JP7636966B2 - ROTOR TEMPERATURE ESTIMATION SYSTEM AND ROTOR TEMPERATURE ESTIMATION METHOD - Google Patents

Description

The present invention relates to a rotor temperature estimation system and a rotor temperature estimation method for a rotating machine.

A method for estimating rotor temperature in rotating machines such as motors and generators is known. A rotor temperature estimator is disclosed for an induction motor, which calculates losses generated in the stator and rotor using the motor speed, stator coil temperature, control command value or detection value of the stator coil current value, slip frequency, and previous estimate of rotor temperature as inputs, and estimates the rotor temperature based on a model set using the balance of thermal energy from the calculated value, the stator coil temperature, and the outside air temperature of the induction motor frame (Patent Document 1).

JP 2020-167779 A

Incidentally, the coil current and slip frequency input when calculating motor losses should change at time intervals of microseconds to milliseconds when the actual motor command value is updated, and the motor rotation speed also changes at time intervals of about milliseconds. However, the measurement sampling used to estimate rotor temperature is often done at time intervals of about a few seconds. In other words, sampling is done at the same time intervals of a few seconds for rotor temperature estimation and motor loss calculation, and the calculation is performed assuming that the value does not change within the sampling time interval for rotor temperature estimation. This reduces the accuracy of motor loss calculations, and with it the accuracy of rotor temperature estimation.

On the other hand, if the sampling time interval for estimating the rotor temperature is shortened to the same time interval as the current control sampling, which is on the order of microseconds to milliseconds, the accuracy of the motor loss calculation improves, but the amount of calculation increases enormously, resulting in high costs for the calculation device.

One aspect of the present invention is a rotor temperature estimation system that estimates the temperature of a rotor of a rotating machine, comprising: a motor loss calculator that calculates the loss of the rotating machine at each sampling time interval that is shorter than the sampling time interval for estimating the temperature of the rotor; a motor loss adjuster that accumulates the loss of the rotating machine calculated by the motor loss calculator up to the sampling time interval for estimating the temperature of the rotor to calculate a motor loss accumulation value; and a rotor temperature estimator that estimates the temperature of the rotor using the motor loss accumulation value.

Here, it is preferable that the sampling time interval shorter than the sampling time interval for estimating the rotor temperature is the sampling time interval for current control of the rotating machine.

It is also preferable that the rotor temperature estimator estimates the rotor temperature using an observer based on a thermal circuit model of the rotating machine.

Another aspect of the present invention is a rotor temperature estimation method for estimating the temperature of a rotor of a rotating machine, which is characterized by calculating losses in the rotating machine at each sampling time interval shorter than the sampling time interval for estimating the temperature of the rotor, accumulating the calculated losses in the rotating machine up to the sampling time interval for estimating the temperature of the rotor to calculate a motor loss cumulative value, and estimating the temperature of the rotor using the motor loss cumulative value.

According to the present invention, it is possible to improve the accuracy of rotor temperature estimation while reducing the computational load in the rotor temperature estimation process.

1 is a diagram showing a configuration of a rotating machine according to an embodiment of the present invention; 1 is a diagram showing a configuration of a rotor temperature estimation system according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration of a control device of the rotor temperature estimation system according to the embodiment of the present invention. FIG. 11 is a diagram showing an example of calculation of loss with respect to stator current in the embodiment of the present invention and the conventional method. FIG. 4 is a diagram illustrating an example of a thermal circuit model according to the embodiment of the present invention.

Figure 1 shows an example of the configuration of a rotating machine 100 for which the rotor temperature is to be estimated. In this embodiment, a three-phase squirrel-cage induction motor is used as an example of the rotating machine 100. However, the rotating machine 100 is not limited to this, and may be a motor, motor generator, or generator of other configurations.

The rotating machine 100 includes a stator 10, a rotor 12, a shaft 14, and a housing 16. In this embodiment, the housing 16 is divided into a first frame 16a and a second frame 16b.

The stator 10 is a component that generates a rotating magnetic field by the motor current flowing through the stator coil. The stator 10 is fixed to the housing 16. The stator 10 is configured with a stator coil attached to a cylindrical stator core. The stator coil includes a three-phase coil having U, V, and W phases. The stator coil may be configured to have coils of multiple phases other than three phases. The three-phase coil is connected to a power supply inverter (not shown). The motor current flowing through the stator coil is controlled according to a torque command value from a control unit (not shown).

The rotor 12 is disposed within the stator 10 with a predetermined gap from the inner peripheral surface of the stator 10. In this embodiment, the rotor 12 is a cage rotor, and is composed of a rotor core made of a magnetic material, a plurality of conductor bars inserted into holes provided at a plurality of positions along the circumferential direction of the rotor core, and end rings connecting the ends of the plurality of conductor bars. The conductor bars and the end rings are formed from a conductive material.

The rotor 12 rotates within the stator 10 due to electromagnetic interaction with the rotating magnetic field generated by the stator 10. A shaft 14 is provided as the axis of rotation of the rotor 12. The shaft 14 is rotatably supported on the housing 16 via a bearing, and is connected to a load 102 outside the housing 16. As a result, the load 102 is rotationally driven as the rotor 12 rotates.

When the rotating machine 100 is in operation, a rotating magnetic field is generated from the stator 10 by passing electricity through the stator coil, which generates an induced current in the conductor bars of the rotor 12, and a rotational force is generated in the conductor bars of the rotor 12 by the electromagnetic force acting between the induced current and the rotating magnetic field. This causes the rotor 12 to rotate around the shaft 14 as the central axis of rotation.

The rotating machine 100 can be mounted on a vehicle such as an electric vehicle or a hybrid vehicle and used. In other words, the rotating machine 100 can be used as a drive device to power the wheels as a traction motor.

As shown in FIG. 1, in the rotating machine 100, the air in the gap between the stator 10 and the rotor 12, the space surrounded by the first frame 16a of the housing 16 and the stator 10 and the rotor 12, the space surrounded by the second frame 16b of the housing 16 and the stator 10 and the rotor 12, and the space outside the housing 16 are designated as air 0, air 1, air 2, and air 3 (outside air), respectively. The air resistance of the rotor 12 to air 0, air 1, and air 2 changes depending on the motor rotation speed.

Figure 2 shows the configuration of the rotor temperature estimation system 200. Figure 3 is a block diagram showing the configuration of the control device 20 that constitutes the rotor temperature estimation system 200. The rotor temperature estimation system 200 performs rotor temperature estimation processing to estimate the temperature of the rotor 12 based on information such as the rotation speed of the rotor 12 in the rotating machine 100, the motor current (or the command value of the motor current), the slip frequency (or the command value of the slip frequency), and the coil temperature.

The rotor temperature estimation system 200 includes a control device 20, a rotation speed sensor 22, a coil temperature sensor 24, and an outside air temperature sensor 26. The control device 20 also includes a motor loss calculator 20a, a motor loss adjuster 20b, and a rotor temperature estimator 20c.

The control device 20 has a calculation processing unit such as a CPU and a storage unit such as a memory. The control device 20 can be, for example, a general computer. The control device 20 functions as a motor loss calculator 20a, a motor loss adjuster 20b, and a rotor temperature estimator 20c by performing rotor temperature estimation processing described below. The rotor temperature estimation processing is performed, for example, by executing a rotor temperature estimation processing program in the control device 20.

The rotation speed sensor 22 detects the rotation speed of the rotor 12 constituting the rotating machine 100 as the motor rotation speed N. The detected motor rotation speed N is input to the control device 20. The rotation speed sensor 22 can be configured, for example, by a resolver that detects the rotation angle of the rotor 12. The coil temperature sensor 24 detects the coil temperature Tcoil of the stator coil of the stator 10 constituting the rotating machine 100. The coil temperature Tcoil corresponds to the stator coil temperature. The detected coil temperature Tcoil is input to the control device 20. The outside air temperature sensor 26 detects the temperature around the rotating machine 100 as the outside air temperature Tair3. The detected outside air temperature Tair3 is input to the control device 20.

In addition, an amount of operation for an acceleration instruction is detected from an acceleration instruction sensor such as an accelerator pedal sensor of a vehicle equipped with the rotating machine 100, and a torque command value TR is calculated according to the amount of operation. The torque command value TR may be calculated from the detected value of the amount of operation for the acceleration instruction and the detected value of a vehicle speed sensor. The detected value of the amount of operation for the acceleration instruction may be directly input to the control device 20, and the torque command value TR may be calculated by the control device 20. The stator coil current Is and slip frequency ωs are calculated based on the torque command value TR and the motor rotation speed N. The stator coil current Is is the primary current of the rotating machine 100, and corresponds to the stator coil current value given to the rotating machine 100 as a control command value. As the stator coil current Is, the effective value of the stator coil current of one specified phase may be calculated, or the effective value of the stator coil current of three phases may be calculated. The stator coil current Is and the slip frequency ωs are input to the control device 20.

In addition, as the stator coil current Is, a detection value detected by a current sensor may be input to the control device 20 instead of a control command value. In this case, the control device 20 may calculate the effective value of the stator coil current of a specific phase based on multiple detections of the stator coil current of one specific phase input from the current sensor. To calculate the effective value, multiple current detection values detected at a specific time interval in the stator coil current of the specific phase can be used. For example, the effective value of the U-phase stator coil current can be calculated from the root mean square of multiple stator coil currents Iu for the U-phase stator coil current Iu detected at a specific time interval. The calculated effective value of the stator coil current of a specific phase can be regarded as the effective value of the three-phase stator coil current. Similarly, as the slip frequency ωs, a detection value detected by a frequency sensor may be input to the control device 20 instead of a control command value.

Specifically, the motor loss calculator 20a calculates the stator iron loss Loss_is, the stator copper loss Loss_cs, and the rotor loss Loss_r using the following formulas (1) to (4). The rotor loss Loss_r is the sum of the rotor iron loss Loss_ir and the rotor copper loss Loss_cr.

Here, Kh_s: hysteresis loss coefficient of stator 10, Kef_s: eddy current loss coefficient of stator 10, Rs: resistance of stator 10 (function of stator temperature Tc), ω: synchronous frequency (function of motor rotation speed N), Is: motor current, Kh_r: hysteresis loss coefficient of rotor 12, Kef_r: eddy current loss coefficient of rotor 12, Rr: resistance of rotor 12 (function of rotor temperature Tr), ωre: drive frequency (synchronous frequency + slip frequency), Ir: motor secondary current.

The synchronous frequency ω is a value derived from the motor rotation speed N measured by the sensor, the stator coil current Is is a measured value or command value from a current sensor, and the drive frequency ωre is a value obtained by adding the command value of the slip frequency to the synchronous frequency ω.

Here, the motor loss calculator 20a sets the sampling time interval ST1 to about microseconds to milliseconds. That is, the motor loss calculator 20a calculates the stator iron loss Loss_is, the stator copper loss Loss_cs, and the rotor loss Loss_r (rotor iron loss Loss_ir, rotor copper loss Loss_cr) at a sampling time interval ST1 of about microseconds to milliseconds. The calculated stator iron loss Loss_is, stator copper loss Loss_cs, and rotor loss Loss_r (rotor iron loss Loss_ir, rotor copper loss Loss_cr) are output to the motor loss regulator 20b.

The motor loss adjuster 20b converts the stator iron loss Loss_is, stator copper loss Loss_cs, and rotor loss Loss_r (rotor iron loss Loss_ir, rotor copper loss Loss_cr) derived in the motor loss calculator 20a at the sampling time interval ST1 into stator iron loss Loss_is2, stator copper loss Loss_cs2, and rotor loss Loss_r2 (rotor iron loss Loss_ir2, rotor copper loss Loss_cr2) at the sampling time interval ST2 of the rotor temperature estimator 20c. The sampling time interval ST2 is a period longer than the sampling time interval ST1, and is preferably set to the same extent as the time interval at which the rotor temperature estimator 20c estimates the rotor temperature, i.e., the same extent as the sampling time interval for current control of the rotating machine 100. For example, the sampling time interval ST2 is preferably set to a time interval of about several seconds.

The motor loss regulator 20b calculates a motor loss accumulation value by accumulating values obtained by multiplying each loss by the sampling time ST1 until the accumulation time of the sampling time interval ST1 becomes equal to the sampling time interval ST2, using the formulas (5) to (8). Note that the rotor loss Loss_r2 is the sum of the rotor iron loss Loss_ir2 and the rotor copper loss Loss_cr2.

Figure 4 shows the relationship between the calculated values of stator iron loss, stator copper loss, and rotor loss and the stator current in the conventional method and the present embodiment. In the conventional method, the motor loss adjuster 20b is not provided, and as shown in the lower part of Figure 4, the motor loss calculator 20a calculates the stator iron loss Loss_is, the stator copper loss Loss_cs, and the rotor loss Loss_r at a sampling time interval ST2 of about several seconds, and during the sampling time interval ST2, the stator iron loss Loss_is, the stator copper loss Loss_cs, and the rotor loss Loss_r are treated as constant and do not change. In contrast, in this embodiment, as shown in the middle of FIG. 4, the motor loss calculator 20a calculates the stator iron loss Loss_is, stator copper loss Loss_cs, and rotor loss Loss_r at a sampling time interval ST1 of about several microseconds to milliseconds, and accumulates these to obtain the stator iron loss Loss_is2, stator copper loss Loss_cs2, and rotor loss Loss_r2 at a sampling time interval ST2 of about several seconds.

The stator iron loss Loss_is2, stator copper loss Loss_cs2, and rotor loss Loss_r2 calculated by the motor loss adjuster 20b are output to the rotor temperature estimator 20c.

The rotor temperature estimator 20c receives the stator iron loss Loss_is2, stator copper loss Loss_cs2, and rotor loss Loss_r2 from the motor loss regulator 20b, as well as the detected value of the outside air temperature Tair3, and calculates an estimate of the rotor temperature Trot from these input values based on a thermal circuit model set using thermal energy balance.

Figure 5 shows a thermal circuit model for the rotating machine 100. In the thermal circuit model shown in Figure 5, the multiple components that are thermally connected in the rotating machine 100 are the stator core, stator coil, rotor side members, the first frame 16a and the second frame 16b of the housing 16, and the load 102. Note that in this thermal circuit model, it is assumed that the temperature of the rotor core and conductor bars of the rotor 12 is equal to the temperature of the shaft 14, and these elements are shown as rotor side members.

In the thermal circuit model shown in FIG. 5, the temperature of the stator core is represented as Tsta, the temperature of the first frame 16a of the housing 16 as Tfr1, the temperature of the second frame 16b of the housing 16 as Tfr2, the temperature of the load 102 as Tload, the temperature of the stator coil as Tcoil, and the temperature of the rotor side member as Trot. In addition, the temperatures of air 0, 1, 2, and 3 are represented as Tair0, Tair1, Tair2, and Tair3, respectively. In the thermal circuit model, these components are connected by thermal resistances.

As shown in FIG. 3, the motor speed N, the stator coil current Is (or the command value of the stator coil current), the slip frequency ωs (or the command value of the slip frequency), and the coil temperature Tcoil are input to the motor loss calculator 20a of the control device 20. Furthermore, the estimated value of the rotor temperature Trot estimated by the previous rotor temperature estimation process is input to the motor loss calculator 20a from the output side of the rotor temperature estimator 20c described later.

The motor loss calculator 20a calculates the stator iron loss Loss_is and stator copper loss Loss_cs as losses occurring in the stator 10, as well as the rotor loss Loss_r occurring in the rotor 12, based on the motor rotation speed N, the stator coil current Is (or the command value of the stator coil current), the slip frequency ωs (or the command value of the slip frequency), the coil temperature Tcoil, and the estimated value of the previous rotor temperature Trot.

Equation (9) is obtained from the thermal circuit model shown in FIG.

The rotor temperature estimator 20c estimates the rotor temperature Trot based on the thermal circuit model expressed by the formula (9). Specifically, the rotor temperature estimator 20c uses an observer expressed by the formula (10).

In the observer of equation (10), superscripted angles (hat marks) are added to x and y, which represent estimated values. As shown in equation (9), u and y are composed of known values input to the rotor temperature estimator 20c. F represents the gain of the observer. Furthermore, coefficients calculated when the motor rotation speed N is an arbitrary rotation speed less than or equal to a predetermined rotation speed are applied to the components of matrix A.

By using formula (10), the rotor temperature Trot contained in x can be estimated. Specifically, the gain F is set so that y-y (hat) in formula (10) asymptotically converges to 0. Then, the rotor temperature Trot that matches the temperature of the rotor side member is calculated. As a result, the rotor temperature estimator 20c estimates the rotor temperature Trot using an observer designed with a thermal circuit model. Note that the rotor temperature estimator 20c may estimate the rotor temperature using a thermal circuit model without using an observer.

As described above, in the rotor temperature estimation system 200 of this embodiment, the motor loss calculator 20a calculates losses at sampling time intervals ST1 of about microseconds to milliseconds, which update the command value for the rotating machine 100. The motor loss regulator 20b then accumulates the losses and converts them into losses at sampling time intervals ST2 of about several seconds. The rotor temperature estimator 20c then estimates the rotor temperature Trot based on the losses at sampling time intervals ST2 of about several seconds. Therefore, the accuracy of the evaluation of losses in the rotating machine 100, which fluctuates at time intervals of about microseconds to milliseconds, can be improved, and the accuracy of the estimation of the rotor temperature Trot based on the evaluation of losses can also be improved. On the other hand, the estimation process of the rotor temperature Trot is performed at time intervals of about several seconds, which prevents the amount of calculations from increasing dramatically, and keeps the cost of the calculation device low.

REFERENCE SIGNS LIST 10 stator, 12 rotor, 14 shaft, 16 housing, 20 control device, 20a motor loss calculator, 20b motor loss adjuster, 20c rotor temperature estimator, 22 rotation speed sensor, 24 coil temperature sensor, 26 outside air temperature sensor, 100 rotating machine, 102 load, 200 rotor temperature estimation system.

Claims (4)

A rotor temperature estimation system for estimating a temperature of a rotor of a rotating machine, comprising:
a motor loss calculator that calculates losses of the rotating machine, including an iron loss of the rotor based on a drive frequency that is the sum of a synchronous frequency and a slip frequency of the rotating machine, and a copper loss of the rotor based on a secondary current of the rotating machine, for each sampling time interval that is shorter than a sampling time interval for estimating the temperature of the rotor;
a motor loss adjuster that calculates a motor loss accumulation value by accumulating the loss of the rotating machine calculated by the motor loss calculator up to a sampling time interval for estimating the temperature of the rotor;
a rotor temperature estimator that estimates a temperature of the rotor using the motor loss accumulation value;
A rotor temperature estimation system comprising: 2. The rotor temperature estimation system according to claim 1,
A rotor temperature estimation system, wherein the sampling time interval shorter than the sampling time interval for estimating the rotor temperature is the sampling time interval for current control of the rotating machine. 3. The rotor temperature estimation system according to claim 1,
a rotor temperature estimator that estimates the temperature of the rotor using an observer based on a thermal circuit model of the rotating machine; A rotor temperature estimation method for estimating a temperature of a rotor of a rotating machine, comprising:
calculating losses of the rotating machine, the losses including an iron loss of the rotor based on a drive frequency that is the sum of a synchronous frequency and a slip frequency of the rotating machine, and a copper loss of the rotor based on a secondary current of the rotating machine, for each sampling time interval that is shorter than a sampling time interval for estimating the temperature of the rotor;
accumulating the calculated loss of the rotating machine up to a sampling time interval for estimating the temperature of the rotor to calculate a motor loss accumulation value;
a rotor temperature estimation method comprising: estimating a temperature of the rotor using the accumulated motor loss value.