JP6238809B2 - Inverter control circuit - Google Patents

Description

  The present invention relates to an inverter control circuit that controls the operation of an inverter.

  When an overcurrent flows through the inverter that drives the load, it is necessary to immediately stop the load driving in order to protect the inverter from thermal destruction. Therefore, when an overcurrent is detected, output cutoff control is performed to cut off the output of the inverter.

  Patent Document 1 discloses an inverter overcurrent protection circuit. The overcurrent protection circuit includes a timer circuit that extends the output cutoff time when an overcurrent is detected. The output signal of the timer circuit is output to both the control circuit and the output cutoff circuit.

JP-A-11-215837

  It is conceivable that the output shut-off control of the inverter is performed by microcomputer software. However, in that case, software evaluation in accordance with international safety standards is required, resulting in an increase in cost. Furthermore, in order to perform software evaluation, it is necessary to disclose the contents of the software, resulting in a technical outflow. There is also a problem that when the output shutoff control function of the microcomputer fails, the inverter cannot be protected from thermal destruction.

  One object of the present invention is to provide an inverter control circuit capable of performing output cutoff control without using software.

In one aspect of the present invention, an inverter control circuit for controlling the operation of an inverter that drives a load is provided. The inverter control circuit includes a microcomputer, a drive circuit, an overcurrent detection circuit, a timer circuit, and a counter circuit. The microcomputer outputs a control signal for controlling the operation of the inverter. The drive circuit is configured only by hardware, and supplies a control signal to the inverter when the cutoff signal is inactivated, and cuts off supply of the control signal to the inverter when the cutoff signal is activated. The overcurrent detection circuit is configured only by hardware, and activates an overcurrent detection signal when the current flowing between the inverter and the load exceeds a threshold value. The timer circuit is configured only by hardware , and activates the cutoff signal for a predetermined time in response to activation of the overcurrent detection signal. The counter circuit is configured only by hardware , counts the number of times that the overcurrent detection signal or the cutoff signal is activated, and activates the stop signal when the number reaches the set number. When the stop signal is activated, the drive circuit cuts off the supply of the control signal to the inverter without depending on the cut-off signal.

  According to the inverter control circuit of the present invention, it is possible to perform the output shut-off control regardless of software. As a result, software evaluation according to international safety standards becomes unnecessary, and an increase in cost is prevented. Furthermore, it is not necessary to disclose the contents of the software, and technical outflow is prevented.

FIG. 1 is a block diagram showing a configuration example of an inverter control circuit according to an embodiment of the present invention. FIG. 2 is a timing chart showing an example of the operation of the inverter control circuit according to the embodiment of the present invention. FIG. 3 is a timing chart showing another example of the operation of the inverter control circuit according to the embodiment of the present invention.

  An inverter control circuit according to an embodiment of the present invention will be described with reference to the accompanying drawings.

Embodiment.
<Configuration>
FIG. 1 is a block diagram showing a configuration example of an inverter control circuit 1 according to an embodiment of the present invention. The inverter control circuit 1 controls the operation of the inverter 3 that drives the load 2. The load 2 is, for example, a compressor.

  The inverter control circuit 1 has an overcurrent detection function for detecting that an overcurrent has flown into the inverter 3 and an output cutoff control function for cutting off the output of the inverter 3 when an overcurrent is detected. More specifically, the inverter control circuit 1 includes a microcomputer 10, a drive circuit 20, an overcurrent detection circuit 30, a timer circuit 40, and a counter circuit 50.

  The microcomputer 10 outputs a control signal PWM that controls the operation of the inverter 3. Typically, the control signal PWM is a signal for PWM control of the switching element of the inverter 3.

  The drive circuit 20 is provided between the microcomputer 10 and the inverter 3, and performs ON / OFF control of supply of the control signal PWM output from the microcomputer 10 to the inverter 3. More specifically, the drive circuit 20 receives a cutoff signal BLK output from a timer circuit 40 described later. When the blocking signal BLK is inactivated (BLK = Low), the drive circuit 20 supplies the control signal PWM as it is to the inverter 3 as the control signal PWM ′. In this case, the inverter 3 operates according to the control signal PWM ′ and drives the load 2.

  On the other hand, when the cut-off signal BLK is activated (BLK = High), the drive circuit 20 cuts off the supply of the control signal PWM (PWM ′) to the inverter 3. In this case, the operation of the inverter 3 is stopped, that is, the output of the inverter 3 is cut off. As a result, driving of the load 2 by the inverter 3 is stopped. Thus, the drive circuit 20 provides an output cutoff control function.

  Further, the drive circuit 20 outputs an error signal / ERR to the microcomputer 10. More specifically, when the cutoff signal BLK is deactivated (BLK = Low), the drive circuit 20 deactivates the error signal / ERR (/ ERR = High). On the other hand, when the cutoff signal BLK is activated (BLK = High), the drive circuit 20 activates the error signal / ERR (/ ERR = Low). When the error signal / ERR is activated, the microcomputer 10 stops the output of the control signal PWM, that is, performs output cutoff control by software.

  The overcurrent detection circuit 30 provides an overcurrent detection function for detecting that an overcurrent has flowed through the inverter 3. More specifically, the overcurrent detection circuit 30 monitors the current flowing between the inverter 3 and the load 2, determines whether the current exceeds the overcurrent level (threshold), and indicates the determination result. An overcurrent detection signal OVC is output. If the current does not exceed the overcurrent level, the overcurrent detection circuit 30 deactivates the overcurrent detection signal OVC (OVC = Low). On the other hand, when the current exceeds the overcurrent level, the overcurrent detection circuit 30 activates the overcurrent detection signal OVC (OVC = High).

  For example, as illustrated in FIG. 1, the overcurrent detection circuit 30 includes a shunt resistor 31 and a comparator 32. The shunt resistor 31 is connected between the node 33 and the ground. A current id corresponding to the current flowing between the inverter 3 and the load 2 flows through the shunt resistor 31, and a voltage Vd corresponding to the current id appears at the node 33. The comparator 32 compares the voltage Vd of the node 33 with a reference voltage Vref set according to the overcurrent level, and outputs the comparison result as an overcurrent detection signal OVC. Specifically, when the voltage Vd is equal to or lower than the reference voltage Vref, the overcurrent detection signal OVC is Low, and when the voltage Vd exceeds the reference voltage Vref, the overcurrent detection signal OVC is High.

  The timer circuit 40 receives the overcurrent detection signal OVC output from the overcurrent detection circuit 30. In response to the overcurrent detection signal OVC, the timer circuit 40 sets the state of the cutoff signal BLK input to the drive circuit 20. More specifically, when an overcurrent is detected and the overcurrent detection signal OVC is activated, that is, when the overcurrent detection signal OVC is changed from Low to High, the timer circuit 40 performs a constant timer period PT. Meanwhile, the blocking signal BLK is activated (BLK = High). When the timer period PT elapses, the timer circuit 40 deactivates the cutoff signal BLK (BLK = Low). As such a timer circuit 40, for example, a monostable multivibrator can be used.

  The counter circuit 50 counts the number of times that an overcurrent is detected by the overcurrent detection circuit 30. Therefore, the counter circuit 50 monitors the cutoff signal BLK output from the timer circuit 40, and counts the number of times that the cutoff signal BLK is activated (BLK = High). Alternatively, the counter circuit 50 may monitor the overcurrent detection signal OVC output from the overcurrent detection circuit 30 and count the number of times that the overcurrent detection signal OVC is activated (OVC = High).

  The counter circuit 50 outputs a stop signal STP having a level corresponding to the count value. More specifically, when the count value is less than the predetermined set value, the counter circuit 50 keeps the stop signal STP inactive (STP = Low). On the other hand, when the count value reaches a predetermined set value, the counter circuit 50 activates the stop signal STP (STP = High).

  The stop signal STP is input to the drive circuit 20 described above. When the stop signal STP is inactivated (STP = Low), the drive circuit 20 performs ON / OFF control of the supply of the control signal PWM to the inverter 3 according to the cutoff signal BLK as described above. On the other hand, when the stop signal STP is activated (STP = High), the drive circuit 20 cuts off the supply of the control signal PWM to the inverter 3 regardless of the cut-off signal BLK. That is, the drive circuit 20 forcibly cuts off the output of the inverter 3.

  The count value of the counter circuit 50 is initialized by an initialization signal INI output from the microcomputer 10. For example, the microcomputer 10 outputs the initialization signal INI to the counter circuit 50 in the initialization sequence, and initializes the count value.

  The count value of the counter circuit 50 is reset by a reset signal RST output from the microcomputer 10. As described above, when the count value reaches a predetermined set value, the stop signal STP is activated and the output of the inverter 3 is cut off. This state is maintained until the reset signal RST is input to the counter circuit 50. When the microcomputer 10 outputs the reset signal RST to the counter circuit 50, the count value is reset and the stop signal STP is deactivated again.

<Operation>
With reference to FIG.2 and FIG.3, operation | movement of the inverter control circuit 1 which concerns on this Embodiment is demonstrated. 2 and 3 are the control signal PWM output from the microcomputer 10, the error signal / ERR and control signal PWM ′ output from the drive circuit 20, the voltage Vd of the node 33, and the overcurrent detection circuit 30. These are the overcurrent detection signal OVC output, the cutoff signal BLK output from the timer circuit 40, and the stop signal STP output from the counter circuit 50.

  First, the case where the microcomputer 10 has not failed will be described with reference to FIG.

  At time t1, the inverter control circuit 1 is turned on. The microcomputer 10 starts outputting the control signal PWM after executing the initialization sequence. The drive circuit 20 supplies the control signal PWM as it is to the inverter 3 as the control signal PWM ′. The inverter 3 operates according to the control signal PWM ′ and drives the load 2. The voltage Vd of the node 33 is equal to or lower than the reference voltage Vref, that is, in a normal range, and the overcurrent detection signal OVC remains inactivated (OVC = Low).

  When the load 2 is, for example, a compressor motor, the compressor motor is locked. When the compressor motor locks, the current id and the voltage Vd increase.

  At time t2, the voltage Vd exceeds the reference voltage Vref, and the overcurrent detection signal OVC becomes High. That is, the overcurrent detection circuit 30 detects the overcurrent and activates the overcurrent detection signal OVC (OVC = High). In response to the activation of the overcurrent detection signal OVC, the timer circuit 40 activates the cutoff signal BLK for a certain timer period PT (BLK = High).

  When the cutoff signal BLK is activated, the drive circuit 20 cuts off the supply of the control signal PWM (PWM ′) to the inverter 3. That is, the output of the control signal PWM ′ from the drive circuit 20 is stopped. As a result, the drive of the compressor motor by the inverter 3 is stopped.

  In response to the activation of the blocking signal BLK, the drive circuit 20 activates the error signal / ERR (/ ERR = Low). In response to the activation of the error signal / ERR, the microcomputer 10 stops the output of the control signal PWM, that is, performs output cutoff control by software. Thereafter, the microcomputer 10 maintains a state where the output of the control signal PWM is stopped.

  When the drive of the compressor motor by the inverter 3 stops, the current id and the voltage Vd decrease. At time t3, the voltage Vd becomes equal to or lower than the reference voltage Vref, and the overcurrent detection signal OVC changes from High to Low. However, the cutoff signal BLK output from the timer circuit 40 remains High.

  At time t4 after the elapse of the timer period PT from time t2, the cutoff signal BLK output from the timer circuit 40 returns from High to Low.

  Note that after a certain time (eg, 3 minutes) has elapsed since the compressor stopped, the microcomputer 10 performs a restart process, whereby the state returns to normal. The predetermined time is determined in advance in consideration of the time during which the pressure in the compressor decreases and the motor load decreases. The predetermined time is preset in a storage means such as a ROM.

  Next, with reference to FIG. 3, the case where the output cutoff control function by the software of the microcomputer 10 has failed will be described. Note that the description overlapping with that in FIG. 2 is omitted as appropriate.

  At time t2, in response to the activation of the cutoff signal BLK, the drive circuit 20 activates the error signal / ERR (/ ERR = Low). Although the error signal / ERR is activated, the microcomputer 10 continues to output the control signal PWM because the output cutoff control function by software is broken. However, since the drive circuit 20 cuts off the supply of the control signal PWM (PWM ′) to the inverter 3, the drive of the compressor motor by the inverter 3 is stopped. That is, even if the output cutoff control function by the software of the microcomputer 10 is broken, the output cutoff control is realized by the drive circuit 20 which is hardware.

  During the timer period PT from time t2 to time t4, the cutoff signal BLK output from the timer circuit 40 remains High, and the output of the control signal PWM ′ from the drive circuit 20 remains stopped. That is, the driving of the compressor motor by the inverter 3 is also stopped.

  At time t4, the cutoff signal BLK output from the timer circuit 40 returns from High to Low. In this example, since the microcomputer 10 continues to output the control signal PWM, the drive circuit 20 resumes outputting the control signal PWM '. However, since the compressor motor remains in the locked state, the current id and the voltage Vd increase again, and an overcurrent is detected again at time t5. As a result, the overcurrent detection signal OVC and the cutoff signal BLK are activated again (OVC = High, BLK = High).

  At time t6, as in the case of time t3 described above, the overcurrent detection signal OVC changes from High to Low, but the cutoff signal BLK output from the timer circuit 40 remains High. That is, the drive of the compressor motor by the inverter 3 remains stopped. Thereafter, the same signal change is repeated.

  Thus, during the timer period PT in which the cutoff signal BLK is High, the drive circuit 20 stops the load drive by the inverter 3. The timer period PT (for example, time t2 to time t4) is longer than the period in which overcurrent is detected (for example, time t2 to t3). That is, the timer circuit 40 plays a role of extending the drive stop period.

  In particular, as shown in FIG. 3, when the output cutoff control function by the software of the microcomputer 10 is broken, the drive state and the drive stop state are alternately repeated, but the drive stop period becomes long. Thus, thermal destruction of the inverter 3 is effectively prevented. The timer period PT is preferably set to such a length that the heat generated by the overcurrent is sufficiently dissipated.

  Further, in the present embodiment, the counter circuit 50 counts the number of overcurrent detections. At time t10 in FIG. 3, the count value reaches a predetermined set value, and the counter circuit 50 activates the stop signal STP (STP = High). When the stop signal STP is activated, the drive circuit 20 cuts off the supply of the control signal PWM to the inverter 3 regardless of the cut-off signal BLK. That is, the drive circuit 20 forcibly maintains the drive stop state. As a result, when the output cutoff control function by the software of the microcomputer 10 is out of order, a situation in which the driving state and the driving stop state are repeated endlessly is prevented. This also contributes to prevention of thermal destruction of the inverter 3.

<Effect>
As described above, according to the present embodiment, the drive circuit 20 is provided between the microcomputer 10 and the inverter 3. The drive circuit 20 cuts off the supply of the control signal PWM (PWM ′) to the inverter 3 in response to the overcurrent detection. Therefore, even if the output cutoff control function by the software of the microcomputer 10 breaks down, the output cutoff control is realized by the drive circuit 20 which is hardware.

  That is, according to the present embodiment, it is possible to perform the output cutoff control regardless of software. As a result, software evaluation according to international safety standards becomes unnecessary, and an increase in cost is prevented. Furthermore, it is not necessary to disclose the contents of the software, and technical outflow is prevented.

  Further, according to the present embodiment, the timer circuit 40 sets the timer period PT, which is the period during which the drive circuit 20 stops the load driving by the inverter 3. More specifically, the timer period PT is set longer than the period during which an overcurrent is detected. That is, the timer circuit 40 plays a role of extending the drive stop period. When the output cutoff control function by the software of the microcomputer 10 is broken, the drive state and the drive stop state are alternately repeated as shown in FIG. 3, but the drive stop period becomes long, so that the inverter 3 Is effectively prevented from thermal destruction.

  Further, according to the present embodiment, the counter circuit 50 counts the number of overcurrent detections. When the count value reaches a predetermined set value, the drive circuit 20 forcibly maintains the drive stop state. As a result, when the output cutoff control function by the software of the microcomputer 10 is out of order, a situation in which the driving state and the driving stop state are repeated endlessly is prevented. This also contributes to prevention of thermal destruction of the inverter 3.

  The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the above-described embodiments, and can be appropriately changed by those skilled in the art without departing from the scope of the invention.

  1 Inverter control circuit, 2 load, 3 inverter, 10 microcomputer, 20 drive circuit, 30 overcurrent detection circuit, 31 shunt resistor, 32 comparator, 33 nodes, 40 timer circuit, 50 counter circuit, BLK cutoff signal, / ERR error signal , INIT initialization signal, OVC overcurrent detection signal, PT timer period, PWM, PWM 'control signal, RST reset signal, STP stop signal, Vref reference voltage, Vd voltage.

Claims (3)

An inverter control circuit that controls the operation of an inverter that drives a load,
A microcomputer that outputs a control signal for controlling the operation of the inverter;
A drive that is configured only by hardware and that supplies the control signal to the inverter when a cut-off signal is inactive, and cuts off the supply of the control signal to the inverter when the cut-off signal is activated Circuit,
An overcurrent detection circuit configured only with hardware and activating an overcurrent detection signal when a current flowing between the inverter and the load exceeds a threshold;
A timer circuit configured only by hardware and activating the cutoff signal for a predetermined time in response to the activation of the overcurrent detection signal;
A counter circuit configured only with hardware , counting the number of times the overcurrent detection signal or the cutoff signal is activated, and activating a stop signal when the count value reaches a set value;
When the stop signal is activated, the drive circuit shuts off the supply of the control signal to the inverter regardless of the shut-off signal. When the blocking signal is activated, the drive circuit activates an error signal,
The inverter control circuit according to claim 1, wherein when the error signal is activated, the microcomputer stops outputting the control signal. The inverter control circuit according to claim 1, wherein the microcomputer outputs an initialization signal for initializing the count value to the counter circuit in an initialization sequence.

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