CN114123934B - Electric drive system locked rotor protection method based on current integration - Google Patents

Abstract

The invention discloses a current integration-based locked-rotor protection method of an electric drive system, which comprises the steps of judging that the rotating speed of a motor is in a locked-rotor rotating speed range, enabling a product to enter locked-rotor, and identifying the maximum value of three-phase current; if the maximum value of the three-phase current is greater than the current limit value I1, accumulating and integrating the current; if the current integral value is greater than the integral limit value sigma 1, the torque output needs to be limited; if the three-phase current maximum value is smaller than the current limit value I2, performing integration of the current in a cumulative manner; if the current integration value is smaller than the integration limit value σ2, the torque output can be appropriately increased. The invention considers the relation between torque and current, and also considers that the electrical angle is unchanged during locked-rotor, the three-phase current is output in a direct current form, and the phase with the largest current in the three phases generates the most serious heat and is most easily damaged, so that the maximum value in the three-phase current is integrated when the locked-rotor occurs, and the product performance can be exerted to the maximum extent on the premise of ensuring the product safety.

Description

Stall protection method for electric drive system based on current integration

Technical Field

The invention relates to the field of motor protection, and in particular to a stall protection method for an electric drive system based on current integration.

Background technique

The working principle of the electric drive system is to generate three-phase AC power by switching and chopping the DC bus voltage by controlling the IGBT according to the change of electrical angle. The magnetic field synthesized by the three-phase AC power interacts with the magnetic field of the motor rotor to drive the rotor to rotate by using the principle of electromagnetism. Electric vehicles have their own gravity and tire friction. Only when the driving force overcomes gravity and friction can the vehicle move forward. The electronic control industry calls the process of outputting torque from the motor to the motor to make it rotate as stalling. During stalling, because the electrical angle of the motor does not change, the duty cycle of the three-phase IGBT switch chopping remains unchanged, and the three-phase current is output in almost DC form. If the product does not have stall protection measures, this working condition is very likely to cause IGBT damage or motor burnout.

The stall protection function is essential for the safe use of the product. A good stall protection function can not only ensure product safety, but also maximize product performance.

In patent document 1 "A motor stall protection method for an electric vehicle electric drive system" (application number: 201110180484.9), the torque from 0 to the maximum torque is divided into more than 3 torque intervals in order from small to large, and a predetermined stall time T is set for each torque interval. The motor controller detects the motor speed and torque in real time, and starts timing when the motor speed is in the stall speed judgment interval. If the motor is in the stall speed judgment interval for a duration t greater than or equal to the predetermined time T corresponding to the torque, it is determined that the motor has been stalled. After the motor is stalled, the motor controller no longer pays attention to the torque demand of the accelerator pedal. The motor controller gradually unloads the motor torque according to the predetermined value, and starts to re-detect the motor speed and torque and timing after each unloading of the motor torque. If the motor is still in a stalled state, the motor torque continues to be unloaded until it is detected that the motor is in a non-stalled state.

In Patent Document 2, "A method for stall protection and torque limiting of an electric drive system" (Application No.: 201110238218.7), the motor is protected from stalling according to the motor stall torque protection characteristic curve, thereby limiting the motor torque output; the output torque of the electric drive system is limited according to the inverter temperature torque limit characteristic curve; the power output is limited according to the inverter temperature overcurrent capability curve, and the current limit is converted to the limit on the motor output torque; the maximum output torque of the output torque electric drive system obtained according to the stall protection and temperature torque limit is limited;

In patent document 3 "A method for stall protection of electric vehicle drive system based on threshold value" (application number: 201710366887.X), stall protection is performed when the motor speed is less than its lower limit threshold value and the motor torque command from the vehicle controller is greater than its upper limit value; and when the motor speed is greater than its upper limit value, or the motor torque command is less than its lower limit threshold value, the stall protection is exited; when the motor speed is less than its lower limit threshold value, the relationship between the motor power module temperature and its threshold value is further determined; after entering the stall protection, the corresponding torque limit threshold value is determined according to the different relationships between the power module temperature and the threshold value, and the motor torque command is limited to below the threshold value to obtain the actual execution torque of the motor.

In patent document 4 "A stall protection method, device, vehicle and storage medium for a motor system" (application number: 201911016513.0), the corresponding current overload coefficient is calculated based on the torque overload coefficient and stall torque coefficient of the motor system and the conversion relationship between torque and current; if the accumulated heat of the motor system exceeds the heat calibration upper limit, the preset derating factor is used to adjust the operating torque of the motor system.

In patent document 5 "Motor Stall Protection System, Method and Motor" (application number: 202010043456.1), when the power device temperature is <C1, the peak torque continues to stall, and the first safety time D1 for continuous stalling under C1 is set. When the continuous stalling time exceeds D1, the first level over-temperature fault is triggered, and the peak torque is reduced to A2 to maintain output; when the temperature of the power device is ≧C1, the carrier frequency is reduced to B, and the peak torque is continued.

In patent document 6 "A stall protection system and method for a motor drive controller for an electric vehicle" (application number: 202010043456.1), the motor speed is preset according to the upper and lower thresholds to determine whether it has entered a stall state, and considering the IGBT loss, the first switching frequency and the second switching frequency of the IGBT are set to achieve stall frequency reduction protection; in the high temperature zone, according to the first entry into the stall flag, the motor execution torque is controlled in sections by judging the IGBT temperature; in the low temperature zone, the upper and lower thresholds are preset according to the collected IGBT temperature, and the motor output torque is controlled by linear interpolation; according to the stall flag, the speed stall flag, the IGBT temperature setting value and the torque limit, different loading/unloading rates are set to control the motor output torque.

The above existing stall protection technologies basically first determine whether the motor enters a stall condition based on the motor speed, and then limit the torque output based on the torque execution time or whether the motor temperature or IGBT temperature exceeds the set value to achieve the purpose of protecting the product.

Patent documents 1, 2, and 4 limit torque output based on torque execution time. Limiting torque output based on torque execution time requires dividing the torque into intervals. If there are too few torque intervals, the torque difference between the two ends of the interval is too large. Because the torque of the entire torque interval must be guaranteed to work safely within the set time, the working time of the small torque in the interval will be shortened, resulting in the product performance not being fully utilized. Even if there are enough torque intervals, there will be a margin for product performance because the heat generation of products with the same torque but different electrical angles is different.

Patent documents 3, 5, and 6 limit torque output based on motor temperature and IGBT temperature. Limiting torque output based on motor temperature and IGBT temperature will cause product damage due to untimely protection if the temperature sensor is not embedded in the phase with the highest heat generation, and will also leave a margin for product performance. Although this can be solved by increasing the number of sensor embedding points, this will inevitably increase product costs.

Summary of the invention

The purpose of the present invention is to provide an electric drive system stall protection method based on current integration, which can maximize the performance of the product when a stall occurs while ensuring product safety and not increasing product costs.

The technical solution of the present invention is:

The electric drive system stall protection method based on current integration comprises the following steps:

S1. Select the maximum value Imax among the three-phase currents Ia, Ib, and Ic of the electric drive system;

S2, judging whether the maximum value Imax of the three-phase current is greater than the current limit I1, if Imax> I1, then accumulating and integrating the maximum value Imax of the three-phase current;

S3. Determine whether the accumulated integral value σ is greater than the integral limit σ1. If σ>σ1, limit the torque output.

Preferably, in step S2, if the maximum three-phase current value Imax is not greater than the current limit value I1, then proceed to steps S4 and S5:

S4, judging whether the maximum value Imax of the three-phase current is less than the current limit I2, if Imax<I2, performing a cumulative subtraction integral on the maximum value Imax of the three-phase current;

S5. Determine whether the accumulated integral value σ' is less than the integral limit σ2. If σ'<σ2, increase the torque output.

Preferably, before entering step S1, step S0 is first performed:

S0, determining whether the motor speed is within the stall speed range, if it is within the stall speed range, executing the stall protection measures of steps S1-S5, if it is not within the stall speed range, exiting the stall protection measures.

Preferably, in step S1, the maximum value Imax among the three-phase currents Ia, Ib, and Ic is the maximum value of the absolute values of the three-phase currents.

Preferably, the current limit value I2<current limit value I1, and the integral limit value σ2<integral limit value σ1.

The advantages of the present invention are:

The electric drive system stall protection method based on current integration of the present invention protects the product based on the consideration of total heat generation. In addition to considering the relationship between torque and current, it also takes into account that the electrical angle remains unchanged during stall, the three-phase current is output in the form of direct current, and the phase with the largest current among the three phases generates the most serious heat and is most easily damaged. Therefore, when stall occurs, the maximum value of the three-phase current is integrated, so that the product performance can be maximized while ensuring product safety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of a method for electric drive system stall protection based on current integration according to the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

The working principle of the solution of the present invention is similar to that of Patent Document 4, both of which are based on the consideration of total heat to protect the product, but Patent Document 4 only considers the relationship between torque and current, and does not consider the imbalance of the three-phase current during stalling, uneven heating inside the product, and the inability to maximize the product performance in order to protect the product from damage. The solution of the present invention integrates the maximum value of the three-phase current when stalling occurs, so that the product performance can be maximized while ensuring product safety.

As shown in FIG1 , the electric drive system stall protection method based on current integration of the present invention comprises the following steps:

S0, determining whether the motor speed is within the stall speed range, if it is within the stall speed range, executing the stall protection measures of steps S1-S5, if it is not within the stall speed range, exiting the stall protection measures.

S1. Select the maximum value Imax among the absolute values of the three-phase currents Ia, Ib, and Ic of the electric drive system.

S2. Determine whether the maximum three-phase current value Imax is greater than the current limit value I1. If Imax> I1, that is, the product will be in danger of burning if it continues to work under this current, then the maximum three-phase current value Imax is accumulated and integrated, and the process goes to step S3; if the maximum three-phase current value Imax is not greater than the current limit value I1, then the process goes to steps S4 and S5.

S3. Determine whether the accumulated integral value σ is greater than the integral limit σ1. If σ>σ1, it means that if this working condition continues to be executed, there is a risk of product burning. In order to ensure the product, the torque output needs to be limited.

S4. Determine whether the maximum three-phase current value Imax is less than the current limit value I2, where the current limit value I2<current limit value I1; if Imax<I2, that is, the product can continue to work under this current without the risk of burning, then the maximum three-phase current value Imax is cumulatively decremented.

S5. Determine whether the accumulated integral value σ' is less than the integral limit σ2, where the integral limit σ2<integral limit σ1; if σ'<σ2, it means that the product is far away from the dangerous working condition and is in a safe range, and the torque output can be appropriately increased.

The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any modifications made according to the spirit of the main technical solution of the present invention should be included in the protection scope of the present invention.

Claims (4)

1. A method for stall protection of an electric drive system based on current integration, characterized in that it comprises the following steps: S1. Select the maximum value Imax among the three-phase currents Ia, Ib, and Ic of the electric drive system; S2, judging whether the maximum value Imax of the three-phase current is greater than the current limit I1, if Imax> I1, then accumulating and integrating the maximum value Imax of the three-phase current; S3, judging whether the accumulated integral value σ is greater than the integral limit σ1, if σ>σ1, limiting the torque output; In step S2, if the maximum value Imax of the three-phase current is not greater than the current limit I1, then proceed to steps S4 and S5: S4, judging whether the maximum value Imax of the three-phase current is less than the current limit I2, if Imax<I2, performing a cumulative subtraction integral on the maximum value Imax of the three-phase current; S5. Determine whether the accumulated integral value σ' is less than the integral limit σ2. If σ'<σ2, increase the torque output. 2. The electric drive system stall protection method based on current integration according to claim 1, characterized in that step S0 is first performed before entering step S1: S0, determining whether the motor speed is within the stall speed range, if it is within the stall speed range, executing the stall protection measures of steps S1-S5, if it is not within the stall speed range, exiting the stall protection measures. 3. The electric drive system stall protection method based on current integration according to claim 1 is characterized in that, in step S1, the maximum value Imax among the three-phase currents Ia, Ib, and Ic is the maximum value of the absolute values of the three-phase currents. 4. The electric drive system stall protection method based on current integration according to claim 1, characterized in that the current limit I2<current limit I1, the integration limit σ2<integration limit σ1.