Power conversion device

Abstract

Provided is a power conversion device that achieves reduction in loss.　This power conversion device comprises: an input-side bridge circuit; an output-side bridge circuit; a transformer disposed between the input-side bridge circuit and the output-side bridge circuit; and a control unit that controls the input-side bridge circuit and the output-side bridge circuit. With respect to m1 that is a Hi period of an input voltage inputted from the input-side bridge circuit to the transformer, m2 that is a Hi period of an output voltage outputted from the transformer to the output-side bridge circuit, and m12 that is a difference between the center of the period of m1 and the center of the period of m2, the control unit controls the input-side bridge circuit and the output-side bridge circuit while switching among a region A, a region B, and a region C, where, when the horizontal axis is (m1-m2) / 2 and the vertical axis is (m1+m2) / 2, (A) the region A is an area surrounded by positions where the horizontal axis is 90 and the vertical axis is 90, where the horizontal axis is |m12| and the vertical axis is |m12|, and where the horizontal axis is |m12| and the vertical axis is 180-|m12|, (B) the region B is an area surrounded by the horizontal axis range from -|m12| to |m12| and the vertical axis range from |m12| to (180-|m12|), and (C) the region C is an area surrounded by positions where the horizontal axis is -90 and the vertical axis is 90, where the horizontal axis is -|m12| and the vertical axis is |m12|, and where the horizontal axis is -|m12| and the vertical axis is 180-|m12|.

Description

Power Conversion Device

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

[0002] As an example of a power conversion device, a power conversion device using a DC / DC converter as a main part or a part thereof is known. As an example, Patent Document 1 discloses a technology for performing soft switching in a DC / DC converter.

[0003] U.S. Patent No. 5,027,264

[0004] The DC-DC converter described in Patent Document 1 includes, for example, a switching circuit, a transformer, an inductance element, a capacitor, and a control unit. The DC-DC converter 1 performs power conversion using electrical energy flowing through the inductance element.

[0005] In the DC / DC converter described in Patent Document 1, soft switching operation is possible in the input bridge circuit and the output bridge circuit by control of the control circuit. However, there exists an operating range in which soft switching operation does not occur due to the phase difference between the input bridge circuit and the output bridge circuit (i.e., the output command value from the control circuit) and the voltage ratio between the input and output voltages. This poses a problem of increased loss.

[0006] Furthermore, depending on the phase difference conditions, the magnitude of losses due to iron loss and copper loss in the transformer may become significant, resulting in a decrease in power conversion efficiency.

[0007] An object of the present invention is to provide a power conversion device that achieves reduced loss.

[0008] 1. A power conversion device comprising: an input-side bridge circuit; an output-side bridge circuit; a transformer disposed between the input-side bridge circuit and the output-side bridge circuit; and a control unit for controlling the input-side bridge circuit and the output-side bridge circuit, wherein the control unit: where m1 is a Hi period of an input voltage input from the input-side bridge circuit to the transformer, m2 is a Hi period of an output voltage output from the transformer to the output-side bridge circuit, and m12 is a difference between the center of the m1 period and the center of the m2 period, and where (m1-m2) / 2 is the horizontal axis and (m1+m2) / 2 is the vertical axis, (A) Region A is defined as a range enclosed by a position on the horizontal axis at 90 and the vertical axis at 90, a position on the horizontal axis at absolute value m12 and the vertical axis at absolute value m12, and a position on the horizontal axis at absolute value m12 and the vertical axis at 180-absolute value m12, (B) Region B is the range bounded by the range on the horizontal axis between −absolute value m12 and absolute value m12 and the range on the vertical axis between absolute value m12 and (180−absolute value m12), (C) Region C is the range bounded by the position on the horizontal axis at −90 and the vertical axis at 90, the position on the horizontal axis at −absolute value m12 and the vertical axis at absolute value m12, and the position on the horizontal axis at −absolute value m12 and the vertical axis at 180−absolute value m12, and the power conversion device in which the control unit controls the input-side bridge circuit and the output-side bridge circuit while switching between regions A, B, and C.

[0009] According to the present invention, it is possible to provide a power conversion device that achieves reduced loss. Further means and effects of the present invention will become apparent throughout the entire specification below.

[0010] 11 is a circuit diagram of a DC / DC converter according to an embodiment; FIG. 12 is an example of input / output waveforms according to an embodiment; FIG. 13 is a diagram showing region divisions of an input / output voltage ratio and an output-side DC current according to an embodiment; FIG. 14 is a diagram showing region divisions of another example of an input / output voltage ratio and an output-side DC current according to an embodiment; FIG. 15 is a diagram showing a method for setting region divisions according to an embodiment; FIG. 16 is a diagram showing an example of control along line (1) of FIG. 3; FIG. 17 is a diagram showing an example of control along line (2) of FIG. 3; FIG. 18 is a diagram showing an example of control along line (3) of FIG. 3; FIG. 19 is a diagram showing an example of control along line (4) of FIG. 3; FIG. 19 is a diagram showing loss conditions in this embodiment and a comparative example; FIG. 20 is a diagram showing regions for explaining waveforms at various points in FIG. 3; FIG. 21 is a waveform diagram at part A of FIG. 21; FIG. 22 is a waveform diagram at part B1 of FIG. 21; FIG. 23 is a waveform diagram at part B2 of FIG. 21; FIG. 24 is a waveform diagram at part C of FIG. 21; FIG. 25 is a waveform diagram at part D1 of FIG. 21; and FIG. 26 is a waveform diagram at part D2 of FIG. 26. An explanatory diagram of an example of a power conversion device; An explanatory diagram of an example of a power conversion device; An explanatory diagram of an example of a charging device; An explanatory diagram of an example of a charging device. FIG. 1 is an explanatory diagram of an example of a charging device.

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings as needed.

[0012] FIG. 1 shows a circuit diagram of an example of a single-phase isolated DC / DC converter. This single-phase isolated DC / DC converter can be used bidirectionally by inverting the input and output, and includes a capacitor 10 that smooths the DC input voltage Vin. A first bridge circuit (e.g., a primary-side bridge circuit 20) is connected to both ends of the capacitor 10. This may also be referred to as an input-side bridge circuit. A primary winding 41 of a transformer for input-output isolation is connected to output-side nodes N1 and N2 of the primary-side bridge circuit via an inductance element. Input-side nodes N11 and N12 of a second bridge circuit (e.g., a secondary-side bridge circuit 50) are connected to a secondary winding 42 of the transformer. The secondary-side bridge may also be referred to as an output-side bridge circuit.

[0013] An isolated DC / DC converter is an example of a power conversion device that uses a transformer (hereinafter referred to as "transformer") to isolate the input side from the output side, converts an input direct current (DC) voltage to a DC voltage of a predetermined level, and outputs the converted DC voltage. This DC / DC converter is of the DAB (Dual Active Bridge) type. It includes a transformer having a primary winding and a secondary winding, an input bridge circuit connected to the primary winding side and configured with switching elements, an output bridge circuit connected to the secondary winding side and configured with switching elements, and a control circuit that operates the switching elements of the input bridge circuit and the output bridge circuit to perform constant voltage or constant current operation.

[0014] For example, when a DC voltage of a predetermined voltage is input, this DC input voltage is converted into an AC (alternating current) voltage by switching elements in the input bridge circuit. The converted AC voltage is then converted into an AC voltage that depends on the turns ratio of the primary and secondary windings of the transformer and its leakage inductance. The converted AC voltage is then switched by switching elements in the output bridge circuit and converted into a predetermined DC voltage, resulting in a constant DC output voltage.

[0015] In the input-side bridge circuit and the output-side bridge circuit, the transformer current charges and discharges the parasitic capacitance of the switching elements. By performing switching when the voltage of the parasitic capacitance is zero after the charging and discharging operation (i.e., zero-voltage switching), switching losses in the switching elements can be suppressed, and surge voltages and noise caused by switching can also be reduced. Furthermore, by performing switching when the transformer current is zero (i.e., zero-current switching), switching losses in the switching elements can also be suppressed, and surge voltages and noise caused by switching can also be reduced.

[0016] Although not shown in Fig. 1, an input voltage detection unit detects a DC input voltage Vin. Also, although not shown, an output voltage detection unit detects a DC output voltage Vout. A load ZL is connected to the output side of the secondary bridge circuit 50 via a smoothing capacitor 60. Furthermore, a control circuit 70 is provided that outputs four first control signals G1, G2, G3, and G4 and four second control signals G11, G12, G13, and G14 for controlling the switching of the primary bridge circuit 20 and the secondary bridge circuit 50.

[0017] The control circuit 70 (control unit) includes, for example, a microcomputer having a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), input / output ports, and various other circuits. The CPU of this microcomputer reads and executes programs stored in the ROM to control the operation of the first bridge circuit and the second bridge circuit. Specifically, it has a function of adjusting the switching timing of the switching elements in the first bridge circuit and the second bridge circuit.

[0018] The control circuit 70 calculates an input / output voltage ratio d (d=Vout / Vin) between the input voltage Vin and the output voltage Vout in the first bridge circuit and the second bridge circuit. Then, based on the input / output voltage ratio d and the target value of the output current flowing through the load ZL, it determines the high period m1 [deg] of the input voltage Vin_ac on the first bridge circuit side, the high period m2 [deg] of the output voltage Vout_ac on the second bridge circuit side, and the phase difference m12 [deg] between the output voltages of the first bridge circuit and the second bridge circuit. For example, the control circuit 70 may be configured to calculate, based on a relational expression or the like, a high period m1 [deg] of the input voltage Vin_ac on the corresponding first bridge circuit side, a high period m2 [deg] of the output voltage Vout_ac on the corresponding second bridge circuit side, and a phase difference m12 [deg] between the output voltages of the first bridge circuit and the second bridge circuit, in response to the calculated input / output voltage ratio d and the target value of the output current flowing through the load ZL.

[0019] Alternatively, in another example, the control circuit 70 may be configured to include a table storing, for the calculated input-output voltage ratio d and the target value of the output current flowing through the load ZL, the corresponding high period m1 [deg] of the input voltage Vin_ac on the first bridge circuit side, the high period m2 [deg] of the output voltage Vout_ac on the second bridge circuit side, and the phase difference m12 [deg] between the output voltages of the first bridge circuit and the second bridge circuit. The domains of m1 and m2 are 0 to 180 deg, and the domain of m12 is −90 to 90 deg. When m12 is positive, power flows from the input side to the output side, and when m12 is negative, power flows from the output side to the input side.

[0020] The primary-side bridge circuit 20 is made up of four first switching elements 201, 202, 203, and 204 connected in a bridge configuration, which are turned on / off by four first control signals G1 to G4, respectively. The first switching elements 201, 202, 203, and 204 are turned on / off by the control signals G1 to G4 input to their gates.

[0021] A first inductance element (not shown) and a primary winding 41 of a transformer 40 are connected in series between output nodes N1 and N2 of the primary bridge circuit 20. A capacitor (not shown) is connected in parallel to each of the first switching elements 201, 202, 203, and 204.

[0022] The first inductance element, together with four capacitors connected in parallel to the first switching element, constitutes an LC resonant circuit. However, in FIG. 1, this inductance element is omitted and instead the primary side leakage inductance inherent in the transformer 40 is configured to have the same function.

[0023] The primary-side bridge circuit 20 converts the DC input voltage Vin into an AC voltage by turning on / off the first switching elements 201 to 204, and supplies the AC voltage to the primary winding 41. Furthermore, current also flows through the first anti-parallel diodes 211 to 214 depending on the states of the first switching elements 201 to 204. The first anti-parallel diodes 211 to 214 may be integrated with or built into the first switching elements 201 to 204, respectively, or may be externally connected in anti-parallel to the first switching elements 201 to 204.

[0024] Furthermore, as an example, first capacitors (not shown) that are first capacitance elements for resonance are connected in parallel to each of the switching elements 201 to 204. The four first capacitors constitute an LC resonance circuit together with the inductance of the primary winding 41, but these first capacitors may also be constituted by the parasitic capacitance of each of the switching elements 201 to 204.

[0025] A second inductance element (not shown) and the secondary winding 42 of the transformer 40 are connected in series between the input nodes N11 and N12 of the secondary bridge circuit 50. In addition, a capacitor (not shown) is connected in parallel to each of the second switching elements 501, 502, 503, and 504.

[0026] The second inductance element, together with four capacitors connected in parallel to the second switching element, constitutes an LC resonant circuit; however, in FIG. 1 , this inductance element is omitted, and instead, the secondary leakage inductance inherent in the transformer 40 is configured to have an equivalent function. In the configuration shown in FIG. 1 , the secondary bridge circuit 50 converts the DC output voltage Vout into an AC voltage and supplies it to the secondary winding 42 by the on / off operation of the second switching elements 501-504. Furthermore, depending on the state of the second switching elements 501-504, a current also flows through the second anti-parallel diodes 511-514. The second anti-parallel diodes 511-514 may be integrated with or built into the second switching elements 501-504, respectively, or may be externally attached in anti-parallel to the second switching elements 501-504.

[0027] Furthermore, second capacitors (not shown) that are second capacitance elements for resonance are connected in parallel to the switching elements 501 to 504. The four second capacitors form an LC resonance circuit together with the inductance of the secondary winding 42, but these second capacitors may also be formed by the parasitic capacitance of each of the switching elements 501 to 504.

[0028] The DC voltage output from the secondary bridge circuit 50 is smoothed by a smoothing capacitor 60 to become a DC output voltage Vout, which is supplied to a load ZL.

[0029] The secondary bridge circuit 50 rectifies the AC voltage supplied from the secondary winding 42 side by the second anti-parallel diodes 511 to 514 and outputs a DC voltage. Alternatively, the secondary bridge circuit 50 has a function of converting the DC input voltage into an AC voltage and supplying it to the secondary winding 42 side by the on / off operation of the switching elements 501 to 504.

[0030] 1 has been described as an example in which no inductance element is disposed between the primary bridge circuit 20 or the secondary bridge circuit 50 and the transformer 40. However, the present invention is not limited to such a configuration, and an inductance element may be disposed between the AC side of one of the primary bridge circuit 20 or the secondary bridge circuit 50 and the transformer 40. Alternatively, an inductance element may be disposed between the AC side of both the primary bridge circuit 20 and the secondary bridge circuit 50 and the transformer 40.

[0031] 2 is a diagram showing voltage waveforms in the isolated DC / DC converter of this embodiment, which will be explained with reference to the numbers in the circuit diagram of FIG.

[0032] 2, the first to fourth rows from the top show the drain-source voltage waveforms of the switching elements 201 to 204. In the fifth row, the vertical axis shows the input voltage Vin_ac, which is the voltage between nodes N1 and N2, and the horizontal axis shows time or phase [deg].

[0033] 2, the sixth to ninth rows from the top show the drain-source voltage waveforms of the switching elements 501 to 504. In the tenth row, the vertical axis shows the output voltage Vout_ac, which is the voltage between the nodes N11 and N12, and the horizontal axis shows the time or phase [deg].

[0034] The phase can also be expressed as an angle, because it is common to generate control waveforms and control timing with one pulse period being 360 degrees.

[0035] As shown in the fifth row of Figure 2, the input voltage Vin_ac has a pulsed voltage waveform. The input voltage Vin_ac has a high period 22 due to an amplitude 221, and its phase difference or angle is m1 [deg]. This is equal to the phase difference between the rising or falling edges of the left leg voltage and the right leg voltage on the primary bridge circuit side. The amplitude 221 of the input voltage Vin_ac is also equal to Vin.

[0036] As shown in the tenth row of FIG. 2 , the output voltage Vout_ac has a pulsed voltage waveform. The output voltage Vout_ac has a high period 25 due to an amplitude 251, and its phase difference or angle is m2 [deg]. This is equal to the phase difference between the rising and falling edges of the left leg voltage and the right leg voltage on the secondary bridge circuit side. The amplitude 251 of the output voltage Vout_ac is also equal to Vout.

[0037] m12 is the phase difference or angle difference between the center of m1 and the center of m2.

[0038] 3 shows the switching modes at various operating points of the isolated DC / DC converter of this embodiment, where the horizontal axis represents the input / output voltage ratio d and the vertical axis represents the output (secondary) DC current.

[0039] The input / output voltage ratio d is defined as d=output voltage / input voltage, where Vout and Vin are Vout and Vin in FIG.

[0040] The left end of the horizontal axis in Figure 3 is d=0. The center of the vertical axis represents 0 amperes. Above the center, i.e., the region where the current is positive, is when power flows from the input side to the output side. Below the center, i.e., the region where the current is negative, is when power flows from the output side to the input side. Symbols A to D in Figure 3 represent switching modes. Note that B can be further subdivided into B1 and B2. Similarly, D can also be further subdivided into D1 and D2.

[0041] In this embodiment, loss reduction is achieved by finely switching the control method according to the input / output voltage ratio and the state of the output side DC current. Switching control at least in the three switching mode regions A, B, and C in Figure 3 is essential for loss reduction in this embodiment.

[0042] The shape of the curve in Figure 3 varies depending on the various constants of the circuit to be controlled. It is also affected to some extent by the controlled object or the load. Therefore, as shown in Figure 4, the curve may be slightly different from that in Figure 3.

[0043] For this reason, the switching characteristics are set in advance at the stage of circuit design and power conversion device design, or before shipping, or at the stage of test operation by the customer, and are recorded in a storage device as a control table or control information in the control circuit 70 of Fig. 1. Note that AI technology can also be used to automatically perform such status detection.

[0044] The definition of the switching mode will be explained using Figure 5. This definition of the switching mode itself is one of the features of the control in this embodiment. In the following, for ease of explanation, the switching mode and the region in which the switching mode is performed will be represented by the same alphabet, such as the range controlled as switching mode A being referred to as region A.

[0045] The regions of each switching mode are defined as follows using m1, m2, and m12 described with reference to FIG. In the case where the horizontal axis of Figure 5 is (m1 - m2) / 2 and the vertical axis is (m1 + m2) / 2, (A) the range surrounded by the position where the horizontal axis is 90 and the vertical axis is 90, the position where the horizontal axis is absolute value m12 and the vertical axis is absolute value m12, and the position where the horizontal axis is absolute value m12 and the vertical axis is 180 - absolute value m12 is defined as region A, (B) the range surrounded by the range on the horizontal axis between - absolute value m12 and absolute value m12 and the range on the vertical axis between absolute value m12 and (180 - absolute value m12) is defined as region B, and (C) the range surrounded by the position where the horizontal axis is -90 and the vertical axis is 90, the position where the horizontal axis is - absolute value m12 and the vertical axis is absolute value m12, and the position where the horizontal axis is - absolute value m12 and the vertical axis is 180 - absolute value m12 is defined as region C.

[0046] The control circuit 70 controls the primary bridge circuit 20 and the secondary bridge circuit 50 while switching between the regions A, B, and C.

[0047] Furthermore, region B can be further subdivided, and region B1 and region B2 can be set so that (B1) the range on the horizontal axis between 0 and absolute value m12 is region B1, and (B2) the range on the horizontal axis between -absolute value m12 and 0 is region B2.

[0048] Region D is determined as the range surrounded by (D) the position where the horizontal axis is -absolute value m12 and the vertical axis is 180-absolute value m12, the position where the horizontal axis is absolute value m12 and the vertical axis is 180-absolute value m12, and the position where the horizontal axis is 0 and the vertical axis is 180.

[0049] Region D can be further subdivided, and (D1) the region surrounded by the position where the horizontal axis is -absolute value m12 and the vertical axis is 180 - absolute value m12, the position where the horizontal axis is 0 and the vertical axis is 180, and the position where the horizontal axis is 0 and the vertical axis is 180 - absolute value m12 can be set as D1. Also, (D2) the region surrounded by the position where the horizontal axis is absolute value m12 and the vertical axis is 180 - absolute value m12, the position where the horizontal axis is 0 and the vertical axis is 180, and the position where the horizontal axis is 0 and the vertical axis is 180 - absolute value m12 can be set as D2.

[0050] The operating conditions of the switching mode in FIG. 3 are such that the state transitions according to the state of the output side DC current as the input / output voltage ratio d increases from 0.

[0051] The switching mode of FIG. 3 will be explained as follows, for example, when the output side DC current is in the conditions (1) to (4) along the broken lines in FIG.

[0052] Under the condition of output side DC current (1), the region switches in the order of D2 → C → B2 → B1 → A.

[0053] Under the condition of output side DC current (2), the region switches in the order of D2 → C → B2 → D2 → D1 → B1 → A.

[0054] Under the condition of output side DC current (3), the region switches in the order of D2 → C → D2 → D1 → B1 → A.

[0055] Under the condition of output DC current (4), the region switches from D2 to D1.

[0056] The above is a transition in the case of constant current drive, in which the output DC current is constant and the output voltage is increased. Similarly, in the case of drive in which both the output DC current and the output voltage are changed, the output current and voltage requirements are set by one or more diagonal lines or curves instead of the dashed lines (1) to (4) in Figure 3, and the region transition in Figure 3 is made along the diagonal lines or curves.

[0057] 6 to 9, we will explain how to control m1 and m2 in FIG. 2 when the transitions from region (1) to region (4) in FIG. 3 occur. In each figure, TP is the case when the input / output voltage ratio d is equal to the value obtained by dividing the number of turns of the secondary winding 42 of the transformer 40 by the number of turns of the primary winding 41 of the transformer 40. If the number of turns of the secondary winding 42 is Nout and the number of turns of the primary winding 41 is Nin, then TP = Nout / Nin. This can also be referred to as the turns ratio.

[0058] When this input / output voltage ratio d is TP, the relationship is: output voltage detection value (Vout)=input voltage detection value (Vin)×transformer turns ratio (Nout / Nin).

[0059] 6 to 9, the horizontal axis represents the input / output voltage ratio d, and the vertical axis represents the phase or angle.

[0060] First, the case of Figure 6 will be described. This is the case where control is performed along line (1) in Figure 3. The characteristic parts of the control in the figure will be described. In region C, as the input / output voltage ratio d increases, m2 decreases more than in region D2, and then increases. That is, in region C2, m2 decreases once, then increases, showing a characteristic shape with a bottom 90. m1 follows an increasing direction.

[0061] Thereafter, when transitioning from region C to region B2 occurs, the control method switches. As a result, both m2 and m1 change abruptly, resulting in a sudden decrease at abrupt decrease portion 91 as shown in the figure. After that, the input-output voltage ratio d increases, but a crossover between m1 and m2 occurs at or near the value at which the input-output voltage ratio d becomes TP. This may be referred to as the transition portion from region B2 to region B1, or the vicinity thereof.

[0062] The input / output voltage ratio d further increases, and the control method switches at the transition from region B (region B1 in the figure) to region A. As a result, a sudden change occurs in both m2 and m1, and they rapidly increase at a sudden increase portion 92 as shown in the figure.

[0063] In this way, even when the control according to (1) in FIG. 3 is described in particular, the control is switched between areas C, B, and A, for example.

[0064] The reason for switching control in this way is to further reduce losses. Losses in DC / DC converters are caused by a variety of factors, including transformer iron loss, transformer copper loss, secondary conduction loss, secondary switching loss, primary conduction loss, and primary switching loss. Conventionally, these loss factors have been controlled without accurately analyzing their influence. However, to further reduce losses, the inventors have clarified in detail how an increase in the secondary DC voltage affects the impact of each of the above factors on losses. Note that an increase in the secondary DC voltage is also related to the input / output voltage ratio d in Figures 6 to 9.

[0065] As a result, the inventors found that the proportion of the impact of each of the above-mentioned factors on loss changes as the secondary-side DC voltage increases. While the disclosure of details in this specification is limited because it would involve the disclosure of know-how, for example, it was found that in region C, as the secondary-side DC voltage increases, the transformer's iron loss gradually increases from an initial small proportion, and increases sharply, especially in regions close to region B. Furthermore, the primary-side switching loss in region C exhibits the largest proportion but is not significantly affected by increases in the secondary-side DC voltage. Meanwhile, the secondary-side switching loss in region C increases with increases in the secondary-side DC voltage. Thus, even within region C, the behavior of each loss factor is complex as the secondary-side DC voltage increases. For this reason, the inventors found that controlling m1 and m2, as shown in Figure 6 , especially controlling m2 so that it has a bottom, contributes to loss reduction even within region C.

[0066] If control continues in region C as the secondary DC voltage increases, the effect of iron loss in the transformer increases rapidly, causing a sudden increase in total loss. Therefore, control is shifted to region B.

[0067] When transitioning from region C to region B, m1 and m2 change suddenly as shown by a sudden decrease portion 91.

[0068] In region B, the transformer iron loss mentioned above drops sharply. Meanwhile, the proportion of the influence of secondary-side switching loss increases sharply, and the proportion of the influence of primary-side switching loss also increases. However, it was found that moving to region B can suppress the increase in total loss, rather than continuing control in region C, which causes the transformer iron loss to increase sharply.

[0069] Within region B, in response to an increase in the secondary DC voltage, increases in transformer iron loss, transformer copper loss, secondary conduction loss, and primary conduction loss are suppressed, and in order to minimize the total loss that also includes primary switching loss and secondary switching loss, control is performed so that m1 and m2 overlap within region B, as shown in FIG. 6.

[0070] Thereafter, as the proportion of secondary-side switching loss continues to increase with an increase in secondary-side DC voltage, a transition to region A is made to suppress an increase in the overall total loss. When transitioning from region B to region A, the proportion of secondary-side switching loss decreases and transformer iron loss increases, but the total loss remains approximately the same before and after the transition from region B to region A. In region A, the amount of transformer iron loss itself does not change significantly after the transition. The secondary-side switching loss, secondary-side conduction loss, and primary-side conduction loss, which had once decreased, increase as the secondary-side DC voltage increases. However, by switching control to region A, it is possible to suppress an increase in the total amount of loss more effectively than if control were continued in region B.

[0071] When transitioning from region B to region A, m1 and m2 change suddenly as shown by the sudden increase portion 92. After that, m1 and m2 decrease. However, at this time, as an example, the magnitude relationship between m1 and m2 is reversed from that in region C. That is, in region C, m1≦m2, and in region A, m1 ≧m2.

[0072] The above patterns can be theoretically shown using a large number of calculation formulas. However, since this would be disclosing detailed know-how, this specification mainly describes the conclusions regarding control obtained as a result of analysis. However, we would like to add that it is possible to present a detailed set of analytical formulas under circumstances where confidentiality is maintained and know-how is not disclosed.

[0073] Next, the case of Fig. 7 will be described. This is the case where control is performed along line (2) in Fig. 3. The characteristic parts of the control in the figure will be described. As the input / output voltage ratio d increases, there is a transition from region D2 to region C. In region C, m2 is controlled to have a bottom 90, as in Fig. 6. In the transition from region C to region B2, m1 and m2 change suddenly at a sudden decrease portion 91.

[0074] When transitioning from B2 to D, m1 and m2 change suddenly at a sudden increase portion 92. Region D can be subdivided into D1 and D2, and m1 and m2 have a crossover when the input / output voltage ratio d is near TP or near the transition from region D2 to region D1.

[0075] When transitioning from D1 to B1, m1 and m2 change suddenly at a sudden decrease portion 91.

[0076] At the transition from B1 to A, m1 and m2 change suddenly at a sudden increase portion 92.

[0077] Next, the case of Fig. 8 will be described. This is the case where control is performed along the line (3) in Fig. 3. The characteristic parts of the control in the figure will be described. As the input / output voltage ratio d increases, there is a transition from region D2 to region C. In region C, m2 is controlled to have a bottom 90, as in Fig. 6.

[0078] Unlike the cases of FIGS. 6 and 7, when transitioning from region C to region D, no sudden change occurs between m1 and m2.

[0079] m1 and m2 have a crossover when the input / output voltage ratio d is near TP or near the transition from region D2 to region D1.

[0080] When transitioning from D1 to B1, m1 and m2 change suddenly at a sudden decrease portion 91. When transitioning from B1 to A, m1 and m2 change suddenly at a sudden increase portion 92.

[0081] Next, the case of Fig. 9 will be described. This is the case where control is performed along the line (4) in Fig. 3. Region D can be subdivided into D1 and D2, and m1 and m2 have a crossover when the input / output voltage ratio d is near TP or near the transition from region D2 to region D1.

[0082] The loss reduction effect achieved by performing the above-described control will be explained with reference to Fig. 10. In Fig. 10, the horizontal axis represents the input / output voltage ratio d, and the vertical axis represents the loss. Note that the vertical axis is set as a numerical value to easily explain the effect.

[0083] In the comparative example, loss is high even when the input / output voltage ratio d is 0, but the loss decreases as the input / output voltage ratio d increases. Then, the input / output voltage ratio d reaches its minimum value near TP. Thereafter, the loss increases again sharply as the input / output voltage ratio d increases.

[0084] On the other hand, in the example of control described in this embodiment, the input / output voltage ratio d is suppressed even near 0, and losses are suppressed compared to the comparative example even in the region where the input / output voltage ratio d is low. After that, losses increase as the input / output voltage ratio d increases, but even beyond the vicinity of TP, a sudden increase in losses as seen in the comparative example is avoided. As a result, loss suppression is achieved over a wide range of the input / output voltage ratio d.

[0085] In this way, the control of this embodiment and the DC / DC converter using it achieve loss suppression. Also, in this way, the control circuit 70 issues pulse commands to the primary bridge circuit 20 and the secondary bridge circuit 50 to control m1 and m2.

[0086] To put it another way, by controlling the Hi period of the input voltage and the Hi period of the output voltage according to the voltage ratio, it is possible to reduce losses in the switching elements, copper losses in the transformer, and iron losses in the transformer, thereby preventing a decrease in power conversion efficiency.

[0087] According to this embodiment, the power conversion efficiency of the power conversion device can be increased compared to the conventional case. Furthermore, even when the output current fluctuates in addition to the input voltage and output voltage fluctuates, the power conversion efficiency can be increased overall in the control of the power conversion device.

[0088] This embodiment describes an example of the control in the first embodiment from the viewpoint of control waveforms.

[0089] Fig. 11 is a diagram equivalent to Fig. 3. It shows the correspondence between the waveforms described in Fig. 3 and each region in Fig. 12 to Fig. 17. In Fig. 12 to Fig. 17, examples of drive waveforms will be described for each of the white circles A, B1, B2, C, D1, and D2 in Fig. 11.

[0090] In Figures 12 to 17, the horizontal axis represents the phase or angle, with one cycle being 360 degrees. The vertical axis represents the waveform value. For the sake of explanation, current and voltage are mixed, so they are shown as waveform values. Also, even with regard to Vin_ac and Vout_ac, which are the same voltage, Vout_ac is significantly amplified compared to Vin_ac, so it is difficult to simultaneously display them on the same scale. Therefore, these figures are merely for the purpose of explaining the waveforms.

[0091] FIG. 12 shows the drive waveform at point A in FIG. 11. Compared to Vin_ac, Vout_ac rises slowly and falls quickly. Iin_ac has a triangular waveform. Note that Iin_ac is generally positive between 90 and 180 degrees and generally negative between 270 and 360 degrees. A more detailed feature is that the sign of Iin_ac is positive or negative near 0 degrees, 90 degrees, 180 degrees, and 270 degrees.

[0092] FIG. 13 shows the drive waveform at point B1 in FIG. 11. Vout_ac rises and falls slowly relative to Vin_ac. Iin_ac has a deformed trapezoidal waveform with a lower tail. It rises as Vin_ac rises, and reaches its maximum absolute value at the rising edge of Vout_ac. It then decreases as an absolute value, begins to decrease as Vin_ac falls, and reaches zero at the falling edge of Vout_ac.

[0093] Figure 14 shows the drive waveform at point B2 in Figure 11. Vout_ac rises and falls slowly relative to Vin_ac. Iin_ac has a deformed trapezoidal waveform with a higher peak at the rear. It rises as Vin_ac rises, reaches an inflection point at the rising edge of Vout_ac, then increases in absolute value, begins to decrease as Vin_ac falls, and reaches 0 at the falling edge of Vout_ac.

[0094] 13 and 14, the inclination of the trapezoid of Iin_ac is reversed. At the boundary between B1 and B2, Iin_ac becomes a trapezoid with no inclination. This is also related to the crossover between m1 and m2 described in the first embodiment.

[0095] FIG. 15 shows the drive waveform at point C in FIG. 11. Vout_ac rises quickly and falls slowly relative to Vin_ac. Iin_ac has a triangular waveform and reaches an absolute maximum at the falling edge of Vin_ac. Note that Iin_ac is generally positive when Vout_ac is positive and generally negative when Vout_ac is negative. More specifically, the sign of Iin_ac is positive or negative near 0°, 90°, 180°, and 270°.

[0096] 16 shows the drive waveform at point D1 in FIG. 11. There is an interval between Vin_ac and Vout_ac on both the rising and falling edges. Iin_ac is based on a triangular wave, but its absolute value peaks at the rising or falling edge of Vout_ac. The waveform has two inflection points, one at the falling edge of Vin_ac and one at the falling edge of Vout_ac.

[0097] 17 shows the drive waveform at point D2 in FIG. 11. There is an interval between Vin_ac and Vout_ac both at the rising edge and the falling edge. Iin_ac is based on a triangular wave, but the peak of its absolute value occurs at the falling edge of Vin_ac as an absolute value. The waveform has two inflection points: one at the rising edge of Vin_ac as an absolute value and one at the falling edge of Vout_ac as an absolute value.

[0098] As described above, by controlling the waveform for each region, it is possible to reduce the loss of the DC / DC converter and improve the conversion efficiency.

[0099] This embodiment is an example in which either or both of Embodiments 1 and 2 are applied to a DC / DC converter, and the DC / DC converter is then applied to a power conversion device. Although the DC / DC converter itself also falls under the category of a power conversion device, in this embodiment the term "power conversion device" is used to refer to a larger device that incorporates a DC / DC converter.

[0100] FIG. 18A is a schematic external view of an example of a power conversion device, and FIG. 18B is a schematic internal configuration diagram of the example of the power conversion device.

[0101] The power conversion device 900 incorporates one or more DC / DC converters 904. As an example, it has a control device 902, as an example, an exhaust port or exhaust fan 903, and as an example, an air intake 905. Power is supplied to the power conversion device 900 via a power line 910, and power is supplied directly or indirectly from the power conversion device 900 to an output destination device via a power supply line 920.

[0102] Power conversion devices can be used in a variety of applications, including, for example, power controllers for solar power generation, battery controllers for power storage devices, and quick chargers for charging electric vehicles.

[0103] As described above, the power conversion device of this embodiment applies either or both of the first and second embodiments to a DC / DC converter, and the DC / DC converter itself or a power conversion device incorporating the DC / DC converter can suppress losses and provide a power conversion device with high conversion efficiency.

[0104] This embodiment is an example in which either or both of the first and second embodiments are applied to a DC / DC converter, and the DC / DC converter is used in a rapid charger. Alternatively, this embodiment is an example in which the power conversion device of the third embodiment is applied to a rapid charger.

[0105] Various types of quick chargers will be described as examples using Figures 19A to 19E. Note that quick chargers are sometimes called EV-chargers when used to supply power to electric vehicles.

[0106] FIG. 19A is an example of a conceptual diagram of the exterior of a standalone quick charger. Power is supplied to a quick charger main body 950 via a power line 910. An example of the quick charger includes a display device 951 for the user to perform charging operations, which displays the charging time, charging status, billing information, etc. 952 is a payment terminal for paying the bill. A connector 961 connects the device to an object to be charged, such as an electric vehicle. 960 is a power supply cable. The connector 961 and power supply cable 960 are constructed in accordance with the corresponding standards.

[0107] Fig. 19B is an example of a schematic internal configuration diagram of Fig. 19A. A DC / DC converter or power conversion device 904 is built in. Power supplied from a power line 910 passes through a control device 902 and is supplied to the DC / DC converter or power conversion device 904. The control device 902 determines whether to shut off the circuit or power in the event of an abnormality, whether to allow power supply in relation to billing processing, and controls the operation of the DC / DC converter or power conversion device 904. Note that the control device 902 may be configured with multiple functional units integrated together or distributed.

[0108] Fig. 19C is another example of a schematic internal configuration diagram of a quick charger. The difference from Fig. 19B is that multiple DC / DC converters or power conversion devices 904 are built in, each connected directly or indirectly to a power supply cable 960 and a connector 961. In this way, by enabling a single quick charger to charge multiple devices, it is possible to reduce the installation space for the quick charger main body 950, reduce overall costs, and simplify management.

[0109] 19D shows that the quick charger is separated into two parts, a power converter side unit 981 and a unit to be charged 982, which together form a quick charger main body 950. The power converter side unit 981 and the unit to be charged 982 are connected by a high-voltage supply cable 970. An air intake 905 may also be provided in all of the examples shown in FIGS. 19A to 19D.

[0110] In this way, by separating the power converter side unit 981 and the charging target side unit 982, the power converter side units 981 can be centrally arranged, particularly in large-scale charging spots where many quick charger main bodies 950 are installed, making management easier. In addition, by arranging the charging target side units 982 close to the charging target, for example close to each parking space in a parking lot, convenience for users can be improved.

[0111] FIG. 19E is an example combining FIG. 19D and FIG. 19C. It should be noted that this also includes a case where multiple charging target units 982 are provided for one power converter unit 981. Also, throughout FIG. 19A to FIG. 19E, it includes both cases where charging is performed directly or indirectly along the path from the rapid charger to the charging target. The connection from the DC / DC converter or power conversion device 904 to the connector 961 also includes both direct and indirect connections. One example of the intention of this description is to realize, for example, a large current by bundling the outputs from multiple DC / DC converters or power conversion devices 904 using a switch or the like and supplying them to a single power supply cable 960.

[0112] 19A to 19E have been described primarily with the intention of supplying power from a quick charger to an external device, such as an electric vehicle. However, the present invention also includes cases where a quick charger receives power from an external device, such as an electric vehicle, and operates as a so-called external power supply. This can also be referred to as a quick power receiving device.

[0113] The DC / DC converters or power conversion devices described in Examples 1 to 3 have low loss and excellent conversion efficiency. Therefore, their application to rapid chargers, which will be installed in large numbers as part of social infrastructure in the future, is an effective technology for reducing power loss throughout society. Furthermore, as shown in FIG. 10 , the DC / DC converters or power conversion devices described in Examples 1 to 3 can operate with reduced loss over a wide output voltage range. Therefore, they are suitable technologies for rapid chargers, which are expected to increasingly use higher charging voltages in the future to reduce charging times. This is evident from the fact that the difference in loss between the comparative example and the examples in FIG. 10 increases as the input / output voltage ratio d increases, i.e., as the output voltage increases. Thus, the performance of rapid chargers incorporating the various technologies described above is an important technology whose usefulness will increase in the future.

[0114] The above examples illustrate the ideas and concepts of the present invention. Of course, the scope of the present invention also includes examples that are realized by combining the examples. Furthermore, as long as the disclosed ideas and concepts are used, any modifications or similar examples are also included within the scope of the present invention.

[0115] Furthermore, one example of the present invention described using the above embodiments can also be expressed as follows.

[0116] <Part 1> A power conversion device comprising: an input-side bridge circuit; an output-side bridge circuit; a transformer arranged between the input-side bridge circuit and the output-side bridge circuit; and a control unit that controls the input-side bridge circuit and the output-side bridge circuit, wherein the control unit: where m1 is a Hi period of the input voltage input from the input-side bridge circuit to the transformer, m2 is a Hi period of the output voltage output from the transformer to the output-side bridge circuit, and m12 is the difference between the center of the m1 period and the center of the m2 period, when (m1-m2) / 2 is set as the horizontal axis and (m1+m2) / 2 is set as the vertical axis, (A) the range surrounded by the position where the horizontal axis is 90 and the vertical axis is 90, the position where the horizontal axis is absolute value m12 and the vertical axis is absolute value m12, and the position where the horizontal axis is absolute value m12 and the vertical axis is 180-absolute value m12, is defined as region A, (B) Region B is defined as a range bounded by the range on the horizontal axis between −absolute value m12 and absolute value m12 and the range on the vertical axis between absolute value m12 and (180−absolute value m12), (C) Region C is defined as a range bounded by a position on the horizontal axis at −90 and the vertical axis at 90, a position on the horizontal axis at −absolute value m12 and the vertical axis at absolute value m12, and a position on the horizontal axis at −absolute value m12 and the vertical axis at 180−absolute value m12, and the control unit controls the input-side bridge circuit and the output-side bridge circuit while switching between region A, region B, and region C. <Part 2> The power conversion device according to <Part 1>, wherein region B is further defined as: (B1) region B1 is defined as a range on the horizontal axis between 0 and absolute value m12, and (B2) region B2 is defined as a range on the horizontal axis between −absolute value m12 and 0. <3> The power conversion device according to <2>, which controls m1 and m2 to have a crossover relationship when an input / output voltage ratio, which is a value obtained by dividing the output voltage output from the transformer to the output-side bridge circuit by the input voltage input to the transformer from the input-side bridge circuit, is close to a value obtained by dividing the number of windings on the output side of the transformer by the number of windings on the input side of the transformer. <4> The power conversion device according to <3>, which controls m2 so that it decreases once and then increases as the input / output voltage ratio increases in region C. <5> The power conversion device according to <4>, which controls m1 and m2 so that they change rapidly when transitioning from region B to another region as the input / output voltage ratio increases.<No. 6> The power conversion device according to <No. 5>, wherein m1 and m2 are controlled to decrease rapidly as the input / output voltage ratio increases, when transitioning from region C to region B. <No. 7> The power conversion device according to <No. 6>, wherein m1 and m2 are controlled to increase rapidly as the input / output voltage ratio increases, when transitioning from region B to region A. <No. 8> The power conversion device according to <No. 7>, wherein (D) control is performed to have a region D surrounded by a position on the horizontal axis of −absolute value m12, a position on the vertical axis of 180−absolute value m12, a position on the horizontal axis of absolute value m12, a position on the vertical axis of 180−absolute value m12, and a position on the horizontal axis of 0 and a position on the vertical axis of 180. <No. 9> The power conversion device according to <No. 8>, wherein m1 and m2 are controlled to increase rapidly as the input / output voltage ratio increases, when transitioning from region B to region D. <No. 10> The power conversion device according to <No. 8>, which controls m1 and m2 to rapidly decrease as the input / output voltage ratio increases during a transition from region D to region B. <No. 11> The power conversion device according to <No. 10>, which controls m2 to be greater than m1 in region C, smaller than m2 in region A, and such that m1 and m2 are equal when the input / output voltage ratio is close to a value obtained by dividing the number of windings on the output side of the transformer by the number of windings on the input side of the transformer. <No. 12> A quick charging device comprising the power conversion device according to any one of <No. 1> to <No. 11>. <No. 13> A quick charging device according to <No. 12>, which has a connector for connection to an automobile and a connection cable connecting the quick charging device and the connection connector. <No. 14> The quick charging device according to <No. 13>, wherein power is supplied directly or indirectly from the power conversion device to the connection connector. <No. 15> The power conversion device supports bidirectional power supply and has a power supply mode in which power is supplied from the power conversion device to the automobile and a power receiving mode in which power is supplied from the automobile to the power conversion device, and in the power receiving mode, the roles of the input side bridge circuit and the output side bridge circuit of the power conversion device are controlled to be reversed.

Claims

1. A power conversion device comprising: an input-side bridge circuit; an output-side bridge circuit; a transformer disposed between the input-side bridge circuit and the output-side bridge circuit; and a control unit that controls the input-side bridge circuit and the output-side bridge circuit, wherein the control unit: where m1 is the Hi period of the input voltage input from the input-side bridge circuit to the transformer, m2 is the Hi period of the output voltage output from the transformer to the output-side bridge circuit, and m12 is the difference between the center of the m1 period and the center of the m2 period, and where (m1 - m2) / 2 is the horizontal axis and (m1 + m2) / 2 is the vertical axis, (A) Region A is defined as the range enclosed by the position where the horizontal axis is 90 and the vertical axis is 90, the position where the horizontal axis is absolute value m12 and the vertical axis is absolute value m12, and the position where the horizontal axis is absolute value m12 and the vertical axis is 180 - absolute value m12, (B) Region B is the range bounded by the range on the horizontal axis between −absolute value m12 and absolute value m12 and the range on the vertical axis between absolute value m12 and (180−absolute value m12), (C) Region C is the range bounded by the position on the horizontal axis at −90 and the vertical axis at 90, the position on the horizontal axis at −absolute value m12 and the vertical axis at absolute value m12, and the position on the horizontal axis at −absolute value m12 and the vertical axis at 180−absolute value m12, and the power conversion device in which the control unit controls the input-side bridge circuit and the output-side bridge circuit while switching between regions A, B, and C.

2. The power conversion device of claim 1, wherein the region B is further defined as: (B1) the range of the horizontal axis between 0 and absolute value m12 is region B1; and (B2) the range of the horizontal axis between -absolute value m12 and 0 is region B2.

3. A power conversion device according to claim 2, wherein m1 and m2 are controlled to cross over when an input / output voltage ratio, which is the value obtained by dividing the output voltage output from the transformer to the output-side bridge circuit by the input voltage input to the transformer from the input-side bridge circuit, is close to the value obtained by dividing the number of windings on the output side of the transformer by the number of windings on the input side of the transformer.

4. The power conversion device according to claim 3, wherein m2 is controlled to have a bottom portion in which it decreases once and then increases as the input / output voltage ratio increases in the region C.

5. The power conversion device according to claim 4, wherein control is performed so that m1 and m2 change suddenly when transitioning from region B to another region as the input / output voltage ratio increases.

6. The power conversion device according to claim 5, wherein control is performed so that m1 and m2 are rapidly decreased when transitioning from region C to region B as the input / output voltage ratio increases.

7. The power conversion device according to claim 6, wherein control is performed so that m1 and m2 increase sharply when transitioning from region B to region A as the input / output voltage ratio increases.

8. (D) A power conversion device as described in claim 7, which is controlled to have a region D surrounded by the position where the horizontal axis is -absolute value m12 and the vertical axis is 180-absolute value m12, the position where the horizontal axis is absolute value m12 and the vertical axis is 180-absolute value m12, and the position where the horizontal axis is 0 and the vertical axis is 180.

9. The power conversion device according to claim 8, wherein control is performed so that m1 and m2 increase sharply when transitioning from region B to region D as the input / output voltage ratio increases.

10. The power conversion device according to claim 8, wherein control is performed so that m1 and m2 are rapidly decreased when transitioning from region D to region B as the input / output voltage ratio increases.

11. A power conversion device according to claim 10, wherein control is performed so that m2 is greater than m1 in region C, m2 is smaller than m1 in region A, and m1 and m2 are equal when the input / output voltage ratio is close to a value obtained by dividing the number of windings on the output side of the transformer by the number of windings on the input side of the transformer.

12. A quick charger having a power conversion device according to any one of claims 1 to 11.

13. The quick charger according to claim 12, further comprising a connector for connection to an automobile, and a connection cable for connecting the quick charger to the connector.

14. The quick charger according to claim 13, wherein power is supplied directly or indirectly from the power converter to the connector.

15. A quick charging device according to claim 14, wherein the power conversion device supports bidirectional power supply and has a power supply mode in which the power conversion device supplies power to the automobile and a power receiving mode in which the power conversion device receives power from the automobile, and in the power receiving mode, the roles of the input-side bridge circuit and output-side bridge circuit of the power conversion device are controlled to be reversed.

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