CN108614158A - A kind of electric automobile insulation resistance detection control circuit and its detection method - Google Patents

Abstract

The invention discloses an electric vehicle insulation resistance detection control circuit and a detection method thereof. The circuit is based on a balanced electric bridge, adopts a photo-controlled relay to control the opening and closing of the corresponding bridge arms of the electric bridge, and adopts a high-precision instrument amplifier to monitor weak voltage signals. Amplification, while realizing the conversion of voltage polarity. Based on the above basic characteristics of the circuit, a four-step insulation resistance calculation method is designed. The electric vehicle insulation resistance detection control circuit and the detection method thereof of the present invention have the advantages of being able to simultaneously measure the insulation resistance of positive and negative terminals, being capable of online detection, high precision, high reliability, and the like.

Description

An electric vehicle insulation resistance detection control circuit and detection method thereof

technical field

The invention relates to an insulation resistance detection control circuit and a detection method, in particular to an electric vehicle insulation resistance detection control circuit and a detection method thereof.

Background technique

Electric vehicles use the power battery pack as the energy source of the whole vehicle. Usually, the power battery voltage of electric vehicles is much higher than 36V, even reaching several hundred volts, far exceeding the safe voltage range of the human body. Therefore, the positive and negative poles of the power battery pack must be well insulated from the vehicle to ensure the personal safety of the drivers and passengers.

Since electric vehicles are complex mechatronic products, including power batteries, drive motors and their controllers, on-board chargers, auxiliary battery charging devices and other high-voltage electrical appliances, the working conditions of these components are relatively harsh, vibration, acid and alkali gas corrosion Changes in temperature, temperature and humidity may cause power cables and other insulating materials to age or even damage the insulation, greatly reducing the insulation strength of the equipment and endangering personal safety. The national standard "GB/18384.3-2015 Electric Vehicle Safety Requirements Part III: Personnel Electric Shock Protection" stipulates that the insulation resistance value divided by the nominal voltage U of the electric vehicle DC system should be greater than 100Ω/V to meet the safety requirements.

Therefore, real-time detection of the insulation resistance between the positive and negative poles of the power battery pack and the body ground is one of the basic safety requirements for electric vehicles.

The existing insulation detection technology can be divided into two categories: "balanced bridge method" and "signal injection method". The basic principle of the balanced bridge method for measuring insulation resistance is as follows: Based on the principle of the bridge circuit, by controlling the opening and closing of the relays on both sides of the positive and negative poles of the power battery pack, several different combination states are obtained to measure the insulation resistance of the system. Although this method has the advantages of simple measurement, it has the following disadvantages: (1) the use of mechanical switch relays has low breaking sensitivity, mechanical wear, and low reliability; (2) multiple operational amplifiers are used, the consistency of the circuit is poor, and the accuracy lower.

The basic principle of the signal injection method for measuring insulation resistance is as follows: a voltage signal of a certain frequency is injected between the DC bus and the car body, and the insulation resistance value is calculated by measuring the feedback signal. This method can detect the simultaneous decrease of the insulation resistance of the positive and negative terminals, and has high reliability. However, the injected signal will cause the ripple of the DC system to increase, affect the quality of the power supply, and then affect the sampling accuracy.

Contents of the invention

In view of the above problems, the present invention proposes a low-error, high-reliability, on-line measurement electric vehicle insulation resistance detection control circuit and a detection method thereof.

On the one hand, the present invention provides an electric vehicle insulation resistance detection control circuit, which is composed of four parts: a DC system to be tested, a detection circuit, a sampling circuit, a single-chip microcomputer and an AD conversion circuit.

The DC system to be tested is composed of a power battery, a positive terminal insulation resistance and a negative terminal insulation resistance. The positive terminal insulation resistance is defined as the resistance value between the positive busbar of the power battery pack and the vehicle body ground; the negative terminal insulation resistance Defined as the resistance value between the negative busbar of the power battery pack and the body ground.

The upper bridge arm of the detection circuit is composed of two detection resistors R ₁ , R ₂ and a light control relay, one end of R ₁ is connected to the positive pole of the power battery, and the other end is connected to the light control relay K ₁ . The other end of K ₁ is connected to R ₂ , and the other end of R ₂ is connected to the body ground. The lower bridge arm of the detection circuit is composed of two detection resistors R ₃ , R ₄ and a light control relay. One end of R ₃ is connected to the body ground, and the other end is connected to the light control relay K ₁ . The other end of K ₁ is connected to R ₄ , and the other end of R ₄ is connected to the negative pole of the power battery pack. Resistors _R2 and _R3 have the same resistance value, and _R1 and R4 have the same resistance value _.

The sampling circuit consists of clamping diodes D ₁ and D ₂ , bidirectional TVS diodes D ₃ and D ₄ , resistors R ₅ and R ₆ , filter capacitors C ₁ , C ₂ , C ₃ , and C ₄ , and a high-precision operational amplifier chip INA2126 One end of D ₁ is connected to the sampling signal line between K ₁ and R ₂ and one end of resistor R ₅ , the other end is connected to the body ground, two-way diodes D ₃ and D ₄ , one end of D ₃ is connected to the other end of resistor R ₅ and the dual _The other end of the second pin of the instrumentation amplifier is connected to the body ground, one end of D4 is connected to the body ground, and the other end is connected to the other end of the resistor _R6 and the 16th pin of the instrumentation amplifier. Resistors R ₇ and R ₈ are respectively connected between pins 3 and 4 of the instrumentation amplifier and pins 13 and 14 to adjust the magnification of the operational amplifier circuit. The output signal of the dual instrumentation amplifier is sent to the AD sampling channel of the single-chip microcomputer through the resistors R ₇ and R ₈ .

The single-chip microcomputer and the AD sampling circuit are composed of the single-chip microcomputer and its built-in 12-bit multi-channel AD sampling circuit.

On the other hand, the present invention also provides a method for detecting the insulation resistance of an electric vehicle. The method for detecting the insulation resistance of an electric vehicle includes the following four steps: the step of measuring the total voltage of the power battery pack, the step of collecting the voltage of the upper bridge arm, and the step of collecting the voltage of the lower bridge arm. A voltage acquisition step and an insulation resistance calculation step.

Beneficial effect:

1. The actual measurement error is within 5%: INA2126 high-precision dual instrumentation amplifier is used, which has low offset voltage (maximum value is 250μV), low voltage drift (maximum value is 3μV/℃) and excellent common-mode rejection; positive The negative bridge arm voltage signal is amplified by an integrated circuit, which ensures good temperature consistency and circuit parameter consistency; AQV258 photoelectric relay is used, which has extremely low on-resistance, which reduces the impact of relay voltage drop on measurement. impact on the outcome.

2. High reliability: adopt D ₁ and D ₂ double diode clamping circuit, when the V ₊ voltage is lower than -0.7V, the diode D ₁ is turned on; when the V _- voltage is higher than 0.7V, the diode D ₂ is turned on ; and then ensured that the voltages of the analog sampling signals 1 and 2 are higher than -0.7V, avoiding the damage of the AD sampling circuit; D ₃ and D ₄ adopt PESD5V0S1 bidirectional TVS diodes, so that the signal processing circuit is free from electrostatic discharge (ESD) and Surge pulse damage; the AQV258 photoelectric relay used has no mechanical electric shock, has the advantages of maintenance-free, high-speed operation, and long life, and has low operating current and small leakage current, which not only ensures the measurement accuracy of the system, but also increases system lifespan.

3. On-line measurement: The invented control method has clear steps, simple process and small amount of calculation, and the real-time calculation of insulation resistance can be completed by using a single-chip microcomputer.

Description of drawings

Figure 1 is a schematic diagram of the electric vehicle insulation resistance detection control circuit;

Fig. 2 is a flow chart of the electric vehicle insulation resistance detection method;

Fig. 3 is an equivalent circuit diagram of an unbalanced bridge detection circuit;

Figure 4 is the equivalent circuit when K1 and K2 are closed at the same time;

Fig. 5 is an equivalent circuit diagram when K1 is closed and K2 is disconnected;

Figure 6 is the equivalent circuit when K2 is closed and K1 is open.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Fig. 1, the present invention provides an electric vehicle insulation resistance detection control circuit, which is composed of four parts: a DC system to be tested, a detection circuit, a sampling circuit, a single-chip microcomputer and an AD conversion circuit.

The DC system to be tested is composed of the power battery, the insulation resistance of the positive terminal and the insulation resistance of the negative terminal. The insulation resistance of the positive terminal is defined as the resistance value between the positive busbar of the power battery pack and the ground of the vehicle body, as shown in Fig. 1 R ₊ shown; the negative terminal insulation resistance is defined as the resistance value between the negative busbar of the power battery pack and the vehicle body ground, as shown in R- _in Figure 1.

The upper bridge arm of the detection circuit is composed of two detection resistors R ₁ , R ₂ and a light control relay, one end of R ₁ is connected to the positive pole of the power battery, and the other end is connected to the light control relay K ₁ . The other end of K ₁ is connected to R ₂ , and the other end of R ₂ is connected to the body ground. The lower bridge arm of the detection circuit is composed of two detection resistors R ₃ , R ₄ and a light control relay. One end of R ₃ is connected to the body ground, and the other end is connected to the light control relay K ₁ . The other end of K ₁ is connected to R ₄ , and the other end of R ₄ is connected to the negative pole of the power battery pack. Resistors _R2 and _R3 have the same resistance value, and _R1 and R4 have the same resistance value _.

The sampling circuit consists of clamping diodes D ₁ and D ₂ , bidirectional TVS diodes D ₃ and D ₄ , resistors R ₅ and R ₆ , filter capacitors C ₁ , C ₂ , C ₃ , and C ₄ , and a high-precision operational amplifier chip INA2126 One end of D ₁ is connected to the sampling signal line between K ₁ and R ₂ and one end of resistor R ₅ , the other end is connected to the body ground, two-way diodes D ₃ and D ₄ , one end of D ₃ is connected to the other end of resistor R ₅ and the dual The second pin of the instrument amplifier, the other end is connected to the body ground, one end of D ₄ is connected to the body ground, and the other end is connected to the other end of the resistor R ₆ and the 16th pin of the instrument amplifier. Resistors R ₇ and R ₈ are respectively connected between pins 3 and 4 of the instrumentation amplifier and pins 13 and 14 to adjust the magnification of the operational amplifier circuit. The output signal of the dual instrumentation amplifier is sent to the AD sampling channel of the single-chip microcomputer through the resistors R ₇ and R ₈ .

The single-chip microcomputer and the AD sampling circuit are composed of the single-chip microcomputer and its built-in 12-bit multi-channel AD sampling circuit.

As shown in Figure 2, the present invention also provides a method for detecting the insulation resistance of an electric vehicle. The method for detecting the insulation resistance of an electric vehicle includes the following four steps: the step of measuring the total voltage of the power battery pack, the step of collecting the voltage of the upper bridge arm, and the step of The bridge arm voltage acquisition step and the insulation resistance calculation step.

As shown in Figure 3, it is the equivalent circuit diagram of the insulation resistance detection bridge circuit, specifically: R ₊ is the insulation resistance of the positive pole of the power battery, R _- is the insulation resistance of the negative pole of the power battery; P is the ground point of the vehicle body; resistance R ₁ , light Control relay K ₁ , resistor R ₂ , resistor R ₃ , light control relay K ₂ , and resistor R ₄ are connected in series in sequence, and the other end of resistor R ₁ is connected to the positive pole of the power battery pack, and one end of resistor R ₄ is connected to the negative pole of the power battery pack. The connection terminals of R ₂ and resistor R ₃ are connected to the body ground; the voltages of the other ends of resistor R ₂ and resistor R ₄ relative to point P are V ₊ and V _- respectively.

The specific measurement steps are as follows:

① Measure the total voltage of the power battery pack

To measure the total voltage of the power battery pack, select the negative pole of the power battery pack as the reference zero potential point, and close the relays K ₁ and K ₂ at the same time, and its equivalent circuit is shown in Figure 4.

As shown in Figure 4, i ₁ and i ₂ are the currents flowing through the upper bridge arm and the lower bridge arm, and the total voltage at both ends of the power battery pack is the voltage between point V _B+ and point P and the voltage between point P and point V _B- The sum of the voltages between.

② Measure the voltage signal of the sampling point of the upper bridge arm

The microcontroller control signal CON1 is set high, and CON2 is set low. At this time, the photorelay K ₁ is closed and K ₂ is open. P is selected as the reference zero potential point, and the voltage signal V ₊ of the monitoring point of the upper bridge arm is measured. The equivalent circuit is shown in Figure 5 Show.

The reference current direction of the positive and negative terminals is shown in Figure 5. The voltage between the resistors R ₁ and R ₂ is detected to be V ₊ by the detection circuit, and the current flowing through R ₁ and R ₂ can be obtained

The voltage between the positive terminal of the power battery pack and the reference point P

Therefore, it can be obtained that the current i ₄ flowing through the insulation resistance R ₊ of the positive terminal, the current i ₁ of the positive terminal of the power battery pack =i ₃ +i ₄ ,

The direction of the negative reference current is shown in Figure 5, so V _B+ +V _B- = _Vtotal , and i ₁ +i ₂ = 0 from the circuit theorem, and the equation is obtained

Among them, V _B+ is the voltage between the positive terminal of the power battery pack and the reference point P, and V _B- is the voltage between the negative terminal of the power battery pack and the reference point P.

③ Measure the voltage signal of the sampling point of the lower bridge arm

The control signal CON1 is set low and CON2 is set high through the single-chip microcomputer. At this time, when the relay K ₁ is disconnected and K ₂ is closed, the equivalent circuit diagram is shown in Figure 6.

Due to changes in the circuit, the actual voltage of the reference zero potential changes, so the voltage and current of the positive and negative electrodes relative to the reference zero potential change, and the following formula is obtained in the same way as the above steps.

④ Calculation of insulation resistance

The sampling point voltages V ₊ and V _- measured through the above steps are divided into the following four situations according to the voltage difference.

Case 1:

When V ₊ and V _- are both equal to zero, the resistance values of the positive insulation resistance R ₊ and the negative insulation resistance R _- are equal to infinity.

Case two:

When V ₊ is zero and V _- is not zero, the insulation resistance R- of the negative terminal is equal to infinity. Open relay K ₁ and close relay K ₂ . The equivalent circuit is shown in Figure 6.

The current i ₁ =i ₄ flowing through the insulation resistance R+ of the positive terminal, the following formula is obtained

Case three:

When V ₊ is not zero and V _- is zero, the negative insulation resistance R ₊ is equal to infinity, the relay K ₁ is closed, and the relay K ₂ is opened. The equivalent circuit is shown in Figure 4.

The current i ₂ =i ₄ flowing through the insulation resistance R _- of the positive terminal, the following formula is obtained

Situation 4:

When V ₊ and V _- are not equal to zero, the calculation process of insulation resistance is as follows:

Subtract (6) from (5) to get

The present invention is described below by means of experimental data.

Based on the invented electric vehicle insulation resistance detection circuit shown in Figure 1, the battery used in the experiment is a ternary lithium battery 18650 with a nominal value of 3.6V and 2.6Ah. 45 batteries are connected in parallel to form a group, and a total of 90 groups are connected in series to form a power supply. The battery pack has a nominal voltage of 330V and a capacity of 117Ah.

The bridge arm sampling resistor adopts the resistance value of R ₁ and R ₄ as 1880kΩ, and the resistance value of R ₂ and R ₃ as 4.7kΩ, both of which are precision MELF resistors with an accuracy of 1%; K ₁ and K ₂ adopt the AQV258 type with a withstand voltage of 1500V Light control relay; clamping diode D ₁ and D ₂ model is CD4148, bidirectional TVS diode D ₃ and D ₄ model is PESD5V0S1; capacitor C ₁ , C ₂ , C ₃ and C ₄ capacity is 0.01μF; resistor R ₅ , R _6. The resistance values of R ₇ and R ₈ are both 100Ω; select the INA2126 dual instrument amplifier with the maximum offset voltage value of 250μV and the maximum voltage drift value of 3μV/℃; the model of the microcontroller is MC9S12XEP100.

In the experiment, resistors with different resistance values were used to simulate the insulation resistance conditions under different conditions, and the invented insulation resistance detection circuit and control method were used to measure it in real time. The measurement results were sent to the display interface of the host computer through the CAN bus, and the results were compared with the FLUKE The results measured by the 1587C model insulation resistance measuring instrument are compared, and the results are shown in Table 1.

Table 1 Measurement Results

Insulation detection is carried out when the test vehicle is running, and the detection cycle is once every 3 seconds. The main controller controls the opening and closing of the photoelectric relays K ₁ and K ₂ to complete the collection of the voltage of the sampling points of the upper and lower bridge arms. According to the invented insulation The resistance detection control method calculates the resistance value of its insulation resistance.

According to the CAN communication bus requirements of electric vehicles, the main controller of the electric vehicle communicates with the battery management system (BMS), and the main controller makes real-time judgment on the measurement results and sends the processed data information to the instrument panel through the CAN bus display in real time. When the insulation resistance value is lower than the safety threshold (100Ω/V) of the alarm, the system executes a first-level alarm and lights up the LED indicator on the instrument panel, so that the driver knows the fault and handles it to ensure safety. The test results show that the measurement error is within 5%, which meets the requirements of the national standard.

Claims (7)

1. a kind of electric automobile insulation resistance detection control circuit, which is characterized in that including straight-flow system to be measured, detection circuit, Sample circuit and microcontroller and A/D converter circuit；

The straight-flow system to be measured is made of power battery pack, anode insulation resistance and negative terminal insulation resistance, the anode insulation Resistance is defined as the resistance value between the power battery pack positive electrode bus and vehicle body ground, and the negative terminal insulation resistance is defined as institute State the resistance value between power battery pack negative electrode bus and vehicle body ground；

The detection circuit includes bridge arm and detection circuit lower bridge arm in detection circuit；Bridge arm is examined by two in the detection circuit Measuring resistance R₁、R₂With photorelay K₁Composition, detection resistance R₁Termination power battery pack anode, described in the other end Meet photorelay K₁, K₁Another termination detection resistance R₂, detection resistance R₂The other end with picking up body；The detection circuit Lower bridge arm is by two detection resistance R₃、R₄With photorelay K₂Composition, detection resistance R₃One end with picking up body, another termination Photorelay K₂, photorelay K₂Another termination detection resistance R₄, detection resistance R₄Another termination power battery pack it is negative Pole；Detection resistance R₂And R₃Resistance value is identical, detection resistance R₁And R₄Resistance value is identical；

The sample circuit is by clamp diode D₁、D₂, two-way TVS diode D₃、D₄, resistance R₅、R₆, filter capacitor C₁、C₂、C₃、 C₄, the double instrument amplifier chip I NA2126UA compositions of high-precision, clamp diode D₁One end is connected to photorelay K₁With inspection Measuring resistance R₂Between sampled signal line and resistance R₅One end, other end connection vehicle body, two-way TVS diode D₃One end connects In resistance R₅The other end, capacitance C₁One end and double the 2nd pin of instrument amplifier, the other end with being connected to vehicle body, two-way TVS bis- Pole pipe D₄With being connected to vehicle body, the other end is connected to resistance R for one end₆The other end, capacitance C₂One end and double instrument amplifiers the 16th Pin；Resistance R₇、R₈It is connected between 3,4 pins of instrument amplifier and 13,14 pins, is put for adjusting operational amplifier circuit Big multiple；The output signal of double instrument amplifiers passes through resistance R₇、R₈It send to the AD sampling channels of microcontroller；

The microcontroller and AD sample circuits are made of microcontroller and its built-in 12 multichannel AD sample circuits.

2. a kind of electric automobile insulation resistor detection method, the electric automobile insulation resistor detection method includes following four Step：Power battery pack total voltage measuring process, upper bridge arm voltage acquisition step, lower bridge arm voltage acquisition step and insulated electro Resistance calculates step.

3. a kind of electric automobile insulation resistor detection method according to claim 2, which is characterized in that insulation resistance detects The equivalent circuit diagram of bridge circuit is：R₊For power battery anode insulation resistance, R_-For power battery cathode insulation resistance；P is vehicle Body earth point；Resistance R₁, photorelay K₁, resistance R₂, resistance R₃, photorelay K₂, resistance R₄It is sequentially connected in series, and resistance R₁ The other end connection power battery pack anode, resistance R₄One end connect power battery pack cathode, resistance R₂With resistance R₃Connection With terminating vehicle body；Resistance R₂With resistance R₄The other end relative to the voltage of P points be respectively V₊And V_-。

4. a kind of electric automobile insulation resistor detection method according to claim 3, which is characterized in that the power battery In packet total voltage measuring process, it is to be closed simultaneously with reference to zero-potential point to measure power battery pack stagnation pressure and choose power battery pack cathode Close relay K₁With K₂, power battery pack total voltage V_AlwaysFor：

Wherein, i₁、i₂To flow through the electric current of upper bridge arm and lower bridge arm.

5. a kind of electric automobile insulation resistor detection method according to claim 4, which is characterized in that the upper bridge arm electricity It presses in acquisition step,

Monolithic machine control signal CON1 sets height, and CON2 is set low, photorelay K₁It is closed, K₂It disconnects, it is with reference to zero potential to choose P Point, bridge arm monitoring point voltage signal V in measurement₊；

Resistance R is detected by detection circuit₁And R₂Between voltage be V₊, you can it obtains and flows through R₁、R₂Electric current

Voltage between power battery pack anode and reference point P

Then it can obtain and flow through anode insulation resistance R₊On electric current i₃, power battery pack anode electric current i₁=i₃+i₄,

Therefore V_B++V_B-=V_Always, i is obtained by Circuit Theorem₁+i₂=0, obtain equation

Wherein, V_B+For the voltage between power battery pack anode and reference point P, V_B-Between power battery pack negative terminal and reference point P Voltage.

6. a kind of electric automobile insulation resistor detection method according to claim 5, which is characterized in that the lower bridge arm electricity It presses in acquisition step,

Control signal CON1 is set to set low by microcontroller, CON2 sets height, relay K₁It disconnects, K₂When closure；

It since circuit changes, changes with reference to the virtual voltage of zero potential, so positive and negative anodes are relative to reference to zero potential Voltage, electric current change, obtain following formula：

7. a kind of electric automobile insulation resistor detection method according to claim 6, which is characterized in that the insulation resistance It calculates in step, measures sample amplitude when reproduced V through the above steps₊With V_-, following four kinds of situations are divided into according to the difference of voltage：

Work as V₊With V_-When being equal to zero, anode insulation resistance R₊With negative terminal insulation resistance R_-Resistance value is equal to infinity；

Work as V₊It is zero, V_-When being not zero, negative terminal insulation resistance R at this time_-Resistance value is equal to infinity, disconnects relay K₁, closing relay Device K₂, flow through anode insulation resistance R₊On electric current i₁=i₄, obtain following formula

Work as V₊It is not in zero, V_-When being zero, negative terminal insulation resistance R at this time₊Resistance value is equal to infinity, closing relay K₁, disconnect after Electric appliance K2 flows through negative terminal insulation resistance R_-On electric current i₂=i₄, obtain following formula

Work as V₊With V_-When being all not equal to zero, the calculating process of insulation resistance is as follows at this time：(5) formula is subtracted each other (6) formula and is obtained