A pre-chargeable DCDC conversion circuit

Abstract

The present invention discloses a prechargeable DC-DC converter circuit, comprising a high-voltage side converter module connected to the primary winding of a main transformer T1, a low-voltage side converter module connected to the secondary winding of the main transformer, and a controller for controlling the high- and low-voltage side converter modules. A precharge module is connected in series to the DC bus of the low-voltage side converter module. The precharge module precharges the capacitor of an electrical device connected to the DC bus of the high-voltage side converter module when the entire device is powered on. The present invention overcomes the shortcomings of the prior art and provides a prechargeable DC-DC converter circuit. The present invention is an improvement based on the original DC-DC converter. The precharge module shares most of the power devices and power circuits with the forward DC-DC converter, adding only a small number of devices. Compared with an independent precharge branch, the precharge module reduces the volume and cost, and has a simple control method.

Description

Technical Field

[0001] The invention belongs to the technical field of electric vehicle charging, and in particular relates to a pre-chargeable DC-DC conversion circuit. Background Art

[0002] With the demand for energy conservation and emission reduction, as well as the control of air pollution, new energy vehicles are gradually being commercialized in the market, and electric vehicles are the main force of new energy vehicles. The electrical equipment of electric vehicles has a large equivalent capacitance. When the whole machine is started, the instantaneous charging current is very large, which can easily burn the circuit or cause unsafe factors. To solve this problem, the existing technology is to connect a pre-charging branch in parallel next to the main relay between the high-voltage battery and the electrical equipment, first slowly charge the capacitor with a small current, and then close the main relay after the capacitor voltage increases and the charging current decreases. In the existing technology, the pre-charging branch is connected in parallel with the main relay S1 (see Figure 1 The control principle block diagram of the entire device of the present invention is shown. The pre-charging branch connected in parallel at both ends of the main relay S1 is the prior art. The pre-charging branch is connected by a dotted line, indicating that such a connection does not exist in the present invention. The pre-charging branch and the DCDC converter are separated, which has the disadvantages of having many components, large size, high cost, and complex control.

[0003] Therefore, how to design a DCDC conversion circuit that integrates the pre-charge function into the DCDC converter, reuses existing DCDC components as much as possible, reduces the size and reduces the cost is a technical problem that needs to be solved urgently in the industry. Summary of the Invention

[0004] In order to solve the above-mentioned defects in the prior art, the present invention proposes a pre-chargeable DCDC conversion circuit.

[0005] The technical solution adopted by the present invention is a pre-chargeable DC-DC conversion circuit, which includes a high-voltage side conversion module connected to the primary winding of the main transformer T1, a low-voltage side conversion module connected to the secondary winding of the main transformer, and a controller for controlling the high and low-voltage side conversion modules. A pre-charging module is connected in series to the DC bus of the low-voltage side conversion module. When the entire machine is powered on, the pre-charging module pre-charges the capacitor of the electrical equipment connected to the DC bus of the high-voltage side conversion module.

[0006] The pre-charging module includes a secondary transformer L1, the primary winding of the secondary transformer is connected in series to the DC bus of the low-voltage side conversion module, one end of the secondary winding of the secondary transformer is connected to the anode of the ninth diode D9, the other end of the secondary winding of the secondary transformer is connected to the negative bus of the high-voltage side conversion module and one end of the fifth capacitor C5, and the cathode of the ninth diode is connected to the other end of the fifth capacitor and the positive bus of the high-voltage side conversion module.

[0007] During pre-charging, the controller sends a first PWM control signal to the power switch in the low-voltage side conversion module to convert the DC power connected to the low-voltage side conversion module into AC power, and transmits electrical energy to the high-voltage side conversion module through the secondary transformer L1 and the ninth diode D9.

[0008] During pre-charging, the controller controls the power switch of the upper bridge arm in the high-voltage side conversion module to be turned off, and sends a second PWM control signal to the power switch in the lower bridge arm in the high-voltage side conversion module.

[0009] The pre-charging includes a slow-start phase and a closed-loop charging phase. In the slow-start phase, the duty cycle of the first PWM control signal ranges from 0% to 50%, and in the closed-loop charging phase, the duty cycle of the first PWM control signal is 50%.

[0010] The high-side conversion module adopts a full-bridge structure, including a first power switch Q1, a second power switch Q2, a third power switch Q3, and a fourth power switch Q4.

[0011] The high-side conversion module adopts a half-bridge rectification structure and includes a first power switch Q1 and a third power switch Q3.

[0012] The low-voltage side conversion module adopts a push-pull structure and includes a fifth power switch Q5 and a sixth power switch Q6.

[0013] The low-voltage side conversion module adopts a full-bridge structure, including a fifth power switch Q5, a sixth power switch Q6, a seventh power switch Q7, and an eighth power switch Q8.

[0014] The beneficial effects of the technical solution provided by the present invention are:

[0015] The present invention overcomes the shortcomings of the prior art and provides a prechargeable DC-DC converter circuit. The present invention is an improvement based on the original DC-DC converter. The precharge module and the forward DC-DC converter share power devices and power circuits, adding only a small number of devices. Compared with an independent precharge branch, the volume and cost are reduced, and the control method is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention is described in detail below with reference to the embodiments and accompanying drawings, in which:

[0017] Figure 1 This is a block diagram of the control principle of the whole machine of the present invention;

[0018] Figure 2 This is a circuit diagram of a full-bridge + push-pull mode according to an embodiment of the present invention;

[0019] Figure 3 It is a timing diagram of pre-charge control of the present invention;

[0020] Figure 4 This is a circuit diagram of a full-bridge + full-wave rectification method according to a second embodiment of the present invention;

[0021] Figure 5 This is a circuit diagram of a full-bridge + full-bridge rectifier according to a third embodiment of the present invention;

[0022] Figure 6 This is a circuit diagram of a four-half-bridge + push-pull mode according to an embodiment of the present invention;

[0023] Figure 7 This is a circuit diagram of a fifth half-bridge + full-wave rectification method according to an embodiment of the present invention;

[0024] Figure 8 This is a circuit diagram of a half-bridge + full-bridge rectifier according to a sixth embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] The present invention discloses a prechargeable DC-DC conversion circuit, comprising a high-voltage side conversion module connected to the primary winding of a main transformer T1, a low-voltage side conversion module connected to the secondary winding of the main transformer, and a controller for controlling the high- and low-voltage side conversion modules. A precharge module is connected in series to the DC bus of the low-voltage side conversion module, and the precharge module precharges the capacitor of the electrical equipment connected to the DC bus of the high-voltage side conversion module when the whole machine is powered on. Precharging belongs to reverse operation. After the precharge is completed: the circuit can be in reverse operation for a long time; it can also stop reverse operation and switch to forward operation, that is, the high-voltage side conversion module supplies power to the capacitor of the electrical equipment normally and supplies power to the low-voltage side conversion module.

[0027] See Figure 1 The control principle block diagram of the whole machine of the present invention is shown. When the whole machine is started, the main relay disconnects the high-voltage battery pack, and the low-voltage battery charges the equivalent capacitor of the electrical equipment through the DCDC conversion circuit ( Figure 1 The bidirectional DCDC converter in the embodiment is the circuit to be protected by this application). The equivalent capacitor of the electrical equipment is first pre-charged slowly with a small current. After the capacitor voltage increases and the charging current decreases, the pre-charging is terminated, the main relay is closed, and the high-voltage battery pack supplies power to the electrical equipment, and the low-voltage battery and other loads on the low-voltage side are supplied through the DCDC converter.

[0028] See Figure 2In the illustrated embodiment 1, the pre-charging module includes a secondary transformer L1, the primary winding of the secondary transformer is connected in series to the DC bus of the low-voltage side conversion module, one end of the secondary winding of the secondary transformer is connected to the anode of the ninth diode D9, the other end of the secondary winding of the secondary transformer is connected to the negative bus of the high-voltage side conversion module and one end of the fifth capacitor C5, and the cathode of the ninth diode is connected to the other end of the fifth capacitor and the positive bus of the high-voltage side conversion module.

[0029] During pre-charging, the controller switches the power switch in the low-voltage side conversion module ( Figure 2 Q5, Q6 in the low-voltage side conversion module) sends a first PWM control signal to convert the DC power connected to the low-voltage side conversion module into AC power, and transmits the power to the high-voltage side conversion module through the secondary transformer L1 and the ninth diode D9.

[0030] During pre-charging, the controller controls the power switch of the upper bridge arm in the high-voltage side conversion module ( Figure 2 Q1, Q2 in the high voltage side is turned off, and the power switch in the lower bridge arm of the high voltage side conversion module ( Figure 2 Q3, Q4 in the circuit sends a second PWM control signal.

[0031] The following combination Figure 2 The working principle of the present invention is described in detail:

[0032] Figure 2 Among them, Q1, Q2, Q3, Q4, Q5, and Q6 are power field-effect transistors, and diodes D1, D2, D3, D4, D5, and D6 are body diodes of Q1, Q2, Q3, Q4, Q5, and Q6 respectively.

[0033] When working in the forward direction, it is a full-bridge working mode. The high-voltage side DC voltage V1 is chopped and converted into AC voltage through MOS tubes Q1~Q4, transmitted to the secondary stage through transformer T1, rectified by Q5 and Q6, and filtered by L1 and capacitor 5, and then converted into DC voltage V2.

[0034] The first PWM control signals S5 and S6 control Q5 and Q6, with the same duty cycle and a phase difference of 180 degrees. The second PWM control signals S3 and S4 control Q3 and Q4, with Q3 and Q4 being turned on and off synchronously and with a frequency twice that of S5 and S6. Reverse operation operates in push-pull plus boost mode. In push-pull mode, the output duty cycles of S5 and S6 are consistent, with a phase difference of 180°. When the duty cycle of S5 and S6 is less than 50%, a slow-start strategy is used. The DC voltage of V2 is chopped and converted into an AC voltage by MOS transistors Q5 and Q6. This voltage is then transferred to V1 via transformer T1. After rectification and filtering by transistors D1 to D4 and capacitors C1 and C2, it is converted to V1. Simultaneous conduction of S3 and S4 stores additional energy in L1, which is released to V1 through the flyback winding. In boost mode, the duty cycles of S5 and S6 are greater than 50% and remain fixed. S1 and S2 are low, and the duty cycles of S3 and S4 are adjusted to control the output voltage. Simultaneous conduction of Q3 and Q4 shorts the V1-side winding of T1, storing energy in inductor L1. When Q3 and Q4 are turned off, the stored energy in L1 is released to V1 through transformer T1 or the flyback winding (depending on the output voltage of V1).

[0035] In a preferred embodiment, the pre-charge includes a slow-start phase and a closed-loop charging phase. During the slow-start phase, the duty cycle of the first PWM control signal ranges from 0% to 50%, while during the closed-loop charging phase, the duty cycle of the first PWM control signal is 50%. The second PWM control is a closed-loop control that can be controlled based on the output voltage. The second PWM control signal ranges from 0% to greater than 50%.

[0036] See Figure 3 The pre-charge control timing diagram shown in Figure 1 shows the slow-start phase on the left and the closed-loop charging phase on the right. The duty cycle of the signals S5 and S6 controlling Q5 and Q6 on the left is less than 50%, but the duty cycle is fixed at 50% on the right.

[0037] In some embodiments, the high-side conversion module adopts a full-bridge structure, including a first power switch Q1, a second power switch Q2, a third power switch Q3, and a fourth power switch Q4.

[0038] In other embodiments, the high-side conversion module adopts a half-bridge rectifier structure, including a first power switch Q1 and a third power switch Q3.

[0039] In some other embodiments, the low-voltage side conversion module adopts a push-pull structure and includes a fifth power switch Q5 and a sixth power switch Q6.

[0040] In some other embodiments, the low-voltage side conversion module adopts a full-bridge structure, including a fifth power switch Q5, a sixth power switch Q6, a seventh power switch Q7, and an eighth power switch Q8.

[0041] See Figure 2 The circuit diagram of the first embodiment of the present invention, which uses a full-bridge plus full-wave rectification scheme, shows a high-voltage side conversion module using a full-bridge structure, including a first power switch Q1, a second power switch Q2, a third power switch Q3, and a fourth power switch Q4. Q1 and Q2 form the two upper bridge arms, while Q3 and Q4 form the two lower bridge arms. The low-voltage side conversion module uses a push-pull structure, including a fifth power switch Q5 and a sixth power switch Q6. Both Q5 and Q6 are connected to the negative DC bus on the voltage side.

[0042] See Figure 4 The circuit diagram of the full-bridge + full-wave rectification method in Example 2 of the present invention shows a high-voltage side conversion module using a full-bridge structure, including a first power switch Q1, a second power switch Q2, a third power switch Q3, and a fourth power switch Q4. Q1 and Q2 form the two upper bridge arms, while Q3 and Q4 form the two lower bridge arms. The low-voltage side conversion module uses a push-pull structure, including a fifth power switch Q5 and a sixth power switch Q6. Both Q5 and Q6 are connected to the positive DC bus on the voltage side.

[0043] See Figure 5 The circuit diagram of the full-bridge + full-bridge rectifier shown in Example 3 of the present invention shows a high-voltage side conversion module using a full-bridge structure, including a first power switch Q1, a second power switch Q2, a third power switch Q3, and a fourth power switch Q4. Q1 and Q2 form the two upper bridge arms, while Q3 and Q4 form the two lower bridge arms. The low-voltage side conversion module uses a full-bridge structure, including a fifth power switch Q5, a sixth power switch Q6, a seventh power switch Q7, and an eighth power switch Q8. Q6 and Q7 switch synchronously, and Q5 and Q8 switch synchronously.

[0044] See Figure 6 The circuit diagram of the four-half-bridge + full-wave rectification scheme in the embodiment of the present invention is shown. The high-voltage side conversion module adopts a half-bridge rectification structure and includes a first power switch Q1 and a third power switch Q3. During pre-charging, Q1 remains off, while Q3 receives control from a second PWM control signal. The low-voltage side conversion module adopts a push-pull structure and includes a fifth power switch Q5 and a sixth power switch Q6. Both Q5 and Q6 are connected to the negative DC bus on the voltage side.

[0045] See Figure 7 The circuit diagram of the fifth half-bridge plus full-wave rectification scheme of the present invention is shown. The high-voltage side conversion module adopts a half-bridge rectification structure and includes a first power switch Q1 and a third power switch Q3. During pre-charging, Q1 remains off, while Q3 receives control from a second PWM control signal. The low-voltage side conversion module adopts a push-pull structure and includes a fifth power switch Q5 and a sixth power switch Q6. Both Q5 and Q6 are connected to the positive DC bus on the voltage side.

[0046] See Figure 8 The circuit diagram of the sixth half-bridge + full-bridge rectifier embodiment of the present invention shows a high-voltage side conversion module using a half-bridge rectifier structure, including a first power switch Q1 and a third power switch Q3. During pre-charging, Q1 remains off, while Q3 receives control from a second PWM control signal. The low-voltage side conversion module uses a full-bridge structure, including a fifth power switch Q5, a sixth power switch Q6, a seventh power switch Q7, and an eighth power switch Q8. Q6 and Q7 switch on and off synchronously, and Q5 and Q8 switch on and off synchronously.

[0047] The above embodiments are for illustration only and are not intended to be limiting. Any equivalent modifications or variations made thereto without departing from the spirit and scope of this application should be included in the scope of the claims of this application.

Claims

1. A prechargeable DC-DC converter circuit, comprising a high-voltage side converter module connected to the primary winding of a main transformer T1, a low-voltage side converter module connected to the secondary winding of the main transformer, and a controller for controlling the high- and low-voltage side converter modules, characterized in that: A pre-charging module is connected in series to the DC bus of the low-voltage side conversion module. When the whole machine is powered on, the pre-charging module pre-charges the capacitor of the electric device connected to the DC bus of the high-voltage side conversion module. The pre-charging module includes a secondary transformer L1, the primary winding of the secondary transformer is connected in series to the DC bus of the low-voltage side conversion module, one end of the secondary winding of the secondary transformer is connected to the anode of the ninth diode D9, the other end of the secondary winding of the secondary transformer is connected to the negative bus of the high-voltage side conversion module and one end of the fifth capacitor C5, and the cathode of the ninth diode is connected to the other end of the fifth capacitor and the positive bus of the high-voltage side conversion module; During pre-charging, the controller sends a first PWM control signal to the power switch in the low-voltage side conversion module to convert the DC power connected to the low-voltage side conversion module into AC power, and transmits the power to the high-voltage side conversion module through the secondary transformer L1 and the ninth diode D9; During pre-charging, the controller controls the power switch of the upper bridge arm in the high-voltage side conversion module to be turned off, and sends a second PWM control signal to the power switch in the lower bridge arm in the high-voltage side conversion module.

2. The prechargeable DC-DC converter circuit according to claim 1, wherein: The pre-charging includes a slow-start phase and a closed-loop charging phase. In the slow-start phase, the duty cycle of the first PWM control signal ranges from 0% to 50%, and in the closed-loop charging phase, the duty cycle of the first PWM control signal is 50%.

3. The prechargeable DC-DC converter circuit according to claim 1, wherein: The high-side conversion module adopts a full-bridge structure, including a first power switch Q1, a second power switch Q2, a third power switch Q3, and a fourth power switch Q4.

4. The prechargeable DC-DC converter circuit according to claim 1, wherein: The high-side conversion module adopts a half-bridge rectification structure and includes a first power switch Q1 and a third power switch Q3.

5. The prechargeable DCDC converter circuit according to claim 1, wherein: The low-voltage side conversion module adopts a push-pull structure and includes a fifth power switch Q5 and a sixth power switch Q6.

6. The prechargeable DC-DC converter circuit according to claim 1, wherein: The low-voltage side conversion module adopts a full-bridge structure, including a fifth power switch Q5, a sixth power switch Q6, a seventh power switch Q7, and an eighth power switch Q8.

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