JP2020191769A - Electric motor demagnetization detection method - Google Patents

Abstract

To provide a demagnetization detection method for an electric motor, which is low cost, highly versatile, and has improved reliability during long-term operation by detecting the demagnetization amount and field temperature from an induced voltage during coasting rotation and monitoring the magnetic life of the permanent magnet field.SOLUTION: A control circuit coasts an electric motor from the energized and controlled rotation state as non-energized to measure a one-phase coil voltage fluctuation width ΔV and an electric angle period t, and stores a value obtained by multiplying the coil voltage fluctuation width ΔV within the obtained electric angle period t by the electric angle period t as an extended induced voltage constant KV, sets one or more desired extended induced voltage constants in advance as a threshold KVth, and determines that demagnetization has occurred when the extended induced voltage constant KV obtained by coasting rotation of the electric motor is equal to or less than the threshold value KVth.SELECTED DRAWING: Figure 3

Description

The present disclosure relates to a demagnetization detection method for, for example, a permanent magnet field type electric motor, and a field temperature detection method associated therewith.

Conventionally, permanent magnet field electric motors (for example, three-phase DC motors) have been widely used for consumer industries from small to large because of their high efficiency and excellent controllability. Structurally, brushless DC motors It is roughly divided into DC motors with brushes, stepping motors, etc. FIG. 13 shows the configuration of a sensorless three-phase brushless direct current (BLDC) motor as a typical motor example. The rotor 2 that rotates about the rotor shaft 1 is provided with a pair of permanent magnet fields 3 having an S pole and an N pole. Armature windings (coils) u, v, and w are arranged on the pole teeth provided in the stator 4 with a phase difference of 120 °, and are star-connected via the neutral point C.

FIG. 14 shows a drive circuit block diagram of the BLDC motor. MOTOR is a sensorless three-phase BLDC motor. The MPU 51 is a microcontroller (control circuit) that controls the rotation stop of the motor in response to the rotation command RUN from the host controller 50, and switches the excitation according to the output of the induced voltage zero cross detection circuit (cellocross comparator: ZERO55). Performs position sensorless drive. The INV 52 is a three-phase half-bridge type inverter circuit (motor output circuit).

FIG. 15 shows a timing chart of 120 ° energization as an example of the drive method of the BLDC motor. Section 1 is from U phase to V phase, section 2 is from U phase to W phase, section 3 is from V phase to W phase, section 4 is from V phase to U phase, and section 5 is from W phase to U phase. Section 6 is energized with a square wave from the W phase to the V phase. The broken line is the induced voltage waveform. HU to HW are Hall sensor output waveforms.

All of these DC motors have a drawback that the permanent magnet used for the field magnetism is demagnetized, and the demagnetization causes problems such as a decrease in output, an increase in heat generation, and an unstable start of position sensorless drive. There are various types of demagnetization, but mainly thermal demagnetization, in which the magnetic force decreases as the temperature of the permanent magnet rises, and irreversible demagnetization, in which the magnetic force irreversibly decreases and does not return to the original value when the high or low temperature limit is exceeded. There are two types. FIG. 1 shows a schematic diagram of the demagnetization curve. The horizontal axis is the temperature T ° C. and the vertical axis is the magnetic flux density β. Lo is the low temperature side and Hi is the allowable temperature on the high temperature side. The magnetic flux density β changes between a and b in response to a temperature change, and once the temperature exceeds the limit, it is irreversibly demagnetized and changes between cd.

Although demagnetization detection is rarely performed in small DC motors, high-power motors (main motors for electric vehicles and compressor motors for home appliances) use neodymium magnets with a large coercive force and are easily irreversibly demagnetized at high temperatures. Methods for reducing demagnetization from both sides of the magnetic circuit or drive circuit have been studied, and many technologies related to rotor structures, field temperature monitoring, and the like have been proposed.

For example, the following documents exist as a method of monitoring the temperature of the permanent magnet field during driving of a motor in real time to prevent demagnetization. Patent Document 1 (Japanese Unexamined Patent Publication No. 2017-28804) superimposes measurement AC power on driving AC power, measures impedance, and estimates the temperature of permanent magnets. Patent Document 2 (Japanese Unexamined Patent Publication No. 2013-255570) calculates the temperature of a permanent magnet using a thermal circuit including the thermal resistance of a motor. Patent Document 3 (Japanese Unexamined Patent Publication No. 2003-19197) estimates the induced voltage from the coil current and compensates for the temperature change of the magnetic pole position. In addition to the above, for example, a method of detecting an increase in current due to demagnetization has also been proposed.

JP-A-2017-28804 Japanese Unexamined Patent Publication No. 2013-255570 Japanese Unexamined Patent Publication No. 2003-19197

Most of the prior arts detect demagnetization and perform demagnetization prevention operation in real time, which leads to complicated drive circuits and high cost, and it is difficult to introduce it into small DC motor systems with strict cost requirements. There is a fact.
Also, since irreversible demagnetization often progresses very slowly over a long period of time, the need to prevent demagnetization in real time is not very high. However, the measurement system is required to have high stability and high accuracy over a long period of time in order to operate reliably even if only the magnetic life is determined, and the accuracy is strict with the conventional complicated estimation calculation method. There are many. Magnetic deterioration due to irreversible demagnetization of the permanent magnet field type motor has not been detected in many applications, and continues to be used even after the magnetic life of the permanent magnet field is exceeded, leading to a decrease in output and an increase in heat generation. ..

The method of measuring the temperature of the permanent magnet to detect the demagnetization of the permanent magnet field is indirect and does not directly detect the demagnetization, so the coil current increases and the field or the temperature of the motor exterior. It cannot be detected that the magnet is demagnetized unless it rises abnormally. Therefore, it is desirable to directly detect the decrease in magnetic force, that is, the amount of demagnetization, rather than the temperature of the permanent magnet.
In addition, there are a wide variety of small DC motors, including brushless DC (BLDC) motors, brushed DC motors, and stepping motors, and there are also various types of phases / poles, magnetizing patterns, circuit configurations, etc. It needs versatility that can be applied to all of these motor systems.
Further, it is desirable that the motor temperature can be detected without a temperature sensor. For example, the host controller can display the motor temperature and automatically adjust the rotation speed of the cooling fan.

As described above, there are various problems in expanding the application range of demagnetization detection not only to high-power motors but also to small DC motors. In summary, it has high versatility that does not depend on the motor structure or energization method, and also detects the field temperature as an auxiliary means for applications that do not require real-time performance or for systems that have already taken demagnetization measures in real time. It is required to realize a demagnetization detection method that can be performed with low-cost and simple hardware and software.

The disclosures applied to some of the embodiments described below are made to solve the above problems, and the purpose thereof is to reduce the permanent magnet field with low cost, versatility and high accuracy. It is an object of the present invention to provide a magnetic detection method and a field temperature detection method, thereby monitoring the magnetic life of a permanent magnet field to improve safety and further enabling field temperature display.

A command from an electric motor equipped with a rotor having a permanent magnet field and a stator having an armature coil, an output circuit for energizing the armature coil so as to urge the rotation of the rotor, and a command from an upper controller. Demagnetization detection of an electric motor having a control circuit that receives and controls energization of the armature coil by the output circuit, and a measurement circuit that measures the coil voltage generated in the armature coil and sends it to the control circuit. In a method, the control circuit coasts a non-energized rotating state of the electric motor to measure the one-phase coil voltage fluctuation width ΔV and the electric angle period t, and obtains the electric angle period. The value obtained by multiplying the coil voltage fluctuation width ΔV in t by the electric angle period t is stored as the extended induced voltage constant KV, and one or more desired extended induced voltage constants are set in advance as the threshold KVth. It is characterized in that if the extended induced voltage constant KV obtained by coasting the electric motor is equal to or less than the threshold value KVth, it is determined that demagnetization has occurred.

The demagnetization detection method according to the present invention basically detects demagnetization only once for each energization period (RUN) of the motor. It is not assumed that the output is controlled in real time to prevent demagnetization. Therefore, a short output off period of several ms is provided immediately after the energization period (RUN), the motor is inertially rotated without applying the brake, and the coil voltage in the open state is measured. At this timing, the motor drive is not affected, the rotation speed is high, and it can be regarded as constant-velocity inertial rotation, and measurement accuracy can be ensured.
Assuming that Vc = coil voltage, I = coil current, R = coil resistance, L = coil inductance, and E = induced voltage, the voltage equation of the motor coil is Vc = IR + Ldi / dt + E. The above voltage equation is simplified as Vc = E when I = 0. At this time, since the load current fluctuation and the coil temperature characteristic can be ignored, the induced voltage can be easily detected and there is no error. Therefore, in order to realize I = 0, the coil energization is cut off and the coil is coasted during measurement. By shutting off the output, it is not directly connected to the power supply line and the coil voltage can be treated as the induced voltage itself. Further, the induced voltage E = βlv (β = magnetic flux density, l = conductor length, v = velocity). Therefore, the induced voltage E is proportional to the magnetic flux density β, and demagnetization can be detected by the induced voltage E. The induced voltage E during coastal rotation is observed as the coil voltage fluctuation width ΔV in the energized section in the arbitrary phase, and if the coil voltage fluctuation width ΔV is handled, the detection of the neutral point potential becomes unnecessary.
Further, if the induced voltage E is divided by the rotation speed N, the induced voltage constant Ke can be obtained, and if the induced voltage constant Ke is handled, demagnetization can be detected independently of the rotation speed N. From the induced voltage E = KeN, N = 1 / t, (however, t = electric angle period), it can be expressed as E = Ke / t, and it is transformed into Ke = Et. Further, as described above, since the induced voltage E during coasting rotation = coil voltage fluctuation width ΔV, Ke = ΔVt, that is, the induced voltage constant Ke during coasting rotation can be obtained by the coil voltage fluctuation width ΔV × electric angle period t. Since the induced voltage constant Ke is also proportional to the magnetic flux density β, demagnetization can be detected.

When a direct current is applied to the brushed DC motor in the output circuit, it is rectified by the brush inside the motor and an alternating current is applied to the coil. Therefore, the induced voltage generated in the coil during coasting rotation is rectified by the brush and observed as a pulsating current close to direct current (hereinafter referred to as the rectified waveform). Therefore, when trying to obtain the induced voltage constant Ke, the calculation load becomes large. Moreover, the measurement accuracy deteriorates due to the influence of brush noise and the like. Therefore, in this detection method, the amplitude of the induced voltage is not estimated, only the fluctuation width ΔV of the coil voltage waveform is treated, and it is expressed as the extended induced voltage constant KV.
It is similar to the induced voltage constant Ke, but it should be noted that the value may be completely different depending on the waveform. The extended induced voltage constant can also be obtained by KV = ΔVt. Since the rectified waveform also reflects the magnetic flux density, demagnetization can be detected using the extended induced voltage constant KV. By treating the coil voltage waveform during coasting rotation as an extended induced voltage constant KV, it is possible to apply the distorted approximate sine wave, approximate rectangular wave, and rectified waveform by ignoring the waveform.

Further, by setting one desired extended induced voltage constant as the threshold value KVth in advance, it is possible to determine the occurrence of one level of demagnetization.
Further, by assuming a plurality of extended induced voltage constants in advance and setting them as a plurality of threshold values KVth1 to n, it is possible to perform a finer demagnetization determination. For example, there are three stages: a threshold value KVth1 smaller than the demagnetization limit value for preventive safety, a threshold value KVth2 equal to the demagnetization limit value for life determination, and a threshold value KVth3 larger than the demagnetization limit value for dealing with an emergency. Is set. The control circuit issues a "high temperature / demagnetization warning" when the extended induced voltage constant KV measured by this exceeds KVth3, a "motor replacement warning" when it exceeds KVth2, and a "demagnetization warning" when it exceeds KVth1. be able to.

The electric motor is de-energized and coasted, and any one-phase coil of the multi-phase coil is connected to the ground potential or power supply potential to open the other phase, and then the coil voltage fluctuation width ΔV and electric angle of the open phase one phase are opened. It is preferable to measure the period t.
Normally, the output of the drive circuit is a booster circuit (charge pump, bootstrap circuit) for pre-driving a FET (Field Effect Transistor) gate, a switching noise removal filter, or in the case of sensorless drive, for neutral point detection. A resistance network etc. is connected. Therefore, a small amount of current flows through the coil, and the coil terminal when not energized is in a high impedance state, so a large potential is generated, the neutral point potential greatly deviates from the value of 1/2 of the power supply voltage, and the number of revolutions. If is high, the induced voltage exceeds the power supply voltage range, and the induced voltage is clamped to the power supply line by the FET body diode.
In order to accurately measure the interline induced voltage while avoiding these neutral point potential fluctuations and induced voltage amplitude changes, it is necessary to disconnect the coil wire from the output means with a relay or the like and receive it with a differential input by a measuring amplifier. There is. Relays and MOS switches (SSRs) have drawbacks such as slow operation time or large ON resistance. Furthermore, in order to operate the measurement amplifier, a + side power supply and a-side power supply must be provided, and the power supply voltage of the amplifier is required to be twice the motor power supply voltage, but it is difficult to manufacture a high voltage operation amplifier. When the motor power supply voltage exceeds 12V, it is necessary to provide a voltage dividing resistor at the input portion of each phase to lower the measured voltage. Therefore, the measuring means becomes very large, error factors increase, and the cost increases.

Therefore, the coil voltage is measured after short-circuiting any one phase other than the measurement phase to the ground potential or the power supply potential by the output means. As a result, the entire coil has only the coil DC resistance component with respect to the power supply line and has a low impedance, so that it is hardly affected by various resistors, capacitors, diodes, etc. connected to the output means. Therefore, even if the measurement is performed with the drive circuit and the coil connected without interrupting the coil wire by a relay or the like, the induced voltage can be accurately measured with almost no influence on the components added to the output means. The measurement circuit can be greatly simplified.
For example, by connecting (short-circuiting) one phase to the ground potential GND as a short-circuit phase, an induced voltage is generated positively or negatively around GND at the other open-phase terminals. The induced voltage waveform becomes a half-wave rectified waveform because the half cycle on the negative voltage side is clamped to the GND potential via the body diode of the output means FET, and the induced voltage cannot be detected during the negative voltage rectification period. However, since the half cycle of the positive voltage is not clamped, the induced voltage can be detected, and the positive peak voltage of the combined induced voltage of the short-circuit phase and the open phase, that is, the line-induced induced voltage (0toPEAK) can be detected from the coil voltage fluctuation width ΔV.
The measurement timing is a section of approximately 120 ° in which both open two phases have a positive voltage. Since a positive voltage peak always exists in this section, the peak voltage can be reliably detected.
According to the above method, the induced voltage on the positive voltage side can be measured without being clamped, and the line induced voltage (0toPEAK) with less error can be measured. Therefore, the extended induced voltage constant KV can be obtained by the method already described. It is possible to detect demagnetization with high accuracy.

The demagnetization amount may be detected from the difference between the extended induced voltage constant KV at the standard temperature or the threshold value KVth and the extended induced voltage constant KV measured this time in the unmagnetized state.
As a result, by detecting the demagnetization amount, the demagnetization amount can be displayed or reflected in the control of the external device, and also in comparison with the demagnetization amount change of the demagnetization curve (see FIG. 1). , It is possible to identify whether the cause of demagnetization is thermal demagnetization or irreversible demagnetization.

The maximum operating temperature is set at the design stage of the motor, the extended induced voltage constant KV when the permanent magnet field is at the maximum operating temperature is estimated or measured before the operation of the motor, and the control circuit sets the obtained value as a threshold value. It is preferable to store it as KVth.
Since the field magnet has the property of demagnetizing at the initial stage of use and then stabilizing, the threshold value must be set in anticipation of the initial demagnetization. Therefore, once the maximum operating temperature is set and the initial demagnetization is generated, it is not necessary to consider the initial demagnetization when operating the motor, and the threshold value can be set very easily.

In the control circuit, the extended induced voltage constant KV is estimated or measured and stored at a plurality of field temperatures of at least three points or more before the operation of the motor, and the field temperature and the extended induced voltage constant KV are stored. It is preferable to obtain a function (approximate formula) representing the relationship, store it in the control circuit, and estimate the field temperature using the function when measuring the extended induced voltage constant KV during operation of the motor.
By actual measurement, a function representing the relationship between the extended induced voltage constant KV and the field temperature T can be obtained, and an approximate curve MOT is drawn as shown in FIG. Therefore, when the extended induced voltage constant KV is obtained by the measurement, the field temperature can be obtained by using an approximate expression. Since the function can be put into practical use even with a quadratic approximation formula, a quadratic function for calculation can be determined by measuring at least three extended induced voltage constants KV.

The control circuit estimates or measures and stores the extended induced voltage constant KV at the standard temperature of the permanent magnet field before operating the electric motor, and measures the extended induced voltage constant KV again at the standard temperature when operating the electric motor. , A new function obtained by correcting the section of the function obtained above based on the difference between the measured value this time and the extended induced voltage constant KV stored before the operation is obtained and stored in the control circuit, and the extended induced voltage constant KV is stored. It is preferable to estimate the field temperature using the corrected new function at the time of measurement.
When irreversible demagnetization occurs, an offset error occurs and the temperature is calculated to be higher than the actual temperature, but if the irreversible demagnetization amount is known, the offset can be compensated. Therefore, before operating the electric motor, the initial extended induced voltage constant KV is obtained and stored at the standard temperature, and when the electric motor is operated, the extended induced voltage constant KV is measured again at the standard temperature as needed, and the initial standard temperature is measured. The difference from the extended induced voltage constant KV in is regarded as irreversible demagnetization, and a new function with a different section of the function obtained above is used as offset compensation.
If offset compensation is performed only for temperature estimation and demagnetization judgment is not performed, demagnetization judgment is performed including irreversible demagnetization, and safety can be ensured.
Therefore, when the motor is in operation, the extended induced voltage constant KV is measured by setting the motor to the standard temperature, and based on this, the section of the function obtained above is corrected to compensate for the offset due to irreversible demagnetization, and the new function is corrected. By calculating the field temperature, the field temperature can be detected accurately even if irreversible demagnetization occurs.

By using the demagnetization detection method of the electric motor described above, the demagnetization and field temperature of the permanent magnet field can be detected with high accuracy, and the output decrease and overheating can be prevented. The host controller can receive the demagnetization determination result and field temperature information, output a demagnetization alarm, and display the field temperature. Alternatively, the external device can be controlled according to the field temperature. In addition, it does not depend on the load current, coil resistance temperature characteristics, and rotation speed when determining demagnetization. It can be applied to a wide range of electric motors including BLDC motors, stepping motors, brushed DC motors, and the like. In addition, the algorithm is clear and can be incorporated into an existing circuit at low cost for practical use.

It is a demagnetization curve. It is a schematic diagram of the coil voltage waveform of various motors. It is a temperature characteristic diagram of the extended induced voltage constant. It is explanatory drawing of the measurement timing. It is a drive circuit block diagram of the sensorless BLDC motor by this invention. It is a detection flowchart of the extended induced voltage constant. It is a coil voltage measurement waveform of a non-magnetized BLDC motor. It is a coil voltage measurement waveform of a demagnetized BLDC motor. It is a drive circuit block diagram of a stepping motor. This is the measured waveform of the coil voltage of the stepping motor. It is a drive circuit block diagram of a DC motor with a brush. This is the measured waveform of the coil voltage of the brushed DC motor. This is a configuration example of a sensorless BLDC motor. It is a drive circuit block diagram of the conventional sensorless BLDC motor. It is a timing chart of 120 ° energization. This is the line-induced voltage waveform when the coil is opened and the motor is inertially rotated. It is a coil voltage waveform when one phase is connected to the ground potential and the motor is inertially rotated. It is a block block diagram of the external measurement circuit connected to the drive circuit (ECU).

Hereinafter, embodiments of the demagnetization detection method for the permanent magnet field type electric motor according to the present invention will be described with reference to the attached drawings, exemplifying three types of electric motors (brushless DC motor, stepping motor, and brushed DC motor). To do.

(Example 1: Brushless DC motor)
A three-phase brushless DC motor will be described as an example of an electric motor. In a three-phase brushless DC motor, the rotor 2 is provided with a permanent magnet field 3, the stator 4 is star-connected by arranging windings with a phase difference of 120 °, and the phase ends are connected to the motor output circuit. In the following, a sensorless BLDC motor, whose use has been expanding in recent years, will be described.

Since the sensorless BLDC motor is illustrated in FIG. 13, the same figure will be referred to for description. FIG. 13 illustrates, as an example, a three-phase brushless DC motor provided with a two-pole permanent magnet field 3 and a stator 4 provided with three slots. The number of poles and the number of phases are arbitrary. The field arrangement may be either an inner rotor type or an outer rotor type. Further, it may be either a permanent magnet embedded type (IPM) motor or a surface permanent magnet type (SPM) motor. A rotor 2 is integrally provided on the rotor shaft 1, and a two-pole permanent magnet is provided as a field magnet. Polar teeth U, V, and W are arranged on the stator 4 with a phase difference of 120 ° so as to face the permanent magnet field 3. Armature windings (coils) u, v, and w are provided on the pole teeth U, V, and W of the stator 4, star connections are made between the phases with a common C, and u, v, and w are wired to the motor output circuit described later. It is a three-phase brushless DC motor.

FIG. 5 illustrates a block configuration diagram of a motor drive circuit of a sensorless BLDC motor. The energization method may be sine wave drive or square wave drive, but here, 120 ° energization is illustrated. With reference to FIG. 14, the same reference numerals are used for the common parts. The difference between the conventional sensorless drive circuit illustrated and the present invention is the part where the coil voltage for one phase is measured by the AD converter (ADC54), and the voltage dividing means for one phase (DIV) composed of two resistors. ) Has been added.

MOTOR is a three-phase sensorless motor. The MPU 51 is a microcontroller (control circuit). The MPU 51 provides field position information that specifies six types of energization patterns for the three-phase coils U, V, and W and 120 ° energization switching sections (sections 1 to 6: see FIG. 15) corresponding to each energization pattern. I remember. The MPU 51 switches and controls the output circuit (INV52) described later in response to a torque command from the host controller 50, and controls the PWM (Pulse Width Modulation) control circuit (PWM53) and coil voltage that arbitrarily switch the excitation state to the three-phase coil. It has a built-in measurable AD converter (Analog-to-Digital Converter (measurement circuit): hereinafter referred to as "ADC54").

The output circuit (INV52) energizes the three-phase coil and performs switching operations such as excitation phase switching or PWM control in order to control the motor torque. The output circuit (INV52) includes a field effect transistor as a switching element and a diode connected in antiparallel to the field effect transistor, and a half-bridge type switching circuit that can be arbitrarily connected to a positive electrode power supply line and a ground power supply line is provided for three phases. Has been done.
In addition, a so-called zero cross point occurs in which the positive and negative of the induced voltage is switched in the middle of the non-energized section. In the sensorless motor, a position sensorless drive is used in which the zero cross point is detected by a zero cross comparator (ZERO55) and a timer is used to provide a delay of 30 ° in the electric angle to perform excitation switching.

In the AD converter (ADC54), any one phase of the coil output is connected via the voltage divider circuit (DIV), the coil voltage is cyclically sampled by the measurement start command from the control circuit (MPU51), and the coil voltage is sequentially analogized. It is digitally converted and the conversion result is sent to the control circuit (MPU51). Normally, the AD converter (ADC54) is built in the control circuit (MPU51), and since the maximum input voltage is low, it is desirable to provide a voltage dividing circuit (DIV) by a resistor to scale the input range.

(Detection of demagnetization by extended induced voltage constant)
As described above, the voltage equation of the motor coil is Vc = IR + LdI / dt + E. However, Vc = coil voltage, I = coil current, R = coil resistance, L = coil inductance, E = induced voltage. The above voltage equation is simplified as Vc = E when I = 0. At this time, since the load current fluctuation and the coil temperature characteristic can be ignored, the induced voltage can be easily detected and there is no error.

In order to realize I = 0, when measuring the coil voltage, the coil energization is cut off and the coil is coasted. The coil that shuts off the energization becomes an open phase, and the neutral point potential of the DC component and the induced voltage of the AC component are generated on the open phase coil voltage Vz.
The induced voltage E = βlv. However, β = magnetic flux density, l = conductor length, v = velocity. Therefore, the induced voltage is proportional to the magnetic flux density, and demagnetization can be detected from the induced voltage.
Induced voltage constant Ke = induced voltage E / rotation speed N. Further, N = 1 / t, where t = electric angle period, and therefore Ke = E · t. Since the induced voltage constant Ke does not depend on the rotation speed N, handling the induced voltage constant Ke eliminates the restriction on the rotation speed at the time of coil voltage measurement.

Furthermore, this detection method extends not only the sinusoidal wave but also the pulsating flow such as the rectified waveform as the AC component of the open phase coil voltage. Therefore, when the coil voltage fluctuation width within the electric angle is ΔV and the electric angle period is t, the AC component constantized by ΔV × t or ΔV / N is defined as the extended induced voltage constant KV.
Therefore, KV = ΔV · t, or KV = ΔV / N
This detection method eliminates the need to detect the neutral point potential and eliminates the restriction of the open phase coil voltage waveform by using the extended induced voltage constant KV in this way. A specific waveform will be illustrated below.

FIG. 2 shows a schematic diagram of coil voltage waveforms during inertial rotation of various motors. The horizontal axis is time Time, and the vertical axis is voltage V. In the open phase coil voltage Vz, the induced voltage is superimposed on the neutral point potential. ΔV is the coil voltage fluctuation width within the electric angle, and t is the electric angle period. Figure A is a waveform example of a sine wave magnetizing brushless DC motor, Figure B is a waveform example of a square wave magnetizing brushless DC motor, Figure C is a waveform example of a stepping motor, and Figure D is a waveform example of a brushed DC motor.
It can be seen from the figure that the rectangular wave area of ΔV × t of each waveform corresponds to the extended induced voltage constant KV, and there is no dependence on the waveform. The induced voltage constant Ke is a 0 to Peak value based on the neutral point potential, but the extended induced voltage constant KV is irrelevant to the neutral point potential and the value is also different from the induced voltage constant Ke. For example, the brushless motor in Fig. A has KV = 2Ke, and the motor with brush in Fig. D has KV = 0.232Ke.

Since the electrical and thermal characteristics of each phase can be considered to be symmetrical, the coil voltage is measured for only one phase. This removes the restriction on the number of phases.
The specific measurement method is to cyclically sample the one-phase coil voltage at high speed with an AD converter (ADC54) during coasting rotation, select the maximum and minimum values from the coil voltage measurement data group corresponding to one electrical angle, and maximize the value. The voltage fluctuation width ΔV is extracted by taking the difference between the value and the minimum value. The electric angle period t is also extracted from the coil voltage measurement data group. The extended induced voltage constant KV is obtained by the coil voltage fluctuation width ΔV × electric angle period t.
If an appropriate threshold value that anticipates demagnetization is set in advance and compared with the obtained extended induced voltage constant KV, whether the demagnetization amount increases and the magnetic flux density drops below the threshold value, that is, the magnetic life It can be determined whether it has become. Further, the demagnetization amount can be detected from the difference between the obtained extended induced voltage constant KV and the threshold value. Further, the demagnetization amount may be detected from the difference between the extended induced voltage constant KV at the standard temperature or the threshold value KVth and the extended induced voltage constant KV measured this time in the unmagnetized state. As a result, by detecting the demagnetization amount, the demagnetization amount can be displayed or reflected in the control of the external device, and also in light of the demagnetization amount change of the demagnetization curve (see FIG. 1). , It is possible to identify whether the cause of demagnetization is thermal demagnetization or irreversible demagnetization.
By using the above method, this detection method is not affected by the motor structure, energization method, load current, coil resistance, etc., and is extremely high without restrictions on the number of phases, power supply voltage, measured rotation speed, coil voltage waveform, etc. Achieves versatility, stability and high accuracy.

(Method of determining threshold value)
In the following, the limit value of the extended induced voltage constant KV will be referred to as the threshold value KVth. The maximum operating temperature Tmax of the electric motor is determined in advance at the design stage from the magnet demagnetization characteristics, the heat resistant temperature of the built-in sensor, and the like. Therefore, the extended induced voltage constant KV is measured in a state where the motor is rotated by the drive circuit actually used for operation and the internal temperature of the motor is raised to the maximum operating temperature Tmax by using a constant temperature bath, and the measured value is measured. The threshold value may be KVth. Since the magnet has the property of demagnetizing at the initial stage of use and then stabilizing, the threshold value must be set in anticipation of the initial demagnetization, making it difficult to estimate the amount of demagnetization. However, if the threshold value is determined by the above method, it can be set to an appropriate value including the initial demagnetization. The maximum operating temperature Tmax is a temperature including self-heating. Generally, the internal temperature of the motor becomes higher than the exterior temperature of the motor due to Joule heat, so that the allowable atmospheric temperature is lower than the maximum operating temperature Tmax by the amount of self-heating.

FIG. 3 shows a temperature characteristic diagram of the extended induced voltage constant KV. The horizontal axis is the temperature T ° C., and the vertical axis is the extended induced voltage constant KV. For KV, the value at a standard temperature of 20 ° C. is set as the reference value 1 in order to make the demagnetization rate easy to understand.
The arrow range on the upper left of FIG. 3 indicates a safe operating region (for example, 0 ° C to 80 ° C). The broken line MAG is the extended induced voltage constant KV temperature characteristic curve estimated from the magnet demagnetization characteristics (for example, -0.10% / ° C.), the dot DATA is the measured value of the extended induced voltage constant KV by the motor, and the solid line MOT is the extended induced voltage constant KV. The approximate expression is displayed in the upper right of FIG. 3 with the approximate curve of the measured value. The solid line MOT'is an approximate curve at the time of irreversible demagnetization, and is a translation of the MOT downward. Tmax is the maximum operating temperature (for example, 100 ° C.), and the threshold value KVth is the extended induced voltage constant KV at the maximum operating temperature Tmax.

If the motor operating time elapses from thousands to tens of thousands of hours and irreversible demagnetization occurs, the intercept of the approximate curve changes and the MOT shifts to MOT', crosses the threshold KVth at a lower temperature, and is determined to be demagnetized. .. The demagnetization determination point (circle) moves to the left on the threshold KVth horizontal line, and the determination temperature drops from the initial 100 ° C. to about 60 ° C. at the time of irreversible demagnetization. This means that the irreversible demagnetization component also contributes to the demagnetization determination, which is an important characteristic for ensuring that the detection method operates on the safe side even if it changes with time. FIG. 3 illustrates a case where the demagnetization amount is 5%, but if the demagnetization amount is 10%, it is determined that the demagnetization is at 20 ° C., and an overheating accident can be prevented.
On the other hand, in the conventional method of detecting the temperature, the detection point becomes a triangle mark on the vertical line of the maximum operating temperature Tmax at the time of irreversible demagnetization, the extended induced voltage constant KV decreases, and the coil current increases accordingly, which is the square of the current. Since heat generation also increases, safety decreases. If the high temperature state continues for a long time, the demagnetization amount may reach 50%, and the heat generation becomes very large, which may cause burnout of parts or fire.
The magnet demagnetization characteristics are obtained by simulation from the magnet material used and the permeance coefficient. However, when measuring the coil voltage, waveform distortion may occur due to the influence of the drive circuit, or it may be rectified and only the positive waveform is output.The threshold cannot be determined only by simulating the magnet demagnetization characteristics, so the final Specifically, it is desirable to actually operate the motor system by combining a motor and a drive circuit to actually measure the extended induced voltage constant KV, and to determine the threshold KVth based on the measured data.

(Measurement timing)
This detection method basically measures the coil voltage and the electric angle period at each end of the energization period (RUN) of the motor to detect demagnetization. It is not assumed that the amount of demagnetization is detected in real time when energized to control the coil output and prevent demagnetization.
A short output off period is provided immediately after the energization period (RUN), and the motor is coasted and measured without applying the brake. At this timing, the motor drive is not affected, the rotation speed is high, and it can be regarded as constant-velocity inertial rotation, and measurement accuracy can be ensured.

The measurement timing will be described with reference to FIG. The horizontal axis is the elapsed time Time, and the vertical axis is the rotation speed N. RUN is the energization period. The circled MEASURE immediately after the output is turned off is the measurement period.
It should be noted that even in RUN (during energization rotation), if the output can be momentarily turned off, measurement can be performed at any timing, and a plurality of measurements can be performed to improve the responsiveness of demagnetization detection. For example, in the case of a refrigerator motor for a compressor that is continuously operated for 24 hours, the measurement may be performed about once an hour. The output off time is about 20 ms, and the influence on the motor operation is small.
Further, after starting the motor, measurement may be performed when the speed reaches the vicinity of the target speed. As a result, even a motor that has already been demagnetized can take safety measures such as detecting demagnetization at the start of rotation and immediately outputting an alarm or stopping the coil output.
Further, the coil voltage may be measured by rotating the motor for a moment while it is stopped and coasting. Alternatively, when rotating by an external force, the coil voltage may be measured at an arbitrary timing to sense demagnetization.

(Detection of demagnetization amount)
Up to this point, the method of digitally detecting the occurrence of demagnetization by comparing the magnitude of the extended induced voltage constant KV and the threshold KVth has been mainly described, but the extended induced voltage constant KV at the standard temperature in the unmagnetized state or the threshold is further described. The demagnetization amount of the analog value can be detected by calculating the difference between KVth and the extended induced voltage constant KV measured this time.
By detecting the amount of demagnetization, the control operation can be enhanced. For example, the demagnetization amount can be displayed numerically, the alarm level can be set in multiple stages, or the host controller can control the external device according to the demagnetization amount.
Furthermore, under conditions such as constant room temperature, the effect of thermal demagnetization due to motor operation is avoided by measuring the extended induced voltage constant KV immediately after starting, and the amount of demagnetization is compared in chronological order to reduce irreversible value. The amount of magnetism can be detected. When the amount of irreversible demagnetization suddenly increases, it can be determined that the situation is abnormal and safety measures such as stopping the motor output can be taken.

(Estimation of field temperature)
Next, the method of estimating the field temperature will be described. In this detection method, as illustrated in FIG. 3, a function (approximate equation) of the extended induced voltage constant KV and the field temperature T can be obtained by actual measurement or the like. Therefore, when the extended induced voltage constant KV is obtained by measurement during operation of the motor, the field temperature can be obtained by calculation using a function. Since the function is sufficiently practical with a quadratic approximation formula, the function can be determined by measuring the extended induced voltage constant KV at the field temperature of at least three points.

Therefore, before operating the motor, the extended induced voltage constant KV is estimated or measured at a plurality of field temperatures of three or more points, and the function of the extended induced voltage constant KV and the field temperature is obtained and stored in the MPU 51 (control circuit). When operating the motor, the field temperature is calculated by a function when measuring the extended induced voltage constant KV. There are many situations where you want to know the temperature of the motor, but it is often not allowed to install a temperature sensor because of cost and reliability. Moreover, it is difficult to detect the temperature of the permanent magnet field. Therefore, the effect of knowing the field temperature without a temperature sensor is great, and new applications for using the motor as a temperature sensor are expanding.
For example, a motor for medical equipment is sterilized at high temperature, but if only the exterior of the motor is cooled and the inside is still hot, torque will be insufficient, which is not preferable, but if the field temperature is displayed, it can be operated safely. Alternatively, it is possible to estimate the ambient temperature by measuring the temperature of the ventilation fan installed on the range hood or ceiling / attic, and automatically adjust the rotation speed of the ventilation fan. Furthermore, it detects an abnormally high temperature and gives a fire alarm. Applications such as outputting are also conceivable.

(Correction method for field temperature estimation)
However, when irreversible demagnetization occurs, an offset error occurs and the temperature is calculated to be higher than the actual temperature. This error can be resolved by compensating for the offset if the irreversible demagnetization amount is known. Therefore, the initial KV at the standard temperature is obtained and stored before operation, the KV is measured again at the standard temperature as needed during operation, and the difference from the KV at the initial standard temperature is the irreversible demagnetization component. And add to the intercept of the function.
Therefore, during operation, the motor is set to the standard temperature, KV is measured, the intercept of the function is corrected based on this, the offset due to irreversible demagnetization is compensated, and the field temperature is calculated by the corrected function.
By performing the above operation, the temperature can be detected accurately even if irreversible demagnetization occurs. Note that offset compensation is performed only for temperature estimation, and if offset compensation is not performed for demagnetization determination, demagnetization determination is performed including irreversible demagnetization, and safety can be ensured.

An example of the demagnetization determination routine will be described with reference to the flowchart of FIG. The extended induced voltage constant KV can be detected and demagnetized can be determined by the following series of procedures. It is assumed that the extended induced voltage constant threshold value KVth is set in advance. An AD converter is used for coil voltage measurement. The electric angle cycle may be measured by a timer, but in this example, it is obtained from the number of sampling cycles.

Start the demagnetization determination routine. First, the coil output is turned off and the motor is coasted. At this time, wait until the spike noise due to the coil energization cutoff converges (inertial rotation: STEP1). Next, the measurement of the electric angle period is started. The first coil voltage measurement is performed and stored in the MPU 51 as the initial value. The AD conversion time is several us, and the measurement is performed in this cycle thereafter (coil voltage measurement 1: STEP2). The second coil voltage measurement is performed and stored in the MPU 51 as the second value (coil voltage measurement 2: STEP3).

The first gradient code is obtained from the first coil voltage measurement value and the second coil voltage measurement value and stored in the MPU 51 (2-1 gradient detection: STEP4). The coil voltage is measured from the third time onward, and the measured value is stored in the MPU 51 (coil voltage measurement n: STEP5). The previous coil voltage measurement value (n-1) is compared with the current coil voltage measurement value (n), and the difference is taken to detect the gradient code (gradient detection: STEP6). This time, it is determined whether or not the coil voltage measurement value matches the initial coil voltage measurement value and the gradient code (measurement completion determination: STEP7). If there is a discrepancy, the coil voltage for the electric angle has not been measured yet, so the process returns to STEP5. If they match, the measurement of the electric angle is completed, and the process proceeds to STEP8.

Next, the electric angle period t, which is the energized section, is calculated (cycle calculation: STEPS8). Specifically, it is calculated by the electrical angle period = sampling period x number of measurements. Next, the maximum value Vmax and the minimum value Vmini are extracted from the measured values of all coil voltages (amplitude extraction: STEP9). Next, the amplitude (coil voltage fluctuation width) ΔV of the coil voltage measurement value is calculated from ΔV = Vmax−Vmini (amplitude calculation: STEP10). Next, the extended induced voltage constant KV is calculated from KV = ΔV × t (KV calculation: STEP11).

Next, the demagnetization determination is made by comparing the magnitude of the extended induced voltage constant KV and the threshold value KVth (demagnetization determination: STEP12). If the extended induced voltage constant KV is larger than the threshold value KVth, an output return operation such as a brake operation is performed as necessary, and the process returns to the main routine (output return operation: STEP13). If the extended induced voltage constant KV is smaller than the threshold value KVth, it is determined that the demagnetization (magnetic life) is performed, and the process proceeds to the demagnetization process (STEP 14).

The extended induced voltage constant KV is obtained by the above procedure, and the demagnetization determination is performed by comparing the magnitude with the threshold value KVth. The execution timing of the demagnetization determination routine is arbitrary, but the higher the rotation speed, the larger the coil voltage, which is advantageous at high speed rotation. The number of detections of the extended induced voltage constant KV is at least once per on-cycle, but it may be repeated a plurality of times in, for example, a thermal time constant period.
The demagnetization process (STEP14) when demagnetization occurs is not particularly specified, but warning display, error code storage in memory, and the like can be considered. Furthermore, it is possible to stop the output in consideration of the seriousness.
The configuration of the motor drive circuit and the configuration of the control program can be considered in various ways, and are not limited to the modes disclosed in the present embodiment. It also includes changes in the circuit configuration and program configurations that can be made if there is one.

Below, the coil voltage measured waveform of the brushless DC motor is shown.
FIG. 7 shows an example of non-demagnetization, which is a one-phase coil voltage waveform when a three-phase brushless DC motor is rotated at a constant speed at a standard temperature of 20 ° C. and is turned off in the middle. The electric angle period t1 = 2.08 ms, and the coil voltage fluctuation width ΔV1 = 8.18 V at the time of opening.
FIG. 8 shows an example at the time of demagnetization, which is a one-phase coil voltage waveform when the motor is heated to 120 ° C., rotated at a constant speed, and turned off in the middle. The electric angle period t2 = 2.08 ms and the coil voltage fluctuation width when opened is ΔV2 = 7.58 V, which is 0.6 V smaller than that in FIG.

A concrete calculation example is shown using the above measured values.
KV at 20 ° C KV1 = ΔV1 · t1 = 17.04 mV · s
85 ° C threshold KVth = 16.19 mV · s (equivalent to 5% demagnetization)
KV at 120 ° C. KV2 = ΔV2 ・ t2 = 15.77 mV ・ s
Since the measured value KV2 is smaller than the threshold value KVth, it is determined to be demagnetized or high temperature.

Examine the temperature resolution from the measured values. The input range of the AD converter is 12V, and the resolution is 3 mV (12 bits). Since the coil voltage fluctuation width changes by 0.6 V per 100 ° C., it is 6 mV / ° C. as a linear approximation. Therefore, the temperature resolution = 3 mV / (6 mV / ° C.) = 0.5 ° C.
Further examine the phase resolution. The sampling period of the AD converter (ADC54) is 5 us. Since the electric angle period is about 2.08 ms in the measured value, 2.08 ms / 5us = 400 samplings / electric angle. Therefore, the phase resolution = 360 ° / 400 = 0.9 °, but the motor rotation speed is 28.8 krpm. The quantization error of the voltage axis caused by the sampling error of 0.9 ° is very small and can be ignored. As the motor rotates at a lower speed, the number of samples increases and the sampling error decreases.
From the above examination, a temperature resolution of about 0.5 ° C. is possible in this example. Incidentally, as the field temperature detection accuracy of the main motor of the electric vehicle, for example, a value such as ± 15 ° C. or 50 ° C. deviation has been reported, and it can be said that this detection method has sufficiently high accuracy.

(Example 2: Stepping motor)
Next, an application example to a stepping motor provided with a permanent magnet field will be described. It needs to coast to detect the extended induced voltage constant KV and is not applicable to open loop positioning operations. FIG. 9 is a block configuration diagram showing a drive circuit of a stepping motor. Reference numerals are used for the parts common to FIG. 5, and the description thereof will be omitted. MOTOR assumes a two-phase hybrid bipolar stepping motor. The output circuit (INV52) is composed of two sets of full bridges, PWM-drives two-phase coils (A + and A−, B + and B−), and advances the rotor at a predetermined angle. The voltage divider circuit (DIV) may be connected to any coil output line.

FIG. 10 is a measured waveform of the coil voltage of the stepping motor. When the output is cut off, the drive circuit used for the actual measurement has the characteristic that the neutral point drops to the GND side, and the expected waveform can be observed only immediately after the output is turned off, but it can be seen that demagnetization detection is possible.
In this way, the coil voltage waveform when not energized is greatly affected by the characteristics of the output stage. If the high-side and low-side impedances of the output stage bridge are matched, the coil voltage waveform with the power supply voltage / 2 as the neutral point can be observed.

(Example 3: DC motor with brush)
Next, an application example to a brushed DC motor will be described. The case where a drive circuit such as an H bridge is used with two coil terminals will be illustrated. Brush life is short and magnetic life is much longer. However, irreversible demagnetization may occur due to extremely cold heat in a stopped state or unexpected extreme overload operation as in the case of an in-vehicle auxiliary motor.

FIG. 11 is a block configuration diagram showing a drive circuit of a brushed DC motor. Reference numerals are used for the parts common to FIG. 5, and the description thereof will be omitted. MOTOR is a brushed DC motor equipped with a three-phase coil. When a voltage is applied to the P terminal and N terminal, it is rectified by the brush inside the motor and a 120 ° square wave is energized. The output circuit (INV52) has a full bridge configuration and PWM drives the P terminal and N terminal to continuously rotate them. The voltage divider circuit (DIV) may be connected to either output line.

FIG. 12 is a measured waveform of the coil voltage of the brushed DC motor. Since the waveform fluctuation range is small, the fluctuation part is enlarged and displayed with an offset. When the output is cut off, a waveform similar to the 120 ° energization that rectifies the three-phase sine wave is observed. Demagnetization detection is possible by calculating the distance between the peak and bottom of the rectified waveform as the coil voltage fluctuation width ΔV. However, since the coil voltage fluctuation width ΔV is smaller than that of the sine wave, it is necessary to perform inertial rotation at high speed.
Since almost the same waveform is observed in 6 sections of the 120 ° energization waveform, the coil voltage fluctuation width ΔV may be detected in only one section. As a result, the measurement time can be reduced to 1/6. The variation due to the deviation of voltage and time for each section can be improved by cutting off the output in the same energized section and measuring, and the repeatability is greatly improved.

(Example 4: Brushless DC motor)
Next, a method of detecting demagnetization by short-circuiting one phase of a three-phase sensorless BLDC motor to the power supply line will be described. Note that Example 4 and Example 5 described later are modified examples of the three-phase sensorless BLDC motor, and are not intended to be applied to a stepping motor or a DC motor with a brush.
When the star-connected three-phase sensorless BLDC motor illustrated in FIG. 13 is coasted by interrupting the drive circuit output with a relay, a combined waveform of two-phase induced voltages is observed between the coil wires. FIG. 16 shows a coil voltage waveform when the coil is separated from the drive circuit and inertially rotated. It is a line-induced voltage waveform that appears at the U-phase terminal when the V-phase terminal is used as a reference potential, and a combined induced voltage between the U-phase and the V-phase is observed. The difference between the reference potential (neutral point) and the peak potential of this waveform is generally called the line-induced voltage (0toPEAK), and is indicated by an arrow E in the figure. What is important here is that the line-induced voltage (PEAKtoPEAK) exceeds the power supply voltage when the rotation speed is high. During drive, the power supply and GND are appropriately selected and half-wave rectified and energized, so the line-induced voltage becomes (0toPEAK) and falls within the power supply voltage, but during free rotation when the output is cut off, it becomes (PEAKtoPEAK) and is doubled. When a voltage is generated and the drive circuit is connected, the amount exceeding the power supply voltage is clamped to the power supply rail by the body diode of the FET and a regenerative current flows.

On the other hand, when measuring the voltage fluctuation width ΔV and the electric angle period t of the one-phase coil described above, any one phase is connected to the ground potential or the power supply potential, and the other phase is coasted and rotated as non-energized. Even so, the line-induced voltage (0toPEAK) can be observed.
Hereinafter, an example of measuring the coil voltage fluctuation width ΔV and the electric angle period t of the three-phase sensorless BLDC motor using, for example, the drive circuit of FIG. 5 will be described. Since the description of the drive circuit has already been completed, it will be omitted. When measuring the coil voltage fluctuation width ΔV and the electric angle period t, only the low side arm of the V phase is turned on to connect the V phase to the GND, and all other output elements are turned off. Then, the combined induced voltage of the U phase and the V phase is generated in the U phase, and the combined induced voltage of the W phase and the V phase is generated in the W phase with reference to the GND. At that time, since the half cycle on the negative voltage side is clamped to the GND via the body diode of the FET, a regenerative current flows and the correct induced voltage cannot be measured.

However, since neither the U phase nor the W phase is clamped during the period when the positive voltage is obtained, the regenerative current does not flow in the coil and the correct induced voltage can be detected. The period is about 120 ° in terms of electrical angle, and due to the structure of the motor, peak induced voltages of U phase and W phase always exist within that period. The reference voltage at this time is the GND potential, and the coil voltage fluctuation width ΔV with 0V as the minimum value and the peak value as the maximum value is an accurate line-induced voltage (0toPEAK). Since the U-phase and W-phase voltage waveforms are half-wave rectified waveforms, they do not exceed the power supply voltage and can be measured even at high speed rotation.
The electric angle period t can be obtained by measuring between the rising edges of the U phase or the W phase. The above measurement can be performed in the W phase instead of the U phase, and the phase short-circuited to the power supply can be any of U to W.

FIG. 17 shows an actually measured waveform of a three-phase coil voltage in which the V phase is short-circuited to GND after the motor output is switched from on to off and inertially rotated. The upper waveform is a motor-on signal, and the measurement start timing is indicated by an arrow OFF. The minimum measurement time may be 1 electric angle, but for the sake of explanation, 6 electric angles are displayed as the measurement period. In the figure, the coil names U to W, the peak voltage is indicated by an arrow Vpk, the electric angle is indicated by an arrow t, and the period during which a peak can be detected is indicated by an arrow Th.
The slight fluctuation of the V-phase voltage reflects the regenerative current, and the peak measurable period when the regenerative current reaches the GND level is zero.
From FIG. 17, it can be seen that either the U phase or the W phase, which is an open phase, can be detected as the peak voltage measurement phase. The negative half cycle is about −0.7V of the clamp voltage. Further, it can be seen that the coil voltage waveform is distorted except for the peak detectable period Th of about 120 ° due to the clamp current, but the clamp current does not flow in the vicinity of the peak, and therefore the peak voltage can be observed correctly.
In general, the line-induced voltage is the phase-to-phase induced voltage × 3 ^(1/2) at the time of ideal sine wave magnetization. In the case of rectangular wave magnetism, it becomes larger, and in the case of magnetism close to the square waveform, it becomes smaller. In an actual motor, it is not possible to calculate an exact interphase induced voltage from the line induced voltage because there is distortion of the magnetized waveform and interphase variation. Therefore, a motor without a common wire cannot measure the exact induced voltage constant Ke. However, since demagnetization is a relative change of the induced voltage constant, an accurate demagnetization rate can be obtained even if demagnetization is detected by the line induced voltage.
According to the above method, it can be realized if there are two voltage dividing resistors and a one-channel AD converter (ADC) for reducing the voltage of the measurement phase and matching the measurement range of the AD converter. Normally, the MPU has an ADC built-in, and the line-induced voltage constant (0toPEAK) and demagnetization rate can be accurately measured by adding only two resistors. In the drive circuit example of FIG. 5, it can be carried out as it is without adding any parts.

(Example 5: Brushless DC motor)
Next, a case where a measurement circuit is added to the outside of the motor drive circuit to detect demagnetization will be described. FIG. 18 shows a block configuration diagram of a three-phase sensorless BLDC motor (MOTOR), a drive circuit (ECU (Electronic Control Unit) 56) thereof, and an external measurement circuit 57 connected externally, and these configurations will be described below.

The drive circuit (ECU 56) has almost the same circuit configuration as the block configuration diagram shown in FIG. 5, and the voltage dividing circuits DIV and ADC 54 are omitted, and a motor-on signal output (MOTOR-ON) is added. This motor on signal (MOTOR-ON) is H when the motor output is on and L when the motor output is off, and both are output to the external measurement circuit 57. In addition to the zero cross detection means (ZERO55), the coil output unit is often provided with a charge pump for FET predrive, a noise filter, a coil current detection means, and the like.

The external measurement circuit 57 includes a control unit (CPU57a) that performs measurement and calculation, a voltage division unit (DIV57b) that divides the measurement phase voltage, and a switch unit (SW57c) that short-circuits the short-circuit phase to GND by FET. In this example, the U phase is the measurement phase and the V phase is the short circuit phase, but the connection phase can be selected arbitrarily. The control unit (CPU57a) of the external measurement circuit 57 is a unipolar AD converter (CPU 57a) that inputs a motor-on signal (MOTOR-ON) input unit from the drive circuit (ECU 56) and a measurement phase signal after voltage division and performs AD conversion. The ADC 57d) and the output unit of the signal MEAS that turns on the switch unit (SW57c) at the time of measurement are provided.
Three wires of outputs U to W are connected from the drive circuit (ECU 56) to the motor (MOTOR). The motor outputs U and V and the drive circuit (ECU 56) connect the motor on signal (MOTOR-ON) and the four lines of the GND line to the external measurement circuit 57. The control power supply to the control unit (CPU57a) may be supplied from the drive circuit (ECU 56) or separately from the DC power supply, and communication with the host controller or the like is naturally assumed, but it is complicated. To avoid this, these descriptions are omitted.

In the measurement procedure, the drive circuit (ECU 56) first rotates the motor (MOTOR), and then the output is turned off and the motor is coasted. The external measurement circuit 57 starts the measurement when the motor-on signal (MOTOR-ON) becomes L, outputs the MEAS signal, short-circuits the V phase to the GND, waits for a time for the switching to stabilize, and then measures the U-phase voltage. Start. The U-phase voltage is cyclically AD-converted by the ADC 57d and the coil voltage is measured. When the completion of measurement for one electric angle cycle is detected from the U-phase voltage value, the MEAS signal is turned off, the V-phase is opened again, and the maximum and minimum values are extracted from the measured U-phase voltage data within the electric angle. Obtain the coil voltage fluctuation width ΔV. Since the negative voltage of the unipolar AD converter ADC57d is measured as 0V, the obtained coil voltage fluctuation width ΔV is the difference voltage between 0V and the peak value. Therefore, the coil voltage fluctuation width ΔV becomes equal to the line-induced voltage (0toPEAK). Further, the extended induced voltage coefficient KV is obtained from the coil voltage fluctuation width ΔV and the electric angle period t, and demagnetization is detected by comparing with the KV value before that. Since the obtained demagnetization rate is not affected by the load current or the coil DC resistance value, a very accurate demagnetization rate can be detected. Further, it is highly versatile because it can measure up to the maximum rotation speed of the motor (MOTOR) and is not easily affected by auxiliary parts around the output portion of the drive circuit (ECU 56).

The configuration of the motor drive circuit and the configuration of the control program can be considered in various ways, and are not limited to the modes disclosed in the present embodiment. It also includes changes in the circuit configuration and program configurations that can be made if there is one.

1 Rotor shaft 2 Rotor 3 Permanent magnet 4 Steader 50 Upper controller 51 MPU (control circuit) 52 Half-bridge type inverter circuit (INV) 53 PWM control circuit 54 AD converter (measurement circuit: ADC) 55 Zero cross comparator 56 ECU ( Drive circuit) 57 External measurement circuit 57a CPU (control unit) 57b DIV (pressure dividing unit) 57c SW (switch unit) 57d ADC (unipolar AD converter)

A command from an electric motor equipped with a rotor having a permanent magnet field and a stator having an armature coil, an output circuit for energizing the armature coil so as to urge the rotation of the rotor, and a command from an upper controller. Demagnetization detection of an electric motor having a control circuit that receives and controls energization of the armature coil by the output circuit, and a measurement circuit that measures the coil voltage generated in the armature coil and sends it to the control circuit. In the method, the control circuit coasts the electric motor from a rotating state in which the electric power is controlled to be de-energized, and connects any one-phase coil of the multi-phase coils to the ground potential or the power supply potential to connect the other phase. After opening, the coil voltage fluctuation width ΔV and the electric angle period t of one phase of the open phase were measured, and the coil voltage fluctuation width ΔV within the obtained electric angle period t was multiplied by the electric angle period t. The value is stored as the extended induced voltage constant KV, one or more desired extended induced voltage constants are set in advance as the threshold KVth, and the extended induced voltage constant KV obtained by coasting the electric motor is the threshold KVth. If the following, it is determined that demagnetization has occurred.

Claims (6)

An electric motor equipped with a rotor having a permanent magnet field and a stator having an armature coil, an output circuit for energizing the armature coil to urge the rotation of the rotor, and a command from a host controller. Demagnetization detection of an electric motor having a control circuit that receives and controls energization of the armature coil by the output circuit, and a measurement circuit that measures the coil voltage generated in the armature coil and sends it to the control circuit. It's a method
The control circuit coasts the electric motor from the energized and controlled rotation state as non-energized to measure the one-phase coil voltage fluctuation width ΔV and the electric angle period t, and the coil voltage within the obtained electric angle period t. The value obtained by multiplying the fluctuation width ΔV by the electric angle period t is stored as the extended induced voltage constant KV, and one or more desired extended induced voltage constants are set in advance as the threshold KVth to allow the electric motor to coast. A method for detecting demagnetization of an electric motor, wherein if the extended induced voltage constant KV obtained by rotation is equal to or less than the threshold value KVth, it is determined that demagnetization has occurred. The motor is coasted with no electricity, and any one-phase coil of the multi-phase coil is connected to the ground potential or power supply potential to open the other phase, and then the coil voltage fluctuation width ΔV and electricity of the open phase one phase The demagnetization detection method for an electric motor according to claim 1, wherein the angular period t is measured. The reduction of the motor according to claim 1 or 2, wherein the demagnetization amount is detected from the difference between the extended induced voltage constant KV or the threshold KVth at the standard temperature in the unmagnetized state and the extended induced voltage constant KV measured this time. Magnetic detection method. The maximum operating temperature is set at the design stage of the motor, the extended induced voltage constant KV when the permanent magnet field is at the maximum operating temperature is estimated or measured before the operation of the motor, and the control circuit sets the obtained value as a threshold value. The demagnetization detection method for an electric motor according to any one of claims 1 to 3, which is stored as KVth. In the control circuit, the extended induced voltage constant KV is estimated or measured and stored at a plurality of field temperatures of at least three points or more before the operation of the motor, and the field temperature and the extended induced voltage constant KV are stored. Any of claims 1 to 4 in which a function (approximate formula) representing the relationship is obtained and stored in the control circuit, and the field temperature is estimated using the function when measuring the extended induced voltage constant KV during operation of the motor. The demagnetization detection method for the electric motor described in. The control circuit estimates or measures and stores the extended induced voltage constant KV at the standard temperature of the permanent magnet field before the motor is operated, and measures the extended induced voltage constant KV again at the standard temperature when the motor is operated. Based on the difference between the measured value this time and the extended induced voltage constant KV stored before operation, a new function obtained by correcting the section of the function obtained in claim 5 is obtained and stored in the control circuit, and the extended induced voltage is stored. The method for detecting demagnetization of an electric motor according to claim 5, wherein the field temperature is estimated by using the corrected new function when measuring the constant KV.