JP5737604B2 - Power converter - Google Patents

Description

  The present invention, for example, in a power conversion device that drives an electric motor such as an inverter or a servo system, detects an abnormality in an optical pulse encoder (hereinafter also simply referred to as an encoder) or an abnormality in a wiring system and stops the operation. The present invention relates to a power conversion device having a countermeasure function.

  Inverters and servo systems that calculate the motor speed and rotor position from the output signal of an encoder attached to the output shaft of the motor and feed back the calculated values to drive the motor at a variable speed have become widespread. In these devices, if the output signal of the encoder is abnormal, it is difficult to operate normally. Therefore, various methods for stopping the operation of the inverter or the like by detecting the encoder abnormality or wiring system abnormality have been proposed. ing.

For example, FIG. 4 is a configuration diagram illustrating a main part of the abnormality monitoring device described in Patent Document 1.
In FIG. 4, 10 is an optical pulse encoder that outputs two-phase (A phase, B phase) analog signals that are 90 degrees out of phase, 20 is a cable made up of a power line, signal line, and ground line, and 30 is an encoder 10. This is a control device for processing the output signal to detect an abnormality of the encoder 10 or an abnormality of the wiring system including the cable 20 and to stop the operation of the inverter for driving the motor.

The encoder 10 includes an optical sensor (not shown) including a light emitting element, a slit, a light receiving element, and the like for generating an A-phase input signal and a B-phase input signal whose phases are different by 90 degrees by the rotation of the motor output shaft. Yes. A phase, B-phase input signals are inputted to the bases of the transistors _Tr 1, _{Tr 2,} transistors _Tr 1, Tr ₂ connection point between the limit resistors _{R 1} through each phase of the signal terminals A, respectively connected to the B Is done. Here, the power supply voltage V _c is supplied from the control device 30 to the encoder 10 via the cable 20.

In the control device 30, a voltage dividing resistor R _x is provided between the power supply terminal V _c , the A-phase signal terminal A, and the ground terminal M, and between the power supply terminal V _c , the B-phase signal terminal B, and the ground terminal M. , R _y are connected to each other.
The A-phase analog signal SigAana and the B-phase analog signal SigBana are respectively input to the analog input units 331A and 331B in the microcomputer 33, and the output signals of the analog input units 331A and 331B are converted into digital signals by the AD conversion units 332A and 332B. Is converted to Subsequent level abnormality detection units 333A and 333B to which these digital signals are input determine whether or not an analog high level or an analog low level is detected as an analog voltage, thereby detecting an abnormality when the motor is stopped (encoder 10). Failure of the output electric circuit, disconnection of the cable 20, short circuit between the signal line and the power source, ground fault, etc.) are detected.

On the other hand, the digital signal processing means 31A, 31B compares the analog signal with a threshold value using a comparator or the like, and creates the A-phase and B-phase digital signals SigA, SigB to be input to the microcomputer 33. Further, the signal synthesizing unit 32 calculates an exclusive OR of the digital signals SigA and SigB, and inputs this to the microcomputer 33 as a synthesized signal SigAB.
The digital signals SigA and SigB and the combined signal SigAB are input to digital input units 334A, 334B and 337 in the microcomputer 33, respectively.

  The output signals of the digital input units 334A and 334B are input to the pulse number comparison abnormality detection unit 336 via the counters 335A and 335B, and the abnormality in the motor rotation (encoder 10) is compared by comparing the number of pulses of the digital signals SigA and SigB. Failure of the output electric circuit, disconnection of the cable 20, short circuit between the signal line and the power source, ground fault, etc.) are detected. The output signal of the digital input unit 337 is input to the pulse width comparison abnormality detection unit 339 via the timer 338, and the motor rotation is similarly performed based on the “H” level pulse width (or cycle) of the composite signal SigAB. Various abnormalities at the time are detected.

JP 2010-203903 A (paragraphs [0029] to [0062], FIG. 1 and the like)

  According to the prior art related to Patent Document 1, it is possible to detect an abnormality in the output circuit of the encoder and the wiring system when the motor is stopped and rotating, and in particular, use various functions of an arithmetic processing unit such as a microcomputer. As a result, the power converter can be reduced in cost and size.

  In the optical pulse encoder, when a failure occurs in an optical sensor component such as a light emitting element, a slit, or a light receiving element provided in the encoder, the output signal becomes a fixed value. This is because when the light emitted from the light emitting element is received by the light receiving element through the slit and converted into an electrical signal, the light emitting element emits light if the light emitting element is not emitting light in the first place or if the light receiving element cannot receive light due to a slit failure. This is because the output signal is fixed without distinction from the case where the light normally emitted from the element is blocked by the slit.

In the prior art described in Patent Document 1, it is possible to detect a failure in the output electric circuit of the encoder when the electric motor is stopped, a break in the cable, a short circuit between the signal line and the power supply, a ground fault, etc. When the optical sensor in the encoder fails as described above, the output signal of the encoder cannot be distinguished from the output signal when the electric motor is stopped, so that an abnormality cannot be detected.
Further, since the output signal of the encoder does not change even when the motor is rotating, the monitoring device determines that the motor is stopped, and in this case, no abnormality can be detected.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable power conversion device that can detect an abnormality of an optical sensor inside an encoder before the operation of an electric motor is started.

In order to solve the above problem, a power conversion device according to claim 1 is a power conversion device that drives a motor at a variable speed by turning on and off a semiconductor switch, and includes a control device that generates a drive signal for the semiconductor switch, In the power converter configured to generate the drive signal by feeding back the rotational speed calculated from the output signal of at least two phases of the optical pulse encoder attached to the electric motor to the control device,
A safety function device that sends a safety measure signal for protecting the electric motor to the control device when detecting an abnormality in at least an output electric circuit or a wiring system of the encoder based on the output signal of the encoder;
The controller is
When a test start command is input from the safety function device before the start of operation of the motor, a DC voltage is applied between the stator windings of the motor for a short period of time to apply torque to the rotor of the motor. Having means for generating,
The safety function device determines that an optical sensor in the encoder is abnormal and outputs the safety countermeasure signal when there is no change in the output signal of the encoder within the application period of the DC voltage.

  The power conversion device according to claim 2 is the power conversion device according to claim 1, wherein the control device applies the DC voltage when a predetermined phase angle command value of an output voltage is input from the safety function device. When the phase angle command value changes, the amplitude of the output voltage is changed to operate the motor to generate torque.

  Furthermore, the power conversion device according to claim 3 is the power conversion device according to claim 1 or 2, wherein the safety measure signal is a safety cutoff signal for turning off all the semiconductor switches and stopping the operation of the motor. Features.

  According to the present invention, before starting the operation of the motor, that is, at the time of stopping the motor, it is possible to detect abnormality of the components constituting the optical sensor such as the light emitting element, the slit, and the light receiving element in the encoder. A highly efficient power conversion device can be provided.

It is a block diagram which shows embodiment of this invention. It is a block diagram of the control apparatus in FIG. It is a T type equivalent circuit diagram for one phase of an induction motor. It is a block diagram which shows the principal part of the abnormality monitoring apparatus described in patent document 1.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, reference numeral 100 denotes a power converter according to the present embodiment, and reference numeral 200 denotes a motor such as a three-phase induction motor driven by the power converter 100. An optical pulse encoder 10 that outputs two position detection signals (A-phase input signal and B-phase input signal) that are 90 degrees out of phase is attached to the output shaft of the electric motor 200. The output signal of the encoder 10 is It is input to the safety function device 40 in the power conversion device 100 via the cable 20.

Here, the safety function device 40 includes, for example, the control device 30 shown in FIG. 4. Based on the output signal of the encoder 10, the level abnormality detection of the analog input signal and the digital input signal are detected as described above. Pulse number comparison abnormality detection and pulse width comparison abnormality detection are performed, and an abnormality detection signal is generated. And based on this abnormality detection signal, it is comprised so that a safety | security cutoff signal may be output with respect to the logic circuit 52 in the control apparatus 50 mentioned later.
The safety shut-off signal is a specific example of the safety measure signal in the claims.

In addition, a safety stop command and a safety deceleration command are input to the safety function device 40. When the safety stop command is input, a safety cutoff signal for immediately stopping the operation of the electric motor 200 is output to the logic circuit 52. On the other hand, when a safety deceleration command is input, the safety function device 40 has an inclination for decelerating the electric motor 200 within a predetermined time (deceleration time) by, for example, a method described in Japanese Patent Application Laid-Open No. 2010-244266. According to this inclination, the speed command value is gradually lowered to decelerate the electric motor 200, and a safety shut-off signal for stopping within the deceleration time is output to the logic circuit 52.
Note that the circuit for generating the safety cutoff signal based on the output signal of the encoder 10 is not limited to the configuration described in FIG. 4 (JP 2010-203903 A) or JP 2010-244266 A. It is not something.

  The safety function device 40 outputs a phase angle command value, a current command value, and a test start command, which will be described later, in addition to the above-described safety cutoff signal, and these command values are input to the control device 50. Here, the test start command is for performing a test for detecting an abnormality of the optical sensor of the encoder 10 before the operation of the electric motor 200 is started (that is, when the motor 200 is stopped). The specific operation of the test will be described later. .

The control device 50 calculates a voltage command value based on the operation command, stop command, speed and torque command values, phase angle command value, and current command value, and compares the voltage command value with the carrier to generate a PWM signal. A control arithmetic unit 51 for calculating, and a logic circuit 52 for generating a drive signal for a three-phase (U, V, W phase) semiconductor switch based on the PWM signal are provided.
The drive signal output from the logic circuit 52 is sent to the drive circuit 60, and the semiconductor switch of the inverter unit 70 is turned on / off to supply a three-phase AC voltage to the electric motor 200.
Since there are various methods for generating a PWM signal in the control arithmetic unit 51, the method is not limited to the carrier comparison method described above.

Next, the configuration of the control calculator 51 will be described with reference to FIG.
The speed / torque adjusting unit 511 calculates a current command value of the electric motor 200 according to the speed command or the torque command, and the current command value is input to the switching unit 512. The switching means 512 is inputted with a DC safe current command value that is less than the rated current value of the electric motor 200 (for example, about 20% to 50% of the rated current) and has a constant magnitude. Here, the safe current command value is a kind of current command value output from the safety function device 40 of FIG.
When a test for detecting an internal failure of the encoder 10 is performed before the operation of the electric motor 200 is started, a test start command is output from the safety function device 40 by an input operation by an operator. When this test start command is input to the switching unit 512 of FIG. 2, the switching unit 512 switches the current command value to the safe current command value and outputs it.

  The current adjusting unit 513 compares the output of the switching unit 512 (the current command value output from the speed / torque adjusting unit 511 during normal operation and the safe current command value when inputting the test start command) with the detected current value. An adjustment calculation is performed so as to be equal to each other, and a voltage command value is output. In FIG. 1, a current detector for obtaining the current detection value is not shown. With this operation, when a test start command is input from the safety function device 40, the direct current flowing through the inverter unit 70 and the electric motor 200 becomes less than the rated current value, so that the failure of the device due to overheating can be prevented.

The coordinate conversion unit 514 performs coordinate conversion of the voltage command value output from the current adjustment unit 513 based on the safe phase angle command value (θ = 0 degrees, 120 degrees, 240 degrees) from the safety function device 40, and Equation 1 Thus, the U, V and W phase voltage command values are respectively calculated. The safe phase angle command value is a kind of phase angle command value in FIG.
[Formula 1]
V _u = V ^* cos θ
V _v = V ^* cos (θ-2π / 3)
V _w = V ^* cos (θ-4π / 3)
V ^* : voltage command value output from the current adjusting means 513

  The phase of the DC voltage supplied to the electric motor 200 is changed by performing coordinate conversion using three patterns of 0 degrees, 120 degrees, and 240 degrees as the safe phase angle command value θ, and a load is connected to the electric motor 200. However, the rotor can be moved instantaneously. This is because, for example, when the electric motor 200 is an induction motor, a magnetic flux is generated according to the phase angle of the applied voltage, and a current flows in the secondary circuit at the moment when the phase angle is changed to generate a minute torque. Is based.

The above operation will be described with reference to FIG. FIG. 3 shows a T-type equivalent circuit for one phase of the induction motor, where V is a terminal voltage, i ₁ is a primary current, i ₂ is a secondary current, R ₁ is a primary resistance, and R ₂ is a secondary resistance. , L ₁ is a primary inductance, L ₂ is a secondary inductance, and L _m is an excitation inductance.

When the safe phase angle command value θ is 0 degree, the U-phase voltage V _u becomes the maximum value (= V ^* ) from the above-described Equation 1. Since V ^* is substantially constant, when there is no change in the phase angle command value θ, the line voltage V _uv between the U and V phases (corresponding to the terminal voltage V in FIG. 3) becomes a DC voltage, and the DC primary current i ₁ flows. Next, when the safety phase angle command value is changed to 120 degrees (= 2π / 3 [rad]), the V-phase voltage V _v becomes the maximum value (= V ^* ) from Equation 1, so the line voltage V The amplitude of _uv changes. Since transitional changes in the primary current of the induction motor in accordance with the this occurs, the induced voltage on the secondary side flows the secondary current i _2.

  An induction motor does not generate torque even when current flows only on the primary side of the induction motor, but torque is generated when current flows instantaneously on the secondary side, and rotational force is generated. However, if the steady state is immediately restored, the secondary current becomes zero and no torque is generated. Thus, if the torque is instantaneously generated by changing the phase angle of the terminal voltage and the rotational force is generated, a situation in which the output signal of the encoder 10 changes can be created.

At this time, in the optical sensor inside the encoder 10, when light is not output due to a failure of the light emitting element, or a failure occurs such that the light receiving element cannot receive light due to a failure of the slit, the above method is used. Even if torque is generated instantaneously in the electric motor 200 and the rotor is slightly rotated, the output signal of the encoder 10 does not change at all before and after the rotation.
Since the safety function device 40 outputs a test start command to the control calculator 51 and monitors the output signal of the encoder 10 when the torque is instantaneously generated in the electric motor 200, the output signal does not change at all. Thus, it can be regarded as a failure of the optical sensor in the encoder 10.
Therefore, by taking safety measures such as fixing all the semiconductor switches of the inverter unit 70 in the OFF state by the safety cutoff signal, it is possible to prevent the control of the electric motor 200 based on the output signal of the encoder 10 in failure.
Note that during this test period, since the rotor only rotates slightly, the load does not move greatly, and the safety function is not impaired by this embodiment.

  In the above embodiment, the case where the safety function device 40 is single has been described. However, if the increase in cost can be allowed, the safety function devices are multiplexed in order to increase the reliability of the safety function, and each abnormality determination result If they are different, it may be determined that the safety function device itself is abnormal.

DESCRIPTION OF SYMBOLS 10: Encoder 20: Cable 40: Safety function apparatus 50: Control apparatus 51: Control computing unit 52: Logic circuit 60: Drive circuit 70: Inverter part 100: Power converter 200: Electric motor 511: Speed / torque adjustment means 512: Switching Means 513: Current adjustment means 514: Coordinate conversion means 515: PWM generation means

Claims (3)

A power conversion device for driving a motor at a variable speed by turning on and off a semiconductor switch, the control device generating a drive signal for the semiconductor switch, and an output signal of at least two phases of an optical pulse encoder attached to the motor In the power converter that generates the drive signal by feeding back the rotation speed calculated from the control device,
A safety function device that sends a safety measure signal for protecting the electric motor to the control device when detecting an abnormality in at least an output electric circuit or a wiring system of the encoder based on the output signal of the encoder;
The controller is
When a test start command is input from the safety function device before the start of operation of the motor, a DC voltage is applied between the stator windings of the motor for a short period of time to apply torque to the rotor of the motor. Having means for generating,
The safety function device determines that the optical sensor in the encoder is abnormal and outputs the safety countermeasure signal when there is no change in the output signal of the encoder within the application period of the DC voltage. Power conversion device. In the power converter device according to claim 1,
The controller is
When the predetermined phase angle command value of the output voltage is input from the safety function device, the DC voltage is applied, and when the phase angle command value changes, the amplitude of the output voltage is changed to rotate the motor. An electric power converter that operates to generate torque in a child. In the power converter device according to claim 1 or 2,
The power conversion apparatus according to claim 1, wherein the safety measure signal is a safety cutoff signal for turning off all the semiconductor switches and stopping the operation of the electric motor.

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