JP4426433B2 - Motor control device - Google Patents

Description

  The present invention relates to a motor control apparatus that controls a motor by inputting a pulse width modulation signal to an inverter, and more specifically, motor control that can stably maintain the rotation of a motor such as a three-phase brushless DC motor. Relates to the device.

  Conventionally, a three-phase brushless DC motor including a stator (stator) and a rotor (rotor) rotatably disposed inside the stator is known. In this brushless DC motor, a rotating magnetic field is generated by energizing a coil wound around the stator in a certain order, and the torque and the number of rotations generated in the rotor are displaced by controlling the intensity and cycle. Thus, rotation control is performed.

  The motor rotation control described above will be described in more detail. The U-phase provided in the three-phase brushless DC motor is provided with an inverter having a three-phase circuit formed by connecting three sets of switching elements connected in series to each other in parallel. , V and W are controlled in voltage applied to each of the three phases. In general, a pulse width modulation (PWM) method is used to generate the voltage at this time. In this PWM system, a PWM signal generated based on the voltage command value of each phase is transmitted to the inverter, and each switching element of the three-phase circuit is controlled on / off at a frequency of several kHz based on this PWM signal. Then, by adjusting the proportion of the ON time, the average voltage of the output to the three-phase brushless DC motor is displaced, and torque and rotation speed are controlled. In the three-phase modulation, the control of the three-phase brushless DC motor is generally performed using all the switching elements in the inverter as described above.

  By the way, the motor control as described above is performed by the two-phase gate signal control (two-phase modulation) in which the pulse for one phase is in a rest state at the time of rotation control at the normal speed, and at the time of rotation control at the low speed. Proposals have been made to perform control using a three-phase gate signal generated based on two-phase gate signal control. In this case, the two-phase gate signal at a low speed becomes a minimal waveform with a small pulse width, thereby preventing a problem that the switching element cannot sufficiently react, thereby smoothly rotating the motor without generating torque unevenness. (See, for example, Patent Document 1).

  In the case of two-phase modulation, there is also a modulation method in which motor control is performed by dividing six switching elements provided in a three-phase circuit into two upper and lower stages. In this upper-and-lower type modulation system, switching of the other two phases is performed by switching the other two phases in a state in which the switching of the switching element of the phase having the largest absolute value of the voltage command value at a certain time is stopped. Realize modulation. In this upper and lower stage modulation scheme, the largest phase voltage command value is controlled by the upper modulation scheme when the value is positive, and by the lower modulation scheme when the value is negative. The motor control is performed while switching so as to.

JP 2003-199381 A

  By the way, in the motor drive device described in the above-described Patent Document 1 and the upper and lower modulation methods, the switching element for two phases is switched from the three-phase circuit in the inverter to change the three-phase brushless DC motor. Since the current flowing in each phase is controlled, the number of elements to be switched is reduced as compared with the conventional one that switches all three phases, and the switching loss is reduced. However, when the three-phase brushless DC motor is continuously rotated in a low speed region, heat is generated due to the energization time of each switching element being increased. This will cause a reduction in torque.

  Therefore, the present invention is configured so that PWM signal generation by two-phase modulation with low switching loss during motor rotation can be appropriately controlled according to the speed range while suppressing temperature rise of the switching element and the inverter as much as possible. Therefore, an object of the present invention is to provide a motor control device that solves the above-described problems.

The present invention according to claim 1 (see, for example, FIGS. 1 to 16) is a three-phase circuit (13) comprising first and second switching element groups (A, B) that generate waveform signals whose logics are opposite to each other. The motor (2) is provided with an inverter (3), and a pulse width modulation signal generated based on voltage command values for the first, second and third phases of the motor (2) is input to the inverter (3). In the motor control device (1) that performs the control of (2),
Of the voltage command values corresponding to each of the first to third phases, the first switching element group (A) corresponding to a phase (a, b, c) that is a positive value and has the largest absolute value. First pulse generating means (11, 12) for energizing the switching elements (a1, b1, c1) of the switching elements (a1, b1, c1) over the entire switching period (T _c ) required for generating one pulse of the pulse width modulation signal;
Of the voltage command values corresponding to each of the first to third phases, the second switching element group (B) corresponding to the phase (a, b, c) which is a negative value and has the largest absolute value. Second switching means (11, 12) for energizing the switching elements (a2, b2, c2) in the energized state throughout the switching period (T _c );
The power loss caused by the input of the pulse width modulation signal generated by the first pulse generation means (11, 12) or the second pulse generation means (11, 12) to the inverter (3) is within a certain value. An elapsed time determination means (7) for determining whether or not a predetermined time (RD1, RD2) set in advance for storage has elapsed;
Control by the first pulse generation means (11, 12) and the second pulse generation means (11, 12) every time the predetermined time (RD1, RD2) is determined by the elapsed time determination means (7). Switching means (10) for switching between control by
The motor control device (1) is characterized by comprising:

According to the second aspect of the present invention (see, for example, FIGS. 1, 9, 10, FIGS. 12 to 14, and FIG. 16), the rotation for determining whether or not the rotation speed of the motor (2) is less than a predetermined value. A speed determining means (5),
The switching means (10)
While the rotation speed determination means (5) determines that the rotation speed of the motor (2) is less than the predetermined value, the elapsed time determination means (7) has passed the predetermined time (RD1, RD2). Switching between the control by the first pulse generation means (11, 12) and the control by the second pulse generation means (11, 12) each time
It exists in the motor control apparatus (1) of Claim 1 characterized by the above-mentioned.

The present invention according to claim 3 (see, for example, FIGS. 1, 9, 10 and FIGS. 12 to 14), the switching means (10)
While the rotation speed determination means (5) determines that the rotation speed of the motor (2) is equal to or higher than the predetermined value, the absolute value of the voltage command values corresponding to the first to third phases is determined. In the range where the voltage command value is positive and the voltage command value is positive, the control is switched to the control by the first pulse generating means (11, 12), and the absolute value of the voltage command values corresponding to the first to third phases Is switched to the control by the second pulse generating means (11, 12) in the range where the voltage command value is negative and the voltage command value is negative.
It exists in the motor control apparatus (1) of Claim 2 characterized by the above-mentioned.

The present invention according to claim 4 (see, for example, FIGS. 2 to 11, 15, and 17) includes first and second switching element groups (A, B) that generate waveform signals whose logics are opposite to each other. An inverter (3) having a three-phase circuit (13), and a pulse width modulation signal generated based on voltage command values for the first, second and third phases of the motor (2). In the motor control device (1) for controlling the motor (2) by inputting to
Of the voltage command values corresponding to each of the first to third phases, the first switching element group (A) corresponding to a phase (a, b, c) that is a positive value and has the largest absolute value. First pulse generating means (11, 12) for energizing the switching elements (a1, b1, c1) of the switching elements (a1, b1, c1) over the entire switching period (T _c ) required for generating one pulse of the pulse width modulation signal;
Of the voltage command values corresponding to each of the first to third phases, the second switching element group (B) corresponding to the phase (a, b, c) which is a negative value and has the largest absolute value. Second switching means (11, 12) for energizing the switching elements (a2, b2, c2) in the energized state throughout the switching period (T _c ),
The power loss caused by the input of the pulse width modulation signal generated by the first or second pulse generation means (11, 12) to the inverter (3) is set within a predetermined value. Based on a predetermined temperature (Lim), temperature determining means (22) for determining whether or not the temperature generated in each of the first and second switching element groups (A, B) is equal to or higher than the predetermined temperature (Lim). When,
When the temperature determining means (22) determines that the first switching element group (A) is equal to or higher than the predetermined temperature (Lim), the control is switched to the control by the second pulse generating means (11, 12), and Switching means (10) for switching to control by the first pulse generating means (11, 12) when the second switching element group (B) is determined to be equal to or higher than the predetermined temperature (Lim);
The motor control device (20) is characterized by comprising:

The present invention according to claim 5 (see, for example, FIGS. 1, 9, 10, and 17), a rotational speed determination means (5) for determining whether the rotational speed of the motor (2) is less than a predetermined value, Further comprising
The switching means (10)
Each time the temperature determination means (22) determines the predetermined temperature (Lim) while the rotation speed determination means (5) determines that the rotation speed of the motor (2) is less than the predetermined value. Switching between control by the first pulse generating means (11, 12) and control by the second pulse generating means (11, 12);
It exists in the motor control apparatus (20) of Claim 4 characterized by the above-mentioned.

  In addition, although the code | symbol in the said parenthesis is for contrast with drawing, this is for convenience for making an understanding of invention easy, and has no influence on the structure of a claim. It is not a thing.

  According to the first aspect of the present invention, the switching means switches between the control by the first pulse generating means and the control by the second pulse generating means every time when the predetermined time has been determined by the elapsed time determining means. When the control is performed, by always using the two-phase modulation method, the number of elements to be switched is reduced as compared with the case of using the three-phase modulation method, and the switching loss (which occurs in each of the first and second switching element groups ( As the power loss is reduced, the heat generated in each element is effectively suppressed. Furthermore, by alternately switching the two modulation methods at regular time intervals to generate the pulse width modulation signal, it is possible to keep the power loss generated in each of the first and second switching element groups within a certain value. That is, it is possible to suppress the decrease in continuous operation time and the maximum torque due to the heat generated in the switching element and the inverter as much as possible by leveling the temperature rise that occurs every fixed time within a predetermined range. It becomes like this. As a result, stable motor control can be performed, and reliability for motor rotation control can be improved.

  According to the second aspect of the present invention, while the switching means determines that the rotation speed of the motor is less than a predetermined value (for example, the low speed rotation range) by the rotation speed determination means, the elapsed time determination means determines whether the predetermined time has elapsed. Since the control by the first pulse generation means and the control by the second pulse generation means are switched every time the progress is judged, the energization time in each of the first and second switching element groups during the low-speed rotation of the motor is increased. It becomes possible to suppress. That is, an increase in power loss in each of the first and second switching element groups due to an increase in energization time is effectively suppressed, and the temperature rise that occurs each time the pulse generating means is switched is adjusted within a predetermined range. Thus, it is possible to suppress the decrease in continuous operation time and the maximum torque due to heat generated in the switching element and the inverter as much as possible. As a result, stable motor control at low speed can be realized, and reliability for motor rotation control can be improved.

  According to the third aspect of the present invention, while the switching means determines that the rotation speed of the motor is less than a predetermined value (for example, the low speed rotation range) by the rotation speed determination means, every time a predetermined time elapses. While the control by the first pulse generation means and the control by the second pulse generation means are switched and the rotation speed determination means determines that the rotation speed of the motor is not less than a predetermined value (for example, a high speed rotation range), the first to Among the voltage command values corresponding to the third phase, when the absolute value is the largest and the voltage command value is in the positive range, the control is switched to the control by the first pulse generating means, and the absolute value is the largest and the voltage command value is the negative. Since the control is switched to the control by the second pulse generating means when it is within the range, the first and second switching elements are switched by switching the pulse generating means at regular intervals during the low-speed rotation of the motor. Can be proportioned within the temperature increase each predetermined in the group. On the other hand, in other speed ranges, the temperature rise of the first and second switching element groups can be suppressed within a predetermined range by effectively switching the pulse generating means for each rotation angle of the motor. This makes it possible to suppress a decrease in continuous operation time and a decrease in maximum torque due to heat generated in the switching element and inverter during motor control, and it is stable at low speeds and other speed ranges. Motor control can be realized, and reliability for motor rotation control can be improved.

  According to the fourth aspect of the present invention, every time when the temperature determination unit determines that either the upper stage or the lower stage switching element is equal to or higher than the predetermined temperature, the control by the first pulse generation unit and the second pulse generation unit are performed. Therefore, when the motor control is performed, the two-phase modulation method is always used, so that the number of elements to be switched is reduced as compared with the case where the three-phase modulation method is used. By reducing the switching loss (power loss) generated in each group, the heat generated in each element is effectively suppressed. Further, by alternately switching the two modulation methods for each temperature generated in the first and second switching element groups and generating a PWM signal, the power loss generated in each of the first and second switching element groups is a constant value. Can fit within. That is, it is possible to suppress the decrease in continuous operation time and the maximum torque due to the heat generated in the switching element and the inverter as much as possible by leveling the temperature rise that occurs every fixed time within a predetermined range. It becomes like this. As a result, stable motor control can be performed, and reliability for motor rotation control can be improved.

  According to the fifth aspect of the present invention, while the rotation speed determination means determines that the rotation speed of the motor is less than a predetermined value (for example, the low speed rotation range), the temperature determination means is the first and second switching elements. Each time it is determined that any one of the temperature is higher than the predetermined temperature, the control by the first pulse generation means and the control by the second pulse generation means are switched, so that the first and second switching elements at the time of low-speed rotation of the motor An increase in energization time for each group can be suppressed. That is, an increase in power loss in each of the first and second switching element groups due to an increase in energization time is effectively suppressed, and the temperature rise that occurs each time the pulse generating means is switched is adjusted within a predetermined range. Thus, it is possible to suppress the decrease in continuous operation time and the maximum torque due to heat generated in the switching element and the inverter as much as possible. As a result, stable motor control at low speed can be realized, and reliability for motor rotation control can be improved.

<First Embodiment>
Hereinafter, a motor control device according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the motor control device according to the first embodiment.

  The motor control apparatus 1 includes an inverter 3 having a three-phase circuit including first and second switching element groups that generate waveform signals whose logics are opposite to each other, and the first, second, and third phases of the motor 2. The motor 2 is controlled by inputting a pulse width modulation signal generated based on the voltage command value to the inverter 2. That is, the motor control device 1 generates a pulse width modulation (PWM) signal and inputs (sends) it to the inverter 3 to control the brushless DC motor 2. Rotational speed determination means) 5, voltage command value detection means 6, timer detection means (elapsed time determination means) 7, modulation method mode setting means 9, modulation method setting means (switching means) 10, pulse signal calculation Means (first pulse generation means, second pulse generation means) 11 and PWM signal generation means (first pulse generation means, second pulse generation means) 12 are provided. As will be described later with reference to FIG. 2, the inverter 3 includes three pairs of semiconductor switching elements (hereinafter abbreviated as switching elements), and an internal temperature of an inverter case (not shown) is provided in the vicinity of the inverter 3. A temperature detection element (not shown) such as a thermistor sensor is provided.

  The rotation speed detection means 5 detects the current rotation speed (that is, at the time of detection) of the brushless DC motor 2 using a rotation sensor or the like, and outputs a detection signal thereof. The voltage command value detection means 6 compares the current command value obtained from the given torque command value with the actual current value, and calculates the voltage command as a result of calculation so that these current command value and the actual current value match. Detect value. The voltage command value is a value that should be the basis of the rotation control of the brushless DC motor 2, and is generated as a sine wave for three phases including the U phase, the V phase, and the W phase of the brushless DC motor 2. The timer detection means 7 detects that a predetermined time interval has elapsed from an arbitrary time point.

  The modulation mode setting unit 9 issues a command (mode command) for switching to one of two modulation mode modes to be described later based on a predetermined mode setting or a detection result by the rotation speed detection unit 5. The two modulation method modes include a voltage command value switching mode for switching between two modulation methods in accordance with the phase having the largest absolute value among the voltage command values for three phases given to the brushless DC motor 2. And a constant time switching mode in which the two modulation methods are switched every time a certain time elapses. In addition, two modulation systems that can be switched in each of these modes are an upper-stage reflux type two-phase modulation system and one of them is a lower-stage reflux type two-phase modulation system, the details of which will be described later with reference to FIGS. To do.

When the above-described modulation method mode setting means 9 determines that the rotational speed of the motor 2 detected by the rotational speed detection means 5 is a predetermined value (for example, 100 rpm) or more (that is, a high speed range), A signal for switching to the voltage command value switching mode is transmitted to the modulation method setting means 10. Further, when it is determined that the rotation speed of the motor 2 is less than a predetermined value (a low speed range), a signal for switching to the constant time switching mode is transmitted to the modulation method setting means 10. Each mode command described above is issued during pulse generation in the pulse generation period T _c immediately before the switching period after switching (hereinafter also referred to as pulse generation period) T _c (see FIGS. 3 and 6).

  When the above-described mode command is the voltage command value switching mode, the modulation method setting unit 10 is a positive value and has the largest absolute value among the voltage command values for three phases from the voltage command value detection unit 6. When there is a phase, a command (switching command) for switching to the upper-stage reflux type two-phase modulation method is transmitted to the pulse signal computing means 11. Further, when there is a phase that is a negative value and has the largest absolute value among the voltage command values for three phases from the voltage command value detection means 6, it is switched to the lower-stage reflux type two-phase modulation method. A switching command is transmitted to the pulse signal calculation means 11.

  Further, when the mode command described above is the fixed time switching mode, the modulation method setting means 10 is the modulation method that has been valid until that time when the timer detection means 7 detects a predetermined time interval. Is sent to the pulse signal computing means 11 to switch to the other modulation method. For example, when the control by the upper-stage reflux type two-phase modulation method has been effective so far, a switching command for switching to the control by the lower-stage reflux type two-phase modulation method is transmitted from that point.

The pulse signal calculation means 11 calculates a required pulse width modulation signal (PWM signal) based on the switching command transmitted from the modulation method setting means 10, and pulses related to the PWM signal by the upper or lower reflux type two-phase modulation method. A control command based on the width and timing is transmitted to the PWM signal generation unit 12. The calculation by the pulse signal calculation means 11 is performed at a timing immediately before the execution of the pulse generation section _{Tc in which} the upper stage or lower stage reflux type two-phase modulation system should be switched. When the motor control apparatus 1 is mounted on a vehicle. If it is assumed, it is performed in response to an accelerator depression operation or the like.

  The PWM signal generation means 12 generates a PWM signal corresponding to the upper stage or lower stage reflux type two-phase modulation system which is effective at that time based on the control command from the pulse signal calculation means 11, Is input (sent into) the switching element. Based on this PWM signal input, the three-phase switching circuit 13 mounted in the inverter 3 shown in FIG. 2 generates a three-phase AC voltage. The brushless DC motor 2 is rotationally controlled by applying the three-phase AC voltage.

  Here, the three-phase switching circuit 13 mounted in the inverter 3 will be described with reference to FIG. FIG. 2 is a connection diagram showing a switching circuit that performs motor control in the inverter.

  The circuit shown in FIG. 2 is a three-phase switching circuit mounted in the main circuit of the inverter 3 and has a function of converting a DC voltage from a battery or the like into a three-phase AC voltage. The switching circuit 13 is a transistor pair in which transistors composed of switching elements such as bipolar transistors and IGBTs (Insulated Gate Bipolar Transistors) are combined in series as a pair of a1 and a2, a pair of b1 and b2, and a pair of c1 and c2, respectively. Three sets of p1, p2, and p3 are connected in parallel to form a three-phase circuit.

  Each node between the two transistors connected to each of the transistor pairs p1, p2, and p3 is connected to the U-phase, V-phase, and W-phase terminals of the brushless DC motor 2, respectively. Electricity is supplied to the DC motor 2 or from the brushless DC motor 2 to each transistor pair. The transistors a1, a2, b1, b2, c1, c2 are connected to diodes da1, da2, db1, db2, dc1, dc2 having a function of protecting each transistor in parallel with these transistors. The diode works to protect each transistor by avoiding a current generated by the back electromotive force of the brushless DC motor 2 or the like.

  In the present embodiment and the second embodiment described below, the three transistors a1, b1, and c1 included in the switching element group A (first switching element group) belong to the upper stage of the three-phase circuit. The switching element is described as “upper stage switching element”. Further, the three transistors a2, b2, and c2 included in the switching element group B (second switching element group) are described as “lower switching elements” as switching elements belonging to the lower stage of the three-phase circuit. In addition, when simply described as a switching element, the transistor a1, a2, b1, b2, c1, and c2 may be collectively referred to, or a general switching element may be referred to as a single switching element. And

  In the first embodiment, the PWM signal generating means 12 generates a PWM signal based on the upper-stage reflux type two-phase modulation method and the lower-stage return type two-phase modulation method, and the PWM signal is included in the switching circuit 13. Each switching is controlled by being input (sent into) the transistors a1, a2, b1, b2, c1, and c2.

  Next, an upper-stage reflux type two-phase modulation method and a lower-stage reflux type two-phase modulation method, which are modulation methods for generating a PWM signal, will be described with reference to FIGS.

FIG. 3 is a timing chart showing an example of the switch states of the upper and lower stages of each phase in the upper-stage reflux type two-phase modulation method. FIG. 3 shows a first phase (a phase), a second phase (b phase), and a third phase (c phase) of a PWM signal having a PWM carrier period (pulse generation period) T _c as the switching period as one pulse. The state of each switching element of the upper stage and lower stage switching element groups) is shown. These switching elements are turned on when the level is high and turned off when the level is low. Note that the a-phase, b-phase, and c-phase are assigned to the U-phase, V-phase, and W-phase of the brushless DC motor 2 according to the voltage command value given at that time.

  First, in the upper-stage reflux type two-phase modulation system, one of the upper-stage switching elements in which the voltage command value is commanded to be the largest positive among the three phases U-phase or W-phase that the brushless DC motor 2 has. One state is set to 100% ON state (energized state), and in FIG. The voltage command values commanded to the a, b, and c phases are Va, Vb, and Vc, respectively. When these are in the relationship of Va> Vb> Vc, the timing chart as shown in FIG. Represented.

In FIG. 3, the time when only one phase is turned on among the upper switching elements of the a, b, and c phases is t ₁ , the time when the two phases are on is t ₂ , and the time when all the three phases are on is t ₃ . The voltages a, b, and c output during the respective times t _{1 to} t ₃ are expressed as V _a1 , V _b1 , V _c1 (t ₁ hour), V _a2 , V _b2 , V _c2 (t ₂ hours), V _a3 , V _b3 , V _c3 (t ₃ hours), and when the inverter input voltage is V _DC , each voltage is a value obtained by the following equations (1) to (9).

As a result, the average values V _a , V _b , and V _c of the voltages of the respective phases that are output during the pulse generation period T _c are values obtained by the following equations (10) to (12).

Further, the upper on-time t _a , t _b , and t _c of each phase when the voltage command value of each phase is given can be obtained from the following equations (13) to (15):

  The following equations (16) to (18) are obtained.

  As a result, the on / off states of the switching elements in the upper and lower switching element groups of the a, b, and c phases are derived as pulse waveforms.

  Here, the relationship between the voltage command values of the a, b, and c phases in the upper-stage reflux type two-phase modulation method and the on-state time of each pulse waveform of the a, b, and c phases shown in FIG. 3 will be described. .

FIG. 4 is a graph showing an example of voltage command values for the a, b, and c phases and the duty in the upper-stage reflux type two-phase modulation. In the upper graph of FIG. 4, the vertical axis is a voltage command value, and the horizontal axis is time. In the lower graph of FIG. 4, the vertical axis represents the duty and the horizontal axis represents time. Note that the duty is a value obtained by dividing the on-state time of each of the a, b, and c phases in the timing chart shown in FIG. 3 by the pulse generation interval _Tc . The width of the horizontal axis of the graph is shown as the length of one cycle of each voltage command value in the upper graph of FIG.

  In a motor such as the brushless DC motor 2, when a target value such as a rotational speed or torque is given, a speed command value, a voltage command value, or the like is obtained in accordance with the target value, and the rotational speed or torque is controlled. In the case of the brushless DC motor 2 in the present embodiment, a torque command value is first given, and a current command value is obtained by being calculated together with other battery voltages and the rotor rotational speed. On the other hand, the actual current value energized at that time is obtained from the motor current obtained from the current sensor or the like and the rotor position information. Then, a current command value that is an operation amount corresponding to the temporal change and the actual current value are compared, and feedback control by PI (Proportion Integral) control or the like so that the actual current value matches the current command value. Is used to calculate the voltage command value.

  The upper graph in FIG. 4 is an example of the voltage command value calculated as described above. The sine wave LN1a is a voltage command value for the a phase, the sine wave LN2a is a voltage command value for the b phase, and the sine wave LN3a is a voltage command value for the c phase, and the phase advances 120 degrees in this order. Further, the range RA shows a range where the a-phase voltage command value takes the largest positive value, and the time point when the pulse waveform of the timing chart shown in FIG. 3 is generated is also included in this range. .

  On the other hand, the lower graph shows the duty of the pulse waveform generated based on the voltage command shown in the upper graph. For example, in the range RA of the lower graph, as is apparent from the timing chart of FIG. 3, the on-time of the upper phase of the a phase with a duty of 100% is indicated by a line LN1b. Then, in accordance with the voltage command shown in the upper graph, after the range RA, the upper on time of the b-phase and the c-phase is indicated as the line LN2b and the line LN3b, respectively.

In the upper reflux type two-phase modulation scheme, each output voltage of the t ₃ hours shown in FIG. 3 0, reflux due to counter electromotive force of the motor is generated.

FIG. 5 is a circuit diagram showing an example of reflux in the upper-stage reflux type two-phase modulation method. A is in the upper reflux type 2-phase modulation method, b, the t ₃ hours upper c all phases are turned on (ON) state, it flows return current bline passing through the upper stage switching element of each phase shown in FIG.

  Next, the lower-stage reflux type two-phase modulation method will be described.

  FIG. 6 is a timing chart showing an example of the switch states of the upper and lower stages of each phase in the lower-stage reflux type two-phase modulation method. FIG. 6 shows the state of each switching element similar to FIG. Note that the a-phase, b-phase, and c-phase are assigned to the U-phase, V-phase, and W-phase of the brushless DC motor 2 according to the voltage command value given at that time.

  First, in the lower-stage reflux type two-phase modulation method, one of the upper switching elements of the phase in which the voltage command value is commanded to be the smallest negative among the three phases U-phase or W-phase that the brushless DC motor 2 has. One state is defined as a 100% off state (rest state), and in FIG. The voltage command values commanded to the a, b, and c phases are Va, Vb, and Vc, respectively. When these are in the relationship of Va> Vb> Vc, the timing chart as shown in FIG. Represented.

In FIG. 6, the time when only one phase is turned on among the upper switching elements of the respective phases a, b and c is t ₁ , the time when the two phases are turned on is t ₂ , and the time when both the three phases are not turned on is t ₀ . To do. The voltages for the a, b, and c phases output during each time from t _{0 to} t ₂ are V _a1 , V _b1 , V _c1 (t ₁ hour), V _a2 , V _b2 , V _c2 (t ₂ hours), V _a0 , V _b0 , V _c0 (t ₀ hours), and the inverter input voltage is V _DC , the voltages described above are values obtained by the following equations (19) to (27), respectively. Become.

As a result, the average values V _a , V _b , and V _c of the voltages of the respective phases that are output during the pulse generation period T _c are values obtained by the following expressions (28) to (30).

Further, the upper on-time t _a , t _b , and t _c of each phase when the voltage command value of each phase is given can be obtained from the following equations (31) to (33):

  The following equations (34) to (36) are obtained.

  As a result, the on / off states of the switching elements in the upper and lower switching element groups of the a, b, and c phases are derived as pulse waveforms.

  Here, the relationship between the voltage command values of the a, b, and c phases in the lower-stage reflux type two-phase modulation method and the on-state time of each pulse waveform of the a, b, and c phases will be described.

  FIG. 7 is a graph showing an example of the voltage command values for the a, b, and c phases and the duty in the lower-stage reflux type two-phase modulation. Since the setting of the coordinate axes of the graph is the same as in FIG. 4, the description of FIG. 4 is used.

An example of the voltage command value is shown in the upper graph of FIG. The sine wave LN4a is a voltage command value for the a phase, the sine wave LN5a is a voltage command value for the b phase, and the sine wave LN6a is a voltage command value for the c phase, and the phase advances by 120 degrees in this order. Further, the range RB ₁ shows a range in which the c-phase voltage command value takes the largest negative value, and the time point when the pulse waveform of the timing chart shown in FIG. 6 is generated is also included in this range. It is.

On the other hand, the lower graph shows the duty of the pulse waveform generated based on the voltage command shown in the upper graph. For example, the range RB ₁ in the lower graph, as is apparent from the timing chart of FIG. 6, the off time of the c-phase upper duty of 0% is indicated by line LN6b. Then, in accordance with the voltage command shown in the upper graph, the range RB ₂ before the range RB ₁ shows the b-phase upper off time, and the range RB ₃ after the range RB ₁ shows the a phase upper off time. It is shown.

In the lower-stage reflux type two-phase modulation method, each output voltage at time t ₀ shown in FIG. 6 becomes 0, and reflux due to the counter electromotive force of the motor occurs. FIG. 8 is a circuit diagram showing an example of reflux in the lower-stage reflux type two-phase modulation method. In the lower-stage reflux type two-phase modulation method, the reflux current bline flows through the lower-stage switching element of each phase shown in FIG. 8 at time t ₀ when the upper stages of all phases a, b, and c are turned off.

  Next, two switching between the above-described upper reflux type two-phase modulation method and lower stage reflux type two-phase modulation method will be described.

  FIG. 9 is a graph showing an example of the duty using each voltage command value for the a, b, and c phases and the upper and lower reflux type two-phase modulation based on the voltage command values alternately. The setting of the coordinate axes of the graph is the same as in FIG. 4, and the description of FIG.

  An example of the voltage command value is shown in the upper graph of FIG. The sine wave LN7a is a voltage command value for the a phase, the sine wave LN8a is a voltage command value for the b phase, and the sine wave LN9a is a voltage command value for the c phase. The lower graph shows the duty of the pulse waveform generated by alternately switching the upper and lower reflux type two-phase modulation based on the voltage command shown in the upper graph.

The range RC ₁ in the upper graph is a range in which the b-phase voltage command value takes the largest negative value. Therefore, the range is modulated by lower-stage reflux type two-phase modulation (described as lower-stage reflux in the lower part of the figure). ), And the b-phase duty is 0% as shown in the lower graph. Next, since the range RC ₂ is a range in which the voltage command value of the a phase takes the largest positive value, the range is modulated by upper-stage reflux type two-phase modulation (described as upper-stage reflux in the lower part of the figure). As shown in the lower graph, the a-phase duty is turned on at 100%. Subsequently, the upper stage or the lower stage reflux type two-phase modulation method is alternately switched from the range RC _{3 to} the range RC ₆ . As described above, the voltage command value of each phase while the brushless DC motor 2 is rotating at a constant speed becomes a sine wave as shown in the upper graph of FIG. 9, and based on these voltage command values, the upper stage When the lower-stage reflux type two-phase modulation is applied, the upper-stage and lower-stage reflux type two-phase modulation methods are alternately switched every 1/6 period (that is, 60 degrees in the rotation angle of the motor).

  The upper-stage reflux type two-phase modulation system and the lower-stage reflux type two-phase modulation system can be arbitrarily selected and applied in any case without performing the switching as described above. However, in order to reduce the switching loss generated in the switching element, it is better to alternately switch the upper-stage reflux type two-phase modulation method and the lower-stage reflux type two-phase modulation method as described above.

  The switching loss generated in the switching element is proportional to the product of the voltage applied to each element and the current flowing through each element. Therefore, in order to reduce the switching loss, the switching element of the phase through which the largest current among the currents flowing through each phase of the brushless DC motor 2 is not switched on / off (that is, the switching element) It is desirable to stop the switching of

  Therefore, it is assumed that the phase of the voltage command value and the phase of the current flowing through the brushless DC motor 2 are substantially equal, and switching of the switching element of the phase having the largest absolute value of the voltage command value is stopped. At this time, if the sine wave of the voltage command value of the phase to be stopped is in the positive range, the absolute value of the voltage command value of this phase is the largest and positive value. The switching of the switching element is stopped. On the other hand, when the sine wave of the voltage command value of the phase to be stopped is in the negative range, the absolute value of the voltage command value of this phase is the smallest and negative value, so switching is performed using lower-stage reflux type two-phase modulation. Stop switching the element. As a result, when reducing the switching loss, it is better to alternately switch the upper-stage reflux type two-phase modulation and the lower-stage reflux type two-phase modulation.

  Next, the temperature rise of the switching element due to the reflux current generated during the upper-stage and lower-stage reflux type two-phase modulation will be described with reference to FIGS.

  As shown in FIG. 9, in the upper-stage reflux type two-phase modulation method, when the output voltage is 0, current flows back through the upper-stage switching element. Therefore, the energization rate in the upper switching element is higher than that in the lower switching element, and the heat generation in the upper switching element is increased. On the other hand, in the lower-stage reflux type two-phase modulation, the energization rate in the lower-stage switching element is higher than that in the upper-stage switching element, so that the lower-stage switching element generates more heat.

  The above can be expressed as a graph when the motor is rotating at a predetermined rotation speed or higher and at a constant rotation as shown in FIG. FIG. 10 is a graph showing the relationship between the switching of the modulation method and the temperature rise of the upper and lower switching elements.

The upper graph of FIG. 10 shows the sine wave of each voltage command value given to the U, V, and W phases of the motor. For each range of 60 degrees that is the rotation angle of the motor from the graph start position on the left end, As shown in the upper part of the graph, the lower-stage reflux type two-phase modulation and the upper-stage reflux type two-phase modulation are alternately switched. The lower graph shows a polygonal line ln ₁ indicating the temperature change of the upper switching element and a polygonal line ln ₂ indicating the temperature change of the lower switching element in accordance with the timing of the upper graph.

As shown in FIG. 10, when the lower-stage reflux type two-phase modulation is applied, the temperature of the lower switching element indicated by the broken line ln ₂ rises, and the temperature of the upper switching element indicated by the broken line ln ₁ during that time. Decrease. On the contrary, when the upper-stage reflux type two-phase modulation is applied, the temperature of the upper switching element indicated by the broken line ln ₁ rises, and the temperature of the lower switching element indicated by the broken line ln ₂ decreases. Thus, by alternately switching between the upper-stage reflux type two-phase modulation and the lower-stage reflux type two-phase modulation, the temperature of either the upper stage switching element or the lower stage switching element does not exceed the temperature limit value Lim.

  Next, when the motor is rotated at a low speed, a graph as shown in FIG. 11 is obtained. FIG. 11 is a graph showing the relationship between the switching of the modulation method in the low speed region of the motor and the temperature rise of the upper and lower switching elements.

In FIG. 11, as in FIG. 10, when the upper-stage reflux type two-phase modulation is applied, the temperature of the upper switching element indicated by the broken line ln ₃ rises, and the lower switching element indicated by the broken line ln ₄ in the meantime. Decreases in temperature. Conversely, when the lower-stage reflux type two-phase modulation is applied, the temperature of the lower switching element indicated by the broken line ln ₄ rises, and the temperature of the upper switching element indicated by the broken line ln ₃ decreases during this time. Has been.

  However, the graph of FIG. 11 is an aspect at the time of low-speed rotation of the motor, and the length of one cycle of the voltage command value is longer than that of the graph of FIG. Since the frequency of the voltage command value is proportional to the rotation speed of the motor, the cycle of the voltage command value becomes longer when the motor rotates at a low speed. When the motor rotates at a low speed, the time during which the same modulation method is continued increases, leading to a temperature rise for the increased time, and exceeding the temperature limit value Lim shown in the lower graph. Occurs. An object of the present invention is to suppress the heat generated in the upper and lower switching elements during such low-speed rotation of the motor.

  Next, the operation of the motor control device 1 which is a feature of the present invention will be described with reference to FIGS.

  FIG. 12 is a flowchart showing a flow of operation when generating a PWM signal in the motor control device. First, the motor control device 1 acquires the temperature of the switching element by a temperature sensor (not shown) such as a thermistor provided in the inverter 3 (step S101). Next, it is determined whether or not the temperature of the switching element is equal to or higher than a predetermined temperature (for example, 80 degrees) (step S102: ≧ predetermined temperature). If the temperature is equal to or higher than the predetermined temperature, switching of the switching element is stopped (step S103).

  When the temperature of the switching element is lower than the predetermined temperature (step S102: <predetermined temperature), the current command value is acquired (step S104), and further the motor current, rotor position, and motor rotation speed are acquired (step S104). S105). Further, a three-phase current value is converted into a two-phase (dq axis) current value based on a motor current and rotor position information obtained from a current sensor (not shown) (step S106). Then, the current command value for each axis d and q is compared with the actual current value, and the voltage command value for each axis d and q is calculated so that the actual current matches the current command value (steps S107 and S108). The two-phase voltage command values for the d and q axes are converted into three-phase voltage command values based on the rotor position information (step S109).

  Next, the rotational speed of the motor is detected by the rotational speed detection means 5, and it is determined whether or not the rotational speed is equal to or greater than a certain value (100 rpm in the present embodiment) (step S110). When the rotational speed of the motor is equal to or greater than a certain value (step S110: ≧ constant value), the voltage command value switching mode is commanded by the modulation mode setting means 9 (step S111). The operation flow in the voltage command value switching mode will be described in detail with reference to FIG.

  On the other hand, when the rotational speed of the motor is less than a certain value (step S110: <constant value), the modulation mode setting means 9 commands a certain time switching mode (step S112). The operation flow in the fixed time switching mode will be described in detail with reference to FIG. When step S111 or step S112 is completed, the PWM signal generator 12 calculates the U, V, and W phase upper and lower pulse signals (step S113), and the process ends.

  FIG. 13 is a flowchart showing the flow of operation in the voltage command value switching mode.

  In step S110 of FIG. 12, when it is determined that the rotational speed of the motor is equal to or greater than a certain value (step S110: ≧ constant value) and the process proceeds to the voltage command value switching mode, U, V, W 3 Among the phase voltage command values, the phase with the maximum absolute value is acquired (step S121). Then, it is determined whether or not the acquired voltage command value is zero or more (step S122). If the acquired voltage command value is greater than or equal to zero (step S122: ≧ 0), the modulation method setting means 10 transmits a command for switching the modulation method to upper-stage reflux type two-phase modulation to the pulse signal calculation means 11 (step S122). S123), the process returns to step S111 in the flowchart of FIG. On the other hand, when the acquired voltage command value is less than zero (step S122: <0), a command for switching the modulation method to the lower-stage reflux type two-phase modulation is transmitted to the pulse signal calculation unit 11 by the modulation method setting means 10. (Step S124), the process returns to step S111 in the flowchart of FIG.

  Next, the fixed time switching mode in the motor control device 1 which is a feature of the present invention will be described. FIG. 14 is a flowchart showing a flow of operations in the constant time switching mode.

  In step S110 of FIG. 12, when it is determined that the rotational speed of the motor is less than a certain value (step S110: <constant value) and the process moves to the certain time switching mode, the previous certain time switching mode is used. After the modulation method is switched, it is determined whether or not a certain time interval detected by the timer detection means 7 has passed (step S131). If the predetermined time has not elapsed (step S131: No), the previous modulation method command is transmitted as it is to the pulse signal calculation means 11 (step S132), and the process returns to the process of step S111 in the flowchart of FIG. On the other hand, when a certain time has elapsed (step 131: Yes), the other modulation method that is not the previous modulation method (for example, if the previous time was the upper-stage reflux type two-phase modulation method, the other modulation method). The command switched to the lower-stage reflux type two-phase modulation method is transmitted to the pulse signal calculation means 11 (step S133), and the process returns to the process of step S111 in the flowchart of FIG.

  When the brushless DC motor 2 is controlled in the constant time switching mode shown in the flowchart of FIG. 14 described above, a graph of results as shown in FIG. 16 can be obtained. FIG. 16 is a graph showing the relationship between the switching of the modulation method in the low speed region of the motor in the constant time switching mode and the temperature rise of the upper and lower switching elements.

That is, the upper graph in FIG. 16 shows the sine wave of each voltage command value given to the U, V, and W phases of the motor, and lower-stage reflux type two-phase modulation at regular time intervals from the leftmost graph start position. And upper-stage reflux type two-phase modulation are alternately switched. The lower graph shows a polygonal line ln ₅ indicating the temperature change of the upper switching element and a polygonal line ln ₆ indicating the temperature change of the lower switching element in accordance with the timing of the upper graph.

In the lower graph of FIG. 16, the temperature of the lower switching element indicated by the broken line ln ₆ rises while the lower-stage reflux type two-phase modulation is performed from the start position of the graph (range RD1), and conversely, the broken line ln ₅ The temperature of the upper switching element shown is decreasing. However, since the brushless DC motor 2 in FIG. 16 rotates in the low speed region, when the predetermined time indicated by the range RD1 has elapsed, the brushless DC motor 2 is switched to the upper-stage reflux type two-phase modulation. As a result, since the modulation method is switched before the temperature of the lower switching element exceeds the temperature limit value Lim (time tim), the temperature of the upper switching element indicated by the broken line ln ₅ is increased, and conversely, the broken line ln ₆ The temperature of the lower switching element shown decreases (range RD2).

Subsequently, since the two modulation schemes are switched every time a predetermined time passes, the temperature of the upper switching element indicated by the broken line ln ₅ and the temperature of the lower switching element indicated by the broken line ln ₆ are mutually exothermic. However, the temperature limit value Lim is not exceeded. Accordingly, it is possible to prevent the switching element from generating heat due to the reflux in the upper-stage and lower-stage reflux type two-phase modulation shown in FIG.

  On the other hand, FIG. 15 is a graph showing the duration of the same modulation method with respect to the rotational speed of the motor, and shows that the time during which the same modulation method is continued is inversely proportional to the inverse of the rotational speed of the motor. Has been. Further, according to FIG. 15, when the motor rotation speed becomes a certain value or less (when it becomes less than the motor rotation speed indicated by the boundary value Limk shown in FIG. 15), the duration of the same modulation method is the limit value. It is also shown that the limit is exceeded. Here, if the motor control device 1 has a temperature protection control function that stops the switching operation when the temperature rise of the switching element is significant, if the limit value Limt is exceeded, The switching operation is stopped by the temperature protection control function.

  In the motor control device 1 having such a temperature protection control function, when the rotation speed of the brushless DC motor 2 becomes less than a predetermined value, the voltage command value switching mode is not used and the above-described operation is performed with reference to FIG. The fixed time switching mode, which is a feature of the present invention, is used. As a result, the above-described temperature protection control is prevented from functioning by switching the modulation method set at that time at regular intervals and balancing the temperature rise of the upper and lower switching elements within a certain range. be able to.

  According to the first embodiment described above, every time the modulation method setting means 10 determines that the predetermined time has elapsed by the timer detection means 7, the control based on the upper reflux type two-phase modulation method and the lower stage reflux type two-phase modulation method are performed. Therefore, when the brushless DC motor 2 is controlled, the two-phase modulation method is always used, thereby reducing the number of elements to be switched as compared with the case of using the three-phase modulation method. The heat loss generated in each element is suppressed by reducing the power loss generated in the lower switching element group. Further, by alternately switching the two modulation methods at regular time intervals to generate a PWM signal, the power loss generated in each of the upper and lower switching element groups is kept within a certain value, that is, the temperature generated at regular time intervals. By leveling the increase within a predetermined range, it is possible to suppress a decrease in continuous operation time and a maximum torque due to heat that can be generated in each switching element and the inverter 3.

  Further, while the modulation method setting means 10 determines that the rotation speed of the motor 2 is less than the predetermined value by the rotation speed detection means 5, the upper stage or Since the lower-stage reflux type two-phase modulation method is switched, it is possible to suppress an increase in energization time in each of the upper-stage and lower-stage switching element groups when the motor 2 rotates at a low speed. That is, an increase in power loss due to an increase in energization time is suppressed, and a temperature rise that occurs each time the two modulation methods are switched is balanced within a predetermined range. In addition, it is possible to suppress a decrease in continuous operation time and a maximum torque due to heat that can be generated in the inverter 3.

  Further, while the modulation method setting means 10 determines that the rotation speed of the motor is less than the predetermined value by the rotation speed detection means 5, the upper-stage reflux type two-phase modulation method and the lower-stage reflux are performed every time a predetermined time elapses. The absolute value of the voltage command values corresponding to the first to third phases is determined while the rotational speed detecting means 5 determines that the rotational speed of the motor is equal to or higher than a predetermined value. Is switched to control by the upper-stage reflux type two-phase modulation method when the voltage command value is in the positive range, and control is performed by the lower-stage reflux type two-phase modulation method when the absolute value is the largest and the voltage command value is in the negative range. Since switching is performed, when the motor rotates at a low speed, the temperature rise in the upper and lower switching elements can be balanced within a predetermined range by switching the modulation method at regular intervals. On the other hand, in other speed ranges, the temperature rise of the upper and lower switching element groups can be suppressed within a predetermined range by effectively switching the modulation method for each rotation angle of the motor. This makes it possible to suppress a decrease in continuous operation time and a decrease in maximum torque due to heat that can be generated in the switching element and the inverter during motor control.

  In the first embodiment described above, the description has been made using only one set value of the rotation speed detected by the rotation speed detection means 5, but a plurality of values can be set freely, and the rotation speed detection means. When 5 detects each set value, mode switching or upper-stage or lower-stage reflux type two-phase modulation system switching may be performed step by step for each of the plurality of speeds.

  In the first embodiment, the modulation mode setting unit 9 determines that the rotation speed of the motor 2 detected by the rotation speed detection unit 5 is equal to or higher than a predetermined value as a high speed range, Although it has been described that the low speed range is determined when the rotational speed of the motor 2 is less than a predetermined value, this motor control is performed with the predetermined value as a threshold value (that is, a boundary value). The determination method is not limited to the above-described determination method, and the following can also be performed. In other words, the above determination condition that “the rotation speed of the motor 2 is equal to or greater than a predetermined value” is replaced with the determination condition that “the rotation speed of the motor 2 exceeds a predetermined value” and the determination condition is satisfied. The determination condition that “the rotation speed of the motor 2 is less than a predetermined value” is replaced with the above determination condition that the rotation speed of the motor 2 is equal to or less than a predetermined value. Of course, a determination method for determining that the low-speed range is satisfied when the condition is satisfied may be used. In this case, it goes without saying that the same effects as the former determination method can be obtained.

<Second Embodiment>
Next, a motor control device according to a second embodiment of the present invention will be described with reference to FIG. FIG. 17 is a block diagram illustrating a configuration of a motor control device according to the second embodiment. The motor control device 20 according to the second embodiment has substantially the same configuration as the motor control device 1 shown in the first embodiment, and the same reference numerals as those in FIGS. 1 to 16 are the same. Or an equivalent part is shown and the description is abbreviate | omitted.

  As shown in FIG. 17, the motor control device 20 includes a rotation speed detection unit 5, a modulation mode setting unit 9, a modulation mode setting unit 10, a pulse signal calculation unit 11, a PWM signal generation unit 12, and a temperature. The determination means 22 is comprised. This temperature determination means 22 receives the temperature data of the upper and lower switching elements mounted on the inverter 3 sent from the temperature detection element 21 such as a thermistor sensor, and whether or not each is equal to or higher than a predetermined temperature (for example, 80 ° C.). Judgment is made.

  The modulation mode setting means 9 in the present embodiment gives a command (mode command) for switching to one of the following two modulation mode modes based on a predetermined mode setting or a detection result by the rotation speed detection means 5. Issued to the modulation scheme setting means 10. The two modulation method modes include a voltage command value switching mode described in the first embodiment, and a temperature switching mode in which two modulation methods are switched for each temperature of the upper or lower switching element. There is.

  When the mode command from the modulation system mode setting means 9 is the temperature switching mode, the modulation system setting means 10 performs switching to switch to the lower reflux type two-phase modulation system when the temperature of the upper switching element is equal to or higher than a predetermined temperature. A command is transmitted to the pulse signal calculation means 11, and when the temperature of the lower switching element is equal to or higher than a predetermined temperature, a switching command for switching to the upper reflux type two-phase modulation method is transmitted to the pulse signal calculation means 11. When the mode command from the modulation mode setting means 9 is the voltage command value switching mode, the same processing as in the case of the first embodiment is performed. Further, the processing of the pulse signal calculation means 11 and the PWM signal generation means 12 subsequent to the modulation method setting means 10 is the same as that of the first embodiment, and the description thereof is omitted.

  By the way, in the motor control device that is the basis of the present invention shown in the first embodiment, the following problems have been raised. In this motor control device, when the rotation of the motor is controlled, the voltage command value switching mode is always set regardless of the number of rotations, and the modulation method is switched to the upper or lower reflux type two-phase modulation method. If the motor enters the low speed range where the rotational speed of the motor is less than the predetermined value with the voltage command value switching mode set, the sine wave cycle of the voltage command value becomes longer as shown in FIG. Increases in the temperature of the inverter 3 (specifically, the upper switching element or the lower switching element).

  In response to the above-described problem shown in FIG. 11, the following control operation is performed in the motor control device 20 in the present embodiment.

  First, during the rotation of the motor 2, while the rotation speed of the motor 2 detected by the rotation speed detection means 5 is determined to be a high-speed rotation range that is equal to or greater than a predetermined value, the voltage mode switching mode is set by the modulation mode setting means 9. Is set. In this high-speed rotation range, each of the upper and lower switching elements detected by the temperature detection element 21 is switched while the upper stage or lower stage reflux type two-phase modulation modulation system is switched for each rotation angle (60 degrees) of the motor. The temperature does not exceed the temperature limit value Lim (see the lower graph in FIG. 10).

  On the other hand, when the rotational speed of the motor 2 is in a low speed rotation range less than a predetermined value and the voltage command value switching mode continues in this low speed rotation range, each of the upper and lower switching elements detected by the temperature detection element 21 is detected. The temperature rises alternately, and each of the temperatures exceeds the temperature limit value Lim as shown in the lower graph of FIG.

  In order to prevent the temperature of each switching element from exceeding the state, in this embodiment, when the modulation method mode setting means 9 is in a low speed range where the rotational speed of the motor 2 is less than a predetermined value. Switches the setting from the voltage command value switching mode to the temperature switching mode.

  In the temperature switching mode, the temperature data from the temperature detection element 21 is determined by the temperature determination means 22, and when the temperature of the upper switching element becomes equal to or higher than the temperature limit value Lim, the lower-stage reflux type two-phase modulation modulation method is used. When the temperature of the switching / lower switching element becomes equal to or higher than the temperature limit value Lim, switching to the upper reflux type two-phase modulation modulation method is performed. By performing such switching operation, the temperature of the upper and lower switching elements does not exceed the temperature limit value Lim, and the temperature of one of the upper and lower switching elements does not rise unevenly, and the temperature is within a certain range. It is kept in a balanced state.

  According to the second embodiment described above, every time the temperature determination means 22 determines that either the upper stage or the lower stage switching element has reached a predetermined temperature or higher, the modulation method setting means 10 is provided with the upper-stage reflux type two-phase. Since the control by the modulation method and the control by the lower-stage reflux type two-phase modulation method are switched, when the brushless DC motor 2 is controlled, the two-phase modulation method is always used as compared with the case where the three-phase modulation method is used. Thus, the number of elements to be switched is reduced, and the power loss generated in each of the upper and lower switching element groups is reduced, thereby suppressing the heat generated in each element. Further, by alternately switching two modulation methods for each temperature generated in the upper and lower switching element groups and generating a PWM signal, the power loss generated in each of the upper and lower switching element groups is kept within a certain value. That is, it is possible to suppress a decrease in continuous operation time and a decrease in maximum torque caused by heat that can be generated in each switching element and inverter 3 by leveling the temperature rise that occurs every certain time within a predetermined range. Become.

  Further, while the modulation method setting means 10 determines that the rotation speed of the motor 2 is less than the predetermined value by the rotation speed detection means 5, either the upper stage or the lower stage switching element is higher than the predetermined temperature by the temperature determination means 22. Since the modulation method is switched every time it is determined that the current value is determined, increase in energization time in each of the upper and lower switching elements when the motor 2 rotates at a low speed can be suppressed. That is, an increase in power loss due to an increase in energization time is suppressed, and a temperature rise that occurs each time the two modulation methods are switched is balanced within a predetermined range. In addition, it is possible to suppress a decrease in continuous operation time and a maximum torque due to heat that can be generated in the inverter 3.

  In the second embodiment described above, the modulation method mode setting means 9 determines that the speed is high when the rotation speed of the motor 2 detected by the rotation speed detection means 5 is greater than or equal to a predetermined value. Although it has been described that the low speed region is determined when the rotational speed of the motor 2 is less than a predetermined value, the rotational speed of the motor 2 is predetermined as described in the first embodiment. Of course, it is possible to switch the mode commands by determining that the high speed range is exceeded and the rotation speed of the motor 2 is equal to or lower than the predetermined value as the low speed range. In this case, it goes without saying that the same effects as the former determination method can be obtained.

  In the second embodiment, the temperature determination means 22 has been described as determining whether either the upper stage or the lower stage switching element has reached a predetermined temperature or higher. As in the case of the number, the modulation method may be switched by determining whether or not the predetermined temperature has been exceeded. In this case, the same method as the above method for determining whether or not the predetermined temperature has been exceeded is used. Of course, it is possible to achieve the effects.

  Although the present invention has been described based on the preferred embodiment, the motor control device of the present invention is not limited to the configuration of the above embodiment, and various modifications and changes can be made to the configuration of the above embodiment. The modified motor control device is also included in the scope of the present invention.

It is a block diagram which shows the structure of the motor control apparatus in 1st Embodiment. It is a connection diagram which shows the switching circuit which performs the motor control in an inverter. It is a timing chart showing an example of the switch state of the upper and lower stages of each phase in the upper-stage reflux type two-phase modulation system. It is a graph which shows an example of each voltage command value to a, b, and c phase, and a duty in upper stage return type 2 phase modulation. It is a circuit diagram which shows an example of the recirculation | reflux in an upper stage recirculation | reflux type | mold 2 phase modulation system. It is the timing chart which showed an example of the switch state of each phase upper and lower stage in a lower stage recirculation | reflux type | mold 2 phase modulation system. It is a graph which shows an example of the duty in each voltage command value to a phase, b, and c phase and lower stage return type 2 phase modulation. It is a circuit diagram which shows an example of the recirculation | reflux in a lower stage recirculation | reflux type | mold 2 phase modulation system. It is a graph which shows an example of the duty which used each voltage command value to a phase, b, and c phase, and the upper stage and lower stage return type 2 phase modulation based on it alternately. It is a graph which shows the relationship between the switching of a modulation system, and the temperature rise of an upper stage and a lower stage switching element. It is a graph which shows the relationship between the switching of the modulation system in the low speed region of a motor, and the temperature rise of an upper stage and a lower stage switching element. It is a flowchart which shows the flow of operation | movement at the time of the PWM signal generation in a motor control apparatus. It is a flowchart which shows the flow of operation | movement of voltage command value switching mode. It is a flowchart which shows the flow of operation | movement of fixed time switching mode. It is a graph which shows the duration of the same modulation system with respect to the rotation speed of a motor. It is a graph which shows the relationship between the switching of the modulation system in the low speed range of the motor by a fixed time switching mode, and the temperature rise of an upper stage and a lower stage switching element. It is a block diagram which shows the structure of the motor control apparatus in 2nd Embodiment.

Explanation of symbols

1 Motor control device 2 Brushless DC motor (motor)
3 Inverter 5 Rotational speed detection means (Rotational speed determination means)
7 Timer detection means (elapsed time judgment means)
10 Modulation method setting means (switching means)
11 Pulse signal calculation means (first pulse generation means, second pulse generation means)
12 PWM signal generating means (first pulse generating means, second pulse generating means)
20 Motor control device A Switching element group (first switching element group)
B Switching element group (second switching element group)
Lim temperature limit value

Claims (5)

An inverter having a three-phase circuit composed of first and second switching element groups each generating a waveform signal whose logic is opposite to each other is generated based on voltage command values for the first, second and third phases of the motor. In the motor control device for controlling the motor by inputting a pulse width modulation signal to the inverter,
Of the voltage command values corresponding to each of the first to third phases, a switching element of the first switching element group corresponding to a phase that is a positive value and has the largest absolute value is the pulse width modulation signal. First pulse generating means for energizing the entire switching period required for generating one pulse of
Of the voltage command values corresponding to each of the first to third phases, the switching elements of the second switching element group corresponding to the phase having a negative value and the largest absolute value are set to the entire switching period. Second pulse generating means for energizing over a period of time;
A preset predetermined time has passed to keep the power loss caused by the input of the pulse width modulation signal generated by the first pulse generation means or the second pulse generation means to the inverter within a certain value. Elapsed time determining means for determining whether or not,
Switching means for switching between the control by the first pulse generation means and the control by the second pulse generation means each time the passage of the predetermined time is determined by the elapsed time determination means;
A motor control device comprising: A rotation speed determination means for determining whether or not the rotation speed of the motor is less than a predetermined value;
The switching means is
While the rotation speed determination unit determines that the rotation speed of the motor is less than the predetermined value, the first pulse generation unit performs the control every time the elapsed time determination unit determines the elapse of the predetermined time. Switching between the control by the second pulse generating means,
The motor control device according to claim 1. The switching means is
While the rotation speed determination means determines that the rotation speed of the motor is greater than or equal to the predetermined value, the absolute value of the voltage command value corresponding to the first to third phases is the largest and the voltage When the command value is in a positive value range, the control is switched to the control by the first pulse generating means, and the absolute value is the largest among the voltage command values corresponding to the first to third phases, and the voltage command value is negative. In the range of values, the control is switched to the control by the second pulse generating means.
The motor control device according to claim 2. An inverter having a three-phase circuit composed of first and second switching element groups each generating a waveform signal whose logic is opposite to each other is generated based on voltage command values for the first, second and third phases of the motor. In the motor control device for controlling the motor by inputting a pulse width modulation signal to the inverter,
Of the voltage command values corresponding to each of the first to third phases, a switching element of the first switching element group corresponding to a phase that is a positive value and has the largest absolute value is the pulse width modulation signal. First pulse generating means for energizing the entire switching period required for generating one pulse of
Of the voltage command values corresponding to each of the first to third phases, the switching elements of the second switching element group corresponding to the phase having a negative value and the largest absolute value are set to the entire switching period. Second pulse generating means for energizing over a period of time;
Based on a predetermined temperature set in advance for keeping the power loss caused by the input to the inverter of the pulse width modulation signal generated by the first or second pulse generation means within a predetermined value, the first And temperature determination means for determining whether or not the temperature generated in each of the second switching element groups is equal to or higher than the predetermined temperature;
When the temperature determining means determines that the first switching element group is equal to or higher than the predetermined temperature, the control is switched to the control by the second pulse generating means, and the second switching element group is determined to be equal to or higher than the predetermined temperature. Switching means for switching to the control by the first pulse generating means,
A motor control device comprising: A rotation speed determination means for determining whether or not the rotation speed of the motor is less than a predetermined value;
The switching means is
While the rotation speed determination means determines that the rotation speed of the motor is less than the predetermined value, the control by the first pulse generation means and the second time each time the temperature determination means determines the predetermined temperature. Switching between control by pulse generation means,
The motor control device according to claim 4.

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