JP3362337B2 - Brushless DC motor drive controller - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless DC motor drive control device for driving and controlling a brushless DC motor using a rectangular wave.

[0002]

2. Description of the Related Art For example, a brushless DC motor used as a drive source for an automobile power steering apparatus is a motor having three or more excitation phases, and its drive is performed by a rectangular wave excitation current.

In the case of a five-phase brushless DC motor, the motor drive circuit (motor drive control device) is arranged so as to surround the outer peripheral surface of the motor rotor (rotor) at an electrical angle of 72 degrees. With respect to the exciting coils a to e of phases (hereinafter, referred to as a phase to e phase), the coils are sequentially phase-by-phase by a 4-phase excitation method in which four phases are simultaneously excited under the control of a control circuit such as a microcomputer. It is switched and excited by a rectangular wave current, and the rotor is driven to rotate.

In this four-phase excitation method, the motor current flows in four of the five phases, but in order to flow the current in a well-balanced manner in each phase, the resistance of each excitation coil should be equal. Has been formed. In the four-phase excitation method of the five-phase brushless DC motor, a phase in which no motor current flows among the five phases is called an “OFF phase”. In a normal rectangular wave drive for a brushless DC motor, "High
Of the pulse width modulation (PWM) consisting of "h" and "Low", the phase that makes the pulse "Low" and the current value becomes zero is "O".
FF phase ”.

FIG. 7 is a characteristic diagram showing a phase current waveform and a torque waveform of each exciting coil in the conventional five-phase brushless DC motor drive control device. As shown in this figure, in the conventional 5-phase brushless DC motor drive control device,
The energization period of the FF phase ends until the next commutation starts. The OFF-phase energization period is a period in which a PWM signal is applied to the OFF-phase after commutation.

[0006]

However, in the conventional brushless DC motor drive controller, although the energization period in the OFF phase pulse width modulation (PWM) drive ends until the next commutation starts, When the rotation speed is low (when the time between two commutations is long), the current in the OFF phase is already in the intermittent current mode in PWM drive by the time the next commutation starts, and this residual current in the OFF phase is It approaches zero, but it does not. The intermittent current mode is a phenomenon in which the current does not have a continuous waveform. OF
Unless the F-phase energization is completely terminated, the residual current continues to flow, and the electromagnetic torque generated by the residual current has the effect of reducing the electromagnetic torque of the entire motor.

Therefore, when the next commutation starts, a step of the torque waveform as shown in FIG. 6 occurs at the place where the torque waveform should have been originally connected. In particular, when the torque constant of the motor is large and the residual current is also large, the step of the torque is large, and the effect of the step may not be negligible.

The difference in torque causes vibration and noise when the motor rotates. Further, in the case of a brushless DC motor for a power steering device, when the steering wheel is slowly rotated, the difference in torque affects the steering feeling and causes noise.

The present invention has been made under the circumstances as described above, and an object of the present invention is to suppress stepwise torque fluctuations when driving and controlling a brushless DC motor using a rectangular wave. (EN) Provided is a brushless DC motor drive control device.

[0010]

The present invention is a brushless D
The present invention relates to a brushless DC motor drive control device that controls the rate of change of the current in the commutation phase so that the total value of the commutation phase current in the excitation coil of the C motor does not change. the residual current of the OFF phases in the Nagaresho to zero, before the said excitation coil
It supplies the driving current by pulse width modulation of the serial OFF phase
Between conductible period, current of the OFF phase has reached the residual current
By limiting the time, the residual current is cut off,
The energization period ends when the OFF-phase current reaches zero.
It is achieved by Changing the PWM signal applied to the OFF phase to Low is to limit the energization period of the OFF phase.

[0011]

Further, the above object of the present invention is that the time from the start of commutation until the current in the OFF phase reaches the residual current is equal to the electrical time constant and resistance value of the equivalent circuit in the OFF phase. a PWM duty ratio applied to the OFF phase during flow, the motor counter electromotive voltage of the brushless DC motor,
The power supply voltage D for the circuit for pulse width modulation
And C line voltage, the initial current value at the time of the commutation, is calculated based on, at the time when the time has elapsed, the OFF phase
This is achieved more effectively by allowing the current to be cut off .

According to the brushless DC motor drive controller of the present invention as described above, when the rotation speed of the brushless DC motor is low, the PWM is switched to the OFF phase in the commutation phase.
The period (energization period) for supplying the drive current can be terminated when the current in the OFF phase reaches zero, whereby the residual current in the OFF phase generated during the previous commutation at the next commutation position can be eliminated. Since it can be zero, it is possible to suppress the occurrence of a step in the torque waveform of the brushless DC motor. Here, when the current of the OFF phase reaches zero, the electrical time constant and resistance value of the equivalent circuit of the OFF phase, the PWM duty ratio applied to the OFF phase at the time of commutation, and the motor reverse of the brushless DC motor. Electromotive force,
The power supply voltage D for the circuit for pulse width modulation
It can be determined based on the C line voltage and the initial current value during commutation.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

In this embodiment, five-phase brushless DC
A motor drive control device will be described as an example. The present invention is
It can be implemented for a multi-phase excitation brushless DC motor, and can be similarly implemented for a three-phase brushless DC motor. Further, there are some means for detecting that the OFF-phase current has reached zero, but in the present embodiment, prediction is made on a "model basis" described later.

FIG. 6 is a circuit diagram showing an outline of the brushless DC motor drive controller of this embodiment.

As shown in FIG. 6, the motor drive control device 20 comprises a control circuit 21, an FET gate drive circuit 22, a motor drive circuit 23, a current detection circuit 24 and a rotor position detection circuit 25.

The control circuit 21 is composed of, for example, a microcomputer and is supplied with a constant voltage from a constant voltage source 26. The control circuit 21 receives the current command Ire from the external circuit 27.
f is input, the motor current detection value I is output from the current detection circuit 24, and the rotor position signal Sa-e is input from the rotor position detection circuit 25.
(= Sa, ..., Se) are input respectively. The control circuit 21 controls the drive current supplied from the motor drive circuit 23 to the coil circuit 12 of the motor based on these input signals.

When the above-mentioned five-phase brushless motor is used as a drive source for the electric power steering device, the external circuit 27 generates a pulse signal corresponding to the rotation speed of the output shaft of the transmission of the vehicle. Referring to a characteristic diagram from a vehicle speed detection value V obtained from the output of the sensor and a detection value T including the direction of the torque obtained from the output of the torque sensor for detecting the steering torque applied to the input shaft of the steering wheel. To retrieve a corresponding motor current value and output it as a current command value signal Iref. This can be configured by a circuit such as a CPU that executes the above operation. Instead of this circuit, each output of the vehicle speed sensor and the torque sensor is input to the control circuit 21, and the current command Iref is generated here. It may be configured as follows.

The motor drive circuit 23 comprises five on the power supply side (upper side) and five on the ground side (lower side) for a total of one.
0 transistors (field effect transistor FET) Ta
It is composed of 1 to Te1 and Ta2 to Te2. These ten transistors Ta1 to Te1 and Ta2 to Te2 have corresponding transistors connected in series on the upper side and the lower side, and these transistor pairs (Ta1-Ta2, Tb1-Tb2, Tc1-Tc2, T1) connected in series.
The upper side terminals of d1−Td2 and Te1−Te2) are the control circuit 21.
In addition, the lower terminal is connected to the current detection circuit 24, and the connection part of each transistor pair is connected to the outer ends of the exciting coils 6a to 6e (the side opposite to the center side of the star connection). There is. The gate voltage of each of the transistors Ta1 to Te2 is controlled by the control circuit 21 based on the detection signal Sa-e from the rotor position detection circuit 25.

The control circuit 21 outputs corresponding gate signals Ga1 to Ge2 to the FET gate drive circuit 22 based on a predetermined gate setting table for the combination of the detection signals Sa-e sent from the rotor position detection circuit 25. Send to. Also,
The control circuit 21 generates a motor driving voltage command signal by current control based on the above-mentioned input signal, and based on this voltage command signal, pulse width modulation (Pulse Width Modula).
signal) and a gate drive signal G1-10 (= Ga1 to Ge2) are generated and supplied to the FET gate drive circuit 22.

<Description of Residual Current in OFF Phase> The duty ratio (Duty ₂ ) of the PWM signal for the OFF phase (for example, the d phase in FIG. 4) is expressed by the following mathematical expression 1.

[0023]

[Formula 1] Duty2 = 0.5 + Km · ω / 2Vb Here, Km is a constant of the motor [volt · sec], and ω
Is the rotational angular velocity of the motor, and Vb is the power supply voltage applied to the excitation coil of the motor.

Here, when the rotation speed of the motor is slow,
Since Km · ω / 2Vb≈0, the duty ratio Duty2
≈0.5 = 50%.

FIG. 1 shows the PWM-of the OFF phase exciting coil.
It is a circuit diagram which shows the equivalent circuit at the time of ON. Figure 2
[Fig. 6] is a circuit diagram showing an equivalent circuit at the time of PWM-OFF of an OFF-phase exciting coil. The voltage Vn at the center connection point (confluence point of each phase) of the exciting coils of each phase is approximately 0.
It becomes 5Vb.

For example, when the duty ratio (Duty ₂ ) in the PWM of the OFF phase is 50%, the DC line voltage Vb and zero are alternately applied to the terminal d of the OFF phase exciting coil. According to the equivalent circuits shown in FIGS. 1 and 2, when the rotational angular velocity ω of the motor is about zero and the voltage applied to the OFF-phase exciting coil is Vd−Vn, the current id flowing in the OFF-phase exciting coil Is as shown in FIG.

As shown in FIG. 3, the average value of the voltage (Vd-Vn) applied to the OFF phase is zero, but the average value of the current id flowing in the OFF phase exciting coil is not zero. The magnitude of the average value of the OFF phase current id (average value of the residual current) is determined by the duty ratio (Du
ty ₂ ), the resistance value in the equivalent circuit of the OFF phase exciting coil, the electrical time constant of the OFF phase exciting coil, and OF
It is related to the back electromotive voltage of the F-phase exciting coil and the DC line voltage which is the power supply voltage for the circuit for pulse width modulation.

<Generation of torque step due to residual current> FIG.
Is a characteristic showing the phase current waveform and torque waveform of each exciting coil when the average value of the current id flowing in the OFF-phase exciting coil (average value of the residual current) is zero, that is, when the residual current is ignored. It is a figure. In this case, the torque waveform is continuous even at the commutation position.

FIG. 7 shows the phase current waveform and the torque waveform of each exciting coil when the residual current is taken into consideration. In this case, the residual current causes a step difference in the torque waveform at the commutation position.

<Estimation of Time when OFF-Phase Current Reaches Zero> At the time of commutation of the brushless DC motor (for example, at the time of commutation of the phase current id => ia passing through the upper FET of FIG. 6, ia indicates the A-phase current.), the OFF-phase current id
Is connected to the ground of the DC line voltage Vb through a diode, and the center point voltage of the Y connection is Vn (≒ 1/2 * V
b), the back electromotive force of the coil is Ed. When the PWM cycle is sufficiently smaller than the electrical time constant of the equivalent circuit of the OFF phase coil, the voltage V applied to the terminals of the OFF phase coil
d can be approximately expressed by the following mathematical expression 2.

[0031]

[Equation 2] Vd = Vb * Duty2 Therefore, when the PWM cycle is sufficiently smaller than the time constant of the equivalent circuit of the OFF-phase coil, the equivalent circuit of the OFF-phase exciting coil is the equivalent circuit of the OFF-phase PWM-ON. It can be represented by an equivalent circuit shown in FIG. 5, which is a combination of FIG. 1 and FIG. 2 which is an equivalent circuit at the time of PWM-OFF.

Therefore, the total of the voltage Voff applied to the OFF phase exciting coil is as shown in the following expression 3.

[0033]

## EQU3 ## Voff = Vd-Vn-Ed The equation showing the voltage Voff of the exciting coil in the OFF phase can be expressed by the following equation 4. OFF phase exciting coil current id
(T) can be expressed by the following equation 5.

[0034]

## EQU00004 ## Voff = Vd-Vn-Ed = Lm * (did / d
t) ＋ id ＊ R

[Equation 5] Here, the initial current id (0) at the start of commutation in the OFF phase exciting coil is Idc / 2, and the electrical time constant of the OFF phase exciting coil is T = Lm / R.

Equivalent voltage V of the OFF phase exciting coil described above
By the resistance of the equivalent circuit of the off and OFF phase exciting coils,
The coil current id drops to Idc / 2 => 0 [A]. Here, Idc is the total value of the exciting current of the motor.

However, Vd = Vb * Duty2, Vn =
0.5Vb, Ed = Km * ω / 2. The current id (t) of the OFF phase excitation coil is id (0) = Idc / 2
The time required to go from id to id (t1) ≈0 is O
Electrical time constant T and resistance R of the equivalent circuit of the FF phase exciting coil, and PWM applied to the OFF phase exciting coil during commutation
It is determined by the duty Duty2, the motor back electromotive force Ed, the DC line voltage Vb, the initial current value id (0) during commutation, and the like.

Here, the duty ratio of the PWM signal (Duty
According to the above equation 1 representing ₂ ), Duty ₂ = 0.5 + Km
In the case of ω / 2Vb, the voltage applied to the coil terminal d is Vd = 0.5 · Vb + Km · ω / 2. Therefore, the voltage Voff applied to the OFF phase exciting coil is 0.
It becomes [V], and the current id (t) of the OFF phase exciting coil
Becomes as shown in the following Expression 6.

[0038]

[Equation 6] Here, initial current id (0) = Idc / 2, electrical time constant T = Lm / R.

According to the above equation 6, the current id (t) of the OFF-phase exciting coil is the initial current id when commutation starts.
The time required to decrease to n [%] of (0) is
It is calculated by the following formula 7.

[0040]

T = −T * ln (n%) For example, the time required to reduce the initial current id (0) of the exciting coil in the OFF phase at the start of commutation to 5% is the OFF phase. Electrical circuit of the equivalent circuit (T = Lm /
R) is about 3 times.

<Limit of OFF-phase energization period> When the rotation speed of the brushless DC motor is slow, the OFF-phase exciting coil is driven by PWM after the commutation starts, and the OFF-phase is turned off before the next commutation starts. Completely cut off the PWM current supply to the phase. That is, the electrical time constant T and resistance R of the equivalent circuit of the OFF-phase exciting coil and the duty ratio Duty2 in PWM applied to the OFF-phase exciting coil during commutation.
, Motor back electromotive force Ed, DC line voltage Vb, O
Based on the initial current id (0) when commutation starts in the FF-phase exciting coil, the OFF-phase exciting coil is set to P
The energization period, which is the period for driving by WM, is determined, and the PWM current supply to the OFF phase is completely turned off except the energization period.
FF.

As a result, the residual current of the OFF-phase exciting coil becomes 0 [A], and the torque waveform of the brushless DC motor becomes a continuous waveform without steps as shown in FIG. Therefore, according to the brushless DC motor drive control device of the present embodiment, since the stepwise fluctuation of the torque does not occur even when the rotation speed is low, the vibration and noise during the rotation of the motor are reduced more than those of the conventional brushless DC motor drive control device. It can be reduced.

[0043]

As described above, according to the present invention, OFF in the commutation phase in the exciting coil of the brushless DC motor is turned off.
Since the period (energization period) for supplying the drive current by pulse width modulation (PWM) to the OFF phase is limited so that the residual current of the phase becomes zero, the residual current of the OFF phase can be suppressed to zero. As a result, it is possible to provide a brushless DC motor drive control device capable of suppressing stepwise fluctuations in torque.

Further, when the brushless DC motor drive control device according to the present invention is used as a power source of an electric power steering, a rapid torque change of the brushless DC motor is small, so that the steering feeling of the electric power steering can be improved. Therefore, vibration noise can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an equivalent circuit when an OFF-phase exciting coil is PWM-ON.

FIG. 2 is a circuit diagram showing an equivalent circuit when an OFF-phase exciting coil is PWM-OFF.

FIG. 3 is a characteristic diagram showing a PWM waveform, an applied voltage waveform, and a residual current waveform of an OFF-phase exciting coil.

FIG. 4 is a characteristic diagram showing a phase current waveform and a torque waveform of each exciting coil in the brushless DC motor drive control device according to the present embodiment.

FIG. 5 is a circuit diagram showing an equivalent circuit of an OFF-phase exciting coil.

FIG. 6 is a circuit diagram showing an outline of a brushless DC motor drive control device of the present embodiment.

FIG. 7 is a characteristic diagram showing a phase current waveform and a torque waveform of each exciting coil in the conventional brushless DC motor drive control device.

[Explanation of symbols]

Ed OFF-phase back electromotive force Lm Inductance in equivalent circuit of OFF-phase exciting coil R resistance in equivalent circuit of OFF-phase exciting coil Vd Voltage applied to terminal of coil of OFF-phase id Current flowing in exciting coil of OFF-phase

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-9-47073 (JP, A) JP-A-4-197096 (JP, A) JP-A-10-155294 (JP, A) JP-A-9- 140182 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02P 6/00-6/24 H02P 5/00 H02P 5/28-5/412 H02P 7/00-7/01 H02P 7/36-7/632

Claims (2)

(57) [Claims] Claim: What is claimed is: 1. A brushless DC motor drive controller for controlling the rate of change of the current in the commutation phase so that the total current value of the commutation phase in the excitation coil of the brushless DC motor does not change. OF in the phase
The residual current of F phases to zero, arrives between conductible life you supplying a driving current by pulse width modulation to the OFF phase of the exciting coil, current of the OFF phase the residual current
Cuts off the residual current by limiting when reached
The current in the OFF phase has reached zero during the energization period.
A brushless DC motor drive controller characterized by being terminated at times . 2. The current of the OFF phase remains after the commutation starts.
Time to reach the distillate current is the electrical time constant and the resistance value of the equivalent circuit of the OFF phase, the PWM duty ratio applied to the OFF phase during commutation, the motor counter electromotive voltage of the brushless DC motor and , a DC line voltage is the power supply voltage of the circuit for the pulse width modulation, the initial current value at the time of the commutation, are calculated based on the time elapsed
At that point, the OFF phase current is cut off.
Brushless DC motor drive control device according to claim 1 are I.