CN109572436B

CN109572436B - Diagnosis system for load circuit and electric vehicle

Info

Publication number: CN109572436B
Application number: CN201811620305.7A
Authority: CN
Inventors: 穆萨利亚卡姆·内贾德·阿里; 梁毕辉; 高攀龙; 白彻瓦·基兰库马尔
Original assignee: Svolt Energy Technology Co Ltd
Current assignee: Svolt Energy Technology Co Ltd
Priority date: 2018-12-28
Filing date: 2018-12-28
Publication date: 2020-08-28
Anticipated expiration: 2038-12-28
Also published as: CN109572436A

Abstract

The invention relates to the field of control circuits, and provides a diagnosis system for a load circuit and an electric vehicle, wherein the diagnosis system comprises: the driver is used for controlling the on or off of an IGBT switch in the load circuit; the diagnosis circuit is used for outputting a diagnosis feedback signal of the IGBT when the IGBT switch is in a conducting or disconnecting state; and a controller for performing the following operations: inputting a control signal to the driver to control the on or off of the IGBT switch; and receiving the diagnosis feedback signal, and determining the state of the IGBT switch according to the diagnosis feedback signal and the control signal. The diagnosis system can realize rapid diagnosis of the state of the IGBT switch without high-voltage measurement, greatly reduces the probability of occurrence of faults such as switch adhesion and the like in the load circuit, and can maintain the long-term stable operation of the load circuit.

Description

Diagnosis system for load circuit and electric vehicle

Technical Field

The invention relates to the field of control circuits, in particular to a diagnosis system for a load circuit and an electric vehicle.

Background

The load circuit of a battery pack in an electric vehicle (which is also commonly referred to as a high-voltage circuit because the voltage of the load circuit supplied with power by the battery pack is generally high) employs a contactor as a circuit switch in order to disconnect the load of the high-voltage battery in case of normal power failure and emergency power failure. And the contactor is controlled by a microcontroller through a driver to energize the contactor coil. However, there are some disadvantages to the contactor in case of emergency power failure: when high currents are switched off, in particular after ageing of the contactor, it is possible that the contactor sticks and the circuit cannot be switched off, which puts the system at high risk and may lead to battery explosion and thus to violation of safety objectives.

For contactor diagnostics, high voltage measurements are typically used to detect faults of abnormal opening and abnormal closing, but the measurement time can be long due to the long setup time of the measurement filter. Therefore, the failure detection time is long.

Disclosure of Invention

In view of this, the present invention is directed to a diagnostic system for a load circuit and an electric vehicle, in which an IGBT switch is used to replace a contactor in a conventional load circuit, so that a state of the IGBT switch can be rapidly diagnosed without high-voltage measurement, a probability of occurrence of a fault such as switch adhesion in the load circuit is greatly reduced, and long-term stable operation of the load circuit can be maintained.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a diagnostic system for a load circuit, the diagnostic system comprising: the driver is used for controlling the on or off of an IGBT switch in the load circuit; the diagnosis circuit is used for outputting a diagnosis feedback signal of the IGBT when the IGBT switch is in a conducting or disconnecting state; and a controller for performing the following operations: inputting a control signal to the driver to control the on or off of the IGBT switch; and receiving the diagnosis feedback signal, and determining the state of the IGBT switch according to the diagnosis feedback signal and the control signal.

Further, the diagnostic circuit includes: a low voltage power supply for supplying power to the diagnostic circuit and the driver.

Further, the controller is further configured to output a diagnostic enable signal, and the diagnostic circuit further includes: a first optocoupler for switching on the diagnostic circuit if the diagnostic enable signal is greater than a turn-on voltage of the first optocoupler; and the comparator is used for comparing the voltage of the low-voltage power supply passing through the first diagnosis resistor with the voltage of the low-voltage power supply passing through the second diagnosis resistor and outputting a comparison result to the controller, wherein the comparison result is the diagnosis feedback signal, and the first diagnosis resistor is larger than the second diagnosis resistor.

Further, the first optical coupler is also used for isolating electrical interference between the output end of the controller and the input end of the comparator.

Further, the comparator is further configured to perform the following operations: when the IGBT switch is conducted and the first optocoupler is conducted, the voltage of the low-voltage power supply after passing through a first diagnosis resistor is larger than the voltage of the low-voltage power supply after passing through a second diagnosis resistor, and a low-level diagnosis feedback signal is output; or under the condition that the IGBT switch is switched off and the first optocoupler is switched on, the voltage of the low-voltage power supply after passing through the first diagnosis resistor is smaller than the voltage of the low-voltage power supply after passing through the second diagnosis resistor, and a high-level diagnosis feedback signal is output.

Further, the controller is further configured to: determining that the state of the IGBT switch is normally closed under the condition that the control signal is a high-level signal and the comparator outputs a high-level diagnosis feedback signal; determining that the state of the IGBT switch is abnormally closed under the condition that the control signal is a high-level signal and the comparator outputs a low-level diagnosis feedback signal; determining that the state of the IGBT switch is normally off under the condition that the control signal is a low-level signal and the comparator outputs a low-level diagnosis feedback signal; or determining that the state of the IGBT switch is abnormal disconnection when the control signal is a low level signal and the comparator outputs a high level diagnosis feedback signal.

Further, the diagnostic system further comprises: a second optocoupler for isolating electrical interference between the output of the comparator and the input of the controller.

Further, the diagnostic system further comprises: an isolator for isolating an electrical connection between the low voltage power supply and the diagnostic circuit.

Further, the diagnostic circuit may further include: and the driver is also used for controlling the IGBT switch to be switched off to disconnect a loop of the load circuit under the condition that the Vce is greater than a preset voltage, wherein the preset voltage is related to a collector-emitter voltage saturation value Vce (sat) of the IGBT switch.

Compared with the prior art, the diagnostic system for the load circuit has the following advantages:

(1) the invention creatively utilizes the IGBT switch to replace a contactor in the traditional load circuit, controls the conduction of the IGBT switch by inputting a control signal to a driver, outputs a diagnosis feedback signal under the condition that the IGBT switch is conducted, and determines the state of the IGBT switch according to the diagnosis feedback signal and the control signal, thereby realizing the rapid diagnosis of the state of the IGBT switch without high-voltage measurement, greatly reducing the probability of the occurrence of faults such as switch adhesion and the like in the load circuit, and maintaining the long-term stable operation of the load circuit.

(2) In the case of a current overload of the load circuit, the driver may feed back a voltage Vce across the collector-emitter of the IGBT switch to the controller, and the controller may turn off the load circuit by sending a control signal to the driver to control the IGBT switch to turn off. The voltage sensor has high response speed, so that the diagnosis circuit can quickly respond to the state of the load circuit, and the load circuit can be timely disconnected when an emergency accident happens, so that the function of over-current protection (OCP) is achieved.

(3) The driver of the diagnosis system is powered by an independent low-voltage power supply, so that the problem of measurement logic errors caused by floating grounding when the IGBT switch is disconnected does not exist, and the accuracy of a diagnosis result is greatly improved; the driver is used as an independent driving circuit and does not occupy a main control unit of a controller of the battery pack, so that the space is saved, the operation rate of the main control unit is improved, and in case of emergency accidents, the IGBT is disconnected under the condition of ensuring the normal operation of the controller, and the load circuit is controlled to be disconnected independently, so that the purpose of emergency power-off is achieved.

Another object of the present invention is to propose an electric vehicle provided with a diagnostic system for a load circuit as described above.

The advantages of the electric vehicle and the diagnosis system for the load circuit are the same compared with the prior art, and are not described in detail herein.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 is a block diagram of a diagnostic system for a load circuit according to an embodiment of the present invention; and

fig. 2 is a block diagram of a diagnostic system for a load circuit according to an embodiment of the present invention.

Description of reference numerals:

10 driver 11 diagnostic circuit

12 controller 13 DC 12V power supply

14 first optocoupler 15 comparator

16 second optocoupler 17 isolator

18 IGBT switch 19 load circuit

20 diagnostic resistor 21 first diagnostic resistor

22 second diagnostic resistance

Detailed Description

In addition, the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict.

The problem of sticking of the contactor is a very common but difficult problem to solve for the load circuit of a conventional battery pack, and the probability of sticking of the contactor increases with time and operating cycle. Because the IGBT switch can bear high current and voltage, the IGBT switch is adopted to replace a contactor in a load circuit of a traditional battery pack, and therefore the problem of adhesion of the contactor can be avoided. Based on the above, the invention provides a diagnosis system for a load circuit and an electric vehicle comprising the diagnosis system for the load circuit.

The present invention will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.

Fig. 1 is a block diagram of a diagnostic system for a load circuit according to an embodiment of the present invention. The diagnostic system may include: a driver 10 for controlling on or off of an IGBT switch in the load circuit; the diagnosis circuit 11 is used for outputting a diagnosis feedback signal of the IGBT when the IGBT switch is in a conducting or disconnecting state; and a controller 12 for performing the following operations: inputting a control signal to the driver to control the on or off of the IGBT switch; and receiving the diagnosis feedback signal, and determining the state of the IGBT switch according to the diagnosis feedback signal and the control signal. The invention creatively adopts the IGBT switch to replace a contactor in the traditional load circuit, controls the conduction of the IGBT switch by inputting a control signal to a driver, outputs a diagnosis feedback signal under the condition that the IGBT switch is conducted, and determines the state of the IGBT switch according to the diagnosis feedback signal and the control signal, thereby realizing the rapid diagnosis of the state of the IGBT switch without high-voltage measurement, greatly reducing the probability of the occurrence of faults such as switch adhesion and the like in the load circuit, and maintaining the long-term stable operation of the load circuit.

The diagnostic circuit may further include: and the driver is also used for controlling the IGBT switch to be switched off to disconnect a loop of the load circuit under the condition that the Vce is greater than a preset voltage, wherein the preset voltage is related to a collector-emitter voltage saturation value Vce (sat) of the IGBT switch. That is, as shown in fig. 2, when the load circuit 19 is overloaded with current, the value of Vce of the IGBT switch 18 increases sharply (for example, equal to the saturation value Vce (sat)), the driver 10 may feed back the saturation value Vce (sat)) to the controller 12, and then the controller 12 sends a low-level control signal to the driver 10 to control the IGBT switch 18 to turn off, thereby turning off the load circuit 19. The voltage sensor has high response speed, so that the diagnosis circuit can quickly respond to the state of the load circuit, and the load circuit can be timely disconnected when an emergency accident happens, so that the function of over-current protection (OCP) is achieved.

The diagnostic circuit may include: a low voltage power supply for supplying power to the diagnostic circuit and the driver. The voltage source may be a dc 12V power source 13, as shown in fig. 2. Of course, the low voltage power supply of the present invention is not limited to a dc 12V power supply, and other suitable low voltage power supplies are possible. The controller may be further configured to output a diagnostic enable signal, and the diagnostic circuit 11 may further include: a first optocoupler 14 for turning on the diagnostic circuit if the diagnostic enable signal is greater than a turn-on voltage of the first optocoupler; and a comparator 15, configured to compare a voltage of the low-voltage power supply across a first diagnostic resistor with a voltage of the low-voltage power supply across a second diagnostic resistor, and output a comparison result to the controller, where the comparison result is the diagnostic feedback signal, where the first diagnostic resistor is greater than the second diagnostic resistor, as shown in fig. 2, that is, different diagnostic feedback signals are output by comparing a voltage drop across the first diagnostic resistor 20 with a voltage drop across the second diagnostic resistor. For example, the low voltage power supply 13 is connected to the negative electrode of the comparator 15 through a node C after the first diagnostic resistor 20; and the low-voltage power supply 13 is connected with the anode of the comparator through a node E behind the second diagnosis resistor 21. When the voltage at node C on the diagnostic circuit is greater than the voltage at node E, the comparator 15 outputs a diagnostic feedback signal at a low level; and when the voltage at the node C on the diagnostic circuit is less than the voltage at the node E, the comparator 15 outputs a diagnostic feedback signal of high level. Of course, the present invention is not limited to the case where the nodes C and E are connected to the negative electrodes and the positive electrodes of the comparators one by one, and the nodes C and E may be connected to the positive electrodes and the negative electrodes of the comparators one by one, but the corresponding determination logic needs to be changed.

In the case where the switching device in the load circuit is a contactor, when the contactor is opened, measurement logic errors may be caused due to the floating ground, which makes fault diagnosis coverage low. The response time for closing or opening the contactor is high for fault recovery, which reduces the recovery time to a bottleneck stage when using a conventional contactor as a circuit switch. For the case that the switching device in the load circuit in the embodiment is an IGBT switch, the driver of the diagnostic system is powered by an independent low-voltage power supply, and the problem of measurement logic errors caused by floating grounding when the IGBT switch is turned off does not exist, so that the accuracy of the diagnostic result is greatly improved. In addition, as the functional characteristics of the IGBT switch do not have the jitter problem when the IGBT switch is switched on or switched off, the jitter elimination module can be omitted by combining software logic, the code space is saved, and the calculation time is reduced.

The first optical coupler is also used for isolating electrical interference between the output end of the controller and the input end of the comparator, so that the accuracy of the diagnosis result can be improved. In order to improve the accuracy of the diagnosis result, the diagnosis system may further include: a second optocoupler 16 for isolating electrical interference between the output of the comparator and the input of the controller. Further, the diagnostic system may further include: an isolator 17 for isolating electrical interference between the low voltage power supply and the diagnostic circuit. Wherein the isolator may be a DC-DC isolator.

As shown in fig. 2, when the first optocoupler 14 is in the conducting state, the voltage at point C on the diagnostic circuit is high or low depending mainly on the state of the IGBT switch 18: when the IGBT switch is turned on, the diagnostic circuit and the load circuit are both in a conducting state, specifically, from the dc 12V power supply 13, through the node D, the first diagnostic resistor 20, the node C, the transistor in the first optocoupler 14, the node A, IGBT switch 18, the node B, and the load, and finally to the negative terminal of the battery pack 22, in which case the voltage at the node C is less than the voltage at the node E because the first diagnostic resistor 20 is greater than the second diagnostic resistor 21; and in the case where the IGBT switch is turned off, the diagnostic circuit is turned on and the load circuit is turned off, specifically, from the dc 12V power supply 13 through the circuit of node D, the first diagnostic resistor 20 and node C to the IGBT switch 18, so that the voltage at node C is approximately equal to 12V and the voltage at node C is greater than the voltage at node E. Thus, the comparator may also be used to perform the following operations: when the IGBT switch is conducted and the first optocoupler is conducted, the voltage on the diagnosis circuit is greater than the voltage of the low-voltage power supply, and a low-level diagnosis feedback signal is output; or when the IGBT switch is switched off and the first optocoupler is switched on, the voltage on the diagnosis circuit is smaller than the voltage of the low-voltage power supply, and a high-level diagnosis feedback signal is output.

Where the diagnostic feedback signal is obtained, the controller may be further operable to: determining that the state of the IGBT switch is normally closed under the condition that the control signal is a high-level signal and the comparator outputs a high-level diagnosis feedback signal; determining that the state of the IGBT switch is abnormally closed under the condition that the control signal is a high-level signal and the comparator outputs a low-level diagnosis feedback signal; determining that the state of the IGBT switch is normally off under the condition that the control signal is a low-level signal and the comparator outputs a low-level diagnosis feedback signal; or determining that the state of the IGBT switch is abnormal disconnection when the control signal is a low level signal and the comparator outputs a high level diagnosis feedback signal.

The controller may be a controller of the battery pack, a separately configured general purpose processor, special purpose processor, conventional processor, Digital Signal Processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, an Application Specific Integrated Circuit (ASIC), Field Programmable Gate Array (FPGA) circuitry, any other type of Integrated Circuit (IC), a state machine, or the like. The driver is an independent driving circuit, does not occupy a main control unit of a controller of the battery pack, saves space, and improves the operation rate of the main control unit to a certain extent. Because the driver is independent of the microcontroller, when an emergency accident happens, the IGBT can be disconnected and the load circuit can be disconnected independently under the condition of ensuring the normal operation of the controller, so that the purpose of emergency power-off is achieved, and the use of other functions is not influenced.

Specifically, the electrical connection of the load circuit 19 will now be explained and explained in detail by taking the diagnostic system shown in fig. 2 as an example.

The whole diagnostic system works as follows: the dc 12V power supply 13 supplies power to the driver 10, and when the power supply signal is active, the driver 10 receives a control signal from a controller (not shown), and controls the on or off state of the IGBT switch through the control signal. In addition, the driver 10 collects the electric signal of the load circuit from the node B through the common driver GND, and outputs the diagnosis feedback signal of the IGBT switch 18 through the diagnosis circuit. Meanwhile, the driver 10 also has a self-diagnosis function and can output a self-diagnosis signal to the controller, specifically, when the load circuit is overloaded with current, the driver 10 can feed back the voltage across the collector and the emitter of the IGBT switch 18 to the controller, and then input a low-level control signal to the driver 10 through the controller to control the IGBT switch 18 to be turned off, so as to turn off the load circuit to perform an overcurrent protection function. The diagnosis circuit 11 is simple in structure and quick in response time, and compared with the existing high-voltage measurement method, the diagnosis circuit 11 can be used for quickly diagnosing the fault information of the IGBT switch.

The diagnosis results of the state of the IGBT switch 18 of the load circuit by the above-described diagnosis system mainly include the following four cases:

first, IGBT switch 18 normally closed condition: after the direct current 12V power supply 13 is turned on, the controller (not shown) outputs a high-level control signal, which is transmitted to the input port of the IGBT switch 18 via the driver 10, so that the IGBT switch 18 is closed, thereby turning on the load circuit 19; meanwhile, the direct current 12V power supply 13 supplies power to the diagnostic circuit 11, the controller sends out a high-level diagnostic enable signal (the level of the diagnostic enable signal is higher than the starting voltage of the light emitting diode in the first optical coupler 14), the light emitting diode is turned on, the triode in the first optical coupler 14 is further turned on, the diagnostic circuit 11 and the load circuit 19 are both in a conducting state, and the voltage of a node E connected with the anode of the comparator 15 is greater than the voltage of a node C connected with the cathode of the comparator 15. Thus, the negative voltage of the comparator 15 is less than the positive voltage, and a high level signal is output, at which time the light emitting diode in the second photo coupler 16 is turned on, and then a high level diagnostic feedback signal is output.

Second case, abnormal closing condition of IGBT switch 18:

when a controller (not shown) outputs a high-level control signal but the IGBT switch 18 is not successfully closed, the load circuit 19 is not turned on, the circuit in which the first diagnostic resistor 20 is located is in an open state, the voltage at the node C connected to the negative electrode of the comparator 15 is approximately 12V, the voltage at the node E connected to the positive electrode of the comparator 15 is less than 12V, the voltage at the negative electrode of the comparator 15 is greater than the voltage at the positive electrode, a low-level signal is output, the light emitting diode in the second optocoupler 16 is not turned on, and a low-level diagnostic feedback signal is output.

Third, IGBT switch 18 normally off condition:

when the dc 12V power supply 13 is turned on, the controller 12 outputs a low-level control signal, and the low-level control signal is transmitted to the input port of the IGBT switch 18 via the driver 10, whereby the IGBT switch 18 is turned off, and the load circuit 19 is turned off. The controller sends out a high-level diagnosis enabling signal to conduct the light emitting diode in the first optical coupler 14 and further conduct the triode in the first optical coupler 14, but at the moment, because the load circuit 19 is not conducted, the circuit where the first diagnosis resistor 20 is located is in an open circuit state, the voltage at the node C connected with the negative electrode of the comparator 15 is approximately equal to 12V, the voltage at the node E connected with the positive electrode of the comparator 15 is less than 12V, at the moment, the voltage of the negative electrode of the comparator 15 is greater than the voltage of the positive electrode, a low-level signal is output, at the moment, the light emitting diode in the second optical coupler 16 is not conducted, and then a low-level diagnosis feedback signal is output

Fourth situation, abnormal turn-off condition of IGBT switch 18:

when the controller outputs a low-level control signal but the IGBT switch 18 is not successfully turned off, the load circuit 19 is not turned on, and the dc 12V power supply 13 supplies power to the diagnostic circuit 11, the controller sends a high-level diagnostic enable signal to turn on the light emitting diode, so as to turn on the triode in the first optocoupler 14, and the diagnostic circuit 11 is in a conducting state. In this case, the voltage of the node E connected to the positive electrode of the comparator 15 is greater than the voltage of the node C connected to the negative electrode of the comparator 15. Thus, the negative voltage of the comparator 15 is less than the positive voltage, and a high level signal is output, at which time the light emitting diode in the second photo coupler 16 is turned on, and then a high level diagnostic feedback signal is output.

The details of the four diagnostic results are shown in table 1:

control signal	Diagnostic feedback signal	IGBT switch state
			1	1	Normal closure
1	0	Abnormal closure
			0	0	Normal disconnection
0	1	Abnormal disconnection

TABLE 1 four diagnostic results for IGBT switch states

In the embodiment, the controller can input the control signal to the driver to control the state of the IGBT switch in the load circuit, and the state of the IGBT switch can be accurately and effectively diagnosed by analyzing the control signal and the diagnosis feedback signal without high-voltage control and corresponding diagnosis; in addition, the IGBT switch can bear high current and voltage, particularly, the operating environment of the IGBT switch has low requirement on temperature, the temperature range of 105 ℃ can be easily reached, and normal use of the IGBT switch is not influenced, so that the probability of occurrence of faults such as switch adhesion and the like in a load circuit based on the IGBT switch is greatly reduced, the service life of the load circuit of the whole battery pack is longer, and the operation period is longer.

In summary, the present invention creatively uses the IGBT switch to replace the contactor in the conventional load circuit, and controls the turn-on of the IGBT switch by inputting the control signal to the driver, and outputs the diagnosis feedback signal when the IGBT switch is turned on, and determines the state of the IGBT switch according to the diagnosis feedback signal and the control signal, so that the state of the IGBT switch can be diagnosed quickly without high voltage measurement, the probability of occurrence of faults such as switch adhesion in the load circuit is greatly reduced, and the long-term stable operation of the load circuit can be maintained.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. A diagnostic system for a load circuit, the diagnostic system comprising:

the driver is used for controlling the on or off of an IGBT switch in the load circuit;

the diagnosis circuit is used for outputting a diagnosis feedback signal of the IGBT when the IGBT switch is in a conducting or disconnecting state; and

a controller to perform the following operations:

inputting a control signal to the driver to control the on or off of the IGBT switch; and

receiving the diagnosis feedback signal, determining the state of the IGBT switch according to the diagnosis feedback signal and the control signal,

the controller is further configured to output a diagnostic enable signal,

the diagnostic circuit includes:

a low voltage power supply for supplying power to the diagnostic circuit and the driver;

a first optocoupler for switching on the diagnostic circuit if the diagnostic enable signal is greater than a turn-on voltage of the first optocoupler; and

the comparator is used for comparing the voltage of the low-voltage power supply passing through the first diagnosis resistor with the voltage of the low-voltage power supply passing through the second diagnosis resistor and outputting a comparison result to the controller, wherein the comparison result is the diagnosis feedback signal,

wherein the first diagnostic resistance is greater than the second diagnostic resistance.

2. The diagnostic system for a load circuit of claim 1, wherein the first optocoupler is further configured to isolate electrical interference between the output of the controller and the input of the comparator.

3. The diagnostic system for a load circuit of claim 1, wherein the comparator is further configured to:

when the IGBT switch is conducted and the first optocoupler is conducted, the voltage of the low-voltage power supply after passing through the first diagnosis resistor is larger than the voltage of the low-voltage power supply after passing through the second diagnosis resistor, and a low-level diagnosis feedback signal is output; or

And under the condition that the IGBT switch is switched off and the first optocoupler is switched on, the voltage of the low-voltage power supply passing through the first diagnosis resistor is smaller than the voltage of the low-voltage power supply passing through the second diagnosis resistor, and a high-level diagnosis feedback signal is output.

4. The diagnostic system for a load circuit of claim 3, wherein the controller is further configured to:

determining that the state of the IGBT switch is normally closed under the condition that the control signal is a high-level signal and the comparator outputs a high-level diagnosis feedback signal;

determining that the state of the IGBT switch is abnormally closed under the condition that the control signal is a high-level signal and the comparator outputs a low-level diagnosis feedback signal;

determining that the state of the IGBT switch is normally off under the condition that the control signal is a low-level signal and the comparator outputs a low-level diagnosis feedback signal; or

And determining the state of the IGBT switch to be abnormal disconnection under the condition that the control signal is a low-level signal and the comparator outputs a high-level diagnosis feedback signal.

5. The diagnostic system for a load circuit of claim 1, further comprising:

a second optocoupler for isolating electrical interference between the output of the comparator and the input of the controller.

6. The diagnostic system for a load circuit of claim 1, further comprising:

an isolator for isolating electrical interference between the low voltage power supply and the diagnostic circuit.

7. The diagnostic system for a load circuit of claim 1, wherein the diagnostic circuit further comprises:

a voltage sensor for collecting voltage Vce at both ends of a collector-emitter of the IGBT switch,

the driver is further used for controlling the IGBT switch to be switched off to disconnect the loop of the load circuit under the condition that the Vce is larger than a preset voltage, wherein the preset voltage is related to a voltage saturation value Vce (sat) at two ends of a collector electrode and an emitter electrode of the IGBT switch.

8. An electric vehicle characterized in that it is provided with a diagnostic system for a load circuit according to any one of claims 1 to 7.