JP2016010243A - AC voltage conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage conversion device which can be stably functioned while taking measures to cope with overcurrent.SOLUTION: The voltage conversion device using a chopper system including a semiconductor switching device and obtaining predetermined AC output of a predetermined voltage from an AC power source further includes an over current control device by which a current of the semiconductor switching device is detected, a voltage to be outputted is reduced to 40% to 60% of the predetermined voltage for 2 to 6 ms in the case where a current exceeding a threshold is detected, and the output voltage is then returned to an original value.

Description

  The present invention relates to an AC voltage converter that converts a voltage value of an AC power supply.

  Conventionally, transformers using windings have been used as voltage converters for AC power supplies. Problems with transformers with windings include size and weight. For example, a transformer for a three-phase power supply having an input voltage of 400V and an output voltage of about 200V, for example, has a weight of about 67 kg and a size of 340 mm × 208 mm × 312 mm on a scale of 10 kVA.

  According to Patent Document 1, a voltage converter using a switching device formed by combining a diode and a semiconductor switch element is presented instead of a transformer using a winding.

JP 2001-100850 A

  A transistor is typically used as the semiconductor switching element. In order to protect the semiconductor switch element, it is necessary to take measures against overcurrent. Normally, when overcurrent flows, the current is stopped. However, in that case, it will not function satisfactorily as a voltage converter.

  In view of the above circumstances, an object of the present invention is to provide a voltage converter that can function stably while taking measures against overcurrent.

As a result of intensive studies by the inventors, the present invention as described below has been completed.
(1) A chopper-type voltage conversion device that includes a semiconductor switching device and obtains an AC output of a predetermined voltage from an AC power source, detects a current of the semiconductor switching device, and detects a current that exceeds a threshold value. An AC voltage conversion device further comprising an overcurrent control device configured to reduce the output voltage to 40-60% of the predetermined voltage for 6 milliseconds and then restore the output voltage. .
(2) The overcurrent control device stores whether or not the current exceeding the threshold value is detected at a specific time, and stops the power supply when the detection of the current exceeding the threshold value is continuously stored a specific number of times. (1) AC voltage conversion apparatus comprised by this.
(3) The AC voltage conversion device according to (1) or (2), wherein the AC power supply has a voltage of 350 to 450 V, a frequency of 45 to 65 Hz, and the predetermined voltage is 80 to 220 V.
(4) The semiconductor switching device further includes a rectifier that includes a bridge diode and obtains a direct current from an alternating current power supply, and the semiconductor switching device is configured to obtain an alternating current output from the direct current by a chopper method. Either AC voltage converter.
(5) The AC voltage conversion device according to any one of (1) to (4), wherein the AC power source is a three-phase power source.

  According to the present invention, even if an overcurrent is detected and a protection operation is performed, the function as a transformer can be continued. In the present invention, the voltage is reduced for a very short time during the protection operation, and the power supply itself is not stopped. For example, when the input AC power supply is 60 Hz, the half cycle of the sine wave is 8.3 milliseconds. In the present invention, since the output voltage is merely reduced for a shorter time, the power can be supplied by charging the internal capacitor of the load without detecting the power failure on the load side of the motor or the like.

  According to the preferred embodiment, the power supply is not immediately stopped when an overcurrent occurs, but it is checked whether or not an overcurrent is detected during a specific time, and when it continues for a predetermined number of times. As long as the power is turned off. Therefore, the power supply is not frequently stopped due to an accidental overcurrent, and since the above-described voltage drop measures are taken for a very short time, the adverse effect of the accidental overcurrent is expected to be reduced.

  According to another preferred embodiment, the AC power source is converted into a direct current, converted into a voltage using a chopper method using a circuit similar to an inverter, and an IPM is used at that time, thereby reducing the number of semiconductors used in the switching device. can do.

It is a schematic diagram of the circuit of the apparatus of this invention. It is a schematic diagram of the circuit of the apparatus for three-phase power supplies of this invention. It is a schematic diagram of a part of the circuit of the device of the present invention.

  The present invention will be described below with reference to the drawings as appropriate. The present invention is not limited to the illustrated embodiment.

  The AC voltage conversion device of the present invention (hereinafter also abbreviated as “device of the present invention”) is intended to input AC power and output AC of a predetermined voltage different from the input power. . “To output an alternating current having a predetermined voltage” means to artificially determine a target voltage and output an alternating current having a voltage as close as possible. The apparatus of the present invention employs a chopper method for voltage conversion. In the chopper method, an arbitrary voltage or current can be artificially generated as an effective value from a direct current or alternating current input by repeatedly turning on and off the current. Generally, an alternating current having a desired voltage can be output by changing a ratio (duty ratio) between the ON time and the OFF time in the above-described ON-OFF. In the present invention, the AC power supply may be supplied to a chopper circuit without changing the AC power, or the AC power supply is rectified to obtain a direct current, and then the obtained direct current is applied to the chopper circuit, and again, You may get an exchange. A semiconductor switching device such as a power transistor is used as a control element in the above-described ON-OFF.

  A specific aspect of the semiconductor switching device is not particularly limited, and conventionally known techniques can be appropriately referred to. FIG. 1 is a schematic diagram of a circuit of the apparatus of the present invention. In the apparatus of FIG. 1, a plurality of semiconductor switching devices 11 to 14 in which diodes D11 to D14 and transistors Q11 to Q14 are connected in antiparallel are used. When the AC power supply 100 is used as it is, a circuit in which two semiconductor switching devices are directly connected in the opposite direction, such as the circuit described in FIG. 1, is preferably used.

  In order to output an alternating current of 60 Hz and 200 V from an alternating current power supply 100 of 60 Hz and 400 V, for example, using an apparatus as shown in FIG. 1, it is preferable to turn on and off at a duty ratio of 50% and a cycle of 50 microseconds. The prior art can be referred to as appropriate for specific ON-OFF implementation means, output voltage stabilization means, and the like. For example, in the circuit of FIG. 1, high-frequency components are removed from the output voltage switched at high speed by a low-pass filter using a coil L11 and a capacitor C11, and an AC voltage similar to that of the input power supply is obtained as an output.

  The AC power source that is the input to the apparatus of the present invention preferably has a voltage of 350 to 450 V and a frequency of 45 to 65 Hz. The target output (predetermined voltage) from the device of the present invention is preferably 80-220V.

  Usually, a semiconductor element has an upper limit of current that may be input, and if an excessive current flows, there is a risk of damage. When a transistor is used as the semiconductor switching device, it is usually necessary to pay attention to the collector current. For example, when an AC power supply of 400 V is input, the maximum collector-emitter voltage is required to be about 1200 V. In this case, the maximum collector current is about 20 A. In particular, when the load is turned on from the power supply OFF state, a large inrush current tends to flow because the internal capacitor of the load is charged in a short time. The apparatus of the present invention is provided with an overcurrent control device (not shown). The overcurrent control device is configured to detect a current of the semiconductor switching device. And when the said current exceeds a threshold value, the voltage reduction measure mentioned later is taken. About a threshold value, it can determine suitably from the rating etc. of each element used for a semiconductor switching device.

  The overcurrent control device used in the device of the present invention does not immediately stop the power supply in the voltage drop measure. The overcurrent control device is configured to reduce the output voltage to 40 to 60% of a predetermined voltage (a voltage to be targeted) for 2 to 6 milliseconds, and then restore the output voltage to the original value. ing. For example, if the input power source is 60 Hz, the half cycle of the sine wave is 8.3 milliseconds. If the voltage is reduced by 2 to 6 milliseconds shorter than the half cycle of the sine wave, the power can be supplied by charging the internal capacitor of the load without detecting the power failure on the load side. In addition, since the output voltage is maintained at a slight level as described above instead of zero, there is an advantage that the power supply to the load is continued. After the above-described voltage drop measure is taken by the overcurrent control device, the operation is restored so that a predetermined voltage is output again.

  For specific means for taking a voltage drop measure for a predetermined short time, the prior art can be referred to as appropriate. For example, the voltage drop measure is realized by setting the ratio (duty ratio) of the ON time and OFF time in the ON-OFF of the semiconductor switching device to 40% to 60% of the duty ratio to be output. If the output is completely cut, the power supply to the load cannot be continued. However, if the voltage drop measure is taken in a very short time, the load can be continuously operated.

  The overcurrent control device can be operated not only for inrush current when turning on the power source of a load such as a motor but also for protection from overcurrent in normal operation.

  When overcurrent continues to flow due to some abnormality, it may be better to forcibly stop power supply. In a preferred aspect of the present invention, the overcurrent control device is configured to store whether or not a current exceeding a threshold value is detected at a specific time. For example, whether or not an overcurrent is detected at a specific time of 0.5 seconds is stored. Here, when an overcurrent is detected, the above-described voltage drop measures are taken. When the specific time is 0.5 seconds, it is stored whether or not an overcurrent is detected every specific time, that is, at a time interval of every 0.5 seconds. When such detection is continuously stored a specific number of times, the overcurrent control device is preferably configured to stop the power supply. For example, when the specific number of times is “10 times”, the power supply is stopped when an overcurrent is detected 10 times continuously during a specific time (eg, 0.5 seconds). The In this example, it is almost equivalent to stopping the power supply by detecting an overcurrent for 5 seconds (0.5 seconds × 10 times). Even in this case, the above-described voltage drop measures are taken every time an overcurrent is detected, and the situation is recovered. The “specific time” that is a time interval for storing whether or not the overcurrent is detected is preferably 0.1 to 1 second, and the “specific number of times” is preferably 5 to 15 times.

  Prior art can be referred to as appropriate for overcurrent detection means, setting criteria for specific time and specific number of times, detection storage means, power supply stop means, and the like. According to this aspect, in the event of an accidental overcurrent, the power supply is not stopped and only a voltage drop measure is taken, and the operation is continued immediately after recovery, and the overcurrent continues for a long time. When the power supply is interrupted, the semiconductor switching device is prevented from being damaged.

  In the present invention, the AC power supply may be single-phase or three-phase. Further, the voltage conversion by the chopper method may be input with the alternating current and output the alternating current, or the voltage conversion by the chopper method may be performed after rectification to direct current. In the aspect of FIG. 1, the AC power source is single-phase, and voltage conversion by the chopper method is performed with AC being maintained.

  FIG. 2 is a schematic diagram of a circuit of a device for a three-phase power source according to the present invention. In the embodiment of FIG. 2, the AC power supply is once rectified to DC. As shown in the figure, it can be rectified by the bridge diodes D21 to D26. Preferably, a capacitor can be further used. For example, from an input voltage of 400V, a direct current of about 560V can be obtained in calculation. An alternating current of a desired voltage can be output from the obtained direct current by voltage conversion by a chopper method. When outputting alternating current from direct current, an inverter circuit can be used. At this time, by changing the ratio (duty ratio) between the ON time and the OFF time in the ON-OFF of the semiconductor switching devices 21 to 26, a desired value can be obtained. An alternating voltage can be output to the load 210. For specific circuit elements and the like, conventional techniques such as an inverter circuit and a switching circuit can be referred to as appropriate.

  The use of switching semiconductor elements can be reduced by appropriately utilizing an IPM for an inverter circuit. At this time, the above-described overcurrent control device can be applied to the semiconductor switching device in the IPM. FIG. 3 is a schematic diagram of a part of the circuit of the apparatus of the present invention. A schematic diagram of the interior of an IPM or the like and a low-pass filter using a coil and a capacitor are depicted. The IPM 30 or the like incorporates semiconductor switching devices 31 to 36. In the present invention, the above-described overcurrent control device (not shown) is applied to these semiconductor switching devices 31 to 36. About the alternating current obtained by the voltage conversion by the chopper method, a high frequency component can be removed by a low-pass filter using the illustrated coils L31 to L33 and capacitors C31 to C33, and a sine wave alternating voltage can be output.

  According to the present invention, the apparatus can be significantly reduced in weight compared to the case of a transformer with windings. For example, a 10 kVA device for three phases is about 12 kg by the application of the present invention, which is about 1/6 of a transformer device by winding. The volume can be reduced, and the cost is the same as the conventional one. Moreover, a power factor of 0.95% or more can be realized.

D11 to D26: Diodes Q11 to Q14: Transistors L11, L31 to L33: Coils C11, C31 to C33: Capacitors 11 to 14, 21 to 26, 31 to 36: Semiconductor switching device 30: IPM 100: AC power supply 210: Load

Claims (5)

  A chopper-type voltage conversion device that includes a semiconductor switching device and obtains an AC output of a predetermined voltage from an AC power source, detects the current of the semiconductor switching device, and 2-6 milliseconds when a current exceeding a threshold is detected An AC voltage converter further comprising an overcurrent control device configured to reduce the output voltage to 40 to 60% of the predetermined voltage during a period of time and then restore the output voltage.   The overcurrent control device is configured to store whether or not a current exceeding a threshold value is detected at a specific time, and to stop power supply when detection of a current exceeding the threshold value is continuously stored a specific number of times. The AC voltage converter according to claim 1.   The AC voltage converter according to claim 1 or 2, wherein the AC power supply has a voltage of 350 to 450V, a frequency of 45 to 65Hz, and the predetermined voltage is 80 to 220V.   4. The rectifier according to claim 1, further comprising a rectifier that includes a bridge diode and obtains a direct current from an alternating current power supply, wherein the semiconductor switching device is configured to obtain an alternating current output from the direct current by a chopper method. AC voltage converter.   The AC voltage converter according to claim 1, wherein the AC power source is a three-phase power source.

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