Power conversion device and method for controlling power

Abstract

The invention provides a power conversion device provided with a bias suppression capacitor, wherein the power conversion device can realize high efficiency, small size and light weight at the same time. This power conversion device converts a first DC voltage supplied from a DC power source to a second DC voltage via a bridge circuit, a transformer, and a rectifier circuit, and is provided with: a first capacitor provided between the bridge circuit and the transformer; a second capacitor provided in parallel or in series with the first capacitor; a first semiconductor switch provided in parallel or in series with the first capacitor; and a switch-based voltage control unit that adjusts the amount of phase shift of the elements constituting the bridge circuit.

Description

Technical Field

[0001] This invention relates to the configuration and control of power conversion devices, and particularly to effective techniques applicable to isolated DC / DC converters that integrate multiple power conversion circuits using transformers. Background Technology

[0002] As a variation of on-board power conversion devices, an isolated DC / DC converter is being developed that integrates a low-voltage battery (LVBAT) DC / DC converter and an AC 100V socket (V2L) DC / AC converter into one unit using a transformer. By integrating multiple power conversion circuits via a transformer, both high efficiency and miniaturization / lightweight design of the power conversion device can be achieved.

[0003] In isolated DC / DC converters that integrate multiple power conversion circuits, the input voltage range widens, necessitating the design of the transformer's primary-side turns (generally by increasing the number of turns) to meet output voltage specifications even when the input voltage decreases. On the other hand, at rated input voltage, primary-side current and secondary-side voltage increase, making it difficult to improve efficiency.

[0004] However, in circuits with more than two bridge arms, a converter that operates by shifting the phase between the bridge arms is called a "phase shift converter".

[0005] As background technology in this field, there is, for example, technology like Patent Document 1. Patent Document 1 discloses a "DC-DC converter with a primary-side phase-shift method, comprising a full-bridge inverter for converting DC voltage to high-frequency voltage and a rectifier circuit for rectifying its output." (Paragraph

[0001] of Patent Document 1)

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Patent No. 6033649 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] In the phase shift converter described above, since the output voltage range can be extended by using a bias suppression capacitor, the output voltage range can be extended by switching capacitors, thereby increasing the number of turns on the primary side.

[0011] However, in existing phase shift converters, two semiconductor devices are generally used as bidirectional switches for capacitor switching, which results in high losses.

[0012] In the aforementioned Patent Document 1, under a light load where the electromagnetic energy stored in the inductor contained in the circuit is relatively small, by making the capacitor switching switch Q5 open, a first capacitor and a second capacitor are connected in series between the output terminals of the inverter, reducing the combined electrostatic capacitance of the two capacitors. As a result, the two capacitors can be fully charged and discharged with the relatively small amount of electromagnetic energy stored in the circuit, thereby realizing soft switching of each switching element of the inverter.

[0013] On the other hand, under heavy loads where the electromagnetic energy stored in the inductor contained in the circuit increases, by turning on the capacitor switching switch Q5, the first capacitor or the second capacitor is connected in parallel with a switching element of a bridge arm of the reference phase or a switching element of a bridge arm of the control phase, thus increasing the electrostatic capacitance of the capacitors used to achieve soft switching of each switching element of the converter. (Paragraph 1 of Patent Document

[0051] )

[0014] In Patent Document 1, the switching circuit consists of two capacitors (capacitors C5 and C6) and one capacitor switching switch Q5, but when using semiconductor devices, it needs to be used as a two-way switch.

[0015] Furthermore, Patent Document 1 does not consider extending the output voltage range using the aforementioned bias suppression capacitor.

[0016] Therefore, the object of the present invention is to provide a power conversion device and its control method that can simultaneously achieve high efficiency and small size and lightweight in a power conversion device equipped with a bias suppression capacitor.

[0017] Methods for solving problems

[0018] To address the aforementioned problems, the present invention provides a power conversion device that converts a first DC voltage supplied from a DC power source into a second DC voltage via a bridge circuit, a transformer, and a rectifier circuit. The power conversion device comprises: a first capacitor disposed between the bridge circuit and the transformer; a second capacitor connected in parallel or series with the first capacitor; a first semiconductor switch connected in parallel or series with the first capacitor; and a voltage control unit based on the switch, which adjusts the phase shift of the elements constituting the bridge circuit.

[0019] Furthermore, the present invention is a control method for the aforementioned power conversion device, wherein when the first DC voltage is lower than a predetermined value, the first semiconductor switch is turned off, and the second DC voltage is controlled by the switch of the bridge circuit; when the first DC voltage is higher than the predetermined value, the first semiconductor switch is turned on, and the range of the second DC voltage is extended by the switch of the bridge circuit.

[0020] The effects of the invention

[0021] According to the present invention, a power conversion device and its control method can be realized in a power conversion device having a bias suppression capacitor, which can achieve both high efficiency and small size and light weight.

[0022] Other issues, structures, and effects not mentioned above will be clarified through the following description of the implementation methods. Attached Figure Description

[0023] Figure 1 This is a circuit diagram showing the schematic configuration of the power conversion device according to Embodiment 1 of the present invention.

[0024] Figure 2 It means Figure 1 A diagram of a modified example of the capacitor switching circuit 103.

[0025] Figure 3 It means Figure 1 A flowchart of the control method for a power conversion device.

[0026] Figure 4 This is a diagram showing the waveform during capacitor switching control.

[0027] Figure 5 This is a diagram showing the waveform of the semiconductor switch S101 in the open state, which represents the parallel configuration of the power conversion device according to Embodiment 2 of the present invention.

[0028] Figure 6A This is a diagram illustrating the action of switching a capacitor switching circuit from open to closed.

[0029] Figure 6B This is a diagram illustrating the action of switching a capacitor switching circuit from open to closed.

[0030] Figure 6C This is a diagram illustrating the action of switching a capacitor switching circuit from open to closed.

[0031] Figure 7 This is a diagram showing the waveform of switch S101 in the off state when the power conversion device of Embodiment 3 of the present invention is connected in series.

[0032] Figure 8A This is a diagram illustrating the action of switching a capacitor switching circuit from open to closed.

[0033] Figure 8B This is a diagram illustrating the action of switching a capacitor switching circuit from open to closed.

[0034] Figure 9 This is a diagram showing the waveform of switch S101 in the open state, indicating the parallel connection mode of the power conversion device of Embodiment 4 of the present invention.

[0035] Figure 10 This is a graph showing the waveform that temporarily increases the peak value of VC1 by reducing the switching frequency.

[0036] Figure 11 This is a flowchart illustrating the control method of the power conversion device according to Embodiment 5 of the present invention.

[0037] Figure 12 This is a diagram showing the waveform during capacitor switching control.

[0038] Figure 13 This is a diagram showing the characteristics of the capacitor switching circuit of the power conversion device according to Embodiment 6 of the present invention when the semiconductor switch S101 continuously switches the capacitor according to the switching duty cycle.

[0039] Figure 14 This is a diagram illustrating the capacitor switching circuit of the power conversion device according to Embodiment 7 of the present invention.

[0040] Figure 15 This is a diagram illustrating the capacitor switching circuit of the power conversion device according to Embodiment 8 of the present invention.

[0041] Figure 16 This is a diagram illustrating the capacitor switching circuit of the power conversion device according to Embodiment 9 of the present invention.

[0042] Figure 17 This is a diagram showing the waveform during capacitor switching control of the power conversion device according to Embodiment 10 of the present invention.

[0043] Figure 18 A circuit diagram showing the approximate configuration of an existing phase shift converter.

[0044] Figure 19 This is a diagram showing the effect of the bias suppression capacitor on the output voltage. Detailed Implementation

[0045] Hereinafter, embodiments of the present invention will be described using the accompanying drawings. Furthermore, in the drawings, the same symbols are used to denote the same components, and detailed descriptions of repeated parts are omitted.

[0046] Example 1

[0047] Reference Figures 1 to 4 as well as Figure 18 , Figure 19 The power conversion device and its control method according to Embodiment 1 of the present invention will be described. Furthermore, Figure 18 and Figure 19 This is a schematic representation of a conventional phase shifter for ease of understanding of the present invention. Figure 18The effect of the bias suppression capacitor on the output voltage () and the effect of the bias suppression capacitor on the output voltage () Figure 19 (The image is shown.)

[0048] Figure 1 This is a circuit diagram showing the general configuration of the power conversion device in this embodiment. Figure 2 It means Figure 1 A diagram of a modified example of the capacitor switching circuit 103.

[0049] like Figure 1 As shown, the power conversion device in this embodiment is a power conversion device that uses a capacitor switching parallel connection method. The power conversion device in this embodiment is an isolated type DC / DC converter, which is not limited to a phase shift converter, but can also be an LLC converter, etc. Symbol 101 is the primary side circuit of the phase shift converter, which is composed of capacitor C1, semiconductor switches S1 to S4, capacitor switching circuit 103, and inductor L1.

[0050] The capacitor switching circuit 103 consists of capacitors C101 and C102 and a semiconductor switch S101. Capacitor C102 is connected in parallel with capacitor C101, and semiconductor switch S101 is connected in parallel with capacitor C101 and in series with capacitor C102.

[0051] In addition, Figure 1 In the example shown, a MOSFET with diode D101 connected in anti-parallel is illustrated as an example of a semiconductor switch S101.

[0052] Symbol 102 represents the secondary side circuit, consisting of inductor L2, capacitor C3, and diodes D1 and D2. The secondary side circuit is not limited to a center-tapped configuration; it can also be a full-bridge configuration, etc. Symbol Tr1 represents a transformer.

[0053] like Figure 2 As shown, the capacitor switching method can also be a series connection. Figure 2 In this example, capacitor C2 and capacitor C1 of capacitor switching circuit 103 are connected in series, and semiconductor switch S1 is connected in series with capacitor C1 and in parallel with capacitor C2. Semiconductor switch S1 is a semiconductor device such as a MOSFET with diode D1 connected in anti-parallel.

[0054] Here, in Figure 18 In existing phase-shift converters, capacitor C3 is sometimes added to suppress transformer bias. For example... Figure 19 As shown, the output voltage range can be extended by changing this capacitor. Therefore, it is proposed that... Figures 1 to 4 The capacitor switching circuit and control method of this embodiment are shown.

[0055] Figure 3 It means Figure 1A flowchart of the control method for a power conversion device.

[0056] like Figure 3 As shown, the semiconductor switch S101 in the capacitor switching circuit 103 is switched according to the input voltage.

[0057] When the power conversion device starts to operate, firstly, in step S1, the primary side circuit 101 and the secondary side circuit 102 are driven.

[0058] Next, in step S2, the input voltage V1 and the output voltage V2 are detected respectively.

[0059] Next, in step S3, the input voltage V1 is compared with a predetermined threshold (reference value) Vth1. If the input voltage V1 is above the threshold Vth1 (yes), proceed to step S4.

[0060] If the input voltage V1 is less than the threshold Vth1 (no), proceed to step S5.

[0061] In step S4, semiconductor switch S101 is turned on, and the process proceeds to step S7. On the other hand, in step S5, the input voltage V1 is compared with a predetermined threshold (reference value) Vth2.

[0062] In step S5, if the input voltage V1 is below the threshold Vth2 (yes), proceed to step S6. If the input voltage V1 is above the threshold Vth2 (no), proceed to step S7.

[0063] In step S6, the semiconductor switch S101 is turned off, and the process proceeds to step S7.

[0064] Next, in step S7, the difference ΔV2 between the measured value of the output voltage V2 and its target value Vref2 is calculated, and it is determined whether ΔV2 is below 0.

[0065] If ΔV2 is less than or equal to 0 (Yes), proceed to step S8. If ΔV2 is greater than or equal to 0 (No), proceed to step S9.

[0066] In step S8, after decreasing the phase shift θ1 of the primary-side circuit 101, the process moves to step S10, where the driving of the primary-side circuit 101 and the secondary-side circuit 102 is stopped. On the other hand, in step S9, after increasing the phase shift θ1 of the primary-side circuit 101, the process moves to step S10, where the driving of the primary-side circuit 101 and the secondary-side circuit 102 is stopped.

[0067] Figure 4 This represents the waveform during capacitor switching control.

[0068] When the input voltage V1 is above the threshold Vth1, semiconductor switch S101 is turned on, and capacitors C101 and C102 are connected in parallel (increasing capacitance), thus reducing the output voltage V2. When the input voltage V1 is below the threshold Vth1, semiconductor switch S101 is turned off, and only capacitor C101 is connected (decreasing capacitance), thereby increasing the output voltage V2. After driving the capacitor switching circuit 103, the phase shift θ1 of the phase shift converter is used to control the output voltage V2. (Explanation of the phase shift converter's drive is omitted.)

[0069] in addition, Figure 2 The series connection method shown can also be controlled in the same way as described above.

[0070] As described above, the power conversion device of this embodiment is a power conversion device that converts a first DC voltage V1 supplied from a DC power source into a second DC voltage V2 via a bridge circuit (primary side circuit 101), a transformer Tr1, and a rectifier circuit (secondary side circuit 102). The power conversion device includes: a first capacitor C101 disposed between the bridge circuit and the transformer Tr1; a second capacitor C102 disposed in parallel or in series with the first capacitor C101; a first semiconductor switch S101 disposed in parallel or in series with the first capacitor C101; and a voltage control unit based on the switch, which adjusts the phase shift of the elements (semiconductor switches S1 to S4) constituting the bridge circuit.

[0071] The second capacitor C102 is connected in parallel with the first capacitor C101, and the first semiconductor switch S101 is connected in parallel with the first capacitor C101 and in series with the second capacitor C102.

[0072] Alternatively, the second capacitor C102 can be connected in series with the first capacitor C101, and the first semiconductor switch S101 can be connected in series with the first capacitor C101 and in parallel with the second capacitor C102.

[0073] In addition, in this embodiment, when the first DC voltage V1 is lower than the predetermined value Vth1, the power conversion device opens the first semiconductor switch S101 and controls the second DC voltage V2 through the switch of the bridge circuit. When the first DC voltage V1 is higher than the predetermined value Vth1, the first semiconductor switch S101 is turned on and the range of the second DC voltage V2 is extended through the switch of the bridge circuit.

[0074] According to this embodiment, since the leakage inductance and magnetizing inductance of the capacitor and transformer generate LC resonance, the gain can be changed according to the capacitance. When the input voltage V1 decreases, the output voltage V2 can be increased by increasing the gain, thus the output voltage range can be extended by controlling the gain.

[0075] In this embodiment, an isolated DC / DC converter with an output voltage control unit (not shown) is used as an example. When the input voltage V1 is lower than a certain threshold Vth1, the output voltage V2 is increased to expand the control range (output voltage range) of the aforementioned output voltage control unit.

[0076] In the aforementioned isolated DC / DC converter (phase-shift converter, LLC converter), it can be confirmed that the output voltage varies due to the capacitance of the capacitor on the primary side. Therefore, by setting a switching switch (semiconductor switch S101) and two capacitors C101 and C102, the output voltage range can be extended with a simple circuit configuration by reducing the capacitance when the input voltage V1 decreases.

[0077] Example 2

[0078] Reference Figures 5 to 6C This section describes the power conversion device and its control method according to Embodiment 2 of the present invention. The circuit configuration of the power conversion device in this embodiment is the same as that in Embodiment 1. Figure 1 )same.

[0079] Figure 5 This is a diagram showing the waveform of the semiconductor switch S101 in the parallel configuration of the power conversion device in this embodiment when it is in the open state.

[0080] When the semiconductor switch S101 is in the off state, since only the capacitor C101 is connected, an AC voltage is applied to the capacitor C101, and a charging and discharging current flows accordingly.

[0081] On the other hand, since the semiconductor switch S101 of capacitor C102 is in the open state, the charging current flows through the body diode D1 and cannot discharge. Therefore, the voltage VC2 of capacitor C102 is clamped at the peak value of the voltage VC1 of capacitor C101, and then becomes a stable state in which no charging current flows.

[0082] Figures 6A to 6C This indicates the action of switching the capacitor switching circuit 103 from off to on.

[0083] like Figure 6A As shown, when VC1 = VC2, since the voltage of semiconductor switch S1 is 0, no current will flow between C1 and C2 even if it is turned on.

[0084] On the other hand, such as Figure 6B and Figure 6C As shown, when there is a potential difference between VC1 and VC2, if the semiconductor switch S1 is turned on while a voltage is applied, a short-circuit current will flow between C1 and C2.

[0085] Short-circuit current is a major cause of increased losses and circuit failures, therefore it is necessary to switch to conduction when VC1 = VC2. Therefore, by... Figure 5 The moment indicated by the black circle in the middle is when the semiconductor switch S101 is turned on, enabling switching without the flow of overcurrent.

[0086] As described above, in this embodiment, the power conversion device switches the first semiconductor switch S101 to conduct when the voltage of the first capacitor C101 is at its maximum.

[0087] In the configuration where the second capacitor C102 is connected in parallel, when the semiconductor switch S101 is in the open state, the voltage of the second capacitor C102 is equal to the maximum value of the voltage of the first capacitor C101. Therefore, when the voltage VC1 of the first capacitor C101 and the voltage VC2 of the second capacitor C102 are equal, that is, when the voltage VC1 of the first capacitor C101 is at its maximum, the switch is turned on.

[0088] When switching from open to closed while a voltage is applied to the semiconductor switch S101, an overcurrent is generated, causing circuit failure. Therefore, switching needs to be performed at the aforementioned moment when no voltage is applied to the semiconductor switch S101. Furthermore, this moment does not require sensing the capacitor voltage but is synchronized with the control of the primary-side circuit, thus enabling implementation even with a sensorless configuration.

[0089] Example 3

[0090] Reference Figures 7 to 8B This invention describes the power conversion device and its control method according to Embodiment 3. The circuit configuration of the power conversion device in this embodiment is the same as that in Embodiment 1. Figure 1 and Figure 2 )same.

[0091] Figure 7 This is a diagram showing the waveform when switch S101 of the power conversion device in this embodiment is in the open state in a series configuration.

[0092] When semiconductor switch S101 is open, capacitors C101 and C102 are connected in series, so a voltage is applied to either capacitor. However, because body diode D101 is connected in parallel with capacitor C102, no negative voltage (the voltage from the anode to the cathode of body diode D101) is applied across capacitor C102 (VC2). Therefore, an AC voltage is applied when VC1≤0 and VC2≥0.

[0093] Figure 8A and Figure 8B This indicates the action of switching the capacitor switching circuit 103 from off to on.

[0094] like Figure 8AAs shown, when VC2=0, since the voltage across semiconductor switch S1 is 0, no current will flow between C2 and S1 even if the switch is turned on. On the other hand, as... Figure 8B As shown, when a voltage is applied to VC2, if the semiconductor switch S1 is turned on while a voltage is applied, a short-circuit current flows between C2 and S1. This short-circuit current is a major cause of increased losses and circuit failures; therefore, it is necessary to switch to on when VC1 = VC2. Therefore, by… Figure 7 The black circle indicates the moment when the semiconductor switch S101 is turned on, enabling switching without the flow of overcurrent.

[0095] Example 4

[0096] Reference Figure 9 and Figure 10 The power conversion device and its control method according to Embodiment 4 of the present invention will be described. The circuit configuration of the power conversion device in this embodiment is the same as that in Embodiment 1. Figure 1 )same.

[0097] Figure 9 This is a diagram showing the waveform when switch S101 of the power conversion device in this embodiment is in the open state in parallel configuration.

[0098] exist Figure 5 When the parallel connection is disconnected and the load or input / output voltage changes, the peak value of the voltage VC1 across capacitor C101 changes. If the peak value of VC1 increases, capacitor C102 recharges, returning to its original state. Figure 5 The same state. However, with the peak value of VC1 decreasing, capacitor C102 cannot discharge, thus becoming... Figure 9 The waveform shown is as follows. In this state, since there is no point where VC1=VC2, overcurrent will occur at any time when switching to conduction.

[0099] Therefore, a control method to solve the above problems is proposed. This involves increasing... Figure 1 The conduction time of semiconductor switches S1 to S4 in the primary side circuit 101 is temporarily increased to enhance the peak value of VC1. Specifically, this can be achieved by reducing the switching frequency or increasing the duty cycle of the switches.

[0100] Figure 10 This represents a waveform that temporarily increases the peak value of VC1 by reducing the switching frequency. By increasing the peak value, it is possible to switch to conduction when VC1 = VC2.

[0101] As described above, in this embodiment, the power conversion device increases the voltage VC1 of the first capacitor C101 by increasing the conduction time of the bridge circuit, so that the voltage VC1 of the first capacitor C101 increases. When the voltage VC1 of the first capacitor C101 is the same as the voltage VC2 of the second capacitor C102, the first semiconductor switch S101 is switched on.

[0102] Due to variations in input / output voltage and load, the peak value of the voltage VC1 across the first capacitor C101 changes. When the peak value of VC1 increases, the voltage VC2 across the second capacitor C102 also increases, so there is no problem. However, when the peak value of VC1 decreases, the voltage VC2 across the second capacitor C102 cannot discharge, and the crossover point between VC1 and VC2 disappears. In this state, a potential difference is generated between the capacitors regardless of the switching time, thus causing overcurrent.

[0103] As a solution, a control method is proposed to increase the peak value of the voltage VC1 of the first capacitor C101. In this control method, the switching on-time is increased by utilizing the variation in the waveform of the voltage VC1 of the first capacitor C101 according to the switching of the bridge circuit on the primary side, thereby increasing the peak value of the voltage VC1 of the first capacitor C101. Methods for increasing the on-time include decreasing the frequency and increasing the duty cycle.

[0104] Due to variations in input / output voltage and load, the peak value of the voltage VC1 across the first capacitor C101 sometimes decreases. At this time ( Figure 10 In the region of f=100kHz, since there is no point where the voltage VC1 of the first capacitor C101 intersects with the voltage VC2 of the second capacitor C102, overcurrent is generated at any switching time. Therefore, when the peak value of the voltage VC1 of the first capacitor C101 decreases, the peak value of the voltage VC1 of the first capacitor C101 increases due to the conduction time of the bridge circuit on the primary side (frequency decreases, duty cycle increases). Figure 10 In the region where f=80kHz (conducting), the circuit switches from off to on at the same time as the voltage VC2 of the second capacitor C102, thereby preventing overcurrent. Figure 10 The region where f=100kHz (disconnected).

[0105] Example 5

[0106] Reference Figure 11 and Figure 12This invention describes the power conversion device and its control method according to Embodiment 5. The circuit configuration of the power conversion device in this embodiment is the same as that in Embodiment 1. Figure 1 )same.

[0107] Figure 11 This is a flowchart illustrating the control method of the power conversion device in this embodiment.

[0108] Steps S1 to S3 are the same as in Example 1. Figure 3 The steps S1 to S3 of the flowchart are the same, so the explanation is omitted.

[0109] In step S3, if the input voltage V1 is above the threshold Vth1 (yes), proceed to step S4. If the input voltage V1 is below the threshold Vth1 (no), proceed to step S7.

[0110] In step S4, it is determined whether the semiconductor switch S101 is in the off state. If it is in the off state (yes), proceed to step S5, where the semiconductor switch S101 is switched from off to on. If it is in the on state (no), proceed to step S11.

[0111] Next, in step S6, after reducing the phase shift θ1 of the primary side circuit 101, the process moves to step S11.

[0112] On the other hand, in step S7, the input voltage V1 is compared with a predetermined threshold (reference value) Vth2. If the input voltage V1 is below the threshold Vth2 (yes), proceed to step S8. If the input voltage V1 is greater than the threshold Vth2 (no), proceed to step S11.

[0113] In step S8, it is determined whether the semiconductor switch S101 is in the ON state. If it is in the ON state (Yes), proceed to step S9, where the semiconductor switch S101 is switched from ON to OFF. If it is in the OFF state (No), proceed to step S11.

[0114] Next, in step S10, after increasing the phase shift θ1 of the primary side circuit 101, the process moves to step S11.

[0115] Steps S11 to S14 are the same as in Example 1 ( Figure 3 Steps S7 to S10 of the flowchart are the same, so the explanation is omitted.

[0116] In this embodiment, as Figure 11 As shown, compared with Example 1 ( Figure 3 Compared to the flowchart, the control of adjusting the phase shift θ1 when switching semiconductor switch S101 is added.

[0117] When semiconductor switch S101 is switched from off to on, the output voltage (gain) decreases, causing the phase shift θ1 to decrease and the output voltage V2 to increase. When semiconductor switch S101 is switched from on to off, the output voltage (gain) increases, causing the phase shift θ1 to increase and the output voltage V2 to decrease.

[0118] Figure 12 express Figure 11 The waveform during control drive.

[0119] Without feedforward control, large voltage fluctuations occur due to gain changes during capacitor switching. On the other hand, with feedforward control added, the voltage fluctuations are corrected by converter voltage control based on gain changes during capacitor switching, thus suppressing voltage fluctuations.

[0120] As described above, in the power conversion device of this embodiment, when the first semiconductor switch S101 is switched on / off, voltage fluctuations are suppressed by feeding forward control of the output voltage control system of the bridge circuit.

[0121] Gain variations are achieved by switching capacitors, thus allowing for anticipation of rapid changes in the output voltage V2. The output voltage is controlled by a bridge circuit on the primary side to follow the target value. However, in conventional feedback control, it is difficult to suppress output voltage fluctuations because the voltage only starts to follow after a rapid change in output voltage.

[0122] Therefore, the output voltage control system of the primary-side bridge circuit is corrected according to the change in gain. In the case of a phase-shift converter, this correction can be achieved by reducing the phase shift, which is a control parameter, as the gain increases due to capacitor switching. By integrating this correction as feedforward control into the switching control flow, it is expected to suppress load variations in response to capacitor switching changes, compared to conventional feedback control.

[0123] Example 6

[0124] Reference Figure 13 This invention describes the power conversion device and its control method according to Embodiment 6. The circuit configuration of the power conversion device in this embodiment is the same as that in Embodiment 1. Figure 1 )same.

[0125] Figure 13 This is a diagram showing the characteristics of the semiconductor switch S101 of the capacitor switching circuit of the power conversion device according to this embodiment when the switching duty cycle continuously switches the capacitor.

[0126] When the semiconductor switch S101 of the capacitor switching circuit 103 is switched, such as Figure 13As shown, the capacitor can be continuously switched according to the duty cycle of the switch.

[0127] Therefore, in the power conversion device of this embodiment, the gain is continuously switched by adjusting the duty cycle by switching the first semiconductor switch S101.

[0128] Through the above control, the capacitor can be continuously adjusted between two values ​​of simple switching control.

[0129] For capacitor C1 with a duty cycle of 0% (continuously off) and capacitor C2 with a duty cycle of 100% (continuously on), by adjusting the duty cycle, the period during which C1 behaves and the period during which C2 behaves can be adjusted to any value between the two.

[0130] By controlling the switching of the switching switch and adjusting the duty cycle, the capacitor can be switched continuously, thus enabling precise control of the output voltage (gain).

[0131] On the other hand, due to switching losses occurring in the switching process, resulting in increased losses and constraints on equipment selection, it is necessary to select the appropriate equipment based on the application.

[0132] Example 7

[0133] Reference Figure 14 The power conversion device and its control method according to Embodiment 7 of the present invention are described.

[0134] Figure 14 This diagram illustrates the capacitor switching circuit of the power conversion device in this embodiment. Figure 1 The capacitor switching circuit 103 combines Figure 2 The circuit configuration of the capacitor switching circuit (modified example).

[0135] like Figure 14 As shown, the capacitor switching circuit of this embodiment has a third capacitor C3 that is different from the first capacitor C1 and the second capacitor C2, and a second semiconductor switch S2 that is different from the first semiconductor switch S1. The third capacitor C3 is connected in series with the first capacitor C1 and the second capacitor C2, and is connected in parallel with the second semiconductor switch S2.

[0136] As in this embodiment, by combining a series-connected capacitor switching circuit and a parallel-connected capacitor switching circuit, it is possible to switch capacitors (gain) with a value of 3 or higher.

[0137] Example 8

[0138] Reference Figure 15 The power conversion device and its control method according to Embodiment 8 of the present invention are described.

[0139] Figure 15 This diagram illustrates the capacitor switching circuit of the power conversion device in this embodiment, which combines multiple... Figure 1 The circuit configuration of the capacitor switching circuit 103 (modified example).

[0140] like Figure 15 As shown, the capacitor switching circuit of this embodiment has a third capacitor C3 that is different from the first capacitor C1 and the second capacitor C2, and a second semiconductor switch S2 that is different from the first semiconductor switch S1. The third capacitor C3 is connected in parallel with the first capacitor C1 and the second capacitor C2, and is connected in series with the second semiconductor switch S2.

[0141] As in this embodiment, the capacitor (gain) can be switched with a value of 3 or more through a multi-stage combined capacitor switching circuit.

[0142] Example 9

[0143] Reference Figure 16 The power conversion device and its control method according to Embodiment 9 of the present invention are described.

[0144] Figure 16 This diagram illustrates the capacitor switching circuit of the power conversion device in this embodiment, which consists of multiple capacitors connected in series. Figure 2 The circuit configuration of the capacitor switching circuit (modified example).

[0145] As in this embodiment, by combining multiple capacitor switching circuits in series, it is possible to switch capacitors (gain) with values ​​of 3 or higher.

[0146] Example 10

[0147] Reference Figure 17 The power conversion device and its control method according to Embodiment 10 of the present invention are described.

[0148] Figure 17 This is a diagram showing the waveform during capacitor switching control of the power conversion device in this embodiment.

[0149] like Figure 17 As shown, in the power conversion device of this embodiment, control is performed with reference to the output voltage V2.

[0150] If the second DC voltage (output voltage V2) is lower than a specified value, control is performed to increase the second DC voltage (output voltage V2).

[0151] By referring to the output voltage V2, the same effect as in Example 1 can be obtained for changes in output voltage and load.

[0152] Furthermore, the present invention is not limited to the above embodiments, but includes various modifications. For example, the above embodiments are detailed examples provided for ease of understanding and explanation of the present invention, and are not necessarily limited to embodiments possessing all the described configurations. Additionally, a portion of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Furthermore, for a portion of the configuration of each embodiment, other configurations can be added, deleted, or replaced.

[0153] Explanation of symbols

[0154] 101… (Phase-shift converter) Primary side circuit, 102… Secondary side circuit, 103… Capacitor switching circuit, C1, C2, C3, C101, C102… Capacitors, D1, D2, D101… Diodes, L1, L2… Inductors, S1~S4, S101… Semiconductor switches, Tr1… Transformer, V1… Input voltage, V2… Output voltage.

Claims

1. A power conversion device, which converts a first DC voltage supplied from a DC power source into a second DC voltage via a bridge circuit, a transformer, and a rectifier circuit, characterized in that, have: A first capacitor is disposed between the bridge circuit and the transformer; The second capacitor is connected in parallel or in series with the first capacitor; A first semiconductor switch, which is connected in parallel or series with the first capacitor; and A switch-based voltage control unit adjusts the phase shift of the elements constituting the bridge circuit.

2. The power conversion device as described in claim 1, characterized in that, The second capacitor is connected in parallel with the first capacitor. The first semiconductor switch is connected in parallel with the first capacitor and in series with the second capacitor.

3. The power conversion device as described in claim 1, characterized in that, The second capacitor is connected in series with the first capacitor. The first semiconductor switch is connected in series with the first capacitor and in parallel with the second capacitor.

4. The power conversion device as described in claim 2 or 3, characterized in that, If the first DC voltage is lower than a predetermined value, the first semiconductor switch is turned off, and the second DC voltage is controlled by the switch of the bridge circuit. When the first DC voltage is above a predetermined value, the first semiconductor switch is turned on, and the second DC voltage range is extended by the switching of the bridge circuit.

5. The power conversion device as described in claim 2, characterized in that, When the voltage of the first capacitor is at its maximum, the first semiconductor switch is switched to conduction.

6. The power conversion device as described in claim 3, characterized in that, When the voltage of the second capacitor is 0V, the first semiconductor switch is switched to conduction.

7. The power conversion device as described in claim 5 or 6, characterized in that, When the peak voltage of the first capacitor is smaller than the voltage of the second capacitor, the voltage of the first capacitor is increased by increasing the conduction time of the bridge circuit. When the voltage of the first capacitor is the same as the voltage of the second capacitor, the first semiconductor switch is switched on.

8. The power conversion device as described in claim 4, characterized in that, When the first semiconductor switch is switched on / off, voltage fluctuations are suppressed by feeding forward control of the output voltage control system of the bridge circuit.

9. The power conversion device as described in claim 4, characterized in that, The first semiconductor switch is controlled to switch on and off, thereby continuously switching the gain by adjusting the duty cycle.

10. The power conversion device as claimed in claim 1, characterized in that, have: A third capacitor, which is different from the first capacitor and the second capacitor; and The second semiconductor switch is different from the first semiconductor switch. The third capacitor is connected in series with the first capacitor and the second capacitor, respectively, and is connected in parallel with the second semiconductor switch.

11. The power conversion device as claimed in claim 1, characterized in that, have: A third capacitor, which is different from the first capacitor and the second capacitor; and The second semiconductor switch is different from the first semiconductor switch. The third capacitor is connected in parallel with the first capacitor and the second capacitor, respectively, and is connected in series with the second semiconductor switch.

12. The power conversion device as claimed in claim 4, characterized in that, If the second DC voltage is lower than a specified value, increase the second DC voltage.

13. A control method for a power conversion device, characterized in that, It is the control method for the power conversion device according to claim 1. If the first DC voltage is lower than a predetermined value, the first semiconductor switch is turned off, and the second DC voltage is controlled by the switch of the bridge circuit. When the first DC voltage is above a predetermined value, the first semiconductor switch is turned on, and the second DC voltage range is extended by the switching of the bridge circuit.

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