JP2010088231A - Driver circuit and its protection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protection method for preventing damage of a switching element by preventing an increase of surge voltage due to sudden stop. <P>SOLUTION: A driver circuit includes: a DC chopper circuit for transforming an input voltage supplied from outside, and for output of a transformed power; and an inverter for generating an AC drive power from a power input from the DC chopper circuit, and for output of the drive power to a driving object. The driver circuit also includes a drive current limiting means limiting a drive current which the inverter outputs to any value not more than a prescribed upper limit value when the voltage of input power is determined to drop to a threshold set to be higher than the operation limit voltage. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a driver circuit including a DC chopper circuit and an inverter, and a protection method thereof.

Patent Document 1 below discloses a motor driver protection circuit that prevents inflow of an overcurrent due to a short circuit accident of a motor driver provided in a vehicle air conditioner and ensures the grounding of a stabilized power circuit. Yes. The motor driver protection circuit includes a motor driver that controls driving of the actuator motor by electric power supplied from the stabilized power supply circuit, and the first ground terminal of the motor driver is connected to the first of the control unit by the first ground wiring. 2 is connected to the ground terminal and grounded to the external first ground connection point. On the other hand, in the stabilized power supply circuit, the second ground wiring connected to the stabilized power supply circuit is connected to the first ground wiring so as to connect to the ground connection point outside the control unit, and to the second ground connection point. The second ground connection point is connected to the power transistor unit to be connected, and the disconnection avoidance diode is provided between the second ground wiring and the power transistor unit so that the cathode is on the power transistor unit side. With such a configuration, even if a short circuit occurs in the motor driver, an overcurrent does not flow to the motor driver due to the stabilized power circuit, and the connection between the stabilized power circuit and the first ground connection point is disconnected. Are connected to the second ground connection point, and the ground of the stabilized power supply circuit is secured.
JP-A-9-93798

  By the way, the above-mentioned prior art controls the stabilized power circuit by controlling the current so that no overcurrent flows to the motor driver and securing the connection between the stabilized power circuit and the second ground connection point. Ensures stable operation and protects the motor driver. However, in such a driver circuit (corresponding to the above-described stabilized power supply circuit and motor driver), when the power source is a battery, the driver input voltage supplied from the battery during driving of the motor increases with time. The phenomenon that it falls is generated.

  And if a driver input voltage falls outside a driver driving | operation possible range, an internal control mechanism will stop in a driver circuit, and a power conversion process will be stopped in connection with it. Then, the driver input current from the battery is stopped, and a large surge voltage is generated in the connector voltage of the switching element constituting the driver circuit due to the influence of the inductance component of the wiring connected to the connector terminal. Then, the switching element may be damaged by this large surge voltage. As described above, the above-described prior art still has a problem that the switching element is damaged by the surge voltage generated by the decrease in the driver input voltage.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a device that can prevent damage to a switching element by preventing an increase in surge voltage caused by an unexpected stop.

In order to achieve the above object, in the present invention, as a first solution means for a driver circuit, a DC chopper circuit that transforms input power supplied from the outside and outputs the transformed power, and the DC chopper circuit, A driver circuit having an inverter that generates alternating current drive power from input power and outputs the drive power to a drive target, up to the threshold set to a voltage higher than the operation limit voltage, the input power Driving current limiting means for limiting the driving current output from the inverter to a predetermined upper limit value or less,
A means of providing is adopted.

In the present invention, as the second solving means relating to the driver circuit, in the first solving means, the driving current limiting means limits the maximum value of the current manipulated variable, thereby limiting the driving current output from the inverter. The method of limiting the value to a predetermined upper limit value or less is adopted.

  In the present invention, as a third solving means related to the driver circuit, in the first or second solving means, the driving current limiting means is configured to input the input up to a threshold set to a voltage higher than an operation limit voltage. If it is determined that the power voltage has decreased, a means for outputting a notification signal for limiting the drive current to the outside is employed.

  In the present invention, as a fourth solving means relating to the driver circuit, in any one of the first to third solving means, the DC chopper circuit is any one of a step-up chopper circuit, a step-down chopper circuit, and a step-up / step-down chopper circuit. Adopt a certain means.

  In the present invention, as a first solving means related to the protection method of the driver circuit, a DC input power supplied from the outside is transformed, and a DC chopper circuit that outputs the transformed power is input from the DC chopper circuit. A method for protecting a driver circuit having an inverter that generates AC drive power from the generated power and outputs the drive power to a drive target, up to a threshold set to a voltage higher than the operation limit voltage, When the voltage of the input power decreases, a means for limiting the drive current output from the inverter to a predetermined upper limit value or less is adopted.

  According to the present invention, when the driver circuit determines that the voltage of the input power has decreased to a threshold set to a voltage higher than the operation limit voltage, the drive current output by the inverter is set to a predetermined upper limit value or less. By providing the drive current limiting means for limiting, it is possible to prevent the control system of the DC chopper circuit from being stopped due to a decrease in the voltage of the input power. Further, by preventing the control system of the DC chopper circuit from being stopped, it is possible to prevent damage to the switching element due to an increase in surge voltage.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing a configuration of a driver circuit A according to the present embodiment. First, the circuit configuration of the driver circuit A will be described with reference to FIG.
The driver circuit A rotates a permanent magnet synchronous motor C, which is a load, by DC driver input power supplied from a battery B. As shown in FIG. 1, the booster chopper circuit 1, inverter 2, U-phase current A detection unit 3, a V-phase current detection unit 4, a W-phase current detection unit 5, a voltage sensor 6 and an inverter control unit 7 are provided. The permanent magnet synchronous motor C is provided with a rotational position detector D. The rotational position detector D detects the rotational position of the rotor of the permanent magnet synchronous motor C. A rotational position detection signal θ indicating the rotational position is output to the speed calculator 7i.

The step-up chopper circuit 1 boosts the voltage of the driver input power supplied from the battery B and supplies it to the inverter 2. The chopper input terminals 1a-1, 1a-2, choke coil 1b, switching transistor 1c, MOSFET 1d , A smoothing capacitor 1e, and chopper output terminals 1f-1 and 1f-2.
The chopper input terminals 1a-1 and 1a-2 are a pair of connection terminals for inputting driver input power to the step-up chopper circuit 1. One chopper input terminal 1a-1 is connected to the positive terminal of the battery B, The other chopper input terminal 1a-2 is connected to the negative terminal of the battery B.

  The choke coil 1b has one end connected to one chopper input terminal 1a-1 and the other end connected to the collector terminal of the switching transistor 1c. The switching transistor 1c has a collector terminal connected to the other end of the choke coil 1b and the source terminal of the MOSFET 1d, and an emitter terminal connected to the other chopper input terminal 1a-2. The base terminal of the switching transistor 1c is connected to a boost chopper circuit control unit (not shown), and a PWM signal as a control signal is input from the inverter control unit 7.

  The MOSFET 1d has a source terminal connected to the other end of the choke coil 1b and the collector terminal of the switching transistor 1c, and a drain terminal connected to one end of the smoothing capacitor 1e and one chopper output terminal 1f-1. As described above, the smoothing capacitor 1e has one end connected to the drain terminal of the MOSFET 1d and one chopper output terminal 1f-1, and the other end connected to the other chopper input terminal 1a-2, the other chopper output terminal 1f-2, and switching. It is connected to the emitter terminal of the transistor 1c. That is, both ends of the smoothing capacitor 1e are connected to the chopper output terminals 1f-1 and 1f-2, respectively. The chopper output terminals 1f-1 and 1f-2 are a pair of connection terminals for outputting the output power of the boost chopper circuit 1 to the inverter 2, and one chopper output terminal 1f-1 is connected to one end of the inverter 2. The other chopper output terminal 1f-2 is connected to the other end of the inverter 2.

The inverter 2 generates three-phase motor drive power including a U phase, a V phase, and a W phase based on the PWM signal input from the inverter control unit 7 and outputs the motor drive power to the permanent magnet synchronous motor C. It comprises inverter input terminals 2a-1, 2a-2, a smoothing capacitor 2b, six switching transistors 2c-1 to 2c-6, and three inverter output terminals 2d-1 to 2d-3.
The inverter input terminals 2a-1 and 2a-2 are a pair of connection terminals for inputting output power from the boost chopper circuit 1 to the inverter 2. One inverter input terminal 2a-1 is a chopper of the boost chopper circuit 1. The other inverter input terminal 2 a-2 is connected to the output terminal 1 f-1 and is connected to the chopper output terminal 1 f-2 of the boost chopper circuit 1.

  The smoothing capacitor 2b has one end connected to the one inverter input terminal 2a-1 and the other end connected to the other inverter input terminal 2a-2. The six switching transistors 2c-1 to 2c-6 constitute first to third switching arms connected in parallel to the smoothing capacitor 2b as shown in the figure. That is, among the six switching transistors 2c-1 to 2c-6, the switching transistor 2c-1 and the switching transistor 2c-2 are the first switching arm, and the switching transistor 2c-3 and the switching transistor 2c-4 are The second switching arm and the switching transistor 2c-5 and the switching transistor 2c-6 constitute a third switching arm, respectively.

  The switching transistor 2c-1 constituting the first switching arm has a collector terminal connected to the one inverter input terminal 2a-1, an emitter terminal connected to the collector terminal of the switching transistor 2c-2, and a base terminal connected to the inverter control unit 7. Each is connected. As described above, the switching transistor 2c-2 has a collector terminal connected to the emitter terminal of the switching transistor 2c-1, an emitter terminal connected to the other inverter input terminal 2a-2, and a base terminal connected to the inverter control unit 7. ing. In such a first switching arm, the connection point between the emitter terminal of the switching transistor 2c-1 and the collector terminal of the switching transistor 2c-1 is the output terminal of the first switching arm.

  The switching transistor 2c-3 constituting the second switching arm has a collector terminal connected to the one inverter input terminal 2a-1, an emitter terminal connected to the collector terminal of the switching transistor 2c-4, and a base terminal connected to the inverter control unit 7. Each is connected. In the switching transistor 2c-4, the collector terminal is connected to the emitter terminal of the switching transistor 2c-3, the emitter terminal is connected to the other inverter input terminal 2a-2, and the base terminal is connected to the inverter control unit 7 as described above. ing. In such a second switching arm, the connection point between the emitter terminal of the switching transistor 2c-3 and the collector terminal of the switching transistor 2c-4 is the output terminal of the second switching arm.

  The switching transistor 2c-5 constituting the third switching arm has a collector terminal connected to the one inverter input terminal 2a-1, an emitter terminal connected to the collector terminal of the switching transistor 2c-6, and a base terminal connected to the inverter controller 7. Each is connected. As described above, the switching transistor 2c-6 has a collector terminal connected to the emitter terminal of the switching transistor 2c-5, an emitter terminal connected to the other inverter input terminal 2a-2, and a base terminal connected to the inverter control unit 7. ing. In such a third switching arm, the connection point between the emitter terminal of the switching transistor 2c-5 and the collector terminal of the switching transistor 2c-6 is the output terminal of the third switching arm.

  A PWM signal as a control signal is input from the inverter control unit 7 to the base terminals of the switching transistors 2c-1 to 2c-6. In the first to third switching arms, each of the switching transistors 2c-1 to 2c-6 is turned on / off based on the PWM signal, so that the phase difference between each of the output ends becomes 120 °, V phase Phase and W phase AC motor drive power is output. The first switching arm outputs U-phase motor driving power, the second switching arm outputs V-phase motor driving power, and the third switching arm outputs W-phase motor driving power.

  The three inverter output terminals 2d-1 to 2d-3 are connection terminals for outputting the three-phase motor drive power to the permanent magnet synchronous motor C. Of the inverter output terminals 2d-1 to 2d-3, the first inverter output terminal 2d-1 is the output terminal of the first switching arm, and the second inverter output terminal 2d-2 is the second switching terminal. The output terminal of the arm and the third inverter output terminal 2d-3 are connected to the output terminal of the third switching arm, respectively. Each of the inverter output terminals 2d-1 to 2d-3 is connected to the permanent magnet synchronous motor C, and U-phase, V-phase, and W-phase AC motor drive power is supplied to the permanent magnet synchronous motor C. Supply.

  The U-phase current detection unit 3 is provided on the U-phase drive signal line that connects the inverter output terminal 2d-1 of the inverter 2 and the U-phase stator winding of the permanent magnet synchronous motor C, and the inverter output terminal 2d- The motor drive current Iu flowing from 1 to the U-phase stator winding is detected and output to the inverter control unit 7. The V-phase current detection unit 4 is provided on a V-phase drive signal line that connects the inverter output terminal 2d-2 of the inverter 2 and the V-phase stator winding of the permanent magnet synchronous motor C, and the inverter output terminal 2d- The motor drive current Iv flowing from 2 to the V-phase stator winding is detected and output to the inverter control unit 7. The W-phase current detection unit 5 is provided on a W-phase drive signal line that connects the inverter output terminal 2d-3 of the inverter 2 and the W-phase stator winding of the permanent magnet synchronous motor C, and the inverter output terminal 2d- The motor drive current Iw flowing from 3 to the W-phase stator winding is detected and output to the inverter control unit 7.

  The voltage sensor 6 has one terminal connected to the positive terminal of the battery B and the chopper input terminal 1a-1, and the other terminal connected to the negative terminal of the battery B and the chopper input terminal 1a-2. The voltage sensor 6 outputs a detection signal Sv indicating the input voltage to the inverter control unit 7.

  FIG. 2 is a functional block diagram showing a functional configuration of the inverter control unit 7 of the driver circuit A according to the present embodiment. The inverter control unit 7 controls the rotation of the permanent magnet synchronous motor C by PWM control of the inverter 2, and as shown in FIG. 2, a three-phase / two-phase conversion unit 7a, a subtraction unit 7b, a speed Controller 7c, limiter 7d, q-axis current controller 7e, d-axis current controller 7f, 2-phase / 3-phase converter 7g, PWM signal generator 7h, speed calculator 7i and limit value controller 7j, q-axis voltage It comprises a limiter 7k and a d-axis voltage limiter 7l. Note that the voltage sensor 6, the limit value control unit 7j, and the limiter 7d constitute drive current limiting means in the present embodiment.

  The three-phase / two-phase converter 7a includes U-phase, V-phase, and W-phase motor drive currents Iu, Iv detected by the U-phase current detector 3, the V-phase current detector 4, and the W-phase current detector 5, respectively. Qw driving current detection amount Iq and d axis driving current detection amount on a two-dimensional coordinate system (coordinate system consisting of q axis and d axis) fixed on the rotor of the permanent magnet synchronous motor C based on Iw Id is calculated, the q-axis drive current detection amount Iq is output to the q-axis current control unit 7e, and the d-axis drive current detection amount Id is output to the d-axis current control unit 7f.

  More specifically, the three-phase / two-phase conversion unit 7a performs a predetermined coordinate conversion on the motor driving currents Iu, Iv, Iw on the three-dimensional coordinate system including the U phase, the V phase, and the W phase, thereby performing the above 2 processing. A q-axis drive current detection amount Iq and a d-axis drive current detection amount Id on the dimensional coordinate system are calculated. The q axis is a coordinate axis set in the opposing direction of the S pole and the N pole of the permanent magnet on the rotating surface of the rotor, and the d axis is a coordinate axis orthogonal to the q axis described above.

The subtractor 7b calculates a difference between the angular velocity command value ω0 supplied from an ECU (Engine Control Units) which is a host controller and the angular velocity ωk of the rotor of the permanent magnet synchronous motor C supplied from the speed calculator 7i as a speed error. It calculates as (DELTA) omega and outputs to the speed control part 7c.
The speed control unit 7c is a kind of PID control unit, calculates a q-axis current manipulated variable Iqs corresponding to the speed error Δω by performing a predetermined proportional integral / differential operation on the speed error Δω, and the q-axis current The manipulated variable Iqs is output to the limiter 7d.

The limiter 7d limits the maximum value of the q-axis current manipulated variable Iqs to be equal to or less than the limit value input from the limit value control unit 7j, and outputs the limit value to the q-axis current control unit 7e.
The q-axis current control unit 7e is a kind of PID control unit. The q-axis current operation amount Iqs whose maximum value is limited by the limiter 7d and the q-axis drive current detection supplied from the three-phase / two-phase conversion unit 7a. An error current ΔIq is calculated as a difference from the amount Iq, and the voltage operation amount Vq is calculated by subjecting the error current ΔIq to predetermined proportional integration / differentiation operations, respectively. The voltage operation amount Vq is calculated as a q-axis voltage limiter 7k. Output to.

The d-axis current control unit 7f is based on the d-axis current operation amount Ids supplied from the ECU and the d-axis drive current detection amount Ids input from the three-phase / two-phase conversion unit 7a. Is calculated, and the d-axis voltage manipulated variable Vd is output to the d-axis voltage limiter 7l.
The q-axis voltage limiter 7k limits the maximum value of the voltage manipulated variable Vq to be equal to or less than a predetermined limit value, and outputs it to the 2-phase / 3-phase converter 7g.
The d-axis voltage limiter 7l limits the maximum value of the voltage manipulated variable Vd to be equal to or less than a predetermined limit value, and outputs the limit to the two-phase / three-phase converter 7g.

  The 2-phase / 3-phase converter 7g converts the q-axis voltage manipulated variable Vq input from the q-axis current controller 7e and the d-axis voltage manipulated variable Vd input from the d-axis current controller 7f into the U-phase, The voltage manipulated variables Vu, Vv, Vw are converted into voltage manipulated variables Vu, Vv, Vw on the three-dimensional coordinate system composed of the V phase and the W phase, and the voltage manipulated variables Vu, Vv, Vw are output to the PWM signal generator 7h.

  The PWM signal generator 7h generates a PWM signal for switching the inverter 2 based on the voltage operation amounts Vu, Vv, Vw and outputs the PWM signal to the inverter 2. The inverter control unit 7 operates based on a sine wave energization method. Therefore, the PWM signal generation unit 7h is configured so that the inverter 2 outputs a motor drive signal over the entire rotation angle (360 °) of the permanent magnet synchronous motor C. A PWM signal is output so as to be output.

The speed calculation unit 7i differentiates the rotational position detection signal θ input from the rotational position detection unit D, thereby calculating the angular speed ωk as the rotational state value of the permanent magnet synchronous motor C, and subtracts the angular speed ωk from the angular speed ωk. Output to.
The limit value control unit 7j determines whether or not the driver input voltage has decreased to a predetermined threshold based on the detection signal Sv input from the voltage sensor 6. When the driver input voltage decreases to the threshold, the limit value control unit 7j The limit value is lowered to the upper limit value and the limit value is output to the limiter 7d.

Next, the operation of the driver circuit A configured as described above will be described in detail with reference to FIG.
FIG. 3 is a waveform diagram showing the driver input voltage, the current of the driver input power (driver input current), and the collector voltage of the switching transistor 1c and the switching transistors 2c-1 to 2c-6. 3A shows the driver input voltage when the driver input voltage is lowered to the driver operation limit voltage, and the solid line waveform shows the driver input voltage of the present embodiment.

  Also, the dotted waveform in FIG. 3B indicates the driver input current when the driver input voltage is reduced to the driver operation limit voltage, and the solid waveform indicates the input voltage of the present embodiment. Further, the dotted waveform in FIG. 3C shows the collector voltage of the switching transistor 1c and the switching transistors 2c-1 to 2c-6 when the driver input voltage is lowered to the driver operation limit voltage, and the solid line waveform is The collector voltage of this embodiment is shown. Note that the driver operation limit voltage in FIG. 3A is a driver input voltage at which the operation of the control system of the step-up chopper circuit 1 stops due to insufficient voltage, and the driver operation limit voltage is a limit value control unit. 7j is the above threshold value that serves as a determination criterion when determining whether or not to lower the limit value.

In the driver circuit A, the driver input power supplied from the battery B is boosted to a predetermined voltage by the boost chopper circuit 1, and the boosted DC power is converted into three-phase motor drive power by the inverter 2 to be a permanent magnet synchronous motor. C is supplied.
In the driver circuit A, the voltage sensor 6 always outputs the detection signal Sc to the limit value control unit 7j of the inverter control unit 7.

And since the electric charge which the battery B has is finite, as shown to (a) of FIG. 3, driver input voltage falls with time.
When the driver input voltage decreases to the driver operation limit voltage shown in FIG. 3A, the limit value control unit 7j decreases the limit value to a predetermined upper limit value and outputs the limit value to the limiter 7d. The limiter 7d limits the maximum value of the q-axis current manipulated variable Iqs to be equal to or less than the limit value input from the limit value control unit 7j, and outputs the limit value to the q-axis current control unit 7e.

  Then, the limiter 7d limits the q-axis current manipulated variable Iqs, so that the inverter 2 sets the current of the motor driving power output to the permanent magnet synchronous motor C to a predetermined upper limit value or less. As a result, the driver input current decreases as shown by the solid line in FIG. Further, this prevents the driver input voltage from dropping below the driver operation limit voltage as shown by the solid line in FIG. The driver circuit A can continue to operate without stopping the control system of the step-up chopper circuit 1 because the driver input voltage does not drop below the driver operable voltage.

  When the limit value of the limiter is not lowered as in the prior art, the driver input voltage falls below the driver operation limit voltage as shown by the dotted line in FIG. (Not shown) stops. As a result, the driver input current rapidly decreases as shown by the dotted line in FIG. A large electromotive force is generated at the collector terminals of the switching transistor 1c and the switching transistors 2c-1 to 2c-6 due to an abrupt drop in the driver input current and the inductance component of the wiring to be connected. As shown by the dotted line, a large surge voltage is generated in the collector voltage. The large surge voltage causes the switching transistor 1c and the switching transistors 2c-1 to 2c-6 to be damaged.

  However, in the driver circuit A, since the control system of the step-up chopper circuit 1 does not stop, the surge voltage generated in the collector voltage is suppressed low as shown by the solid line in FIG. 3C, and the switching transistor 1c and the switching transistor 2c-1 The damage of ˜2c-6 can be prevented.

As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, For example, the following modifications can be considered.
(1) Although the driver circuit A provided with the boost chopper circuit 1 has been described in the above embodiment, the boost chopper circuit in the present invention is not limited to this. In addition to the step-up chopper circuit, the DC chopper circuit includes a step-down chopper circuit and a step-up / step-down chopper circuit. The step-up chopper circuit in the present invention can be applied to such a step-down chopper circuit and step-up / step-down chopper circuit.

(2) In the above embodiment, the limit value control unit lowers the limit value and decreases the motor drive current. However, the ECU notifies the ECU of a notification signal to limit the motor drive current to the permanent magnet synchronous motor C. It may be outputted and the ECU may notify the outside by a display unit or the like.

It is a circuit diagram which shows the structure of the driver circuit A which concerns on one Embodiment of this invention. It is a functional block diagram which shows the function structure of the inverter control part 7 of the driver circuit A which concerns on one Embodiment of this invention. It is a wave form diagram which shows the driver input voltage of the driver circuit A which concerns on one Embodiment of this invention, a driver input current, and the collector voltage of the switching transistor 1c and the switching transistors 2c-1 to 2c-6.

Explanation of symbols

DESCRIPTION OF SYMBOLS A ... Driver circuit, B ... Battery, C ... Permanent magnet synchronous motor, D ... Rotation position detection part, 1 ... Boost chopper circuit, 1a-1, 1a-2 ... Chopper input terminal, 1b ... Choke coil, 1c ... Switching transistor 1d ... MOSFET, 1e ... smoothing capacitor, 1f-1,1f-2 ... chopper output terminal, 2 ... inverter, 2a-1,2a-2 ... inverter input terminal, 2b ... smoothing capacitor, 2c-1 to 2c-6 ... Switching transistor, 2d-1 to 2d-3 ... Inverter output terminal, 3 ... U-phase current detector, 4 ... V-phase current detector, 5 ... W-phase current detector, 6 ... Voltage sensor, 7 ... Inverter controller 7a, 3-phase / 2-phase converter, 7b, subtractor, 7c, speed controller, 7d, limiter, 7e, q-axis current controller, 7f, d-axis current controller, 7g, 2-phase / 3-phase change. Parts, 7h ... PWM signal generating section, 7i ... speed calculating unit, 7j ... limiting value control unit, 7k ... q-axis voltage limiter, 7l ... d-axis voltage limiter

Claims (5)

A DC chopper circuit that transforms DC input power supplied from the outside, outputs the transformed power, and generates AC drive power from the power input from the DC chopper circuit, and outputs the drive power to the drive target A driver circuit having an inverter to
When it is determined that the voltage of the input power has decreased to a threshold set to a voltage higher than the operation limit voltage, drive current limiting means for limiting the drive current output by the inverter to a predetermined upper limit value or less,
A driver circuit comprising the driver circuit.   2. The driver circuit according to claim 1, wherein the drive current limiting unit limits the drive current output from the inverter to a predetermined upper limit value or less by limiting a maximum value of a current operation amount.   When the driving current limiting means determines that the voltage of the input power has decreased to a threshold set to a voltage higher than the operating limit voltage, the driving current limiting means outputs a notification signal to the outside to limit the driving current. 3. The driver circuit according to claim 1, wherein the driver circuit is characterized in that:   4. The driver circuit according to claim 1, wherein the DC chopper circuit is any one of a step-up chopper circuit, a step-down chopper circuit, and a step-up / step-down chopper circuit. A DC chopper circuit that transforms DC input power supplied from the outside, outputs the transformed power, and generates AC drive power from the power input from the DC chopper circuit, and outputs the drive power to the drive target A method of protecting a driver circuit having an inverter that includes:
A method for protecting a driver circuit, wherein when the input power voltage drops to a threshold value set to a voltage higher than an operation limit voltage, the drive current output from the inverter is limited to a predetermined upper limit value or less. .

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