; a second circuit having a rectifier circuit that converts power output from the second coil; and a third circuit having a second switch that converts power output from the third coil. When the power value input to the first circuit is less than a reference value, the control unit controls the second switch so that the voltage value converted by the second switch is equal to or less than the voltage value input to the first circuit multiplied by the ratio of the number of turns of the third coil to the number of turns of the first coil.

[0007] According to the present invention, soft switching can be achieved even under light load conditions.

[0008] 1 is a block diagram showing a power conversion system 1 including a power conversion device 10 according to a first embodiment, and peripheral devices 2 and 3 connected to the power conversion device 10. FIG.Ｌ１ 3 is a graph showing the relationship between the reactive current I and the voltage V3 converted by the second switch QQ. ｎｏｎ When there is no reactive current (comparison example) and ｎｏｎ When there is (embodiment), the current I flows through the first coil 121. Ｌ１ 4 is a circuit diagram showing an example of a detailed circuit configuration of the power conversion device 10 of FIG. 1. FIG. 5 is a timing chart showing an example of a switching pattern of the first switch elements S1 to S4 and the second switch elements Q1 to Q4 of FIG. 4. FIG. 6 is a graph showing the relationship between the phase difference θ31 between the first switch SS and the second switch QQ and the voltage value V3 converted by the second switch QQ. FIG. 7 is a graph showing the relationship between the power value P １ｉｎ 8 is a graph showing an example of the time change of the power value P input to the first circuit 14, the activation state of the second switch QQ, and the voltage V3 converted by the third circuit 14. １ｉｎ 9 is a graph showing another example of the time change of the activation state of the second switch QQ and the voltage V3 converted by the third circuit 14. FIG. 9 is a circuit diagram showing an example of the detailed circuit configuration of the power conversion device 10 of FIG. 1 according to the second embodiment. FIG. 10 is a graph showing the time change of the power value P １ｉｎ 11 is a circuit diagram showing an example of a detailed circuit configuration of the power conversion device 10 of FIG. 1 according to a third embodiment. FIG. 12 is a graph showing a current I required for soft switching. ＺＶＳ A large reactive current Z exceeds ｏｖｅｒ 13 is a graph illustrating an example of a control method for the power conversion device 10 according to the third embodiment. FIG. 14 is a graph illustrating the control method for the power conversion device 10 according to the third embodiment. １ｉｎ , the activation state of the second switch, the current I Ｌ１ 15 is a graph showing an example of time-dependent changes in the parameters (power P １ｉｎ , the activation state of the second switch, the current IＬ１ , switching frequency F) over time.

[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 A power conversion system 1 including a power conversion device 10 according to a first embodiment, and peripheral devices 2 and 3 connected to the power conversion device 10, will be described with reference to FIG. 1 . The power conversion system 1 includes the power conversion device 10 having one input and two outputs, and a control unit 20 that controls the power conversion device 10. The power conversion device 10 includes a first circuit 11, a transformer 12, a second circuit 13, and a third circuit 14. The first circuit 11 includes a first switch SS that converts input power. The transformer 12 includes a first coil 121 to which the power converted by the first circuit 11 is input, a second coil 122 that converts and outputs the voltage input to the first coil 121, and a third coil 123 that converts and outputs the voltage input to the first coil 121. The second circuit 13 includes a rectifier circuit UU that converts the power output from the second coil 122. The third circuit 14 has a second switch QQ that converts the power output from the third coil 123 .

[0011] The control unit 20 controls the power value P １ｉｎ is less than the reference value Th1, as shown in equation (1), the second switch QQ is controlled so that the voltage value V3 converted by the second switch QQ is equal to or less than the value obtained by multiplying the voltage value V1 input to the first circuit by the ratio (N3 / N1) of the number of turns N3 of the third coil 123 to the number of turns N1 of the first coil 121. Note that the first embodiment illustrates the case where N3 / N1=1.

[0012] V3≦V1×N3 / N1...(1)

[0013] Power P input to the first circuit 11 １ｉｎWhen the power V3 converted by the second switch QQ is small, that is, when the power supplied from the second circuit 13 to the first load 3 is small (when the load is light), the soft switching (ZVS) of the first switch SS fails. By controlling the second switch QQ so that the voltage V3 converted by the second switch QQ decreases, a reactive current I ｎｏｎ As a result, a current I flows through the first coil 121. Ｌ１ As a result, the power P input to the first circuit 11 increases. １ｉｎ Since the reactive current I ｎｏｎ Injecting this current enables soft switching of the first circuit 11. Hereinafter, the no-load and light-load periods will be collectively referred to as the light-load period.

[0014] In the first embodiment, the first circuit 11 converts DC power output from the DC voltage source 2 into AC power and outputs it to the first coil 121. The transformer 12 converts the input voltage to the first coil 121 into an output voltage of the second coil 122 according to the winding ratio (N2 / N1) between the first coil 121 and the second coil 122. The transformer 12 converts the input voltage to the first coil 121 into an output voltage of the third coil 123 according to the winding ratio (N3 / N1) between the first coil 121 and the third coil 123. The second circuit 13 converts the AC power output from the second coil 122 into DC power using a rectifier circuit UU and outputs it to the first load 3. The third circuit 14 converts the AC power output from the third coil 123 into DC power using a second switch QQ and outputs it.

[0015] The first circuit 11 converts DC power into AC power by operating a first switch SS. The third circuit 14 converts AC power into DC power by operating a second switch. The third circuit 14 may have any circuit configuration as long as it is a switch-type power conversion circuit. The second circuit 13 may be a rectifier circuit UU using a diode or the like. Furthermore, a resonant coil 15 may be connected in series between the first circuit 11 and the first coil 121.

[0016] As shown in FIG. 2, a current I Ｌ１ , the current I supplied to the first load 3 ｌｏａｄ (Hereinafter, "load current I ｌｏａｄ The load current I ｌｏａｄ However, if the current value of the first switch SS is smaller than that required for realizing soft switching, the first switch SS performs hard switching, and the switching efficiency of the first switch SS decreases.

[0017] On the other hand, in the first embodiment, no load is connected to the output side of the third circuit 14. When the voltage V3 converted by the second switch QQ drops, a reactive current I flows in the first coil 121 of the transformer 12. ｎｏｎ As a result, a current I flows through the first coil 121. Ｌ１ is the load current I ｌｏａｄ Reactive current I ｎｏｎ The lower the voltage V3 converted by the second switch QQ, the lower the reactive current I ｎｏｎ The voltage V3 converted by the second switch QQ can be changed in the range of 0 V to 360 V by controlling the second switch QQ. 360 V is an example of the voltage output from the DC voltage source 2. Therefore, the control unit 20 determines the current value I Ｌ１ is smaller than the current value required to realize soft switching of the first switch SS (light load), the second switch QQ is controlled so that the voltage value V3 converted by the second switch QQ satisfies the condition shown in equation (1). As a result, the voltage value V3 becomes smaller than 360 V, and the reactive current I ｎｏｎ is generated, and a current I flows through the first coil 121. Ｌ１ increases.

[0018] As shown in the comparative example of FIG. 3, the current I supplied to the first load 3 ｌｏａｄ However, the current value I required to realize soft switching of the first switch SS is ＺＶＳ If the load current I is smaller than 1, the switching loss of the first switch SS increases. ｌｏａｄ Reactive current I ｎｏｎAdding these, the current value I ＺＶＳ or the current value I ＺＶＳ By passing a larger current through the first coil 121, soft switching of the first switch SS can be achieved.

[0019] In the first embodiment, the power conversion device 10 or the power conversion system 1 can be mounted on an electric vehicle. In this case, the DC voltage source 2 can be a drive power source or a high-power battery for driving the electric vehicle. The first circuit 11, the transformer 12, and the second circuit 13 operate as an isolated DC-DC converter. For example, the first circuit 11, the transformer 12, and the second circuit 13 step down a high voltage (e.g., 360 V) of a high-power battery to a low voltage (e.g., 14 V) and supply power to an on-board auxiliary device (an example of a first load 3). The on-board auxiliary device 3 a includes a navigation system, power windows, brakes, wipers, headlights, and door locks. The first load 3 may be an auxiliary device battery (14 V battery) for supplying power to the on-board auxiliary device instead of the on-board auxiliary device.

[0020] On the other hand, by including the second switch QQ, the third circuit 14 can be used as a means for improving the efficiency of the isolated DC-DC converter composed of the first circuit 11, the transformer 12, and the second circuit 13, as described above.

[0021] In the first embodiment, the case where no load is connected to the output side of the third circuit 14 has been described. However, when a load is connected, the second switch QQ can also be used as a means for supplying a desired voltage to the load. Examples of loads connected to the output side of the third circuit 14 include power steering. When this power steering is used, the voltage applied can be controlled to, for example, 48 V by the second switch QQ. In other words, in the embodiment shown in FIG. 4 , when a load is connected to the output side of the third circuit 14, the second switch QQ is used as a means for applying a desired voltage to the load. When no load is connected to the output side of the third circuit 14 (or when the load does not generate power), the second switch QQ can be used as a means for improving the efficiency of the isolated DC-DC converter.

[0022] The control unit 20 can be placed outside the electric vehicle by performing road-to-road communication with the power conversion device 10. The control unit 20 may be mounted on the electric vehicle and communicate with the power conversion device 10 via a wire such as a Controller Area Network (CAN) wiring.

[0023] The control unit 20 can be realized using a microcomputer equipped with a CPU (Central Processing Unit), memory, and input / output units. A computer program (control program) for causing the microcomputer to function as the control unit 20 is installed in the microcomputer and executed. As a result, the microcomputer functions as multiple information processing units included in the control unit 20. Note that while an example in which the control unit 20 is realized by software is shown here, it is of course also possible to configure the control unit 20 by providing dedicated hardware for executing each piece of information processing. The control unit 20 may also serve as an electronic control unit (ECU) used for other vehicle-related control.

[0024] An example of a detailed circuit configuration of the power conversion device 10 of Fig. 1 will be described with reference to Fig. 4. The first circuit 11 has first switch elements S1 to S4 as an example of a first switch SS, and the third circuit 14 has second switch elements Q1 to Q4 as an example of a second switch QQ. Furthermore, the second circuit 13 has a rectifier circuit 133 using two diodes U1 and U2 as an example of a rectifier circuit UU. The first coil 121, the second coil 122, and the third coil 123 are magnetically coupled by a core (iron core) 124.

[0025] Each of the first circuit 11 and the third circuit 14 has an H-bridge circuit including four switch elements. That is, a first leg and a second leg are connected in parallel between a high-voltage line and a low-voltage line. The switch elements constituting the H-bridge circuit can be composed of semiconductor devices including, for example, an IGBT (insulated gate bipolar transistor) and a MOSFET (metal-oxide semiconductor field-effect transistor). By applying an on signal or an off signal to the gate electrode of the MOSFET, the conductive state (on) and the cut-off state (off) of the switch can be controlled.

[0026] First switch elements S1 and S2 are connected in series on a first leg of the first circuit 11, and first switch elements S3 and S4 are connected in series on a second leg of the first circuit 11. One terminal of the resonant coil 15 is connected between the first switch elements S1 and S2, and one terminal of the first coil 121 is connected between the first switch elements S3 and S4. The other terminal of the resonant coil 15 is connected to the other terminal of the first coil 121. The first circuit 11 may have a smoothing capacitor 111 connected in parallel to the first leg and the second leg. The first circuit 11 may have a power detection unit 112 arranged between the DC voltage source 2 and the first switch elements S1 to S4. The power detection unit 112 detects the power P input to the first circuit 11. １ｉｎ Detects the power P １ｉｎ The power detection unit 112 transmits a signal indicating this to the control unit 20. The power detection unit 112 may have any circuit configuration and may use any known technology.

[0027] The second switch elements Q1 and Q2 are connected in series on the first leg of the third circuit 14, and the second switch elements Q3 and Q4 are connected in series on the second leg of the second circuit 13. One terminal of the resonant coil 142 is connected between the second switch elements Q1 and Q2, and one terminal of the third coil 123 is connected between the second switch elements Q3 and Q4. The other terminal of the resonant coil 142 is connected to the other terminal of the third coil 123. The third circuit 14 may include a smoothing capacitor 141 connected in parallel to the first leg and the second leg. The third circuit 14 may include a voltage detection unit 143 that detects the voltage V3 converted by the second switch elements Q1 to Q4. The voltage detection unit 143 transmits a signal indicating the detected voltage V3 to the control unit 20. The circuit configuration of the voltage detection unit 143 is not limited, and known technology may be used.

[0028] The rectifier circuit 133 is a center-tap rectifier circuit using two diodes U1 and U2, but may also be a bridge-type rectifier circuit. The anodes of the diodes U1 and U2 are common, and the cathodes of the diodes U1 and U2 are connected to both terminals of the second coil 122. The rectifier circuit 133 outputs the potentials of the anodes of the diodes U1 and U2 and the potential at the midpoint of the second coil 122. The center-tap rectifier circuit 133 forms a full-wave rectifier circuit similar to a bridge-type rectifier circuit, but allows for a reduction in the number of diodes. The second circuit 13 may include a smoothing circuit 134 consisting of an inductor 1341 and a capacitor 1342 on the output side of the rectifier circuit 133. The second circuit 13 may also include a voltage detector 135 disposed between the smoothing circuit 134 and the first load 3. The voltage detection unit 135 detects the voltage V2 converted by the rectifier circuit 133 and smoothed by the smoothing circuit 134, and transmits a signal indicating the detected voltage V2 to the control unit 20. The circuit configuration of the voltage detection unit 135 is not important, and any known technology may be used.

[0029] An example of a switching pattern of the first switch elements S1 to S4 and the second switch elements Q1 to Q4 in Fig. 4 will be described with reference to Fig. 5. The switching pattern is a waveform that is generated by a driver circuit (not shown) to turn on / off each switch and input to the gate electrode of the MOSFET. The switching pattern is controlled by the control unit 20.

[0030] The first switch elements S1 and S2 on the first leg alternately turn on and off. When the first switch element S1 is on, the first switch element S2 is off, and when the first switch element S1 is off, the first switch element S2 is on. Similarly, the first switch elements S3 and S4 on the second leg alternately turn on and off. All of the first switch elements S1 to S4 alternately turn on and off in the same cycle, and the proportion of times they are on in one cycle, i.e., the duty ratio, is 50%.

[0031] Similarly, the second switch elements Q1 and Q2 on the first leg alternately turn on and off. When the second switch element Q1 is on, the second switch element Q2 is off, and when the second switch element Q1 is off, the second switch element Q2 is on. Similarly, the second switch elements Q3 and Q4 on the second leg alternately turn on and off. All of the second switch elements Q1 to Q4 alternately turn on and off in the same cycle, and the proportion of on-states in one cycle, i.e., the duty ratio, is 50%. The cycles of the second switch elements Q1 to Q4 are the same as the cycles of the first switch elements S1 to S4.

[0032] The control unit 20 controls the phase θ1 of the first switch SS and the phase difference θ31 between the first switch SS and the second switch QQ. As shown in FIG. 5 , the "phase θ1 of the first switch SS" is the phase difference between the on / off switching phase of the first switch elements S1 and S2 on the first leg and the on / off switching phase of the first switch elements S3 and S4 on the second leg. That is, the "phase θ1 of the first switch SS" is the phase difference between the first leg and the second leg of the first circuit 11. Note that in FIG. 5 , the phase difference between the rising edge (off to on) of the first switch element S4 and the falling edge (on to off) of the first switch element S3 relative to the rising edge (off to on) of the first switch element S1 and the falling edge (on to off) of the first switch element S2 is indicated as "phase θ1." Not limited to this, the phase difference between the phase of the falling edge (on → off) of the first switch element S4 and the phase of the rising edge (off → on) of the first switch element S3 relative to the phase of the falling edge (on → off) of the first switch element S1 and the phase of the rising edge (off → on) of the first switch element S2 is also the same "phase θ1."

[0033] On the other hand, the "phase difference θ31 between the first switch SS and the second switch QQ" is the phase difference between the phase of on / off switching of the first switch element S1 and the phase of on / off switching of the second switch element Q1. The first switch elements S1 to S4 and the second switch elements Q1 to Q4 have the same cycles and duty ratios. Therefore, the phase difference between the phase of on / off switching of the first switch elements S2 to S4 and the phase of on / off switching of the second switch elements Q2 to Q4 is also the same "phase difference θ31."

[0034] The control unit 20 controls the phase θ1 of the first switch SS to control the voltage V2 converted by the second circuit 13 to a constant voltage (e.g., 14 V). The control unit 20 controls the phase difference θ31 between the first switch SS and the second switch QQ to control the voltage V3 converted by the third circuit 14 to a desired value.

[0035] As shown in FIG. 6 , as the phase difference θ31 between the first switch SS and the second switch QQ decreases, the voltage V3 converted by the second switch QQ decreases. When the phase difference θ31 is less than 90°, the voltage V3 becomes less than 360 V, satisfying the condition shown in equation (1). Here, N3 / N1 = 1, and the voltage V1 input to the first circuit 11 is 360 V. The control unit 20 controls the phase difference θ31 so as to satisfy the condition shown in equation (1) based on the relationship between the phase difference θ31 and the voltage V3 shown in FIG. 6 . The control unit 20 can also control the voltage V3 to 0 V (zero volts) by setting the phase difference θ31 to zero. 0 V includes a range from exactly 0 V to near 0 V, specifically, up to a few percent of the voltage V1, for example, up to approximately 10 V. The method for controlling the voltage V3 converted by the third circuit 14 is not limited to the above-described method. 5, the second switch elements Q1 and Q2 may be synchronized with the first switch elements S1 and S2, and a phase difference may be provided only between the second switch elements Q3 and Q4 and the first switch elements S3 and S4, thereby controlling the amount of power received by the third circuit 14. This makes it possible to change the voltage V3 converted by the third circuit 14.

[0036] Referring to FIG. 7, the power value P １ｉｎ An example of the time change of the activation state of the second switch QQ and the voltage V3 converted by the third circuit 14 will be described. １ｉｎ is equal to or greater than the reference value Th1, the load current I ｌｏａｄ Therefore, the control unit 20 controls the power value P１ｉｎ is equal to or greater than the reference value Th1, the control unit 20 suspends control of the second switch QQ. This places the second switch QQ in an open state. At this time, the third circuit 14 becomes equivalent to a rectifier circuit using the body diode of the second switch QQ (or a diode connected in parallel in the case of an IGBT), so the voltage (360 V) input to the third circuit 14 is output as is. By suspending control of the second switch QQ, the control unit 20 can reduce the switching loss of the third circuit 14 that occurs when the second switch QQ is operated.

[0037] The power value P input to the first circuit 11 １ｉｎ When the phase difference θ31 becomes less than the reference value Th1 (light load LL), the control unit 20 activates the second switch QQ, which has been inactive. The control unit 20 controls the phase difference θ31 with reference to the graph shown in FIG. 6, thereby reducing the voltage V3 converted by the second switch QQ to a value lower than 360 V. As a result, as shown in FIG. 2, the reactive current I ｎｏｎ is generated and a current I flows through the first coil 121. Ｌ１ The reference value Th1 may be set by calculating the power value at which soft switching of the first switch SS becomes impossible from the specifications and circuit constants of the first switch elements S1 to S4.

[0038] Referring to FIG. 8, the power value P １ｉｎ Another example of the time change of the activation state of the second switch QQ and the voltage V3 converted by the third circuit 14 will be described below. As shown in Fig. 7, when the second switch QQ is activated and the voltage V3 converted by the second switch QQ is reduced to a non-zero finite value, a switching loss occurs in the second switch QQ. Therefore, as shown in Fig. 8, the power value P １ｉｎis less than the reference value Th1 (light load LL), the control unit 20 activates the second switch QQ to reduce the voltage V3 converted by the second switch QQ to 0 V. This makes it possible to suppress the voltage applied to the second switch QQ of the third circuit 14 to near 0 V. As a result, it is possible to reduce the switching loss of the third circuit 14 that occurs when the second switch QQ is operated. Note that the first embodiment assumes that no load is connected to the output side of the third circuit 14. In such a case, the third circuit does not need to output power, so the voltage V3 can be suppressed to 0 without any problems. In FIG. 8, the power value P １ｉｎ is equal to or greater than the reference value Th1, the control unit 20 suspends control of the second switch QQ in the same manner as in FIG.

[0039] Second Embodiment A power conversion device 10 and peripheral devices 2 and 3 connected to the power conversion device 10 according to a second embodiment will be described with reference to Fig. 9 . Fig. 9 corresponds to an example of a detailed circuit configuration of the power conversion device 10 of Fig. 1 . The example shown in Fig. 9 differs from the example of Fig. 4 in that the third circuit 14 further includes a DC / AC inverter 144 to which power converted by the second switch QQ (second switch elements Q1 to Q4) is input. The other configurations of Fig. 9 except for the third circuit 14 are the same as those of Fig. 4 , and therefore will not be described again.

[0040] The DC-AC inverter 144 has an H-bridge circuit including four third switch elements Y1 to Y4. That is, a first leg and a second leg are connected in parallel between a high-voltage line and a low-voltage line. The third switch elements Y1 to Y4 that make up the H-bridge circuit can be configured with semiconductor devices including, for example, IGBTs and MOSFETs. By applying an on signal or an off signal to the gate electrode of the MOSFET, the conductive state (on) and cut-off state (off) of the switch can be controlled.

[0041] Third switch elements Y1 and Y2 are connected in series on a first leg of the DC-AC inverter 144, and third switch elements Y3 and Y4 are connected in series on a second leg of the DC-AC inverter 144. Both terminals of the voltage detection unit 143 are connected between the third switch elements Y1 and Y2 and between the third switch elements Y3 and Y4, respectively. The third circuit 14 may include a smoothing circuit 145 that smoothes the AC power converted by the DC-AC inverter 144. The smoothing circuit 145 has an inductance 1451 and a capacitor 1452. The AC voltage converted from the DC voltage (voltage V3) by the DC-AC inverter 144 is output to the outlet 146 via the smoothing circuit 145. The DC-AC inverter 144 converts the AC voltage to, for example, a commercial power supply voltage (AC 100 V) used in Japan and outputs the converted voltage.

[0042] The power conversion device 10 or the power conversion system 1 according to the second embodiment can be mounted on an electric vehicle. By providing an outlet 146 inside the vehicle cabin, the second circuit 13 can supply power to the onboard auxiliary equipment 3a while supplying power to electrical appliances inside and outside the vehicle. The DC-DC converter for the onboard auxiliary equipment, which is an example of the first load 3, and the DC-AC inverter for the outlet 146, which were previously mounted separately on the electric vehicle, can be integrated. In other words, by integrating the input side circuit (first circuit 11) and the transformer 12, the power output from the two output side circuits (second circuit 13, third circuit 14) can be individually controlled.

[0043] As in the first embodiment, the control unit 20 controls the power value P １ｉｎ is less than the reference value Th1, as shown in the formula (1), the second switch QQ (second switch elements Q1 to Q4) is controlled so that the voltage value V3 converted by the second switch QQ (second switch elements Q1 to Q4) is equal to or less than the value obtained by multiplying the voltage value V1 input to the first circuit 11 by the ratio (N3 / N1) of the number of turns N3 of the third coil 123 to the number of turns N1 of the first coil 121. As a result, even under a light load, a reactive current I ｎｏｎ is injected to enable soft switching of the first circuit 11.

[0044] If the voltage V3 converted by the second switch elements Q1 to Q4 is lowered in order to achieve soft switching of the first switch SS, the third circuit 14 will be unable to output the desired power or voltage to the load (electrical appliance) connected to the output of the third circuit 14. On the other hand, if the third circuit 14 has a DC-AC inverter 144 downstream of the second switch elements Q1 to Q4, even if the voltage V3 converted by the second switch elements Q1 to Q4 is somewhat low, by controlling the downstream DC-AC inverter 144, the desired power or voltage can be output to the load (electrical appliance) to which the power converted by the DC-AC inverter 144 is supplied. Therefore, the presence of the third circuit 14 makes it possible to integrate a DC-AC inverter for an outlet into an isolated DC-DC converter for on-board accessories, thereby outputting 100 V AC while simultaneously improving the efficiency of the DC-DC converter.

[0045] As shown in FIG. 10, the control unit 20 controls the power value P １ｉｎ When the reference value Th1 is less than the reference value Th1 (light load LL), the lower limit of the voltage V3 converted by the second switch QQ (second switch elements Q1 to Q4) is set to the maximum value (e.g., 141 V) of the AC voltage converted by the DC-AC inverter. If the voltage V3 converted by the second switch QQ is significantly reduced while the DC-AC inverter 144 is outputting an AC voltage, the DC-AC inverter 144 will not be able to output the desired AC voltage. The lower limit of the voltage V3 converted by the second switch QQ is set to the maximum value of the AC voltage converted by the DC-AC inverter. When outputting a commercial power supply voltage (100 V AC) used in Japan, the maximum value of the AC voltage is 141 V. This allows the DC-AC inverter 144 to output the desired AC voltage. This control method is particularly effective when the DC-AC inverter 144 is supplying AC power to a load connected to an outlet 146.

[0046] On the other hand, when the DC-AC inverter 144 is inactive, that is, when the DC-AC inverter 144 is not supplying AC power to the load, it is not necessary to set the lower limit value of the voltage V3. Therefore, the control unit 20 sets the lower limit value of the power value P １ｉｎ 8, when the voltage V3 converted by the second switch QQ (second switches Q1 to Q4) is less than the reference value Th1, the second switch QQ may be controlled so that the voltage V3 converted by the second switch QQ (second switches Q1 to Q4) becomes 0 V. When the DC-AC inverter 144 is in a resting state, the voltage V3 converted by the second switch QQ is controlled to 0 V or close to 0 V, thereby reducing the switching loss of the third circuit 14 that occurs when the second switch QQ is operated.

[0047] Unlike the first embodiment, the second embodiment is based on the assumption that a load (electric appliance) is connected to the output side of the third circuit 14. Therefore, the control unit 20 controls the power value P １ｉｎ is equal to or greater than the reference value Th1, the second switch QQ (second switches Q1 to Q4) may be activated without being suspended. When the second switch QQ is suspended, the body diode of the second switch QQ operates as a rectifier, and the voltage (360 V) input to the third circuit 14 is supplied to the DC-AC inverter 144 as is. However, the control unit 20 may control the second switches Q1 to Q4 to adjust the power and voltage supplied to the DC-AC inverter 144.

[0048] Third Embodiment A power conversion device 10 according to a third embodiment and peripheral devices 2 and 3 connected to the power conversion device 10 will be described with reference to Fig. 11. Fig. 11 corresponds to an example of a detailed circuit configuration of the power conversion device 10 of Fig. 1. The example shown in Fig. 11 differs from the example of Fig. 4 in that the first circuit 11 controls the current I flowing through the first coil 121 of the transformer 12. Ｌ１ 11 except for the first circuit 11 is the same as that in FIG. 4, and therefore a repeated description will be omitted.

[0049] The current detection unit 113 detects the current I converted by the first switch elements S1 to S4 and output from the first circuit 11. Ｌ１The current detection unit 113 detects the detected current I Ｌ１ The voltage detection unit 135 transmits a signal indicating this to the control unit 20. The circuit configuration of the voltage detection unit 135 is not limited, and any known technology may be used.

[0050] As shown in FIG. 2, the reactive current I ｎｏｎ is generated, and the current value I Ｌ１ increases, contributing to the soft switching of the first switch SS. Meanwhile, as shown in FIG. Ｌ１ is the current required for soft switching, I ＺＶＳ A large reactive current Z exceeding ｏｖｅｒ does not contribute to the soft switching of the first switch SS, but only increases the conduction loss of the first switch SS and the second switch QQ. Ｌ１ Specifically, the control unit 20 changes the voltage V3 converted by the second switch QQ while measuring the power value P １ｉｎ is less than the reference value Th1, the current value I Ｌ１ The voltage V3 converted by the second switch QQ (second switch elements Q1 to Q4) is changed in accordance with the voltage V3. This reduces the minimum reactive current I required for soft switching. ｎｏｎ , and the conduction loss of the first switch SS and the second switch QQ can be minimized. ｌｏａｄ When the reactive current I required for soft switching decreases, ｎｏｎ increases, and the voltage V3 required for soft switching also decreases. ｌｏａｄ ) fluctuates, and the reactive current I required for soft switching ｎｏｎ It can also handle changes in the value of

[0051] For example, the voltage V3 converted by the second switch QQ may be controlled according to the flowchart shown in Fig. 13. In step S11, the current detection unit 113 detects the current I flowing through the first coil 121 of the transformer 12. Ｌ１is detected, and the current I Ｌ１ The control unit 20 then transmits a signal indicating the current I Ｌ１ is the current required for soft switching, I ＺＶＳ If it exceeds the threshold (YES in step S12), the soft switching is successful and the reactive current I ｎｏｎ Since there is no need to further increase the voltage V3, the process proceeds to step S13, and the control unit 20 increases the voltage V3. If the voltage V3 is not exceeded (NO in step S12), soft switching has not been achieved, and the reactive current I ｎｏｎ Since it is necessary to further increase the voltage V3, the process proceeds to step S14, where the control unit 20 reduces the voltage V3. The control unit 20 repeatedly executes steps S11 to S14 at a predetermined control period to convert the voltage V3 converted by the second switch elements Q1 to Q4 into the voltage V ＺＶＳ Therefore, the control unit 20 can converge the reactive current I to the minimum required to realize soft switching. ｎｏｎ It is possible to generate the following.

[0052] As shown in FIG. 14, the power P １ｉｎ Even if the reactive current I fluctuates, the control method of FIG. ｎｏｎ That is, the power P １ｉｎ When the load is light (LL) and the current I Ｌ１ is the current I ＺＶＳ The voltage V3 converted by the second switch QQ is optimized so as to match the power P １ｉｎ When the current I flows through the first coil 121, the current I Ｌ１ However, the control unit 20 reduces the voltage V3 converted by the second switch QQ, and the reactive current I ｎｏｎ This increases the temporarily reduced current I Ｌ１ is the current I ＺＶＳ In this way, the power P １ｉｎ Even if the reactive current Iｎｏｎ is optimized to obtain the minimum reactive current I required to achieve soft switching. ｎｏｎ The current required for soft switching is I ＺＶＳ may be determined in advance from the characteristics of the switch and the circuit constants, or may be set to a value obtained through an experiment.

[0053] On the other hand, the above method requires that V3 be set to a value other than 0 V in order to suppress the reactive current to a necessary and sufficient level, which results in switching loss due to activation of the second switch QQ. Therefore, in order to reduce switching loss, it is desirable to set V3 to 0 V, but in that case, as described above, an extremely large reactive current is generated, which increases the conduction loss due to the first switch SS and the second switch QQ.

[0054] Reactive current I ｎｏｎ To reduce the power P to the minimum required level, the control unit 20 may increase the switching frequency F of the first switch SS and the second switch QQ instead of the voltage V3 converted by the second switch QQ. １ｉｎ is less than the reference value Th1, the current value I Ｌ１ The switching frequency F of the first switch SS and the second switch QQ may be changed depending on the reactive current I ｎｏｎ The relation between the switching frequency F and the reactive current I ｎｏｎ decreases.

[0055]

[0056] By using this method to suppress an increase in reactive current, the reactive current can be suppressed to the minimum necessary while keeping the voltage V3 at 0 V using the second switch QQ. This makes it possible to achieve soft switching of the first switch SS while significantly reducing the switching loss of the second switch QQ.

[0057] For example, the switching frequency F of the first switch SS and the second switch QQ may be controlled according to the flowchart shown in Fig. 15. Steps S11 and S12 in Fig. 15 are common to steps S11 and S12 in Fig. 13. The current I Ｌ１ is the current required for soft switching, I ＺＶＳ If it exceeds (YES in step S12), the soft switching is successful, so the reactive current I ｎｏｎ Therefore, the process proceeds to step S23, and the control unit 20 increases the switching frequency F to reduce the reactive current I ｎｏｎ On the other hand, if it does not exceed the limit (NO in step S12), the soft switching is not realized, so the reactive current I ｎｏｎ Therefore, the process proceeds to step S24, and the control unit 20 reduces the switching frequency F to increase the reactive current I ｎｏｎ The control unit 20 repeatedly executes steps S11, S12, S23, and S24 at a predetermined control period, thereby increasing the minimum reactive current I required to realize soft switching. ｎｏｎ It is possible to generate the following.

[0058] The control unit 20 determines the current value I Ｌ１ By changing the switching frequency F of the first switch SS and the second switch QQ while measuring the ＺＶＳ This can minimize switching losses.

[0059] As shown in FIG. 16, the power P １ｉｎ Even if the reactive current I ｎｏｎ That is, the power P １ｉｎ When the load is light (LL) and the current I Ｌ１ is the current I ＺＶＳThe switching frequency F of the first switch SS and the second switch QQ is optimized so that the power P input to the first circuit 11 matches the １ｉｎ When the current I flows through the first coil 121, the current I Ｌ１ The control unit 20 reduces the switching frequency F of the first switch SS and the second switch QQ, thereby reducing the reactive current I ｎｏｎ This increases the temporarily reduced current I Ｌ１ is the current I ＺＶＳ In this way, the power P １ｉｎ Even if the reactive current I ｎｏｎ is optimized to obtain the minimum reactive current I required to achieve soft switching. ｎｏｎ It is possible to generate a reactive current I ｎｏｎ In order to optimize the above, the control unit 20 may simultaneously execute the control method shown in FIG. 13 and the control method shown in FIG.

[0060] 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.

[0061] REFERENCE SIGNS LIST 10 Power conversion device 11 First circuit 12 Transformer 13 Second circuit 14 Third circuit 20 Control unit 121 First coil 122 Second coil 123 Third coil 144 DC / AC inverter N1 Number of turns of first coil N3 Number of turns of third coil QQ Second switch SS First switch Th1 Reference value UU Rectifier circuit

Claims

1. A method for controlling a power conversion device by a control unit, The power conversion device is a first circuit having a first switch for converting input power; a transformer having a first coil to which the power converted by the first circuit is input, a second coil that converts the voltage input to the first coil and outputs the converted voltage, and a third coil that converts the voltage input to the first coil and outputs the converted voltage; a second circuit having a rectifier circuit that converts the power output from the second coil; a third circuit having a second switch that converts the power output from the third coil; The control unit When the power value input to the first circuit is less than a reference value, the second switch is controlled so that the voltage value converted by the second switch is equal to or less than the value obtained by multiplying the voltage value input to the first circuit by the ratio of the number of turns of the third coil to the number of turns of the first coil. A method for controlling a power conversion device.

2. The control method for the power conversion device according to claim 1, the control unit suspends control of the second switch when a power value input to the first circuit is equal to or greater than the reference value. A method for controlling a power conversion device.

3. 3. A control method for a power conversion device according to claim 1 or 2, the control unit controls the second switch so that a voltage value converted by the second switch becomes 0 V when a power value input to the first circuit is less than the reference value. A method for controlling a power conversion device.

4. 3. A control method for a power conversion device according to claim 1 or 2, the third circuit includes a DC / AC inverter to which the power converted by the second switch is input. A method for controlling a power conversion device.

5. 5. A method for controlling a power conversion device according to claim 4, the control unit sets a lower limit value of the voltage converted by the second switch to a maximum value of the AC voltage converted by the DC / AC inverter when the power value input to the first circuit is less than the reference value. A method for controlling a power conversion device.

6. A control method for the power conversion device according to claim 4, the control unit controls the second switch so that a voltage value converted by the second switch becomes 0 V when the DC / AC inverter is in a stopped state and a power value input to the first circuit is less than the reference value. A method for controlling a power conversion device.

7. 3. A control method for a power conversion device according to claim 1 or 2, the control unit changes the voltage converted by the second switch in accordance with a value of a current flowing through a first coil of the transformer when a value of power input to the first circuit is less than the reference value; A method for controlling a power conversion device.

8. 3. A control method for a power conversion device according to claim 1 or 2, the control unit simultaneously increases the switching frequencies of the first switch and the second switch when the power value input to the first circuit is less than the reference value. A method for controlling a power conversion device.

9. 3. A control method for a power conversion device according to claim 1 or 2, the control unit changes the switching frequency of the first switch and the second switch in accordance with a value of a current flowing through a first coil of the transformer when a value of power input to the first circuit is less than the reference value; A method for controlling a power conversion device.

10. a first circuit having a first switch for converting input power; a transformer having a first coil to which the power converted by the first circuit is input, a second coil that converts the voltage input to the first coil and outputs the converted voltage, and a third coil that converts the voltage input to the first coil and outputs the converted voltage; a second circuit having a rectifier circuit that converts the power output from the second coil; a third circuit having a second switch that converts the power output from the third coil; A control unit; A power conversion system comprising: The control unit When the power value input to the first circuit is less than a reference value, the second switch is controlled so that the voltage value converted by the second switch is equal to or less than the value obtained by multiplying the voltage value input to the first circuit by the ratio of the number of turns of the third coil to the number of turns of the first coil. Power conversion systems.