Electric braking method for motor

Abstract

According to the electric braking method for the motor, a driving system is included, the driving system is provided with the motor and a frequency converter, alternate blocking of an upper bridge arm switch tube and a lower bridge arm switch tube is carried out according to current information of the motor, and therefore more voltage vectors can be used for controlling the braking torque of the motor; the method is characterized in that when two-phase current of a motor flows to a frequency converter or only one-phase current flows out of the frequency converter, an upper bridge arm switch tube is blocked; when two-phase current of the motor flows out of the frequency converter or only one-phase current flows to the frequency converter, a lower bridge arm switch tube is blocked. By alternately blocking the switch tubes of the upper bridge arm and the lower bridge arm, larger braking torque and smaller torque pulsation can be provided, heat dissipation of the IGBT / diodes is balanced, and meanwhile power supply from an intermediate circuit of the frequency converter to the permanent magnet motor is prevented.

Description

Technical Field

[0001] The present invention relates to a method for safely controlling the braking torque of a drive system having a motor, and particularly to an electrical braking method for a motor. Background Art

[0002] With the development of elevator technology, the safety requirements for elevators are getting higher and higher. In some usage scenarios, situations such as elevator runaway may occur, for example, due to the inability of the elevator brake to fully brake the traction wheel.

[0003] In order to ensure that the elevator can effectively decelerate or limit the elevator runaway speed, usually the three-phase input of the motor is short-circuited, and the braking force generated by the permanent magnets of the permanent magnet synchronous motor (PM motor) is used to decelerate the elevator or limit the elevator runaway speed (i.e., the "star connection short-circuit technology", a type of safe electrical braking).

[0004] One of the commonly used star connection short-circuit methods in current elevator control systems is to use a "star connection short-circuit contactor". A star connection short-circuit contactor is added between the frequency converter and the PM motor to achieve short-circuiting of the three-phase input of the motor. However, this star connection short-circuit contactor must be selected to withstand the motor current and be able to connect and / or cut off this current. These contactors are often large and costly. In addition, contactors including moving parts have a certain limited lifespan and must be replaced after a relatively small number of operations.

[0005] The second commonly used star connection short-circuit method is to use "electronic star connection short-circuit", that is, while the frequency converter blocks the driving signal of the upper bridge arm, the switching tubes of the lower bridge arm are controlled to conduct, so as to achieve short-circuiting of the three-phase input of the motor.

[0006] However, when the amount of PM motor magnets is relatively small, the maximum torque of traditional star connection short-circuit braking is not enough to ensure that the elevator runaway speed does not exceed the specified range. It is necessary to replace the PM motor with a motor having a larger amount of magnets to limit the elevator runaway speed, but this will come at a high economic cost.

[0007] Chinese Patent Application Publication No. CN114835048A discloses that a capacitor is connected in series in the star connection short-circuit contactor circuit. The capacitive reactance of the capacitor has a canceling effect on the inductive reactance of the motor inductor, so as to improve the situation that the current in the traditional star connection short-circuit braking circuit lags behind the induced voltage E, thereby increasing the traditional star connection short-circuit braking torque. However, this solution requires additional costs and is not applicable to "electronic star connection short-circuit".

[0008] In addition, the braking torque of the star connection short-circuit technology shows a characteristic of first increasing and then decreasing as the speed of the PM motor increases. As a result, at high speeds, the braking torque of the star connection short-circuit is very small; in addition, this torque only depends on the design and speed of the PM motor and cannot effectively control the braking torque, and is not applicable to occasions of rapid braking or emergency braking.

[0009] Chinese invention patent CN202211353591.1 discloses a braking method. On the premise that the driving signal of the upper-bridge-arm switching tube of the frequency converter is blocked, by turning off in advance the driving signal of the corresponding lower-bridge-arm switching tube when the phase current of the permanent magnet synchronous motor flows to the frequency converter, the power factor of the phase current and the corresponding counter electromotive force is improved, thereby increasing the braking torque. Although this method can increase the braking torque, the braking torque ripple of this method is relatively large, generating vibration and noise, and the braking current is concentrated in the IGBT / diode of the lower bridge arm, which is not conducive to heat dissipation. Summary of the Invention

[0010] The object of the present invention is to provide an electric braking method for a motor, which can safely generate a controllable braking torque, and the braking torque is larger than the traditional star-sealing braking torque, and it is applicable to occasions where safe rapid braking or emergency braking is required.

[0011] To achieve the above object of the invention, the electric braking method for a motor of the present invention includes a drive system, the drive system having a motor and a frequency converter. According to the current information of the motor, the upper and lower bridge arm switching tubes are alternately blocked, so that more voltage vectors can be utilized for the control of the braking torque of the motor; or a certain bridge arm switching tube is always blocked, and according to the current information of the motor, a suitable voltage vector is selected for the control of the braking torque of the motor.

[0012] In a preferred embodiment of the present invention, when the phase current of two phases of the motor flows to the frequency converter or only the phase current of one phase flows out of the frequency converter, the upper-bridge-arm switching tube is blocked, and the lower-bridge-arm switching tube performs PWM chopping; when the phase current of two phases of the motor flows out of the frequency converter or only the phase current of one phase flows to the frequency converter, the lower-bridge-arm switching tube is blocked, and the upper-bridge-arm switching tube performs PWM chopping; or the upper-bridge-arm switching tube is always blocked, and the lower-bridge-arm switching tube performs PWM chopping; or the lower-bridge-arm switching tube is always blocked, and the upper-bridge-arm switching tube performs PWM chopping.

[0013] In a preferred embodiment of the present invention, when the upper-bridge-arm switching tube is blocked, the lower-bridge-arm switching tube performs PWM chopping to control the braking torque of the motor; and / or when the lower-bridge-arm switching tube is blocked, the upper-bridge-arm switching tube performs PWM chopping to control the braking torque of the motor.

[0014] In a preferred embodiment of the present invention, it is set that: the phase current of the PM motor is positive when flowing to the PM motor, and the current state is defined as '1'; the phase current of the PM motor is negative when flowing to the frequency converter, and the current state is defined as '0'. Then, the plane can be divided into six sectors according to the positive and negative signs of the three-phase current or the current vector angle.

[0015] First sector: When -30° < θ iWhen ≤ 30°, the state of the three-phase current is '100';

[0016] Second sector: When 30° < θ i ≤ 90°, the state of the three-phase current is '110';

[0017] Third sector: When 90° < θ i ≤ 150°, the state of the three-phase current is '010';

[0018] Fourth sector: When 150° < θ i ≤ 210°, the state of the three-phase current is '011';

[0019] Fifth sector: When 210° < θ i ≤ 270°, the state of the three-phase current is '001';

[0020] Sixth sector: When 270° < θi ≤ 330°, the state of the three-phase current is '101';

[0021] In the first sector, the third sector, and the fifth sector, the drive signals of the upper-bridge switching tubes of the frequency converter are blocked; in the second sector, the fourth sector, and the sixth sector, the drive signals of the lower-bridge switching tubes of the frequency converter are blocked, that is, the drive signals of the upper and lower-bridge switching tubes are alternately blocked.

[0022] Define that when the upper-bridge switching tube or diode is conducting as '1', and when the lower-bridge switching tube or diode is conducting as '0'. The effective voltage vectors output by the frequency converter are as Figure 5 shown.

[0023] ① When the state of the three-phase current is '100', that is, in the first sector, the drive signals of the upper-bridge switching tubes of the frequency converter are blocked, and the lower-bridge switching tubes use partial combinations or all combinations or a certain one of the voltage vectors U3(010), U4(011), U5(001), U0(000) for PWM chopping to control the braking torque of the motor; or

[0024] ② When the state of the three-phase current is '110', that is, in the second sector, the drive signals of the lower-bridge switching tubes of the frequency converter are blocked, and the upper-bridge switching tubes use partial combinations or all combinations or a certain one of the voltage vectors U4(011), U5(001), U6(101), U0(111) for PWM chopping to control the braking torque of the motor; or

[0025] ③When the state of the three-phase current is '010', i.e., the third sector, block the drive signals of the upper-bridge-arm switching devices of the frequency converter. The lower-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a single one of the voltage vectors U5(001), U6(101), U1(100), U0(000) to control the braking torque of the motor; or

[0026] ④When the state of the three-phase current is '011', i.e., the fourth sector, block the drive signals of the lower-bridge-arm switching devices of the frequency converter. The upper-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a single one of the voltage vectors U1(100), U2(110), U6(101), U0(111) to control the braking torque of the motor; or

[0027] ⑤When the state of the three-phase current is '001', i.e., the fifth sector, block the drive signals of the upper-bridge-arm switching devices of the frequency converter. The lower-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a single one of the voltage vectors U1(100), U2(110), U3(010), U0(000) to control the braking torque of the motor;

[0028] ⑥Or when the state of the three-phase current is '101', i.e., the sixth sector, block the drive signals of the lower-bridge-arm switching devices of the frequency converter. The upper-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a single one of the voltage vectors U2(110), U3(010), U4(011), U0(111) to control the braking torque of the motor.

[0029] In a preferred embodiment of the present invention, when the drive signals of the upper-bridge-arm switching devices of the frequency converter are blocked all the time,

[0030] ①When the state of the three-phase current is '100', i.e., the first sector, the lower-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a single one of the voltage vectors U3(010), U4(011), U5(001), U0(000) to control the braking torque of the motor; or

[0031] ②When the state of the three-phase current is '110', i.e., the second sector, the lower-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a single one of the voltage vectors U5(001), U0(000) to control the braking torque of the motor;

[0032] ③When the state of the three-phase current is '010', i.e., the third sector, the lower-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a single one of the voltage vectors U5(001), U6(101), U1(100), U0(000) to control the braking torque of the motor; or

[0033] ④ When the state of the three-phase current is '011', i.e., the fourth sector, the lower-arm switching devices use partial combinations or all combinations or a single one of the voltage vectors U1(100) and U0(000) for PWM chopping to control the braking torque of the motor; or

[0034] ⑤ When the state of the three-phase current is '001', i.e., the fifth sector, the lower-arm switching devices use partial combinations or all combinations or a single one of the voltage vectors U1(100), U2(110), U3(010), and U0(000) for PWM chopping to control the braking torque of the motor; or

[0035] ⑥ When the state of the three-phase current is '101', i.e., the sixth sector, the lower-arm switching devices use partial combinations or all combinations or a single one of the voltage vectors U3(010) and U0(000) for PWM chopping to control the braking torque of the motor.

[0036] In a preferred embodiment of the present invention, when the driving signals of the lower-arm switching devices of the frequency converter are always blocked,

[0037] ① When the state of the three-phase current is '100', i.e., the first sector, the upper-arm switching devices use partial combinations or all combinations or a single one of the voltage vectors U4(011) and U0(111) for PWM chopping to control the braking torque of the motor; or

[0038] ② When the state of the three-phase current is '110', i.e., the second sector, the upper-arm switching devices use partial combinations or all combinations or a single one of the voltage vectors U4(011), U5(001), U6(101), and U0(111) for PWM chopping to control the braking torque of the motor; or

[0039] ③ When the state of the three-phase current is '010', i.e., the third sector, the upper-arm switching devices use partial combinations or all combinations or a single one of the voltage vectors U6(101) and U0(111) for PWM chopping to control the braking torque of the motor; or

[0040] ④ When the state of the three-phase current is '011', i.e., the fourth sector, the upper-arm switching devices use partial combinations or all combinations or a single one of the voltage vectors U1(100), U2(110), U6(101), and U0(111) for PWM chopping to control the braking torque of the motor; or

[0041] ⑤ When the state of the three-phase current is '001', i.e., the fifth sector, the upper-arm switching devices use partial combinations or all combinations or a single one of the voltage vectors U2(110) and U0(111) for PWM chopping to control the braking torque of the motor; or

[0042] ⑥When the state of the three-phase current is '101', i.e., the sixth sector, the upper-bridge switching devices perform PWM chopping using some combinations or all combinations or a single one of the voltage vectors U2(110), U3(010), U4(011), U0(111) to control the braking torque of the motor.

[0043] In a preferred embodiment of the present invention, the control of the braking torque of the motor is made based on torque prediction or torque current prediction or output power prediction or current target prediction.

[0044] In a preferred embodiment of the present invention, the torque prediction is divided into maximum torque prediction, torque target prediction with minimum torque error, and multi-vector torque target prediction.

[0045] In a preferred embodiment of the present invention, the maximum torque prediction is made according to the following cost function formula:

[0046]

[0047] In a preferred embodiment of the present invention, the maximum torque prediction control includes current control. For example, software peak current control or hysteresis current control with a control period is used. When the motor current exceeds the set threshold, the drive signals of all the switching devices of the upper and lower bridges are blocked; or average current control using a PI regulator is adopted, and the PWM duty output by the PI regulator is used for the optimal voltage vector obtained by optimization, or the PWM duty output by the PI regulator is used for the alternative voltage vectors for optimization.

[0048] In a preferred embodiment of the present invention, for the maximum torque prediction control, the PWM Duty changes with the speed. The greater the speed, the smaller the PWM Duty, to prevent excessive current at medium and high speeds.

[0049] In a preferred embodiment of the present invention, the torque target prediction with minimum torque error and the multi-vector target torque prediction are made according to the following cost function formula:

[0050] T e_err (k + 1) = T e_ref -T e (k + 1).

[0051] In a preferred embodiment of the present invention, the torque target is related to the rotational speed and the DC bus voltage.

[0052] In a preferred embodiment of the present invention, the current target prediction is made according to the following cost function formula:

[0053]

[0054] where η is the weight coefficient of the quadrature-axis current, and η≥1.

[0055] In a preferred embodiment of the present invention, the multi-vector torque target prediction and multi-vector current target prediction control include combining two or more non-zero voltage vectors into a virtual vector to participate in the optimization of voltage vectors, and then equally dividing the optimal voltage vector obtained by the optimization into two or more parts, and performing optimization again among the vectors of each part.

[0056] In a preferred embodiment of the present invention, based on the predictive control-based electric machine braking torque control, a speed closed-loop control is performed, and the output of the speed loop is used as the torque target or the current target.

[0057] In a preferred embodiment of the present invention, when the motor speed is lower than a certain threshold n1, it is switched to the traditional electronic star-sealing braking. The threshold n1 generally can be taken as the rotational speed corresponding to the vicinity of the maximum star-sealing torque during traditional star-sealing braking.

[0058] During the high-speed emergency stop of the elevator, for the PM motor, current can be generated in the motor through PWM chopping, so as to perform current sector division and alternate blocking. For asynchronous motors, etc., PWM chopping needs to be performed when the residual magnetism has not completely disappeared to make the motor generate current. Otherwise, because the rotor has no permanent magnet, current cannot be generated and it cannot be used for rapid braking or emergency braking.

[0059] Due to the adoption of the above technical solutions, in this case, by alternately blocking the switching tubes of the upper and lower bridge arms, it is possible to prevent power supply from the intermediate circuit of the frequency converter to the motor, while providing a larger braking torque, a smaller torque ripple, and balanced heat dissipation of the IGBT / diode.

[0060] One advantage of the method according to the present invention is that: realizing electric braking does not require a separate switch, but can be purely achieved through the frequency converter. This saves costs and space. In addition, if the number of components is reduced, the overall reliability of the system is also improved. Brief Description of the Drawings

[0061] Figure 1 It is a schematic diagram of a drive system (the rectification part is omitted) of a permanent magnet synchronous motor.

[0062] Figure 2 It is a schematic diagram of an equivalent circuit during traditional star-sealing braking.

[0063] Figure 3 It is a schematic diagram of an exemplary curve of the braking torque of traditional star-sealing braking and the present invention with respect to speed.

[0064] Figure 4 It is a schematic diagram of current vector sector division.

[0065] Figure 5 It is a schematic diagram of voltage vector sector division.

[0066] Figures 6a to 6f It is a schematic diagram of current vector sectors and corresponding voltage vectors.

[0067] Figure 7 It is a principle block diagram of maximum torque predictive control for STO_60 and STO_360.

[0068] Figure 8 It is the simulation result of braking torque during maximum torque predictive control for STO_60 and STO_360.

[0069] Figure 9a It is the simulation result of braking torque during maximum torque predictive control under different bus voltages for STO_360.

[0070] Figure 9b It is the simulation result of braking torque during maximum torque predictive control under different bus voltages for STO_60.

[0071] Figure 10a It is the simulation result of torque target prediction for STO_360.

[0072] Figure 10b It is the simulation result of torque target prediction for STO_60.

[0073] Figure 11 It is for current vector sectors R1, R3, R5 and corresponding subdivided voltage vectors

[0074] Figure 12 It is the principle block diagram of STO_60 and STO_360 schemes based on multi-vector torque target / current target predictive control

[0075] Figure 13a It is the simulation result of the STO_360 scheme based on multi-vector torque target predictive control.

[0076] Figure 13b It is the simulation result of the STO_60 scheme based on multi-vector torque target predictive control.

[0077] Figure 14 It is the simulation result of the STO_60 scheme based on current target predictive control.

[0078] Figure 15 It is the simulation result of the STO_60 scheme based on current target predictive control with weight factors. Specific implementation manners

[0079] The present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0080] Reference Figure 1 , by blocking the drive signals of the controllable switch tubes T1, T2, T3 (such as IGBTs) of the upper bridge arm of the frequency converter, and keeping the drive signals of the controllable switch tubes T4, T5, T6 (such as IGBTs) of the lower bridge arm always effective, or by blocking the drive signals of the controllable switch tubes T4, T5, T6 (such as IGBTs) of the lower bridge arm of the frequency converter, and keeping the drive signals of the controllable switch tubes T1, T2, T3 (such as IGBTs) of the upper bridge arm always effective, the "electronic star sealing" of the prior art can be achieved. Since one bridge arm of the frequency converter is always blocked, it prevents Figure 1 the C1 and C2 in the intermediate circuit (as well as the power grid power supply) from providing driving energy to the PM motor. In this case, the PM motor cannot generate torque other than in combination with braking. Therefore, "electronic star sealing" is a safe electrical braking. The equivalent circuit at this time is as Figure 2 shown. The resistance R1, R2, and R3 of each phase winding of the PM motor, the inductance L1, L2, and L3 of each phase winding, and the back electromotive force e1, e2, and e3 generated by the rotation of the motor form a braking circuit. For this braking circuit, its braking torque shows a characteristic of increasing first and then decreasing with the increase of the speed of the PM motor, as Figure 3 shown by the curve 31 in. This is because as the speed of the motor increases, the generated back electromotive force e increases, the current flowing through this braking circuit increases, and the generated braking torque also increases. However, because the inductive reactance of the inductance of the PM motor also increases with the increase of the speed, the ratio of the inductive reactance to the resistance in this braking circuit also increases with the increase of the speed, causing the current in this braking circuit to develop in a direction leading the back electromotive force e by 90°, resulting in a decrease in the braking torque after a certain speed of the PM motor.

[0081] In elevator applications, the curve 32 represents the unbalanced torque generated due to the mass difference between the car and the counterweight. Since the amount of permanent magnets used in the PM motor is relatively small, the peak value of the braking torque of this braking circuit shown by the curve 31 may be less than the unbalanced torque. The braking torque of this braking circuit is always less than the unbalanced torque, and the speed of the PM motor cannot be controlled and will rotate faster and faster, and the runaway speed of the elevator cannot be limited within the specified range.

[0082] Only when the phase current of the PM motor is negative (the phase current of the PM motor is positive when flowing into the PM motor), that is, when the phase current flows from the PM motor to the frequency converter, the controllable switch tubes T4, T5, and T6 of the lower bridge arm will be controlled by the phase drive signals corresponding to the phase current; when the phase current is positive, even if the phase drive signal corresponding to the phase current is valid, T4, T5, and T6 will not turn on, and the current flows through the diodes D4, D5, and D6 anti-parallel to T4, T5, and T6 to the motor. Only when the phase current of the PM motor is positive, the controllable switch tubes T1, T2, and T3 of the upper bridge arm will be controlled by the phase drive signals corresponding to the phase current; when the phase current is negative, even if the phase drive signal corresponding to the phase current is valid, T1, T2, and T3 will not turn on, and the current flows through the diodes D1, D2, and D3 anti-parallel to T1, T2, and T3 to the motor.

[0083] Reference Figure 1 , assuming that the U, V, and W phase current values are

[0084]

[0085] where I s is the amplitude of the phase current, and θ i is the phase angle of the U-phase current.

[0086] The phase current of the PM motor is positive when flowing into the PM motor, and the current state is defined as '1'; the phase current of the PM motor is negative when flowing into the frequency converter, and the current state is defined as '0'. Then, the plane can be divided into six sectors R1 to R6 according to the positive and negative signs of the three-phase current or the current vector angle, as Figure 4 shown.

[0087] R1: When -30° < θ i ≤ 30°, the state of the three-phase current is '100';

[0088] R2: When 30° < θ i ≤ 90°, the state of the three-phase current is '110';

[0089] R3: When 90° < θ i ≤ 150°, the state of the three-phase current is '010';

[0090] R4: When 150° < θ i ≤ 210°, the state of the three-phase current is '011';

[0091] R5: When 210° < θ i ≤ 270°, the state of the three-phase current is '001';

[0092] R6: When 270° < θ i ≤ 330°, the state of the three-phase current is '101';

[0093] Define that when the upper-bridge-arm switch or diode is conducting, it is "1", and when the lower-bridge-arm switch or diode is conducting, it is "0". The effective voltage vectors output by the frequency converter are as Figure 5 shown, dividing the plane into six sectors S1 to S6.

[0094] On the premise that the driving signal of the lower-bridge-arm switch of the frequency converter is blocked, when the phase current of the PM motor is positive, the frequency converter is equivalent to the normal working state, and the switching state can be '1' or '0'; when the motor phase current is negative, the frequency converter is equivalent to the upper-bridge-arm conducting state, and the switching state is '1'. On the premise that the driving signal of the upper-bridge-arm switch of the frequency converter is blocked, when the phase current of the PM motor is negative, the frequency converter is equivalent to the normal working state, and the switching state can be '1' or '0'; when the motor phase current is positive, the frequency converter is equivalent to the lower-bridge-arm conducting state, and the switching state is '0'.

[0095] ① When the state of the three-phase current is '100', that is, in the R1 sector, block the driving signal of the upper-bridge-arm switch of the frequency converter, and the lower-bridge-arm switch uses partial combinations or all combinations or a certain one of the voltage vectors U3(010), U4(011), U5(001), U0(000) for PWM chopping (Duty can be from 0 to 100%) to control the braking torque of the motor; or

[0096] ② When the state of the three-phase current is '110', that is, in the R2 sector, block the driving signal of the lower-bridge-arm switch of the frequency converter, and the upper-bridge-arm switch uses partial combinations or all combinations or a certain one of the voltage vectors U4(011), U5(001), U6(101), U0(111) for PWM chopping to control the braking torque of the motor; or

[0097] ③ When the state of the three-phase current is '010', that is, in the R3 sector, block the driving signal of the upper-bridge-arm switch of the frequency converter, and the lower-bridge-arm switch uses partial combinations or all combinations or a certain one of the voltage vectors U5(001), U6(101), U1(100), U0(000) for PWM chopping to control the braking torque of the motor; or

[0098] ④ When the state of the three-phase current is '011', that is, in the R4 sector, block the driving signal of the lower-bridge-arm switch of the frequency converter, and the upper-bridge-arm switch uses partial combinations or all combinations or a certain one of the voltage vectors U1(100), U2(110), U6(101), U0(111) for PWM chopping to control the braking torque of the motor; or

[0099] ⑤When the state of the three-phase current is '001', i.e., the R5 sector, block the drive signals of the upper-bridge-arm switching tubes of the frequency converter. The lower-bridge-arm switching tubes use partial combinations or all combinations or a certain one of the voltage vectors U1(100), U2(110), U3(010), U0(000) for PWM chopping to control the braking torque of the motor; or

[0100] ⑥When the state of the three-phase current is '101', i.e., the R6 sector, block the drive signals of the lower-bridge-arm switching tubes of the frequency converter. The upper-bridge-arm switching tubes use partial combinations or all combinations or a certain one of the voltage vectors U2(110), U3(010), U4(011), U0(111) for PWM chopping to control the braking torque of the motor.

[0101] That is, according to the current information of the motor, six sectors are divided. The drive signals of the upper-bridge-arm switching tubes of the frequency converter are blocked in the R1, R3, and R5 sectors, and the drive signals of the lower-bridge-arm switching tubes of the frequency converter are blocked in the R2, R4, and R6 sectors, that is, the drive signals of the upper and lower bridge arm switching tubes are alternately blocked. For convenience, it is hereinafter simply referred to as STO_60. Its braking torque can be greatly increased compared with the traditional star-blocking braking torque, such as Figure 3 curve 33; at the same time, since the motor current can be controlled to be sinusoidal or quasi-sinusoidal, its torque ripple is also small. At the same time, the IGBT / diodes of the upper and lower bridge arm switching tubes are alternately turned on, and the heat dissipation is balanced.

[0102] When the drive signals of the upper-bridge-arm switching tubes of the frequency converter are always blocked, that is, when the drive signals of the upper-bridge-arm switching tubes are blocked in all the R1 - R6 sectors,

[0103] ①When the state of the three-phase current is '100', i.e., the R1 sector, the lower-bridge-arm switching tubes use partial combinations or all combinations or a certain one of the voltage vectors U3(010), U4(011), U5(001), U0(000) for PWM chopping to control the braking torque of the motor; or

[0104] ②When the state of the three-phase current is '110', i.e., the R2 sector, the lower-bridge-arm switching tubes use partial combinations or all combinations or a certain one of the voltage vectors U5(001), U0(000) for PWM chopping to control the braking torque of the motor.

[0105] ③When the state of the three-phase current is '010', i.e., the R3 sector, the lower-bridge-arm switching tubes use partial combinations or all combinations or a certain one of the voltage vectors U5(001), U6(101), U1(100), U0(000) for PWM chopping to control the braking torque of the motor; or

[0106] ④ When the state of the three-phase current is '011', i.e., in the R4 sector, the lower-arm switching devices use partial combinations, or all combinations, or a single one of the voltage vectors U1(100) and U0(000) for PWM chopping to control the braking torque of the motor; or

[0107] ⑤ When the state of the three-phase current is '001', i.e., in the R5 sector, the lower-arm switching devices use partial combinations, or all combinations, or a single one of the voltage vectors U1(100), U2(110), U3(010), and U0(000) for PWM chopping to control the braking torque of the motor; or

[0108] ⑥ When the state of the three-phase current is '101', i.e., in the R6 sector, the lower-arm switching devices use partial combinations, or all combinations, or a single one of the voltage vectors U3(010) and U0(000) for PWM chopping to control the braking torque of the motor.

[0109] When the drive signals of the lower-arm switching devices of the frequency converter are continuously blocked, i.e., when the drive signals of the lower-arm switching devices are blocked in all sectors from R1 to R6,

[0110] ① When the state of the three-phase current is '100', i.e., in the R1 sector, the upper-arm switching devices use partial combinations, or all combinations, or a single one of the voltage vectors U4(011) and U0(111) for PWM chopping to control the braking torque of the motor; or

[0111] ② When the state of the three-phase current is '110', i.e., in the R2 sector, the upper-arm switching devices use partial combinations, or all combinations, or a single one of the voltage vectors U4(011), U5(001), U6(101), and U0(111) for PWM chopping to control the braking torque of the motor; or

[0112] ③ When the state of the three-phase current is '010', i.e., in the R3 sector, the upper-arm switching devices use partial combinations, or all combinations, or a single one of the voltage vectors U6(101) and U0(111) for PWM chopping to control the braking torque of the motor; or

[0113] ④ When the state of the three-phase current is '011', i.e., in the R4 sector, the upper-arm switching devices use partial combinations, or all combinations, or a single one of the voltage vectors U1(100), U2(110), U6(101), and U0(111) for PWM chopping to control the braking torque of the motor; or

[0114] ⑤ When the state of the three-phase current is '001', i.e., in the R5 sector, the upper-arm switching devices use partial combinations, or all combinations, or a single one of the voltage vectors U2(110) and U0(111) for PWM chopping to control the braking torque of the motor; or

[0115] ⑥When the state of the three-phase current is '101', i.e., the R6 sector, the upper-bridge switching devices use partial combinations or all combinations or a single one of the voltage vectors U2(110), U3(010), U4(011), and U0(111) for PWM chopping to control the braking torque of the motor.

[0116] For convenience, continuously blocking the drive signals of the lower-bridge switching devices of the above frequency converter or continuously blocking the drive signals of the upper-bridge switching devices of the frequency converter is simply referred to as STO_360.

[0117] The state equation of the permanent magnet synchronous motor can be written as

[0118]

[0119] p is the differential operator, u d , u q are the direct-axis and quadrature-axis stator voltages; i d , i q are the direct-axis and quadrature-axis stator currents; L d , L q are the direct-axis and quadrature-axis inductances; R s is the stator resistance, ω e is the electrical angular velocity, ψ r is the rotor flux linkage. Discretizing Equation (1) gives the predicted motor current as

[0120]

[0121] In the formula, T s is the discrete control period; k is the k-th discrete control period; i d (k + 1), i q (k + 1) are the predicted values of the direct-axis and quadrature-axis stator currents at the (k + 1)T s moment; i d (k), i q (k) are the actual values of the direct-axis and quadrature-axis stator currents at the kT s moment; u d (k), u q (k) are the projection components of the voltage vector on the direct-axis and quadrature-axis at the kT s moment; ω e (k) is the electrical angular velocity at the kT s moment. Among them, i d (k), i q (k) can be obtained by performing coordinate transformation on the motor phase current measured by the current sensor, and ω e (k) can be obtained by the position sensor of the motor.

[0122] The torque equation of the permanent magnet synchronous motor is

[0123]

[0124] where n p is the number of pole pairs of the motor. According to (2) and (3), the predicted torque is

[0125]

[0126] Example 1: Maximum torque predictive control

[0127] The idea of maximum torque predictive control is to select an appropriate voltage vector to maximize the torque output. Equation (4) can be used as the cost function for torque prediction optimization, and the selection of the voltage vector is restricted by the current vector intervals under STO_60 and STO_360 as described above. Taking the case where the current vector is in sector R1 under STO_60 as an example, the drive signals of the upper-bridge arm switching tubes of the frequency converter are blocked, and the voltage vectors U3(010), U4(011), U5(001), and U0(000) are traversed to determine the optimal voltage vector. Under the optimal voltage vector control, the braking torque of the motor is the largest.

[0128] As can be seen from equations (2) and (3), under the control of different voltage vectors, the current and braking torque of the motor are different. Therefore, the braking torques of the motor under the control of different voltage vectors can be compared to determine the optimal voltage vector from multiple voltage vectors to maximize the braking torque of the motor.

[0129] Figure 7 is the principle block diagram of the STO_60 and STO_360 schemes based on maximum torque predictive control. Figure 8 is the simulation result under STO_60 and STO_360 based on maximum torque predictive control.

[0130] It should be noted that in order to prevent excessive current at medium and high speeds, current control can be added on the basis of maximum torque predictive control. For example, software peak current control or hysteresis current control with a control period can be used to block the drive signals of all the switching tubes of the upper and lower bridge arms when the motor current exceeds the set threshold; average current control with a PI regulator can also be used, and the PWM duty output by the PI regulator is used for the optimal voltage vector obtained by optimization, or the PWM duty output by the PI regulator is used for the alternative voltage vectors for optimization. PWMDuty that changes with speed can also be added on the basis of maximum torque predictive control, that is, the higher the speed, the smaller the PWM Duty, so as to prevent excessive current at medium and high speeds.

[0131] Example 2: Torque target predictive control

[0132] The torque of the STO_360 and STO_60 schemes of maximum torque predictive control under 650V*100% bus voltage, 650V*70% bus voltage, 650V*50% bus voltage, 650V*30% bus voltage, and 650V*10% bus voltage is shown in Figure 9. It can be seen from Figure 9 that under different DC bus voltages, the torque output ability of the motor will change. The lower the bus voltage, the smaller the maximum torque that can be output, and the smaller the torque ripple.

[0133] According to Figure 9, the speed and DC bus voltage can be used as the basis for selecting the target torque to obtain a torque capacity table, such as the target value of the torque taking the upper envelope or above of the maximum torque. Predictive control can compare the predicted torque with the target torque by setting the target torque, and predict the voltage vector with the smallest error between the output torque and the target torque. The cost function is

[0134] T e_err (k + 1)=T e_ref -T e (k + 1)(5)

[0135] In the formula, T e_ref is the target torque, T e (k + 1) is the predicted torque, and T e_err (k + 1) is the error between the target torque and the predicted torque.

[0136] The idea of torque target predictive control is to select an appropriate voltage vector to minimize the error between the target torque and the predicted torque. Equation (5) can be used as the cost function for torque target predictive optimization. The selection of its voltage vector is restricted by the current vector intervals under STO_60 and STO_360 as described above. Taking the case of STO_60 and the current vector in sector R1 as an example, the drive signals of the upper bridge arm switching tubes of the frequency converter are blocked, and the voltage vectors U3(010), U4(011), U5(001), and U0(000) are traversed to determine the optimal voltage vector. Under the optimal voltage vector control, the error between the target torque and the predicted torque is minimized.

[0137] The torque of the STO_60 and STO_360 schemes based on torque target prediction under a constant bus voltage Udc = 650V is shown in Figure 10. The torque ripple output by the STO_360 scheme based on torque target prediction is smaller than that of the STO_360 scheme of maximum torque prediction. The maximum torque ripple is reduced from 528 Nm to 100 Nm; the torque ripple of the STO_60 scheme based on torque target prediction is slightly smaller than that of the STO_60 scheme based on maximum torque prediction, and the torque ripple is reduced from 263 Nm to 206 Nm.

[0138] To further reduce the torque ripple, the control period can be shortened.

[0139] Embodiment 3 Multi-Vector Torque Target Prediction Control

[0140] The selection of the torque target value and the prediction cost function are the same as those described in Embodiment 2. Only the differences are introduced here.

[0141] 1) At STO_60

[0142] When the current vector is in sectors R1, R3, and R5, each voltage sector can be evenly divided into two or more sectors, such as four sectors, as shown. When the current vector is in sectors R2, R4, and R6, the voltage sectors R2, R4, and R6 can also be evenly divided into two or more sectors, such as four sectors. Taking the current vector in sector R1 as an example, 6 virtual voltage vectors can be generated in voltage sectors S3 and S4. The prediction of the optimal vector can be achieved in two steps. The first step: find the optimal voltage vector among 3 effective vectors and 6 virtual voltage vectors to minimize the torque error. The second step: assume that the vector searched in the first step is U3, then divide the searched optimal voltage vector U3 into five equal parts, which already includes the zero vector, and search for the optimal vector again among these five equal parts of vectors. This method of finding the optimal vector in two steps is called the multi-vector torque target prediction control strategy. The more the sector is subdivided, the closer the searched optimal voltage vector is to the actual required voltage vector; the more the optimal voltage vector is divided equally, the smaller its error, but the more complex the implementation is. Figure 11 The principle block diagram of the STO_60 scheme based on multi-vector torque target prediction control is as shown. The optimal reference vector generates the drive signals of each switch tube through the Space Vector Pulse Width Modulation (SVPWM) module.

[0143] It should be noted that the SVPWM module needs to select the zero vectors U0(000) and U0(111) according to the sector where the current vector is located. That is, when the current vector is in sectors R1, R3, and R5, only the zero vector U0(000) is selected; when the current vector is in sectors R2, R4, and R6, only the zero vector U0(111) is selected. Figure 12 The simulation results of this scheme are as shown. It can be seen that this scheme can reduce the torque high-frequency ripple compared with the STO_60 scheme based on maximum torque prediction control, and the maximum torque ripple is reduced from 263 Nm to 140 Nm.

[0144] 2) STO_360 and the drive signals of the upper bridge arm switch tubes of the frequency converter are always blocked

[0145] Figure 13b

[0146]

[0147] ​​​The driving signal of the upper-bridge-arm switching tube of the frequency converter is always blocked. When the current vector is in sectors R1, R3, and R5, each voltage sector can be evenly divided into four sectors, as Figure 11 shown. Taking the current vector in sector R1 as an example, 6 virtual voltage vectors can be generated in voltage sectors S3 and S4. The prediction of the optimal vector can be achieved in two steps. The first step: find the optimal voltage vector among the 3 effective vectors and 6 virtual voltage vectors to minimize the torque error; The second step: assume that the vector searched in the first step is U3, then divide the searched optimal voltage vector U3 into five equal parts, which already includes the zero vector, and search for the optimal vector again among these five equal parts of vectors.

[0148] When the current vector is in sectors R2, R4, and R6, since only one effective voltage vector and the zero vector can be utilized, therefore, directly execute the second-step prediction.

[0149] The principle block diagram of the STO_360 scheme based on multi-vector torque target predictive control is as Figure 12 shown, and the optimal reference vector generates the driving signals of each switching tube through the SVPWM module.

[0150] It should be noted that since the driving signal of the upper-bridge-arm switching tube of the frequency converter is always blocked, the SVPWM module can only select the zero vector U0(000).

[0151] Figure 13a For the STO_360 scheme based on the multi-vector torque target predictive control strategy, it can be seen that the maximum torque ripple has dropped from 528 Nm to 30 Nm.

[0152] 3) STO_360 and the driving signal of the lower-bridge-arm switching tube of the frequency converter is always blocked

[0153] The driving signal of the lower-bridge-arm switching tube of the frequency converter is always blocked. When the current vector is in sectors R2, R4, and R6, each voltage sector can also be evenly divided into four sectors. Taking the current vector in sector R2 as an example, 6 virtual voltage vectors can be generated in voltage sectors S4 and S5. The prediction of the optimal vector can be achieved in two steps. The first step: find the optimal voltage vector among the 3 effective vectors and 6 virtual voltage vectors to minimize the torque error; The second step: assume that the vector searched in the first step is U5, then divide the searched optimal voltage vector U5 into five equal parts, which already includes the zero vector, and search for the optimal vector again among these five equal parts of vectors.

[0154] When the current vector is in sectors R1, R3, and R5, since only one effective voltage vector and the zero vector can be utilized, therefore, directly execute the second-step prediction.

[0155] The principle block diagram of the STO_360 scheme based on multi-vector torque target predictive control is as follows Figure 12 shown. The optimal reference vector generates the drive signals of each switching tube through the SVPWM module.

[0156] It should be noted that since the drive signals of the switching tubes on the lower bridge arm of the frequency converter are always blocked, the SVPWM module can only select the zero vector U0(111).

[0157] Figure 13a For the STO_360 scheme based on the multi-vector torque target predictive control strategy, it can be seen that the maximum torque ripple is reduced from 528 Nm to 30 Nm.

[0158] It should be noted that when Ld of the PM motor is equal to Lq or the reluctance torque is negligible, from the torque formula (3) of the motor, it can be known that the output torque is proportional to the torque current. Therefore, the above schemes of Embodiments 1 to 3 are also applicable to torque current prediction. In addition, at a certain speed, since the output power is proportional to the torque, the above scheme is also applicable to output power prediction.

[0159] Embodiment 4 Current Target Predictive Control

[0160] The selection of the torque target value is as in Embodiment 2, and the q-axis current reference value can be calculated from the torque reference value. The current target predictive control can control the d-axis current to 0 to maximize the braking torque on the premise of the same stator current magnitude by setting the d and q-axis current reference values, and control the q-axis current to the q-axis current reference value to minimize the braking torque ripple. The cost function of the current target predictive control is

[0161]

[0162] The idea of the current target predictive control is to select an appropriate voltage vector to minimize the error between the target current and the predicted current. Equation (6) can be used as the cost function for current target predictive optimization. The selection of its voltage vector is restricted by the current vector intervals under STO_60 and STO_360 as described above. Taking the case of STO_60 and the current vector in Sector R1 as an example, the drive signals of the switching tubes on the upper bridge arm of the frequency converter are blocked, and the voltage vectors U3(010), U4(011), U5(001), and U0(000) are traversed to determine the optimal voltage vector. Under the optimal voltage vector control, the error between the target current and the predicted current is minimized.

[0163] To further reduce the torque ripple, the method of finding the optimal vector in two steps in Embodiment 3 can be adopted, that is, multi-vector current target predictive control.

[0164] In an example, the principle of the STO_60 scheme of multi-vector current target predictive control is as follows Figure 12As shown, the simulation results of this scheme are as Figure 14 shown. The torque ripple of the STO_60 scheme based on current target prediction is slightly smaller than that of the STO_60 scheme based on maximum torque prediction.

[0165] Since the torque ripple is mainly related to the ripple of the quadrature-axis current, in order to reduce the torque ripple under a large reference torque, a weight factor can be set to enhance the priority of the quadrature-axis current, thereby reducing the ripple of the quadrature-axis current. The cost function can be changed to

[0166]

[0167] where η is the weight coefficient of the quadrature-axis current, and η ≥ 1.

[0168] Figure 15 It is the output torque when the operating frequency is 30Hz, in the STO_60 scheme based on current target prediction, the reference value of the quadrature-axis current is -82A; in the STO_60 scheme based on current target prediction with a weight factor, the reference value of the torque is -1400N.m, and η = 10. It can be seen that the STO_60 scheme of current target prediction with the addition of the quadrature-axis current weight factor effectively reduces the torque ripple under a large torque.

[0169] Example 5

[0170] Preferably, the traditional electronic star-sealing braking of the prior art does not require information such as an encoder. To improve reliability, the traditional electronic star-sealing braking can be adopted at low speeds. When the speed is higher than a certain threshold, it is switched to the vector control scheme of alternately blocking the upper and lower bridge arms of the STO_60 or the vector control scheme of continuously blocking a certain bridge arm of the STO_360. This threshold n1 can generally be taken as the rotational speed corresponding to the vicinity of the maximum star-sealing torque during traditional star-sealing braking. In this way, when the unbalanced torque is small, the speed stabilizes at Figure 3 a certain point on curve 31, and only when the unbalanced torque is greater than the traditional star-sealing braking torque, the elevator continues to accelerate and coast before switching to the said vector control scheme.

[0171] In addition, in order to prevent frequent switching, a hysteresis loop of the prior art can be set. Preferably, the speed value of the hysteresis loop can be taken as less than n1 by 2Hz.

[0172] It should be noted that speed closed-loop control can be performed on the basis of the above-mentioned motor braking torque control based on predictive control, and the output of the speed loop is used as the torque target or current target. When the brake fails after the elevator stops normally and the car door of the elevator is closed, a reasonable speed curve can be set to run to the end stage at a controllable speed, reducing the long-term operation in the star-connection braking state. In addition, for the high-speed emergency stop of the elevator, a reasonable deceleration curve can be set. When the brake is normal, it does not participate in braking, and the deceleration of the light-load downward or the heavy-load upward will not exceed the requirements, and it only participates in braking when the brake fails.

[0173] It should be noted that when the elevator makes a high-speed emergency stop, for a PM motor, current can be generated in the motor through PWM chopping, so as to perform current sector division and alternating blocking. For an induction motor, etc., PWM chopping needs to be performed when the residual magnetism has not disappeared completely to generate current in the motor. Otherwise, since the rotor has no permanent magnet, current cannot be generated and it cannot be used for rapid braking or emergency braking.

Claims

1. An electric braking method for a motor, including a drive system, the drive system having a motor and an inverter, characterized in that, Based on the current information of the motor, alternately block the upper and lower bridge arm switching tubes, utilize more voltage vectors for the control of the braking torque of the motor, or continuously block a certain bridge arm switching tube, and select appropriate voltage vectors according to the current information of the motor for the control of the braking torque of the motor.

2. The electric braking method for a motor according to claim 1, characterized in that, When two-phase phase currents of the motor flow into the frequency converter or only one-phase phase current flows out of the frequency converter, block the upper bridge arm switching tube; when two-phase phase currents of the motor flow out of the frequency converter or only one-phase phase current flows into the frequency converter, block the lower bridge arm switching tube; or continuously block the upper bridge arm switching tube and perform PWM chopping on the lower bridge arm switching tube; or continuously block the lower bridge arm switching tube and perform PWM chopping on the upper bridge arm switching tube.

3. The electric braking method for a motor according to claim 2, characterized in that, When blocking the upper bridge arm switching tube, perform PWM chopping on the lower bridge arm switching tube to control the braking torque of the motor; and / or when blocking the lower bridge arm switching tube, perform PWM chopping on the upper bridge arm switching tube to control the braking torque of the motor.

4. The electric braking method for a motor according to claim 3, wherein It is set that: the phase current of the PM motor is positive when flowing into the PM motor, and the current state is defined as '1'; the phase current of the PM motor is negative when flowing into the frequency converter, and the current state is defined as '0'. Then, the plane can be divided into six sectors according to the positive and negative signs of the three-phase current or the current vector angle. First sector: When -30° < θ i ≤ 30°, the state of the three-phase current is '100'; Second sector: When 30° < θ i ≤ 90°, the state of the three-phase current is '110'; Third sector: When 90° < θ i ≤ 150°, the state of the three-phase current is '010'; Fourth sector: When 150° < θ i ≤ 210°, the state of the three-phase current is '011'; Fifth sector: When 210° < θ i ≤ 270°, the state of the three-phase current is '001'; Sixth sector: When 270° < θ i ≤ 330°, the state of the three-phase current is '101'; In the first sector, the third sector, and the fifth sector, block the drive signals of the upper bridge arm switching tubes of the frequency converter; in the second sector, the fourth sector, and the sixth sector, block the drive signals of the lower bridge arm switching tubes of the frequency converter, that is, alternately block the drive signals of the upper and lower bridge arm switching tubes; or continuously block a certain bridge arm switching tube.

5. The electric braking method for a motor according to claim 4, wherein ① When the state of the three-phase current is '100', that is, in the first sector, block the drive signal of the upper bridge arm switching tube of the frequency converter, and the lower bridge arm switching tube performs PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors to control the braking torque of the motor; or ② When the state of the three-phase current is '110', that is, in the second sector, block the drive signal of the lower bridge arm switching tube of the frequency converter, and the upper bridge arm switching tube performs PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors to control the braking torque of the motor; or ③ When the state of the three-phase current is '010', that is, in the third sector, block the drive signal of the upper bridge arm switching tube of the frequency converter, and the lower bridge arm switching tube performs PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors to control the braking torque of the motor; or ④ When the state of the three-phase current is '011', that is, in the fourth sector, block the drive signal of the lower bridge arm switching tube of the frequency converter, and the upper bridge arm switching tube performs PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors to control the braking torque of the motor; or ⑤ When the state of the three-phase current is '001', that is, in the fifth sector, block the drive signal of the upper bridge arm switching tube of the frequency converter, and the lower bridge arm switching tube performs PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors to control the braking torque of the motor. ⑥ Or when the state of the three-phase current is '101', i.e., the sixth sector, block the drive signals of the lower-bridge-arm switching devices of the frequency converter, and the upper-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors to control the braking torque of the motor.

6. The electric braking method for a motor according to claim 4, characterized in that, When the drive signals of the upper-bridge-arm switching devices of the frequency converter are blocked all the time, ① When the state of the three-phase current is '100', i.e., the first sector, the lower-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors U3(010), U4(011), U5(001), U0(000) to control the braking torque of the motor; or ② When the state of the three-phase current is '110', i.e., the second sector, the lower-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors U5(001), U0(000) to control the braking torque of the motor; ③ When the state of the three-phase current is '010', i.e., the third sector, the lower-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors U5(001), U6(101), U1(100), U0(000) to control the braking torque of the motor; or ④ When the state of the three-phase current is '011', i.e., the fourth sector, the lower-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors U1(100), U0(000) to control the braking torque of the motor; or ⑤ When the state of the three-phase current is '001', i.e., the fifth sector, the lower-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors U1(100), U2(110), U3(010), U0(000) to control the braking torque of the motor; or ⑥ When the state of the three-phase current is '101', i.e., the sixth sector, the lower-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors U3(010), U0(000) to control the braking torque of the motor.

7. The electric braking method for an electric machine according to claim 4, characterized in that, When the drive signals of the lower-bridge-arm switching devices of the frequency converter are blocked all the time, ① When the state of the three-phase current is '100', i.e., the first sector, the upper-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors U4(011), U0(111) to control the braking torque of the motor; or ② When the state of the three-phase current is '110', i.e., the second sector, the upper-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors U4(011), U5(001), U6(101), U0(111) to control the braking torque of the motor; or ③ When the state of the three-phase current is '010', i.e., the third sector, the upper-bridge-arm switching devices perform PWM chopping using partial combinations or all combinations or a certain one of the voltage vectors U6(101), U0(111) to control the braking torque of the motor; or ④When the state of the three-phase current is '011', i.e., the fourth sector, the upper-bridge switching devices perform PWM chopping using partial combinations or all combinations or a single one of the voltage vectors U1(100), U2(110), U6(101), U0(111) to control the braking torque of the motor; or ⑤When the state of the three-phase current is '001', i.e., the fifth sector, the upper-bridge switching devices perform PWM chopping using partial combinations or all combinations or a single one of the voltage vectors U2(110), U0(111) to control the braking torque of the motor; or ⑥When the state of the three-phase current is '101', i.e., the sixth sector, the upper-bridge switching devices perform PWM chopping using partial combinations or all combinations or a single one of the voltage vectors U2(110), U3(010), U4(011), U0(111) to control the braking torque of the motor.

8. The electric braking method for an electric machine according to claim 5 or 6 or 7, characterized in that, The control of the braking torque of the motor is made based on torque prediction or torque current prediction or output power prediction or current target prediction.

9. The electric braking method for a motor according to claim 8, characterized in that, The torque prediction is divided into maximum torque prediction, torque target prediction with minimum torque error, and multi-vector target torque prediction.

10. The electric braking method for an electric machine according to claim 9, characterized in that, The maximum torque prediction is made according to the following cost function formula: Alternatively, the torque target prediction with minimum torque error and the multi-vector target torque prediction are made according to the following cost function formula: T e_err (k + 1) = T e_ref -T e (k + 1). Alternatively, the current target prediction is made according to the following cost function formula: where η is the weight coefficient of the quadrature-axis current and η ≥ 1.

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