JP3567542B2 - Sensorless motor drive circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sensorless motor drive circuit.
[0002]
[Prior art]
As a driving circuit for a sensorless motor, for example, a circuit for driving a three-phase brushless motor is known. The circuit for driving the three-phase brushless motor uses an induced voltage (counter electromotive voltage) generated in the exciting coil without using a rotation detecting element such as a Hall element to supply a current to the exciting coil. The pattern is switched.
[0003]
FIG. 5 shows a starting method when starting a conventional sensorless motor. In FIG. 5, according to the sensorless motor starting method, the back electromotive voltages U, V, and W obtained from the three-phase excitation coils are input to the plus input terminals of the comparators 1, 2, and 3 of the comparison circuit. It has become. Then, the neutral point voltage (common voltage) of the motor is input to the negative input terminals of the comparators 1, 2, and 3.
The comparison voltage signals Uin, Vin, Win of the comparators 1, 2, 3 do not come out normally when the motor is started because the back electromotive voltages U, V, W are small or absent. Therefore, the comparison voltage signals Uin, Vin, Win form the output voltage Z via the exclusive OR gate 4, and the frequency comparator 5 determines the signal frequency of the output voltage Z and the starter output 7 output from the starter 6. Compare with a predetermined frequency. Then, the frequency comparator 5 generates the energization pattern switching signal 8 by selecting the higher one of the two. Thus, the energization pattern for the three excitation coils CU, CV, CW is switched according to the energization pattern switching signal.
[0004]
[Problems to be solved by the invention]
However, in such a conventional sensorless motor starting method, as described above, if the back electromotive voltage does not enter for a certain period of time as described above, the energizing pattern switching signal is used to forcibly switch the energizing pattern using the starter output 7. 8 is generated to start the motor. Therefore, in this method, a starter 6 that is effective only at the time of starting the motor, a switching circuit 9 for switching the output voltage Z required at the time of steady rotation, and a frequency comparator 5 are required, and the circuit becomes large. There are drawbacks.
[0005]
Therefore, the present invention has been made to solve the above-mentioned problem, and it is not necessary to switch between a circuit that operates only at the time of steady rotation of the rotor and a circuit that starts at the time of startup and at the time of low rotation. It is an object of the present invention to provide a sensorless motor drive circuit that can drive the motor smoothly.
[0006]
[Means for Solving the Problems]
An object of the present invention is to provide a sensorless motor drive circuit which includes a rotor and a plurality of phases of excitation coils for the rotor, and switches the energization pattern for the plurality of phases of excitation coils to rotate the rotor. A starter section for adding an analog voltage to the DC voltage at the neutral point to form a starter signal, a starter signal, and a back electromotive voltage from the exciting coil of each phase are input, and the starter signal A comparison circuit for obtaining a comparison voltage signal by comparing the back electromotive voltages from the excitation coils of each phase; and a switching circuit for delaying the comparison voltage signal of the comparison circuit by a predetermined electrical angle to switch the energization pattern of the excitation coils of a plurality of phases. This is achieved by a sensorless motor drive circuit including a delay circuit that generates an energization pattern switching signal.
[0007]
According to the present invention, the starter section adds an analog voltage to the DC voltage at the neutral point of the motor to form a starter signal. Then, the comparison circuit compares the starter signal with the back electromotive voltage from the excitation coil of each phase to generate a comparison signal. The delay circuit delays the comparison voltage signal of the comparison circuit by a predetermined electrical angle, and switches the energization pattern of the excitation coils of a plurality of phases. The starter section applies an analog voltage to the DC at the neutral point of the motor, thereby creating a pseudo zero-cross point at the time of starting the motor and at low rotation of the motor, thereby operating the comparison circuit. Then, the delay circuit delays the comparison voltage signal of the comparison circuit by a predetermined electrical angle to generate an energization pattern switching signal, and sequentially switches the energization patterns of the exciting coils of a plurality of phases at the time of the delay.
[0008]
Since the starter signal obtained by adding the DC voltage of the neutral point of the motor and the analog voltage is sufficiently smaller than the back electromotive voltage at the time of steady rotation of the motor, it is effective only at the time of starting the motor and at the time of low speed rotation. It eliminates the need for a frequency comparator and a switching device that were conventionally required.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
The embodiments described below are preferred specific examples of the present invention, and therefore, various technically preferable limitations are given. However, the scope of the present invention particularly limits the present invention in the following description. It is not limited to these forms unless otherwise stated.
[0010]
FIG. 1 is a block diagram showing a sensorless motor drive circuit according to the present invention.
In the figure, a motor 10 has three phases of excitation coils (also referred to as drive coils) CU, CV, CW, and a rotor R. By switching the order of applying drive current to the three-phase excitation coils CU, CV, and CW, the rotor R rotates.
This motor is a three-phase sensorless brushless motor as described above. That is, when the rotor R of the motor is started, the excitation coils CU, CV of each phase are utilized by using the back electromotive voltages U, V, W generated in the excitation coil without using a rotation detecting element such as a Hall element. , CW, the switching pattern (timing) of the drive current supplied to the CW is switched.
Therefore, the excitation coil CU is connected to the drive unit 11 and the comparison circuit 12. Similarly, the excitation coil CV is connected to the drive unit 11 and the comparison circuit 12. The exciting coil CW is connected to the drive 11 and the comparison circuit 12.
The neutral point MP of the brushless motor 10 is connected to the comparison circuit 12. Thereby, the comparison circuit 12 can receive the back electromotive voltages U, V, and W from the three-phase excitation coils CU, CV, and CW, and receive the common voltage MPV from the neutral point MP of the brushless motor 10. It has become.
[0011]
The comparison circuit 12 and the starter unit 13 connected to the comparison circuit 12 will be described with reference to FIGS.
The comparison circuit 12 receives the back electromotive voltages U, V, and W as described above, and also receives the common voltage MVP. The comparison circuit 12 has three comparators 21, 22, 23, and the like. The outputs of these three comparators 21, 22, 23 are connected to the exclusive OR gate 24 of the delay circuit 14.
The counter electromotive voltage U is input to the positive input terminal of the comparator 21, the counter electromotive voltage V is input to the positive input terminal of the comparator 22, and the counter electromotive voltage W is input to the positive input terminal of the comparator 23. It has become. The common voltage MPV is input to the minus input terminals of the three comparators 21, 22, 23 via the adder 35.
[0012]
The comparator 21 compares the back electromotive voltage U with the starter signal WP and outputs a comparison voltage signal Uin to the exclusive OR gate 24 side. Similarly, the comparator 22 compares the back electromotive voltage V with the starter signal WP and outputs the comparison voltage signal Vin to the exclusive OR gate 24 side. The comparator 23 compares the back electromotive voltage W with the starter signal WP and outputs a comparison voltage signal Win to the exclusive OR gate 24 side.
[0013]
A feature of the embodiment of the present invention is that the starter unit 30 is input to the adder 35 of the common voltage input terminal. That is, the starter output voltage SO generated by the starter unit 30 is added to the common voltage MPV. The common voltage MPV is a DC voltage, and the starter output voltage SO that is an analog voltage is added to the common voltage MPV of the DC voltage in the adder 35. The reason why the analog starter output voltage SO is applied is to operate the comparators 21, 22, and 23.
[0014]
As a result, the adder 35 can supply the above-described starter signal WP to each of the minus input terminals of the comparators 21, 22, and 23. The starter signal WP is a signal obtained by adding an analog superimposed voltage to a DC voltage as shown in FIGS. 2 and 3, and has a gentle waveform as shown in FIG. The starter output voltage SO is a signal having a predetermined frequency and amplitude. For example, the frequency is calculated based on inertia and start-up torque. For example, in the case of a CD-ROM (read-only compact disk), it is about 10 Hz. is there. The amplitude is, for example, not less than the voltage at which the comparator operates and not more than 50% of the back electromotive voltage at the lowest rotational speed actually used.
The starter signal WP generates pseudo zero cross points P1, P2, and P3 as illustrated in FIG. 3 when the rotor R of the brushless motor 10 is started and at a low rotation, and the comparators 21, 22, 23 in FIG. To work.
[0015]
The exclusive OR gate 14 of the delay circuit 14 in FIG. 2 has a function of delaying the energization pattern switching signal from the comparison voltage signals Uin, Vin, Win of these comparators 21, 22, 23 by, for example, 30 degrees in electrical angle to be delayed. Have.
Returning to FIG. 1, the delay circuit 14 is connected to the logic circuit 50. The logic circuit 50 generates timings for detecting sinking, source, and back electromotive voltage of each phase for sensorless from the 8-bit signals of the comparison voltage signals Uin, Vin, and Win.
The logic circuit 50 supplies the logic circuit 50 with an energization pattern switching signal PC which is a signal of each of the delay U, the delay V, and the delay W (see FIG. 3) output from the NAND gates 40, 41, and 42, respectively. The drive unit 11 supplies power to the three-phase excitation coils CU, CV, and CW based on a command of a power supply pattern switching signal from the logic circuit 50.
[0016]
The delay circuit 14 delays the electric conduction pattern switching signal obtained from the comparison circuit 12 by 30 degrees at electric angles such as electric angles T1, T2, and T3 shown in FIG. Is output to the sensorless three-phase energizing logic circuit 50. In other words, a falling portion A1 of the delay U is formed at a point in time when a delayed electrical angle of 30 degrees (T3) has elapsed from the rising portion A of the output voltage signal Uin from the comparators 21, 22, 23. Similarly, with respect to the rising B of the output signal Vin, the falling portion B1 of the delay V is formed when the electrical angle 30 degrees (T2) is delayed. When the electrical angle 30 degrees (T1) delayed from the rising portion C of the output signal Win has elapsed, a falling portion C1 of the delay W is formed.
[0017]
Next, the operation of the above-described sensorless motor drive circuit will be described.
First, when the rotor R in FIG. 1 is to be started from a stopped state, the counter-electromotive voltages U, V, W are appropriately applied to the comparison circuit 12 from the three-phase excitation coils CU, CV, CW. Therefore, the comparison voltage signals Uin, Vin, Win are not normally output from the comparison circuit 12 to the delay circuit 14 in FIG. Therefore, the following signal processing is performed in order to start and rotate the rotor R by switching the energization coils CU, CV, and CW.
[0018]
The starter output voltage SO from the starter unit 30 is applied to the common voltage MPV in FIG. In other words, the starter signal WP shown in FIG. 2 is given to the comparators 21, 22, and 23 by giving the starter output voltage SO to the adder 35 with respect to the common voltage which is a DC voltage. Thus, the starter signal WP as shown in FIG. 3 is generated, and the comparators 21, 22, and 23 operate. Therefore, the comparison voltage signals Uin, Vin, Win are sequentially output to the exclusive OR gate 24 side.
[0019]
Then, the delay circuit 14 sequentially delays the signal from the exclusive OR gate 24 by an electrical angle of 30 degrees. That is, the rising portion C (pseudo zero-cross point P1) of the comparison voltage signal Win from the comparator 23 is delayed by the electrical angle 30 degrees (T1) delayed by the delay circuit 14, and the falling portion of the signal voltage delay W C1 is formed. A pseudo counter electromotive voltage W is generated at the timing of the falling portion C1 of the signal voltage delay W.
[0020]
Similarly, the rising portion B (pseudo zero cross P2) of the comparison voltage signal Vin from the comparator 22 is delayed by the delay circuit 14 by an electrical angle of 30 degrees (T2), and the falling portion of the signal voltage delay V B1 is formed. In response to the falling portion B1, a pseudo counter electromotive voltage V is generated instead of the counter electromotive voltage W.
[0021]
Similarly, the rising portion A of the comparison voltage signal Uin from the comparator 21 is delayed by T3 by the electrical angle 30 degrees by the delay circuit 14 to form a falling portion A1 of the signal voltage delay U. At the time of the falling portion A1, a pseudo back electromotive voltage U is generated instead of the pseudo back electromotive voltage V.
[0022]
In this manner, the back electromotive voltages W, V, and U are sequentially switched by the energization pattern switching signal PC, and the logic circuit 50 gives a command to the drive unit 11 at this switching timing. The drive unit 11 supplies a drive current (excitation current) to each of the corresponding excitation coils CU, CV, CW based on this command, so that the rotor R starts to start. The phenomenon of switching to the back electromotive voltages W, V, and U at the zero-cross points P1, P2, and P3 in this manner also occurs during the steady rotation of the rotor R.
[0023]
Even when the rotation of the rotor R reaches the steady rotation, the starter signal WP (common mix signal) in FIG. 2 is sufficiently smaller than the back electromotive voltages U, V, W during the steady rotation. In this case, there is almost no variation in the back electromotive voltage during steady rotation. In addition, since the starter signal WP is sufficiently smaller than the back electromotive voltages U, V, W during the steady rotation of the rotor R as described above, the starter signal WP is effective only at the time of startup and steady rotation. is there. Therefore, according to the embodiment of the present invention, as in the related art, a circuit provided with a frequency comparator and a switching device and operated only when the rotor is in a steady state, and a circuit that starts when the rotor R is started and when the rotor is rotated at a low speed are switched. And it is possible to cover from the start of the rotor R to the steady rotation with one circuit.
[0024]
The back electromotive voltages U, V, and W are, for example, voltages of about several volts, and the starter output voltage SO applied to the common voltage MPV is a voltage of about several tens mV. The extremely small starter output voltage SO may be a voltage at which the comparators 21, 22, and 23 operate. Further, the frequency of the starter output voltage SO is, for example, about 10 Hz in the case of a CD-ROM. This is because the energization timing is switched before the rotor starts moving, and the rotor cannot rotate.
Although the starter output voltage SO is an analog voltage, its amplitude may be any value as long as the amplitude is such that the comparators 21, 22, and 23 operate. For example, in the case of a CD-ROM, 100 mVpp (peak-to-peak voltage). ), But the magnitude is a value that does not affect the back electromotive voltages U, V, and W.
[0025]
At a common voltage (neutral point voltage) which is a DC voltage, the MPV causes fluctuation due to a starter output voltage SO which is an analog voltage. When the rotor R reaches a steady rotation, the fluctuation of the voltage is reversed. It does not affect the electromotive voltages U, V, W.
[0026]
FIG. 4 shows another embodiment of the embodiment of the present invention. In this embodiment, the starter unit 30 has one transistor Tr. When a starter signal SS is supplied to the base of the transistor Tr, a common voltage that is a DC voltage is converted into a starter signal WP. The other points are the same as those in the embodiment of FIG. 2 and the description thereof is omitted.
[0027]
As described above, in the present invention, a starter signal WP is formed by mixing (adding) a starter output voltage which is an analog voltage with a DC common voltage when driving a sensorless motor. By applying the signal WP to the input section 100 of the back electromotive voltages U, V, and W, the comparators 21, 22, and 23 are operated to smoothly start the rotor R and perform steady rotation. Therefore, there is no need to switch circuits between the start of the rotor and the steady rotation of the rotor, which are required in the related art.
[0028]
Also, when the sensorless motor is started, the starter frequency of the starter output voltage SO is mixed as an analog voltage with the common voltage MPV of the neutral point MP of the motor 10 so that the pseudo back electromotive voltage U as shown in FIG. , V, and W, the energization pattern to the excitation coils CU, CV, and CW can be switched.
By the way, in the above-described embodiment, an example of a brushless motor having a three-phase excitation coil is shown. However, the present invention is not limited to this, and may be applied to a brushless motor having a two-phase excitation coil. it can.
[0029]
【The invention's effect】
As described above, according to the present invention, it is not necessary to switch between a circuit that operates only at the time of steady rotation of the rotor and a circuit that is started at the time of startup and at the time of low rotation. Can be driven.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a sensorless motor drive circuit of the present invention.
FIG. 2 is a diagram illustrating a comparison circuit, a delay circuit, and a starter unit of the sensorless motor drive circuit of FIG. 1;
FIG. 3 is a diagram showing timings in the circuits of FIGS. 1 and 2;
FIG. 4 is a diagram showing another embodiment of the present invention.
FIG. 5 is a diagram showing a comparison circuit, a frequency comparator, a switch, and the like of a conventional sensorless motor drive circuit.
[Explanation of symbols]
Reference Signs List 10 brushless motor 12 comparison circuit 14 delay circuit 30 starter unit CU, CV, CW excitation coil M sensorless motor MPV common voltage (DC voltage at neutral point of motor)
R Rotor SO Starter output voltage (analog voltage)
T1, T2, T3 Delayed electrical angle Tr Transistor U, V, W Back electromotive voltage Uin, Vin, Win Comparison voltage signal WP Starter signal PC Energizing pattern switching signal

Claims (4)

In a sensorless motor drive circuit that includes a rotor and a plurality of phase excitation coils for the rotor, and switches an energization pattern for the plurality of phase excitation coils to rotate the rotor,
A starter unit for forming a starter signal by adding an analog voltage to a DC voltage at a neutral point of the motor;
A starter signal and a back electromotive voltage from the excitation coil of each phase are input, and a comparison circuit that obtains a comparison voltage signal by comparing the starter signal and the back electromotive voltage from the excitation coil of each phase,
A delay circuit that delays the comparison voltage signal of the comparison circuit by a predetermined electrical angle and generates an energization pattern switching signal for switching the energization pattern of the multi-phase excitation coil;
A sensorless motor drive circuit, comprising: The sensorless motor drive circuit according to claim 1, further comprising a three-phase excitation coil. 3. The sensorless motor drive circuit according to claim 2, wherein the delayed electrical angle is 30 degrees. The sensorless motor drive circuit according to claim 1, wherein the starter unit includes a transistor for adding an analog voltage to a DC voltage at a neutral point of the motor.

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