Hybrid active discharge circuit and control method thereof

Abstract

The invention discloses a hybrid active discharge circuit and a control method thereof, wherein the hybrid active discharge circuit comprises a controller and a high-voltage power battery, the high-voltage power battery is respectively connected to a high-voltage inverter and a high-voltage DC / DC through a DC bus, the high-voltage DC / DC is connected to a low-voltage battery, a high-voltage capacitor is connected between the positive and negative buses of the DC bus, the high-voltage inverter is connected to a high-voltage AC load, the low-voltage battery is connected to a low-voltage battery load, and a discharge branch is arranged at an input end of the high-voltage DC / DC connected to the DC bus; in the early stage of discharge, the high-voltage capacitor charges the low-voltage battery through the high-voltage DC / DC; in the late stage of discharge, the high-voltage capacitor discharges through the discharge branch; a part of the discharged electric energy is transmitted to the low-voltage battery, a part is consumed in an HVDCDC converter, and the other part is consumed in a miniaturized power discharge resistor, and the hybrid active discharge circuit has the advantages of fast discharge speed, small size of the power discharge resistor, low cost, easy control and high reliability.

Description

Technical Field

[0001] The present invention relates to the field of high-voltage power systems for electric vehicles, and particularly to a hybrid active discharge circuit and its control method. Background Art

[0002] The input voltage at the inverter in electric vehicles and hybrid electric vehicles is higher than 60Vdc. To protect personal safety, a discharge circuit is required to be equipped on the DC side capacitor of the inverter to reduce the voltage of the DC side capacitor. The currently commonly used active discharge method is to add an external active discharge circuit and use a power resistor for discharging. However, an additional constant power control circuit is required, increasing the cost. The power discharge resistor is large in size, and may also be damaged after multiple discharges.

[0003] Therefore, designing a discharge circuit that saves energy, is small in size, has a long lifespan, and works reliably is a technical problem urgently to be solved in the industry. Summary of the Invention

[0004] To solve the above-mentioned defects existing in the prior art, the present invention proposes a hybrid active discharge circuit and its control method.

[0005] The technical solution adopted by the present invention is to design a hybrid active discharge circuit, which includes a controller and a high-voltage power battery. The high-voltage power battery is respectively connected to a high-voltage inverter and a high-voltage DC / DC through a DC bus. The high-voltage DC / DC is connected to a low-voltage battery. A high-voltage capacitor is connected between the positive and negative buses of the DC bus. The high-voltage inverter is connected to a high-voltage AC load. The low-voltage battery is connected to a low-voltage battery load. A discharge branch is provided at the input end of the high-voltage DC / DC connected to the DC bus; in the early stage of discharge, the high-voltage capacitor charges the low-voltage battery through the high-voltage DC / DC; in the later stage of discharge, the high-voltage capacitor discharges through the discharge branch.

[0006] The discharge branch includes a series-connected discharge resistor PTC and a discharge switch Q1, and the discharge switch Q1 is controlled by the controller.

[0007] A power switch SW1 is connected in series between the high-voltage power battery and the DC bus.

[0008] The DC bus is also connected to other high-voltage electrical equipment.

[0009] The high-voltage DC / DC includes a primary conversion module, a high-frequency transformer, and a secondary conversion module connected in sequence. The primary conversion module adopts a full-bridge topology structure. The secondary conversion module adopts a synchronous rectification topology structure. The secondary conversion module includes a sixth switch Q6 and a seventh switch Q7; the sixth switch Q6 and the seventh switch Q7 adopt MOS tubes with body diodes.

[0010] The present invention also designs a control method for a hybrid active discharge circuit. The discharge circuit uses the above-mentioned hybrid active discharge circuit. The control method includes: in the early stage of discharge, the high-voltage capacitor charges the low-voltage battery through a high-voltage DC / DC; in the later stage of discharge, the high-voltage capacitor discharges through a discharge branch.

[0011] After the discharge starts, the voltage of the high-voltage capacitor is detected. When the voltage of the high-voltage capacitor is higher than the threshold voltage, the high-voltage capacitor charges the low-voltage battery through a high-voltage DC / DC; when the voltage of the high-voltage capacitor is not higher than the threshold voltage, the high-voltage capacitor discharges through a discharge branch; when the voltage of the high-voltage capacitor is lower than the threshold voltage, the discharge ends.

[0012] When it is detected that the voltage of the high-voltage capacitor is not higher than the threshold voltage, the discharge switch Q1 is controlled to conduct continuously for a short time in the previous period for pre-discharge, and the discharge switch Q1 is controlled to conduct intermittently with a PWM signal in the later period for discharge.

[0013] When pre-discharging, the voltage drop rate of the high-voltage capacitor is detected. When the voltage drop rate of the high-voltage capacitor is not lower than the threshold rate, the discharge ends, and a discharge fault signal is sent out at the same time.

[0014] After the discharge, the discharge duration T is started to be timed. When the discharge duration T is greater than or equal to the discharge duration threshold Tn, the discharge ends.

[0015] The control method specifically includes the following steps:

[0016] Step 1: Detect whether there is a discharge enable signal. If not, go to end the discharge. If so, go to Step 2;

[0017] Step 2: Start timing the discharge duration T;

[0018] Step 3: The high-voltage capacitor charges the low-voltage battery through a high-voltage DC / DC;

[0019] Step 4: Detect whether the voltage of the high-voltage capacitor is lower than or higher than the threshold voltage. If it is higher than the threshold voltage and the discharge duration T is less than the discharge duration threshold Tn, go to Step 3. If it is not higher than the threshold voltage, go to Step 5;

[0020] Step 5: Stop the high-voltage DC / DC from charging the low-voltage battery;

[0021] Step 6: Control the discharge switch Q1 to conduct continuously for a short time for pre-discharge;

[0022] Step 7: Detect the voltage drop rate of the high-voltage capacitor and judge whether the voltage drop rate of the high-voltage capacitor is lower than the threshold rate. If it is lower than the threshold rate, go to Step 8. If it is not lower than the threshold rate, end the discharge and send out a discharge fault signal;

[0023] Step 8: Use a PWM signal to control the intermittent conduction of the discharge switch Q1 for discharging;

[0024] Step 9: Determine whether the high-voltage capacitor voltage is lower than the threshold voltage. If it is lower than the threshold voltage, go to Step 10. If it is not lower than the threshold voltage and the discharge duration T is less than the discharge duration threshold Tn, go to Step 8;

[0025] Step 10: End the discharge.

[0026] The discharge duration threshold Tn is 3 seconds, and the value range of the threshold voltage is 50 to 60 volts.

[0027] When the high-voltage capacitor charges the low-voltage battery through the high-voltage DC / DC, the sixth switch Q6 and the seventh switch Q7 can control synchronous rectification, or rectification can be performed through their body diodes.

[0028] The beneficial effects of the technical solution provided by the present invention are as follows:

[0029] The present invention adopts a hybrid active discharge mode. The discharge path changes from a single consumption on the power discharge resistor to a part of the energy being transmitted to the low-voltage battery, a part of the energy being consumed in the HVDCDC converter, and another part of the energy being consumed in the miniaturized power discharge resistor, having the advantages of fast discharge speed, small size of the power discharge resistor, low cost, easy control, and high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be described in detail below with reference to the embodiments and the drawings, where:

[0031] Figure 1 is the principle block diagram of a preferred embodiment of the present invention;

[0032] Figure 2 is the circuit diagram of the HVDCDC converter in a preferred embodiment of the present invention;

[0033] Figure 3 is the control flowchart of a preferred embodiment of the present invention;

[0034] Figure 4 is the waveform timing diagram of a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] The present invention discloses a hybrid active discharge circuit. Refer to Figure 1The principle block diagram of the preferred embodiment of the present invention shown includes a controller and a high-voltage power battery. The high-voltage power battery is respectively connected to a high-voltage inverter and a high-voltage DC / DC through a DC bus. The high-voltage DC / DC is connected to a low-voltage battery. A high-voltage capacitor is connected between the positive and negative buses of the DC bus. The high-voltage inverter is connected to a high-voltage AC load. The low-voltage battery is connected to a low-voltage battery load. A discharge branch is provided at the input end of the high-voltage DC / DC connected to the DC bus; in the early stage of discharge, the high-voltage capacitor charges the low-voltage battery through the high-voltage DC / DC; in the later stage of discharge, the high-voltage capacitor discharges through the discharge branch.

[0037] Figure 1 In it, C1 is the equivalent input capacitance of the high-voltage inverter, including the DC-LINK capacitance and other internal capacitances. C2 is the equivalent input capacitance of the high-voltage DC / DC (HVDCDC), including the DC-LINK capacitance and other internal capacitances. Cn is the equivalent input capacitance of other high-voltage devices, including devices such as on-board chargers and high-voltage air conditioners. SW1 is the main relay of the high-voltage battery, including two relay contacts of main positive and main negative. After the high-voltage inverter or HVDCDC receives the active discharge command, by turning on the HVDCDC to work, the energy on the high-voltage capacitors C1, C2, Cn is used to charge the low-voltage battery and consumed in the working process of the HVDCDC, such as switching losses, etc.

[0038] In the preferred embodiment, the discharge branch includes a series-connected discharge resistor PTC and a discharge switch Q1, and the discharge switch Q1 is controlled by the controller. The discharge switch Q1 can adopt MOSFET. Due to the limitation of the output voltage level of the HVDCDC, after its HV input voltage drops to a relatively low level, that is, the HV threshold voltage noted in this patent, it cannot continue to use the energy on the high-voltage capacitors C1, C2, Cn to charge the low-voltage battery and consume it in the working process of the HVDCDC. Therefore, this patent adds the PTC discharge method to supplement the active discharge after the HV voltage drops below the HV voltage threshold voltage. The PTC active discharge consumes the remaining energy on the high-voltage capacitors C1, C2, Cn in the form of heat on the PTC resistor. Figure 2 In it, the power discharge resistor is not limited to the PTC resistor, and other resistor types such as wire-wound resistors and cement resistors can also be used.

[0039] Figure 1 In it, the thin-line arrow is the power flow direction during discharge, flowing from the high-voltage inverter, the primary side of the HVDCDC, and other high-voltage electrical equipment to the low-voltage battery and the low-voltage battery load.

[0040] Figure 1In addition to raising the output voltage of the HVDC-DC to consume the energy of the high-voltage capacitor, the operating frequency can also be raised within the safe operating range to actively discharge by using the switching loss of the HVDC-DC.

[0041] Aiming at the problems and deficiencies in the existing technology, the present invention provides a hybrid active discharge circuit and its control method. The discharge path changes from a single power discharge resistor consumption to a variety of hybrid active discharge methods such as part of the energy being transmitted to the low-voltage battery, part of the energy being consumed in the HVDC-DC converter, and another part of the energy being consumed in the miniaturized power discharge resistor. Based on this hybrid active discharge control method, the high-voltage inverter of an electric vehicle can achieve the characteristics of fast discharge speed, reduced size of the power discharge resistor or even no need for a power discharge resistor, low cost, easy control, and high reliability.

[0042] In a preferred embodiment, a power switch SW1 is connected in series between the high-voltage power battery and the DC bus. When it is necessary to charge the high-voltage power battery or the high-voltage power battery needs to supply power to the load, the controller turns on the power switch SW1. When the controller issues an active discharge command or an active discharge command is caused by an internal fault of the high-voltage inverter, the power switch SW1 will be cut off to prevent a greater safety accident.

[0043] In a preferred embodiment, the DC bus is also connected to other high-voltage electrical equipment.

[0044] See Figure 2 Referring to the circuit diagram of the HVDC-DC converter of the preferred embodiment of the present invention shown, the high-voltage DC / DC includes a primary conversion module, a high-frequency transformer, and a secondary conversion module connected in sequence. The primary conversion module adopts a full-bridge topology structure, and the secondary conversion module adopts a synchronous rectification topology structure. The secondary conversion module includes a sixth switch Q6 and a seventh switch Q7; the sixth switch Q6 and the seventh switch Q7 adopt MOS tubes with body diodes. The primary conversion module converts the high-voltage direct current in C1, C2, and even Cn into a DC pulse, which is transmitted to the secondary conversion module through the high-frequency transformer, and the secondary conversion module rectifies and charges the low-voltage battery. Figure 2 Where Vhv is the high-voltage capacitor voltage.

[0045] The present invention also discloses a control method for a hybrid active discharge circuit. The discharge circuit adopts the above-mentioned hybrid active discharge circuit. The control method includes: in the early stage of discharge, the high-voltage capacitor charges the low-voltage battery through the high-voltage DC / DC; in the later stage of discharge, the high-voltage capacitor discharges through the discharge branch. It should be noted that after receiving the active discharge command issued by the controller, the high-voltage DC / DC is started and its output voltage is raised to charge the low-voltage battery. The specific voltage value to be raised is determined by the HVDC-DC hardware parameters and the voltage battery parameters.

[0046] After the discharge starts, the voltage of the high-voltage capacitor is detected. When the voltage of the high-voltage capacitor is higher than the threshold voltage, the high-voltage capacitor charges the low-voltage battery through a high-voltage DC / DC; when the voltage of the high-voltage capacitor is not higher than the threshold voltage, the high-voltage capacitor discharges through a discharge branch; when the voltage of the high-voltage capacitor is lower than the threshold voltage, the discharge ends. In devices of different models, the threshold voltage may vary and is not specifically defined in this patent.

[0047] In a preferred embodiment, when it is detected that the voltage of the high-voltage capacitor is not higher than the threshold voltage and before the PTC starts to discharge, to protect the PTC and its series-connected MOSFET Q1, the discharge switch Q1 is controlled to conduct continuously for a short time for pre-discharge in the previous period, that is, PTC pre-discharge. This PTC pre-discharge process is enabled by giving a short-time PTC discharge enable signal. In the latter period, the discharge switch Q1 is controlled to conduct intermittently with a PWM signal for discharging. The PTC discharge adopts a PWM pulse enable discharge method to reduce the loss and thermal stress of the PTC resistor and MOSFET Q1, thereby improving reliability. Figure 3 Before the HVDCDC discharge starts, the same method as the PTC pre-discharge can also be added for HVDCDC pre-discharge to detect whether there are faults such as relay adhesion.

[0048] In a preferred embodiment, when pre-discharging, the voltage drop rate of the high-voltage capacitor is detected. When the voltage drop rate of the high-voltage capacitor is not lower than the threshold rate, the discharge ends and a discharge fault signal is sent out simultaneously.

[0049] Figure 3 After detecting faults such as the HV voltage cannot be reduced normally, or the HV voltage drop rate does not meet the design requirements, or the discharge time times out (3 s), etc., it is reported to the body controller for protection warning.

[0050] In a preferred embodiment, after receiving the active discharge instruction sent by the controller, the timer starts to time the discharge duration T. When the discharge duration T is greater than or equal to the discharge duration threshold Tn, the discharge ends.

[0051] Refer to Figure 3 The control flowchart of the preferred embodiment of the present invention shown, the control method specifically includes the following steps:

[0052] Step 1: Detect whether there is a discharge enable signal. If not, go to end the discharge; if so, go to step 2;

[0053] Step 2: Start timing the discharge duration T;

[0054] Step 3: The high-voltage capacitor charges the low-voltage battery through a high-voltage DC / DC;

[0055] Step 4: Detect whether the high-voltage capacitor voltage is higher than the threshold voltage. If it is higher than the threshold voltage and the discharge duration T is less than the discharge duration threshold Tn, go to Step 3. If it is not higher than the threshold voltage, go to Step 5;

[0056] Step 5: Stop the high-voltage DC / DC from charging the low-voltage battery;

[0057] Step 6: Control the discharge switch Q1 to conduct continuously for a short time for pre-discharge (this step corresponds to the time period T1 - T2 in Figure 4 );

[0058] Step 7: Detect the voltage drop rate of the high-voltage capacitor and determine whether the voltage drop rate of the high-voltage capacitor is lower than the threshold rate. If it is lower than the threshold rate, go to Step 8. If it is not lower than the threshold rate, end the discharge and send a discharge fault signal;

[0059] Step 8: Control the discharge switch Q1 to conduct intermittently with a PWM signal for discharge (this step corresponds to the time period T2 - T3 in Figure 4 );

[0060] Step 9: Determine whether the high-voltage capacitor voltage is lower than the threshold voltage. If it is lower than the threshold voltage, go to Step 10. If it is not lower than the threshold voltage and the discharge duration T is less than the discharge duration threshold Tn, go to Step 8;

[0061] Step 10: End the discharge.

[0062] In a preferred embodiment, the discharge duration threshold Tn is 3 seconds, and the value range of the threshold voltage is 50 to 60 volts.

[0063] In a preferred embodiment, when the high-voltage capacitor charges the low-voltage battery through the high-voltage DC / DC, the sixth switch Q6 and the seventh switch Q7 can control synchronous rectification, or can be rectified through their body diodes. Refer to Figure 3 , when the high-voltage DC / DC charges the low-voltage battery, the synchronous rectifier tubes Q6 and Q7 of the secondary side of the high-voltage DC / DC can also be not turned on, and their parasitic body diodes are used to increase the discharge loss and accelerate the active discharge speed.

[0064] Figure 4 The waveform timing diagram of the preferred embodiment of the present invention is shown.

[0065] The start and output level of the HVDCDC are controlled, and the enabling of the PTC discharge circuit is controlled. The two control objects are respectively implemented through the drive signals of Q2 - Q5 and Q6 - Q7, and the drive signal of Q1. Among them, Q6 and Q7 are the synchronous rectifier tubes on the secondary side of the HVDCDC.

[0066] An active discharge command is received at time T0.

[0067] From T0 to T1, the output voltage of the HVDC-DC increases, and active discharging starts to transfer the energy of the high-voltage capacitor to the low-voltage battery and partly consume it inside the HVDC-DC.

[0068] From T1 to T2, PTC pre-discharging occurs. This PTC pre-discharging process is determined by giving a short-time PTC discharge enable signal and monitoring whether the change in the HV voltage conforms to the preset HV drop rate.

[0069] From T2 to T3, PTC discharging occurs, and the remaining energy after the HVDC-DC discharges is consumed on the PTC resistor. This process adopts a PWM discharging method to reduce the average losses of the PTC resistor and Q1.

[0070] At the moment of T3, the HV capacitor voltage drops below the safe voltage.

[0071] The above embodiments are only for illustrative purposes and do not serve as a limitation. Any equivalent modification or change that does not depart from the spirit and scope of this application shall be included in the scope of the claims of this application.

Claims

1. A hybrid active discharge circuit control method, characterized in that The hybrid active discharge circuit includes a controller and a high-voltage power battery. The high-voltage power battery is connected to a high-voltage inverter and a high-voltage DC / DC through a DC bus. The high-voltage DC / DC is connected to a low-voltage battery. A high-voltage capacitor is connected between the positive and negative buses of the DC bus. The high-voltage inverter is connected to a high-voltage AC load. The low-voltage battery is connected to a low-voltage battery load. The input end of the high-voltage DC / DC connected to the DC bus is provided with a discharge branch. The discharge branch includes a discharge resistor PTC and a discharge switch Q1 connected in series, and the discharge switch Q1 is controlled by a controller; The control method comprises: in the early stage of discharge, the high-voltage capacitor charges the low-voltage battery through the high-voltage DC / DC; in the late stage of discharge, the high-voltage capacitor discharges through the discharge branch; The control method specifically comprises the following steps: Step 1: Check whether there is a discharge enable signal. If not, end the discharge. If yes, go to step 2. Step 2, start timing the discharge time T; Step 3: The high voltage capacitor charges the low voltage battery via the high voltage DC / DC; Step 4: Check whether the high-voltage capacitor voltage is lower than or higher than the threshold voltage. If it is higher than the threshold voltage and the discharge time T is less than the discharge time threshold Tn, go to step 3; if it is not higher than the threshold voltage, go to step 5. Step 5: Stop the high-voltage DC / DC from charging the low-voltage battery; Step 6, controlling the discharge switch Q1 to be continuously turned on for a short period of time to perform pre-discharge; Step 7, detecting the voltage drop rate of the high-voltage capacitor, and determining whether the voltage drop rate of the high-voltage capacitor is lower than a threshold rate. If so, proceed to step 8; if not, terminate the discharge and send a discharge fault signal. Step 8, use the PWM signal to control the discharge switch Q1 to intermittently conduct for discharge; Step 9, determine whether the high-voltage capacitor voltage is lower than the threshold voltage, if so, go to step 10, if not lower than the threshold voltage and the discharge time T is less than the discharge time threshold Tn, go to step 8; Step 10: End the discharge.

2. The hybrid active discharge circuit control method according to claim 1, characterized in that A power switch SW1 is connected in series between the high-voltage power battery and the DC bus.

3. The hybrid active discharge circuit control method according to claim 1, characterized in that ,The DC bus is also connected to a vehicle charger or a high voltage air conditioner.

4. The hybrid active discharge circuit control method according to any one of claims 1 to 3, characterized in that The high-voltage DC / DC includes a primary conversion module, a high-frequency transformer, and a secondary conversion module connected in sequence. The primary conversion module adopts a full-bridge topology structure, and the secondary conversion module adopts a synchronous rectification topology structure. The secondary conversion module includes a sixth switch Q6 and a seventh switch Q7; the sixth switch Q6 and the seventh switch Q7 adopt MOS tubes with body diodes.

5. The hybrid active discharge circuit control method according to claim 1, characterized in that After the discharge starts, the high-voltage capacitor voltage is detected. When the high-voltage capacitor voltage is higher than the threshold voltage, the high-voltage capacitor charges the low-voltage battery through the high-voltage DC / DC; when the high-voltage capacitor voltage is not higher than the threshold voltage, the high-voltage capacitor discharges through the discharge branch; when the high-voltage capacitor voltage is lower than the threshold voltage, the discharge ends.

6. The hybrid active discharge circuit control method as claimed in claim 5, characterized in that ,When it is detected that the voltage of the high voltage capacitor is not higher than the threshold voltage, the discharge switch Q1 is controlled to be turned on continuously for a short time in the first period for pre-discharge, and the PWM signal is used to control the discharge switch Q1 to be turned on intermittently for discharge in the latter period.

7. The hybrid active discharge circuit control method according to claim 6, characterized in that ,During pre-discharge, the voltage drop rate of the high voltage capacitor is detected. When the voltage drop rate of the high voltage capacitor is not lower than the threshold rate, the discharge is terminated and a discharge fault signal is issued.

8. The hybrid active discharge circuit control method according to claim 7, characterized in that ,After discharging, the discharge time T is started to be counted. When the discharge time T is greater than or equal to the discharge time threshold Tn, the discharge is ended.

9. The hybrid active discharge circuit control method according to claim 1, characterized in that , the discharge time threshold Tn is 3 seconds, and the threshold voltage ranges from 50 to 60 volts.

10. The hybrid active discharge circuit control method according to claim 4, characterized in that When the high-voltage capacitor charges the low-voltage battery through the high-voltage DC / DC, the sixth switch Q6 and the seventh switch Q7 can control them to perform synchronous rectification, or they can perform rectification through their body diodes.

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