JPH0365092A - Brushless motor circuit provided with current limiting function - Google Patents

Abstract

PURPOSE:To prevent breakdown of a switching element by performing pulse width control of an inverter circuit based on the detection value of motor currents flowing in the switching element of the inverter circuit so as to quicken motor current limiting operation and limiting the currents of the element itself by means of the load currents flowing in the switching element of a chopper circuit. CONSTITUTION:The motor currents IM to a brushless motor 70 are converted into voltage V2 by the resistance 65 inside an inverter circuit 60, and are compared with the set value VY in a comparator 96 for current limitation. When the motor currents IM are excessive, the pulse width of the chopper signal PC2 from a pulse width modulation circuit 100 is narrowed, and the on-time of the inverter circuit 60 is shortened so as to throttle the motor currents IM. The load currents IL flowing in a chopper circuit 20 are converted into voltage V1 by a detection circuit 31, and those are monitored by a current limiting circuit 35. When the load currents IL are detected as excessive by the comparison with the set value VX, the pulse width of the chopper signal PC1 from a pulse width modulation circuit 50 is narrowed by the signal phix: at a level of L, and the on-times of transistors 22 and 24 are shortened. so as to throttle load currents IL.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a brushless motor circuit with a current limiting function.

[Prior Art] FIG. 2 is a block diagram of a conventional brushless motor circuit with a current limiting function, which employs a so-called PWM inverter chopping method.

The rectifier/smoothing circuit io converts an AC input of, for example, 100V into a DC input, and provides a DC high voltage to the chopper circuit 20. The chopper circuit 20 includes an on/off circuit for chopping (switching elements such as transistors) and a smoothing circuit, and converts a DC high voltage input into a DC low voltage and outputs the same. The differential amplifier 43 calculates the deviation of the output voltage VM of the chopper circuit 20 with respect to the DC set voltage VU and outputs the deviation. The pulse width modulation circuit 50 proportionally converts the output voltage φM of the differential amplifier 43 into a pulse width, and sets the on-time of the switching elements constituting the chopper circuit 20, thereby adjusting the output voltage VM of the chopper circuit 20. Set.

At this time, the pulse width of the chopper signal Pc1 given from the pulse width modulation circuit 50 to the chopper circuit 20 is the voltage φ□
This is determined by comparing the magnitude of the signal with, for example, a 20 kHz triangular wave signal. The above rectifier/smoothing circuit IO, chopper circuit 20, differential amplifier 43, and pulse width modulation circuit 50 constitute a switching regulator 55. The chopper circuit 2 is controlled by this switching regulator 55.
A constant DC voltage VM is obtained from o.

This constant voltage VM is applied to the stator winding of the brushless motor 70 via the inverter circuit 6o to create a rotating magnetic field. When using a three-phase brushless morph, the inverter circuit 6o includes, for example, three transistors forming an upper arm and three transistors forming a lower arm.

However, each transistor constituting the lower arm is subjected to pulse width modulation via a Darlington connection transistor.

A position detector made of a Hall element is arranged near the rotor made of a permanent magnet of the brushless motor 70, and a rotor position detection circuit 80 is composed of a logic circuit including this detector.
detects the position of the rotor of the brushless motor 70 and issues on/off commands to the inverter circuit 60 to sequentially supply current to specified stator windings, and also generates speed pulses with a repetition frequency corresponding to the motor speed. Output PR. When using a Hall element to detect the position of the rotor, the number of speed pulses PR is, for example, 1 to 12 pulses per motor rotation.

The F/V conversion circuit 90 proportionally converts the repetition frequency of this speed pulse PR into a DC voltage and outputs it. This F
As the /V conversion circuit 90, for example, a differential circuit, a one-shot multivibrator, and a smoothing circuit connected in series is used. The differential amplifier 91 calculates the deviation of the output voltage V 1 of the F/V conversion circuit 90 with respect to the speed command voltage V8. The pulse width modulation circuit 100 includes a differential amplifier 9
The output voltage φR of 1 is proportionally converted into a pulse width, and the lower arm transistor of the inverter circuit 60 is subjected to pulse width modulation. The pulse width of the chopper signal P applied from the pulse width modulation circuit 100 to the inverter circuit 60 is determined by comparing the voltage φR with a triangular wave signal of, for example, 220 kHz.

In the inverter circuit 60, a resistor 65 is connected in series to the lower arm transistor, and the brushless motor 70
The motor current 1M supplied to the motor is proportionally converted into a voltage V2 by this resistor 65.

This voltage V2 is applied to a current limiting circuit 9 consisting of a comparator.
4, the magnitude is compared with the DC setting voltage VY.

When this current limiting circuit 94 detects an excessive motor current IN, it forcibly lowers the output voltage φM of the differential amplifier 43 by outputting an L level voltage φ. As a result, the pulse width of the chopper signal Pc of the pulse width modulation circuit 50 becomes narrower, the output voltage VM of the chopper circuit 20 decreases, and the motor current 1M is throttled.

The brushless motor circuit with a current limiting function described above is used, for example, to drive an automatic door. In this motor circuit, the DC voltage VM, that is, the motor voltage, applied from the switching regulator 55 to the brushless motor 70 via the inverter circuit 60 is constant. However, since the on-time of each transistor constituting the lower arm of the inverter circuit 80 is pulse width modulated by speed feedback, the brushless motor 70 is controlled to a constant speed according to the magnitude of the speed command voltage V8, and the brushless motor 70 is controlled to a constant speed according to the magnitude of the speed command voltage V8. Torque can be increased. Furthermore, when an excessive current I flows through the brushless motor 70, the output voltage VM of the chopper circuit 20 is reduced by the action of the current limiting circuit 94, and the motor current 1M is throttled.

[Problems to be Solved by the Invention] In the conventional brushless morph circuit with a current limiting function, the detected value of the motor current 1M flowing through the switching element of the inverter circuit 60 is returned to the switching element of the chopper circuit 20, and the latter switching element is Since the motor current IN was controlled and limited, the chopper circuit 2
0 has a smoothing circuit, etc., the effectiveness of limiting the motor current 1M, that is, the response is poor, and there is a problem that a time delay occurs in the current limiting operation.

Furthermore, since the switching element of the chopper circuit 20 was not protected, this element was sometimes destroyed.

The present invention has been made in view of the above circumstances, and
The purpose is to speed up the motor current limiting operation and protect the switching elements of the chopper circuit from destruction.

[Means for Solving the Problems] A brushless morph circuit with a current limiting function according to the present invention is a motor circuit that supplies the output of a chopper circuit to a stator winding of a brushless motor via an inverter circuit, and has a DC setting. A first differential amplifier that calculates the deviation of the chopper circuit output voltage with respect to the voltage, and a proportional conversion of the output voltage of the first differential amplifier to a pulse width to set the on-time of the switching element forming the chopper circuit. and a first pulse width modulation circuit, which forcibly narrows the output pulse width of the first pulse width modulation circuit when it is detected that the load current flowing through the switching element of the chopper circuit is excessive. It includes a load current limiting circuit that throttles the load current flowing through the switching element. Furthermore, the rotor position detection circuit detects the position of the rotor of the brushless motor and issues on/off commands to the inverter circuit, as well as outputs speed pulses with a repetition frequency that corresponds to the motor speed, and the repetition frequency of this speed pulse. an F/V conversion circuit that proportionally converts the voltage into a DC voltage and outputs it; a second differential amplifier that calculates the deviation of the output voltage of the F/V conversion circuit from the speed command voltage; and a second pulse width modulation circuit that proportionally converts the output voltage of the dynamic amplifier into a pulse width to set the on-time of the switching elements constituting the inverter circuit. A motor current limiting circuit is provided which forcibly narrows the output pulse width of the second pulse width modulation circuit to throttle the motor current when a certain condition is detected.

[Function] The chopper circuit, the first differential amplifier, and the first pulse width modulation circuit constitute a switching regulator that can obtain a constant voltage output. The output of the chopper circuit, ie, the output of the switching regulator, is supplied to the stator winding of the brushless motor via the inverter circuit to generate a rotating magnetic field. The speed of the rotor of this brushless motor is fed back to the inverter circuit through a rotor position detection circuit, an F/V conversion circuit, a second differential amplifier, and a second pulse width modulation circuit. That is, the on-time of the switching elements constituting the inverter circuit is pulse width modulated according to the magnitude of the speed command voltage, and constant speed control is executed.

The motor current flowing through the switching elements of the inverter circuit is constantly monitored by a motor current limiting circuit. When the motor current limit circuit detects excessive motor current,
This limiting circuit directly forcibly narrows the output pulse width of the second pulse width modulation circuit to throttle the motor current.

On the other hand, the load current flowing through the switching elements of the chopper circuit is constantly monitored by the load current limiting circuit. When the load current limiting circuit detects this excessive current, the first
The output pulse width of the pulse width modulation circuit is forcibly narrowed to reduce the load current. However, the load current limiting circuit is set so that the limiting operation for the load current flowing through the switching element of the chopper circuit is not normally performed even while the motor current is being limited. This load current limiting circuit operates to protect the switching elements of the chopper circuit in the event that the motor current limiting circuit does not operate or if a serious failure such as a motor load short circuit occurs.

[Embodiment] FIG. 1 is a circuit diagram of a brushless motor circuit with a current limiting function according to an embodiment of the present invention.

For example, a 100V AC power source 2 is connected to the rectifier/smoothing circuit 10. This rectifier/smoothing circuit 10 converts an AC input into a DC input and provides a DC high voltage to a chopper circuit 20 . In this chopper circuit 20, the output voltage of the rectifier/smoothing circuit IO is applied to the primary winding of the pulse transformer 21, the primary winding of the current transformer 31, and the main switching element NP.
N Applied to the series circuit of transistor 22. The base circuit of this main transistor 22 is connected to the collector circuit of another NPN transistor 24 (subtransistor) insulated by another pulse transformer 23. The 27th order circuit of the current transformer 31 constituting the load current detection circuit 30 proportionally converts the collector current of the main transistor 22, ie, the load current (2), into a DC voltage Vl. This voltage vl is input to the inverting input terminal of the comparator 3B that constitutes the load current limiting circuit 35. A DC setting voltage Vx is applied to a non-inverting input terminal of the comparator 36 from a DC voltage setting circuit 37 which is a resistive voltage dividing circuit. Comparator 36 outputs voltage signal φ via diode 38. The secondary side of the pulse transformer 21, to which the main transistor 22 is connected to the primary winding, is connected to the inverter circuit 60 via a smoothing circuit 25 composed of a diode, a coil, and an output capacitor.

The voltage across the output capacitor of the chopper circuit 20 is determined not only by the inverter circuit 60 but also by the two resistors 41 and 42.
It can also be applied to a voltage divider circuit formed by connecting in series. The connection point voltage VM of both resistors 41 and 42 is used to monitor the output voltage of the chopper circuit 20. That is, this voltage vM is applied to the differential amplifier 43 as an inverting input.

A DC setting voltage vU is applied to a non-inverting input terminal of the differential amplifier 43 from a DC voltage setting circuit 45 which is a resistive voltage dividing circuit, and a voltage feedback circuit 40 is formed here.

The output voltage φ□ of the differential amplifier 43 is the pulse width modulation circuit 5
0 is applied to the non-inverting input terminal of the comparator 51 through a resistor. The anode of the diode 38 in the load current limiting circuit 35 is connected to this non-inverting input terminal via another resistor. Comparator 5i
The voltage at the non-inverting input terminal of is compared in magnitude with the output signal T1 of the triangular wave oscillation circuit 52 input to the inverting input terminal to form a chopper signal Pct. The chopper signal Pct is applied to the base of the sub-transistor 24 of the chopper circuit 20, and is applied to the base of the main transistor 22 via the pulse transformer 23.
Turn on and off. That is, the pulse width modulation circuit 50 normally proportionally converts the output voltage φH of the differential amplifier 43 into a pulse width to set the output voltage VM of the chopper circuit 20. Note that the frequency of the triangular wave signal T1 is, for example, 20kHz.
It is.

The rectifying/smoothing circuit 10, chopper circuit 20, load current detection circuit 30, load current limiting circuit 35, voltage feedback circuit 40, and pulse width modulation circuit 50 described above constitute a switching regulator 55 with a current limiting function.

The output voltage of the chopper circuit 20 is applied to the stator winding of the brushless motor 70 via the inverter circuit 60 to create a rotating magnetic field. When using a three-phase brushless motor, the inverter circuit 60 includes three PNP transistors (upper arm) 81a.

61b, 61c and three NPN) transistors (lower arm) 62a, 62b, 62c. A flywheel diode is connected to each transistor. However, each transistor e2a constituting the lower arm
, 82b, 82c are connected to the collectors of other PNP transistors 63a, 63b, 83c, respectively, and the emitters of these transistors Ha, 83b, 63c are connected to one common PNP transistor for applying pulse width modulation.
It is connected to DC power supply VBB via transistor 64. In addition, each transistor 62a forming the lower arm,
The emitters of 82b and 82c are connected to the chopper circuit 2 through a common current detection resistor 65 through which motor current IN flows.
Connected to 0.

The brushless motor 70 has a rotor made of, for example, two-pole permanent magnets, around which three-phase stator windings are equally spaced at 120 degrees. Furthermore, three position detectors 81 made of Hall elements are equally spaced at 120 degrees near the rotor, and these detectors output speed signals A, B, and C corresponding to the rotor position of the brushless motor 70, respectively. These speed signals A, B, and C are input to the drive logic circuit 82 to generate on/off commands U for the upper arm of the inverter circuit 60.
, V, W, and on/off commands x, y, for the lower arm.
It is converted to z. However, on/off commands U and V for the upper arm.

W is a PNP transistor 61a, Blb, f31c
The on/off commands x, y, and z for the lower arm are directly driven by the PNP transistor 63a.
, Bib, NPN) through the bases of 83c, respectively. Further, the drive logic circuit 82 generates a speed pulse PR based on the speed signals A, B, and C. The rate of this speed pulse PR is, for example, 12 pulses per rotation of the brushless motor 70. However, since the circuit configuration of the drive logic circuit 82 is well known, detailed explanation thereof will be omitted. Note that the position detector 81 and the drive logic circuit 82 constitute a rotor position detection path 80.

The speed pulse PR is input to the F/V conversion circuit 90.

The F/V conversion circuit 90 is a differential circuit, a one-shot multi-by-break circuit, and a smoothing circuit connected in series, and converts the repetition frequency of the speed pulse PR into a DC voltage VR proportional to the repetition frequency. This F/V conversion circuit 90
The output voltage VR is input to the inverting input terminal of the differential amplifier 91. This differential amplifier 91 receives a speed command voltage V8 from a DC voltage setting circuit 93, which is a resistive voltage dividing circuit, to a non-inverting input terminal, and outputs a voltage V8 from an F/V conversion circuit 90.
The deviation from the speed command voltage V8 is calculated. In addition,
The F/V conversion circuit 90 and the differential amplifier 91 constitute a speed feedback circuit 92.

In the inverter circuit 60, the motor current IN is proportionally converted into a DC voltage V2 by a resistor 65. This voltage V2 is input to an inverting input terminal of a comparator 96 that constitutes a motor current limiting circuit 95. A DC setting voltage VY is applied to a non-inverting input terminal of the comparator 96 from a DC voltage setting circuit 97 which is a resistive voltage dividing circuit. Comparator 9B receives voltage signal φ via diode 98.
.

Output.

The output voltage φR of the differential amplifier 9 (of the pulse width modulation circuit 1
The comparator that constitutes 00 (applied to the non-inverting input terminal of 01 via a resistor. This non-inverting input terminal has a
The anode of diode 98 in motor current limiting circuit 95 is connected via another resistor. Comparator 1
The voltage at the non-inverting input terminal 01 is compared in magnitude with the output signal T2 of the triangular wave oscillation circuit 102 input to the inverting input terminal, and becomes a chopper signal Pc2. This chopper signal Pc
2 drives the base of the common PNP transistor 64 in the inverter circuit 60 to
lower arm transistor 62a.

62b and [12c are subjected to pulse width modulation. That is, this pulse width modulation circuit 100 normally proportionally converts the output voltage φR of the differential amplifier 91 into a pulse width to set the on-time of the lower arm transistors 62a, 82b, and 62c. Note that the frequency of the triangular wave signal T2 is, for example, 20k.
It is Hz.

In the switching regulator 55 , the rectifier/smoothing circuit 10 converts an AC input of, for example, 100 V supplied from the AC power supply 2 into a DC current, and supplies the DC high voltage to the chopper circuit 20 . The chopper circuit 20 converts this DC high voltage input into a DC low voltage and supplies it to the inverter circuit BO. At this time, as long as the output of the comparator 36 of the load current limiting circuit 35 is at H level, the output voltage VM of the chopper circuit 20 is controlled by the magnitude of the DC setting voltage vU according to the chopper signal Pc1 output from the pulse width control circuit 50. It is held at a constant value according to.

On the other hand, in the position detection circuit 80, the position detector 81 is
Speed signals A, B, and C corresponding to changes in the rotor position of the brushless motor 70 are output, respectively.

These speed signals A, B, and C are used as on/off commands U, V to the inverter circuit 60 by the drive logic circuit 82.
, W, X, Y, Z.

At this time, the upper arm transistor 6 of the inverter circuit 60
La, 61b, 61c and the lower arm transistor 62a.

82b and B2c are selected, and a current flows through a specified stator winding according to the rotor position of the brushless motor 70, a rotating magnetic field is generated, and the rotor rotates. However, since the current supply to the stator winding is limited to the ON time of the common PNP transistor 64, the brushless motor 70
As long as the output of comparator 9B of motor current limiting circuit 95 is at H level, constant speed control is executed according to the magnitude of speed command voltage V8 by chopper signal Pc2 output from pulse width control circuit 100. Ru.

As explained above, unless the load current limiting circuit 35 operates, the output voltage V of the switching regulator 55
Since M is constant, constant speed control of the brushless motor 70 is possible. Therefore, this motor circuit is suitable for performing constant speed control down to low speeds, such as when driving an automatic door.

Now, the motor current 1 supplied to the brushless motor 70
M is proportionally converted to voltage V2 by resistor 65 in inverter circuit 60. This voltage V2 is compared in magnitude with a DC set voltage VY by a comparator 96 of a motor current limiting circuit 95. This motor current limiting circuit 95 outputs an L level voltage φY when detecting an excessive motor current 1M. When the L level voltage φY is output, a current is drawn into the comparator 96 through the diode 98, so the input voltage of the pulse width modulation circuit 100 is forcibly lowered regardless of the magnitude of the output voltage φ7 of the differential amplifier 91. It will be done. As a result, the pulse width of the chopper signal Pc2 becomes narrower, and the lower arm transistor 62a of the inverter circuit 60.

The on time of 62b and 82c is shortened, and the motor current 1
M is squeezed.

On the other hand, the load current LL flowing through the main transistor 22 of the chopper circuit 20 is proportionally converted into a voltage Vl through an insulated detection circuit 30, and then constantly monitored by a load current limiting circuit 35. When the load current limiting circuit 35 detects an excessive load current I by comparison with the DC set voltage Vx, the current limiting circuit 35 outputs an L level voltage signal φX. When the L-level voltage φ is output, current is drawn into the comparator 36 through the diode 38, so that the input terminal of the pulse width modulation circuit 50 is forced to close regardless of the magnitude of the output voltage φH of the differential amplifier 43. be lowered. As a result, the chopper signal Pc
1 becomes narrower, the on-time of the sub-transistor 24 and the main transistor 22 becomes shorter, and the load current IL decreases.
is squeezed. However, even while the motor current I is limited by the current limiting circuit 95, the load current
The DC setting voltage vX is set so that the limiting operation for , is not executed. This load current limiting circuit 35 operates to protect the main transistor 22 of the chopper circuit 20 in the event that the motor current limiting circuit 95 does not operate or if a serious failure such as a load short circuit of the brushless motor 7o occurs.

[Effects of the Invention] As explained above, the brushless morph circuit with a current limiting function according to the present invention can control the inverter circuit without returning the detected value of the motor current flowing through the switching element of the inverter circuit to the switching element of the chopper circuit. According to the present invention, the motor current is limited by direct pulse width control, and the switching element of the chopper circuit also limits its own current based on the load current flowing through the switching element. It is possible to speed up the process and at the same time prevent the switching elements of the circuit from being destroyed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a brushless motor circuit with a current limiting function according to an embodiment of the present invention, and FIG. 2 is a diagram of a conventional brushless motor circuit with a current limiting function. Explanation of symbols IO... Rectification/smoothing circuit, 20... Chiyo-Nno < circuit, 22... Transistor, 30... Load current detection circuit, 31... Current transformer, 35... Load current Limiting circuit, 40... Voltage feedback circuit, 43... Differential amplifier, 50... Nockles width modulation circuit, 55... Switching regulator, e o... Inverter circuit, 61a, Blb, 81c, 62a , 62b. 82c...transistor, 65...resistor, 70...
... Brushless motor, 80 ... Rotor position detection circuit, 81 ... Position detector, 82 ... Drive logic circuit, 9
0... F/V conversion circuit, 91... Differential amplifier, 92
...Speed feedback circuit, 94...Current limit circuit, 95.
...Motor current limiting circuit, 100...Pulse width modulation circuit, lL...Load current, ■...Motor current, P
, P...Chopper signal, M
CI C2 P...Speed pulse, ■...Speed command voltage, V
u. RS Vx, Vy...DC setting voltage.

Claims (1)

[Claims] 1. A motor circuit that supplies the output of a chopper circuit to a stator winding of a brushless motor via an inverter circuit, the motor circuit comprising: a first circuit that calculates a deviation of a chopper circuit output voltage from a DC set voltage; The chopper circuit includes a differential amplifier and a first pulse width modulation circuit that proportionally converts the output voltage of the first differential amplifier into a pulse width to set the on time of a switching element constituting the chopper circuit. The brushless motor comprises a load current limiting circuit that forcibly narrows the output pulse width of the first pulse width modulation circuit to throttle the load current when it is detected that the load current flowing through the switching element of the brushless motor is excessive. A rotor position detection circuit that detects the position of the rotor and issues on/off commands to the inverter circuit, as well as outputs speed pulses with a repetition frequency that corresponds to the motor speed, and converts the repetition frequency of this speed pulse into a DC voltage. An F/V conversion circuit that performs proportional conversion and outputs the same, a second differential amplifier that calculates the deviation of the output voltage of this F/V conversion circuit from the speed command voltage, and an output of this second differential amplifier. and a second pulse width modulation circuit that proportionally converts the voltage into pulse width to set the on-time of the switching elements that make up the inverter circuit, and detects that the motor current flowing through the switching elements of the inverter circuit is excessive. 1. A brushless motor circuit with a current limiting function, comprising a motor current limiting circuit that forcibly narrows the output pulse width of the second pulse width modulation circuit to throttle the motor current when the pulse width modulation circuit occurs.