Power converter

Abstract

To provide a power conversion device that achieve low loss, high power, high efficiency, and maintained vehicle range.SOLUTION: A power conversion device includes a transformer and first to third switching circuits, and the third switching circuit includes a rectifier circuit, a smoothing capacitor that smooths 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 and the first switching element and a third DC power source, and when power is supplied from the 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.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] A bi-directional charging and power feeding device, which is one of the power conversion devices mainly mounted on electric vehicles etc., is generally called an OBC (On Board Charger). With the development of technology, higher power, smaller size, and lower loss are required. Furthermore, a method of integrating a DC / DC converter for feeding power from an HV (High Voltage) battery to an LV (Low Voltage) and achieving miniaturization of the entire in-vehicle power supply system has also been reported. For example, in Patent Document 1 below, by switching the ON / OFF of a switching element when control is required and keeping the switching state of the switching element always on when control is not required, a power conversion device that reduces loss and ensures the operating range of all connected loads is described.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventional OBCs employ an LLC resonant converter design to achieve high power output, high efficiency, and low losses. In this LLC resonant OBC, a miniaturization method can be easily conceived by adding windings to the isolation transformer and integrating it with a DC / DC converter from the HV to the LV. In this method, even in the power path that does not use an OBC, i.e., the path from the HV battery to the LV battery while the vehicle is running, the switching elements are controlled by frequency modulation and phase shift based on constants such as a resonant LC designed to match the output power and efficiency of the OBC.

[0005] However, regarding this power supply mode from the HV battery to the LV battery, if the voltage of the lithium-ion battery on the HV side is high, the frequency becomes the upper limit, and output control is performed only by phase shift, which can result in a large peak current. This leads to increased semiconductor losses and a problem of reduced power supply efficiency from the HV battery to the LV battery. Furthermore, since the power supply from the HV battery to the LV battery while the vehicle is running is related to the vehicle's driving range, the above problem also leads to a problem of reduced vehicle driving range.

[0006] In light of this, the objective of the present invention is to provide a power conversion device that achieves reduced losses, increased power output, higher efficiency, and maintenance of vehicle range. [Means for solving the problem]

[0007] The power conversion device of the present invention comprises a transformer having a first winding, a second winding, and a third winding magnetically coupled; a first switching circuit connected to the first winding for mutually converting first DC power and AC power with a first DC power source; a second switching circuit connected to the second winding for mutually converting the AC power and second DC power with a second DC power source; and a third switching circuit connected to the third winding for converting the AC power to third DC power and supplying it to a third DC power source, wherein the third switching circuit includes a rectifier circuit for converting the AC power to 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 when supplying power from the second DC power source to the third DC power source, the first switching element is switched ON / OFF based on the operation of the second switching circuit. [Effects of the Invention]

[0008] We can provide power conversion devices that achieve reduced losses, increased power output, higher efficiency, and maintain vehicle range. [Brief explanation of the drawing]

[0009] [Figure 1] Explanatory diagram of a power conversion device according to the first embodiment of the present invention [Figure 2] A diagram illustrating the operation of the second switching circuit and the third switching circuit according to the first embodiment of the present invention. [Figure 3] A diagram illustrating the operation of a switching element according to a second embodiment of the present invention. [Figure 4] A diagram illustrating the operation of a switching element according to a third embodiment of the present invention. [Figure 5] Explanatory diagram of a power conversion device according to a fourth embodiment of the present invention [Figure 6] 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.

[0010] Embodiments of the present invention will be described below with reference to the drawings. The following description and drawings are illustrative for illustrating the present invention, and have been omitted and simplified as appropriate for clarity of explanation. The present invention can also be carried out 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 their 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 configuration of the present invention) (Figure 1) The on-board charging device 7, which is a power conversion device that can be connected to an external power source, can charge the on-board second DC power source V2 and third DC power source V3 by being connected to an external AC power source 6, for example, as shown in the figure. Note that the AC power source 6 connected to the charging device 7 is just an example, and the charging device 7 may have a configuration that allows it to be charged by being connected to an external DC power source. The charging device 7 is a bidirectional charging and power supply device that can also supply power from the vehicle to the outside.

[0013] The second DC power source V2 is an HV battery such as a lithium-ion battery (e.g., 200V to 400V). The third DC power source V3 is an auxiliary battery, such as an LV battery (e.g., 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 has a first switching circuit 1 and a second switching circuit 2, and converts the power supplied from the AC power source 6 using the first switching circuit 1 and the second switching circuit 2, and supplies it to the second DC power source V2.

[0015] In addition, the charging device 7 has a third switching circuit 3. The 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 the transformer 12. The DC / DC converter 9 converts the power supplied from the AC power supply 6 through the first switching circuit 1 and the third switching circuit 3 and supplies it to the third DC power supply V3. Note that the charging device 7 adopts the LLC resonant converter method in order to implement a design that realizes high power, high efficiency, and low loss of the OBC circuit.

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

[0017] The first switching circuit 1 has two switching legs in which the switching elements Q1, Q2 and the switching elements Q3, Q4 are respectively connected in series. The first switching circuit 1 also has a capacitor C1 connected in parallel to the two switching legs. The first switching circuit 1 is connected to the resonant capacitor Cr1 and the resonant reactor Lr1. The excitation inductance Lm is connected in parallel to the first winding N1.

[0018] The second switching circuit 2 has two switching legs in which the switching elements Q5, Q6 and the switching elements Q7, Q8 are respectively connected in series. The second switching circuit 2 also has a capacitor C2 connected in parallel to the two switching legs. The second switching circuit 2 is connected to the resonant capacitor Cr2 and the resonant reactor Lr2.

[0019] Note that the resonant reactors Lr1 and Lr2 may be the leakage inductances of the transformer 12.

[0020] The third switching circuit 3 has the function of a step-down chopper that controls voltage reduction from the input voltage in the charging device 7. The third switching circuit 3 includes a rectifier circuit 10 composed of switching elements Q9 and Q10 that converts the converted AC power into third DC power, a smoothing capacitor C that smooths the third DC power output from the rectifier circuit 10, a first switching element S1 connected in series with the smoothing capacitor C, the smoothing capacitor C and the first switching element S1 which are the rectified output, a third DC power supply V3, and a switching element S2 provided between them, an inductor element L which is a smoothing reactor, and a diode D1. The second switching element S2 controls the conduction from the rectifier circuit 10 to the inductor element L by turning on / off the second switching element S2.

[0021] Regarding the charging of the vehicle in 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 supply 6. The AC / DC converter 5 converts the received AC power into first DC power and supplies the first DC power to the capacitor C1 of the first switching circuit 1. The charging device 7 converts the first DC power applied to the 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 second DC power in the second switching circuit 2 and applies it to the capacitor C2 and the second DC power supply V2. Also, the charging device 7 converts the input AC power into third DC power in the third switching circuit 3 and applies it to the capacitor C and the third DC power supply V3.

[0022] (Comparison between the conventional configuration and the configuration of the present invention) Conventionally, the converter circuit of the charging device 7 is designed to have low loss when charging the HV battery (the second DC power supply V2) from an external power source. Specifically, the charging device 7 is a converter that receives the rectified output in the third switching circuit 3 by the capacitor C.

[0023] However, when the vehicle is in motion, that is, in the power supply path from the second DC power source V2 to the third DC power source V3, the charging device 7, which is designed to minimize losses, has a limited range of low-loss voltages and power ranges. If the voltage range deviates significantly from the assumed value, the amount of frequency modulation increases, the peak current increases, and losses increase. If the second DC power source V2 is rapidly depleted due to such increased losses, a problem arises in that the vehicle's driving range is shortened.

[0024] Therefore, the present invention provides a first switching element S1 connected in series with the capacitor C on the output side of the rectifier circuit 10, and while the vehicle is running, the second switching element S2 is turned ON, and the first switching element S1 is turned ON / OFF to design a converter that can switch the rectified output in the third switching circuit 3 to an inductor element L.

[0025] Furthermore, the period during which the first switching element S1 is ON is synchronized with the period during which voltage is applied to the transformer 12. In other words, the first switching element S1 is turned ON only when voltage is applied to the transformer 12, and turned OFF when no voltage is applied to the transformer 12. In this way, the first switching element S1 and the smoothing capacitor C can be used as a surge absorption circuit, and the voltage spike can be suppressed.

[0026] In this converter, where the rectified output is an inductor element L, a voltage is applied to the rectified output of the rectifier circuit 10 when both switching elements Q5 and Q8 are ON or both are OFF, and the inductor element L acts as a chopper. In other words, when supplying power from the second DC power supply V2 to the third DC power supply V3, the first switching element S1 is switched ON / OFF based on the operation of the second switching circuit 2, the second switching element S2 is kept in the ON state at all times, and the first switching element S1 and capacitor C form an active clamp to protect the switching elements from jump voltages. In this case, the first switching circuit 1 uses a phase shift operation to control the output voltage during the period of voltage application to the transformer 12.

[0027] This approach allows for the selection of a circuit design with lower losses depending on whether the vehicle is charging or driving, making it easier to control the voltage and thus enabling the correct voltage to be output to the third DC power supply V3. Furthermore, even if the voltage of the second DC power supply V2, which is the power source, increases, the inductor element L enables low semiconductor losses. This also makes it possible to achieve both high efficiency of the bidirectional charging device 7 and a long driving range for the vehicle.

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

[0029] (Figure 2) The operation of the second switching circuit 2 and the third switching circuit 3 according to embodiments of the present invention will now be described. In the second switching circuit 2, the switching legs consisting of switching elements Q5 and Q6 and the switching legs consisting of switching elements Q7 and Q8 both operate with a duty cycle of 50%, as shown in the figure, and operate with a phase shift between them. As a result, as shown in Vtr in Figure 2, it is possible to apply voltage to the transformer 12 only when both switching elements Q5 and Q8 are ON, or when both switching elements Q6 and Q7 are ON. In this way, the duty cycle of the voltage applied to the transformer 12 is controlled by shifting the phase.

[0030] However, an inductor element L is necessary to convert the voltage to the DC voltage of the third DC power supply V3 with such a duty cycle. Therefore, as mentioned above, in the switching circuit 3, a first switching element S1 is connected in series with the smoothing capacitor C, and the first switching element S1 is turned ON only when voltage is applied to the transformer 12, while the second switching element S2 is kept in a constantly ON state. In this way, the above-mentioned effects can be achieved.

[0031] (modified version) When a voltage is applied to the transformer 12, if the first switching element S1 is kept OFF, current flows through the parasitic diode of the first switching element S1, which is a MOSFET, and the parasitic capacitance is charged. After current has flowed through the parasitic diode of the first switching element S1, if the first switching element S1 is turned ON, the first switching element S1 will be turned ON while the drain-source voltage of the first switching element is low and conducting through the diode. As a result, the first switching element S1 will be ZVS (Zero Voltage Switching), and the losses of the first switching element S1 can be reduced.

[0032] Thus, the timing at which the first switching element S1 switches from OFF to ON may be controlled to occur after a predetermined time has elapsed from the timing at which voltage is first applied to the transformer 12. This enables ZVS (Zero Voltage Switching) in the first switching element S1 and reduces the losses of the first switching element S1. Furthermore, reducing the losses of the first switching element S1 contributes to extending the vehicle's driving range.

[0033] (Second embodiment) (Figure 3) In the second embodiment, the configuration of the charging device 7 is described by replacing the external AC power supply 6 and AC / DC converter 5 with a first DC power supply. When the charging device 7 simultaneously supplies power from the first DC power supply to the second DC power supply V2 and the third DC power supply V3, or when it simultaneously supplies power from the second DC power supply V2 to the first DC power supply and the third DC power supply V3, 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 kept in the ON state at all times, and the smoothing capacitor C is used as a voltage source to switch the second switching element S2 ON / OFF and operate the chopper. The chopper consists of the second switching element S2, a diode D1, and an inductor element L. In this way, voltage adjustment is performed on the LV battery side, and the third switching circuit 3 is controlled by pulse width control of the second switching element S2. As a result, even when the second DC power supply V2 is being charged using a bidirectional charging and power supply device with a low-loss circuit design, the correct voltage can be supplied to the auxiliary battery, the third DC power supply V3, and the voltage of the third DC power supply V3 can be stably controlled.

[0035] When power is simultaneously supplied from the second DC power supply V2 to both the first DC power supply and the third DC power supply V3, the second switching circuit 2 controls the voltage across the capacitor C of the third switching circuit 3, which in turn controls the voltage of the third DC power supply V3. In this way, the third DC power supply V3 can be stably controlled regardless of which simultaneous power supply is used.

[0036] (Third embodiment) (Figure 4) A threshold voltage is set for the second DC power supply V2. When supplying power from the second DC power supply V2 to the third DC power supply V3 while the vehicle is in motion, if the voltage of the second DC power supply V2 is greater than this threshold, the second switching circuit 2 and the third switching circuit 3 operate in the same manner as shown in Figure 2 above. However, when supplying power from the second DC power supply V2 to the third DC power supply V3, if the voltage of the second DC power supply V2 is lower than the threshold voltage set for the second DC power supply V2, the second switching circuit 2 and the third switching circuit 3 switch to the operation shown in Figure 4.

[0037] As shown in the diagram, when the voltage of the second DC power supply V2 is lower than the set threshold, the first switching element S1 of the third switching circuit 3 is kept in the ON state, and the switching element S2 is also kept in the ON state, so that the rectified output is received by the smoothing capacitor C. At this time, the voltage across the smoothing capacitor C is the voltage of the third DC power supply V3. This is because, in some cases, switching to a resonant converter circuit design that receives the rectified output with a capacitor C rather than an inductor element L can achieve lower losses.

[0038] The phases of the switching legs, consisting of switching elements Q5 and Q8 that switch with a duty cycle of 50% at this time, and the switching legs, consisting of switching elements Q6 and Q7, do not necessarily need to be shifted as shown in the figure; the voltage of the smoothing capacitor C may be controlled by modulating the frequency.

[0039] In this way, by selectively choosing the converter circuit type according to the operating mode, converter circuits with low loss voltage and narrow voltage conversion ratio ranges, and where the rectified output is a capacitor C, can be efficiently utilized. This eliminates the increase in peak current caused by the large frequency modulation amount exceeding the voltage conversion ratio range. As a result, battery power supply losses during driving can be reduced, and the vehicle's driving range can be extended.

[0040] (Fourth embodiment) (Figures 5 and 6) In the fourth embodiment, a bidirectional chopper circuit 11 is inserted between the second DC power supply V2 and the capacitor C2 in the charging device 7 of the previously described embodiment. The bidirectional chopper circuit 11 boosts the voltage of the capacitor C2 to the threshold voltage when the voltage of the second DC power supply V2 is below a predetermined threshold, and does not boost the voltage above that threshold, outputting the voltage of the second DC power supply V2 as is for the capacitor C2.

[0041] By doing so, the voltage required for the converter circuit can be maintained within a narrow range, and resonant capacitors Cr1, Cr2, resonant reactors Lr1, Lr2, and excitation inductance Lm can be selected specifically for this range, thus reducing the voltage conversion range required for the converter circuit. In this way, by narrowing the voltage range for both the resonant converter circuit and the power supply circuit from the HV battery to the LV battery, the charging device 7 can be designed as a highly efficient circuit, contributing to reduced losses. In addition, this can be used to extend the vehicle's driving range.

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

[0043] The configuration described above is for a bidirectional charging power converter mounted on a vehicle, but the configuration of the present invention can also be applied to a type of bidirectional charging power converter that is not mounted on a vehicle.

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

[0045] (1) The power conversion device comprises a transformer 12 in which a first winding N1, a second winding N2, and a third winding N3 are magnetically coupled; a first switching circuit 1 connected to the first winding N1 and mutually converting first DC power and AC power with a first DC power supply; a second switching circuit 2 connected to the second winding N2 and mutually converting AC power and second DC power with a second DC power supply V2; and a third switching circuit 3 connected to the third winding N3 and converting AC power to third DC power and supplying it to a third DC power supply V3. The third switching circuit 3 comprises a rectifier circuit 10 that converts AC power to third DC power; a smoothing capacitor C that smooths 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 element L provided between the smoothing capacitor, the first switching element, and the third DC power supply. When supplying power from the second DC power supply V2 to the third DC power supply V3, the first switching element S1 is switched ON / OFF based on the operation of the second switching circuit 2. In this way, a power conversion device can be provided that achieves low loss, high power output, high efficiency, and maintenance of vehicle range.

[0046] (2) The third switching circuit 3 has 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 kept ON and the second switching element S2 is switched ON / OFF. In this way, even when the second DC power supply V2 is being charged, the correct voltage can be supplied to the third DC power supply V3.

[0047] (3) When supplying power 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 lower than a preset threshold, the first switching element S1 is kept in the ON state. This contributes to reducing losses and extending the vehicle's driving range.

[0048] (4) The first switching element S1 turns ON when voltage is applied to the transformer 12 and turns OFF when no voltage is applied to the transformer 12. In this way, the first switching element S1 is treated as a surge absorption circuit, thereby achieving low loss.

[0049] (5) After a predetermined time has elapsed from the moment when voltage is first applied to the transformer 12, the first switching element S1 is switched from OFF to ON. This makes it possible to reduce losses.

[0050] (6) A voltage conversion circuit (bidirectional chopper circuit) 11 that converts voltage bidirectionally is provided between the second switching circuit 2 and the second DC power supply V2. This contributes to the realization of a low-loss, highly efficient bidirectional charging device 7 and an extension of the vehicle's driving range.

[0051] (7) The power converter is mounted on the vehicle and, during charging, switches the first switching element S1 ON / OFF based on the operation of the second switching circuit 2, and during driving, maintains the first switching element S1 in the ON state and switches the second switching element S2 ON / OFF. In this way, it is possible to provide a vehicle equipped with a power converter that achieves low loss, high power output, high efficiency, and maintenance of the vehicle's driving range.

[0052] It should be noted that the present invention is not limited to the embodiments described above, and various modifications and combinations of other configurations can be made without departing from the spirit of the invention. Furthermore, the present invention is not limited to having all the configurations described in the embodiments described above, and may also include configurations in which some of those configurations are omitted. [Explanation of Symbols]

[0053] 1. First switching circuit N1 First winding 2. Second switching circuit N2 Second winding V2 2nd DC power supply 3. Third switching circuit N3 Third winding V3 3rd DC power supply S1 First switching element S2 Second switching element C smoothing capacitor D1 diode L Inductor element 5 AC / DC Converters 6 AC power supply 7 Bidirectional charging device 9 LLC Resonant DC-DC Converter (LLC Converter) 10 Rectifier circuit 11. Bidirectional Chopper Circuit 12 transformers

Claims

1. A transformer in which the first winding, the second winding, and the third winding are magnetically coupled, A first switching circuit connected to the first winding, which mutually converts first DC power and AC power with a first DC power supply, A second switching circuit connected to the second winding, which mutually converts the AC power and the second DC power with the second DC power supply, A power conversion device comprising: a third switching circuit connected to the third winding, which converts the AC power into a third DC power and supplies it to a third DC power source, The third switching circuit includes a rectifier circuit that converts the AC power to the third DC power, a smoothing capacitor that smooths 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 supplying power 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. Power converter.

2. A power conversion device according to claim 1, The third switching circuit includes a second switching element that controls conduction from the rectifier circuit to the inductor element. When power is supplied simultaneously from the first DC power supply to the second DC power supply and the third DC power supply, or when power is supplied simultaneously from the second DC power supply to the first DC power supply and the third DC power supply, the first switching element is kept in the ON state and the second switching element is switched ON / OFF. Power converter.

3. A power conversion device according to claim 1, 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 less than a preset voltage threshold, the first switching element is kept in the ON state. Power converter.

4. A power conversion device according to claim 1, The first switching element turns ON when a voltage is applied to the transformer and turns OFF when no voltage is applied to the transformer. Power converter.

5. A power conversion device according to claim 4, After a predetermined time has elapsed since the voltage was first applied to the transformer, the first switching element is switched from OFF to ON. Power converter.

6. A power conversion device according to claim 1, A voltage conversion circuit is provided between the second switching circuit and the second DC power supply to convert the voltage bidirectionally. Power converter.

7. The power conversion device described in claim 2 is mounted on a vehicle, During charging, the ON / OFF state of the first switching element is switched based on the operation of the second switching circuit. During operation, the second switching element is kept in the ON state, and the first switching element is switched ON / OFF. Power converter.

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