JP6613379B2 - Motor drive device - Google Patents

Description

  Embodiments of the present invention relate to a motor drive device that includes an inverter that converts a DC voltage into an AC voltage by switching, and that outputs the output of the inverter as drive power to a three-phase motor.

  A motor drive device that includes an inverter that converts a DC voltage into an AC voltage of a predetermined frequency by switching, and that outputs the output of the inverter as drive power to the motor, detects the current flowing in the motor winding, and from the detected current The speed of the motor (angular speed of the rotor) is estimated, and switching of the inverter is controlled so that this estimated speed becomes the target speed. Specifically, a command signal whose voltage level changes according to the target speed and the difference between the estimated speed and the target speed is generated, and the voltage level of the command signal and the voltage level of the carrier signal (triangular wave signal) are determined. Compare and generate pulse width modulation signal (Pulse Width Modulation) signal so-called PWM signal whose pulse width (ON period and on / off duty of on-pulse) is determined according to the comparison result, and inverter switching according to the PWM signal The element is turned on / off.

JP 2007-159335 A

  The pulse width of the PWM signal generated according to the target speed and the difference between the estimated speed and the target speed becomes shorter as the target speed is lower. On the other hand, the pulse width of the switching element has a minimum level (also referred to as a minimum pulse width) that cannot be further reduced due to the characteristics of the switching element. When the pulse width of the PWM signal falls below the minimum level, such as when the motor is started or rotated at a low speed, the switching element cannot be turned on and off accurately, and the motor cannot be driven stably.

  The object of the embodiment of the present invention is to maintain the pulse width of the pulse width modulation signal to be equal to or more than the minimum of the ON period of the switching element, so that the switching element can be accurately turned on and off without malfunction. It is an object to provide a motor drive device excellent in performance.

  The motor drive device according to claim 1 includes an inverter and a controller. The inverter has a plurality of switching elements, and supplies a driving voltage to the three-phase motor by turning these switching elements on and off. The controller drives the switching element on and off by a pulse width modulation signal having a variable pulse width. In particular, the controller calculates the pulse width modulation signal in a two-phase modulation format, and if the calculated shortest pulse width of the pulse width modulation signal is less than a set value, the controller calculates the calculated pulse width modulation signal as the shortest pulse. The pulse width modulation signal is corrected to a three-phase modulation type pulse width modulation signal whose width is equal to or larger than the set value and has the same interphase voltage as the calculated pulse width modulation signal, and the switching element is driven on and off by the corrected pulse width modulation signal. To do.

FIG. 1 is a block diagram showing a configuration of an embodiment. FIG. 2 is a flowchart illustrating control according to an embodiment. FIG. 3 is a waveform diagram showing an example in which the pulse width of the PWM signal in the two-phase modulation format calculated to be output in the next carrier period T of the embodiment is equal to or larger than a set value. FIG. 4 is a waveform diagram illustrating an example in which the pulse width of a PWM signal in a two-phase modulation format calculated to be output in the next carrier period T of an embodiment is less than a set value. FIG. 5 is a waveform diagram showing a three-phase modulation type PWM signal obtained by correcting the PWM signal shown in FIG. FIG. 6 is a waveform diagram showing a two-phase modulation type PWM signal obtained by correcting the PWM signal shown in FIG.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a converter 2 is connected to a commercial AC power source 1, and an inverter 10 is connected to the output terminal of the converter 2. The converter 2 includes a diode bridge 3 that converts an AC voltage of the commercial AC power supply 1 into a DC voltage, and a smoothing capacitor 4 that smoothes the output voltage of the diode bridge 3. The inverter 10 is a three-phase inverter, which is a series circuit of a pair of switching elements T1 and T2 for U phase, a series circuit of a pair of switching elements T3 and T4 for V phase, and a pair of switching elements T5 and T6 for W phase. The output voltage of the converter 2 is converted into an AC voltage having a predetermined frequency and a predetermined level by turning on and off the switching elements T1 to T6, and the converted voltage is supplied to a three-phase brushless DC motor (hereinafter referred to as a DC motor) 20. Output as drive voltage. The switching elements T1 to T6 are, for example, MOSFETs or IGBTs.

  The DC motor 20 includes a stator (armature) 21 having three-phase windings Lu, Lv, and Lw, and a rotor (rotor) 22 in which a plurality of permanent magnets are embedded. The DC motor 20 is used as a motor for driving a compressor, for example.

  A shunt resistor 11 serving as a current detection unit is inserted and connected to the negative line between the converter 2 and the inverter 10. When current flows from the inverter 10 to the phase windings Lu, Lv, and Lw of the DC motor 20 by switching of the inverter 10, a voltage is generated in the shunt resistor 11. A voltage generated in the shunt resistor 11 is supplied to the controller 30.

  The controller 30 performs two-phase modulation or three-phase modulation on a pulse width modulation signal (referred to as a PWM signal) whose pulse width (on-pulse ON period and on / off duty) changes so that the speed of the DC motor 20 becomes the target speed ωref. And performs so-called sensorless vector control for turning on and off the switching elements T1 to T6 of the inverter 10 in accordance with the generated PWM signal. The current detection unit 31, the speed estimation unit 32, the speed control unit 33, A PWM signal generator 34 is included.

  The current detecting unit 31 performs A / D (analog / digital) conversion and reads the voltage generated in the shunt resistor 11 and reads each phase winding Lu, DC of the DC motor 20 from the read result and the output of the inverter 10 at the time of reading. The current flowing through Lv and Lw is detected. Note that a shunt resistor may be inserted and connected to each of the three-phase connection lines between the inverter 10 and the DC motor 20 to detect a current flowing directly in each phase winding of the DC motor 20.

  The speed estimation unit 32 estimates the rotor speed (angular speed of the rotor 22) ωest and the rotor position (rotational position of the rotor 22) of the DC motor 20 after startup by calculation based on the detection current of the current detection unit 31.

  The speed control unit 33 determines the output voltage to be output by the inverter according to the target speed ωref input from the outside and the difference between the estimated speed ωest and the target speed ωref of the speed estimation unit 32, and the determined output voltage To the PWM signal generator 34. The speed control unit 33 executes the determination and command of the output voltage for each carrier cycle for generating the PWM signal or for each predetermined carrier cycle.

  In addition, the speed control unit 33 generates an output voltage for forced commutation having a predetermined fixed pattern at the time of starting the motor when the start of operation is instructed by the external signal X1 instructing operation / stop. The unit 34 is commanded. Furthermore, the speed control unit 33 switches between a start-up operation mode by forced commutation and a position detection operation (vector control operation) mode by rotor position estimation, and notifies the PWM signal generation unit 34 of the switching.

  The PWM signal generation unit 34 performs pulse width modulation based on a comparison between the voltage level of the two-phase modulated wave signal corresponding to the output voltage commanded from the speed control unit 33 and the voltage level of the carrier signal (triangular wave signal) having a predetermined period. The three-phase U-phase PWM signal, V-phase PWM signal, and W-phase PWM signal are generated. In response to these PWM signals, the switching elements T1 to T6 of the inverter 10 are turned on and off. Thereby, the phase windings Lu, Lv, and Lw current of the DC motor 20 flow.

  The PWM signal generation unit 34 includes, as main functions for generating each PWM signal, a pulse width determination unit (determination unit) 34a, a first control unit (first control unit) 34b, and a mode determination unit (mode determination unit). ) 34c, a second controller (second controller) 34d, a third controller (third controller) 34e, and a fourth controller (fourth controller) 34f. These functions are constructed by a software program incorporated in the microcomputer constituting the controller 30. Further, the speed estimation unit 32 and the speed control unit 33 described above are also constructed by a software program incorporated in a microcomputer constituting the controller 30. In addition, it is also possible to employ construction using a logic circuit composed of semiconductor elements instead of construction using these software programs. However, the construction with a logic circuit composed of semiconductor elements is not general because the circuit configuration becomes extremely complicated.

  The first control unit 34b is based on the two-phase modulated wave signal corresponding to the output voltage commanded from the speed control unit 33 and a carrier signal having a predetermined period, and generates a PWM signal in a two-phase modulation format to be generated in the next carrier period T. (PWM signal pattern) is calculated. The two-phase modulated wave signal for generating the PWM signal by two-phase modulation is the remaining 2 in which the voltage of any one phase becomes 0 V in the range of 120 degrees in one period of the three-phase sine wave signal. The waveforms of the two phases are shifted by 120 degrees from each other. By comparing the voltage level of the two-phase modulated wave signal with the voltage level of the carrier signal, a two-phase modulation type PWM signal as shown in FIG. 3 and FIG. 4 is generated. When this two-phase modulation type PWM signal is used, the number of times of switching is reduced compared to the case of using a three-phase modulation type PWM signal, and the switching loss can be reduced to improve the efficiency.

  The pulse width determination unit 34a has a pulse width (referred to as an ON period) t1 of each of the U-phase PWM signal, the V-phase PWM signal, and the W-phase PWM signal to be generated in the next carrier cycle T calculated by the first control unit 34b. And whether or not the ON period t1 is equal to or longer than the set value ts is determined. Here, the on-pulse means a signal for turning on the upper switching elements T1, T3, T5 of each phase. Since these PWM signals are generated by two-phase modulation, one of the PWM signals does not include an on-pulse. A PWM signal of a phase that does not include an on-pulse is not subject to determination. The pulse width determination unit 34a performs this determination every time the first control unit 34b calculates a PWM signal to be generated in the next carrier period T.

  An example of each PWM signal in the two-phase modulation format calculated by the first controller 34b is shown in FIG. The energized phase U-phase and V-phase PWM signals each include an on-pulse, and the non-energized phase (reference potential phase) W-phase PWM signal does not include an on-pulse. Since the ON period t1 of the ON pulse in the U-phase and V-phase PWM signals of the energized phase is equal to or greater than the set value ts, the determination result of the pulse width determination unit 34a is affirmative. On the other hand, FIG. 4 shows a two-phase modulation type PWM signal calculated by the first controller 34b at another timing. In this case, since the ON period t1 of the ON pulse in the U-phase PWM signal is less than the set value ts, the determination result of the pulse width determination unit 34a is negative.

  The second control unit 34b receives the determination result of the pulse width determination unit 34a, and when the determination result is affirmative, that is, as shown in FIG. 3, the on period t1 of all the on-pulses in each PWM signal is greater than or equal to the set value ts. In some cases, each PWM signal in the two-phase modulation format calculated by the first control unit 34b is actually generated in the next carrier period T, and the switching elements T1 to T6 of the inverter 10 are driven by the generated PWM signals.

  Based on a command from the speed control unit 33, the mode determination unit 34c determines whether the control state of the controller 30 is a start-up operation mode by forced commutation or a position detection operation (vector control) based on normal rotor position estimation. It is determined whether the mode is (operation).

  When the determination result of the pulse width determination unit 34a is negative and the determination result of the mode determination unit 34c is a start-up operation mode, each PWM signal in the three-phase modulation format generated by the third control unit 34e, which will be described in detail later, is used. Switching elements T1 to T6 of inverter 10 are driven. On the other hand, when the determination result of the pulse width determination unit 34a is negative and the determination result of the mode determination unit 34c is the mode of the position detection operation based on the rotor position estimation, the second control unit 34f, which will be described in detail later, generates the second Switching elements T1 to T6 of inverter 10 are driven by each PWM signal in the phase modulation format.

  Subsequently, a method for generating each PWM signal waveform by the third control unit 34e and the fourth control unit 34f will be described in detail.

  In the period of forced commutation for starting up the DC motor 20, the third control unit 34e sets the on-period t1 of the on-pulse in any of the two-phase modulation type PWM signals calculated by the first control unit 34b. When the value is less than ts, each PWM signal in the two-phase modulation format calculated by the first control unit 34b is calculated by the first control unit 34b with the shortest ON period (shortest pulse width) t1 being equal to or greater than the set value ts. Correct each PWM signal in three-phase modulation format that has the same interphase voltage as each PWM signal in two-phase modulation format, and actually generate each corrected PWM signal in three-phase modulation format in the next carrier period T The switching elements T1 to T6 of the inverter 10 are driven by the PWM signals in the three-phase modulation format. Each PWM signal in the two-phase modulation format before correction is shown in FIG. 4, and each PWM signal in the three-phase modulation format after correction is shown in FIG.

  Specifically, the third control unit 34e includes an on-period t1 of on-pulses in the U-phase and V-phase PWM signals of two energized phases among the PWM signals of the two-phase modulation format calculated by the first control unit 34. Of the two-phase modulation format calculated by the first control unit 34 by adding an ON pulse having the same width as the set value ts to the remaining one W phase PWM signal of the non-energized phase. The PWM signal is corrected to a three-phase modulation type PWM signal. In particular, as means for increasing the on-period t1 of the on-pulse in the U-phase and V-phase PWM signals in the energized phase by the set value ts, the same time width “ts / 2” is set before and after the on-pulse in the U-phase and V-phase PWM signals. Add on-pulses respectively. As means for adding an ON pulse having the same width as the set value ts to the W phase PWM signal of the non-energized phase, the ON pulse having the same width as the set value ts is used as the ON pulse of the U phase and the V phase PWM signal whose center position is the ON pulse. Add to match the center position of. Since the on-pulse in the U-phase and V-phase PWM signals of the energized phase is originally located at the center of the carrier cycle T, the on-pulse in the W-phase PWM signal of the non-energized phase after correction is also located at the center of the carrier cycle T. become.

  In this way, by adding an ON pulse having the same time width (set value ts) to all of the U-phase PWM signal, the V-phase PWM signal, and the W-phase PWM signal in the two-phase modulation format, the U-phase in the three-phase modulation format. A PWM signal, a V-phase PWM signal, and a W-phase PWM signal can be generated. In this three-phase modulation type PWM signal, all on-pulses have a time width equal to or greater than the set value ts, and the interphase voltage is the same as that of the two-phase modulation type PWM signal.

  In the position detection operation after the start of the DC motor 20 is completed, the fourth control unit 34f sets the ON period t1 of any one of the two-phase modulation type PWM signals calculated by the first control unit 34b. If it is less than the value ts, the on-period t1 of the shortest on-pulse in each PWM signal of the two-phase modulation format calculated by the first control unit 34b is corrected in the increasing direction so as to be equal to or greater than the set value ts, and each corrected PWM signal Are actually generated in the next carrier cycle T, and the switching elements T1 to T6 of the inverter 10 are driven by the generated PWM signals in the two-phase modulation format. Each PWM signal in the two-phase modulation format before correction is shown in FIG. 4, and each PWM signal in the two-phase modulation format after correction is shown in FIG.

  Specifically, the fourth control unit 34f includes an on-period t1 of on-pulses in the U-phase and V-phase PWM signals of the two energized phases among the PWM signals of the two-phase modulation format calculated by the first control unit 34. Are each increased by a set value ts, and no operation is performed on the remaining one W phase PWM signal of the non-energized phase. In particular, as a specific example of increasing the on-pulse duration t1 of the U-phase and V-phase PWM signals in the energized phase by the set value ts, an on-pulse having a constant width Δt is added before and after the on-pulse in the U-phase and V-phase PWM signals, respectively. To do. The constant width Δt is a value [= (ts−t1) / 2] which is a half of the difference between the set value ts and the on-period (shortest pulse width) t1 of the shortest on-pulse. That is, after the correction, the on-period t1 of the shortest on-pulse becomes the same as the set value ts. Since the ON pulse in the U phase and V phase PWM signals of the energized phase is originally located at the center of the carrier cycle T, the ON pulse in the corrected U phase and V phase PWM signals is also located at the center of the carrier cycle T.

Next, the control executed by the controller 30 will be described with reference to the flowchart of FIG.
When the controller 30 receives an external signal X1 for starting, that is, switching from the stop state to the operation (YES in step S1), the controller 30 forcibly pulls the rotor 22 of the DC motor 20 for the next carrier cycle T. The three-phase PWM signal of the two-phase modulation format to be generated is calculated (step S2). Subsequently, the controller 30 obtains the on-period (shortest pulse width) t1 of the shortest on-pulse among the calculated on-pulses in each PWM signal (step S3). Then, the controller 30 determines whether or not the obtained on period t1 is equal to or longer than the set value ts (step S4). If the determination result is affirmative (t1 ≧ ts; YES in step S4), the controller 30 actually generates a three-phase PWM signal in the two-phase modulation format calculated in step S2, and an inverter is generated according to the generated PWM signal. Ten switching elements T1 to T6 are turned on and off (step S8).

  In the ON period of the switching elements T1 to T6 of the inverter 10, there is a minimum level (also referred to as a minimum pulse width) that cannot be further reduced due to the characteristics of the switching elements T1 to T6. When the on-period of the on-pulse in the three-phase PWM signal falls below the minimum, such as when the DC motor 20 starts up or rotates at a low speed, the switching elements T1 to T6 cannot be accurately turned on / off. The set value ts corresponds to this minimum limit.

  As the switching elements T1 to T6 are turned on / off, the controller 30 detects a motor current (step S9). Subsequently, the controller 30 determines whether or not the position detection operation is being executed (step S10). Until the rotor position can be estimated based on the motor current after receiving the external signal X1 indicating the start, the controller 30 performs the start operation by forced commutation and has not yet entered the position detection operation.

  During the startup operation by forced commutation (NO in step S10), the controller 30 determines whether or not the position detection operation is possible (step S11). Here, if the motor current detected in step S9 has reached a predetermined value, the controller 30 determines that the motor activation is completed and the position detection operation is possible (YES in step S11). If the motor current detected in step S9 does not reach the predetermined value, the controller 30 determines that the position detection operation is not yet possible (NO in step S11).

  When the position detection operation is not possible (NO in step S11), that is, when the activation of the DC motor 20 is not completed, the controller 30 outputs the output voltage of the inverter 10 for forcibly commutating the DC motor 20 and The output frequency is set to be gradually increased according to a predetermined fixed pattern (step S12). Subsequently, the controller 30 determines whether or not the external signal X1 indicating the stop is received (step S13).

  If the external signal X1 indicating the stop is not received (NO in step S13), the controller 30 returns to step S2 and generates two phases to be generated in the next carrier cycle T in order to obtain the output voltage set in step S12. A modulation-type three-phase PWM signal is calculated (step S2). With this generation, the controller 30 executes the processing from step S3.

  Thereafter, when the activation of the DC motor 20 is completed and the position detection operation is possible (YES in step S11), the controller 30 sets the mode of the position detection operation (vector control operation) (step S14). . Then, the controller 30 sets the output voltage and output frequency of the inverter 10 for controlling the speed of the DC motor 20 according to the target speed ωref and the difference between the estimated speed ωest and the target speed ωref (step S15). Subsequently, the controller 30 determines whether or not the external signal X1 indicating the stop is received (step S13).

When the external signal X1 indicating the stop is not received (NO in Step S13), the controller 30 returns to Step S2 and generates two phases to be generated in the next carrier cycle T in order to obtain the output voltage set in Step S15. A modulation-type three-phase PWM signal is calculated (step S2). With this generation, the controller 30
The process from step S3 is executed.

  In step S3, when the determined ON period t1 is less than the set value ts (t1 <ts; NO in step S4), the controller 30 determines whether or not the position detection operation is being performed (step S5).

  If the start-up operation by forced commutation is being performed (NO in step S5), the controller 30 causes the PWM signal of the two-phase modulation format calculated in step S2 to be as shown in FIG. 5 under the control of the third control unit 34e described above. The PWM signal is corrected to a three-phase modulation type PWM signal (step S6). That is, the on-period t1 of the on-pulse in each of the two energized phases of the PWM signal calculated in step S2 is increased by the set value ts, and the remaining one non-energized phase PWM signal is increased. Is added with an ON pulse having the same width as the set value ts, thereby obtaining a three-phase modulation type PWM signal. Then, the controller 30 actually generates the three phases of the three-phase modulation format obtained by the correction, and drives the switching elements T1 to T6 of the inverter 10 on and off according to the generated PWM signal (step S8). Subsequently, the controller 30 repeats the processing from step S9.

  On the other hand, if it is determined in step S9 that the position detection operation is possible (YES), the controller 30 converts the two-phase modulation type PWM signal calculated in step S2 into FIG. 6 under the control of the fourth control unit 34f described above. The PWM signal is corrected to the same two-phase modulation type PWM signal as shown (step S7). That is, the on-period t1 of the on-pulse in each of the two energized phases of the PWM signal calculated in step S2 is increased by the set value ts, and the remaining one non-energized phase PWM signal is increased. By not performing any operation on, each PWM signal in the two-phase modulation format is obtained. Then, the controller 30 actually generates the U-phase PWM signal, the V-phase PWM signal, and the W-phase PWM signal in the two-phase modulation format obtained by the correction, and the switching elements T1 to T1 of the inverter 10 according to the generated PWM signals. T6 is turned on and off (step S8). Subsequently, the controller 30 repeats the processing from step S9.

  In this way, during the position detection operation, the shift in the interphase voltage is ignored and priority is given to the efficiency improvement by the two-phase modulation. Each PWM signal in the two-phase modulation format generated by the correction has a waveform in which an ON pulse having a constant width Δt is added before and after the ON pulse originally present in each PWM signal in the energized phase. The constant width Δt is a value [= (ts−t1) / 2] which is a half of the difference between the set value ts and the on-period (shortest pulse width) t1 of the shortest on-pulse. That is, the on-period t1 of the shortest on-pulse in each PWM signal in the two-phase modulation format after correction is a set value ts that can drive the switching elements T1 to T6 stably.

  Summarizing the above operations, until the start is completed, the two-phase modulation format of the two-phase modulation format is obtained on condition that the on-period t1 of the minimum on-pulse in the PWM signal of the two-phase modulation format calculated in advance is longer than the set value ts. The inverter 10 is driven by the PWM signal. Thereby, efficient driving | operation becomes possible. On the other hand, when the on-period t1 of the minimum on-pulse of the PWM signal of the two-phase modulation format calculated in advance is shorter than the set value ts, the on-period t1 of the minimum on-pulse is calculated as the set value ts. The inverter 10 is driven by the three-phase modulation type PWM signal corrected as described above and the three-phase modulation type PWM signal having the same interphase voltage as the two-phase modulation type PWM signal calculated in advance. Thereby, the DC motor 20 can be driven stably even during the start-up operation in which the driving tends to be unstable.

  As described above, when the DC motor 20 is started, first, a forced commutation PWM signal is generated by two-phase modulation and the switching elements T1 to T6 are driven on and off. The number of on / off times of the switching elements T1 to T6 can be reduced and the efficiency is improved as compared with the case where the switching elements T1 to T6 are driven on and off by generating by three-phase modulation.

  When the on-period t1 of any on-pulse in the PWM signal for forced commutation generated by the two-phase modulation during the forced commutation at the time of start is less than the set value ts, the two-phase PWM remains generated by the two-phase modulation. If the ON period t1 of the on-pulse in the signal is corrected in the increasing direction, the level of the output voltage of the inverter 10 differs from that before the correction, so the ON period of the set value ts is set for all the PWM signals in the U, V, and W phases. Add the on-pulse you have. Thus, while maintaining the level of the output voltage of the inverter 10 unchanged from that before the correction, the ON period t1 of each PWM signal is set to the set value ts that is the minimum value of the ON period of the switching elements T1 to T6. It can be maintained above. Since the level of the output voltage of the inverter 10 is not different from that before the correction, the DC motor 20 does not suffer a problem such as step-out and the on period t1 of each PWM signal is set to be more than the minimum of the on period of the switching elements T1 to T6. Therefore, the switching elements T1 to T6 can be accurately turned on and off without malfunction.

  Moreover, as a correction means, an on-pulse having an on-period ts is added to the PWM signal of one phase having no on-pulse in accordance with the center of the carrier cycle, and the PWM signals of the other two phases having the on-pulse are added to each PWM signal. On the other hand, since an equal ON period ts / 2 is added before and after the ON pulse, the phase of the output voltage of the inverter 10 is the same among the R phase, S phase, and T phase. Therefore, the activated DC motor 20 can be driven stably.

  Even in the position detection operation after the start-up of the DC motor 20 is completed, the switching elements T1 to T6 are turned on and off by the respective PWM signals for speed control generated by the two-phase modulation. The number of off times can be reduced, and the efficiency is improved.

  Further, when the on-period t1 of any on-pulse in each PWM signal generated by two-phase modulation during the position detection operation is less than the set value ts, the on-period t1 of each on-pulse of each PWM signal is the same as each other ( Since the correction is made in the increasing direction only during the period of ts-t1), the on-period t1 of the on-pulse in each PWM signal for speed control can be maintained above the minimum of the on-period of the switching elements T1 to T6. Therefore, the switching elements T1 to T6 can be accurately turned on and off without malfunction.

  In this case, since it is a two-phase modulation, the on-pulse on period t1 in the two-phase PWM signal is corrected, and the remaining one-phase PWM signal having no on-pulse originally maintains the zero level. Although the output voltage level of the DC motor 20 is slightly different from that before the correction, since the driving of the DC motor 20 is in a stable operation because it is during the position detection operation, the DC motor is displaced by a small voltage level deviation due to this correction. There is no problem such as step-out in 20, so that improvement in efficiency by two-phase modulation can be prioritized.

  As a means for correcting from the two-phase modulation format to the three-phase modulation format during forced commutation at start-up, all PWM signals of each PWM signal in the two-phase modulation format have ON pulses having an ON period of the set value ts. Although added, a three-phase modulation signal having the same output as the original PWM signal in the two-phase modulation format is generated by a general sine wave-triangular wave comparison method, so that the minimum on period t1 of the on pulse is equal to or greater than the set value ts. If so, that's fine.

  Further, the output target of the inverter 10 during the forced commutation is to increase the predetermined output voltage and output frequency at a predetermined rate as time elapses. It is also possible to grasp in advance the output timing that is less than ts. Therefore, during the forced commutation at the time of start-up, each PWM signal in the three-phase modulation format that can ensure the minimum on-period t1 of the on-pulse to be output is equal to or larger than the set value ts is stored in advance, and the minimum on-period t1 of the on-pulse is determined. It is also possible to generate each stored PWM signal in the three-phase modulation format at the timing when it becomes less than the set value ts. However, in this case, since it is necessary to store each PWM signal to be output in accordance with the above timing over the entire period of forced commutation operation, a memory having a large storage capacity must be used.

  The above embodiments are presented as examples, and are not intended to limit the scope of the invention. These novel embodiments and modifications can be implemented in various other forms, and various omissions, rewrites, and changes can be made without departing from the spirit of the invention. In these embodiments and modifications, the scope of the invention is included in the gist, and is included in the invention described in the claims and the equivalent scope thereof.

  The motor drive device according to the embodiment of the present invention can be used for a motor that drives a compressor, for example.

Claims (6)

An inverter having a plurality of switching elements, and supplying a driving voltage to the three-phase motor by turning these switching elements on and off;
A controller for turning on and off the switching element by a pulse width modulation signal having a variable pulse width, and
The controller is
When the pulse width modulation signal in the two-phase modulation format is calculated and the shortest pulse width of the calculated pulse width modulation signal is less than a set value, the calculated pulse width modulation signal is calculated using the shortest pulse width as the set value. Correction to the pulse width modulation signal of the three-phase modulation format in which the phase voltage is the same as the calculated pulse width modulation signal as described above, and the switching element is driven on and off by the corrected pulse width modulation signal.
The motor drive device characterized by the above-mentioned. An inverter having a plurality of switching elements, and supplying a driving voltage to the three-phase motor by turning these switching elements on and off;
A controller for turning on and off the switching element by a pulse width modulation signal having a variable pulse width, and
The controller is
First control means for calculating a two-phase modulation type pulse width modulation signal;
Determination means for determining whether or not the shortest pulse width of the pulse width modulation signal calculated by the first control means is a set value or more;
If the determination result of the determination means is affirmative, second control means for driving the switching element on and off by the pulse width modulation signal calculated by the first control means;
Wherein when the determination result of the determination means is negative, the said pulse width modulation signal calculated by the first control means is the shortest pulse width is more than the set value and wherein the pulse width calculated by the first control means modulation Third control means for correcting to a pulse width modulation signal of a three-phase modulation format in which the interphase voltage is the same as the signal, and driving the switching element on and off by the corrected pulse width modulation signal;
including,
The motor drive device characterized by the above-mentioned. An inverter having a plurality of switching elements, and supplying a driving voltage to the DC brushless three-phase motor by turning these switching elements on and off;
A controller for turning on and off the switching element by a pulse width modulation signal having a variable pulse width, and
The controller is
First control means for calculating a two-phase modulation type pulse width modulation signal;
Determination means for determining whether or not the shortest pulse width of the pulse width modulation signal calculated by the first control means is a set value or more;
If the determination result of the determination means is affirmative, second control means for driving the switching element on and off by the pulse width modulation signal calculated by the first control means;
If the determination result of the determination means is negative during the forced commutation period for starting the motor, the pulse width modulation signal calculated by the first control means is the shortest pulse width greater than or equal to the set value. In addition, the pulse width modulation signal is corrected to a three-phase modulation type pulse width modulation signal having the same interphase voltage as the pulse width modulation signal calculated by the first control means, and the switching element is driven on and off by the corrected pulse width modulation signal. Third control means for
After the start of the motor is completed, if the determination result of the determination unit is negative, the shortest pulse width of the pulse width modulation signal calculated by the first control unit is corrected in an increasing direction so as to be equal to or greater than the set value. A fourth control means for driving the switching element on and off by the corrected pulse width modulation signal;
including,
The motor drive device characterized by the above-mentioned. The third control means increases the pulse widths of the pulse width modulation signals of two energized phases among the pulse width modulation signals calculated by the first control means by the set value, respectively, and the first control means The pulse width modulation signal calculated by the first control means by adding a pulse having the same width as the set value to the pulse width modulation signal of one non-conduction phase among the pulse width modulation signals calculated in To the pulse width modulation signal of the three-phase modulation format,
The motor driving device according to claim 2 or claim 3, wherein The third control means includes
Of the pulse width modulation signals calculated by the first control means, the pulse widths of the pulse width modulation signals of the two energized phases are made equal to or greater than the set value by adding a constant width pulse before and after each pulse. Increase,
In the pulse width modulation signal of one non-energized phase among the pulse width modulation signals calculated by the first control means, the same width as the set value at a position corresponding to the pulse of the pulse width modulation signal of the energized phase The motor drive device according to claim 4, wherein the center position of the pulse is added to a state where the center position of the pulse coincides with the center position of the pulse of the pulse width modulation signal of the energized phase. The fourth control means increases the pulse width of the pulse width modulation signal calculated by the first control means to the set value or more by adding a pulse having a constant width before and after each pulse.
The motor driving device according to claim 3.

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