Overload protection method for electric drive system

Abstract

The invention discloses an overload protection method for an electric drive system. The overload protection method comprises the steps of collecting temperature and / or current data corresponding to the electric drive system; respectively comparing the temperature and / or current data with a preset temperature or current overload protection threshold value and an overload pre-protection threshold value, and judging whether to limit the output torque and the power or not; wherein the overload pre-protection threshold value is smaller than the overload protection threshold value; when the temperature or the current exceeds the overload pre-protection threshold value and is smaller than the overload pre-protection threshold value, the output torque power is limited through an overload pre-protection strategy; and when the temperature or the current exceeds an overload protection threshold value, an overload protection strategy is adopted to limit the output torque power. Before the overload protection threshold value is reached, the possibility of reaching the overload protection threshold value is reduced in an overload pre-protection mode, and the operation reliability of the system is improved.

Description

Technical Field

[0001] The present invention relates to the field of electric drive protection for new energy vehicles, and in particular to an overload protection method for an electric drive system of a new energy vehicle. Background Art

[0002] With the vigorous development of the new energy electric vehicle industry and the demand for energy storage applications in the military, industrial and agricultural, residential, medical, commercial, and communications industries, the electric drive system, as the core component of the new energy vehicle, has higher and higher requirements for its own power and economy. It also requires that the protection and control of the electric drive system can give full play to the performance of the electric drive system while ensuring that the electric drive system is fault-free. In this regard, the electric drive control system sets overload protection thresholds for various physical characteristics of the electric drive. When a characteristic indicator of the electric drive system exceeds the overload protection design indicator of the electric drive, the characteristic parameter will be limited to ensure that the electric drive does not exceed the characteristic parameter operation, protect the electric drive from failure, and ensure the normal operation of the vehicle.

[0003] However, the overload protection threshold is set according to the design characteristics of the electric drive. When the electric drive exceeds the parameter, protection is a passive protection. Once the parameter exceeds the parameter, it means that the electric drive system cannot continue to operate according to the current operating parameters. Parameter limitation is required to ensure that the operating parameters fall below the overload protection threshold. Generally, the torque or power limitation is relatively large, which will cause the output power of the electric drive to drop significantly, and then cause the vehicle power to drop, affecting the normal operation of the vehicle. In serious cases, it may cause personal injury and property loss.

[0004] When the operating parameters of the vehicle's electric drive system exceed the standard, the torque rate is set by setting the overload protection threshold. Technical defects include:

[0005] 1. The torque is limited according to the external characteristics of the electric drive design instead of gradient torque limit in advance, which will lead to the waste of electric drive system performance;

[0006] 2. Allowing the operating parameters of the electric drive system to exceed the overload protection threshold, causing the overload to become more serious;

[0007] 3. The restriction strategies after reaching the overload protection threshold are mostly drastic restrictions, which will cause a cliff-like power loss of the whole vehicle and poor comfort. Summary of the invention

[0008] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an overload protection method for an electric drive system. Before the overload protection threshold is reached, the possibility of reaching the overload protection threshold is reduced by overload pre-protection, thereby improving the operating reliability of the system.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is: an electric drive system overload protection method, comprising:

[0010] Collect temperature and / or current data corresponding to the electric drive system;

[0011] Compare the temperature and / or current data with the preset temperature or current overload protection threshold and overload pre-protection threshold to determine whether to limit the output torque and power; wherein the overload pre-protection threshold is less than the overload protection threshold;

[0012] When the temperature or current exceeds the overload pre-protection threshold and is less than the overload protection threshold, the output torque power is limited by the overload pre-protection strategy; when the temperature or current exceeds the overload protection threshold, the overload protection strategy is used to limit the output torque power.

[0013] In the overload pre-protection strategy, the output torque and power are limited according to the collected current and temperature data, and the torque and power limit range is smaller than the limit range under the overload protection strategy.

[0014] After determining to enter the overload pre-protection strategy, the overload progress P is calculated based on the collected current or temperature, and the corresponding power limit value is obtained according to the overload progress P corresponding to the calculated temperature or current, and the output power and torque are limited based on the power limit value.

[0015] The motor controller or vehicle controller calculates the corresponding overload progress P based on the temperature or current parameters of the electric drive system, and then the vehicle controller VCU starts to execute torque limitation.

[0016] In the overload pre-protection strategy, the calculation of the overload progress P is: P = k*t; where k is the pre-overload progress coefficient, and t is the time to enter the overload pre-protection stage.

[0017] In the overload pre-protection strategy, multiple overload pre-protection thresholds corresponding to temperature or current are set; the multiple overload pre-protection thresholds divide the overload pre-protection stage into multiple pre-overload level intervals, and each overload level interval is calibrated with a corresponding coefficient k.

[0018] When it is detected that the temperature or current value is within the pre-overload level interval, the corresponding coefficient k is obtained, and the overload progress P is calculated based on the coefficient k and the time of entering the interval.

[0019] The vehicle controller obtains the corresponding torque and power limit values ​​of the electric drive system according to the overload progress P and the current overload level, and performs limit control on the electric drive system based on the torque and power limit values.

[0020] A comparison table of pre-overload level-overload progress-power limit value is set in advance, and the current power limit value is obtained by looking up the table.

[0021] When the overload progress P calculated based on current or temperature is greater than the overload progress threshold, the VCU starts to execute torque limitation, and obtains the corresponding torque and power limit values ​​of the electric drive system according to the overload progress P and the current overload level;

[0022] When the overload progress P calculated based on current and temperature is greater than the overload progress threshold, the VCU performs power output control according to the minimum torque.

[0023] The advantages of the present invention are: performing protection parameter calculation (overload progress calculation) in advance and executing overload pre-protection can more effectively protect the electric drive system; the overload pre-protection adopts multi-gradient intelligent limitation, which can avoid cliff-like protection of the electric drive system and achieve a balance between power and comfort; without any hardware processing, the working characteristics of the electric drive system are optimized through software strategies, which can enable the electric drive to exert the characteristics between the rated and peak values ​​to a greater extent, and the cost is low, only the software cost exists, and it can be reused on different electric drives through software to reduce the implementation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The following is a brief description of the contents expressed in the drawings of the present invention and the symbols in the drawings:

[0025] Figure 1 It is the electric drive current overload progress rate diagram of the present invention;

[0026] Figure 2 It is a graph of the temperature overload progress rate of the electric drive of the present invention;

[0027] Figure 3 It is a torque limit diagram of the VCU of the present invention according to the electric drive current and temperature overload progress;

[0028] Figure 4 This is the overload pre-protection control flow chart of the present invention. DETAILED DESCRIPTION

[0029] The specific implementation of the present invention will be further explained in detail below by describing the optimal embodiment with reference to the accompanying drawings.

[0030] This embodiment provides an overload pre-protection control strategy, which refers to multiple electric drive system related parameters, and performs gradient parameter restrictions before the electric drive system operating parameters reach and exceed the overload protection threshold. It first enters the overload pre-protection, so that the motor operating parameters slowly tend to the overload protection threshold but do not reach the overload protection threshold, so that the electric drive system does not significantly reduce the output power. This enables the electric drive system to operate for a long time and at high power, bringing users an ultimate experience of comfort. The specific scheme is as follows Figure 1-4 As shown, an electric drive system overload protection method includes:

[0031] Collect temperature and / or current data corresponding to the electric drive system, either one or both of them can be collected;

[0032] Compare the temperature and / or current data with the preset temperature or current overload protection threshold and overload pre-protection threshold to determine whether to limit the output torque and power; the overload pre-protection threshold is less than the overload protection threshold; preset the temperature overload protection threshold and temperature overload pre-protection threshold corresponding to the temperature and the current overload protection threshold and current overload pre-protection threshold corresponding to the current. Then determine the protection state to be entered based on the real-time current voltage or current collected; wherein:

[0033] When the temperature or current exceeds the corresponding overload pre-protection threshold and is less than the overload protection threshold, the overload pre-protection strategy is used to limit the output torque power; when the temperature or current exceeds the overload protection threshold, the overload protection strategy is used to limit the output torque power. When the temperature or current exceeds the corresponding overload pre-protection threshold and is less than the overload protection threshold, the overload pre-protection stage is entered. In this stage, the overload pre-protection strategy is used to limit the torque of the electric drive to avoid overload. When the temperature or current exceeds the overload protection threshold, the overload protection stage is entered, and the overload protection strategy is used to limit torque protection.

[0034] In the overload pre-protection stage, the torque and power limits are smaller than those in the overload protection stage, that is, in the overload pre-protection strategy, the output torque and power are limited according to the collected current and temperature data, and the torque and power limits are smaller than those in the overload protection strategy. Before the electric drive system reaches multiple hardware overload protection fault levels, small torque and power limits are imposed in advance to reduce the overload progress and avoid entering the overload protection stage.

[0035] After determining to enter the overload pre-protection strategy, the overload progress P is calculated based on the collected current or temperature, and the corresponding power limit value is obtained according to the overload progress P corresponding to the calculated temperature or current, and the output power and torque are limited based on the power limit value.

[0036] The motor controller or vehicle controller calculates the corresponding overload progress P based on the temperature or current parameters of the electric drive system, and then the vehicle controller VCU starts to execute torque limitation.

[0037] In the overload pre-protection strategy, the calculation of the overload progress P is: P = k*t; where k is the pre-overload progress coefficient, and t is the time to enter the overload pre-protection stage.

[0038] In the overload pre-protection strategy, multiple overload pre-protection thresholds corresponding to temperature or current are set; multiple overload pre-protection thresholds divide the overload pre-protection stage into multiple pre-overload level intervals, and each overload level interval is calibrated with a corresponding coefficient k. When the temperature or current value is detected within the pre-overload level interval, the corresponding coefficient k is obtained, and the overload progress P is calculated based on the coefficient k and the time of entering the interval.

[0039] Then the vehicle controller obtains the corresponding torque and power limit values ​​of the electric drive system according to the overload progress P and the current overload level, and performs limit control on the electric drive system based on the torque and power limit values.

[0040] The maximum output current of the motor controller is 690A. Different levels of overload pre-protection thresholds can be formulated for this current threshold, and overload progress integration at different rates can be performed according to different overload pre-protection thresholds. The levels of current overload pre-protection thresholds in the overload pre-protection strategy are as follows:

[0041] 517A≤Pre-overload level 1<552A;

[0042] 552A≤Pre-overload level 2<620A;

[0043] 620A≤Pre-overload level 3<690A;

[0044] 690A≤Pre-overload level 4;

[0045] A parameter k is pre-calibrated for each level, and then the corresponding P can be obtained according to the level of the current collected in real time. Similarly, the temperature is divided into multiple levels according to the temperature threshold, and a k value is assigned to each level, and then the corresponding P value is calculated.

[0046] The vehicle controller pre-sets a comparison table of pre-overload level-overload progress-power limit value. The vehicle controller obtains the current power limit value by looking up the table according to the obtained vehicle progress P and pre-overload level, and then executes control to complete the power limitation.

[0047] When the overload progress P calculated based on current or temperature is greater than the overload progress threshold, the VCU starts to execute torque limitation, and obtains the torque and power limit values ​​of the corresponding electric drive system according to the overload progress P and the current overload level; when the overload progress P calculated based on current or temperature is greater than the overload progress threshold, the VCU performs power output control according to the minimum torque, so that when one of them exceeds the progress threshold, it means that the baseline of pre-protection has just been reached. At this time, the protection purpose is achieved through the strategy to avoid the escalation of overload; when both exceed the overload progress threshold, it means that the overload has a tendency to worsen, and a larger limit is used to achieve a smaller torque execution power to avoid temperature or current overlimit. When the torque limit values ​​calculated based on temperature and current are different, the larger limit value of torque and power limit is taken to limit the power torque, so as to achieve the purpose of protection.

[0048] The overload pre-protection strategy of the above scheme can protect against overload, reduce overload current and temperature, and further recover from overload. When the temperature and current still rise after the overload pre-protection strategy is executed due to a fault or other factors, and reach the overload protection threshold, the overload protection strategy is used to limit the torque and power. Under the overload protection strategy, multiple fault levels are set according to temperature or current, and the torque is greatly limited according to the fault level, thereby reducing the impact of temperature and high current on the electric drive system.

[0049] In this embodiment, the overload protection of the electric drive system is achieved by combining an overload pre-protection strategy with an overload protection strategy, wherein: by increasing the current and temperature overload progress parameter feedback of the electric drive system (including the motor and the motor controller), a vehicle torque reduction strategy, that is, an overload pre-protection strategy, is formulated, so that the electric drive system can provide power to the limit without causing the operating parameters to exceed the overload protection threshold of the "killer protection"; the killer protection strategy is the overload protection strategy, and in the overload protection strategy, by setting the overload protection threshold, when the electric drive system exceeds the standard operation, "killer protection" is performed to ensure that the electric drive system will not suffer irreversible damage; overload pre-protection, before the electric drive system reaches multiple overload protection fault levels of the hardware, a small amount of torque and power limitation is performed in advance to reduce the overload progress.

[0050] In this embodiment, the overload protection strategy is called a killer protection strategy. An overload protection threshold is set. When the electric drive system exceeds the standard, a "killer protection" is performed to ensure that the electric drive system will not be irreversibly damaged. The electric drive system (including the motor and the motor controller) current and temperature overload progress parameter feedback is increased to formulate a vehicle torque reduction strategy, that is, an overload pre-protection strategy, so that the electric drive system can provide power to the limit without causing the operating parameters to exceed the overload protection threshold of the "killer protection";

[0051] The design ideas of the embodiments of the present invention are as follows:

[0052] 1. The electric drive controller, vehicle controller or domain controller formulates a set of overload pre-protection thresholds that are different from the "killer protection" overload protection thresholds based on the design indicators of the electric drive system;

[0053] 2. Develop overload progress strategies with different rates for different overload pre-protection thresholds;

[0054] 3. Integrate the motor and electronic control temperature, current and time, and calculate the overload progress according to the overload progress rate strategy;

[0055] 4. Formulate overload progress---torque and power limit strategies: mainly formulate torque and power limits of different amounts (rates) for different overload progress;

[0056] 5. Execute overload pre-protection according to overload progress --- torque and power limitation strategy.

[0057] 6. Dynamically calculate the overload progress, and ultimately control the output torque of the electric drive system, that is, the output power of the electric drive system, to achieve the goal of reducing the MCU output phase current, the temperature of power devices such as IGBT / SIC, and the motor temperature.

[0058] "Killer Protection" overload protection threshold:

[0059] Existing electric drive systems, whether using AC permanent magnet synchronous motors or AC asynchronous motors, require the use of DC / AC converters, that is, electric drive controllers (inverters) that invert current and output it to the motor. Regardless of whether the motor is three-phase star-connected or delta-connected, there will be phase current.

[0060] Taking the AC permanent magnet synchronous motor as an example, the MCU output phase current can be Park transformed in FOC control and decomposed into D\Q axis current. Taking into account the iron loss and copper loss heating of the motor, a simple phase current-torque-temperature correspondence model can be formed.

[0061] Before the motor undergoes magnetic weakening, it is in the constant torque area. At this time, the phase current is large → the motor torque is large, and the motor generates a lot of heat, which can easily cause the current and temperature to exceed the design indicators of the motor and electronic control. In this regard, the motor controller or the vehicle controller sets current and temperature protection thresholds for the motor and electronic control. When the actual current and temperature exceed the threshold, the vehicle controller or the motor controller will request and respond to torque limitation, thereby reducing the electric drive operating current, and then reducing the electric drive temperature, thereby achieving the purpose of protecting the motor and electronic control.

[0062] Generally, a three-level overload protection threshold design is performed for current and temperature overload.

[0063] Level 1: general fault, only an alarm is given, and no restriction is made;

[0064] Level 2: Serious fault, alarm, and power limitation to 50% of the current power;

[0065] Level 3: The most serious fault, an alarm is given, and power is limited to 0;

[0066] The above is the general design of the overload protection threshold of the "killer protection". Generally, the thresholds of level 1, level 2, and level 3 are designed to be close, for example

[0067] The maximum physical temperature of the motor is 165°C.

[0068] Level 1: Generally, manufacturers will not set a level 1 alarm;

[0069] Level 2: Temperature ≥ 150°C will trigger a Level 2 alarm;

[0070] Level 3: Temperature ≥ 160°C will trigger a level 3 alarm;

[0071] This design results in:

[0072] 1. Level 1: In case of general failure, there is no limit, which will cause the over-limit progress to continue to deteriorate and trigger a level 2 serious failure;

[0073] 2. Level 2: In case of serious fault, the limit is large, which will cause the power of the whole vehicle to drop sharply;

[0074] 3. Level 3: In the most serious fault, the actual temperature of the motor is far from the actual tolerance temperature of the motor, which may cause problems such as demagnetization of the permanent magnet of the motor, aging of the insulation layer and leakage;

[0075] Overload pre-protection threshold, overload progress

[0076] In theory, the motor controller can collect the motor, electronic control current and temperature parameters to deal with overtemperature and overcurrent of the motor and electronic control, and make an overload progress curve through calculation, which can be sent out through the bus.

[0077] For example, the maximum output current of the motor controller is:

[0078] The maximum output current of the motor controller is 690A. Different levels of overload pre-protection thresholds can be formulated for this current threshold, and overload progress integration at different rates can be performed according to different overload pre-protection thresholds. For example:

[0079] Current overload pre-protection threshold:

[0080] 517A≤Pre-overload level 1<552A;

[0081] 552A≤Pre-overload level 2<620A;

[0082] 620A≤Pre-overload level 3<690A;

[0083] 690A≤Pre-overload level 4;

[0084] Current overload progress:

[0085] Overload progress rate 1: 517A ≤ pre-overload level 1 < 552A, start 180S overload progress integration, after 180s, the integration progress reaches 100% (k = 100 / 180);

[0086] Overload progress rate 2: 552A≤Pre-overload level 2<620A, start 120S overload progress integration, after 120s, the integration progress reaches 100% (k=100 / 120);

[0087] Overload progress rate 3: 620A≤Pre-overload level 3<690A, start 90S overload progress integration, after 90s, the integration progress reaches 100% (k=100 / 90);

[0088] Overload progress rate 4: 690A ≤ pre-overload level 4, start 60S overload progress integration, after 60s, the integration progress reaches 100% (k = 100 / 60);

[0089] The time required for the 0~100% overload progress under different overload currents is different, that is, the rate of overload progress (coefficient k) is different. For details, please refer to Figure 1 .

[0090] Another example is electricity and temperature (or electronically controlled temperature):

[0091] The maximum temperature of the motor is 165°C. Based on this temperature threshold, the overload pre-protection threshold and overload progress integral rate strategy can be formulated:

[0092] Temperature overload pre-protection threshold

[0093] 120℃≤Pre-overload level 1<130℃;

[0094] 130℃≤Pre-overload level 2<140℃;

[0095] 140℃≤Pre-overload level 3<150℃;

[0096] 150℃≤pre-overload level 4;

[0097] Temperature Overload Progress

[0098] Overload progress rate 1: 120℃≤Pre-overload level 1<130℃, start 180S overload progress integration, after 180s, the integration progress reaches 100% (k=100 / 180);

[0099] Overload progress rate 2: 130℃≤Pre-overload level 2<140℃, start 120S overload progress integration, after 120s, the integration progress reaches 100% (k=100 / 120);

[0100] Overload progress rate 3: 140℃≤Pre-overload level 3<150℃, start 90S overload progress integration, after 90s, the integration progress reaches 100% (k=100 / 90);

[0101] Overload progress rate 4: 150℃≤pre-overload level 4, start 60S overload progress integration, after 60s, the integrated progress reaches 100% (k=100 / 60);

[0102] From the above description, it can be seen that the time required for 0-100% overload progress at different overload temperatures is different, that is, the rate of overload progress (coefficient k) is different. For details, please refer to Figure 2 .

[0103] 4. Overload pre-protection

[0104] After describing the "killer protection" overload protection threshold, overload pre-protection threshold, and overload progress, start formulating the overload pre-protection strategy.

[0105] The basic principle is to detect the current and temperature parameters of the motor and electronic control through the motor controller or the vehicle controller, and calculate and compare them with the overload pre-protection threshold to form an overload progress, which is sent through the bus and received by the vehicle controller or the motor controller. The electric drive torque (power) is limited before the electric drive system reaches the overload protection threshold, thereby reducing the motor and electronic control current and ultimately controlling the motor and electronic control temperature.

[0106] The specific protection scheme is shown in the following case:

[0107] The motor controller or vehicle controller refers to the current overload progress and temperature overload progress of the electric drive to limit the torque (power) of the electric drive. Similar to the different integral rates of the current and temperature overload progress of the electric drive, the torque (power) limit can also be set at different rates, so that the performance and comfort of the vehicle or the power system can be taken into account;

[0108] Figure 3 In the design, when the overload progress of the electric drive system's current or temperature exceeds 60%, the electric drive torque is limited. When the torque limitation causes the electric drive current and temperature to fall below the overload progress integral condition, the overload progress integral falls, thereby achieving dynamic adjustment of the overload progress-torque limitation.

[0109] according to Figure 3When the electric drive current and temperature overload progress exceeds 60%, the VCU starts to request torque limit; when the electric drive current and temperature overload progress exceed 60% at the same time, the VCU executes according to the minimum torque limit.

[0110] When the overload progress cannot be effectively controlled and the overload progress reaches 100%, a Level 2 alarm will be triggered, entering the "killer protection" to achieve the final limit. Generally, by setting the limit parameters reasonably, the overload progress can be avoided from reaching 100%. The electric drive current and temperature overload progress can be issued by the motor control; the torque limit can be executed by the motor controller or the vehicle controller; the overload progress and torque limit rate can be set according to performance and comfort requirements.

[0111] In the transmission of the overload progress P, a communication protocol (translation mechanism) is first set. For example, the first and second bytes of the message sent by the CAN bus are the hexadecimal numbers 0x3FEE, which are converted to decimal 16366, and then multiplied by a precision coefficient of 0.00556, the result is 90.99, and then the symbol of the converted number is set to "%", and the final result is 90.99%. The reverse operation is to remove the sign of a percentage, and then divide it by the coefficient to get a decimal number, and then convert it to a hexadecimal number;

[0112] After the communication protocol is set, the electric control (motor controller) compares the current and temperature collected by the current sensor and temperature sensor with the threshold set by the controller's internal program. When the threshold is exceeded, the controller chip starts to integrate the time. For example, when the timing starts, the percentage is 0%. After 180s, the percentage integral is 100%. According to this proportional relationship, when the time integral reaches 163.79s, the corresponding percentage is 90.99%. According to this integral comparison table (that is, the electric drive temperature overload progress rate diagram, the horizontal axis is time, and the vertical axis is overload progress. This figure shows different integrals. With the time integration, the electronic controller calculates a value, such as 90.99. According to the setting of the communication protocol, the electronic controller divides this value by the coefficient 0.00556 to get the decimal number 16366, which is then converted into a hexadecimal number 0x3FEE. The hexadecimal number is then sent to the vehicle controller through the CAN bus. The vehicle controller translates it according to the agreement of the communication protocol, that is, converts the hexadecimal number into a decimal number, multiplies it by the coefficient and adds a sign, and finally translates it into 90.99%.

[0113] VCU performs torque limitation according to the received overload progress, such as 90.99%. The principle is: first, VCU will write a comparison table into the VCU program in advance (that is, the electric drive current, temperature overload progress torque limitation diagram, the horizontal axis is the overload progress, the vertical axis is the torque limit percentage, and it is converted into a two-dimensional table through a two-dimensional vector diagram), and this comparison table can be calibrated according to the driving evaluation; then VCU will look up the table according to the overload progress of 90.99% sent by the electronic control through the CAN bus, and the VCU will get the torque limit percentage of 80% at this time, and start to limit the torque (power) of the electric drive system, allowing the torque of the electric drive to be 80% of the current torque.

[0114] The technical principle of torque limitation by pre-overload in this embodiment is described as follows:

[0115] Pre-overload means to pre-judge the overload trend, rather than to protect after the killer protection threshold is actually triggered. This is also the main feature of the present invention, the pre-protection point. An overload pre-protection threshold is set before the overload protection threshold. When the overload protection threshold is reached, it means that the situation is very serious and should be handled quickly. At this time, it may cause damage to the electric drive system. Before reaching the overload protection threshold, in fact, before reaching close to the overload protection threshold, there may be risks. Before this, intervention control is required to avoid reaching the overload protection threshold as much as possible. Taking human blood pressure as an example, if the high pressure reaches 200, blood vessels will burst, then this 200 is the killer threshold. In order to perform pre-overload protection, pre-treatment is started when the high pressure reaches more than 140, instead of waiting until the high pressure reaches 200 for treatment. Moreover, according to the degree of high pressure, the treatment methods are also different. For example, if the high pressure is 145, it may be enough to stop smoking, stop drinking, and pay attention to rest. If the high pressure is 150, it may be necessary to use drug treatment. If the high pressure is 180, it may be necessary to be hospitalized for follow-up treatment (different levels, different overload progress, different treatment levels, and different torque limit amplitudes). This solution is to protect the electric drive system in advance through a pre-overload protection solution.

[0116] The invention provides protection in advance to prevent the current and temperature from reaching the critical protection point. The essential goal of the protection of the electric control and the motor is to control the temperature not to exceed the standard. The principle of temperature rise is that the current flowing through the conductor generates heat, that is, Q = I 2 *R*T, through the heat calculation formula, we can draw the following conclusions: 1. The accumulation of heat is proportional to the current flowing through the conductor, the resistance (impedance) of the conductor, and the time;

[0117] At a certain point in time or during a certain period of time: For the collection of motor temperature, an NTC resistor is placed inside the stator slot of the motor or at the end of the stator coil for temperature collection. For electronic control, the main temperature control is IGBT or SIC (power chip), and its temperature collection is generally carried out by placing NTC outside the core of the power component for collection or by calculation through algorithms (heat formula and other models). After the current flows through the conductor, the conductor generates heat due to its own resistance. The heat is then transferred to the sensor and then calculated by the chip with a lag (for example, through copper wire conduction, and the power chip conducts from the inside of the core to the outside). Therefore, combined with Conclusion 1, we can get Conclusion 2, that the generation and conduction of temperature lags behind the current. Therefore: According to Conclusion 2

[0118] 1) If the torque (power) limit is directly performed by collecting temperature, the temperature is not at the highest point when the protection starts, which means that the temperature may rise after the protection starts. This hysteresis will trigger a higher level of torque limit, and eventually lead to a cliff-like limit;

[0119] 2) The current is collected by the sensor (Hall or shunt) and uploaded to the controller. It is then filtered by the controller chip and other logical calculations to calculate the true effective value (RMS). This value is not constant, because the vehicle motor is different from the industrial motor in steady state operation. The road conditions and throttle are different, and the current of the vehicle motor changes in real time. If the current is directly collected to limit the torque (power), due to the real-time changes in the current, the future temperature curve is predicted directly through the heat formula through the model calculation, which will lag and have a large entropy value. However, if we divide the current into segments. For example, if the current between ≥517A and <552A is taken as the pre-overload level 1 threshold, for the current in this section, whether it is 517.8A or 532.9A, there is no need to differentiate the heat formula and then integrate the heat. Instead, the current in this section is associated with time. 0~180s is the main parameter for assessment. As long as the current falls within this section, according to the overload progress P=k*t, where the coefficient k=100 / 180, the overload progress is 50% after the integration time reaches 90s. The protection created in this way is more linear rather than random.

[0120] Similarly, the temperature is pre-overloaded and segmented, and segmented pre-protection is also performed for real-time changing temperatures, which has the same effect.

[0121] Why are different pre-overload sections (levels) set? How is the coefficient k corresponding to each level determined? In the front-end R&D calibration project, the motor and electronic control are measured on the dynamometer bench for current-time-temperature curve (there are many peripheral parameters, such as the inlet temperature, water flow, ambient temperature, wind speed, etc. of thermal management. Generally, during testing, all these influencing factors will be converted into one variable: cooling water inlet temperature). Through the measurement, multiple sets of data can be obtained. Through data analysis, it can be known how long the temperature of the motor and electronic control will reach in a certain current section. After this measurement, different current sections, different time sections, and temperature rising trends can be clarified. Through this data, the current section and coefficient k of the pre-overload protection can be formulated. Therefore, in the method provided by this patent, the overload progress coefficient k can be calibrated for different motors and electronic controls;

[0122] After the VCU obtains the overload progress, how is the torque (power) limit coefficient k of the VCU formulated? This is also a calibrable quantity, because this limit coefficient affects the vehicle's power and protection effect. For example, if the overload progress reaches 70%, the VCU limits the torque to 90, and the power does not decrease much, but it will cause the temperature to drop slowly, or even the temperature to continue to rebound. If the overload progress reaches 70%, the VCU limits the torque to 50%, which immediately reduces the current, and the temperature drops quickly, but the power also decreases a lot. Therefore, the VCU's limit coefficient is a calibrable quantity. The reference factors for calibration are strongly related to driving ratings, operating scenarios, and electric drive system characteristics. This is a back-end R&D calibration project. Through calibration, a set of suitable k value curves is finally evaluated. The k value mentioned above has the slope k of the current overload progress curve ( Figure 1 ), with temperature overload progress curve slope k( Figure 2 ), with torque limit curve slope k( Figure 3 ), can be calibrated.

[0123] Obviously, the specific implementation of the present invention is not limited to the above-mentioned methods. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention, they are all within the protection scope of the present invention.

Claims

1. An electric drive system overload protection method, characterized in that: include: Collect temperature and / or current data corresponding to the electric drive system; Compare the temperature and / or current data with the preset temperature or current overload protection threshold and overload pre-protection threshold to determine whether to limit the output torque and power; The overload pre-protection threshold is less than the overload protection threshold; When the temperature or current exceeds the overload pre-protection threshold and is less than the overload protection threshold, the output torque power is limited by the overload pre-protection strategy; when the temperature or current exceeds the overload protection threshold, the overload protection strategy is used to limit the output torque power.

2. The electric drive system overload protection method according to claim 1, characterized in that: In the overload pre-protection strategy, the output torque and power are limited according to the collected current and temperature data, and the torque and power limit range is smaller than the limit range under the overload protection strategy.

3. An electric drive system overload protection method according to claim 1 or 2, characterized in that: After determining to enter the overload pre-protection strategy, the overload progress P is calculated based on the collected current or temperature, and the corresponding power limit value is obtained according to the overload progress P corresponding to the calculated temperature or current, and the output power and torque are limited based on the power limit value.

4. The electric drive system overload protection method according to claim 3, characterized in that: The motor controller or vehicle controller calculates the corresponding overload progress P based on the temperature or current parameters of the electric drive system, and then the vehicle controller VCU starts to execute torque limitation.

5. An electric drive system overload protection method according to any one of claims 2 to 4, characterized in that: In the overload pre-protection strategy, the calculation of the overload progress P is: P = k*t; where k is the pre-overload progress coefficient, and t is the time to enter the overload pre-protection stage.

6. The electric drive system overload protection method according to claim 5, characterized in that: In the overload pre-protection strategy, multiple overload pre-protection thresholds corresponding to temperature or current are set; the multiple overload pre-protection thresholds divide the overload pre-protection stage into multiple pre-overload level intervals, and each overload level interval is calibrated with a corresponding coefficient k.

7. An electric drive system overload protection method according to claim 6, characterized in that: When it is detected that the temperature or current value is within the pre-overload level interval, the corresponding coefficient k is obtained, and the overload progress P is calculated based on the coefficient k and the time of entering the interval.

8. An electric drive system overload protection method according to claim 6 or 7, characterized in that: The vehicle controller obtains the corresponding torque and power limit values ​​of the electric drive system according to the overload progress P and the current overload level, and performs limit control on the electric drive system based on the torque and power limit values.

9. An electric drive system overload protection method according to claim 8, characterized in that: A comparison table of pre-overload level-overload progress-power limit value is set in advance, and the current power limit value is obtained by looking up the table.

10. The electric drive system overload protection method according to claim 8, characterized in that: When the overload progress P calculated based on current or temperature is greater than the overload progress threshold, the VCU starts to execute torque limitation, and obtains the corresponding torque and power limit values ​​of the electric drive system according to the overload progress P and the current overload level; When the overload progress P calculated based on current and temperature is greater than the overload progress threshold, the VCU performs power output control according to the minimum torque.

Images