JP2014168340A - Motor control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor control device that estimates a temperature of switching elements in a drive circuit without using temperature sensors.SOLUTION: When an ECU 12 is powered on, an initial temperature estimation section 71 measures an on resistance of one predetermined FET and estimates a temperature of the FET on the basis of the measured on resistance and a temperature-on-resistance characteristic of the FET. The initial temperature estimation section 71 sets the estimated temperature of the FET as an initial temperature of a drive circuit 32. A temperature computation section 72 computes a temperature of the drive circuit 32 on the basis of an amount of heat generation of the entire drive circuit, a predetermined amount of heat radiation of the entire drive circuit and a temperature of the drive circuit 32 computed in the preceding cycle by the temperature computation section 72. Specifically, an initial value of the temperature of the drive circuit 32 computed in the preceding cycle is the initial temperature of the drive circuit 32 estimated by the initial temperature estimation section 71.

Description

  The present invention relates to a motor control device that controls an electric motor used in an electric power steering device or the like.

A drive circuit for an electric motor used in an electric power steering apparatus includes a plurality of switching elements such as a field effect transistor (FET). These switching elements are on / off controlled in accordance with the steering situation to drive the electric motor, thereby realizing appropriate steering assistance in accordance with the steering situation.
The FET used in the drive circuit of the electric motor is damaged when the temperature becomes too high. Therefore, the temperature of the FET is monitored, and when the temperature of the FET exceeds a predetermined temperature, the motor current is limited.

JP 2009-126240 A JP-A-2005-080485 JP 62-292576 A

It is conceivable that a thermistor is arranged in the vicinity of each FET and the temperature of the FET is detected by the thermistor. However, such a temperature detection method requires a thermistor and complicates the configuration of the drive circuit.
An object of the present invention is to provide a motor control device that can estimate the temperature of a switching element in a drive circuit without using a temperature sensor.

  The invention according to claim 1 is a motor control device (12) for controlling the electric motor (18), and includes a plurality of switching elements (51-56), and a drive circuit (32) for driving the electric motor. And an initial temperature estimating means (34, 35, 71) for estimating an initial temperature which is a temperature when the drive circuit is turned on when the power is turned on, and a calorific value calculating means (calculating the calorific value of the entire drive circuit) 34, 72), the initial temperature of the drive circuit estimated by the initial temperature estimation means, and the heat generation amount of the entire drive circuit calculated by the heat generation amount calculation means, the temperature of the drive circuit is determined. Temperature calculating means (72) for calculating, and the initial temperature estimating means detects a current flowing through at least one switching element when the power is turned on, and a terminal of the switching element. The voltage is detected, the on-resistance of the switching element is calculated based on the detected current and the voltage between the terminals, and the initial temperature of the drive circuit is estimated based on the calculated on-resistance of the switching element. This is a motor control device. In addition, although the alphanumeric character in parentheses represents a corresponding component in an embodiment described later, of course, the scope of the present invention is not limited to the embodiment. The same applies hereinafter.

According to the present invention, the temperature of the drive circuit can be calculated without using a temperature sensor. Thereby, the temperature of the switching element in the drive circuit can be estimated without using a temperature sensor.
According to a second aspect of the present invention, the calorific value calculation means includes a total current detection means (34) for detecting a total current flowing through the drive circuit, and a preset value when the electric motor is driven. 2. The unit according to claim 1, further comprising: means for calculating a heat generation amount of the entire drive circuit based on an average resistance value of the entire drive circuit and a total current detected by the total current detection unit. It is a motor control device.

  According to a third aspect of the present invention, the temperature calculation means includes an initial temperature of each of the switching elements estimated by the initial temperature estimation means, a heat generation amount of the entire drive circuit calculated by the heat generation amount calculation means, 3. The motor control device according to claim 1, wherein the motor control device is configured to calculate a temperature of the drive circuit using a preset heat radiation amount of the entire drive circuit. 4.

FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering device to which a motor control device according to an embodiment of the present invention is applied. FIG. 2 is a block diagram showing an electrical configuration of the ECU as the motor control device. FIG. 3 is a characteristic diagram showing an example of the temperature-on resistance characteristic of the FET 51. FIG. 4 is a flowchart illustrating a procedure of temperature monitoring processing executed by the temperature monitoring unit.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering device to which a motor control device according to an embodiment of the present invention is applied.
The electric power steering apparatus 1 includes a steering wheel 2 as a steering member for steering the vehicle, a steering mechanism 4 that steers the steered wheels 3 in conjunction with the rotation of the steering wheel 2, and steering by the driver. And a steering assist mechanism 5 for assisting. The steering wheel 2 and the steering mechanism 4 are mechanically coupled via a steering shaft 6 and an intermediate shaft 7.

The steering shaft 6 includes an input shaft 8 connected to the steering wheel 2 and an output shaft 9 connected to the intermediate shaft 7. The input shaft 8 and the output shaft 9 are connected via a torsion bar 10 so as to be relatively rotatable.
A torque sensor 11 is disposed around the steering shaft 6. The torque sensor 11 detects the steering torque applied to the steering wheel 2 based on the relative rotational displacement amount of the input shaft 8 and the output shaft 9.

  The steered mechanism 4 includes a rack and pinion mechanism including a pinion shaft 13 and a rack shaft 14 as a steered shaft. The steered wheel 3 is connected to each end of the rack shaft 14 via a tie rod 15 and a knuckle arm (not shown). The pinion shaft 13 is connected to the intermediate shaft 7. The pinion shaft 13 rotates in conjunction with the steering of the steering wheel 2. A pinion 16 is connected to the tip of the pinion shaft 13 (the lower end in FIG. 1).

  The rack shaft 14 extends linearly along the left-right direction of the automobile (a direction orthogonal to the straight-ahead direction). A rack 17 that meshes with the pinion 16 is formed at an intermediate portion in the axial direction of the rack shaft 14. By the pinion 16 and the rack 17, the rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. The steered wheels 3 can be steered by moving the rack shaft 14 in the axial direction.

When the steering wheel 2 is steered (rotated), this rotation is transmitted to the pinion shaft 13 via the steering shaft 6 and the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into an axial movement of the rack shaft 14 by the pinion 16 and the rack 17. Thereby, the steered wheel 3 is steered.
The steering assist mechanism 5 includes an electric motor 18 for assisting steering and a speed reduction mechanism 19 for transmitting the output torque of the electric motor 18 to the steering mechanism 4. In this embodiment, the electric motor 18 is a three-phase brushless motor. The electric motor 18 includes a rotor (not shown) as a field and a stator (not shown) including U-phase, V-phase, and W-phase field windings (not shown). In the vicinity of the electric motor 18, a rotation angle sensor 23 made of, for example, a resolver for detecting the rotation angle θ of the rotor of the electric motor 18 is disposed. The speed reduction mechanism 19 includes a worm gear mechanism that includes a worm shaft 20 and a worm wheel 21 that meshes with the worm shaft 20. The speed reduction mechanism 19 is accommodated in a gear housing 22 as a transmission mechanism housing.

The worm shaft 20 is rotationally driven by the electric motor 18. The worm wheel 21 is coupled to the steering shaft 6 so as to be rotatable in the same direction. The worm wheel 21 is rotationally driven by the worm shaft 20.
When the worm shaft 20 is rotationally driven by the electric motor 18, the worm wheel 21 is rotationally driven and the steering shaft 6 rotates. The rotation of the steering shaft 6 is transmitted to the pinion shaft 13 via the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. Thereby, the steered wheel 3 is steered. That is, the wheel 3 is steered by rotating the worm shaft 20 by the electric motor 18.

The electric motor 18 is controlled by an ECU (Electronic Control Unit) 12 as a motor control device. The ECU 12 receives a steering torque detected by the torque sensor 11, an output signal of the rotation angle sensor 23, a vehicle speed detected by the vehicle speed sensor 24, and the like.
FIG. 2 is a schematic diagram showing an electrical configuration of the ECU 12 as a motor control device.

  In this embodiment, the ECU 12 controls the electric motor 18 by a vector control method. In the vector control method, current values of the U phase, V phase, and W phase in the three-phase fixed coordinate system are converted into two-phase currents in the two-phase rotating coordinate system, and the motor is controlled using the two-phase currents. . The two-phase rotational coordinate system is a coordinate system defined by a d-axis along the magnetic pole direction of the rotor and a q-axis orthogonal to the d-axis. The two-phase current in the two-phase rotating coordinate system includes a d-axis current component and a q-axis current component.

The power source of the ECU 12 is turned on when the ignition key is turned on. When the ignition key is turned off, an ignition off command is input to the ECU 12. After the ignition off command is input, the power source of the ECU 12 is turned off.
The ECU 12 includes a microcomputer 31, a drive circuit 32, a phase current detection unit 33, a total current detection unit 34, and a voltage detection unit 35.

  The drive circuit 32 supplies power to the electric motor 18 and is controlled by the microcomputer 31. The drive circuit 32 is composed of a three-phase inverter circuit and includes a plurality of switching elements 51 to 56. In this embodiment, each switching element 51-56 is comprised from FET (Field Effect Transistor). In the drive circuit 32, a series circuit of a pair of FETs 51 and 52 corresponding to the U phase of the electric motor 18, a series circuit of a pair of FET 53 and FET 54 corresponding to the V phase, and a pair of FET 55 and FET 56 corresponding to the W phase. A series circuit is connected in parallel between the DC power supply 25 and the ground. In the following, among the pair of FETs of each phase, the one on the power supply 25 side may be referred to as “high-side FET” and the one on the ground side may be referred to as “low-side FET”.

A connection point between the pair of FETs 51 and 52 corresponding to the U phase is connected to the U phase field winding of the electric motor 18. A connection point between the pair of FETs 53 and 54 corresponding to the V phase is connected to the V phase field winding of the electric motor 18. A connection point between the pair of FETs 55 and 56 corresponding to the W phase is connected to the W phase field winding of the electric motor 18.
Current sensors 26, 27, and 28 for detecting each phase current of the electric motor 18 are provided on each connection line for connecting the low-side FETs 52, 54, and 56 to the ground. The phase current detector 33 detects each phase current of the electric motor 18 based on the output signals of the current sensors 26, 27, and 28.

A shunt resistor 29 is connected between the ground-side connection point of the low-side FETs 52, 54, and 56 and the ground. The total current detector 34 detects the total current flowing through the drive circuit 32 based on the voltage across the shunt resistor 29.
The voltage detector 35 detects the voltage of each part for detecting the voltage across the terminals of at least one FET. The voltage of each part includes, for example, the voltage of each terminal of the electric motor 18 and the voltage of the power supply 25.

  Returning to FIG. 2, the microcomputer 31 includes a CPU and a memory (ROM, RAM, nonvolatile memory, etc.), and functions as a plurality of function processing units by executing a predetermined program. . The plurality of function processing units include a current command value setting unit 41, a rotation angle calculation unit 42, a coordinate conversion unit 43, a current deviation calculation unit 44, a PI (proportional integration) control unit 45, and a coordinate conversion unit. 46, a PWM (Pulse Width Modulation) control unit 47, and a temperature monitoring unit 48 are included.

Based on the detected steering torque Th detected by the torque sensor 11 and the vehicle speed V detected by the vehicle speed sensor 24, the current command value setting unit 41 sets a current command value that is a command value of the current to be passed through the electric motor 18. To do. Specifically, the current command value setting unit 41 refers to a d-axis current command value I _d ^* and a q-axis current command value I _q ^* (hereinafter, collectively referred to as “two-phase current command value I _dq ^* ”). ) Is generated. More specifically, the current command value generation unit 41 sets the q-axis current command value I _q ^* to a significant value and sets the d-axis current command value I _d ^* to zero. The two-phase current command value I _dq ^* set by the current command value setting unit 41 is given to the current deviation calculation unit 44.

The rotation angle calculation unit 42 calculates the rotation angle (electrical angle; hereinafter referred to as “rotor angle θ”) of the rotor of the electric motor 18 based on the output signal of the rotation angle sensor 23.
The phase current detection unit 33 is based on the output signals of the current sensors 26, 27, and 28. The U-phase current I _U , the V-phase current I _V and the W-phase current I _{W of} the electric motor 18 Detects “three-phase detection current I _UVW ”). The three-phase detection current I _UVW detected by the phase current detection unit 33 is given to the coordinate conversion unit 43.

The coordinate conversion unit 43 converts the three-phase detection current I _UVW (U-phase current I _U , V-phase current I _V and W-phase current I _W ) of the UVW coordinate system detected by the phase current detection unit 33 into the dq coordinate system. Two-phase detection currents I _d and I _q (hereinafter collectively referred to as “two-phase detection current I _dq ”). These are supplied to the current deviation calculation unit 44. For the coordinate conversion in the coordinate conversion unit 43, the rotor angle θ calculated by the rotation angle calculation unit 42 is used.

The current deviation calculation unit 44 calculates a deviation between the two-phase current command value I _dq ^* set by the current command value setting unit 41 and the two-phase detection current I _dq given from the coordinate conversion unit 43. More specifically, the current deviation calculation unit 44 calculates the deviation of the d-axis detection current I _d with respect to the d-axis current command value I _d ^* and the deviation of the q-axis detection current I _q with respect to the q-axis current command value I _q ^* . To do. These deviations are given to the PI control unit 45.

The PI control unit 45 performs a PI calculation on the current deviation calculated by the current deviation calculation unit 44, whereby a two-phase voltage command value V _dq ^* (d-axis voltage command value V _d ^* and q-axis voltage command value V _q ^* ) is generated. The two-phase voltage command value V _dq ^* is given to the coordinate conversion unit 46.
The coordinate conversion unit 46 converts the two-phase voltage command value V _dq ^* into the three-phase voltage command value V _UVW ^* . For this coordinate conversion, the rotor angle θ calculated by the rotation angle calculation unit 42 is used. The three-phase voltage command value V _UVW ^* includes a U-phase voltage command value V _U ^* , a V-phase voltage command value V _V ^*, and a W-phase voltage command value V _W ^* . This three-phase voltage command value V _UVW ^* is given to the PWM control unit 47.

The operation mode of the PWM control unit 47 includes a normal mode and a special mode that is forcibly controlled by the temperature monitoring unit 48. In the normal mode, the PWM control unit 47 uses a U-phase PWM control signal and a V-phase with a duty corresponding to the U-phase voltage command value V _U ^* , the V-phase voltage command value V _V ^*, and the W-phase voltage command value V _W ^* , respectively. A PWM control signal and a W-phase PWM control signal are generated. Further, the PWM control unit 47 generates gate signals for the FETs 51 to 56 in the drive circuit 32 based on these PWM control signals and supplies them to the FETs 51 to 56. As a result, a voltage corresponding to the three-phase voltage command value V _UVW ^* is applied to the field winding of each phase of the electric motor 18.

The temperature monitoring unit 48 is supplied with the total current detected by the total current detection unit 34 and the voltage of each unit detected by the voltage detection unit 35. The temperature monitoring unit 48 includes an initial temperature estimation unit 71, a temperature calculation unit 72, and an overheat protection unit 73.
The initial temperature estimation unit 71 estimates the temperature of the drive circuit 32 when the power is turned on (hereinafter referred to as “initial temperature”) by utilizing the fact that the on-resistance of the FET depends on the temperature of the FET. Specifically, the initial temperature estimation unit 71 measures the on-resistance of one predetermined FET when the ECU 12 is turned on, and based on the measured on-resistance and the temperature-on resistance characteristic of the FET. Estimate the temperature of the FET. Then, the initial temperature estimation unit 71 sets the estimated temperature of the FET as the initial temperature of the drive circuit 32.

  For example, the case where the initial temperature of the drive circuit 32 is estimated based on the on-resistance of the U-phase high-side FET 51 will be described. In the nonvolatile memory, a map describing the temperature-on resistance characteristics of the FET 51 is stored in advance. FIG. 3 shows an example of the temperature-on resistance characteristic of the FET 51. When the ECU 12 is turned on, the initial temperature estimation unit 71 first controls the PWM control unit 47 to turn on the high-side FET 51 and the low-side FET 52 corresponding to the U phase, and turn on the other phase FETs 53 to 56. Turn off. Thereby, a current flows through the FET 51 and the FET 52. The value of the current flowing through the FET 51 is detected by the total current detection unit 34. The initial temperature estimation unit 71 takes in the current flowing from the total current detection unit 34 to the FET 51.

The initial temperature estimating unit 71 calculates the voltage across the terminals of the FET 51 based on the voltage of each unit detected by the voltage detecting unit 35. Specifically, the voltage between the terminals of the FET 51 is obtained as a difference between the voltage of the power supply 25 and the voltage at the connection point between the FET 51 and the FET 52 (the voltage at the U-phase terminal of the electric motor 18).
Thereafter, the initial temperature estimation unit 71 calculates the on-resistance of the FET 51 by dividing the voltage between the terminals of the FET 51 by the current flowing through the FET 51. Next, the initial temperature estimation unit 71 estimates the temperature of the FET 51 based on the calculated ON resistance of the FET 51 and a map describing the temperature-ON resistance characteristics of the FET 51. Then, the initial temperature estimating unit 71 sets the estimated temperature of the FET 51 as the initial temperature T ₀ of the drive circuit 32. Thereafter, the initial temperature estimation unit 71 sets the operation mode of the PWM control unit 47 to the normal mode. Thereby, the PWM control unit 47 starts a normal operation (operation according to the three-phase voltage command value V _UVW ^* ).

The temperature calculation unit 72 calculates the temperature of the drive circuit 32 every predetermined calculation cycle Δt. Specifically, the temperature calculation section 72, first, calculates the calorific value Q _n of the entire driving circuit. Specifically, the temperature calculation section 72 obtains the total current I _T, which is detected by the total current detector 34. Then, the temperature calculation unit 72 calculates the acquired total current _IT and the average resistance value of the entire drive circuit when the electric motor 18 is driven (hereinafter referred to as “average resistance value R of the entire drive circuit during motor driving”). And the calculation cycle Δt, the calorific value Q _{n of the} entire drive circuit is calculated using the following equation (1). The average resistance value R of the entire drive circuit during motor driving is obtained in advance by experiments and stored in a nonvolatile memory.

^{_{Q n = I T 2 · R}} · Δt ... (1)
Next, the temperature calculation unit 72 generates a calorific value Q _{n of the} entire drive circuit, a predetermined heat dissipation amount R of the entire drive circuit, and a temperature T _n−1 of the drive circuit 32 previously calculated by the temperature calculation unit 72. based on bets, using the following equation (2), calculates the temperature T _n of the drive circuit 32. The heat radiation amount R of the entire drive circuit is obtained in advance by experiments and stored in the nonvolatile memory.

T _n = T _n−1 + Q _n −R (2)
However, the initial temperature T ₀ estimated by the initial temperature estimation unit 71 is used as the initial value of T _n−1 .
The overheat protection unit 73 determines whether or not the temperature T _n of the drive circuit 32 calculated by the temperature calculation unit 72 exceeds a predetermined value α. When the temperature T _n of the drive circuit 32 exceeds the predetermined value α, the overheat protection unit 73 outputs a current command value limit command to the current command value setting unit 41. When the current command value limit command is given from the temperature monitoring unit 48, the current command value setting unit 41 limits the current command value so that the absolute value of the current command value is equal to or less than a predetermined value.

FIG. 4 is a flowchart showing the procedure of the temperature monitoring process executed by the temperature monitoring unit 48.
When the power source of the ECU 12 is turned on, the initial temperature estimation unit 71 estimates the initial temperature T ₀ of the drive circuit 32 (step S1).
The initial temperature of the drive circuit 32 by the initial temperature estimation unit 71 is estimated, the temperature calculation section 72 obtains the total current I _T, which is detected by the total current detector 34 (Step S2). The process of step S2 is performed every predetermined calculation period Δt until an ignition-off command is input (until YES in step S7 described later). Temperature calculation unit 72, based on the equation (1), calculates the calorific value Q _n of the entire driving circuit (step S3). Then, the temperature calculation unit 72 calculates the temperature T _n of the drive circuit 32 based on the equation (2) (step S4).

When the temperature T _n of the drive circuit 32 by the temperature calculation unit 72 is calculated, overheat protection unit 73, the temperature T _n of the drive circuit 32 to determine whether it exceeds a predetermined value alpha (Step S5). If the temperature T _n of the drive circuit 32 is equal to or less than the predetermined value alpha (Step S5: NO), the overheat protection unit 73, ignition-off command it is determined whether or not the input (step S7). If the ignition-off command has not been input (step S7: NO), the process returns to step S2.

When it is determined in step S5 that the temperature T _n of the drive circuit 32 exceeds the predetermined value α (step S5: YES), the overheat protection unit 73 supplies a current to the current command value setting unit 41. A command value restriction command is output (step S6). The current command value setting unit 41 limits the absolute value of the current command value to a predetermined value or less when a current command value restriction command is given. Thereby, since the value of the current flowing through the electric motor 18 is limited, the temperature rise of each of the FETs 51 to 56 is suppressed. Thereafter, the overheat protection unit 73 determines whether or not an ignition-off command is input (step S7). If the ignition-off command has not been input (step S7: NO), the process returns to step S2.

If it is determined in step S7 that an ignition-off command has been input (step S7: YES), the temperature monitoring process is terminated.
According to the embodiment, the temperature of the drive circuit 32 can be calculated without using a temperature sensor. Thereby, the temperature of FET51-56 in the drive circuit 32 can be estimated, without using a temperature sensor. When the temperature of the drive circuit 32 exceeds the predetermined value α, the current flowing through the electric motor 18 can be limited. Thereby, overheating of FET51-56 can be prevented beforehand.

  As mentioned above, although embodiment of this invention was described, this invention can also be implemented with another form. For example, in the embodiment, when the initial temperature estimation unit 71 estimates the initial temperature based on the on-resistance of the U-phase high-side FET 51, the initial-temperature estimation unit 71 turns on the U-phase high-side FET 51 and the low-side FET 52. Although a current is passed through the FET 51, a current may be passed through the FET 51 by turning on the high-side FET 51 of the U phase and the low-side FET of the other phase.

Moreover, although the said embodiment demonstrated the structure which uses FET as a switching element, you may use semiconductor elements other than FET, such as IGBT (Insulated Gate Bipolar Transistor).
In addition, various design changes can be made within the scope of matters described in the claims.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 12 ... ECU, 26, 27, 28 ... Current sensor, 29 ... Shunt resistance, 32 ... Drive circuit, 33 ... Phase current detection part, 34 ... Total current detection part, 35 ... Voltage detection part, DESCRIPTION OF SYMBOLS 41 ... Current command value setting part, 48 ... Temperature monitoring part, 51-56 ... FET, 71 ... Initial temperature estimation part, 72 ... Temperature calculation part, 73 ... Overheat protection part

Claims (3)

A motor control device for controlling an electric motor,
A drive circuit including a plurality of switching elements and driving the electric motor;
An initial temperature estimating means for estimating an initial temperature which is a temperature when the drive circuit is powered on when the power is turned on;
A calorific value calculating means for calculating the calorific value of the entire drive circuit;
Temperature calculation means for calculating the temperature of the drive circuit using the initial temperature of the drive circuit estimated by the initial temperature estimation means and the heat generation amount of the entire drive circuit calculated by the heat generation amount calculation means; Including
The initial temperature estimating means includes
When the power is turned on, the current flowing in at least one switching element is detected, the voltage between the terminals of the switching element is detected, and the on-resistance of the switching element is calculated based on the detected current and the voltage between the terminals. A motor control device configured to estimate an initial temperature of the drive circuit based on the on-resistance of the switching element. The calorific value calculation means includes:
Total current detecting means for detecting the total current flowing in the drive circuit;
Based on an average resistance value of the entire drive circuit that is set in advance and when the electric motor is driven, and a total current detected by the total current detection means, The motor control device according to claim 1, further comprising means for calculating a calorific value.   The temperature calculation means includes an initial temperature of each switching element estimated by the initial temperature estimation means, a heat generation amount of the entire drive circuit calculated by the heat generation amount calculation means, and a preset entire drive circuit. The motor control device according to claim 1, wherein the motor control device is configured to calculate a temperature of the drive circuit using a heat radiation amount of the motor.

Images