A control method for a new energy vehicle battery self-heating system

Abstract

The technical solution adopted by the present invention is: a control method for a new energy vehicle battery self-heating system, comprising the following steps: after the motor controller receives the vehicle self-heating mode request, it determines whether the current vehicle state meets the conditions for entering the self-heating mode; if the request is met, it gives a positive response to the request end and enters the self-heating mode, otherwise it responds with a negative response and does not enter the self-heating mode; after entering the self-heating mode, the motor controller determines whether the current motor is in the torque mode state; if the motor is not in the torque mode state, the inverter applies pulse voltages of different frequencies to the motor to achieve AC charging and discharging to achieve battery self-heating; if the motor is in the torque mode state, the torque Map of the motor controller is adjusted to increase the heat loss of the system and heat the battery through a thermal cycle. The present invention achieves the purpose of internal and external heating of the motor while ensuring the lowest motor noise.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy electric vehicles, and in particular relates to a control method for a new energy vehicle battery self-heating system. Background Art

[0002] The battery life of new energy vehicles is greatly affected by temperature. In low temperature environments, the chemical activity of lithium batteries is severely reduced, causing the effective capacity of the power battery to drop significantly, resulting in a serious reduction in the battery life of new energy vehicles, seriously affecting the driving experience. In addition, when charging the battery under low temperature conditions, lithium plating is prone to occur, which seriously affects the battery life.

[0003] Currently, there are two main ways to improve the low-temperature performance of lithium batteries, internal heating and external heating. Internal heating is to apply an alternating current at both ends of the lithium battery, and use the internal impedance of the lithium battery to generate heat to achieve overall heating of the battery. The traditional internal heating method requires changes to the battery cell structure, which affects the energy density of the battery, and requires external equipment, which increases the cost; the external heating method achieves thermal conduction heating of the battery by adding an external heating device, and the heating efficiency is low. This solution requires additional auxiliary control equipment and there is a risk of uneven heating, which not only increases hardware costs, but also poses a safety hazard. The use of the battery's internal self-heating solution can make the single cell heated evenly, heat quickly, and be highly efficient, without additional components, and at a low cost. Summary of the invention

[0004] The purpose of the present invention is to solve the shortcomings of the above-mentioned background technology and provide a control method for the self-heating system of the battery of a new energy vehicle. By forming a loop through the battery and the motor winding, the internal heating and external heating of the battery are combined to ensure the battery heating rate.

[0005] The technical solution adopted by the present invention is: a control method for a new energy vehicle battery self-heating system, the system includes a motor controller, a battery, a motor and an inverter, the battery forms a loop with the motor winding via the inverter, the motor controller obtains the motor state in real time and controls the motor through the inverter; the method includes the following steps:

[0006] After receiving the vehicle self-heating mode request, the motor controller determines whether the current vehicle state meets the conditions for entering the self-heating mode; if the request is met, a positive response is fed back to the request end and the self-heating mode is entered; otherwise, a negative response is given and the self-heating mode is not entered;

[0007] After entering the self-heating mode, the motor controller determines whether the motor is currently in the torque mode state;

[0008] If the motor is not in torque mode, pulse voltages of different frequencies are applied to the motor through the inverter to achieve AC charging and discharging to achieve battery self-heating;

[0009] If the motor is in torque mode, the torque map of the motor controller is adjusted to increase the heat loss of the system and heat the battery through the cooling water circulation system.

[0010] The above technical solution also includes the following steps: in the self-heating mode, if the motor controller determines that the motor or inverter exceeds the temperature threshold, the self-heating mode is temporarily exited, and the self-heating mode is entered again after the temperature of the motor or inverter drops to the set value. The present invention ensures the safety of the entire vehicle by setting an exit mechanism for the self-heating mode.

[0011] The above technical solution also includes the following steps: when the motor controller receives a request for the vehicle to exit the self-heating mode, the motor controller exits the self-heating mode. The present invention ensures the safety of the vehicle by setting an exit mechanism for the self-heating mode.

[0012] In the above technical solution, the conditions for entering the self-heating mode are as follows: the temperature of the motor and controller does not exceed the set threshold and there is bus voltage output, which effectively ensures overall safety.

[0013] In the above technical solution, the process of applying pulse voltages of different frequencies to the motor through the inverter to realize AC charging and discharging to realize battery self-heating includes:

[0014] The q-axis voltage output by the inverter is 0, and the d-axis voltage output by the inverter is a pulse voltage; the battery is charged and discharged by AC under the action of the motor winding to achieve internal heating of the battery. The present invention uses d-axis current to charge and discharge the battery, thereby ensuring the overall efficiency of the heating process.

[0015] In the above technical solution, the d-axis voltage output by the inverter is an AC voltage signal with alternating amplitude and output frequency that is a fixed frequency superimposed on a random frequency, which effectively reduces torque pulsation, effectively reduces noise during battery self-heating, and improves user experience.

[0016] In the above technical solution, the d-axis voltage amplitude u output by the inverter is d Calculate using the following formula: d =U dc *0.667

[0017] Among them U dc Indicates the actual bus voltage.

[0018] In the above technical solution, the inverter output frequency is calculated using the following formula:

[0019] f ud =F ud_min+F rdm ;

[0020] where F ud_min The minimum permissible frequency when the d-axis voltage is output, which is the minimum frequency under the condition that the motor phase current does not flow; F rdm It is a superimposed random frequency component. The setting standard of the random frequency component is to maximize the effective value of the output bus current while minimizing the output noise, thereby improving the heating efficiency and ensuring the overall safety.

[0021] In the above technical solution, the output amplitude of the d-axis voltage output by the inverter within half a cycle is u d， The output amplitude in half a cycle is -u d .

[0022] In the above technical solution, by adjusting the current torque Map of the motor controller, the process of improving the heat loss of the system includes: obtaining the short-circuit current of the motor, selecting 80% of the short-circuit current as the d-axis current Id, and finding the intersection with the MTPA current torque Map under the d-axis current as the maximum torque Te_S of the modified Map; fixing the d-axis current Id, calibrating the q-axis current Iq according to the original MTPA current torque Map based on the torque command with equal steps from 0 to Te_S, as the adjusted MTPA current torque Map; Te_S to peak torque is output according to the MTPA current torque Map before adjustment; after the motor speed reaches the limit ellipse, it searches for the best along the limit ellipse until it reaches the MTPV curve. The present invention ensures the accuracy of torque output while realizing the self-heating process.

[0023] The beneficial effects of the present invention are as follows: the present invention proposes a battery self-heating scheme, which forms a loop through the battery and the motor winding. When the motor is stationary, the motor is applied with pulse voltages of different frequencies through the inverter to realize AC charging and discharging, realize the purpose of heating the motor internally, and ensure the minimum noise of the motor; when responding to the torque request of the whole vehicle, the efficiency of the motor electronic control can be reduced by adjusting the torque Map, and the battery pack can be heated by thermal cycle to ensure the output torque accuracy while realizing the rapid heating of the battery. The present invention applies pulse voltages of different frequencies to the motor through the inverter to realize AC charging and discharging, realize the internal heating of the battery, and obtain the maximum alternating current by applying the optimal voltage, which can quickly realize the uniform heating of the battery internally, and reduce the torque pulsation by superimposing random frequencies, effectively reduce the noise during the self-heating of the battery, and improve the user experience. The present invention has the advantages of fast heating, uniform heating, high efficiency, and low cost. In order to ensure the service life of the battery, the present invention can consider sacrificing the system efficiency, by reducing the system efficiency, improving the system heat loss, and realizing the external heating of the battery by thermal conduction through thermal cycle, while ensuring the output torque accuracy, realizing the rapid heating of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a system block diagram of the present invention;

[0025] Figure 2 It is a schematic diagram of the process of the present invention;

[0026] Figure 3 This is a schematic diagram of the output d-axis voltage waveform of the present invention;

[0027] Figure 4 It is a schematic diagram of the current map of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments to facilitate a clear understanding of the present invention, but they do not constitute a limitation on the present invention.

[0029] like Figure 1-2 As shown, the present invention provides a control method for a new energy vehicle battery self-heating system, the system includes a motor controller, a battery, a motor and an inverter, the battery forms a loop with the motor winding via the inverter, the motor controller obtains the motor state in real time and controls the motor through the inverter; the method includes the following steps:

[0030] After receiving the vehicle self-heating mode request, the motor controller determines whether the current vehicle state meets the conditions for entering the self-heating mode; the conditions for entering the self-heating mode are as follows: the motor and controller temperature does not exceed the set threshold and there is bus voltage output. The self-heating mode request is generated in real time by the vehicle VCU according to the vehicle state information.

[0031] If the request is satisfied, a positive response is fed back to the requesting end and the self-heating mode is entered; otherwise, a negative response is given and the self-heating mode is not entered;

[0032] After entering the self-heating mode, the motor controller determines whether the motor is currently in the torque mode state;

[0033] If the motor is not in torque mode, pulse voltages of different frequencies are applied to the motor through the inverter to achieve AC charging and discharging to achieve battery self-heating;

[0034] If the motor is in torque mode, the torque map of the motor controller is adjusted to increase the heat loss of the system and heat the battery through thermal cycles.

[0035] In the self-heating mode, if the motor controller determines that the motor or inverter exceeds the temperature threshold, it will temporarily exit the self-heating mode and wait for the motor or inverter temperature to drop to the set value before entering the self-heating mode.

[0036] When the motor controller receives the vehicle self-heating exit request, it exits the self-heating mode. The vehicle self-heating exit request is generated in real time by the vehicle VCU according to the vehicle status information.

[0037] Specifically, when the motor is stationary, the heat in the battery is generated by the internal resistance of the battery. When the vehicle is stationary, the loop formed by the motor winding and the internal resistance of the battery must ensure that the motor generates a large current without generating effective torque. This current generates reactive power. According to the inductor energy storage formula:

[0038]

[0039] It can be seen that the reactive power consumed by the inductor is:

[0040]

[0041] The reactive power comes from the battery, and then the bus current:

[0042] I dc (t n )=P(t n ) / U dc (3)

[0043]

[0044] The heating power of the internal resistance is:

[0045] P Rs =I dc Rm 2 *Rs (5)

[0046] Where: W, L, i are the energy stored in the motor, the motor inductance, and the current flowing through the inductance; P(t n )、i(t n )、i(t n-1 ) are the reactive power consumed by the motor, t n and t n-1 The current value of the inductor at the moment; I dc (t n ), U dc ,I dc Rms are the DC bus current t n The value at the moment, bus voltage and DC bus effective value; P Rs , Rs are the battery internal resistance heating power and battery internal resistance respectively.

[0047] Obviously, in order to obtain greater battery heating power, the maximum bus current effective value must be guaranteed, and the reactive power consumed by the inductor must be large enough, that is, the current flowing through the inductor must be large and the slope must be fast.

[0048] The motor voltage-torque equation is:

[0049]

[0050]

[0051]

[0052] Where: u d 、u q are the motor stator voltages in the motor dq coordinate system respectively; i d 、i q are the motor stator current in the motor dq coordinate system, L d and Lq are the equivalent inductances of the motor D and Q axes; R s is the resistance of the motor stator winding, ω e , N p are the motor electrical angular velocity, rotor flux and motor pole pair number respectively, and Te is the motor output torque.

[0053] From formulas (6) and (7), we can see that in the static state, when the motor resistance is ignored and the pulse voltage is directly added to the d-axis, the current rising slope is a fixed value, which is related to the motor d-axis inductance, that is:

[0054]

[0055] At this time, the current rise slope is the fastest, meeting the heating requirements inside the battery.

[0056] In order to obtain the fastest current rising slope, the present invention realizes the maximum reactive power through the form of pulse voltage injection method, thereby achieving the highest bus AC current and the fastest heating effect. The specific principle is as follows:

[0057] According to formula (8), in order to obtain the maximum reactive power without generating torque, the q-axis output current must be zero, that is, the q-axis voltage u q is 0.

[0058] The present invention outputs the q-axis voltage u q Set it to 0 so that the torque output is always zero. In order to obtain the maximum DC bus pulse current, the d-axis voltage is output in pulses.

[0059] During the battery heating process, the fixed frequency winding d-axis current will cause noise problems. In order to reduce the noise, the output pulse voltage frequency can be randomized to disperse the noise energy and improve the vehicle noise. The specific methods are as follows:

[0060] Set the q-axis voltage to 0 output and the d-axis voltage to u d =Udc *0.667, the voltage is the bus voltage U dc The maximum voltage value that the motor voltage is allowed to output;

[0061] Set the d-axis output voltage frequency f ud =F ud_min +F rdm , where F ud_min is the d-axis voltage U dc *0.667 output, the minimum allowable frequency, at this time the output motor phase current does not flow, can be obtained by calibration F ud_min , F rdm It is a superimposed random frequency component. The setting of this random frequency component ensures the maximization of the effective value of the output bus current while ensuring the optimal output noise, which can be obtained by calibration.

[0062] Under the above-set d-axis output frequency, the d-axis voltage output u is within half a cycle. d Output within half cycle -u d The schematic diagram is as follows Figure 3 As shown. That is, the output d-axis voltage is an alternating amplitude, and the output frequency is an AC voltage signal with a fixed frequency superimposed on a random frequency, which ensures the output reactive power change rate and effectively controls the noise generated by the motor winding.

[0063] Specifically, when the motor responds to the vehicle's torque command, in order to ensure the vehicle's torque output, the purpose of heating the battery can no longer be achieved through high-frequency pulse voltage output. The torque Map can be adjusted to reduce the efficiency of the motor's electronic control, and the battery pack can be heated through a thermal cycle to ensure the output torque accuracy while achieving rapid battery heating.

[0064] The motor controller's task is to convert the vehicle's torque command into a current command and close the loop to control the output motor current. According to formula (8), the same torque output can be composed of countless combinations of id and iq. The purpose of traditional current control is to obtain the maximum system efficiency, that is, the current combination satisfies the combination of MTPA+limit voltage ellipse until MTPV. This combination ensures the minimum current output under the same torque output and the optimal system efficiency. In order to ensure the battery life under extremely cold conditions, it is possible to consider sacrificing system efficiency, by reducing system efficiency, increasing system heat loss, and transferring the heat generated by the increased heat loss to the cooling water system. The cooling water system uses the above heat to heat the battery externally through heat conduction in a thermal cycle. The specific implementation steps are:

[0065] Get the motor short-circuit current I short, select 80% of the short-circuit current as the d-axis current Id, and find the intersection with MTPA under the d-axis current as the maximum torque Te_S of the corrected Map; fix the d-axis current Id, and calibrate the q-axis current Iq according to the original MTPA current-torque Map based on the torque command with equal steps from 0 to Te_S, as the adjusted MTPA current-torque Map; Te_S to peak torque is output according to the MTPA current-torque Map before adjustment; after the motor speed reaches the limit ellipse, optimize along the limit ellipse until MTPV.

[0066] like Figure 4 As shown, the OAC curve is the MTPA current-torque curve, and the HGF is the MTPV curve, where the horizontal axis is the d-axis current and the vertical axis is the q-axis current. ω1, ω2, and ω3 are the motor angular velocities, and the ellipses shown in the figure are their corresponding limit ellipses. Among them, ω1>ω2>ω3. H is the short-circuit current point of the motor, where OE=0.8*OH, that is, point E is the calibrated d-axis current ID. Based on the torque command with step lengths from 0 to Te_S, the q-axis current Iq is calibrated according to the original current-torque Map, that is, the B / D / I point is found, and the curve formed by BDIE is used as the adjusted MTPA current-torque Map.

[0067] The current map in the battery self-heating mode is as follows:

[0068] When the motor rotation angular velocity is less than ω1, the current Map follows the EIDBC curve; that is, under the torque command from 0 to Te_S, the fixed d-axis current and the calibrated q-axis current corresponding to the adjusted MTPA current-torque Map are output, and from Te_S to the peak torque, the MTPA current-torque Map before adjustment is output.

[0069] When the motor rotation angular velocity is ω2, the current Map follows the EIDF curve; that is, before the motor speed reaches the limit ellipse, the fixed d-axis current and the calibrated q-axis current corresponding to the MTPA current-torque Map adjusted according to the torque command output follow the EID curve; after the motor speed reaches the limit ellipse, the optimal MTPV curve is searched along the limit ellipse of ω2 to find point F.

[0070] When the motor rotation angular velocity is ω3, the current Map follows the EIG curve; that is, before the motor speed reaches the limit ellipse, the fixed d-axis current and the calibrated q-axis current corresponding to the MTPA current-torque Map adjusted according to the torque command output follow the EI curve; after the motor speed reaches the limit ellipse, the optimal MTPV curve is searched along the limit ellipse of ω3 to find the G point.

[0071] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A control method for a new energy vehicle battery self-heating system, the system comprising a motor controller, a battery, a motor and an inverter, the battery forms a loop with the motor winding via the inverter, the motor controller obtains the motor state in real time and controls the motor through the inverter; the characteristics are: The method comprises the following steps: After receiving the vehicle self-heating mode request, the motor controller determines whether the current vehicle state meets the conditions for entering the self-heating mode; if the request is met, a positive response is fed back to the request end and the self-heating mode is entered; otherwise, a negative response is given and the self-heating mode is not entered; After entering the self-heating mode, the motor controller determines whether the motor is currently in the torque mode state; If the motor is not in torque mode, pulse voltages of different frequencies are applied to the motor through the inverter to achieve AC charging and discharging to achieve battery self-heating; If the motor is in torque mode, the current torque map of the motor controller is adjusted to increase the heat loss of the system and heat the battery through the cooling water circulation system; The process of applying pulse voltages of different frequencies to the motor through the inverter to achieve AC charging and discharging to achieve battery self-heating includes: The q-axis voltage output by the inverter is 0, and the d-axis voltage output by the inverter is a pulse voltage; the battery is charged and discharged by AC under the action of the motor winding to achieve internal heating of the battery; By adjusting the current-torque Map of the motor controller, the process of improving the heat loss of the system includes: obtaining the short-circuit current of the motor, selecting 80% of the short-circuit current as the d-axis current Id, and finding the intersection with the MTPA current-torque Map under the d-axis current as the maximum torque Te_S of the corrected Map; fixing the d-axis current Id, and calibrating the q-axis current Iq according to the original MTPA current-torque Map based on the torque command with equal steps from 0 to Te_S as the adjusted MTPA current-torque Map; Te_S to the peak torque is output according to the MTPA current-torque Map before adjustment; after the motor speed reaches the limit ellipse, it searches for the best along the limit ellipse until the MTPV curve is reached.

2. The control method of a new energy vehicle battery self-heating system according to claim 1, characterized in that: The following steps are also included: In the self-heating mode, if the motor controller determines that the motor or inverter exceeds the temperature threshold, it will temporarily exit the self-heating mode and wait for the motor or inverter temperature to drop to the set value before entering the self-heating mode.

3. The control method of a new energy vehicle battery self-heating system according to claim 1, characterized in that: The following steps are also included: When the motor controller receives a request to exit self-heating of the vehicle, it exits the self-heating mode.

4. The control method of a new energy vehicle battery self-heating system according to claim 1, characterized in that: The d-axis voltage output by the inverter is an AC voltage signal with alternating amplitude and an output frequency that is a fixed frequency superimposed with a random frequency.

5. The control method of a new energy vehicle battery self-heating system according to claim 4, characterized in that: The d-axis voltage amplitude u output by the inverter d Calculate using the following formula: d =U dc *0.667 Among them U dc Indicates the actual bus voltage.

6. The control method of a new energy vehicle battery self-heating system according to claim 5, characterized in that: The inverter output frequency is calculated using the following formula: where F ud_min The minimum permissible frequency when the d-axis voltage is output, which is the minimum frequency under the condition that the motor phase current does not flow; F rdm It is a superimposed random frequency component, and the setting standard of the random frequency component is to maximize the effective value of the output bus current while minimizing the output noise.

7. A control method for a new energy vehicle battery self-heating system according to claim 6, characterized in that: The output amplitude of the inverter output d-axis voltage in half a cycle is u d , the output amplitude in half a period is -u d .

8. The control method of a new energy vehicle battery self-heating system according to claim 1, characterized in that: The conditions for entering the self-heating mode are as follows: the temperature of the motor and controller does not exceed the set threshold and there is bus voltage output.

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