High-voltage power supply protection circuit

Abstract

The utility model relates to the technical field of high-voltage driving systems, and discloses a high-voltage power supply protection circuit. The device specifically comprises a main positive relay KM1 which is provided with a first coil and a first normally open contact; the pre-charging relay KM3 is provided with a second coil and a second normally open contact; the power supply branch is connected in series with the first normally open contact and is connected in series between the positive electrode of the power battery pack and a load Rc; the pre-charging branch circuit is connected in series with the second normally open contact and is connected in parallel with the first normally open contact; the current transformer TA is used for generating a fault signal when the current at the parallel node is greater than a preset threshold value; the control unit BMU is respectively connected with the first coil and the second coil, and the control unit BMU is used for keeping the first coil in a power-off state when a fault signal is generated; according to the utility model, the power supply of the power battery pack to the load can be cut off in time when a large current is generated on the power supply branch, so that the high-voltage power supply can be effectively carried out.

Description

TECHNICAL FIELD

[0001] The utility model relates to high pressure drive system technical field, specifically, relate to a high voltage power supply protection circuit. BACKGROUND

[0002] High pressure drive system as the core of electric automobile, generally by high voltage power battery, battery management system BMS, motor controller and drive motor are constituteed, wherein BMS is responsible for the charge and discharge control and health state monitoring of power battery pack in high voltage power battery, and motor controller is responsible for the drive control of drive motor.

[0003] The control method of the existing pre-charging branch is to determine a resistance value and an electric power value that are both far beyond the system demand as the pre-charging resistance, and to pre-charge at a fixed time by the battery management system BMS control unit BMU according to the action time of the relay, thereby giving the high voltage power battery a sufficient protection time.

[0004] Because there are a large number of capacitive devices in the motor controller, when the automobile is in a cold start state, the capacitor element has no residual voltage or low residual voltage, and when the battery management system BMS directly controls the high voltage power battery to supply power to the motor controller, it is equivalent to the corresponding load of the motor controller being in a short circuit state for the high voltage power battery, and the instantaneous impact current will cause damage to the electrical elements in the system, easily causing problems such as sticking of the contacts of the main positive and main negative relays, heating of the wires, and bulging of the battery; and some motor controllers have a capacitive active discharge function, which further increases the capacitance of the battery and the load, and the high voltage drive system is prone to failure during long-term operation. INVENTION CONTENTS

[0005] The utility model provides a kind of high voltage power supply protection circuit and its pre-charging resistance calculation method, which can overcome certain or some defects of prior art.

[0006] To achieve the above object, the utility model is realized by the following technical scheme, a kind of high voltage power supply protection circuit, comprising:

[0007] The main positive relay KM1 has a first coil and a first normally open contact;

[0008] The pre-charging relay KM3 has a second coil and a second normally open contact;

[0009] The power supply branch is connected in series with the first normally open contact, and the power supply branch is connected in series between the positive electrode of the power battery pack and the load Rc;

[0010] The pre-charging branch is connected in series with the second normally open contact, and the pre-charging branch is connected in parallel with the first normally open contact;

[0011] A current transformer TA is arranged at the parallel node of the pre-charge branch and the first normally open contact, and the current transformer TA is used to generate a fault signal when the current at the parallel node is greater than a preset threshold; and

[0012] A control unit BMU connected with the first coil and the second coil respectively, and the control unit BMU is used to keep the first coil in a power-off state when the fault signal is generated.

[0013] Based on the above, the power supply of the load by the power battery pack can be cut off in time when a larger current is generated on the power supply branch, so that the high-voltage power supply is effectively ensured.

[0014] As a preferred, the pre-charge branch includes a pre-charge resistor Rp connected in series with the second normally open contact. Therefore, the generation of instantaneous impact current can be prevented, so that the high-voltage power supply is effectively ensured.

[0015] As a preferred, a main negative relay KM3 is further included, which has a third coil and a third normally open contact, the third coil is connected to the control unit BMU, and the third normally open contact is connected in series between the negative electrode of the power battery pack and the load Rc. Therefore, the on-off control of the negative electrode of the power battery pack can be preferably realized.

[0016] As a preferred, a battery pack equivalent internal resistance R B is connected in series between the positive electrode of the power battery pack and the first normally open contact. Therefore, the calculation of the actual output voltage of the power battery pack can be preferably realized.

[0017] As a preferred, an equivalent capacitor C is connected in parallel across the load Rc. Therefore, the calculation of the capacitance value of the capacitive component on the load side can be preferably realized. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a high-voltage system power supply framework diagram in embodiment 1;

[0019] Figure 2 It is a circuit diagram of a high-voltage power supply protection circuit in embodiment 1. DETAILED DESCRIPTION

[0020] In order to further understand the content of the utility model, the utility model is described in detail in combination with the embodiments. It should be understood that the embodiments are only used to explain the utility model and are not limited.

[0021] Embodiment 1

[0022] The existing high-voltage drive system as the core of the electric vehicle is generally composed of a high-voltage power battery, a BMS (battery management system), a motor controller and a drive motor, wherein the BMS manages the high-voltage power battery, is responsible for charge and discharge control and health state monitoring of the high-voltage power battery, and the motor controller is responsible for drive control of the motor. During the running of the vehicle, the energy flow is as shown in the high-voltage system power supply framework. Figure 1 The high-voltage power battery pack transmits energy to the motor controller through the control of the BMS, and the energy reaches the motor through the control of the motor controller to drive the vehicle to run.

[0023] Since there are a large number of capacitive devices in the motor controller, when the vehicle is in a cold start state, the capacitive elements have no residual voltage or low residual voltage, and when the battery management system BMS directly controls the high-voltage power battery to supply power to the motor controller, it is equivalent to the corresponding load of the motor controller being in a short-circuit state for the high-voltage power battery, and the instantaneous impact current will cause damage to the electrical elements in the system, and problems such as sticking of the contacts of the main positive and main negative relays, heating of the wires and bulging of the battery are prone to occur; and part of the motor controller has a capacitive active discharge function, which further increases the capacitance of the battery and the load, and the high-voltage drive system is prone to failure during long-term operation, so it is necessary to control the charging current of the motor controller through the battery management system BMS.

[0024] As shown in Figure 2 , the embodiment provides a high-voltage power supply protection circuit, which comprises:

[0025] a main positive relay KM1 having a first coil and a first normally open contact;

[0026] a pre-charge relay KM3 having a second coil and a second normally open contact;

[0027] a power supply branch connected in series with the first normally open contact, the power supply branch being connected in series between the positive electrode of the power battery pack and the load Rc;

[0028] a pre-charge branch connected in series with the second normally open contact, the pre-charge branch being connected in parallel with the first normally open contact;

[0029] a current transformer TA arranged at a parallel node of the pre-charge branch and the first normally open contact, the current transformer TA being configured to generate a fault signal when the current at the parallel node is greater than a preset threshold; and

[0030] a control unit BMU connected with the first coil and the second coil respectively, the control unit BMU being configured to keep the first coil in a power-off state when the fault signal is generated.

[0031] Based on the above, the embodiment can cut off the power supply of the power battery pack to the load in a more timely manner when a larger current is generated on the power supply branch, thereby ensuring that the high-voltage power supply is effectively performed.

[0032] In the embodiment, the pre-charge branch includes a pre-charge resistor Rp connected in series with the second normally open contact. Therefore, the generation of instantaneous impact current can be prevented, and the high-voltage power supply can be effectively ensured.

[0033] In the embodiment, a main negative relay KM3 is further included, which has a third coil connected to the control unit BMU and a third normally open contact connected in series between the negative electrode of the power battery pack and the load Rc. Therefore, the on-off control of the negative electrode of the power battery pack can be effectively achieved.

[0034] In the embodiment, a battery pack equivalent internal resistance R B is connected in series between the positive electrode of the power battery pack and the first normally open contact. Therefore, the calculation of the actual output voltage of the power battery pack can be effectively achieved.

[0035] In the embodiment, an equivalent capacitor C is connected in parallel across the load Rc. Therefore, the calculation of the capacitance value of the capacitive component on the load side can be effectively achieved.

[0036] In the embodiment, the control process of the battery management system BMS is as follows:

[0037] The battery management unit BMU controls the main negative relay KM2 and the pre-charge relay KM3 to be closed, and simultaneously detects the current through the current transformer TA. At this time, the current flows through the pre-charge resistor Rp to charge the equivalent capacitor C. When the battery management unit BMU detects that the charging current at the current transformer TA is less than a preset threshold value, KM1 is first closed. If the current is still less than the preset threshold value, the pre-charge relay KM3 is disconnected. If the current is still greater than the preset threshold value after the main positive relay KM1 is closed, the main positive relay KM1 is disconnected. The equivalent capacitor C is charged again through the pre-charge resistor Rp, and the current is detected again. If the charging current is less than the preset threshold value, the pre-charge relay KM3 is disconnected. Otherwise, the above logic is repeated until the current meets the threshold condition.

[0038] Embodiment 2

[0039] The embodiment provides a pre-charge resistor calculation method based on a high-voltage power supply protection circuit. The method adopts the high-voltage power supply protection circuit as described in Embodiment 1, and includes the following steps:

[0040] Step S1: When the first normally open contact and the second normally open contact are both closed, the relationship between the voltage across the equivalent capacitor C and the charging time t of the equivalent capacitor C is calculated.

[0041] Step S2: Based on the relationship between the voltage across the equivalent capacitor C and the charging time t of the equivalent capacitor C in Step S1 and the resistance value rp of the pre-charge resistor Rp, the relationship between the charging current i(t) on the pre-charge branch and the charging time t of the equivalent capacitor C is calculated.

[0042] Step S3: calculating the resistance of the pre-charge resistor Rp based on the relationship between the charging current i(t) on the pre-charge branch and the charging time t of the equivalent capacitor C in combination with the relationship between the charging current i(t) on the pre-charge branch and the voltage up across the pre-charge resistor Rp.

[0043] In this embodiment, in step S1, when the first and second normally open contacts are closed at the same time, the relationship between the voltage across the equivalent capacitor C and the charging time t of the equivalent capacitor C specifically includes the following steps:

[0044] Step S101: at the time of charging time t=0, the relationship among the voltage up across the pre-charge resistor Rp, the voltage uc across the equivalent capacitor C, and the voltage U across the battery pack equivalent internal resistor RB and the power battery pack in series, i.e., up+uc=U B B ;

[0045] Step S102: calculating the relationship among the voltage up across the pre-charge resistor Rp, the resistance rp of the pre-charge resistor Rp, and the current i flowing through the pre-charge resistor Rp, i.e., up=i×rp;

[0046] Step S103: solving the formulas in steps S101 and S102 and , we get:

[0047] (1)

[0048] where A is a constant linearly related to the initial voltage Uc of the capacitor, and in combination with engineering practice, the type is set to take , then , and the relationship between the voltage uc(t) across the equivalent capacitor C and the charging time t of the equivalent capacitor C in the above formula (1) is:

[0049] (2).

[0050] In this embodiment, in step S2, the formula (2) is calculated in combination with the resistance rp of the pre-charge resistor Rp, and the relationship between the charging current i(t) on the pre-charge branch and the charging time t of the equivalent capacitor C is obtained, i.e.:

[0051] (3).

[0052] In this embodiment, in step S3, the formula (3) is simplified to calculate the resistance of the pre-charge resistor Rp, i.e.:

[0053] ; (4) ​

[0054] wherein, Up is the exit voltage of the pre-charge resistor Rp.

[0055] Based on the above, the embodiment can calculate the resistance value of the pre-charge resistor Rp more accurately.

[0056] Embodiment 3

[0057] In the formula (4) of embodiment 2, it can be seen that the expression for precisely controlling the selection of the pre-charge resistor Rp is too complex and difficult to solve, which is not conducive to quick selection. Therefore, the embodiment provides a pre-charge resistor calculation method based on a high-voltage power supply protection circuit, which is used to quickly estimate the resistance value and power of the pre-charge resistor Rp in any of the high-voltage power supply protection circuits in the above embodiment 1.

[0058] As can be seen from formula (4), the exit voltage Up of the pre-charge resistor is positively correlated with the selection of the pre-charge resistor Rp, that is, inversely proportional to the exit voltage of the capacitor pre-charge circuit. Therefore, the higher the resistance value of the pre-charge resistor Rp, the smaller the exit voltage of the capacitor pre-charge circuit, and the smaller the impact on the high-voltage power battery pack when charging with the main positive loop. After comprehensive consideration, in this embodiment, the first preset value Up1 and the second preset value Up2 of the voltage across the pre-charge resistor Rp are taken as Up1 = 94.5%U B and Up2 = 89.12%U B， The approximate values rp1 and rp2 of the pre-charge resistor Rp are calculated and taken in combination with formulas (1) to (4). The calculation can obtain:

[0059] , (5)

[0060] , (6)

[0061] When the capacitance C of the peripheral load and the pre-charge time are determined, the resistance value required by the pre-charge resistor can be quickly determined according to formulas (5) and (6). The interval composed of the numerical values of rp1 and rp2 is the resistance value interval of the pre-charge resistor Rp.

[0062] In this embodiment, it also includes step S4: calculating the power P of the pre-charge resistor Rp, and the specific steps are as follows:

[0063] The approximate values of the first charging time t1 and the second charging time t2 of the equivalent capacitance C can be taken from formulas (5) and (6), that is, t1 = 1.7τ and t2 = 2.4τ; wherein, τ = rp×C, τ is the engineering time constant, and the maximum action time of the relay is generally less than 10 ms. Taking the engineering time τ = 10 ms, t1 = 17 ms and t2 = 24 ms; The selection of t here is related to the sampling time of the DC transformer and the software execution time of the BMU. The power P of the pre-charge resistor Rp is calculated as follows:

[0064] ; (7)

[0065] Simplifying formula (7) can obtain:

[0066] ; (8)

[0067] Wherein, the interval formed by the numerical value of t1 and t2 is the charging time t of the pre-charge resistor Rp.

[0068] Therefore, according to the method described in the embodiment, only the capacitance of the load side and the planned pre-charge duration need to be estimated, and the resistance value of the required pre-charge resistor Rp can be determined according to formula (5) and (6), and the power of the pre-charge resistor Rp can be determined according to formula (8).

[0069] In summary, the pre-charge resistor calculation method based on the high-voltage power supply protection circuit provided in the embodiment is used to quickly estimate the resistance value and power of the pre-charge resistor Rp in the high-voltage power supply protection circuit described in any of the above embodiments 1 or 2. Although the calculation accuracy is reduced, considering that the resistance value of the actual resistor is a fixed value, and in engineering applications, it is mostly a standard product, the selection efficiency is improved, and the resistor selection error is not caused. Compared with the traditional pre-charge method, the control is more precise, the selection is more suitable for actual application, and the high cost caused by over-capacity selection is reduced.

[0070] It is easy to understand that those skilled in the art can combine, split, recombine, etc. the embodiments of the present application on the basis of one or more embodiments provided in the present application to obtain other embodiments, and these embodiments do not exceed the protection scope of the present application.

[0071] The above describes the present application and its embodiments in a schematic manner, and the description is not restrictive. The embodiments shown are only part of the embodiments of the present application, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by the present application, without departing from the spirit of the present application, similar structural forms and embodiments can be designed without creative design, which should belong to the protection scope of the present application.

Claims

1. A high voltage power supply protection circuit, characterized by, Comprise: a main positive relay KM1 having a first coil and a first normally open contact; a pre-charge relay KM3 having a second coil and a second normally open contact; a power supply branch in series with the first normally open contact, the power supply branch being in series between a positive pole of the power battery pack and a load Rc; a pre-charge branch in parallel with the second normally open contact, the pre-charge branch being in parallel with the first normally open contact; a current transformer TA provided at a parallel node of the pre-charge branch and the first normally open contact, the current transformer TA being configured to generate a fault signal when a current at the parallel node is greater than a preset threshold; and a control unit BMU connected with the first coil and the second coil respectively, the control unit BMU being configured to keep the first coil in a de-energized state when the fault signal is generated.

2. A high voltage supply protection circuit according to claim 1, characterized in that: The pre-charge branch comprises a pre-charge resistor Rp in series with the second normally open contact.

3. A high voltage supply protection circuit according to claim 2, wherein Further comprising a main negative relay KM2 having a third coil and a third normally open contact, the third coil being connected to the control unit BMU, and the third normally open contact being in series between a negative pole of the power battery pack and the load Rc.

4. A high voltage supply protection circuit according to claim 3, characterised in that: A battery equivalent resistance R is connected in series between the positive pole of the power battery pack and the first normally open contact B .

5. A high voltage supply protection circuit according to claim 4, wherein An equivalent capacitor C is connected in parallel across the load Rc.

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