JP2021027625A - Demagnetization determination method - Google Patents

Abstract

To provide a demagnetization determination method capable of accurately determining the demagnetization of a permanent magnet of a permanent synchronous motor.SOLUTION: When a vehicle is idling (S1: YES), a command value of a current supplied to a motor is set to zero (S4), and a counter electromotive voltage generated in the motor in that state is detected (S5). Based on the counter electromotive voltage, it is determined whether a permanent magnet used in a rotor of a motor 2 is demagnetized. Specifically, the rotation speed of the motor 2 is detected, and a counter electromotive voltage constant is obtained by dividing the counter electromotive voltage by the rotation speed (S6). When the counter electromotive voltage constant is less than a threshold, it is determined that the permanent magnet is demagnetized (S7: YES, S8).SELECTED DRAWING: Figure 2

Description

The present invention relates to a demagnetization determination method for determining demagnetization of a permanent magnet of a permanent magnet synchronous motor.

For hybrid vehicles (HVs) and electric vehicles (EVs), there are motors as driving sources for driving and PCUs (Power Control Units) that control the input and output of power to the motors. Is installed.

Permanent Magnet Synchronous Motors (PMSMs) are widely used as motors. A permanent magnet synchronous motor is a synchronous motor that uses a permanent magnet, which is a ferromagnet, for the rotor. The magnetic flux of a permanent magnet has the property of decreasing with increasing temperature and returning to its original state when cooled. However, when a certain amount of current is applied to the permanent magnet synchronous motor at a high temperature, an irreversible change occurs in the permanent magnet, and the magnetic flux of the permanent magnet remains reduced. When this demagnetization occurs, the torque of the permanent magnet synchronous motor during normal use decreases. Therefore, in the permanent magnet synchronous motor, it is necessary to determine whether or not the permanent magnet is demagnetized.

Therefore, the magnetic flux (magnetic flux density) of the permanent magnet is calculated from the voltage equation of the permanent magnet synchronous motor using the voltage and current supplied to the permanent magnet synchronous motor and the rotation speed of the permanent magnet synchronous motor, and based on this, the magnetic flux (magnetic flux density) of the permanent magnet is calculated. A method for determining demagnetization of a permanent magnet has been proposed (see, for example, Patent Document 1).

JP-A-2010-239790

However, since the voltage equation includes constants such as winding resistance and inductance of the permanent magnet synchronous motor, the value of the magnetic flux calculated from the voltage equation varies among individuals due to the variation of the constants among individuals. Therefore, the accuracy of the demagnetization determination is not good in the method according to the conventional proposal.

An object of the present invention is to provide a demagnetization determination method capable of accurately determining the demagnetization of a permanent magnet of a permanent magnet synchronous motor.

In order to achieve the above object, the demagnetization determination method according to the present invention is a method for determining the demagnetization of the permanent magnet of a permanent magnet synchronous motor mounted as a driving source for traveling in a vehicle, and is a permanent magnet synchronous method. The command value of the current supplied to the permanent magnet synchronous motor is set to zero when the motor is idle without power running and regenerative operation, and when the current value flowing through the permanent magnet synchronous motor is zero, the permanent magnet synchronization This is a method of detecting a countercurrent voltage generated from a voltage value supplied to an electric motor and determining whether or not the permanent magnet is demagnetized based on the detected countercurrent voltage.

According to this method, the command value of the current supplied to the permanent magnet synchronous motor is set to zero when the vehicle is idling, and the counter electromotive voltage generated in the permanent magnet synchronous motor in that state is detected. Then, based on the counter electromotive voltage, it is determined whether or not the permanent magnet is demagnetized.

The counter electromotive voltage correlates with the counter electromotive voltage constant of the permanent magnet synchronous motor, and the counter electromotive voltage constant correlates with the magnetic flux of the permanent magnet. Therefore, it can be determined whether or not the permanent magnet is demagnetized based on the counter electromotive voltage. Moreover, since this method does not use constants that vary among individual permanent magnet synchronous motors, it is possible to accurately determine the demagnetization of the permanent magnets. As a result, by notifying the user of the demagnetization of the permanent magnet, it is possible to prevent dissatisfaction with the deterioration of drivability due to the insufficient torque of the permanent magnet synchronous motor due to the demagnetization.

In the determination of whether or not the permanent magnet is demagnetized, the counter electromotive force constant is obtained by detecting the rotation speed of the permanent magnet synchronous motor and dividing the counter electromotive force by the rotation speed, and the counter electromotive voltage constant is calculated. If it is less than the threshold value, it may be determined that the permanent magnet is demagnetized.

Further, even if the command value of the current is set to zero while the vehicle is idling, the predetermined first time has elapsed from the end of the previous running and the predetermined second time has passed since the start of the current running. Good. Thereby, the demagnetization of the permanent magnet can be determined in the cold state where the permanent magnet synchronous motor is cold. As a result, it is possible to prevent the temporary decrease in magnetic flux due to the temperature rise of the permanent magnet from being erroneously determined as demagnetization, and the accuracy of the demagnetization determination of the permanent magnet can be further improved.

According to the present invention, the demagnetization of the permanent magnet of the permanent magnet synchronous motor is accurately determined.

It is a figure which shows the structure of the main part of the vehicle which concerns on one Embodiment of this invention. It is a flowchart which shows the flow of demagnetization determination processing.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Main part composition of the vehicle>
FIG. 1 is a diagram showing a configuration of a main part of a vehicle 1 according to an embodiment of the present invention.

The vehicle 1 is a hybrid vehicle (HV) equipped with a motor 2 as a driving source for traveling. For example, a series type hybrid system is adopted for the vehicle 1. In the series type hybrid system, the power of the engine is converted into electric power by the motor for power generation, the motor 2 is driven by the electric power, and the power of the motor 2 is transmitted to the drive wheels.

The motor 2 is a permanent magnet synchronous motor (PMSM) that uses a permanent magnet that is a ferromagnetic material for the rotor. The motor 2 functions as an electric motor and also as a generator.

Further, the vehicle 1 is equipped with a drive battery 3 and a PCU (Power Control Unit) 4.

The drive battery 3 is an assembled battery in which a plurality of secondary batteries are combined, and is, for example, a lithium ion battery. The drive battery 3 outputs, for example, DC power of about 200 to 350 V.

The PCU 4 is connected to the motor 2 and the drive battery 3. The PCU 4 has a built-in inverter 5 and a microcomputer (microcontroller unit) 6. The inverter 5 is configured by providing a series circuit of two semiconductor switching elements corresponding to each of the U phase, V phase, and W phase of the motor 2 and connecting the series circuits in parallel with each other.

During the power running operation in which the motor 2 functions as an electric motor, the DC power output from the drive battery 3 is converted into AC power by the inverter 5, and the AC power is supplied from the inverter 5 to the motor 2. On the other hand, during the regenerative operation in which the motor 2 functions as a generator, the power from the drive wheels is converted into AC power by the motor 2. At this time, the motor 2 becomes a resistance of the drive system, and the regenerative braking force due to the resistance acts on the drive wheels. The AC power generated by the motor 2 is converted into DC power by the inverter 5 and charged into the drive battery 3.

The microcomputer 6 detects the rotation speed of the motor 2. Specifically, the motor 2 is provided with a rotation sensor (not shown) that outputs a pulse signal synchronized with the rotation of the motor 2, and the microcomputer 6 is based on the period of the pulse signal output from the rotation sensor. Obtain the number of rotations of the motor 2. Further, the microcomputer 6 detects the voltage appearing between the motor 2 and the inverter 5.

The voltage can be detected indirectly by stopping the switching of the inverter 5 and directly detecting the voltage, without stopping the switching of the inverter 5 from the input voltage to the inverter 5 and the output voltage pulse width from the inverter 5 to the motor 2. It may be a method of calculating.

Further, the vehicle 1 is equipped with an ECU (Electronic Control Unit) 7. The ECU 7 has a built-in non-volatile memory such as a CPU and flash memory and a volatile memory such as a DRAM (Dynamic Random Access Memory). Although only one ECU 7 is shown in FIG. 1, the vehicle 1 is equipped with a plurality of ECUs having the same configuration as the ECU 7 in order to control each part. A plurality of ECUs including the ECU 7 are connected so as to be capable of bidirectional communication by a CAN (Controller Area Network) communication protocol. Further, the ECU 7 is communicably connected to the microcomputer 6 of the PCU 4.

The ECU 7 controls the operation of the inverter 5 of the PCU 4 via the microcomputer 6 based on information received from another ECU or the microcomputer 6 of the PCU 4.

<Demagnetization judgment processing>
FIG. 2 is a flowchart showing the flow of the demagnetization determination process.

The ECU 7 executes the demagnetization determination process shown in FIG. 2 while the vehicle 1 is traveling in order to determine the demagnetization of the permanent magnet used in the rotor of the motor 2.

In the demagnetization determination process, first, it is determined whether or not the vehicle 1 is running in the idle state in which the motor 2 is not in power running operation or regenerative operation (step S1). If the vehicle 1 is not idling (NO in step S1), the demagnetization determination process does not proceed to the next step.

When the vehicle 1 is idle (YES in step S1), it is determined whether or not a predetermined first time has elapsed from the end of the previous travel to the present time. The first time is set to, for example, a time sufficient for the temperature of the motor 2 to drop to the first temperature, which is room temperature or a temperature close to room temperature, after the vehicle 1 finishes the previous running.

When the first time has passed from the end of the previous run of the vehicle 1 to the present time (YES in step S2), the time elapsed from the start of the current run to the present time of the vehicle 1 is predetermined. Determine if it is within the second hour. The second time is set based on, for example, the time required for the motor 2 to rise from the first temperature to the second temperature at which the magnetic flux of the permanent magnet of the motor 2 begins to decrease as the vehicle 1 travels.

Whether the first time has not passed from the end of the previous run of the vehicle 1 to the present time (NO in step S2), or the elapsed time from the start of the current run to the present time of the vehicle 1 is the second. If it exceeds 2 hours (NO in step S3), the demagnetization determination process is terminated.

When the elapsed time from the start of the vehicle 1 to the present time is within the second hour (YES in step S3), the command value of the current supplied from the inverter 5 of the PCU 4 to the motor 2 is zero (0). ) Is set (step S4). Then, the zero command value is transmitted from the ECU 7 to the microcomputer 6 of the PCU 4, and the operation of the inverter 5 is controlled by the microcomputer 6, so that the current supplied from the inverter 5 to the motor 2 becomes zero.

The setting of the zero command value is continued for a certain period of time. During this period, the microcomputer 6 detects the voltage appearing between the motor 2 and the inverter 5. Since no current is supplied from the inverter 5 to the motor 2, the voltage that appears between the motor 2 and the inverter 5 at this time is a counter electromotive voltage generated by the rotation of the rotor of the motor 2. That is, the counter electromotive voltage generated in the motor 2 is detected by the microcomputer 6 during the period in which the zero command value is set (step S5).

Further, the microcomputer 6 detects the rotation speed of the motor 2. The counter electromotive voltage and the rotation speed of the motor 2 detected by the microcomputer 6 are transmitted from the microcomputer 6 to the ECU 7. When the counter electromotive voltage and the rotation speed of the motor 2 are input to the ECU 7, the counter electromotive voltage constant of the motor 2 is calculated by dividing the counter electromotive voltage by the rotation speed (step S6).

After that, it is determined whether or not the counter electromotive voltage constant of the motor 2 is less than a predetermined threshold value (step S7). When the counter electromotive voltage constant is less than the threshold value (YES in step S7), it is determined that the permanent magnet of the motor 2 is demagnetized (step S8), and the demagnetization determination process is completed. On the other hand, when the counter electromotive voltage constant is equal to or greater than the threshold value (NO in step S7), it is determined that the permanent magnet of the motor 2 has not been demagnetized, and the demagnetization determination process is completed.

<Effect>
As described above, when the vehicle 1 is idle, the command value of the current supplied to the motor 2 is set to zero, and the counter electromotive voltage generated in the motor 2 is detected in that state. Then, based on the counter electromotive voltage, it is determined whether or not the permanent magnet used in the rotor of the motor 2 is demagnetized. Specifically, the rotation speed of the motor 2 is detected, the counter electromotive voltage constant is obtained by dividing the counter electromotive voltage by the rotation speed, and when the counter electromotive voltage constant is less than the threshold value, the permanent magnet is reduced. It is determined that it is magnetic.

In this demagnetization determination method, since constants having variations among individual motors 2 are not used, the demagnetization of permanent magnets can be accurately determined. As a result, when the permanent magnet is demagnetized, for example, a warning indicating that the permanent magnet is demagnetized is displayed on the multi-information display incorporated in the combination meter to reduce the permanent magnet. The magnetism can be notified to the user. Then, the notification can prevent dissatisfaction with the deterioration of drivability due to insufficient torque of the motor 2 due to demagnetization.

Further, when the first time has elapsed from the end of the previous running of the vehicle 1 to the present time, and the elapsed time from the start of the current running to the present time of the vehicle 1 is within the second hour. , It is determined whether or not the permanent magnet of the motor 2 is demagnetized. As a result, the demagnetization of the permanent magnet is determined in a cold state where the motor 2 is cold. Therefore, it is possible to prevent the temporary decrease in magnetic flux due to the temperature rise of the permanent magnet from being erroneously determined as demagnetization, and the accuracy of the demagnetization determination of the permanent magnet can be further improved.

<Modification example>
Although one embodiment of the present invention has been described above, the present invention can also be implemented in other embodiments.

For example, in the above-described embodiment, the first time has elapsed from the end of the previous travel of the vehicle 1 to the present time, and the elapsed time from the start of the current travel of the vehicle 1 to the present time is the second. If it is within the time, it is assumed that the motor 2 is in a cold state, and the demagnetization of the permanent magnet of the motor 2 is determined. However, it suffices if the cold state of the motor 2 is guaranteed at the time of the demagnetization determination. For example, the history of the operation of the motor 2 while the vehicle 1 is running is recorded in the memory of the microcomputer 6 of the PCU 4, and the vehicle 1 is the last time. When the first time has passed from the end of the running of the motor 2 to the present time and it is determined from the history from the start of the running this time that the temperature of the motor 2 has not reached the second temperature, the motor 2 is permanent. Demagnetization of the magnet may be determined.

Further, since field weakening control is applied when the rotation speed of the motor 2 is equal to or higher than the predetermined rotation speed, the determination of demagnetization of the permanent magnet of the motor 2 is executed when the rotation speed of the motor 2 is less than the predetermined rotation speed. It is preferable to be done. As a result, it is possible to suppress erroneous determination of demagnetization due to field weakening control.

Further, in the above-described embodiment, the case where the technique according to the present invention is applied to a hybrid vehicle adopting the series method is taken as an example, but the technique according to the present invention is applied to a hybrid vehicle adopting another method. It may be applied not only to a hybrid vehicle but also to an electric vehicle not equipped with an engine as long as it is a vehicle equipped with a motor as a driving source for traveling.

In addition, various design changes can be made to the above-mentioned configuration within the scope of the matters described in the claims.

1: Vehicle 2: Motor (permanent magnet synchronous motor)

Claims (2)

It is a method of determining the demagnetization of the permanent magnet of a permanent magnet synchronous motor mounted on a vehicle as a driving source for traveling.
When the permanent magnet synchronous motor is idling without power running and regenerative operation, the command value of the current supplied to the permanent magnet synchronous motor is set to zero.
When the command value of the current is set to zero, the counter electromotive voltage generated in the permanent magnet synchronous motor is detected.
A demagnetization determination method for determining whether or not the permanent magnet is demagnetized based on the detected counter electromotive voltage. Detecting the rotation speed of the permanent magnet synchronous motor,
The first aspect of claim 1, wherein the counter electromotive voltage constant is obtained by dividing the counter electromotive voltage by the rotation speed, and when the counter electromotive voltage constant is less than the threshold value, it is determined that the permanent magnet is demagnetized. Demagnetization judgment method.

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