JPH02111220A - Protecting device for brushless dc motor - Google Patents

Abstract

PURPOSE:To prevent an inverter power converter from damaging and the perma nent magnet of a rotor from demagnetizing by setting the maximum value of a rotating speed change rate per unit time of the rotor, comparing the change rate of the actual rotating speed with the set value, and stopping in emergency a motor in case of its malfunction. CONSTITUTION:A position detection signal discriminator 10 inputs the real rotating speed N of a rotor 5a from a microcomputer (muc) 7, further inputs position detection signals (a), (b), (c) from a counterelectromotive force position detector 6, determines whether the detection of the maximum change rate (dN/ dt)max of the rotating speed per unit time of the rotor having a minimum inertial moment, set therein from the detector 6 is according to an erroneous detection due to a noise or the like or not, and outputs an emergency stop command to the muc 7 as an erroneous detection determination signal E. The muc 7 stops a base driver 9 and an inverter 4 with the command. Thus, it can prevent Tr1-Tr6 from damaging and the rotor 5a from demagnetizing.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to brushless DC motors, and in particular, to protection suitable for avoiding demagnetization and failure of inverter circuits due to malfunctions during position detection of brushless DC motors. Regarding equipment.

[Conventional technology]

A brushless DC motor, which can be considered a type of synchronous motor based on its operating principle, has a rotor made of permanent magnets. When current is supplied to each phase of the armature winding in turn, torque is generated by the magnetic field from the rotor's permanent magnets and the current in the armature winding, and the frequency of the current supplied to the armature winding changes. The rotors rotate at a synchronized number of rotations.

Since a brushless DC motor does not have brushes or a commutator, it uses an inverter made up of power conversion elements such as transistors to sequentially supply current to each phase of the armature winding. Therefore, it is necessary to detect the magnetic pole position of the rotor and switch the phase of the armature winding to which current is supplied by using an inverter in accordance with the position of the rotor. However, since the rotor made of permanent magnets rotates, a back electromotive force is generated in the stationary armature winding.

When an inverter supplies current to the armature winding where a back electromotive force is generated, torque is generated in the forward direction (same direction as the rotational direction). To deal with this excessive torque, inverters for induction motors, including conventional brushless DC motors, use high-speed fuses or detect the inverter input current or inverter output current to urgently shut off the inverter power conversion elements. This is intended to protect the conversion element.

In addition, in a conventional brushless DC motor, Japanese Patent Laid-Open No. 59-16279 is related to a back electromotive force position detection circuit that uses a filter and a comparator to obtain a position detection signal.
3 and Japanese Patent Publication No. 59-36519, there is Japanese Patent Application Laid-Open No. 62-123979 which is related to correction for the inability to detect a position due to a phase shift of a position detection signal.

[Problem to be solved by the invention]

In a brushless DC motor, if the position detection signal cannot be constantly detected due to noise, failure or malfunction of the detection circuit, disconnection of the detection wiring, etc., current will be supplied to the wrong phase of the armature winding and the inverter will There is a problem in that excessive torque is generated when the input DC voltage and the voltage induced in the armature winding are added (this state is called reverse phase).

Even if the conventional protection method described above is applied to this reverse phase problem, the inverter power conversion element may be destroyed.

It is difficult to prevent demagnetization of the rotor's permanent magnets.

Demagnetization of a permanent magnet is a phenomenon in which when a large current flows through the armature winding, the magnetic field of the permanent magnet is canceled by the magnetic field generated by the current, and the magnetic flux of the permanent magnet decreases. .

An object of the present invention is to provide a protection device for a brushless DC motor that can prevent destruction of an inverter power conversion element and demagnetization of a permanent magnet of a rotor even if a 1-position detection signal cannot be detected normally. .

cam] The above purpose is to set the maximum value of the rotation speed change rate per unit time of the rotor, and to compare the actual rotation speed change rate with this set value. This is achieved by determining whether the position detection is normal or not, and in the case of abnormality, by emergency stopping the motor.

[Effect]

If the position detection signal is abnormal, the actual rotation speed change rate will be significantly different from the set value. Therefore, the occurrence of an abnormality can be detected by comparing the actual rotational speed change rate with the set value. For this reason,
If the motor is stopped when an abnormality is detected, destruction of the inverter power conversion element and demagnetization of the permanent magnet can be avoided.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram of a brushless DC motor, an inverter, and a speed control circuit equipped with a protection device according to an embodiment of the present invention. In FIG. 1, the AC rtt pressure of the AC power supply 1 is applied to the rectifier circuit 2 and the smoothing capacitor 3 by
The voltage is converted into a DC voltage Ed and supplied to the inverter 4. This inverter 4 includes transistors T r l to Tr
6 and freewheeling diodes D1 to D6, and its AC output voltages VA, VB
, VC is a transistor on the positive potential side of the DC voltage Ed]
The 6 brushless DC motor 5 is controlled by a chopper operation in which the energizing period (electrical angle 120 degrees) of Tr 1 to Tr 3 is subjected to pulse width modulation. It consists of a phase rtt and a state winding 5b, and each AC output voltage (VtVc) of the inverter 4 is applied to each phase of the armature winding 5b.

A speed control circuit that controls the speed of the brushless DC motor 5 uses a microcomputer 7 and an output voltage of an inverter j4 to control the magnetic pole position of the rotor 5a.

A back electromotive voltage position detection circuit 6 detects VB and VC, and a resistor R1 detects the DC current value of the DC section, and the motor current I is determined from this detected value and commands I+ and C from the microcomputer 7.
A current control unit 8 that creates a chopper signal C that controls L.
, a chopper signal C from the current control section 8 and a command signal (drive signal) B from the microcomputer 7.
The pace driver 9 controls the base currents of the transistors Tr1 to Tr6.

The position detection signal determination circuit 10, which is a protection device according to an embodiment of the present invention, detects the back emitter 4 by the detection signal a of the normal position detection circuit 6,
b, c and the actual rotational speed signal N from the microcomputer 7
In response to this, a determination is made as will be described later, and a determination signal E is sent to the microcomputer 7.

FIG. 2 is a diagram showing details of the relationship between the back electromotive force position detection circuit 6, the microcomputer 7, and the position detection signal determination circuit 10 shown in FIG. The microcomputer 7 is C
It is equipped with a P U 7 a, a ROM 7 b, a RAM 7 c, a timer 7 d, and an input/output capo door e.
Various control processing programs necessary to drive the brushless DC motor 5 are stored in M7b. This microcomputer 7 receives the output signal a of the back electromotive force position detection circuit 6.

b and c, and outputs a driver signal B to the pace driver 9 and a current command ILC to the current control unit 8.

The back electromotive voltage position detection circuit 6 filters the output voltage (terminal voltage) Vc of the inverter 4 with a filter consisting of a capacitor C1°C4 and resistors R2 and R5 to obtain a voltage Vc'.
The output voltage (terminal voltage) Va of the inverter 4 is calculated using a filter consisting of capacitors C2 and C5 and resistors R3 and R6.
is filtered to obtain the voltage Vs', and the output voltage of the inverter 4 (
Terminal voltage)■^Filter to obtain voltage V^',
These voltages VA', Va', Vc' and the resistances R8, R9, of these voltages VA'Va'+Vc'
The midpoint voltage VN of the star connection by RIO is connected to the comparators CPI, CP2 . A comparison is made using CP3, and the comparison result is used as a position detection signal a g b HO corresponding to the rotor position. FIG. 3 shows the voltages V^ and Va mentioned above.

vc, ■^', ■B', vc' and voltage VN, and signal a
, b, and Q waveform diagrams.

The position detection signal determination circuit 1o determines the actual rotational speed N of the rotor 5a.
is taken in from the microcomputer 7, and a position detection signal a is received from the back electromotive voltage position detection circuit 6.

b and c are imported and set internally. From the maximum rate of change (d N / d t ) - ax in the number of rotations per unit time of the rotating body having the minimum moment of inertia, it can be determined whether the detection by the back electromotive force position detection circuit 6 is an erroneous detection due to noise or the like. If it is determined that it is an erroneous detection, an emergency stop command is sent to the microcomputer 7 as a determination signal E.
Output to. Upon input of this emergency stop command, the microcomputer 7 stops the pace driver 9 and stops the inverter 4. As a result, the transistor Tr
i to Tr6 are not destroyed, and the first rotor 5a is not demagnetized.

FIG. 4 is a detailed configuration diagram of the position detection signal determination circuit 10. The position detection signal determination circuit 10 includes a counter 10a,
Arithmetic circuit 10b, trigger circuit 10c, and counter 0
d, comparator 10e, and flip-flop log
, 10f, and an OR gate 10h. counter 0
As shown in FIG. 5, a counts the time interval T (time of 60 electrical degrees) at which the position detection signals a, b, and c change.

The arithmetic circuit 10b calculates the count value T of the counter 0a, the actual rotation value N from the microcomputer 7, and the maximum rate of change value (
From d N / d t ) max, the following formula (1),
According to (2), the minimum value of the time interval T m t. and the maximum value T wa a x is calculated.

Tl1tn= 1 / (N + (d N/ d t
)-ax X T) ”'(1) T, a, = 1
/(N (d N/ d t)-axX T)”
(2) The trigger circuit 10c detects changes in the 1-position detection signals a, b, and Q and outputs a start pulse S to the counter 10d, as shown in FIG. With this start pulse S, the counter 10d has an initial value of T m a x
It takes in the countdown, and the count value is 1.
When the count reaches 1011, a count-up signal U is output. The fact that this count-up signal U is output indicates that the position detection signals a, b, and Q do not change even after a time period of T□8 or more has elapsed. In other words, when the actual rotational speed N decreases and the rate of decrease becomes equal to or higher than the set maximum rate of change, it can be determined that the back electromotive voltage position detection circuit 6 is malfunctioning due to noise or the like.

The value T and the calculated value T wr t n are compared, and Tl1in
>T, the signal D% ratio is output. The fact that the signal + signal is output from the comparator 10a indicates that the position detection signal a*b+Q has changed in a time less than or equal to T +a t n. In other words, this indicates that the rotational speed N has changed below the set maximum rate of change, and it can be determined that the back electromotive voltage position detection circuit 6 is malfunctioning due to noise or the like.

The flip-flops 10f and 10g are
hold, OR gateco, oh is Noritsubu flop 1
The logical sum of 0f and 1.0g is output to the microcomputer 7 as an emergency stop signal E. microcomputer 7
Upon receiving this command E, it stops the drive signal B and also sets the current commands I+ and c to zero, thereby stopping the driving force of the brushless DC motor 5.

When the microcomputer 7 receives the emergency stop signal E, it temporarily stops the inverter 4 as described above, and then outputs a reset signal to the position detection signal determination circuit 10. Specifically, the flip-flop 10f resets the abnormal state held at Log. This results in 1
The position detection and determination of the position detection signal are continued to determine whether the position detection has returned to normal. Microcomputer 7.

If it is detected using the internal timer 7d that the position detection has returned to normal within a certain period of time, the pace driver 9
A hetribe signal B is output, a current command ILC calculated from the rotation speed N is output to the current control unit 8, and the drive of the brushless DC motor is restarted.

In the above-described embodiment, the 1-position detection signal determination circuit 10 is configured by hardware, but the operation of the position detection signal determination circuit 10 can also be realized by software in the microcomputer 7.

In this case, for example, the procedure is as follows.

The maximum rate of change in the number of rotations per unit time (a N / at ) wax of a rotating body with the minimum moment of inertia is.

Position detection signal a stored in ROM 7b.

b and e are input from the input/output port door e and are temporarily stored in the RAM 7c. The CPU 7a receives position detection signals a, b, c.
is imported from the input/output port door e, and the previously imported RA
By comparing the contents temporarily stored in M7C,
Detects a change in the position detection signal. When the CPU 7a detects a change in the position detection signal, the CPU 7a temporarily stores the count value of the timer 7d in the RAM 7c, and subtracts the count value stored in the RAM 7c from the value of the timer 7d's run 1 when the position detection signal changes next time. Calculate the time interval T.

Next, the calculations (1) and (2) above are performed by the CPU 7a, and r m 1 n , T m a ! are found and temporarily stored in the RAM 7c. The CPTJ 7a adds 1゛□n+Tmax to the count value of the timer 7d, and the result is T+T-t. , T + 1'-ax as R
Temporarily stored in AM7c.

When detecting a change in the position detection signal, the result of adding the count value of the timer 7d and -1-] is T + "I"
-ax, the count value is the addition result T+T□8
If it exceeds this, it is assumed that the position detection circuit has malfunctioned and an emergency stop is performed. Also, when a change in the position detection signal is detected, the count value of the timer 7d.

+ The above addition result T+'l''-In is compared, and if the value of Callan 1 does not exceed the addition result T+T111, an emergency stop is performed as an error in the position detection circuit. Further, when a malfunction of the position detection circuit is detected, the drive of the brushless DC motor 5 is temporarily stopped, the above-mentioned position detection and judgment operation of the position detection signal are continued, and the timer 7d
If it is detected that the position detection signal has returned to normal within a certain period of time.

The drive of the brushless DC motor 5 is restarted.

According to each of the above embodiments, when it is determined that the position detection has malfunctioned, the drive of the brushless DC motor 5 is temporarily stopped, and the position detection is continued to determine whether the position detection returns to normal. When this is detected, the drive of the brushless DC motor is restarted, so that destruction of the power conversion element of the inverter and demagnetization of the permanent magnet of the rotor can be prevented, and the rotation of the brushless DC motor 5 can be maintained. This has the effect of increasing reliability.

〔Effect of the invention〕

According to the present invention, even if the position detection signal is not normally detected due to noise, a failure of the detection circuit, or a break in the malfunction detection wiring, the inverter can prevent the inverter from energizing the armature windings in the opposite phase. This has the effect of protecting the power conversion elements of the inverter from being destroyed and the permanent magnets of the single rotor from being demagnetized.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of a brushless DC motor, an inverter, and a speed control circuit equipped with a protection device according to an embodiment of the present invention, and FIG. 2 is a diagram showing the back electromotive force position detection circuit and microcomputer shown in FIG. 3 is a signal waveform diagram illustrating the operating principle of the back electromotive force position detection circuit; FIG. 4 is a detailed configuration diagram of the position detection signal determination circuit shown in FIG. 1; FIG. 5 is an explanatory diagram of the counter shown in FIG. 4, and FIG. 6 is an explanatory diagram of the trigger circuit shown in FIG. 4. 1... AC power supply, 2... Rectifier circuit, 3... Smoothing capacitor, 4... Inverter, 5... Brushless DC motor. 6... Back electromotive force position detection circuit, 7... Microcomputer, 8... Current control section, 9... Pace driver, 10... Position detection signal determination circuit (protection device). ＋II□fCustomer I1; No.0 1 '-'Fy

Claims (1)

[Claims] 1. In a brushless DC motor equipped with a position detection circuit that obtains a position detection signal corresponding to the magnetic pole position of the rotor from the inverter output voltage, a means for setting the maximum rotation speed change rate of the rotor and an actual rotation speed of the rotor are provided. The brushless direct current is characterized by comprising means for comparing the rate of change of the rotational speed with the maximum rotational speed change rate and determining the presence or absence of an abnormality based on the comparison result, and means for stopping the inverter when it is determined that there is an abnormality. Motor protection device.