JP2005210813A - Brushless dc motor system and brushless dc motor drive method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for suitably driving a brushless DC motor in a wide range of a speed zone. <P>SOLUTION: This brushless DC motor system includes the brushless DC motor 5, an inverter 3, current sensors 6u, 6v and 6w that detect armature currents of the brushless DC motor 5, and control device 8 that generates a PWM signal S<SB>PWM</SB>in response to the armature currents. The inverter 3 drives the brushless DC motor 5 in response to the PWM signal S<SB>PWM</SB>. The control device 8 selects one of control method groups including sensorless vector control and V/f control as a selection control method is response to a speed command ω<SP>*</SP>. The control device 8 selects the sensorless vector control as the selection control method when the speed command ω<SP>*</SP>is in a first speed region ω<SB>s2</SB>-ω<SB>s3</SB>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a brushless DC motor system and a brushless DC motor driving method, and more particularly to improvement of a driving algorithm of a brushless DC motor.

  A brushless DC motor having a permanent magnet as a field magnet mounted on a rotor is widely used as a motor realizing high efficiency in a small and medium capacity range of several tens of kW or less. In the brushless DC motor, since a permanent magnet is used as a field, a field current for generating a field magnetic flux is not consumed. For this reason, the brushless DC motor can achieve high efficiency.

  The driving method of the brushless DC motor greatly affects the characteristics of the brushless DC motor. For this reason, various driving methods have been proposed in order to improve the characteristics of the brushless DC motor.

Patent Document 1 discloses a technique for estimating the position and rotation speed (rotation speed) of a rotor of a motor from a current flowing through the motor and performing vector control using the estimation result. In this technique, the position and rotational speed of the rotor are estimated using a motor model.
JP-A-8-308286

Patent Document 2 discloses a PWM driving method in which a brushless DC motor is driven using a rectangular wave in a low speed range and is driven using a pseudo sine wave in a high speed range. In the known PWM driving method, the harmonic loss is reduced by driving with a rectangular wave in a low speed range where the harmonic loss is large. On the other hand, in the high speed range, the energization angle is increased by driving with a pseudo sine wave, thereby improving the voltage utilization rate. Due to these actions, the driving efficiency is improved in the known driving method.
JP 2003-209988 A (refer to paragraphs [0072] to [0073] in particular)

  Patent Document 2 further discloses that drive efficiency can be further improved by performing field-weakening control when a brushless DC motor is driven using a pseudo sine wave in a high speed range. Field weakening control is a technique that reduces the induced voltage generated in the armature by controlling the armature current so as to weaken the field, thereby enabling the motor to operate at a high speed. In a brushless DC motor, field weakening control can be performed by controlling the d-axis current of the armature current to be negative.

  One problem with field-weakening control in the high speed range is that the stability of the operation of the brushless DC motor in the high speed range decreases due to the difficulty in generating a pseudo sine wave having an ideal waveform. is there. It is substantially difficult to make the induced voltage induced in the armature winding of the brushless DC motor and the strength of the rotating magnetic field generated in the stator of the brushless DC motor to be a perfect sine wave. It is difficult to generate a pseudo sine wave having A pseudo sine wave having a non-ideal waveform reduces the effectiveness of field weakening control and reduces the operational stability of the brushless DC motor at high speeds.

  From such a background, it is desired to provide a technique for enabling a brushless DC motor to be suitably operated in a wide speed range.

  An object of the present invention is to provide a technique for enabling a brushless DC motor to be suitably operated in a wide speed range.

  The means for achieving the above object will be described below. In order to clarify the correspondence between the description of [Claims] and the description of [Best Mode for Carrying Out the Invention], the technical matters included in the means include [for carrying out the invention]. The number / symbol used in the best form] is added. However, the added numbers and symbols shall not be used for the interpretation of the technical scope of the invention described in [Claims].

A brushless DC motor system according to the present invention includes a brushless DC motor (5) having a rotor having a field and a stator having an armature, an inverter (3), and a brushless DC motor (5 ) Including a current sensor (6u, 6v, 6w) for detecting an armature current supplied to the armature, and a control device (8) for generating a PWM signal (S _PWM ) in response to the armature current. . The inverter (3) drives the brushless DC motor (5) in response to the PWM signal (S _PWM ). In response to a speed command (ω ^* ) for instructing the rotational speed of the rotor of the brushless DC motor (5), the control device (8) includes a sensorless vector control and a V / f control. One is selected as a selection control method. When the speed command (ω ^* ) is in the first speed range (ω _s2 −ω _S3 ), the control device (8) selects sensorless vector control as the selection control method, and the speed command (ω ^* ) is The selection control method is switched from sensorless vector control to V / f control in response to increasing from the first speed region (ω _s2 −ω _S3 ) and exceeding the first threshold speed (ω _S3 ).

Sensorless vector control that independently controls the q-axis current and d-axis current can increase the output torque of the brushless DC motor (5), while the pseudo sine wave waveform is usually not ideal. Therefore, the stability of the operation of the brushless DC motor in the high speed range is poor. On the other hand, V / f control is suitable for operation of a brushless DC motor at high speed. Therefore, in response to the speed command (ω ^* ) exceeding the first threshold speed (ω _S3 ), the selection control method is switched from sensorless vector control to V / f control, so that the brushless DC motor can be operated in a wide speed range. Can be suitably operated.

Specifically, the control device (8), when sensorless vector control is selected as the selection control method,
(A) calculating an estimated speed of the rotor and an estimated position of the rotor from the armature current;
(B) generating a q-axis current command value and a d-axis current command value from the difference between the speed command and the estimated speed;
(C) calculating a q-axis current and a d-axis current of the armature current from the estimated position of the rotor and the armature current;
(D) From the difference between the q-axis current command value and the q-axis current and the difference between the d-axis current command value and the d-axis current, the inverter (3) supplies the brushless DC motor (5). Calculating a q-axis voltage and a d-axis voltage of the three-phase AC voltage;
(E) It is programmed to execute the step of generating the PWM signal (S _PWM ) from the q-axis voltage and the d-axis voltage, and V / f control is selected as the selection control method When,
(F) calculating a γ-axis current and a δ-axis current from the armature current;
(G) generating a frequency command ω _f ^* of a three-phase AC voltage that the inverter (3) supplies to the brushless DC motor (5) from the rotor speed command and the γ-axis current;
(H) The following formula expressed using the back electromotive force coefficient Λ _d ^{* of the} brushless DC motor (5) and the offset voltage V _ofsq :
v _q = Λ _d ^* · ω _f ^* −V _ofsq ,
To calculate a γ-axis voltage v _γ of the three-phase AC voltage that the inverter (3) supplies to the brushless DC motor (5) from the frequency command ω _f ^* ,
(I) calculating a δ-axis voltage of the three-phase AC voltage from the δ-axis current;
(J) executing the step of generating the PWM signal (S _PWM ) from the γ-axis voltage calculated in the step (h) and the δ-axis voltage calculated in the step (i). Preferably it is programmed.

  In order to take advantage of the sensorless vector control, the control device (8) performs field weakening control in response to the estimated speed and the speed command when the sensorless vector control is selected as the selection control method. The d-axis current command value is preferably programmed so as to be generated.

  The maximum value of the output torque of V / f control is smaller than that of sensorless vector control. This means that the V / f control is not appropriate when the output torque of the brushless DC motor (5) is large. For this reason, it is preferable that the switching from the sensorless vector control to the V / f control in the selection control method is not performed when the output torque of the brushless DC motor (5) is larger than a predetermined reference torque.

The control device (8) selects the V / f control as the selection control method when the speed command (ω ^* ) of the brushless DC motor (5) is in the second speed range (ω ^* > ω _s4 ), and , In response to the speed command (ω ^* ) decreasing from the second speed range (ω ^* > ω _s4 ) to be smaller than the second threshold speed (ω _s4 ), the selection control method is changed to V / f It is preferable that the control is switched from control to sensorless vector control, and the second threshold speed (ω _s4 ) is smaller than the first threshold speed (ω _s3 ). By making the speed command for switching from V / f control to sensorless vector control smaller than the speed command for switching the sensorless vector control from sensorless vector control to V / f control, the selection control method can achieve V / f control and sensorless control. Hunting with the vector control can be prevented.

The switching from the V / f control to the sensorless vector control is preferably performed in response to a DC voltage (V _DC ) used by the inverter (3) to drive the brushless DC motor (5). The rotational speed of the rotor capable of performing sensorless vector control changes according to the direct current voltage (V _DC ). Therefore, by switching the selection control method in response to the direct current voltage (V _DC ), it is possible to prevent the selection control method from being switched to the sensorless vector control at the rotational speed of the rotor that is not compatible with the sensorless vector control.

When the speed command (ω ^* ) of the brushless DC motor (5) is in a third speed range (ω _s1 −ω _s2 ) lower than the first speed range, the control device (8) has a non-energized section, In addition, the PWM signal (S _PWM ) may be generated so that a drive voltage having a waveform composed of equal-width rectangular pulses having substantially equal pulse widths is supplied from the inverter (3) to the brushless DC motor (5). Is preferred. The sensorless vector control described above is not suitable for a brushless DC motor (5) at a low speed for a load having a large torque pulsation. On the other hand, a control method for supplying a drive voltage having a waveform composed of equal-width rectangular pulses having a non-energized section and a substantially equal pulse width to the brushless DC motor (5) is a brushless DC motor in a low speed range. It is suitable for the drive of (5). By using such a control method in the low speed region, stable driving of the brushless DC motor (5) can be realized.

The brushless DC motor driving method of the present invention is a brushless DC motor driving method for driving the brushless DC motor (5) using the inverter (3). The brushless DC motor driving method is as follows:
(A) detecting an armature current supplied from the inverter (3) to the armature of the brushless DC motor (5);
(B) Select one of a group of control methods including sensorless vector control and V / f control in response to a speed command (ω ^* ) indicating the rotational speed of the rotor of the brushless DC motor (5). Selecting a control method;
(C) generating a PWM signal (S _PWM ) according to the selection control method and in response to the armature current;
(D) causing the inverter (3) to drive the brushless DC motor (5) in response to a PWM signal (S _PWM ).

In the brushless DC motor driving method, when sensorless vector control is selected as the selection control method, the following steps (E) to (I):
(E) calculating an estimated speed of the rotor and an estimated position of the rotor from the armature current;
(F) generating a q-axis current command value and a d-axis current command value from the difference between the speed command and the estimated speed;
(G) calculating a q-axis current and a d-axis current of the armature current from the estimated position of the rotor and the armature current;
(H) From the difference between the q-axis current command value and the q-axis current and the difference between the d-axis current command value and the d-axis current, the inverter (3) supplies the brushless DC motor (5). Calculating a q-axis voltage and a d-axis voltage of the three-phase AC voltage to be
(I) When a step of generating a PWM signal (S _PWM ) from the q-axis voltage and the d-axis voltage is performed and V / f control is selected as the selection control method, the following (J) to (J N) Step:
(J) calculating a γ-axis current and a δ-axis current from the armature current;
(K) generating a frequency command ω _f ^* of a three-phase AC voltage supplied from the inverter (3) to the brushless DC motor (5) from the rotor speed command and the γ-axis current;
(L) The following formula expressed using the back electromotive force coefficient Λ _d ^{* of the} brushless DC motor (5) and the offset voltage V _ofsq :
v _q = Λ _d ^* · ω _f ^* −V _ofsq ,
To calculate a γ-axis voltage v _γ of the three-phase AC voltage that the inverter (3) supplies to the brushless DC motor (5) from the frequency command ω _f ^* ,
(M) calculating a δ-axis voltage of the three-phase AC voltage from the δ-axis current;
(N) It is preferable that a step of generating a PWM signal (S _PWM ) is performed from the γ-axis voltage calculated in the (L) step and the δ-axis voltage calculated in the (M) step. is there.

  The present invention provides a technique for enabling a brushless DC motor to be suitably operated in a wide speed range.

Configuration of First First System In one embodiment of the present invention, as shown in FIG. 1, a brushless DC motor system includes an AC power source 1, an AC-DC converter 2, an inverter 3, and a brushless DC motor. And 5. AC power supply 3 supplies an AC voltage _{V AC} to the AC-DC converter 2. AC-DC converter 2 converts an AC voltage _{V AC} to a DC voltage _{V DC,} supplies a DC voltage _{V DC} to the inverter 3 of the voltage source. The inverter 3 is connected to the brushless DC motor 5 through a u-phase power supply line 4u, a v-phase power supply line 4v, and a w-phase power supply line 4w. The inverter 3 generates a three-phase drive voltage from the direct-current voltage _VDC , and the generated three-phase drive voltage is brushless DC via the u-phase power supply line 4u, the v-phase power supply line 4v, and the w-phase power supply line 4w. The u-phase armature winding, the v-phase armature winding, and the w-phase armature winding of the motor 5 are supplied. The armature winding of the brushless DC motor 5 generates a rotating magnetic field from the supplied three-phase driving voltage.

In order to realize sensorless control of the brushless DC motor 5, current detectors 6u, 6v, and 6w are provided in the u-phase power supply line 4u, the v-phase power supply line 4v, and the w-phase power supply line 4w, respectively. The current detector 6u measures the u-phase current i _u flowing through the u-phase armature coil, the current detector 6v measures the v-phase current i _v flowing through the v-phase armature coil, and the current detector 6w measuring the w-phase current i _w flowing through the w-phase armature coils. The measured u-phase current i _u , v-phase current i _v , and w-phase current i _w are, as will be described later, PWM control (that is, sensorless vector control and V / f control) that outputs a pseudo sine wave. Used for. At this time, only two of the u-phase current i _u , the v-phase current i _v , and the w-phase current i _w are measured, and the other is:
i _u + i _v + i _w = 0,... (1)
Can be calculated from When only two of the u-phase current i _u , the v-phase current i _v , and the w-phase current i _w are measured, one of the current detectors 6 _u , 6 v, 6 w corresponding to the current that is not measured is necessary. Such a configuration is preferable in terms of cost reduction.

In addition, the u-phase power supply line 4u, the v-phase power supply line 4v, and the w-phase power supply line 4w are connected to the voltage detector 7. The voltage detector 7 is a u-phase induced in the u-phase armature winding, the v-phase armature winding, and the w-phase armature winding of the armature by the magnetic interaction from the rotor of the brushless DC motor 5. The induced voltage v _ui , the v phase induced voltage v _vi , and the w phase induced voltage v _wi are measured. The u-phase induced voltage v _ui , the v-phase induced voltage v _vi , and the w-phase induced voltage v _wi are measured in the non-energized sections of the u phase, the v phase, and the w phase, respectively. As will be described later, the u-phase induced voltage v _ui , the v-phase induced voltage v _vi , and the w-phase induced voltage v _wi are used for equi-width PWM control.

The current detectors 6u, 6v, 6w and the voltage detector 7 are connected to the MPU 8. The MPU 8 includes the armature currents i _u , i _v , and i _w measured by the current detectors 6 _u , 6 _v , 6 _w , the u-phase induced voltage v _ui , the v-phase induced voltage v _vi , measured by the voltage detection circuit 8, and In response to the w-phase induced voltage v _wi , the PWM signal S _PWM for controlling the inverter 3 is generated. The PWM signal S _PWM is generated such that the rotor speed is controlled by a speed command ω ^* given to the MPU 8. Switching transistors (not shown) constituting the inverter 3 are turned on / off in response to the PWM signal S _PWM , whereby a three-phase drive voltage is supplied to the armature winding of the brushless DC motor 5. All the operations of the MPU 8 are executed according to the control computer program.

A voltage detection circuit 9 that measures the DC voltage V _DC is connected to a power supply line that supplies the DC voltage V _DC from the AC-DC converter 2 to the inverter 3. The voltage detection circuit 9 supplies a voltage notification signal for notifying the measured DC voltage _VDC to the MPU 8.

Control Method Used to Drive Second Brushless DC Motor 5 As shown in FIG. 2, the MPU 8 performs open loop control, equal width PWM control, sensorless according to the speed command ω ^* of the brushless DC motor 5. One control method is selected from vector control and V / f control, and the inverter 3 that drives the brushless DC motor 5 is controlled according to the control method. Roughly, open-loop control is used at the beginning of the startup of the brushless DC motor 5, uniform width PWM control is used in the low speed region, sensorless vector control is used in the medium speed region, and V / f control is used in the high speed region. Is used. In the present embodiment, switching between control methods achieves both a wide speed range and high torque output.

1. Open-loop control Open-loop control generates a PWM signal S _PWM in accordance with a pattern prepared in advance in a storage device (not shown) of the MPU 8 and has a predetermined waveform in the armature winding of the brushless DC motor 5 This is a control method for supplying a drive voltage. During the execution of the open loop control, the armature currents i _u , i _v , i _w , and the induced voltages v _ui , v _vi , v _wi are not fed back. The open loop control is used when the sensorless control cannot be performed because the rotational speed of the rotor is 0 or extremely low, that is, when the brushless DC motor 5 is started.

2. Equal width PWM control The equal width PWM control is a control for supplying a driving voltage having a waveform composed of a plurality of rectangular pulses having the same pulse width to the brushless DC motor 5. FIG. 2A shows a voltage waveform between the two phases of the three-phase drive voltage supplied to the brushless DC motor 5. The conduction angle of the three-phase drive voltage supplied to the brushless DC motor 5 is typically 120 °. As will be described later, it is important to execute the equal width PWM control that the energization angle is not 180 °, that is, the drive voltage includes the non-energization section.

In order to drive the brushless DC motor 5 by the equal width PWM control, the MPU 8 needs to acquire the position and rotation speed of the rotor. This is because the position of the rotor is necessary to properly control the phase of the drive voltage supplied to each phase, and in order to control the rotational speed of the rotor to the speed command ω ^* , the rotational speed of the rotor must be In addition, it is necessary to appropriately determine the width of the rectangular pulse included in the drive voltage.

In order to perform appropriate equal width PWM control, the MPU 8 calculates the position and rotational speed of the rotor from the induced voltages v _ui , v _vi , and v _wi induced in the armature winding of each phase in the non-energized section. . Most simply, the rotor position and rotational speed are calculated from the time at which the induced voltages v _ui , v _vi , and v _wi cross the reference voltage level. From the calculated rotor position and rotational speed, the phase of the drive voltage and the pulse width of the rectangular pulse constituting it are determined.

The advantage that the equal width PWM control has over the sensorless vector control and the V / f control is the stability when the brushless DC motor 5 is operated at a low speed. One problem with sensorless control of the brushless DC motor 5 is that when the brushless DC motor 5 is operated at a low speed, a signal having an amplitude large enough to accurately estimate the position and rotational speed is obtained. It is difficult. However, the equal width PWM control in which a non-energized section is provided in the three-phase drive voltage supplied to the brushless DC motor 5 is performed by measuring the induced voltages v _ui , v _vi , and v _wi in the non-energized section. Even if 5 is operated at a low speed, the position and rotational speed of the rotor can be accurately measured. This effectively improves the stability of the brushless DC motor 5 during low speed operation.

3. Sensorless vector control In sensorless vector control, the position and rotational speed of the rotor are estimated from the armature current of the brushless DC motor 5 and supplied to the brushless DC motor 5 in response to the estimated position and rotational speed of the rotor. The control is to control the q-axis current and the d-axis current of the armature current to be performed. In the following, the position and the rotational speed of the estimated rotor, respectively, the estimated position theta ^~, called ^~ estimated speed omega. In the present embodiment in which the voltage-type inverter 3 is used, as shown in FIG. 2B, the drive voltage is controlled by PWM control, so that a current having a substantially sinusoidal shape is generated by the brushless DC motor 5. To be supplied.

(1) Details of Sensorless Vector Control FIG. 3 is a block diagram of sensorless vector control performed by the MPU 8. Sensorless vector control by the MPU 8 includes A / D conversion 11, 3-phase / 2-phase conversion 12, speed / position estimation calculation 13, speed control calculation 14, current control calculation 15, 2-phase / 3-phase conversion 16, A / D conversion. 17 and PWM calculation 18. In the MPU 8, the operation shown in FIG. 3 is performed every clock cycle of the system clock.

In the A / D conversion 11, the output signals output from the current measuring devices 6u, 6v, 6w are A / D converted, and u-phase current i _u , v-phase current i _v , and w-phase current i _w (or of these) Are taken into the MPU 8.

In the three-phase to two-phase conversion 12, the MPU 8 applies the u-phase current i _u , the v-phase current i _v , and the w-phase current i _w (or two of them) acquired by the A / D conversion 11. , 3-phase 2-phase conversion using the estimated position theta ^~ of the rotor calculated by the previous clock cycle is performed, q-axis current and d-axis current is calculated.

In the speed / position estimation calculation 13, the q-axis current and the d-axis current calculated by the three-phase / two-phase conversion 12, and the q-axis voltage v _q and the d-axis calculated by the current control calculation 15 in the previous clock cycle. and a voltage v _d, estimated position theta ^~ and estimated speed omega ^~ of the rotor current of the ^rotor, as well as the estimated position theta ₂₃ ^~ of the rotor in the next clock cycle is calculated. The estimated positions θ ^~ , θ ₂₃ ^~ , and the estimated speed ω ^~ are calculated using a motor model of the brushless DC motor 5. It is emphasized that the estimated position θ ^~ is described by the dq coordinate system. This is one of the considerations when the control method is switched between sensorless vector control and V / f control. The procedure for calculating the estimated positions θ ^˜ , θ ₂₃ ^˜ and the estimated speed ω ^˜ will be described in detail later.

The speed control calculation 14, the calculated deviation between the estimated speed omega ^~ speed command omega ^* and the rotor, so that the deviation approaches 0, q-axis current command value i _q ^* and d-axis current command value i _d ^* And are generated. Generally, the d-axis current command value i _d ^* is zero. However, the d-axis current command value i _d ^* is set to a negative value when field-weakening control is required because the speed command ω ^* is high.

The current control operation 15, the deviation between the q-axis current command value i _q ^* and the q-axis current, and d deviation between the axis current command value i _d ^* and the d-axis current i _d is calculated, these deviations 0 The q-axis voltage v _q and the d-axis voltage v _d are determined so as to approach each other. The determination of the q-axis voltage v _q and d-axis voltage v _d, the estimated speed of the rotor omega ^~ is used.

In the two-phase / three-phase conversion 16, two-phase three-phase conversion is performed on the determined q-axis voltage v _q and d-axis voltage v _d , and u of the three-phase drive voltage to be supplied to the brushless DC motor 5. A phase voltage v _u , a v phase voltage v _v , and a w phase voltage v _w are calculated. In the two-to-three phase conversion, estimated position theta ₂₃ ^~ of the rotor in the next clock cycle is used.

In the PWM calculation 17, a PWM signal for controlling the inverter 3 so that a three-phase drive voltage having the calculated u-phase voltage v _u , v-phase voltage v _v , and w-phase voltage v _w is supplied to the brushless DC motor 5. S _PWM is generated. For generation of the PWM signal S _PWM , the magnitude of the DC voltage _VDC supplied from the AC-DC converter 2 to the inverter 3 is referred to. DC voltage _{V DC} is obtained A / D conversion 18 for the voltage notification signal output from the voltage detection circuit 9 is performed, PWM signal _{S PWM} is generated by referring to the DC voltage _{V DC.} A switching transistor of the inverter 3 are turned on or off in response to the generated PWM signal S _PWM.

(2) the estimated position theta ^~, theta ₂₃ ^~, and the estimated velocity omega calculation Figure 4 ^- is the estimated position theta ^~ carried out at a speed and position estimation calculation 13, theta ₂₃ ^~, and estimated speed ^omega-steps of calculating the FIG. The outline of the speed / position estimation calculation 13 is as follows; using a motor model describing the characteristics of the brushless DC motor 5 (that is, the voltage equation established for the brushless DC motor 5), the model q-axis current i _qm ^˜ , Model d-axis current i _qm ^˜ is calculated. Furthermore, the model difference between the q-axis current _{i qm} ^~ and q-axis current _{i q,} and model from the difference between the d-axis current _{i dm} ^~ and d-axis current _{i d,} the estimated position of the rotor theta ^~ and estimated speed of the rotor ω ^Is asked for. Furthermore, by correction according to the estimated speed omega ^~ for the estimated position theta ^~ of the rotor is applied, the estimated positions theta ₂₃ ^~ of the rotor in the next clock cycle is calculated.

The estimated positions θ ^˜ , θ ₂₃ ^˜ and estimated speed ω ^˜ are calculated by motor model calculation 21, q-axis current error calculation 22a, d-axis current error calculation 22b, electromotive force estimation calculation 23a, speed error estimation calculation 23b, LPF. A (low pass filter) calculation 24, a speed estimation calculation 25, a position estimation calculation 26, and a two-phase / three-phase conversion correction calculation 27 are configured.

ここで，θは回転子速度，Ｒは巻線抵抗，Ｌ_ｄは，ｄ軸インダクタンス，Ｌ_ｑは，ｑ軸インダクタンス，Ｋ_ｅは，速度起電力係数である。 In the motor model calculation 21, from the q-axis current i _q and the d-axis current calculated by the three-phase / two-phase conversion 12 and the q-axis voltage v _q and the d-axis voltage v _d calculated by the current control calculation 15, The model q-axis current i _qm ^˜ and the model d-axis current i _qm ^˜ are calculated using the motor model of the brushless DC motor 5. For calculating the model q-axis current i _qm ^˜ and the model d-axis current i _qm ^˜ , the estimated speed electromotive force e ^˜ calculated in the previous clock cycle and the rotor estimated speed ω ^˜ are used. Estimated speed electromotive force e and ^~ a speed electromotive force that is estimated to have been induced in the armature winding of the brushless DC motor 5. The voltage equations used to calculate the q-axis current i _qm ^˜ and the model d-axis current i _qm ^˜ are typically as follows:

Here, θ is the rotor speed, R is the winding resistance, L _d is the d-axis inductance, L _q is the q-axis inductance, and _Ke is the speed electromotive force coefficient.

In q-axis current error calculating 22a, Model q-axis current _{i qm} ^~ and error .DELTA.i _q between the q-axis current _{i q} is calculated, the d-axis current error calculating 22b, model d-axis current _{i qm} ^~ and d-axis current i error Δi _d is calculated with _d.

In estimated speed electromotive force calculation 23a, the estimated speed electromotive force e ^~ from the q-axis current error .DELTA.i _q is calculated, the speed error estimating arithmetic 23b, the estimated speed error [Delta] [omega ^~ from d-axis current error .DELTA.i _d is calculated. Since the error between the estimated current calculated based on the estimated speed electromotive force and the actual current corresponds to the estimation error of the speed electromotive force, the speed electromotive force is estimated by feedback to the estimated value of the error current. The same applies to the speed.

In LPF operation 24, the low-frequency component [Delta] [omega _L ^~ are taken out of the estimated speed error [Delta] [omega ^~.

In the speed estimation calculation 25, the estimated speed ω ^{˜ of the} rotor is calculated from the estimated speed electromotive force e ^˜ , the estimated speed error Δω ^˜ , and its low frequency component Δω _L ^˜ . In particular, the estimated velocity ^omega-in the is calculated as follows: using the velocity electromotive force is approximately proportional to the rotational speed of the rotor, a first order approximation of the estimated velocity of the estimated speed electromotive force e rotors ^From A value is calculated. The calculated first-order approximation is, the estimated speed error [Delta] [omega ^~, its is a low-frequency component [Delta] [omega _L ^~ correction used in the estimated speed omega ^~ of the rotor is calculated.

In the position estimation calculation 26, by integrating the estimated speed omega ^~ of the rotor, the estimated position of the rotor theta ^~ are calculated.

In 2-phase / 3-phase conversion correction calculation 27, by correction according to the estimated speed omega ^~ for the estimated position theta ^~ of the rotor is applied, the estimated positions theta ₂₃ ^~ of the rotor in the next clock cycle is calculated The

By the above computations, the estimated position theta ^~ of the ^rotor, the estimated position theta ₂₃ ^~ of the rotor in the estimated speed omega ^~ and the next clock cycle is calculated.

(3) Advantages and disadvantages of sensorless vector control As shown in FIG. 6, the advantage of sensorless vector control is that for the same motor output current (that is, a certain inverter whose switching element capacity is set to a certain value). The output torque is large. The sensorless vector control capable of independently controlling the q-axis current i _q and the d-axis current i _d can output a larger output torque than other control methods. In addition, the sensor-less vector control, it is possible to perform field weakening control by controlling the d-axis current i _d. The field weakening control enables the brushless DC motor 5 to operate at high speed.

  However, due to the limitation of the voltage supplied to the brushless DC motor 5, it is inevitable that a certain upper limit is imposed on the rotational speed of the brushless DC motor 5 even with field weakening control. V / f control, which will be described later, is used to increase the upper limit of the rotational speed of the brushless DC motor 5.

4). V / f control V / f control generates an angular frequency command ω _f ^* of a three-phase AC voltage to be supplied to the brushless DC motor 5 from the armature current of the brushless DC motor 5. The γ-axis voltage v _γ of the three-phase AC voltage supplied to the
^{_{v γ = Λ δ * × ω}} f * -V ofsγ, ··· (1)
Is generated so that In Expression (1), Λ _δ ^* is a counter electromotive voltage coefficient of the brushless DC motor 5, and V _ofsγ is an offset voltage. If the offset voltage V _ofsγ is ignored, v _γ / f ^* becomes a constant value Λ _δ ^* for the angular frequency command f ^* (= ω _f ^* / 2π) and the γ-axis voltage v _γ . As known to those skilled in the art, the γ-δ coordinate system defines the γ axis in the direction of the rotating magnetic flux generated by the armature and the δ axis in the direction perpendicular to the γ axis at 90 °. Coordinate system.

  As shown in FIG. 5, the V / f control includes A / D conversion 31, 3-phase / 2-phase conversion 32, angular frequency / position command generation calculation 33, voltage command generation calculation 34, 2-phase / 3-phase. A conversion 35, a PWM calculation 36, and an A / D conversion 37 are included. While the V / f control is performed, the operation shown in FIG. 5 is performed every clock cycle of the system clock in the MPU 8.

In the A / D conversion 31, the output signals output from the current measuring devices 6u, 6v, 6w are A / D converted, and u-phase current i _u , v-phase current i _v , and w-phase current i _w (or of these) Are taken into the MPU 8.

In the three-phase / two-phase conversion 32, the MPU 8 performs the u-phase current i _u , the v-phase current i _v , and the w-phase current i _w (or two of them) acquired by the A / D conversion 31. The three-phase / two-phase conversion is performed using the rotor position command θ ^* calculated in the previous clock cycle, and the γ-axis current and the δ-axis current are calculated. Note that the position command θ ^* is described in the γ-δ coordinate system.

In the angular frequency / position command generation calculation 33, the angular frequency command ω _f ^{* of the} three-phase AC voltage supplied to the brushless DC motor 5 and the rotor position command θ ^* are calculated from the speed command ω ^* and the γ-axis current. The

The angular frequency command ω _f ^* is given by the following formula:
ω _f ^* = ω ^* −k _ω × i _γ , (2a)
Is calculated using _kω is a positive constant. According to the equation (2), when the γ-axis current i _γ increases, that is, when the output torque increases, the angular frequency command ω _f ^* decreases, and when the γ-axis current i _γ decreases, that is, when the output torque decreases. The angular frequency command ω _f ^* increases. By using equation (2), when the output torque is increased it is prevented from stalling by reducing the angular frequency command omega _f ^*, when the output torque is decreased, increasing the angular frequency command omega _f ^* By doing so, the rotor is controlled not to accelerate.
On the other hand, the position command θ ^* is calculated by integrating the speed command ω ^* . That is,
θ ^* = ∫ω ^* dt. ... (2b)

In the voltage command generation calculation 34, the following formula:
^{_{v γ = Λ δ * × ω}} f * -V ofsγ, ··· (3a)
v _δ = −K _δ × i _δ , (3b)
Thus, the γ-axis voltage v _γ and the δ-axis voltage v _δ are calculated. As described above, Λ _δ ^* is a counter electromotive voltage coefficient of the brushless DC motor 5, and V _ofsγ is an offset voltage. K _d is a positive constant. Expression (3a) is a basic expression for V / f control.

In the two-phase / three-phase conversion 35, the two-phase / three-phase conversion is performed on the determined γ-axis voltage v _γ and δ-axis voltage v _δ and u of the three-phase drive voltage to be supplied to the brushless DC motor 5 is obtained. A phase voltage v _u , a v phase voltage v _v , and a w phase voltage v _w are calculated. In this two-phase / three-phase conversion, the rotor position command θ ^* is used.

In the PWM calculation 36, a PWM signal that controls the inverter 3 so that the three-phase drive voltage having the calculated u-phase voltage v _u , v-phase voltage v _v , and w-phase voltage v _w is supplied to the brushless DC motor 5. S _PWM is generated. For generation of the PWM signal S _PWM , the magnitude of the DC voltage _VDC supplied from the AC-DC converter 2 to the inverter 3 is referred to. DC voltage _{V DC} is obtained A / D conversion 37 for the voltage notification signal output from the voltage detection circuit 9 is performed, PWM signal _{S PWM} is generated by referring to the DC voltage _{V DC.} A switching transistor of the inverter 3 are turned on or off in response to the generated PWM signal S _PWM.

Referring to FIG. 6, the advantage of V / f control is that brushless DC motor 5 can be operated at high speed. The angular frequency command ω _f ^* is determined in response to the γ-axis current, that is, in response to the output torque, and the γ-axis voltage is determined from the angular frequency command ω _f ^{* according} to the equation (3a), so that the high-speed region The rotational speed of the rotor at is stabilized. In addition, the rotor position estimate theta ^~ and estimated speed omega ^~ a V / f control is not performed using the motor model, the calculation amount is small, is suitable for the control during high speed operation.

Switching of the third control method Outline of switching of control method In order to take advantage of each of the above-described open loop control, equi-width PWM control, sensorless vector control, and V / f control, the control method is switched according to the speed command ω ^* .

FIG. 7A shows a preferred control method switching method. When the brushless DC motor 5 is started, first, a small speed command ω ^* is given to the MPU 8, and then the speed command ω ^* is increased. As the speed command ω ^* increases, the rotational speed of the rotor also increases. The open loop control is performed until the speed command ω ^* exceeds the rotational speed ω _s1 .

When the speed command ω ^* is increased and exceeds the rotational speed ω _s1 , the control method is switched to the equal width PWM control. As described above, the equal width PWM control is suitable for sensorless control at a low speed for a load having a large torque pulsation.

When the speed command ω ^* is further increased and exceeds the rotational speed ω _s2 , the control method is switched from the equal width PWM control to the sensorless vector control. The steady operation of the brushless DC motor 5 is performed by sensorless vector control. By executing the sensorless vector control, the brushless DC motor 5 can be operated with a high output torque.

When the speed command ω ^* is further increased and exceeds the rotational speed ω _s3 , the control method is switched from sensorless vector control to V / f control. As described above, the V / f control is suitable for high-speed operation of the brushless DC motor 5.

When the brushless DC motor 5 is operated under V / f control, if the speed command ω ^* decreases and becomes smaller than the rotational speed ω _s4 (<ω _s3 ), the control method is returned to sensorless vector control. It is useful for preventing hunting that the rotational speed ω _s4 that is switched from V / f control to sensorless vector control is smaller than the rotational speed ω _s3 that is switched from sensorless vector control to V / f control. . Since the rotational speed ω _s4 is smaller than the rotational speed ω _s3, it is possible to prevent the control method from being frequently switched between the sensorless vector control and the V / f control.

If the speed command ω ^* decreases when the brushless DC motor 5 is operated by sensorless vector control, the control method can be maintained as sensorless vector control as shown in FIG. 7A. is there. Instead, as shown in FIG. 7B, when the speed command ω ^* decreases and becomes smaller than the rotational speed ω _s5 (<ω _s2 ), the control method may be switched to the equal width PWM control. Is possible. Maintaining the control method as sensorless vector control even when the speed command ω ^* is small is effective for suppressing the number of switching of the control method. On the other hand, the fact that the control method is switched to the equal width PWM control in response to the decrease in the speed command ω ^* is effective in improving the stability of operation during low-speed operation. It is useful for preventing hunting that the rotational speed ω _{s5 at which} the control method is switched from the sensorless vector control to the equal width PWM control is smaller than the rotational speed ω _{s2 at} which the control method is switched from the constant width PWM control to the sensorless vector control. .

  In order to more suitably switch the control method, the switching between the sensorless vector control and the V / f control is preferably performed according to the procedure described below.

2. Switching from sensorless vector control to V / f control One of the requirements that must be satisfied when the control method is switched from sensorless vector control to V / f control requires torque that cannot be output by V / f control. In some cases, the control method must be maintained with sensorless vector control. Torque that can be output by V / f control is smaller than that of sensorless vector control. Therefore, when the required torque cannot be output in the V / f control, the speed command ω ^* must be reduced without switching to the V / f control.

Conversely, if the required torque is not large but the desired rotational speed cannot be obtained with sensorless vector control, it is preferable to switch to V / f control and increase the speed command ω ^*. is there.

FIG. 8 is a flowchart showing a process of switching the control method to V / f control, which is preferable for satisfying these requirements. While the sensorless vector control is being performed, the MPU 8 determines whether the speed command ω ^* is greater than the rotational speed ω _s3 (step S01).

When the speed command ω ^* is greater than the rotational speed ω _s3 , the MPU 8 determines whether the requested torque is a torque that can be output by V / f control (step S02). More specifically, MPU 8 obtains the output torque T from the q-axis current i _q, determines whether the output torque T is larger than a predetermined reference torque. The reference torque is determined as the maximum torque that can be output by the V / f control, or a torque slightly smaller than that. If the output torque is greater than the predetermined reference torque, the speed command ω ^* that has been increased from the rotational speed ω _s3 is decreased and returned to the rotational speed ω _s3 (step S03), and sensorless vector control is continued ( Step S04). When the output torque T is smaller than the predetermined reference torque, the MPU 8 switches the control method to V / f control (step S05).

If it is determined in step S01 that the speed command ω ^* is smaller than the rotational speed ω _s3 , the MPU 8 determines the speed command ω ^* as the estimated speed ω ^~ calculated by the speed / position estimation calculation 13 (see FIG. 3) described above. (Step S06). Specifically, MPU 8, the difference between the speed command omega ^* and the estimated speed omega and ^~ is larger states than the predetermined reference value [Delta] [omega _TH, it is determined whether or not continued for a predetermined period of time Δt or more. When the state continues for the period Δt or longer, the MPU 8 determines whether the torque command value T ^* obtained from the q-axis current i _q is larger than a predetermined reference torque (step S07). If the torque command value T ^* is greater than a predetermined reference torque, the difference in the speed command omega ^* and the estimated speed omega and ^~ is due to overload. In this case, sensorless vector control is continued (step S04). On the other hand, when the torque command value T ^* is smaller than a predetermined reference torque, the difference in the speed command omega ^* and the estimated speed omega and ^~ is not overloaded, the speed command omega ^* is due to being too small . In this case, it is determined again so that the speed command ω ^* is increased (step S08), and the control method is switched to V / f control (step S05).

The control method is switched to V / f control by the above processing, or is maintained in the sensorless vector control, so that control is performed according to the torque to be output from the brushless DC motor 5 and the appropriateness of the speed command ω ^*. The method is switched.

The method is another request to be satisfied when switched to V / f control from the sensor-less vector control, the rotor is calculated in the rotor of the estimated position theta ^~ and, V / f control calculated in sensorless vector control This is to maintain consistency with the position command θ ^* . As described above, the estimated position theta ^~ is calculated by d-q coordinate system, the position command theta ^* is to be calculated by the gamma-[delta] coordinate system, the estimated position theta ^~ and position command theta ^* is usually It does not match. Therefore, it is not desirable that the estimated position θ ^~ is used as it is as the initial position command θ ^* of the V / f control after switching to the V / f control because it causes the rotation of the rotor to become unstable.

In order to maintain consistency between the estimated rotor position θ ^~ calculated in sensorless vector control and the rotor position command θ ^* calculated in V / f control, the estimated position θ ^~ was corrected and corrected. estimated position theta ^~ is used as a position command theta ^* initial value of V / f control. In the first clock cycle immediately after switching to V / f control, the γ-axis current and the δ-axis current are calculated using the initial value of the position command θ ^* . Most simply, the following formula:
θ _ini ^* = θ ^to + Δθ, (4)
Can be used to correct the estimated position θ ^to calculate the initial value θ _ini ^* of the position command. Δθ is a constant correction angle. More preferably, the initial value θ _ini ^* of the position command for V / f control is determined according to the q-axis current i _q .
θ _ini ^* = θ ^to + k _q · i _q , (5)
Is calculated by k _q is a constant. The determination of the initial value θ _ini ^* of the position command for V / f control in this way improves the stability of the rotor rotation when the control method is switched from sensorless vector control to V / f control. .

3. Switching from V / f control to sensorless vector control One of the requirements to be satisfied when the control method is switched from V / f control to sensorless vector control is that the rotational speed of the rotor is controlled by field-weakening control of sensorless vector control. It is within the achievable speed range. What is important here is that the speed range in which the field-weakening control can be realized is the amplitude of the three-phase drive voltage supplied from the inverter 3 to the brushless DC motor 5, that is, the DC voltage V supplied from the AC-DC converter 2 to the inverter 3. It depends on _DC . The higher the three-phase drive voltage supplied to the brushless DC motor 5, that is, the DC voltage _VDC , the higher the speed range in which field-weakening control can be realized. Therefore, the rotational speed of the rotor that can be switched to the sensorless vector control as the control method is higher as the DC voltage _VDC is higher. Therefore, it is preferable that the lower limit value of the rotor operation command ω ^* that is switched from the V / f control to the sensorless vector control is determined to be higher as the DC voltage _VDC is higher.

FIG. 9 is a flowchart showing an example of a process for switching the control method to sensorless vector control in order to satisfy the above requirements.
If the speed command ω ^* is equal to or greater than the rotational speed ω _s4 ⁽¹⁾ (step S11), V / f control suitable for high-speed operation is continued unconditionally (step S12). Note that the rotational speed ω _s4 ⁽¹⁾ is smaller than the rotational speed ω _{s3 at} which the control method is switched from sensorless vector control to V / f control.

When the speed command ω ^* is smaller than the rotational speed ω _s4 ^{(1) and} larger than the rotational speed ω _s4 ⁽²⁾ (> ω _s4 ⁽¹⁾ ) (steps S11 and 13), the MPU 8 It is determined whether or not the supplied DC voltage V _DC is smaller than the first threshold voltage V _TH ⁽¹⁾ (step S14). If the DC voltage V _DC is equal to or higher than the first threshold voltage V _TH ⁽¹⁾ , the MPU 8 switches the control method to sensorless vector control (step S15). Otherwise, the MPU 8 maintains the control method as V / f control (step S12).

On the other hand, when the speed command ω ^* is equal to or lower than the rotational speed ω _s4 ⁽²⁾ and larger than the rotational speed ω _s4 ⁽³⁾ (steps S11, S13, S16), the MPU 8 is connected to the inverter 3 by the direct current. It is determined whether or not the voltage V _DC is smaller than the second threshold voltage V _TH ⁽²⁾ (<V _TH ⁽¹⁾ ) (step S14). If the DC voltage V _DC is equal to or higher than the second threshold voltage V _TH ⁽²⁾ , the MPU 8 switches the control method to sensorless vector control (step S15). Otherwise, the MPU 8 maintains the control method as V / f control (step S12).

When the speed command ω ^* is equal to or less than the rotational speed ω _s4 ⁽³⁾ (steps S11, S13, S16), the MPU 8 switches the control method to sensorless vector control regardless of the DC voltage _VDC .

Similarly to when switching from sensorless vector control to V / f control, when the control method is switched from V / f control to sensorless vector control, the rotor position command θ ^* calculated in V / f control and the sensorless it is desirable that consistency with the estimated position theta ^~ of the rotor is calculated in the vector control is maintained. To satisfy this requirement, the corrected position command theta ^{*, *} corrected estimated command theta is used as the estimated position theta initial value of ^~ sensorless vector control. In the first clock cycle immediately after switched to sensorless vector control, q-axis current and d-axis current is calculated using the initial value of ^~ theta its estimated position.
Most simply, the following formula:
θ _ini ^〜 = θ ^* −Δθ, (6)
The initial value theta _ini ^~ the estimated position of the sensor-less vector control position command theta ^* is corrected by using a can be calculated. Δθ is a constant correction angle. More preferably, the initial value theta _ini ^~ estimated position theta ^~ sensorless vector control in accordance with the gamma-axis current i _gamma,
θ _ini ^〜 = θ ^* −k _γ · i _γ , (7)
Is calculated by Thus the initial value theta _ini ^~ the estimated position of the sensor-less vector control is determined, when the control method is switched from V / f control in sensorless vector control, to improve the stability of the rotation of the rotor.

FIG. 1 is a block diagram showing a brushless DC motor system according to an embodiment of the present invention. FIG. 2A shows a waveform of a three-phase drive voltage supplied to the brushless DC motor when the equal width PWM control is performed. FIG. 2B shows a waveform of a three-phase drive voltage supplied to the brushless DC motor when sensorless vector control and V / f control are performed. FIG. 3 is a block diagram showing calculations performed in sensorless vector control. FIG. 4 is a block diagram showing calculations performed for speed / position estimation. FIG. 5 is a block diagram showing a calculation performed in the V / f control. FIG. 6 is a graph showing the dependency of the output torque of the equal width PWM control, sensorless vector control, and V / f control on the rotation speed. FIG. 7A is a graph showing a control method switching method. FIG. 7B is a graph showing another switching method of the control method. FIG. 8 is a flowchart showing a procedure for switching the control method from sensorless vector control to V / f control. FIG. 9 is a flowchart showing a procedure for switching the control method from V / f control to sensorless vector control.

Explanation of symbols

1: AC power supply 2: AC-DC converter 3: Inverter 4u, 4v, 4w: u-phase power supply line, v-phase power supply line, w-phase power supply line 5: brushless DC motor 6: current sensor 7: power supply detection circuit 8: MPU

Claims (9)

A brushless DC motor having a rotor with a field and a stator with an armature;
An inverter,
A current sensor for detecting an armature current supplied from the inverter to the armature;
In response to a speed command for instructing the rotational speed of the rotor of the brushless DC motor, one of control method groups including sensorless vector control and V / f control is selected as a selection control method, and the selection control is performed. And a controller for generating a PWM signal in response to the armature current in accordance with the method,
The inverter drives the brushless DC motor in response to the PWM signal;
The control device selects the sensorless vector control as the selection control method when the speed command is in the first speed range, and increases the first threshold speed by increasing the speed command from the first speed range. A brushless DC motor system which switches the selection control method from the sensorless vector control to the V / f control in response to exceeding. The brushless DC motor system according to claim 1,
The control device, when the sensorless vector control is selected as the selection control method,
(A) calculating an estimated speed of the rotor and an estimated position of the rotor from the armature current;
(B) generating a q-axis current command value and a d-axis current command value from the difference between the speed command and the estimated speed;
(C) calculating a q-axis current and a d-axis current of the armature current from the estimated position of the rotor and the armature current;
(D) From the difference between the q-axis current command value and the q-axis current, and the difference between the d-axis current command value and the d-axis current, a three-phase AC voltage supplied to the brushless DC motor by the inverter calculating a q-axis voltage and a d-axis voltage;
(E) programmed to execute the step of generating the PWM signal from the q-axis voltage and the d-axis voltage;
The control device, when the V / f control is selected as the selection control method,
(F) calculating a γ-axis current and a δ-axis current from the armature current;
(G) generating a frequency command ω _f ^* of a three-phase AC voltage supplied from the inverter to the brushless DC motor from the rotor speed command and the γ-axis current;
(H) The following equation expressed using the back electromotive force coefficient Λ _d ^{* of the} brushless DC motor and the offset voltage V _ofsq :
v _q = Λ _d ^* · ω _f ^* −V _ofsq ,
To calculate a γ-axis voltage v _γ of a three-phase AC voltage supplied from the inverter to the brushless DC motor from the frequency command ω _f ^* ,
(I) calculating a δ-axis voltage of the three-phase AC voltage from the δ-axis current;
(J) Brushless programmed to execute the step of generating the PWM signal from the γ-axis voltage calculated in step (h) and the δ-axis voltage calculated in step (i) DC motor system. The brushless DC motor system according to claim 2,
The control device may generate the d-axis current command value so that field weakening control is performed in response to the estimated speed and the speed command when the sensorless vector control is selected as the selection control method. Brushless DC motor system programmed into. The brushless DC motor system according to claim 3,
The selection control method is not switched from the sensorless vector control to the V / f control when the output torque of the brushless DC motor is larger than a predetermined reference torque. Brushless DC motor system. The brushless DC motor system according to claim 1,
The control device selects the V / f control as the selection control method when the speed command of the brushless DC motor is in the second speed region, and the speed command decreases from the second speed region. In response to becoming smaller than the second threshold speed, the selection control method is switched from the V / f control to the sensorless vector control,
The brushless DC motor system, wherein the second threshold speed is smaller than the first threshold speed. The brushless DC motor system according to claim 5,
The inverter receives a DC voltage, drives the brushless DC motor using the received DC voltage,
Switching from the V / f control to the sensorless vector control is performed in response to the DC voltage brushless DC motor system. The brushless DC motor system according to claim 1,
When the speed command of the brushless DC motor is in a third speed range lower than the first speed range, the control device has a non-energized section and has a substantially equal pulse width. A brushless DC motor system that generates the PWM signal so that a drive voltage having a waveform composed of pulses is supplied from the inverter to the brushless DC motor. A brushless DC motor driving method for driving a brushless DC motor using an inverter,
(A) detecting an armature current supplied from the inverter to the armature of the brushless DC motor;
(B) A step of selecting one of a group of control methods including sensorless vector control and V / f control as a selection control method in response to a speed command instructing the rotation speed of the rotor of the brushless DC motor. When,
(C) generating a PWM signal according to the selection control method and in response to the armature current;
And (D) causing the inverter to drive the brushless DC motor in response to the PWM signal. The brushless DC motor driving method according to claim 8,
When the sensorless vector control is selected as the selection control method, the following steps (E) to (I):
(E) calculating an estimated speed of the rotor and an estimated position of the rotor from the armature current;
(F) generating a q-axis current command value and a d-axis current command value from the difference between the speed command and the estimated speed;
(G) calculating a q-axis current and a d-axis current of the armature current from the estimated position of the rotor and the armature current;
(H) From the difference between the q-axis current command value and the q-axis current, and the difference between the d-axis current command value and the d-axis current, the inverter supplies a three-phase AC voltage to the brushless DC motor. calculating a q-axis voltage and a d-axis voltage;
(I) The step of generating the PWM signal from the q-axis voltage and the d-axis voltage is performed,
When the V / f control is selected as the selection control method, the following steps (J) to (N):
(J) calculating a γ-axis current and a δ-axis current from the armature current;
(K) generating a frequency command ω _f ^* of a three-phase AC voltage supplied from the inverter to the brushless DC motor from the rotor speed command and the γ-axis current;
(L) The following formula expressed using the back electromotive force coefficient Λ _d ^{* of the} brushless DC motor and the offset voltage V _ofsq :
v _q = Λ _d ^* · ω _f ^* −V _ofsq ,
To calculate a γ-axis voltage v _γ of a three-phase AC voltage supplied from the inverter to the brushless DC motor from the frequency command ω _f ^* ,
(M) calculating a δ-axis voltage of the three-phase AC voltage from the δ-axis current;
(N) A brushless DC motor driving method in which a step of generating the PWM signal is performed from the γ-axis voltage calculated in the (L) step and the δ-axis voltage calculated in the (M) step.

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