JP3286830B2 - Motor overcurrent protection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as a means for protecting a drive circuit for controlling the rotation and the direction of rotation of a motor by a pulse width modulation method, in particular, a means for preventing a power switching element included in the drive circuit from being destroyed. The present invention relates to an overcurrent protection device.

[0002]

2. Description of the Related Art An overcurrent protection device is provided in order to prevent an overcurrent from flowing into a drive circuit for controlling the rotation and the direction of rotation of an electric motor, thereby preventing a power switching element constituting the drive circuit from being destroyed. Provided. As a conventional example of this overcurrent protection device, for example, Japanese Patent Application Laid-Open No. 61-15571
There is known an "overcurrent protection device for a PWM inverter" described in Japanese Patent Application Laid-Open (JP-A) No. 10-125139. This device monitors a gate signal pattern that simultaneously ignites the gates of power switching elements constituting an inverter drive circuit, and shuts off a gate signal to the power switching elements when an abnormal pattern is detected for a predetermined time. Thus, an overcurrent is prevented.

[0003]

However, the overcurrent protection device for a PWM inverter described above operates only when a gate signal pattern that simultaneously ignites the gates of the power switching elements is generated. Even if the control circuit or the like malfunctions and the motor locks, a gate signal pattern for generating a normal maximum torque continues to be output. Therefore, there is a problem that the destruction of the power switching element cannot be reliably prevented.

An object of the present invention is to solve such a problem,
It is an object of the present invention to provide an overcurrent protection device that can reliably prevent a power switching element from being destroyed when a pulse width modulation signal that gives a maximum torque to a motor is repeatedly output.

[0005]

According to the present invention, there is provided an overcurrent protection apparatus for controlling a rotation and a rotation direction of an electric motor based on a pulse width modulation signal input periodically. A protection unit that measures a pulse width or a pulse pause period of the pulse width modulation signal, and shuts off an input pulse width modulation signal to the drive circuit when the pulse width is repeatedly output beyond a predetermined time. Features.

[0006] The protection means sets, for example, the pulse width or pulse pause period of the pulse width modulation signal having the period T to a period t (= T
(Natural number) clock signal for each cycle T, a first setting circuit for setting the upper limit of the duration of the pulse width, and a value measured by the first measuring means for the first time. A second measuring means for measuring the number of times exceeding the set value of the setting circuit; and a second setting circuit for setting an upper limit value of the number of times, wherein the value measured by the second measuring means is the second value.
The pulse width modulation signal is cut off when a value set by a setting circuit is exceeded.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram of an overcurrent protection device according to an embodiment of the present invention. This overcurrent protection device includes a first modulation signal PWM1 and a reset signal RST.
And a control circuit 1 for generating a control signal SIGN, a first modulation signal PW
M1, a measurement circuit 2 for generating a second modulation signal PWM2 based on a reset signal RST, a one-shot signal OST and a clock signal CLK, a clock generation circuit 3 for generating a clock signal CLK, and a one-shot for generating a one-shot signal OST A circuit 4 and a drive circuit 5 for controlling the rotation and the rotation direction of the electric motor 6 based on the control signal SIGN and the second modulation signal PWM2 are provided. The drive circuit 5 includes a plurality of power switching elements (transistors).

The first modulation signal PWM1 has a carrier cycle T (se
c) is a pulse width modulated signal in which the duty changes,
The clock signal CLK is a signal having a period t (= T / natural number). The one-shot signal OST is, for example, a pulse signal having a width of t / 2, and is output at a period T with a rising edge of the second modulation signal PWM2 as a trigger. Reset signal
RST is a signal output at an arbitrary timing.

The duty ratio H (%) of the first modulation signal PWM1
Represents the pulse width, that is, the period of logic 1 level (“1”) as X
(Sec), it is expressed by the following equation (1). H = 100 · X / T (1)

FIG. 2 is a diagram showing an example of a circuit configuration of the measuring circuit 2, FIG. 3 is a diagram showing an example of a circuit configuration of the drive circuit 5, and FIG. Also,
5 is an explanatory diagram of a change state of the pulse width, FIG. 6 is an equivalent circuit of the electric motor 6, and FIG. 7 is an explanatory diagram of a control section in the electric motor 6.

First, the operation of each section having the above configuration will be specifically described with reference to the drawings. When the reset signal RST is input from the control circuit 1 when the power is turned on, the measuring circuit 2
The reset signal RST is input to the reset terminal MR of the flip-flop circuit (FF circuit) 13 as shown in FIG.
The measuring circuit 2 also outputs the output of the FF circuit 13 and the control circuit 1
AND condition with the first modulation signal PWM1 output from the
The output of the second modulation signal PWM2
Is sent to the one-shot circuit 4 and the drive circuit 5.

The one-shot circuit 4 has a second modulation signal PWM2 (= first modulation signal PWM1) which is an output of the AND circuit 17.
Triggered by the rising edge of, a one-shot signal OST having a pulse width of t / 2 is generated at a period T and sent to the measurement circuit 2 (see FIG. 4).

The drive circuit 5 includes a pair of transistors Tr1 for determining the rotation direction of the electric motor 6 based on the control signal SIGN.
8, while turning on / off Tr19, and turning on / off the transistors Tr20 and Tr21 that determine the supply current IM to the electric motor 6 based on the second modulation signal PWM2 (see FIG. 3). That is, the control signal SIGN from the control circuit 1
Is "1", the transistor Tr19 is turned on. At this time, the transistor Tr18 is turned off by the action of the NOT circuit 22 that logically inverts the control signal SIGN. Conversely, when the control signal SIGN is "0", the transistor Tr19 turns off and the transistor Tr18 turns on. On the other hand, the transistor Tr21 is turned on when the control signal SIGN is "1" and the second modulation signal PWM2 is "1". At this time, the transistor Tr20 is turned off. Conversely, the control signal SIGN
Is “0” and the second modulation signal PWM2 is “1”, AND
The transistor Tr21 is turned off by the operation of the circuit 24.
Then, the transistor Tr20 is turned on by the operation of the NOT circuit 22 and the AND circuit 24. Thereby, the rotation and the rotation direction of the electric motor 6 are controlled.

Here, when the second modulation signal PWM2 is "1" (that is, PWM2 = PWM1) and the control signal SIGN is also "1", the current I supplied from the plus side of the DC power supply is the transistor T
The current flows through r18 to the electric motor 6 as the current IM. As shown in FIG. 6, this current IM returns from the motor 6 to the drive circuit 5 again through the armature resistor 25, and flows to the minus side of the DC power supply through the transistor Tr21. In this case, the applied voltage VM (see FIG. 6) to the electric motor 6 can be approximated by the duty ratio H of each of the modulation signals PWM1 and PWM2. For example, the DC power supply supplies the drive circuit 5 with a voltage V
Is supplied, the voltage VM applied to the electric motor 6 can be approximated by the equation (2) by the duty ratio H of the first modulation signal PWMN1 (= PWM2). VM = V · H (2)

Here, V is a supply voltage (V) from a DC power supply.
It is. Since the applied voltage VM can be approximated in this manner, the current IM (A) shown in the equation (3) flows through the motor 6 by the armature resistance 25, and the torque P (kg · cm) shown in the equation (4)
Occurs. IM = VM / RM (3) P = KE · I (4) where RM is the armature resistance (Ω) of the motor 6 and KE is the torque constant (kg · cm / A) of the motor 6 , I are supply currents from the DC power supply.

Now, assuming that the motor 6 is controlled in the rising section S and the falling section S in the speed curve 26 of FIG.
max is required. The duty ratio Hmax of the first modulation signal PWM1 (= PWM2) for causing the motor 6 to generate the torque Pmax is calculated by the equations (2) to (4). FIG.
This shows how the pulse width of the first modulation signal PWM1 (= PWM2) changes in this case, and shows a pattern A (pulse width X
a, It changes like a pattern B having a longer pulse width Xb than the pulse pause period Za). The pulse pause period Zb (sec) in the pattern B is expressed by the following equation (5). Zb = T− (Hmax · T) (5)

The measuring circuit 2 first determines the pulse pause period Zb
Is measured by the counter 7. The counter 7 includes a clock signal CLK from the clock generation circuit 3 and a first modulation signal PWM1.
AND circuit 1 for determining a logical result condition with a logical inversion signal of
The count value is reset by a one-shot signal OST from the one-shot circuit 4. Output value D1 of counter 7
Is input to the DA terminal of the comparator 8. In the comparator 8,
The output value D1 is compared with the set value S1 of the setting circuit 9. In the present embodiment, the lower limit value of the pulse pause period (upper limit value of pulse width continuation length = Zmin / t = Zb / t: digital value)
Is set as the set value S1, and this is input to the DB terminal of the comparator 8. The comparator 8 calculates the input value (D1) of the DA terminal.
> Outputs "0" when the relationship of the input value (S1) of the DB terminal is established, that is, in the case of the pattern A in FIG. 5, and outputs "1" in the opposite case, that is, in the case of the pattern B in FIG. I do.

The counter 10 counts the number of times “1” is output from the comparator 8. The one-shot signal OST from the one-shot circuit 4 is input to the clock terminal CK, and the reset from the control circuit 1 is performed. The output of the AND circuit 16 for determining the AND condition of the signal RST and the output of the comparator 8 is input to the reset terminal MR. The output value D2 of the counter 10 is input to the DA terminal of the comparator 11. Comparator 1
At 1, the output value D2 is compared with the set value S2 of the setting circuit 12. In the present embodiment, the acceleration section S shown in FIG.
A value obtained by dividing (sec) by the period T (sec) is set as a set value S2, and this is input to the DB terminal of the comparator 11 in advance.

The comparator 11 calculates the input value (D2) of the DA terminal>
When the relationship of the input value (S2) of the DB terminal is established, that is, when the pattern B of FIG. 5 is repeatedly output, "1" is output, and this is input to the clock terminal CK of the FF circuit 13 which is a holding circuit. I do. At this time, the FF circuit 13 outputs “0”. When this output is input to the AND circuit 17, the second modulation signal PWM2 to the drive circuit 5 is set to "0". That is, the second modulation signal PWM2 (first modulation signal PWM1) is cut off. In this case, the reset signal RS
The logic state of the second modulation signal PWM2 is not changed until T is input.

As described above, when the motor 6 is accelerated or decelerated, FIG.
Is output from the control circuit 1, and when the pattern B is repeatedly output exceeding a set value, the measurement circuit 2 outputs the modulated signal PWM1 (=
PWM2) is cut off, so the motor 6 can be locked,
Even if the control system goes out of control, overcurrent does not flow to the drive circuit 5, and the conventional problem is solved.

[0021]

As is apparent from the above description, according to the present invention, even when the motor is locked due to malfunction of the control system or the like, the pulse width modulation signal having the duty ratio for generating the maximum torque continues to be output. When the duty of the pulse width modulation signal exceeds the set value and the pulse width modulation signal is repeatedly output, the pulse width modulation signal is cut off, so that an overcurrent does not flow to the drive circuit. Thereby, the destruction of the power switching element can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram of an overcurrent protection device according to an embodiment of the present invention.

FIG. 2 is a detailed configuration diagram of a measurement circuit according to the present embodiment.

FIG. 3 is a detailed configuration diagram of a drive circuit according to the present embodiment.

FIG. 4 is an operation timing chart of the embodiment.

FIG. 5 is an explanatory diagram showing a change state of a pulse width in a pulse width modulation signal.

FIG. 6 is an equivalent circuit of a motor.

FIG. 7 is a diagram illustrating an example of a rotation control mode of the electric motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Control circuit 2 Measurement circuit 3 Clock generation circuit 4 One-shot circuit 5 Drive circuit 6 Motor 7,10 Counter 8,11 Comparator 9,12 Setting circuit 13 FF circuit 14,16,17 AND circuit 18-21 Included in drive circuit Transistor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 7/48 H02H 3/08 H02P 7/63

Claims (1)

(57) [Claims] 1. A pulse width modulation signal input periodically.
Drive circuit for controlling rotation and direction of rotation of motor based on
And the pulse width or pulse pause of the pulse width modulation signal
The pulse width is measured at each cycle, and the pulse width exceeds a predetermined length.
Input pulse width to the drive circuit when output is repeated
Protection means for blocking the modulation signal, wherein the protection means has a pulse width of a pulse width modulation signal having a period T.
Alternatively, the pulse pause period is set to a clock of cycle t (= T / natural number).
A first measuring means for measuring at every cycle T using a
A first setting circuit for setting a continuous length upper limit value of the pulse width;
The value measured by the first measuring means is set in the first setting circuit.
A second measuring means for measuring the number of times exceeding a predetermined value, and the number of times
A second setting circuit for setting an upper limit value of
The value measured by the measuring means exceeds the value set in the second setting circuit.
Shut off the pulse width modulation signal when
Motor overcurrent protection device.