EPS motor control DC-LINK temperature estimation method

Abstract

The invention relates to the technical field of steering systems, in particular to an EPS motor control DC-LINK temperature estimation method. The specific process comprises the following steps: S1, calculating a ripple current when an EPS motor controls DC-LINK to work; s2, obtaining the real-time equivalent series resistance of the EPS motor under different working conditions for controlling the DC-LINK; s3, calculating the real-time dissipation power of the EPS motor for controlling the DC-LINK to work; s4, obtaining a temperature rise curve of the EPS motor control DC-LINK under a specific condition through an experimental test; s5, calculating transient thermal resistance; s6, calculating the core temperature rise of the capacitor; and S7, calculating the actual temperature. Compared with the prior art, the EPS motor control DC-LINK temperature estimation method provided by the invention has the advantages that the EPS motor operation state parameters and the motor control temperature are calculated, and the DC-LINK real-time temperatures of the steering system under different operation conditions are estimated in combination with test data, so that a power-assisted motor control strategy is adjusted according to the DC-LINK real-time temperatures; and it is ensured that the steering system cannot be burnt out due to the too high DC-LINK temperature, and therefore the reliability and safety of operation of the steering system are improved.

Description

Technical Field

[0001] The invention relates to the technical field of steering systems, in particular to a method for estimating temperature of a DC-LINK controlled by an EPS motor. Background Art

[0002] The ability of the car steering system to correctly execute the driver's steering intention is an important guarantee for ensuring the safe driving of the car. For the electric power steering system, ensuring the safe and reliable operation of the electronic components related to the motor control is the basis. Among them, DC-LINK (DC link capacitor) is an important component connecting the power supply and the three-phase bridge of the power motor control. Its main function is to limit the fluctuation of the power bus voltage within a certain range and prevent the bus voltage from causing damage to other electronic components (such as MOSFET) due to excessive instantaneous fluctuations. Therefore, it is crucial for accurate and safe control of the motor, but DC-LINK is a component with relatively weak reliability in the motor control system.

[0003] The failure of DC-LINK is mainly due to excessive power dissipation, which causes the device temperature to rise too high and burn out. At the same time, due to the harsh working environment temperature of the steering gear, higher requirements are placed on its operating reliability. Generally, the operating temperature of DC-LINK is not allowed to exceed 125℃. Therefore, the temperature of DC-LINK must be monitored in real time to prevent it from failing due to overheating, which will affect the normal operation of the steering system and then affect the driving safety of the vehicle. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a method for estimating the temperature of a DC-LINK controlled by an EPS motor, which can avoid failure of the DC-LINK due to overheating when the vehicle is running, thereby improving the reliability and safety of the vehicle steering system control.

[0005] In order to achieve the above purpose, a method for estimating the temperature of the EPS motor control DC-LINK is designed, which is characterized by: the specific process is as follows:

[0006] S1, calculates the ripple current of the EPS motor control DC-LINK when it is working according to the motor working state parameters, including the real-time phase current, phase voltage, bus voltage, modulation ratio and power factor of the EPS motor control;

[0007] S2, calculate the relationship between the equivalent series resistance of the EPS motor control DC-LINK and the operating temperature, the switching frequency of the three-phase bridge and the working time, and obtain the real-time equivalent series resistance of the EPS motor control DC-LINK under different working conditions by combining the above relationship;

[0008] S3, combining the EPS motor control DC-LINK ripple current and the real-time equivalent series resistance to calculate the real-time power dissipation of the EPS motor control DC-LINK;

[0009] S4, obtain the temperature rise curve of EPS motor control DC-LINK under specific conditions through experimental testing;

[0010] S5, using Foster thermal network model to fit the transient thermal resistance of the EPS motor control DC-LINK during operation;

[0011] S6, calculating the capacitor core temperature rise when the EPS motor control DC-LINK is working according to the real-time dissipated power and transient thermal resistance of the EPS motor control DC-LINK;

[0012] S7, combining with the internal temperature sensor of the EPS motor control, calculates the core temperature rise of the EPS motor control DC-LINK and obtains the actual temperature of the EPS motor control DC-LINK.

[0013] In step S1, the calculation process of the ripple current effective value Irms of the EPS motor control DC-LINK is as follows:

[0014] S11, obtaining the average phase voltage Um and bus voltage Udc controlled by the EPS motor according to the motor operation state parameters;

[0015] S12, calculate the modulation degree

[0016] S13, obtaining the vector currents Id and Iq of the dq axes in the EPS motor control;

[0017] S14, calculate the effective value of phase current

[0018] S15, according to the relationship between the ripple current effective value of the EPS motor control DC-LINK and various parameters of the EPS motor control: Combining the formulas of step S12 and step S14, we can deduce Among them, I0 is the effective value of phase current, M is the modulation index, is the power factor.

[0019] In step S2, the calculation process of the equivalent series resistance value RESR of the EPS motor control DC-LINK is as follows:

[0020] S21, according to the equivalent series resistance value R of EPS motor control DC-LINK ESR The curve relationship with the EPS motor control working frequency f is fitted into the formula: Among them, M is the frequency constant, N is the frequency coefficient, Q is the frequency index, and e is the natural index;

[0021] S22, according to the equivalent series resistance value R of the EPS motor control DC-LINK ESR The curve relationship with the EPS motor control working temperature T is fitted into the formula: R ESR (T) = C + D · 10 (F·T) ; Where C is the temperature constant, D is the temperature coefficient, and F is the temperature index;

[0022] S23, according to the equivalent series resistance value R of the EPS motor control DC-LINK ESR The curve relationship with the EPS motor control working time t is fitted into the formula: R ESR (t) = H + A·log (B·t) ; Where H is the time constant, A is the time coefficient, B is the time index, and e is the natural index;

[0023] S24, according to the formulas of step S21, step S22, and step S23, comprehensively obtain R ESR =G(f, T, t); where G represents a function related to frequency, temperature and time.

[0024] In step S3, the calculation formula of the real-time power dissipation of the EPS motor control DC-LINK is: Where P is the power dissipation of the EPS motor control DC-LINK, I rms is the effective value of the ripple current, R ESR is the equivalent series resistance value.

[0025] In step S5, the calculation formula of the transient thermal resistance when the EPS motor controls the DC-LINK is: τ i =R i C i ; Among them, R i is the thermal resistance coefficient, τ i is the time constant, C i Thermal melting coefficient, t is the working time of EPS motor control.

[0026] In step S6, the calculation formula of the capacitor core temperature rise when the EPS motor controls the DC-LINK is: ΔT = P·Z th ; Where P is the power dissipation of the EPS motor control DC-LINK, Z th It is the transient thermal resistance of EPS motor control DC-LINK when it is working.

[0027] In step S7, the calculation formula of the actual temperature of the EPS motor control DC-LINK is: T c =ΔT+T a; Among them, ΔT is the capacitor core temperature rise when the EPS motor controls the DC-LINK, T a The ambient temperature when the EPS motor controls the DC-LINK.

[0028] Compared with the prior art, the present invention provides a method for estimating the DC-LINK temperature of an EPS motor control. By calculating the EPS motor operating state parameters and the motor control temperature and combining the test data, the real-time temperature of the DC-LINK of the steering system under different operating conditions is estimated, so that the power-assisting motor control strategy is adjusted according to the real-time temperature of the DC-LINK, ensuring that the steering system will not burn out due to excessively high DC-LINK temperature, thereby improving the reliability and safety of the steering system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of EPS motor control architecture.

[0030] Figure 2 Schematic diagram of ideal capacitance and actual capacitance.

[0031] Figure 3 This is the structural diagram of the vector control of the steering gear power motor.

[0032] Figure 4 It is a schematic diagram of the process of the present invention.

[0033] Figure 5 R is the equivalent series resistance value of the EPS motor control DC-LINK ESR The relationship curve diagram with the EPS motor control operating frequency f.

[0034] Figure 6 R is the equivalent series resistance value of the EPS motor control DC-LINK ESR The relationship curve between the EPS motor control operating temperature T.

[0035] Figure 7 R is the equivalent series resistance value of the EPS motor control DC-LINK ESR The relationship curve between the working time t of the EPS motor control.

[0036] Figure 8 The figure is a relationship curve diagram of the equivalent series resistance value RESR of the EPS motor control DC-LINK under different working hours, the EPS motor control working frequency f and the EPS motor control working temperature T.

[0037] Fig. 9 This is the temperature rise curve of the EPS motor control DC-LINK under specific working conditions.

[0038] Fig.10This is the transient thermal resistance curve of the EPS motor control DC-LINK under specific working conditions.

[0039] Fig.11 This is the structure diagram of the fifth-order Foster thermal network model.

[0040] Fig.12 It is a comparison chart of the calculation results of the present invention and the actual test results. DETAILED DESCRIPTION

[0041] The present invention will be further described below with reference to the accompanying drawings.

[0042] like Figure 1 As shown in FIG. 1 , it is a schematic diagram of the EPS motor control architecture, and its control architecture mainly consists of electronic and electrical components including at least one inductor 13, a power chip 14, a control unit 15, a MOS tube 16, a pre-drive chip 17, a DC-LINK capacitor 18, a three-phase bridge 19, a phase separator 19 and a three-phase motor 20. After the vehicle power supply 22 passes through the filter circuit (inductor 13 and DC-LINK capacitor 18), it provides 12V DC power to the entire steering system. The power chip 14 is responsible for allocating and managing the voltage input of each component. The electronic control unit 15 is responsible for coordinating the power output of the steering system based on the received signal, and drives the three-phase motor 21 to provide power for the system after power amplification through the pre-drive chip 17. In order to reduce the failure rate of the steering system losing power, by adding a phase separator 20, the three-phase motor can still operate after a single-phase failure. At the same time, in order to prevent the failure of the steering system components caused by the reverse connection of the vehicle power supply, a reverse polarity protector MOS tube 16 is introduced to increase the robustness of the steering system.

[0043] Among them, the electronic component DC-LINK capacitor 18 is an important component connecting the power supply and the three-phase bridge for power-assisted motor control. Its main function is to limit the fluctuation of the power bus voltage within a certain range to prevent the instantaneous fluctuation of the bus voltage from being too large and causing damage to other electronic components (such as MOSFET). Therefore, it is crucial to the accurate and safe control of the motor. However, DC-LINK is a component with relatively weak reliability in the motor control system. Its failure is mainly due to excessive dissipated power causing the device temperature to rise too high and thus burn out. Therefore, the temperature of DC-LINK must be monitored in real time to prevent it from failing due to overheating.

[0044] like Figure 2 As shown in the figure, it is a schematic diagram of ideal capacitor and actual capacitor. The ideal capacitor only has capacitance, but the actual capacitor will generate inductance between the pins and between the two stages of the capacitor, that is, Figure 2 The equivalent series inductance (ESL) shown in the figure; in addition, resistance (ESR) will also be generated between the actual capacitor pins and between the two capacitor stages, that is, Figure 2The equivalent series resistance shown in the figure is: ESL mainly depends on the type and package of the capacitor. The circuits that need to consider ESL are generally high-speed circuits with high signal frequencies, while the influence of ESL can be ignored in ordinary circuits. ESR mainly depends on the operating temperature, operating frequency and wire resistance of the capacitor. ESR not only affects the filtering effect and causes high-frequency signal attenuation, but also generates power consumption.

[0045] From the above analysis, we can know that the actual DC-LINK capacitor will generate power consumption due to the existence of ESR, and the dissipated power mainly depends on the ripple current passing through the DC-LINK and the size of the ESR. The dissipated power calculation formula is: Where P is the power dissipation of the EPS motor control DC-LINK, I rms is the effective value of the ripple current, R ESR is the equivalent series resistance value.

[0046] Because I rms The ripple current mainly depends on the EPS motor control state parameters, including the real-time phase current, phase voltage, bus voltage, modulation ratio and power factor of the EPS motor control. Therefore, in order to calculate I rms The above EPS motor control related parameters need to be obtained.

[0047] like Figure 3 The figure shows the structure diagram of the vector control of the power steering motor, which mainly adopts a dual closed-loop structure of speed and current. In the EPS motor control system, the rotor position sensor (RPS) detects the position of the rotor magnetic pole in real time, and can obtain the absolute position of the rotor and the actual speed of the motor. The difference between the speed reference and the speed feedback is adjusted by the ASR to obtain the current loop dq axis current setting; the phase current detected by the current sampling resistor is transformed by Clarke and Park to obtain the feedback stator current I d and I q The current loop reference and feedback difference are transformed by ACR and Park inverse transformation to obtain the voltage reference in the α-β coordinate system, and then the desired gate PWM signal is generated through SVPWM technology to the inverter. When the EPS motor parameters are determined, the electromagnetic torque is only related to the current I d and I q Related, through I d and I q Independent control of the permanent magnet motor can achieve precise control of the torque.

[0048] Therefore, the DC-LINK ripple current can be obtained by calculating the EPS motor power output control parameters during the operation of the steering gear. The relationship between the effective value of the DC-LINK ripple current and the motor control parameters is as follows: Among them, I 0is the effective value of the phase current, I d ,I q is the vector current of dq axis in EPS motor control; M is the modulation index, U m is the average phase voltage of EPS motor control, U dc is the bus voltage value controlled by the EPS motor, is the power factor (the maximum value for permanent magnet synchronous motor is 0.95).

[0049] In summary, it can be deduced that:

[0050] A large number of experimental results and theoretical analysis show that the value of the DC-LINK equivalent series resistance (ESR) is related to the DC-LINK operating frequency f, operating temperature T and operating time t. Therefore, in order to accurately obtain the DC-LINK equivalent series resistance value, it is necessary to calculate the relationship between ESR and the operating frequency f, operating temperature T and operating time t respectively, and combine the three to obtain the equivalent series resistance of the DC-LINK under different conditions.

[0051] like Figure 5 As shown in the figure, it is a curve diagram of the relationship between the equivalent series resistance RESR of a certain type of DC-LINK and the operating frequency. From the results in the figure, it can be seen that as the operating frequency increases, RESR gradually decreases, and when the frequency is low, RESR is more sensitive to the change of frequency, while when the frequency is high, RESR basically does not change with the change of frequency. Assume that RESR and the operating frequency f can be expressed by the following formula: By using the formula Figure 5 By fitting the data of the curve, the values ​​of parameters M, N and Q can be obtained, and then the calculation expression of RESR and working frequency f of the DC-LINK can be obtained. M is the frequency constant, N is the frequency coefficient, Q is the frequency index, e is the natural index, and the specific values ​​of parameters M, N and Q are shown in Table 1.

[0052] Table 1

[0053] M(mΩ) N(mΩ) Q(1 / HZ) -0.49 5.91 -0.06

[0054] like Figure 6 As shown in the figure, it is a curve diagram of the relationship between the equivalent series resistance RESR of a certain type of DC-LINK and the operating temperature T. The results in the figure show that the higher the operating temperature of the DC-LINK, the smaller the equivalent series resistance RESR is, and the trend of RESR reduction slows down as the temperature continues to rise. Assume that RESR and the operating temperature T can be expressed by the following formula: ESR (T) = C + D · 10 (F·T) , by using the formula Figure 6By fitting the data of the curve, the values ​​of parameters C, D and F can be obtained, and then the calculation expression of RESR and operating temperature T of the DC-LINK can be obtained. C is the temperature constant, D is the temperature coefficient, and F is the temperature index. The specific values ​​of parameters C, D and F are shown in Table 2.

[0055] Table 2

[0056] C(mΩ) D(mΩ) F(1 / ℃) 161.9 129 -0.028

[0057] like Figure 7 As shown in the figure, it is a relationship diagram between the equivalent series resistance RESR of a certain type of DC-LINK and the working time t. The results in the figure show that the value of the equivalent series resistance RESR of the DC-LINK gradually increases with the increase of working time, and the trend of RESR increase slows down with the increase of working time. Since the increase of working time will cause the DC-LINK to degrade, and the degradation is mainly caused by the chemical reaction inside the DC-LINK, according to the Aron Unis model, it can be assumed that RESR and working time t can be expressed by the following formula: R ESR (t) = A·e (B·t) , by using the formula Figure 7 By fitting the data of the curve, the values ​​of parameters A and B can be obtained, and the calculation expression of RESR and working time t of the DC-LINK can be obtained. H is the time constant, A is the time coefficient, B is the time index, e is the natural index, and the specific values ​​of parameters A and B are shown in Table 3.

[0058] Table 3

[0059] H(mΩ) A(mΩ) B(1 / h) 0.19 55.36 0.22

[0060] Since the working conditions of DC-LINK are relatively complex, it may operate at different frequencies and temperatures within its service life. As the working conditions change, the equivalent series resistance RESR of DC-LINK will also change greatly, which will affect the power dissipation of DC-LINK during operation. Therefore, it is necessary to calculate the real-time equivalent series resistance RESR of DC-LINK under different operating conditions. Since the relationship between equivalent series resistance RESR and operating frequency f, operating temperature T and operating time t is known, the numerical calculation formula of equivalent series resistance RESR under different operating conditions is obtained through mathematical operation: R ESR =G(f, T, t), where G is a function related to frequency, temperature and time.

[0061] like Figure 8As shown in the figure, it is a relationship curve diagram of the equivalent series resistance RESR, the operating frequency f and the operating temperature T under different working time conditions. By using this graph, the RESR of the DC-LINK under specific working time, working temperature and working frequency can be obtained, which lays the foundation for calculating the dissipated power of the DC-LINK when it is running under different working conditions.

[0062] In order to calculate the actual temperature of the DC-LINK under different operating conditions, it is necessary to obtain the ambient temperature of the DC-LINK and the temperature increased due to power consumption. Therefore, the real-time operating temperature calculation formula of the DC-LINK is: T c =ΔT+T a ; Where Tc, ΔT and Ta are the working core temperature of the DC-LINK capacitor, the temperature rise caused by the operation of the DC-LINK and the ambient temperature when the DC-LINK is working.

[0063] According to the law of heat conduction, the temperature difference between any two points is equal to the device power multiplied by the thermal resistance between the two points. Therefore, the temperature rise calculation formula of DC-LINK during operation is: ΔT=P·Z th ; Where P is the power dissipation of the EPS motor control DC-LINK, Z th is the transient thermal resistance of the EPS motor control DC-LINK when it is working. th The calculation formula is: τ i =R i C i ; Among them, R i is the thermal resistance coefficient, τ i is the time constant, C i is the thermal melting coefficient, and t is the working time of EPS motor control.

[0064] like Fig. 9 As shown in FIG. 1 , it is the temperature rise curve of DC-LINK when working under typical specific working conditions, and the specific working conditions mainly include specific working current (15A), specific working environment temperature (80°C) and specific working frequency (100KHZ), etc. According to the above RESR calculation method, it can be known that RESR of DC-LINK capacitor under this specific working condition is 0.02Ω, and combined with formula 1, it can be calculated that the working power dissipation of DC-LINK is 4.5W.

[0065] like Fig.10 As shown in the figure, it is the transient thermal resistance curve of DC-LINK under typical specific working conditions. By fitting this curve, the transient thermal resistance value of the DC-LINK under typical specific working conditions can be obtained.

[0066] like Fig.11As shown in the figure, it is a fifth-order Foster thermal network model diagram. Usually, the fifth-order Foster thermal network model can accurately express the transient thermal resistance. Therefore, the parameters of the fifth-order Foster thermal network model of DC-LINK can be obtained by calculation and fitting as shown in Table 4.

[0067] Table 4

[0068] parameter 1st order model 2nd order model 3rd order model 4th-order model 5th-order model Ri / K / W 17.8 13.17 6.2 15.37 8.65 τi / s 274.83 259.98 20.61 260.68 172.9

[0069] like Figure 4 As shown in the figure, it is a flow chart of the method of the present invention. First, the working ripple current and equivalent series resistance of the DC-LINK are calculated, and then the working dissipated power of the DC-LINK capacitor is obtained. Then, according to the transient thermal resistance value of the DC-LINK, the working temperature rise of the DC-LINK under any working condition can be calculated. Combined with the influence of the ambient temperature, the real-time temperature estimation of the DC-LINK can be finally realized.

[0070] like Fig.12 As shown, the calculation results of the process of the present invention are compared with the actual test results under a certain working condition. The initial ambient temperature is selected as 80°C. The results show that the DC-LINK temperature calculated using the above scheme is consistent with the measured data, which reflects the effectiveness of the method of the present invention.

Claims

1. A method for estimating the temperature of a DC-LINK for controlling an EPS motor, characterized in that: The specific process is as follows: S1, calculates the ripple current of the EPS motor control DC-LINK when it is working according to the motor working state parameters, including the real-time phase current, phase voltage, bus voltage, modulation ratio and power factor of the EPS motor control; S2, calculate the relationship between the equivalent series resistance of the EPS motor control DC-LINK and the operating temperature, the switching frequency of the three-phase bridge and the working time, and obtain the real-time equivalent series resistance of the EPS motor control DC-LINK under different working conditions by combining the above relationship; S3, combining the EPS motor control DC-LINK ripple current and the real-time equivalent series resistance to calculate the real-time power dissipation of the EPS motor control DC-LINK; S4, obtain the temperature rise curve of EPS motor control DC-LINK under specific conditions through experimental testing; S5, using Foster thermal network model to fit the transient thermal resistance of the EPS motor control DC-LINK during operation; S6, calculating the capacitor core temperature rise when the EPS motor control DC-LINK is working according to the real-time dissipated power and transient thermal resistance of the EPS motor control DC-LINK; S7, combining with the internal temperature sensor of the EPS motor control, calculates the core temperature rise of the EPS motor control DC-LINK and obtains the actual temperature of the EPS motor control DC-LINK.

2. The method for estimating the temperature of a DC-LINK for controlling an EPS motor according to claim 1, characterized in that: In step S1, the EPS motor controls the effective value of the ripple current of the DC-LINK. rms The calculation process is as follows: S11, according to the motor operating state parameters, obtain the average phase voltage U of the EPS motor control m And bus voltage value U dc ; S12, calculate the modulation degree S13, obtain the vector current I of the dq axis in the EPS motor control d ,I q ; S14, calculate the effective value of phase current S15, according to the relationship between the ripple current effective value of the EPS motor control DC-LINK and various parameters of the EPS motor control: Combining the formulas of step S12 and step S14, we can deduce Among them, I0 is the effective value of phase current, M is the modulation index, is the power factor.

3. The method for estimating the temperature of a DC-LINK for controlling an EPS motor according to claim 1, characterized in that: In step S2, the equivalent series resistance value R of the EPS motor control DC-LINK is ESR The calculation process is as follows: S21, according to the equivalent series resistance value R of EPS motor control DC-LINK ESR The curve relationship with the EPS motor control working frequency f is fitted into the formula: Among them, M is the frequency constant, N is the frequency coefficient, Q is the frequency index, and e is the natural index; S22, according to the equivalent series resistance value R of the EPS motor control DC-LINK ESR The curve relationship with the EPS motor control working temperature T is fitted into the formula: R ESR (T) = C + D · 10 (F·T) ; Where C is the temperature constant, D is the temperature coefficient, and F is the temperature index; S23, according to the equivalent series resistance value R of the EPS motor control DC-LINK ESR The curve relationship with the EPS motor control working time t is fitted into the formula: R ESR (t) = H + A·log (B·t) ; Where H is the time constant, A is the time coefficient, B is the time index, and e is the natural index; S24, according to the formulas of step S21, step S22, and step S23, comprehensively obtain R ESR =G(f, T, t); where G represents a function related to frequency, temperature and time.

4. The method for estimating the temperature of a DC-LINK for controlling an EPS motor according to claim 1, characterized in that: In step S3, the calculation formula of the real-time power dissipation of the EPS motor control DC-LINK is: Where P is the power dissipation of the EPS motor control DC-LINK, I rms is the effective value of the ripple current, R ESR is the equivalent series resistance value.

5. The method for estimating the temperature of a DC-LINK for controlling an EPS motor according to claim 1, characterized in that: In step S5, the calculation formula of the transient thermal resistance when the EPS motor controls the DC-LINK is: τ i =R i C i ; Among them, R i is the thermal resistance coefficient, τ i is the time constant, C i Thermal melting coefficient, t is the working time of EPS motor control.

6. The method for estimating the temperature of a DC-LINK for controlling an EPS motor according to claim 1, characterized in that: In step S6, the calculation formula of the capacitor core temperature rise when the EPS motor controls the DC-LINK is: ΔT = P·Z th ; Where P is the power dissipation of the EPS motor control DC-LINK, Z th It is the transient thermal resistance of EPS motor control DC-LINK when it is working.

7. The method for estimating the temperature of a DC-LINK for controlling an EPS motor according to claim 1, characterized in that: In step S7, the calculation formula of the actual temperature of the EPS motor control DC-LINK is: T c =ΔT+T a ; Among them, ΔT is the capacitor core temperature rise when the EPS motor controls the DC-LINK, T a The ambient temperature when the EPS motor controls the DC-LINK.

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