JPH09154294A - Driving of brushless dc motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately calculate a variation rate of a terminal voltage during a high speed rotation by calculating variation rate depending on the number of rotations of the motor and determining a commutation time depending on the calculated variation rate. SOLUTION: A selector 3 is provided to select one phase of the non-feeding phase among a DC power source 1, an inverter 2 and 3-phase coil. An analog value of terminal voltage of the selected terminal is ADD-converted 4 and the converted digital voltage is input to a controller 5. The effective induced voltage information from a coil is only an induced voltage from the coil which is not fed of one of three phases. A control means 5 inputs a detected value of the induced voltage, obtains a variation rate for the time of voltage, namely gradient of voltage and the time until the target voltage value is obtained to control a switching element of the inverter 2. Thereby, the motor can be controlled with higher accuracy from the low to the high speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a brushless DC motor, and more particularly to a so-called brushless DC motor sensorless drive capable of detecting the rotor position without using magnetic detection means such as a Hall element. Regarding the method.

[0002]

2. Description of the Related Art Generally, drive control of a brushless DC motor needs to be performed by closely associating the magnetic pole position of a rotor with the position of a winding to be passed. The output torque of the motor is generated by the interaction between the magnetic flux of the magnetic pole of the rotor and the current flowing through the winding of the stator. For this reason, in driving a brushless DC motor, it is necessary to generate a maximum torque by controlling the rotation of the motor by passing a current through the winding of the phase existing in the vicinity of the maximum magnetic flux generated from the magnetic poles of the rotor. . Further, the drive control of the brushless DC motor is performed by momentarily switching the phase through which the current should flow according to the rotation of the magnetic pole position of the rotor. The time of commutation, which is the switching of this phase, is the maximum magnetic pole position. If it deviates significantly from this, the torque generated thereby will decrease, and in the worst case, the motor will step out and stop.

Therefore, in the drive control of the brushless DC motor, it is necessary to detect the magnetic pole position of the rotor by some means and perform the control.

As the prior art relating to the rotor magnetic pole position detection circuit of this type of sensorless type brushless DC motor,
For example, the technique described in Japanese Patent Laid-Open No. 7-123773 is known.

This prior art uses an A / D converter for directly sampling and detecting the motor terminal voltage of the non-energized phase of the motor without using a low-pass filter, and a detection voltage using two points of the sampling values. The change rate with respect to time is calculated and extrapolated to obtain the induced voltage information.The rotor position is estimated based on this induced voltage information, and the commutation time is determined from the result to determine the appropriate time. It is to carry out commutation.

[0006]

Conventionally, the motor terminal voltage of the non-energized phase of the motor is directly sampled without using a low-pass filter, the rate of change of the detected voltage with respect to time is obtained from the sampling values at two points, and this is calculated. A method for obtaining induced voltage information by extrapolation and estimating the rotor position based on this induced voltage information is described in, for example, Japanese Patent Laid-Open No. 7-123773. In this prior art, in principle, the terminal voltage of the non-energized phase must always be detected at two points or more, and the rotation speed of the motor becomes high,
If two or more terminal voltages cannot be detected, the rate of change of the detected voltage with respect to time cannot be calculated, so that the commutation time cannot be determined and the motor stops.

An object of the present invention is to solve the above-mentioned problems of the prior art, to accurately calculate the rate of change of the terminal voltage with time even when the motor rotates at high speed, and to correctly estimate the magnetic pole position of the rotor. It is to provide a method of driving a brushless DC motor capable of realizing the above.

[0008]

According to the present invention, the above object is to detect the motor terminal voltage of the non-energized phase of the motor by directly sampling without using a low pass filter.
The / D converter and the rate of change of the terminal voltage with time from this detected value are used as induced voltage information, the rotor position is estimated based on this induced voltage information, and the commutation time is determined from the result to determine the appropriate value. When commutation is performed at time and two or more terminal voltages can be detected, the rate of change of the terminal voltage with respect to time is obtained from the detected values of these two points, and if two or more voltage cannot be detected, Based on the calculated rate of change of the terminal voltage with respect to time, the rate of change of the terminal voltage with time according to the motor speed is estimated, and extrapolated interpolation is used to obtain the induced voltage information. The position of the rotor is estimated, the commutation time is determined from the result, and the control unit drives the brushless DC motor so as to perform commutation at an appropriate time.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a method for driving a brushless DC motor according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing the system configuration of a brushless DC motor to which the driving method according to the present invention is applied, and FIG. 2 is a diagram showing the flow control of the motor at an ideal commutation time so that the motor has a constant speed. Showing schematically the waveforms of the induced voltage of the motor, the detection terminal voltage, and the processing voltage in the state where the motor rotates, FIG. 3 shows the number of times the terminal voltage can be detected with respect to the motor rotation speed, and FIG. 4 shows the motor rotation speed. It is a figure showing the amount of change of the terminal voltage per unit time with respect to.
In FIG. 1, 1 is a DC power supply, 2 is an inverter circuit, and 3
Is a selector, 4 is an A / D converter, 5 is a control unit, 6 is a driver circuit unit, 7 is a stator, 8 is a rotor, and 9 is a load.

A brushless DC motor drive system to which the present invention is applied, as shown in FIG. 1, is a selector 3 for selecting one of the non-energized phases of the DC power supply 1, the inverter circuit 2 and the windings of three phases. , A / D converter that converts the analog value of the terminal voltage of the selected terminal into a digital value so that it can be calculated by an electronic computer 4, determines the rate of change and commutation time from the detected voltage, and sets the inverter circuit 2 A controller 5 for outputting a signal to a driver to be controlled 5, a driver circuit 6 of an inverter circuit 6, a stator 7 of a three-phase brushless DC motor in which U, V, and W phase windings are connected at one end, and a permanent magnet is used. A rotor having a magnetic pole, a load 9 connected to a motor
It consists of.

A motor driving method according to an embodiment of the present invention described below is a 120-degree conduction type driving capable of obtaining a high output torque, and a motor controlling method is a DC voltage conduction ratio. This is a so-called PWM control for controlling, and the switching element for chopping is connected to the positive voltage side of the DC power supply 1.

A switching element for chopping may be connected to the negative voltage side of the DC power source 1,
Further, although the inverter circuit 2 is omitted in the figure,
Three sets of switching elements are provided so as to correspond to the windings of each phase.

In general, in a DC motor driven by a 120-degree energization type by the inverter circuit 2, effective induced voltage information from the winding is obtained from the winding of one phase which is always not energized among the windings of three phases. Is the induced voltage only, and the induced voltage during the period when the chopping by the inverter circuit is not performed is effective. Therefore, the selector 3 has a switching function of switching the terminals of the detected phases according to the current flow mode, and the A / D converter 4 converts the voltage value, which is an analog value, into a digital value in synchronization with the PWM signal. It has a so-called A / D conversion function.

The control unit 5 receives the detected value of the induced voltage and calculates the rate of change of the voltage with respect to time, that is, the slope of the voltage, based on the detected value of the induced voltage. The function of extrapolating the slope, the function of calculating the time from the slope to the target voltage value, the function of outputting a signal for controlling the driver circuit unit 6 for controlling the switching element of the inverter circuit 2, and the above-mentioned detection. It is composed of a microcomputer having a function of storing a value and a slope.

Further, the driver circuit section 6 has a function of driving a switching element forming the inverter circuit 2 in response to a signal from the control section 5.

In the above-described embodiment of the present invention, the control section 5 and the driver circuit section 6 of the switching element of the inverter circuit 2 are constituted by different circuits, but these functions are integrated. Alternatively, a microcomputer may be used as the control unit.

The stator 7 constituting the motor is composed of three-phase windings of windings U, V, W which are magnetically poled by passing an electric current, and one ends of these windings are connected to each other. . The rotor 8 is a permanent magnet having a magnetic pole, and rotates in accordance with the change in the proper magnetic pole position of the stator described above.

Next, in the brushless DC motor constructed as described above, the respective windings of the stator 7 are controlled to flow at an ideal commutation time, and the motor is assumed to be rotating at a constant speed. The state will be described with reference to FIG.

FIG. 2A shows an induced voltage waveform of each phase that occurs as a physical phenomenon in this state, and FIG. 2B shows a terminal voltage waveform of each phase winding detected in full-wave driving. ,
2C is an enlarged waveform of the terminal voltage to be detected, FIG.
In the present invention, (d) is a signal waveform that can be obtained by extrapolating from the amount of change of the detected value with respect to a point that cannot be detected by detecting the terminal voltage waveform in synchronization with the PWM signal.

As shown in FIG. 2, when the motor commutates at an ideal commutation time and rotates at a constant speed, a voltage as shown in FIG. 2A is induced as a physical phenomenon. This induced voltage is induced by the magnetic poles of the rotor, and its Peak to Peak value is proportional to the rotation speed of the motor,
The transient value is determined in correlation with the magnetic pole position of the rotor. Normal,
The commutation time of the motor can be determined based on this induced voltage information.

That is, the ideal commutation time (maximum output can be obtained) of the motor is the points tp1 and tp2 shown in the drawing where the induced voltages of the adjacent phases intersect,
According to one embodiment of the present invention, the voltage at this time is defined as the maximum value e (tp1) of the voltage which is an upward convex inflection point and the minimum value e (tp2) of the voltage which is a downward convex inflection point. It is what you want. When the motor is rotating at a constant speed, the maximum value and the minimum value of the voltage at that time are almost equal in any adjacent phases.

On the other hand, what can be detected as an actual system is the terminal voltage of the stator winding of the motor, which has a waveform as shown in FIG. 2 (b). This detected waveform shows the voltage between the negative side of the DC power supply and the terminal of each phase winding, and is a mixture of the drive voltage and the induced voltage applied to rotate the motor. Then, in the 120-degree conduction type drive of the motor, the effective induced voltage information is the period Ts shown in FIG. Therefore, only one of the three phases is always present.

Further, the period Ts of effective induced voltage information Also, in the section in which the current flows through the freewheeling diode during commutation, the potential is fixed to the positive or negative value of the DC voltage, and when the inverter circuit is performing the PWM signal, chopping is performed. Figure 2
It does not become continuous as shown in (b). Therefore, it is necessary to detect the induced voltage by some method and determine the commutation time by performing arithmetic processing based on the information.

Therefore, in one embodiment of the present invention, effective induced voltage information is obtained from only one of the three phases in the period Ts shown in FIG. Therefore, the selector 3 selects and switches one non-energized one phase of the three-phase winding of the motor according to the conduction mode, and the enlarged waveform of the terminal voltage shown in FIG. As shown in, the current does not flow through the freewheeling diode in the inverter circuit 2 and the terminal voltages e (t1) and e (t2), e (t3), e ( By sampling t (nm)) or the like, although the information is discrete, the induced voltage information is directly picked up from the terminal voltage.

Further, according to one embodiment of the present invention, the rate of change Δv / Δt of the voltage with respect to time is calculated from the induced voltage information discretely obtained by the control unit 5, and the difference between discrete values (the broken line portion in the figure) is calculated. The induced voltage is obtained by extrapolation interpolation and continuously connected for three phases to obtain a processed waveform having a triangular wave signal waveform as shown in FIG. 2D.

As described with reference to FIG. 2, when the flow of current to the windings of each phase is controlled at the ideal commutation time and the motor is rotating at a constant speed, as shown in FIG. 2 (d). In each adjacent phase, the voltage at the point where the induced voltages of the adjacent phases intersect (the maximum value of the voltage that is the upward convex inflection point, the minimum value that is the downward convex inflection point) is Also becomes almost constant, and the emax and emin of the processed waveform can be obtained from the voltage value at each inflection point of this signal at this time. From this, in order to obtain the optimum commutation time, the induced voltage in each phase is detected, and the induced voltage obtained from the rate of change with respect to time at that time is emax. And emin It suffices to calculate the time at which

That is, when the rate of change K of the detected voltage and the terminal voltage at that time with respect to time is approximated by a linear function and calculated by (Equation 1), when the rate of change of the terminal voltage is positive, the terminal voltage used for the calculation is The time tbm from the detection time to the point time is
In (Equation 2), when the terminal voltage is negative, the time tbm to the point time
Can be calculated by (Equation 3). Further, the detection time of the terminal voltage used for the calculation is tn Then, the commutation time tp Can be calculated by (Equation 4). At this time, m is an integer and A / D
Considering the resolution of the converter, it is desirable to change it according to the motor rotation speed.

K = Δv / Δt = {e (tn) −e (t (nm))} / (tn−t (nm)) (Equation 1) tbm = {emax−e (tn)} / K (Equation 2) tbm = {e (tn) -emin} / K ... (Equation 3) tp = tn + tbm ... It changes drastically. Number of detections of the terminal voltage with respect to the motor speed Sn Is the motor rotation speed N (rpm), the number of poles P of the three-phase motor, and the PWM cycle Tpwm
From (s), it can be calculated by (Equation 5).

Sn = (60 / N) · {1 / (3 · P)} · (1 / Tpwm) (Equation 5) Using this (Equation 5), the number of poles of the motor is 4 and the PWM cycle is FIG. 3 shows the number of times the terminal voltage is detected with respect to the motor speed when the speed is 200 μs.

As can be seen from FIG. 3, the number of times the terminal voltage is detected decreases significantly as the motor speed increases. In a real control system,
2 to 3 because the time required to calculate the commutation time is required
It is desirable to secure the number of detections more than once. Therefore, the motor controllable range is about 6000 rpm from Fig. 3.
It is as follows. Although the number of times of detection can be increased by shortening the PWM cycle, this method is not necessarily the best method from the viewpoint of the frequency characteristics of the inverter module and the cost reduction.

In this embodiment, high-quality control is performed from the detected value of one terminal voltage to the high speed rotation range without shortening the PWM cycle.

Induced voltage V0 Is proportional to the motor rotation speed N from the principle of the motor, and the induced voltage constant Ke Is expressed by (Equation 6).

V0 = KeN (Equation 6) Since the magnitude of the terminal voltage is proportional to the induced voltage, the amount of change in the voltage per unit time is also proportional to the motor rotation speed, and the terminal voltage with respect to time is changed. The rate of change is approximated by the following (Equation 7).

Δv / Δt = α · N (Equation 7) At this time, α represents a constant peculiar to the motor, which represents the rate of change of the terminal voltage with respect to the motor rotation speed. Actually, FIG. 4 is a diagram in which the terminal voltage is detected in synchronization with the PWM cycle at the time of driving the motor, and the amount of change in the voltage is converted into the amount of change in voltage per unit time. Depends on. Therefore, the motor rotation speed is calculated from the commutation time, and when the voltage values at two points can be detected within one flow period, the terminal voltage change amount with respect to the motor rotation speed is calculated to detect the terminal voltage. When the number of times is decreased, the rate of change of the terminal voltage is detected by extrapolating the rate of change of the terminal voltage according to the number of motor revolutions without detecting the terminal voltages at two points in one conduction period. Can be calculated. In other words, by approximating the other parts from the two points in FIG. 4 with a linear function and extrapolating and interpolating to calculate the rate of change of the terminal voltage with respect to time, as in the case where the number of detections of the terminal voltage is large. , The next rotating flow time can be determined in real time.

When the number of detections is large, the amount of change in the terminal voltage during motor driving with time can be calculated, stored and learned from the detected value of the terminal voltage. Without setting input
Similar control can be realized. Further, since the induced voltage information depends on the rotation speed and the magnetic pole position of the rotor, the embodiment of the present invention can correct the induced voltage due to the rotation pulsation even if the rotation pulsation occurs in the motor by the above correction. Since it changes, an appropriate commutation time can always be determined. As a result, the commutation time can be accurately determined based on the rate of change of the terminal voltage with respect to the time corresponding to the rotation speed, and good motor control can be realized from the low rotation range to the high rotation range.

[0037]

As described above, according to the present invention,
Even if the number of times the terminal voltage is detected decreases, by detecting the terminal voltage at one point, it is possible to stably estimate the rotor position from the rate of change of the terminal voltage with time.
The motor can be controlled accurately from the low speed range to the high speed range.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a system configuration of a brushless DC motor to which a driving method according to the present invention is applied.

FIG. 2 schematically shows waveforms of a motor induced voltage, a detection terminal voltage, and a processing voltage in a state in which a commutation is controlled at an ideal commutation time with respect to a motor and the motor is rotating at a constant speed. It is a figure.

FIG. 3 is a diagram showing the number of times the terminal voltage can be detected with respect to the motor rotation speed within one flow period.

FIG. 4 is a diagram showing a change amount of a terminal voltage per unit time with respect to a motor rotation speed.

[Explanation of symbols]

1 ... DC power supply, 2 ... inverter circuit, 3 ... selector, 4
... A / D converter, 5 ... control unit, 6 ... driver circuit unit, 7
... stator, 8 ... rotor, 9 ... load, tp1, e (tp1),
tp2, e (tp2) ... Optimal commutation time and voltage value at that time, T
s … Induced voltage information period, emax … Inflection point voltage convex above induced voltage, emin ... an inflection point voltage that is convex below the induced voltage, t
1, t2, tn, t (nm) ... Sampling time, e (t1),
e (t2), e (tn), e (t (nm)) ... Sampling voltage,
Δv ... voltage change amount, Δt ... time change amount, tn The time when the calculation process is started, tbm ... The reference time from the time when the calculation process is started to the next rotational flow determination time.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoru Hirose 5-20-1 Kamimizumoto-cho, Kodaira-shi, Tokyo Incorporated company Hitachi Ltd. Semiconductor Division (72) Inventor Kazuo Tahara 7, Omika-cho, Hitachi City, Ibaraki No. 1 in Hitachi, Ltd. Hitachi Research Laboratory

Claims (2)

[Claims] 1. A terminal voltage of a non-energized phase of a brushless DC motor having a permanent magnet and an armature winding, and one end of each phase of the armature winding being commonly connected is detected and detected. In a method of driving a brushless DC motor, which determines the commutation time based on the rate of change of the terminal voltage with respect to time, the rate of change corresponding to the motor rotation speed is calculated, and the commutation time is calculated based on the calculated rate of change. A method for driving a brushless DC motor, characterized in that 2. The method for driving a brushless DC motor according to claim 1, wherein the brushless DC motor is driven by using an inverter circuit.