Power conversion device

Abstract

The power conversion device includes a transformer and first to third switching circuits. The third switching circuit includes a rectifying circuit, a smoothing capacitor that smoothes a third direct current output from the rectifying circuit, a first switching element connected in series with the smoothing capacitor, and an inductance element provided between the smoothing capacitor and the first switching element and a third direct current power supply. When power is supplied from a second DC power source to the third DC power source, the first switching element is switched on / off on the basis of the operation of the second switching circuit.

Description

Technical Field

[0001] The present invention relates to a power conversion device. Background Art

[0002] As one of the power conversion devices mainly installed in electric vehicles, the bidirectional charging power supply device is generally called OBC (On Board Charger). With the development of technology, it is required to be high-power, miniaturized, and low-loss. In addition, a method of merging a DC / DC converter that supplies LV (Low Voltage) power from an HV (High Voltage) battery with an OBC to achieve the miniaturization of the entire vehicle power supply system has been reported. For example, the following patent document 1 describes a power conversion device that switches the on / off state of a switching element when control is required, and sets the switching state of the switching element to always be on when control is not required, thereby reducing losses and ensuring the operating range of all connected loads. Prior art literature Patent Literature

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-158353 Summary of the Invention Problems to be solved by the invention

[0004] Conventional OBCs employ LLC resonant converters to achieve high power, high efficiency, and low losses. This LLC resonant OBC easily allows for a miniaturized approach by adding windings to the isolation transformer and integrating it with the DC / DC converter from the HV to the LV. This approach also controls switching elements in the power path that doesn't utilize the OBC, namely, the path from the HV battery to the LV battery during vehicle operation, through frequency modulation and phase shifting based on resonant LC constants designed to suit the OBC's output power and efficiency.

[0005] However, regarding this power supply mode from the HV battery to the LV battery, when the voltage of the lithium-ion battery on the HV battery side is high, the frequency becomes the upper limit, and output control is performed solely through phase shifting, resulting in a large peak current. This increases semiconductor losses, leading to a decrease in the efficiency of power supply from the HV battery to the LV battery. Furthermore, since the power supply from the HV battery to the LV battery during vehicle operation is related to the vehicle's cruising range, the occurrence of this problem also shortens the vehicle's cruising range.

[0006] In view of the above, an object of the present invention is to provide a power conversion device that achieves low loss, high power, high efficiency, and maintenance of vehicle cruising range. Technical means to solve the problem

[0007] A power conversion device according to the present invention includes: a transformer having a first winding, a second winding, and a third winding magnetically coupled together; a first switching circuit connected to the first winding for converting first DC power and AC power between a first DC power source and a second switching circuit connected to the second winding for converting the AC power and the second DC power between a second DC power source and a third switching circuit connected to the third winding for converting the AC power into a third DC power and supplying the third DC power to the third DC power source; the third switching circuit including: a rectifier circuit for converting the AC power into the third DC power; a smoothing capacitor for smoothing the third DC power output from the rectifier circuit; a first switching element connected in series with the smoothing capacitor; and an inductor element provided between the smoothing capacitor, the first switching element, and the third DC power source, and switching the first switching element on and off based on the operation of the second switching circuit when power is supplied from the second DC power source to the third DC power source. Effects of the Invention

[0008] A power conversion device can be provided that achieves low loss, high power, high efficiency, and maintains the vehicle's cruising range. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is an explanatory diagram of the power conversion device according to the first embodiment of the present invention. Figure 2 1 and 2 are diagrams illustrating the operations of the second switching circuit and the third switching circuit according to the first embodiment of the present invention. Figure 3 It is a diagram showing the operation of the switching element according to the second embodiment of the present invention. Figure 4 It is a diagram showing the operation of the switching element according to the third embodiment of the present invention. Figure 5 It is an explanatory diagram of a power conversion device according to a fourth embodiment of the present invention. Figure 6 This is a diagram illustrating the voltage range of the second switching circuit and the second DC power supply according to the fourth embodiment of the present invention. DETAILED DESCRIPTION

[0010] The following describes embodiments of the present invention with reference to the accompanying drawings. The following description and drawings are examples for illustrating the present invention and have been omitted or simplified as appropriate for clarity. The present invention may also be implemented in various other forms. Unless otherwise specified, each component may be singular or plural.

[0011] The positions, sizes, shapes, and ranges of the components shown in the drawings may not represent actual positions, sizes, shapes, and ranges in order to facilitate understanding of the invention. Therefore, the present invention is not necessarily limited to the positions, sizes, shapes, and ranges disclosed in the drawings.

[0012] (First embodiment and overall structure of the present invention) ( Figure 1 ) The onboard charging device 7, a power conversion device capable of connecting to an external power source, can charge the onboard second DC power source V2 and third DC power source V3 by connecting to, for example, an AC power source 6 external to the vehicle (illustrated). The AC power source 6 connected to the charging device 7 is merely an example; the charging device 7 may also be configured to be capable of charging by connecting to a DC power source external to the vehicle. The charging device 7 is a bidirectional charging and power supply device capable of supplying power from the vehicle to the outside.

[0013] The second DC power supply V2 is an HV battery such as a lithium ion battery (eg, 200V to 400V). The third DC power supply V3 is an auxiliary battery such as an LV battery (eg, 12V) that powers the vehicle's electrical system.

[0014] The charging device 7 includes an AC / DC converter 5 and a DC / DC converter 9. The DC / DC converter 9 includes a first switching circuit 1 and a second switching circuit 2. The DC / DC converter 9 converts the power supplied from the AC power supply 6 using the first switching circuit 1 and the second switching circuit 2, and supplies the converted power to the second DC power supply V2.

[0015] The charging device 7 also includes a third switching circuit 3. This third switching circuit 3 is magnetically connected to the first switching circuit 1 and the second switching circuit 2 of the DC / DC converter 9 via a transformer 12. The DC / DC converter 9 uses the first switching circuit 1 and the third switching circuit 3 to convert the power supplied from the AC power source 6 and supply it to the third DC power source V3. Furthermore, the charging device 7 employs an LLC resonant converter to achieve a high-power, high-efficiency, and low-loss OBC circuit design.

[0016] In the charging device 7, the transformer 12 is a three-winding transformer with at least three magnetically coupled windings. A first switching circuit 1 is connected to a first winding N1 of the three windings. A second switching circuit 2 is connected to a second winding N2 of the three windings. A third switching circuit 3 is connected to a third winding N3 of the three windings.

[0017] The first switching circuit 1 includes two switching branches, each with switching elements Q1, Q2, and switching elements Q3, Q4 connected in series. Furthermore, the first switching circuit 1 includes a capacitor C1 connected in parallel with the two switching branches. The first switching circuit 1 is connected to a resonant capacitor Cr1 and a resonant reactor Lr1. A magnetizing inductor Lm is connected in parallel with the first winding N1.

[0018] The second switching circuit 2 includes two switching branches, each of which has switching elements Q5, Q6, and switching elements Q7, Q8 connected in series. Furthermore, the second switching circuit 2 includes a capacitor C2 connected in parallel with the two switching branches. The second switching circuit 2 is connected to a resonant capacitor Cr2 and a resonant reactor Lr2.

[0019] In addition, the resonant reactors Lr1 and Lr2 can also serve as the leakage inductance of the transformer 12 .

[0020] The third switching circuit 3 functions as a step-down chopper, controlling the voltage in the charging device 7 to be lower than the input voltage. The third switching circuit 3 includes a rectifier circuit 10, a smoothing capacitor C, a first switching element S1, a switching element S2, an inductor L serving as a smoothing reactor, and a diode D1. The rectifier circuit 10, comprised of switching elements Q9 and Q10, converts the converted AC power into a third DC power. The smoothing capacitor C smoothes the third DC power output from the rectifier circuit 10. The first switching element S1 is connected in series with the smoothing capacitor C. The switching element S2 is provided between the smoothing capacitor C (rectified output), the first switching element S1, and the third DC power supply V3. The second switching element S2 controls conduction from the rectifier circuit 10 to the inductor L by turning the second switching element S2 on and off.

[0021] Regarding charging a vehicle with external power supply, the specific power conversion and output in the charging device 7 will be described. The charging device 7 receives AC power from an external AC power source 6. The AC / DC converter 5 converts the received AC power into a first DC power and supplies the first DC power to capacitor C1 of the first switching circuit 1. The charging device 7 converts the first DC power applied to capacitor C1 into AC power in the first switching circuit 1 and outputs it to the second switching circuit 2 and the third switching circuit 3 via the transformer 12. The charging device 7 converts the input AC power into a second DC power in the second switching circuit 2 and applies it to capacitor C2 and the second DC power source V2. Furthermore, the charging device 7 converts the input AC power into a third DC power in the third switching circuit 3 and applies it to capacitor C and the third DC power source V3.

[0022] (Comparison between the Conventional Structure and the Structure of the Present Invention) Conventionally, the converter circuit of the charging device 7 is designed to reduce losses when charging the HV battery (second DC power supply V2) from an external power source. Specifically, the charging device 7 is a converter in which a capacitor C receives the rectified output of the third switching circuit 3 .

[0023] However, when the vehicle is in motion, i.e., when the power supply path from the second DC power source V2 to the third DC power source V3 is in operation, the low-loss voltage and power range of the charger 7, which is designed to be low-loss, is limited. If the voltage range deviates significantly from the expected value, the frequency modulation amount increases, the peak current increases, and the loss increases. If this increase in loss leads to a significant depletion of the second DC power source V2, the vehicle's cruising range may be shortened.

[0024] Therefore, the present invention provides a design of a converter, which is provided with a first switching element S1 connected in series with a capacitor C on the output side of a rectifier circuit 10, turns on a second switching element S2 while the vehicle is running, and turns on / off the first switching element S1, thereby switching the rectifier output in the third switching circuit 3 to the inductor element L.

[0025] Furthermore, the period during which the first switching element S1 is on is synchronized with the application of voltage to the transformer 12. That is, the first switching element S1 is on only during the period during which voltage is applied to the transformer 12, and is off during the period during which no voltage is applied to the transformer 12. This allows the first switching element S1 and the smoothing capacitor C to function as a surge absorption circuit, thereby suppressing the surge voltage.

[0026] Furthermore, a converter whose rectified output is an inductor element L refers to a design in which a voltage is applied to the rectified output of the rectifier circuit 10 when both switching elements Q5 and Q8 are on or off, resulting in the inductor element L acting as a chopper. Specifically, when power is supplied from the second DC power source V2 to the third DC power source V3, the first switching element S1 switches between on and off according to the operation of the second switching circuit 2, while the second switching element S2 remains on at all times. The first switching element S1 and capacitor C form an active clamp, protecting the switching elements from the effects of bouncing voltage. Furthermore, the first switching circuit 1 in this case controls the phase shift of the output voltage while voltage is applied to the transformer 12.

[0027] This allows the selection of a circuit design with lower losses depending on whether the vehicle is charging or driving, facilitating voltage control and enabling accurate voltage output to the third DC power supply V3. Furthermore, even if the voltage of the second DC power supply V2, serving as the power supply source, increases, the inductor element L can achieve reduced semiconductor losses. This also allows for both high efficiency of the bidirectional charging device 7 and an extended vehicle range.

[0028] Switching elements Q1-Q8, first switching element S1, and second switching element S2 are MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors) or IGBTs (Insulated Gate Bipolar Transistors). Switching elements Q9 and Q10 of rectifier circuit 10 are MOSFETs or diodes. Diode D1 can also be a MOSFET. DC power supplies V2 and V3 can also serve as loads requiring any DC voltage.

[0029] ( Figure 2 ) The operation of the second switching circuit 2 and the operation of the third switching circuit 3 in the embodiment of the present invention will be described. As shown in the figure, in the second switching circuit 2, the switching branch composed of switching elements Q5 and Q6 and the switching branch composed of switching elements Q7 and Q8 are both operated with a duty cycle of 50%, and are operated with phases shifted from each other. As a result, Figure 2 As shown in Vtr, voltage can be applied to the transformer 12 only during the period when both switching elements Q5 and Q8 are on or when both switching elements Q6 and Q7 are on. In this way, the duty ratio of the voltage applied to the transformer 12 is controlled by shifting the phase.

[0030] However, in order to convert the voltage at such a duty cycle into the DC voltage of the third DC power supply V3, an inductor element L is required. Therefore, as described above, in the switching circuit 3, a first switching element S1 is connected in series with the smoothing capacitor C. The first switching element S1 is turned on only when voltage is applied to the transformer 12, while the second switching element S2 remains in the on state at all times. This achieves the aforementioned operational advantages.

[0031] (Variation) When voltage is applied to the transformer 12, while the first switching element S1 is kept off, current flows through the parasitic diode of the first switching element S1, which is a MOSFET, charging the parasitic capacitance. After current flows through the parasitic diode of the first switching element S1, turning on the first switching element S1 causes the voltage between the drain and source of the first switching element to be low, while the diode is conducting. This allows the first switching element S1 to achieve ZVS (Zero Voltage Switching), reducing losses in the first switching element S1.

[0032] In this way, the timing at which the first switching element S1 switches from off to on can be controlled to occur after a predetermined time has passed since voltage application to the transformer 12 began. This allows the first switching element S1 to achieve ZVS, reducing losses in the first switching element S1. Furthermore, reducing losses in the first switching element S1 can contribute to an increased cruising range for the vehicle.

[0033] (Second embodiment) ( Figure 3 ) In the second embodiment, the configuration of the external AC power supply 6 and AC / DC converter 5 is replaced with a first DC power supply in the charging device 7. When power is supplied from the first DC power supply to the second DC power supply V2 and the third DC power supply V3 simultaneously, or when power is supplied from the second DC power supply V2 to the first DC power supply and the third DC power supply V3 simultaneously, the charging device 7 maintains the first switching element S1 of the third switching circuit 3 in the on state and switches the second switching element S2 on / off.

[0034] During simultaneous power supply, the first switching element S1 of the third switching circuit 3 is always kept in the on state, and the smoothing capacitor C serves as the voltage source. The second switching element S2 is switched on and off to activate the chopper. The chopper is composed of the second switching element S2, a diode D1, and an inductor L. In this way, by regulating the voltage on the LV battery side and controlling the third switching circuit 3 through pulse width control of the second switching element S2, a correct voltage can be supplied to the third DC power supply V3, serving as the auxiliary battery, even while the second DC power supply V2 is being charged by the bidirectional charging and power supply device using a low-loss circuit design. Furthermore, the voltage of the third DC power supply V3 can be stably controlled.

[0035] When power is supplied simultaneously from the second DC power supply V2 to the first DC power supply and the third DC power supply V3, the second switching circuit 2 controls the voltage of the capacitor C of the third switching circuit 3, and the third switching circuit 3 controls the voltage of the third DC power supply V3. Thus, regardless of the simultaneous supply of power, the third DC power supply V3 can be stably controlled.

[0036] (Third embodiment) ( Figure 4 ) A threshold value is set for the voltage of the second DC power supply V2. When the voltage of the second DC power supply V2 is greater than the threshold value, the second switch circuit 2 and the third switch circuit 3 are connected to the above-mentioned Figure 2However, when the voltage of the second DC power supply V2 is lower than the threshold value set for the voltage of the second DC power supply V2, the second switch circuit 2 and the third switch circuit 3 are switched to Figure 4 The action shown.

[0037] As shown in the figure, when the voltage of the second DC power supply V2 is lower than a set threshold, the first switching element S1 of the third switching circuit 3 is always kept on, and the switching element S2 is also always kept on, so that the rectified output is received by the smoothing capacitor C. At this time, the voltage of the smoothing capacitor C is the voltage of the third DC power supply V3. This is because the resonant converter circuit design that switches to receiving the rectified output via the capacitor C can sometimes achieve lower losses compared to receiving the rectified output via the inductor element L.

[0038] At this time, the phases of the switching branch composed of switching elements Q5 and Q8 and the switching branch composed of switching elements Q6 and Q7, which are switched at a duty cycle of 50%, do not necessarily need to be staggered as shown in the figure. The voltage of the smoothing capacitor C can also be controlled by modulating the frequency.

[0039] By limiting the selection of converter circuits to suit the operating mode, it is possible to effectively utilize low-loss voltages or those with a narrow voltage conversion ratio range, or converter circuits whose rectified output is fed to capacitor C. This eliminates the increase in peak current caused by the frequency modulation amount exceeding the voltage conversion ratio range. This reduces battery power loss during driving and contributes to extending the vehicle's cruising range.

[0040] (Fourth embodiment) ( Figure 5 、 Figure 6 ) In the fourth embodiment, in the charging device 7 of the above-described embodiment, a bidirectional chopper circuit 11 is provided between the second DC power supply V2 and the capacitor C2. The bidirectional chopper circuit 11 boosts the voltage of the capacitor C2 to a voltage equal to or lower than a predetermined threshold when the voltage of the second DC power supply V2 is below the threshold. Above the threshold, the voltage of the second DC power supply V2 is output as is, without boosting, as the voltage of the capacitor C2.

[0041] This allows the voltage required by the converter circuit to be maintained within a narrowed range, allowing the selection of resonant capacitors Cr1 and Cr2, resonant reactors Lr1 and Lr2, and magnetizing inductor Lm specialized for this range. Consequently, the voltage conversion range required by the converter circuit is reduced. This narrowing of the voltage ranges for both the resonant converter circuit and the power supply circuit from the HV battery to the LV battery facilitates the design of high-efficiency circuits for the charger 7, contributing to reduced losses. This also extends the vehicle's cruising range.

[0042] Thus, by providing bidirectional chopper circuit 11, a voltage conversion circuit that performs bidirectional voltage conversion, between second switching circuit 2 and second DC power supply V2, the voltage conversion range of DC / DC converter 9, which is composed of first switching circuit 1, second switching circuit 2, and third switching circuit 3, is narrowed. This facilitates the design of a high-efficiency circuit for bidirectional charging device 7.

[0043] The configuration described above is a power conversion device that performs bidirectional charging and is mounted on a vehicle. However, the configuration of the present invention can also be applied to a power conversion device that performs bidirectional charging and is not mounted on a vehicle.

[0044] According to the embodiment of the present invention described above, the following effects are achieved.

[0045] (1) The power conversion device includes: a transformer 12 formed by magnetically coupling a first winding N1, a second winding N2, and a third winding N3; a first switching circuit 1 connected to the first winding N1 and converting first DC power and AC power between the first DC power source and the second DC power source; a second switching circuit 2 connected to the second winding N2 and converting AC power and the second DC power between the second DC power source and the third DC power source; and a third switching circuit 3 connected to the third winding N3 and converting AC power into third DC power and supplying it to the third DC power source V3. The third switching circuit 3 includes: a rectifier circuit 10 that converts AC power into third DC power; a smoothing capacitor C that smoothes the third DC power output from the rectifier circuit 10; a first switching element S1 connected in series with the smoothing capacitor C; and an inductor L provided between the smoothing capacitor, the first switching element, and the third DC power source. When power is supplied from the second DC power source V2 to the third DC power source V3, the first switching element S1 is switched on / off according to the operation of the second switching circuit 2. As a result, it is possible to provide a power conversion device that achieves low loss, high output, high efficiency, and maintenance of the vehicle's cruising range.

[0046] (2) The third switching circuit 3 includes a second switching element S2 that controls conduction from the rectifier circuit 10 to the inductor element L. When power is supplied simultaneously from the first DC power supply V1 to the second DC power supply V2 and the third DC power supply V3, or when power is supplied simultaneously from the second DC power supply V2 to the first DC power supply and the third DC power supply V3, the first switching element S1 is maintained in the on state, while the second switching element S2 is switched on and off. This ensures that a correct voltage can be supplied to the third DC power supply V3 even while the second DC power supply V2 is being charged.

[0047] (3) When power is supplied from the second DC power supply V2 to the third DC power supply V3 and the output voltage of the second DC power supply V2 is less than a predetermined threshold, the first switching element S1 is maintained in the on state. This contributes to reducing losses and extending the vehicle's cruising range.

[0048] (4) The first switching element S1 is turned on while voltage is applied to the transformer 12, and is turned off while no voltage is applied to the transformer 12. Thus, the first switching element S1 can be configured as a surge absorption circuit, thereby achieving low loss.

[0049] (5) The first switching element S1 is switched from off to on after a predetermined time has passed since the start of voltage application to the transformer 12. This can reduce losses.

[0050] (6) A voltage conversion circuit (bidirectional chopper circuit) 11 for bidirectional voltage conversion is provided between the second switching circuit 2 and the second DC power supply V2. This contributes to the realization of a low-loss, high-efficiency bidirectional charging device 7 and extends the vehicle's cruising range.

[0051] (7) The power conversion device is mounted on a vehicle. During charging, the first switching element S1 is switched on / off based on the operation of the second switching circuit 2. During driving, the first switching element S1 is maintained in the on state, and the second switching element S2 is switched on / off. Thus, a vehicle equipped with a power conversion device that achieves low loss, high power, high efficiency, and a maintained vehicle cruising range can be provided.

[0052] In addition, the present invention is not limited to the above-mentioned embodiment, and various modifications or other configurations can be combined within the scope of the present invention. In addition, the present invention is not limited to the structure having all the configurations described in the above-mentioned embodiment, and also includes a structure in which part of the configuration is deleted. Explanation of symbols

[0053] 1First switch circuit N1 first winding 2 Second switch circuit N2 second winding V2 second DC power supply 3Third switch circuit N3 third winding V3 third DC power supply S1 first switching element S2 second switching element C Smoothing capacitor D1 diode L inductor element 5AC / DC converter 6AC power supply 7. Bidirectional charging device 9LLC resonant DC / DC converter (LLC converter) 10 Rectifier circuit 11 Bidirectional chopper circuit 12 transformers.

Claims

1. A power conversion device, characterized in that: include: a transformer formed by magnetically coupling a first winding, a second winding, and a third winding; a first switching circuit connected to the first winding and configured to convert first DC power and AC power between the first DC power source and the first switching circuit; a second switching circuit connected to the second winding and configured to convert the AC power into the second DC power and vice versa; as well as a third switching circuit connected to the third winding, converting the AC power into a third DC power and supplying the third DC power to a third DC power source; The third switching circuit includes: a rectifier circuit that converts the AC power into the third DC power; a smoothing capacitor that smoothes the third DC power output from the rectifier circuit; a first switching element connected in series with the smoothing capacitor; and an inductor element provided between the smoothing capacitor, the first switching element, and the third DC power supply. When electric power is supplied from the second DC power supply to the third DC power supply, the first switching element is switched on / off based on the operation of the second switching circuit.

2. The power conversion device according to claim 1, wherein The third switching circuit includes a second switching element for controlling conduction from the rectifier circuit to the inductor element. When power is supplied from the first DC power supply to the second DC power supply and the third DC power supply simultaneously, or when power is supplied from the second DC power supply to the first DC power supply and the third DC power supply simultaneously, the first switching element is maintained in an on state and the on / off state of the second switching element is switched.

3. The power conversion device according to claim 1, wherein: When power is supplied from the second DC power supply to the third DC power supply and the voltage of the second DC power supply is lower than a preset voltage threshold, the first switching element is maintained in the on state.

4. The power conversion device according to claim 1, wherein: The first switching element is turned on while a voltage is applied to the transformer, and is turned off while no voltage is applied to the transformer.

5. The power conversion device according to claim 4, wherein: After a predetermined time has passed since the start of voltage application to the transformer, the first switching element is switched from off to on.

6. The power conversion device according to claim 1, wherein: A voltage conversion circuit for bidirectionally converting voltages is provided between the second switching circuit and the second DC power supply.

7. A power conversion device, characterized in that: The power conversion device according to any one of claims 1 to 6 is mounted on a vehicle. During charging, the first switching element is switched on / off according to the operation of the second switching circuit. During driving, the first switching element is maintained in an on state, and the second switching element is switched on / off.

Images