Active short-circuit exit control method for electric vehicle motor

Abstract

The invention discloses an active short-circuit exit control method for an electric vehicle motor. When the motor enters an active short-circuit state, the bus capacitor voltage Udc is discharged to a voltage Udc_set through a discharge device; the discharged capacitor voltage Udc1 is obtained by sampling the bus voltage, and the inverter power device performs a switching action at a certain duty cycle. During the power device shutdown period, if the motor line back electromotive force voltage is higher than the capacitor voltage Udc1 or lower than ‑Udc1, the motor charges the capacitor through a freewheeling device in the inverter; after the power device switches for a period of time, it switches back to the active short-circuit state, reads the capacitor voltage Udc2, and if Udc1 is greater than Udc2, the motor speed is low, the motor line back electromotive force is low, and the capacitor cannot be charged, then the active short-circuit state is exited, and if Udc2 is greater than Udc1, the capacitor is charged through the freewheeling device of the inverter. The method realizes effective control of the motor active short-circuit exit.

Description

Technical Field

[0001] The invention relates to the technical field of electric vehicle control, and in particular to an active short-circuit exit control method for an electric vehicle motor. Background Art

[0002] In order to improve the protection of electric vehicle power system, vehicle motors are usually equipped with active short-circuit function. When the vehicle fails at high speed, if the main relay is disconnected inexplicably and the inverter is shut down, the back electromotive force of the permanent magnet motor is high. Through the inverter's freewheeling device, the motor energy is fed back to the controller's film capacitor, and the film capacitor voltage increases, which poses a risk of breakdown. To address this problem, after the inverter is shut down when the vehicle fails at high speed, the motor performs active short-circuit operation, and the motor energy is consumed inside the motor instead of charging the film capacitor, thereby protecting the film capacitor. At the same time, in order to reduce the cost of electric drive, electric vehicles will remove the rotary transformer and use a position sensor-free algorithm to calculate the motor speed. When the motor enters the active short-circuit state, the speed cannot be calculated, because the speed is the main basis for judging the entry and exit of the active short-circuit, which will result in the inability to exit the active short-circuit normally, thus affecting the driving experience. Although the speed can be obtained by the three-phase current zero crossing, it depends on the good state of the current sensor. If the vehicle failure is caused by the damage of the current sensor, the speed cannot be obtained by this method, and then it is impossible to judge and control the motor to exit the active short-circuit state in time. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide an electric vehicle motor active short-circuit exit control method. The method overcomes the defects of the traditional motor active short-circuit exit mechanism. Without adding additional circuits and equipment, the motor speed is obtained by bus voltage sampling and calculation. When the motor is in an active short-circuit state, the exit mechanism no longer relies on other sensors to obtain the motor speed, thereby realizing effective control of the motor active short-circuit exit.

[0004] In order to solve the above technical problems, the electric vehicle motor active short circuit exit control method of the present invention comprises the following steps:

[0005] Step 1: If the motor is shut down at high speed and the main relay of the battery is abnormally tripped, the motor enters an active short-circuit state. At this time, the motor energy is consumed through its own coil resistance, and the bus capacitor voltage Udc is discharged to the voltage Udc_set through the discharge device;

[0006] Step 2: obtain the capacitor voltage Udc1 after discharge by sampling the bus voltage, control the inverter power device to perform switching action with a duty cycle dutySet, and when the upper bridge or lower bridge power device of the inverter is turned off, if the motor line back electromotive force voltage is higher than the capacitor voltage Udc1 or lower than -Udc1, the motor charges the capacitor through the freewheeling device in the inverter;

[0007] Step 3: After controlling the inverter power device switch for a period of time Tset, the upper bridge or lower bridge of the inverter is switched back to the active short-circuit state. At this time, the capacitor voltage Udc2 is read through the bus voltage sensor. If Udc1 is greater than Udc2, the motor speed is low and the motor line back electromotive force is low, resulting in the inability to charge the capacitor. The active short-circuit state is exited. If Udc2 is greater than Udc1, the capacitor is charged through the inverter's freewheeling device.

[0008] Step 4: Calculate the motor speed using the capacitor RC charging formula.

[0009] V(t)=V0+(V u (n)-V0)×[1-e -t / RC ]

[0010] Wherein, Vo = Udc1, t = Tset, V(t) = Udc2, R is the resistance value, C is the capacitance value, Vu(n) is the motor line back electromotive force, Vu(n) is linearly related to the motor speed n, Vu(n) = k × n, k is the coefficient obtained by testing;

[0011] Step 5: When the calculated motor speed is greater than the active short-circuit threshold, the active short-circuit does not exit, and the discharge device is controlled to put the capacitor voltage at the voltage Udc_set. Steps 2 to 4 are repeated to re-detect the motor speed. If the motor speed is lower than the active short-circuit threshold, the active short-circuit is exited.

[0012] Further, the motor line back electromotive force voltage in step 2 is calculated in the following manner:

[0013] During the capacitor charging process, the charging time t is the set value, the charging voltage is the motor back electromotive force voltage, and the charging process follows the RC charging and discharging principle. The current motor speed is set to n, and the motor back electromotive force amplitude is u(n). Then the three back electromotive forces of the motor are:

[0014] UN(t)=u(n)×sin(Wt)

[0015] VN(t)=u(n)×sin(Wt-π×2 / 3)

[0016] WN(t)=u(n)×sin(Wt-π×4 / 3)

[0017] The back electromotive force voltages of each line of the motor are:

[0018]

[0019]

[0020]

[0021] Wherein, W is the electrical angular velocity of the motor, W = n × motorPoles × 2 × π / 60, MotorPoles is the number of pole pairs of the motor. When the back electromotive force voltage of any motor line is higher than the capacitor voltage Udc1 or lower than -Udc1, when the inverter is fully closed, the motor charges the capacitor through the inverter's freewheeling device.

[0022] Further, the capacitor voltage Udc2 in step 3 is calculated in the following manner:

[0023] The formula for the change in capacitor voltage when the motor charges the capacitor is:

[0024] V(t)=V0+(V u -V0)×[1-e -t / RC ]

[0025] Where, t is the charging time, R is the total resistance value in the charging circuit, C is the capacitance, Vo is the initial voltage value on the capacitor, Vu is the target voltage value of charging, and V(t) is the voltage value on the capacitor at any time t.

[0026] If the active short circuit is realized by fully opening the lower bridge and fully closing the upper bridge, the lower bridge is modified to be non-fully open, and the lower bridge is changed to switch according to the duty cycle dutySet, setting dutySet=1 for the lower bridge to be closed, and dutySet=0 for the lower bridge to be turned on; if the active short circuit is realized by fully opening the upper bridge and fully closing the lower bridge, the upper bridge is modified to be non-fully open, and the upper bridge is changed to switch according to the duty cycle dutySet, setting dutySet=1 for the upper bridge to be closed, and dutySet=0 for the upper bridge to be turned on; then the charging time in each switching cycle is △t=dutySet×1 / freq, where freq is the switching frequency, and the switching action time is Tset. In order to reduce the impact of the non-rectifying cycle within Tset, Tset is set to be greater than the electrical cycle value of 5 times the rated speed. Because the Tset time is short, the motor speed changes slightly, and the motor back electromotive force voltage amplitude is regarded as unchanged during Tset. Then the capacitor voltage is expressed as:

[0027]

[0028] Among them, V u (t)=max(|UV(t)|,|VW(t)|,|WU(t)|), UV(t), VW(t), WU(t) are the back electromotive force voltages of each line of the motor respectively, and the initial voltage V(0)=Udc1. Then the capacitor voltage V(Tset) after Tset can be obtained. This voltage is equal to the voltage Udc2 detected by the bus voltage sensor after Tset, that is, V(Tset)=Udc2.

[0029] Since the electric vehicle motor active short-circuit exit control method of the present invention adopts the above-mentioned technical scheme, that is, when the motor enters the active short-circuit state, the motor energy is consumed through its own coil resistance, and the bus capacitor voltage Udc discharges the capacitor voltage to the voltage Udc_set through the discharge device; the discharged capacitor voltage Udc1 is obtained by sampling the bus voltage, and the inverter power device that realizes the active short-circuit function performs switching action with a duty cycle dutySet. During the period when the power device is turned off, if the motor line back electromotive force voltage is higher than the capacitor voltage Udc1 or lower than -Udc1, the motor charges the capacitor through the freewheeling device in the inverter; the power device switches back to the active short-circuit state after a period of time Tset, and reads the capacitor voltage Udc2. If Udc1 is greater than Udc2, the motor speed is low, and the motor line back electromotive force is low, resulting in the inability to charge the capacitor, then the active short-circuit state is exited, and if Udc2 is greater than Udc1, the capacitor is charged through the freewheeling device of the inverter. This method overcomes the defects of the traditional motor active short-circuit exit mechanism. Without adding additional circuits and equipment, the motor speed is obtained by calculating the bus voltage sampling. When the motor is in an active short-circuit state, the exit mechanism no longer relies on other sensors to obtain the motor speed, thereby achieving effective control of the motor's active short-circuit exit. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments:

[0031] Figure 1 This is a simplified block diagram of the electric vehicle motor drive control system;

[0032] Figure 2 for Figure 1 Simple schematic diagram of the inverter structure;

[0033] Figure 3 A flowchart of the method is shown in FIG. DETAILED DESCRIPTION

[0034] Implementation example Figure 1 , Figure 2 and Figure 3 As shown, the inverter S008 is a multi-phase inverter, not limited to the three-phase two-level inverter in this example, and the motor S009 is a multi-phase permanent magnet motor, not limited to the three-phase permanent magnet motor in this example;

[0035] Step 1: When the motor S009 is running at high speed, the controller detects a fault, causing the inverter S008 power device to shut down, and the main relay S005 of the battery S001 trips abnormally. To prevent the motor energy from passing Figure 2The power devices S107, S108, S109, S110, S111, and S112 flow to the capacitor S006, causing the capacitor S006 to be over-voltage and breakdown risk, and the power devices in the inverter S008 are controlled to make the motor S009 enter an active short circuit. Here, the active short circuit is considered to be realized by the lower three bridges, that is, the active short circuit is realized by turning on the fourth power switch S104, the fifth power switch S105, and the sixth power switch S106; the capacitor voltage Udc is put to the voltage Udc_set through the discharge device S007;

[0036] Step 2: The capacitor voltage Udc1 is obtained by sampling the bus voltage, and the inverter power device is controlled to perform switching action with a duty cycle dutySet. When the upper bridge or lower bridge power device of the inverter is turned off, if the motor line back electromotive force voltage is higher than the capacitor voltage Udc1 or lower than -Udc1, the motor charges the capacitor through the freewheeling device in the inverter;

[0037] The motor line back EMF voltage is calculated as follows:

[0038] The current motor speed is set to n (rpm), and the back EMF amplitude of the motor is u (n) (the back EMF is positively correlated with the motor speed, and the correlation coefficient can be measured in advance). Then the three back EMF voltages of the motor are

[0039] UN(t)=u(n)×sin(Wt)

[0040] VN(t)=u(n)×sin(Wt-π×2 / 3)

[0041] WN(t)=u(n)×sin(Wt-π×4 / 3)

[0042] Since only one back EMF level cannot determine whether a charging circuit is formed, it is necessary to obtain the back EMF voltage of each line of the motor, as follows:

[0043]

[0044]

[0045]

[0046] Wherein, W is the motor electrical angular velocity, W = n × motorPoles × 2 × π / 60, MotorPoles is the number of motor pole pairs, when any motor line back electromotive force voltage is higher than the capacitor voltage Udc1 or lower than -Udc1, when the inverter upper bridge or lower bridge S101 ... S106 is fully closed, the motor charges the capacitor through the corresponding two of the inverter's freewheeling devices S107 ... S112;

[0047] Step 3: After controlling the inverter power device switch for a period of time Tset, the inverter switches back to the active short-circuit state. At this time, the capacitor voltage Udc2 is read through the bus voltage sensor. If Udc1 is greater than Udc2, the motor speed is low and the motor line back electromotive force is low, resulting in the inability to charge the capacitor. The active short-circuit state is exited. If Udc2 is greater than Udc1, the capacitor is charged through the inverter's freewheeling device.

[0048] Among them, the capacitor voltage Udc2 can be calculated as follows:

[0049] The formula for the change in capacitor voltage when the motor charges the capacitor is:

[0050] V(t)=V0+(V u -V0)×[1-e -t / RC ]

[0051] Where, t is the charging time, R is the total resistance value in the charging circuit, C is the capacitance, Vo is the initial voltage value on the capacitor, Vu is the target voltage value of charging, and V(t) is the voltage value on the capacitor at any time t;

[0052] If the active short circuit is realized through the inverter upper bridge S101, S102, S103, the upper bridge is controlled to switch according to the duty cycle dutySet, and dutySet=1 is set to turn off the upper bridge S101, S102, S103, and dutySet=0 is set to turn on the upper bridge S101, S102, S103; if the active short circuit is realized through the inverter lower bridge S104, S105, S106, the lower bridge is controlled to switch according to the duty cycle dutySet, and dutySet=1 is set to turn on the lower bridge S104, S105, S106. 05, S106 is closed, dutySet = 0 means lower bridge S104, S105, S106 are turned on; then the charging time in each switching cycle is △t = dutySet × 1 / freq, where freq is the switching frequency, and the switching action time is Tset. In order to reduce the impact of the non-rectifying cycle in Tset, Tset is set to be greater than 5 times the rated speed. Since the Tset time is short, the motor speed changes slightly. During the Tset period, the motor back electromotive force voltage amplitude is considered to be unchanged, and the capacitor voltage is expressed as:

[0053]

[0054] Among them, V u(t)=max(|UV(t)|,|VW(t)|,|WU(t)|), UV(t), VW(t), WU(t) are the back electromotive force voltages of the motor lines respectively, and the initial voltage V(0)=Udc1, then the capacitor voltage V(Tset) after Tset can be obtained, which is equal to the voltage Udc2 detected by the bus voltage sensor after Tset, that is, V(Tset)=Udc2

[0055] Step 4: Calculate the motor speed using the capacitor RC charging formula.

[0056] V(t)=V0+(V u (n)-V0)×[1-e -t / RC ]

[0057] Wherein, Vo = Udc1, t = Tset, V(t) = Udc2, R is the resistance value, C is the capacitance value, Vu(n) is the motor line back electromotive force, Vu(n) is linearly related to the motor speed n, Vu(n) = k × n, k is the coefficient obtained by testing;

[0058] Step 5: When the calculated motor speed is greater than the active short-circuit threshold, the active short-circuit does not exit, and the discharge device is controlled to put the capacitor voltage at the voltage Udc_set. Steps 2 to 4 are repeated to re-detect the motor speed. If the motor speed is lower than the active short-circuit threshold, the active short-circuit is exited.

[0059] In the control system without position sensor of permanent magnet motor of electric vehicle, when the motor enters active short circuit, the control system cannot obtain the motor speed, and thus cannot judge when the motor exits the active short circuit state. This method can obtain the motor speed only by bus voltage sampling calculation without adding additional circuits and equipment, and realize effective control of motor active short circuit exit.

Claims

1. An active short-circuit exit control method for an electric vehicle motor, characterized in that This method comprises the following steps: Step 1: If the motor is shut down at high speed and the main relay of the battery is abnormally tripped, the motor enters an active short-circuit state. At this time, the motor energy is consumed through its own coil resistance, and the bus capacitor voltage Udc is discharged to the voltage Udc_set through the discharge device; Step 2: obtain the capacitor voltage Udc1 after discharge by sampling the bus voltage, control the inverter power device to perform switching action with a duty cycle dutySet, and when the upper bridge or lower bridge power device of the inverter is turned off, if the motor line back electromotive force voltage is higher than the capacitor voltage Udc1 or lower than -Udc1, the motor charges the capacitor through the freewheeling device in the inverter; Step 3: After controlling the inverter power device switch for a period of time Tset, the upper bridge or lower bridge of the inverter is switched back to the active short-circuit state. At this time, the capacitor voltage Udc2 is read through the bus voltage sensor. If Udc1 is greater than Udc2, the motor speed is low and the motor line back electromotive force is low, resulting in the inability to charge the capacitor. The active short-circuit state is exited. If Udc2 is greater than Udc1, the capacitor is charged through the inverter's freewheeling device. Step 4: Calculate the motor speed using the capacitor RC charging formula. V(t)=V0+(V u (n)-V0)×[1-e -t / RC ] Among them, Vo = Udc1, t = Tset, V(t) = Udc2, R is the resistance value of the charging circuit, C is the capacitance value, Vu(n) is the motor line back electromotive force, Vu(n) is linearly related to the motor speed n, Vu(n) = k × n, k is the coefficient obtained by testing; Step 5: When the calculated motor speed is greater than the active short-circuit threshold, the active short-circuit does not exit, and the discharge device is controlled to put the capacitor voltage at the voltage Udc_set. Steps 2 to 4 are repeated to re-detect the motor speed. If the motor speed is lower than the active short-circuit threshold, the active short-circuit is exited.

2. The electric vehicle motor active short-circuit exit control method according to claim 1, characterized in that: In step 2, the motor line back electromotive force voltage is calculated in the following manner: During the capacitor charging process, the charging time t is the set value, the charging voltage is the motor back electromotive force voltage, and the charging process follows the RC charging and discharging principle. The current motor speed is set to n, and the motor back electromotive force amplitude is u(n). Then the three back electromotive forces of the motor are: UN(t)=u(n)×sin(Wt) VN(t)=u(n)×sin(Wt-π×2 / 3) WN(t)=u(n)×sin(Wt-π×4 / 3) The back electromotive force voltages of each line of the motor are: Wherein, W is the electrical angular velocity of the motor, W = n × motorPoles × 2 × π / 60, MotorPoles is the number of pole pairs of the motor. When the back electromotive force voltage of any motor line is higher than the capacitor voltage Udc1 or lower than -Udc1, when the inverter is fully closed, the motor charges the capacitor through the inverter's freewheeling device.

3. The electric vehicle motor active short-circuit exit control method according to claim 1 or 2, characterized in that: In step 3, the capacitor voltage Udc2 is calculated in the following way: The formula for the change in capacitor voltage when the motor charges the capacitor is: V(t)=V0+(V u -V0)×[1-e -t / RC ] Where, t is the charging time, R is the total resistance value in the charging circuit, C is the capacitance, Vo is the initial voltage value on the capacitor, Vu is the target voltage value of charging, and V(t) is the voltage value on the capacitor at any time t. If the active short circuit is realized by fully opening the lower bridge and fully closing the upper bridge, the lower bridge is modified to be non-fully open, and the lower bridge is changed to switch according to the duty cycle dutySet, setting dutySet=1 for the lower bridge to be closed, and dutySet=0 for the lower bridge to be turned on; if the active short circuit is realized by fully opening the upper bridge and fully closing the lower bridge, the upper bridge is modified to be non-fully open, and the upper bridge is changed to switch according to the duty cycle dutySet, setting dutySet=1 for the upper bridge to be closed, and dutySet=0 for the upper bridge to be turned on; then the charging time in each switching cycle is Δt=dutySet×1 / freq, where freq is the switching frequency, and the switching action time is Tset. In order to reduce the impact of the non-rectifying cycle within Tset, Tset is set to be greater than the electrical cycle value of 5 times the rated speed. Because the Tset time is short, the motor speed changes slightly, and the motor back electromotive force voltage amplitude is regarded as unchanged during Tset. Then the capacitor voltage is expressed as: Among them, V u (t)=max(|UV(t)|,|VW(t)|,|WU(t)|), UV(t), VW(t), WU(t) are the back electromotive force voltages of each line of the motor respectively, and the initial voltage V(0)=Udc1. Then the capacitor voltage V(Tset) after Tset can be obtained. This voltage is equal to the voltage Udc2 detected by the bus voltage sensor after Tset, that is, V(Tset)=Udc2.

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