Power converter

Abstract

To restrain an output voltage during the startup of a bidirectional DC / DC converter.SOLUTION: A control circuit executes at least one of first phase shift control and second phase shift control. The first phase shift control is to output a secondary side control signal so as to apply a positive voltage to a secondary side winding after outputting a primary side control signal so as to apply a positive voltage to a primary side winding when the voltage of a capacitor is higher than a battery voltage primary side conversion value at the startup of a bidirectional DC / DC converter. The second phase shift control is to output the primary side control signal so as to apply a positive voltage to the primary side winding after outputting the secondary side control signal so as to apply a positive voltage to the secondary side winding.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] This disclosure relates to a power conversion device.

Background Art

[0002] The power conversion device disclosed in Patent Document 1 includes a bidirectional DC / DC converter and a capacitor provided at the input end of the bidirectional DC / DC converter. The bidirectional DC / DC converter includes a transformer, a primary full-bridge circuit, and a secondary full-bridge circuit. The power conversion device is used, for example, to charge a battery.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the bidirectional DC / DC converter is started, output power may be generated due to the difference between the voltage of the capacitor and the primary-side converted value of the battery voltage. The primary-side converted value of the battery voltage is a value obtained by multiplying the voltage of the battery by the turns ratio of the transformer. When output power is generated at the start of the bidirectional DC / DC converter, fluctuations in the voltage of the capacitor may cause overvoltage or overcurrent.

Means for Solving the Problems

[0005] A power conversion device that solves the above problems comprises a bidirectional DC / DC converter connected to a battery, and a capacitor provided at the input terminal of the bidirectional DC / DC converter, wherein the bidirectional DC / DC converter comprises a transformer having a primary winding and a secondary winding, a circuit connected to the primary winding comprising a primary full-bridge circuit having a plurality of primary switching elements, a circuit connected to the secondary winding comprising a secondary full-bridge circuit having a plurality of secondary switching elements, and outputs a primary control signal that switches the primary switching elements on and off and a secondary control signal that switches the secondary switching elements on and off, thereby converting the input voltage input to the primary full-bridge circuit to the secondary full-bridge circuit The bidirectional DC / DC converter includes a control circuit that converts the output voltage from the ridge circuit to an output voltage and outputs it to the battery, wherein the battery voltage multiplied by the turns ratio of the transformer is defined as the primary-side equivalent battery voltage, the control circuit performs at least one of the following: a first phase shift control that outputs a primary-side control signal so that a positive voltage is applied to the primary-side winding when the capacitor voltage is higher than the primary-side equivalent battery voltage when the bidirectional DC / DC converter is started, and then outputs a secondary-side control signal so that a positive voltage is applied to the secondary-side winding; and a second phase shift control that outputs a secondary-side control signal so that a positive voltage is applied to the secondary-side winding, and then outputs a primary-side control signal so that a positive voltage is applied to the primary-side winding.

[0006] By performing at least one of the first phase shift control and the second phase shift control, the output power during startup of the bidirectional DC / DC converter can be suppressed. The above power conversion device may include an AC / DC converter that converts AC power to DC power and outputs it to the bidirectional DC / DC converter. [Effects of the Invention]

[0007] According to the present invention, the output power during startup of a bidirectional DC / DC converter can be suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a circuit diagram of a power converter. [Figure 2] Figure 2 is a flowchart showing the startup control. [Figure 3] Figure 3 shows the relationship between the amount of phase shift and the output power. [Modes for carrying out the invention]

[0009] An embodiment of a power conversion device will be described. As shown in Figure 1, the power supply system 100 comprises a grid power supply 101, a battery 120, and a power converter 10. The battery 120 is, for example, a secondary battery capable of charging and discharging DC power. The secondary battery is, for example, a lithium-ion battery or a lead-acid battery.

[0010] <Power converter> The power converter 10 comprises an AC / DC converter 13 and a bidirectional DC / DC converter 14.

[0011] The AC / DC converter 13 is electrically connected to the grid power supply 101. The AC / DC converter 13 converts the AC power input from the grid power supply 101 into DC power and outputs it to the bidirectional DC / DC converter 14.

[0012] The bidirectional DC / DC converter 14 is a dual active bridge type DC / DC converter. The bidirectional DC / DC converter 14 is installed between the AC / DC converter 13 and the battery 120. The bidirectional DC / DC converter 14 can convert the DC power input from the AC / DC converter 13 into power and output it to the battery 120. The bidirectional DC / DC converter 14 can convert the DC power input from the battery 120 into power and output it to the AC / DC converter 13.

[0013] The bidirectional DC / DC converter 14 includes a transformer 20. The transformer 20 is an isolated type. The transformer 20 comprises a magnetic core 21, a primary winding 22, and a secondary winding 23. The primary winding 22 and the secondary winding 23 are wound around the core 21. The transformer 20 has a reactor L1. The reactor L1 may be an element such as a choke coil, or it may be the leakage inductance of the primary winding 22 and the secondary winding 23.

[0014] The bidirectional DC / DC converter 14 includes a primary-side full-bridge circuit 30. The primary-side full-bridge circuit 30 includes a first leg 31 and a second leg 32. The first leg 31 and the second leg 32 are connected in parallel with each other. The first leg 31 includes a first switching element Q1, a second switching element Q2, and diodes D1 and D2. The first switching element Q1 and the second switching element Q2 are connected in series with each other. The second leg 32 includes a third switching element Q3, a fourth switching element Q4, and diodes D3 and D4. The third switching element Q3 and the fourth switching element Q4 are connected in series with each other. The first switching element Q1 and the third switching element Q3 constitute the upper arm. The second switching element Q2 and the fourth switching element Q4 constitute the lower arm.

[0015] The first switching element Q1, the second switching element Q2, the third switching element Q3, and the fourth switching element Q4 are a plurality of primary-side switching elements Q1 to Q4. The primary-side switching elements Q1 to Q4 are, for example, n-type MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The primary-side switching elements Q1 to Q4 may also be p-type MOSFETs, IGBTs (Insulated Gate Bipolar Transistors), or GaN-HEMTs.

[0016] Diodes D1 to D4 are respectively connected in parallel to primary - side switching elements Q1 to Q4. Diodes D1 to D4 may be parasitic diodes or elements.

[0017] The connection points of the first switching element Q1 and the second switching element Q2, and the connection points of the third switching element Q3 and the fourth switching element Q4 are respectively connected to the primary - side winding 22. Thereby, the primary - side full - bridge circuit 30 is connected to the primary - side winding 22.

[0018] The bidirectional DC / DC converter 14 includes a secondary - side full - bridge circuit 40. The secondary - side full - bridge circuit 40 includes a third leg 41 and a fourth leg 42. The third leg 41 includes a fifth switching element Q5, a sixth switching element Q6, and diodes D5, D6. The fifth switching element Q5 and the sixth switching element Q6 are connected in series with each other. The fourth leg 42 includes a seventh switching element Q7, an eighth switching element Q8, and diodes D7, D8. The seventh switching element Q7 and the eighth switching element Q8 are connected in series with each other. The fifth switching element Q5 and the seventh switching element Q7 constitute the upper arm. The sixth switching element Q6 and the eighth switching element Q8 constitute the lower arm.

[0019] The fifth switching element Q5, the sixth switching element Q6, the seventh switching element Q7, and the eighth switching element Q8 are a plurality of secondary - side switching elements Q5 to Q8. The secondary - side switching elements Q5 to Q8 are, for example, n - type MOSFETs. The secondary - side switching elements Q5 to Q8 may be p - type MOSFETs, IGBTs, or GaN - HEMTs.

[0020] Diodes D5 to D8 are respectively connected in parallel to secondary - side switching elements Q5 to Q8. Diodes D5 to D8 may be parasitic diodes or elements.

[0021] The connection points between the fifth switching element Q5 and the sixth switching element Q6, and the connection points between the seventh switching element Q7 and the eighth switching element Q8, are each connected to the secondary winding 23. As a result, the secondary full-bridge circuit 40 is connected to the secondary winding 23.

[0022] The third leg 41 and the fourth leg 42 are connected to the battery 120 in parallel with each other. The secondary full-bridge circuit 40 is electrically connected to the battery 120. The output power of the secondary full-bridge circuit 40 is supplied to the battery 120. As a result, the power converter 10 charges the battery 120.

[0023] The power converter 10 includes an intermediate capacitor 50. The intermediate capacitor 50 is a link capacitor or a smoothing capacitor. The intermediate capacitor 50 is connected in parallel with the first leg 31 and the second leg 32. The intermediate capacitor 50 is provided between the AC / DC converter 13 and the bidirectional DC / DC converter 14. The intermediate capacitor 50 is a capacitor provided at the input terminal of the bidirectional DC / DC converter 14.

[0024] The power converter 10 includes a first voltage sensor 61. The first voltage sensor 61 detects the voltage VH of the intermediate capacitor 50. The power converter 10 includes a second voltage sensor 62. The second voltage sensor 62 detects the voltage of the battery 120.

[0025] The power converter 10 includes a control circuit 71. The control circuit 71 includes a processor and a memory unit. The processor is, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or a DSP (Digital Signal Processor). The memory unit includes RAM (Random Access Memory) and ROM (Read Only Memory). The memory unit stores program code or instructions configured to cause the processor to perform processing. The memory unit, i.e., the computer-readable medium, includes any available medium that can be accessed by a general-purpose or dedicated computer. The control circuit 71 may be composed of hardware circuits such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control circuit 71, which is a processing circuit, may include one or more processors that operate according to a computer program, one or more hardware circuits such as an ASIC or FPGA, or a combination thereof.

[0026] The control circuit 71 controls the power converter 10. When the control circuit 71 switches the primary-side switching elements Q1 to Q4 on and off, it outputs a primary-side control signal to the primary-side switching elements Q1 to Q4. When the control circuit 71 switches the secondary-side switching elements Q5 to Q8 on and off, it outputs a secondary-side control signal to the secondary-side switching elements Q5 to Q8.

[0027] When the grid power supply 101 is electrically connected to the AC / DC converter 13, the control circuit 71 converts the AC power input from the grid power supply 101 to the power converter 10 into DC power and outputs it to the battery 120. More specifically, the control circuit 71 inputs DC power to the bidirectional DC / DC converter 14 by operating the AC / DC converter 13. The control circuit 71 switches the primary switching elements Q1 to Q4 by outputting primary control signals to the primary switching elements Q1 to Q4. The control circuit 71 switches the secondary switching elements Q5 to Q8 by outputting secondary control signals to the secondary switching elements Q5 to Q8. As a result, the input voltage input to the primary full-bridge circuit 30 is converted into an output voltage output from the secondary full-bridge circuit 40 and output to the battery 120.

[0028] The primary-side full-bridge circuit 30 switches between a first operation, which simultaneously turns on the first switching element Q1 and the fourth switching element Q4, and a second operation, which simultaneously turns on the second switching element Q2 and the third switching element Q3. Therefore, the primary-side control signal is output when switching between the first and second operations.

[0029] The secondary full-bridge circuit 40 switches between a third operation, which simultaneously turns on the fifth switching element Q5 and the eighth switching element Q8, and a fourth operation, which simultaneously turns on the sixth switching element Q6 and the seventh switching element Q7. Therefore, the secondary control signal is output when switching between the third and fourth operations.

[0030] When the first operation is performed in the primary full-bridge circuit 30, the third operation is performed in the secondary full-bridge circuit 40. When the second operation is performed in the primary full-bridge circuit 30, the fourth operation is performed in the secondary full-bridge circuit 40.

[0031] This section describes the startup control performed by the control circuit 71 when the bidirectional DC / DC converter 14 is started up. <Startup control> As shown in Figure 2, in step S1, the control circuit 71 determines whether the voltage VH of the intermediate capacitor 50 is higher than the primary-side converted battery voltage VCHG when the bidirectional DC / DC converter 14 is started. The voltage VH of the intermediate capacitor 50 can be obtained from the first voltage sensor 61. The primary-side converted battery voltage VCHG is the value obtained by multiplying the voltage of the battery 120 by the turns ratio of the transformer 20. The voltage of the battery 120 can be obtained from the second voltage sensor 62. The turns ratio of the transformer 20 is the number of turns of the primary winding 22 / the number of turns of the secondary winding 23. The turns ratio of the transformer 20 can be known in advance. If the determination result of step S1 is positive, the control circuit 71 performs the process of step S2.

[0032] In step S2, the control circuit 71 performs first phase shift control. First phase shift control is a control that outputs a primary side control signal so that a positive voltage is applied to the primary side winding 22, and then outputs a secondary side control signal so that a positive voltage is applied to the secondary side winding 23.

[0033] The first phase shift control is a control that delays the phase of the secondary control signal relative to the primary control signal. That is, after the first operation is performed in the primary full-bridge circuit 30, the third operation is performed in the secondary full-bridge circuit 40. After the second operation is performed in the primary full-bridge circuit 30, the fourth operation is performed in the secondary full-bridge circuit 40.

[0034] Phase shift amount θ when performing the first phase shift control ini [°] may be a fixed value or a variable value. For example, the phase shift amount θ ini This can be calculated from equation (1). Phase shift amount θ when performing the first phase shift control. ini This can be said to be the time from when the primary control signal is transmitted until the secondary control signal is transmitted. Equation (1) is derived by circuit analysis.

[0035]

number

[0036] If the result of step S1 is negative, the control circuit 71 performs the determination in step S3. In step S3, the control circuit 71 determines whether the voltage VH of the intermediate capacitor 50 is lower than the primary-side battery voltage VCHG when the bidirectional DC / DC converter 14 is started. If the result of the determination in step S3 is positive, the control circuit 71 performs the process in step S4.

[0037] In step S4, the control circuit 71 performs second phase shift control. Second phase shift control is a control that outputs a secondary control signal so that a positive voltage is applied to the secondary winding 23, and then outputs a primary control signal so that a positive voltage is applied to the primary winding 22.

[0038] The second phase shift control is a control that advances the phase of the secondary control signal relative to the primary control signal. That is, after the third operation is performed in the secondary full-bridge circuit 40, the first operation is performed in the primary full-bridge circuit 30. After the fourth operation is performed in the secondary full-bridge circuit 40, the second operation is performed in the primary full-bridge circuit 30.

[0039] Phase shift amount θ when performing second phase shift control ini [°] may be a fixed value or a variable value. For example, the phase shift amount θ ini This can be calculated from equation (2). Phase shift amount θ when performing second phase shift control ini This can be said to be the time from when the primary control signal is transmitted until the secondary control signal is transmitted. Equation (2) is derived by circuit analysis.

[0040]

number

[0041] [Operation of this embodiment] The ideal value of the output power P of the bidirectional DC / DC converter 14 can be expressed by equation (3).

[0042]

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[0043] However, due to the effects of dead time and input / output voltage, the output power P of the bidirectional DC / DC converter 14 may not be ideal. Therefore, when primary and secondary control signals are output so that a positive voltage is applied to both the primary winding 22 and the secondary winding 23 simultaneously, the output power P may not be zero.

[0044] If the output power P is not zero and the voltage VH of the intermediate capacitor 50 is higher than the primary-side equivalent value of the battery voltage VCHG, an overcurrent may occur. If the output power P is not zero and the voltage VH of the intermediate capacitor 50 is lower than the primary-side equivalent value of the battery voltage VCHG, an overvoltage may occur.

[0045] Figure 3 shows the relationship between the phase shift and the output power P. Line L11 shows the characteristics of an ideal output power P. Line L12 shows the characteristics of an actual output power P. Note that the relationship between the phase shift and the output power P can vary depending on various factors such as dead time, input / output power, and the primary-side battery voltage (VCHG). The relationship between the phase shift and the output power P shown by line L12 in Figure 3 is an example where these factors are set to specific values.

[0046] As can be seen from Figure 3, when the phase shift amount is 0, the actual output power P is not 0. In the example in Figure 3, the phase shift amount is θ ini From the above, if the phase shift amount is less than 0, the output power P can be suppressed compared to the case where the phase shift amount is 0.

[0047] [Effects of this embodiment] (1) The control circuit 71 performs a first phase shift control when the voltage VH of the intermediate capacitor 50 is higher than the primary-side equivalent value of the battery voltage VCHG. The control circuit 71 performs a second phase shift control when the voltage VH of the intermediate capacitor 50 is lower than the primary-side equivalent value of the battery voltage VCHG. This suppresses the output power P of the bidirectional DC / DC converter 14 when it starts up.

[0048] (2) The power converter 10 includes an intermediate capacitor 50 between the AC / DC converter 13 and the bidirectional DC / DC converter 14. In this case, if a large output power P is generated when the bidirectional DC / DC converter 14 is started up, the voltage of the intermediate capacitor 50 will fluctuate, causing overvoltage and overcurrent. However, according to this embodiment, the output power P when the bidirectional DC / DC converter 14 is started up can be suppressed, and therefore the voltage fluctuation of the intermediate capacitor 50 can be suppressed.

[0049] [Example of changes] The embodiment can be implemented with the following modifications. The embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0050] ○The control circuit 71 may perform only one of the first phase shift control or the second phase shift control. For example, if the voltage VH of the intermediate capacitor 50 is always higher than the primary-side battery voltage VCHG, the control circuit 71 may perform only the first phase shift control.

[0051] ○The power converter does not need to have an AC / DC converter 13. In this case, the capacitor connected to the input terminal of the bidirectional DC / DC converter 14 is an input capacitor. [Explanation of symbols]

[0052] 10...Power converter, 13...AC / DC converter, 14...Bidirectional DC / DC converter, 20...Transformer, 22...Primary winding, 23...Secondary winding, 30...Primary full-bridge circuit, 40...Secondary full-bridge circuit, 50...Intermediate capacitor (a type of capacitor), 71...Control circuit, 120...Battery.

Claims

1. A bidirectional DC / DC converter connected to the battery, The bidirectional DC / DC converter includes a capacitor provided at the input terminal, The aforementioned bidirectional DC / DC converter is A transformer having a primary winding and a secondary winding, A circuit connected to the primary winding, comprising a primary full-bridge circuit having a plurality of primary switching elements, A circuit connected to the secondary winding, comprising a secondary full-bridge circuit having a plurality of secondary switching elements, The control circuit outputs a primary control signal to switch the primary switching element on and off, and a secondary control signal to switch the secondary switching element on and off, thereby converting the input voltage input to the primary full-bridge circuit into an output voltage output from the secondary full-bridge circuit and outputting it to the battery. If the value obtained by multiplying the battery voltage by the turns ratio of the transformer is taken as the primary-side equivalent value of the battery voltage, The aforementioned control circuit is A power converter that performs at least one of the following: a first phase shift control that outputs a primary control signal so that a positive voltage is applied to the primary winding when the voltage of the capacitor is higher than the primary-side equivalent value of the battery voltage when the bidirectional DC / DC converter is started, and then outputs a secondary control signal so that a positive voltage is applied to the secondary winding; and a second phase shift control that outputs a secondary control signal so that a positive voltage is applied to the secondary winding when the voltage of the capacitor is lower than the primary-side equivalent value of the battery voltage when the bidirectional DC / DC converter is started, and then outputs a primary control signal so that a positive voltage is applied to the primary winding.

2. The power conversion device according to claim 1, further comprising an AC / DC converter that converts alternating current power to direct current power and outputs it to the bidirectional DC / DC converter.

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