JP4533034B2 - AC power conditioner - Google Patents

Description

  The present invention relates to an AC power adjustment device for opening and closing AC power supplied to a load.

  In an apparatus such as a power conversion apparatus or a power control apparatus, an AC power adjustment apparatus including an AC switch 3 is used to open and close AC power supplied from an AC power supply 10 to a load 11 as shown in FIG. . For example, in the instantaneous voltage drop protection device described in Patent Documents 1 and 2, etc., a pair of thyristors as switching elements connected in parallel in the reverse direction, or a bidirectional three-terminal thyristor (triac) that performs the same function is an alternating current. Used as a switch 3.

  However, as is well known, since a thyristor cannot self-extinguish, an additional circuit such as a commutation circuit is required to open an AC switch once closed at an arbitrary timing. It becomes complicated. Further, since the thyristor generates a voltage drop of about 1.6 V due to the element itself, a power loss corresponding to the voltage drop occurs. In the AC switch inserted in the power supply line of the AC power adjusting apparatus, the AC switch is always conductive when a power is supplied, and a relatively large current flows. Therefore, the power loss as described above becomes a large loss for the user.

  On the other hand, MOSFETs (field effect transistors) have been widely used as power switching elements in recent years. In a MOSFET, conduction / non-conduction between the source (S) terminal and the drain (D) terminal is determined only by the voltage applied to the gate (G) terminal, so an additional circuit such as a commutation circuit is required like a thyristor. And not. However, when the AC switch in the AC power adjusting apparatus as described above is replaced with a MOSFET, there are the following problems. That is, MOSFETs generally have a smaller maximum rated current (output capacity) than thyristors. Therefore, for example, when an excessive current flows due to a short circuit of the load or a sudden decrease in load resistance, the load is damaged in a relatively short time. Even when a fuse or the like is inserted in order to prevent an excessively large current from flowing, the MOSFET itself is often damaged before the fuse is blown.

JP-A-8-65921 JP 2000-152519 A

  The present invention has been made in view of these points, and its main object is to cut off AC power supplied to a load at an arbitrary timing without adopting a complicated circuit configuration. Another object of the present invention is to provide an AC power adjusting device that can prevent the AC switch itself from being destroyed even in an abnormal state.

In order to solve the above problems, the present invention provides an AC power adjustment device for opening and closing AC power supplied to a load.
a) an AC switch comprising a first switch using a thyristor as a switching element and a second switch using a MOSFET, which are inserted in the power supply line and connected in parallel;
with said current when started to supply an alternating current to a load through b) said AC switch to determine whether it is greater than a predetermined value, said current when that supplies alternating current to the load through the AC switch Current determination means for determining whether or not is greater than or equal to a predetermined value;
c) A means for controlling conduction / non-conduction of the first and second switches, wherein at the start of energization, the second switch is controlled to be non-conduction and the first switch is conducted, and the current determination means When it is determined that the current is less than the predetermined value, the second switch is turned on and the first switch is turned off. In the normal state, the first switch is turned off and the second switch is turned on. Control means for switching the first switch to be conductive and the second switch to be non-conductive when the current determination means determines that the current is greater than or equal to a predetermined value;
It is characterized by having.

  In the AC power adjustment device according to the present invention, a thyristor generally used as a power switching element and a MOSFET are used in combination. In the normal state, the first switch using the thyristor is turned off, the second switch using the MOSFET is turned on, and an alternating current is supplied to the load through the second switch. Since the MOSFET is turned on and off according to the voltage applied to the gate terminal regardless of the voltage applied between the source terminal and the drain terminal, the AC current can be cut off at an arbitrary timing regardless of the phase of the AC power. Can do. Further, since the voltage drop between the source terminal and the drain terminal when the MOSFET is conductive is 1 [V] or less, typically about 0.8 [V], the power loss is smaller than that of the thyristor, and the same. When driving the load, the amount of power used can be suppressed.

  For example, when an abnormal situation occurs, such as when the load is accidentally short-circuited or when the load resistance falls rapidly, an excessive current flows through the load through the AC switch. At this time, the current determination means determines that the current is excessive by detecting that the output current supplied to the load has reached a predetermined value or more. Upon receiving this determination result, the control means immediately gives a control signal to each switching element (thyristor and MOSFET) so as to switch the first switch from non-conduction to conduction and the second switch from conduction to non-conduction. . Thereby, an excessive current that exceeds a predetermined value flows through the thyristor instead of the MOSFET.

  In general, a MOSFET can perform a high-speed switching operation as compared with a thyristor, but has a small maximum rated current. That is, when an excessive current flows, it is easily damaged in a short time. In the AC power adjustment apparatus according to the present invention, when an excessive current flows as described above, the current through the MOSFET is cut off, and the current is supplied to the thyristor side where the maximum rated current is large and is not easily damaged. Flowing. Therefore, it is possible to prevent the MOSFET from being destroyed by an excessive current.

  The control means once again switches to AC power supply through the first switch, and immediately after the output current returns to the original normal value (for example, a value less than the predetermined value), the control means again. It is preferable to switch the first switch to non-conductive and the second switch to conductive. As a result, when an excessive current flows only temporarily, the normal state can be quickly restored after the abnormal state is resolved.

  Moreover, as a preferable aspect of the present invention, a configuration may be adopted in which a fuse is inserted in the power supply line before the AC switch. In this configuration, as described above, when the thyristor does not return to the normal state in a short time after switching so that an excessive current flows in the thyristor, the fuse blows faster than the thyristor is destroyed by the excessive current. The current itself flowing through the AC switch is cut off. Therefore, since both the thyristor and the MOSFET are free from destruction and the fuse is blown out, only the fuse needs to be replaced as repair. Thereby, even in the case of such a malfunction, the labor for repair is reduced, and the cost required for repair can be greatly suppressed as compared with the case where the MOSFET is destroyed.

  An AC power adjusting apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a main part of an AC power adjusting apparatus according to this embodiment.

  For example, an AC 100 [V] or 200 [V] single-phase AC power supply 10 is connected to the input terminals 1a and 1b of the AC power regulating apparatus according to this embodiment, and the output terminals 7a and 7b are driven by AC power. A load 11 is connected. On the line between the input terminal 1a and the output terminal 7b, a fuse 2, an AC switch 3, and a current detection current transformer 6 are provided in this order. The AC switch 3 includes a first switch 4 in which two thyristors are connected in parallel in the reverse direction as a switching element, and a second switch 5 including a power MOSFET as a switching element. The current transformer 6 detects the current output from the output terminal 7 a, and the detection signal is input to the control unit 8. The control unit 8 is mainly configured by a microprocessor including a CPU, a ROM, a RAM, and the like. The gate terminal of the thyristor of the first switch 4 and the second switch are connected via the drive circuit 9 according to a control program written in the ROM in advance. A control signal is supplied to each of the gate terminals of the five MOSFETs.

  Next, the operation of the AC power adjustment apparatus having the above configuration will be described with reference to the control flowchart of FIG. It is assumed that both the first and second switches 4 and 5 are in a non-conducting state in the initial state, that is, the state before supplying AC power to the load.

  When receiving an instruction to supply AC power to the load 11, the controller 8 first sends a control signal to turn on the thyristor via the drive circuit 9 (step S1). As a result, the first switch 4 is closed and conducted, and AC power is supplied to the load 11 through the thyristor. After starting the power supply, the control unit 8 reads the current detection value from the current transformer 6 (step S2), and determines whether this detection value is equal to or greater than a predetermined value (step S3). This predetermined value is determined according to, for example, the maximum rated current value of the MOSFET of the second switch 5.

  If it is determined in step S3 that the detected current value is equal to or greater than the predetermined value, it is determined that there is an initial abnormality such as the output terminals 7a and 7b being short-circuited or the resistance of the load 11 being abnormally small. To do. However, as will be described later, the maximum rated current of the thyristor is relatively large, and even if the current exceeds a predetermined value, it may endure for a certain period of time. Therefore, the process returns to step S1 and passes through the first switch 4. Continue the power supply. If the load abnormality does not recover during such power supply continuation, the fuse 2 is melted and power supply from the AC power supply 10 is stopped as will be described later. In addition, when it determines with an electric current value being more than predetermined value by step S3, you may make it alert | report abnormality to a user by the method of lighting a display lamp.

  On the other hand, if it is determined in step S3 that the current detection value is less than the predetermined value, it is determined that there is no initial abnormality or that the abnormality has been resolved during the power supply as described above, and the first switch Instead of opening 4, a control signal is sent to turn on the MOSFET and turn off the thyristor so that the second switch 5 is closed (step S 5). When the MOSFET is turned on, the source terminal-drain terminal of the MOSFET becomes conductive in the AC switch 3, and AC power is supplied to the load 11 through the second switch 5. At this time, the thyristor of the first switch 4 is non-conductive.

  Thereafter, the control unit 8 reads the current detection value by the current transformer 6 in the same manner as in step S2 (step S6), and determines whether or not the detection value is equal to or greater than a predetermined value (step S7). The predetermined value at this time may be the same as the predetermined value in step S3, but is not necessarily the same. If it is determined in step S7 that the detected current value is less than the predetermined value, it is determined that power supply is normally performed, and the process returns to step S5, and the alternating current through the second switch 5 is turned on with the MOSFET turned on. Continue to supply power.

  On the other hand, when it is determined in step S7 that the detected current value is equal to or greater than the predetermined value, it is determined that an excessive current that is not in a normal state flows due to, for example, a load abnormality or a short circuit. At this time, the control unit 8 immediately turns off the MOSFET via the drive circuit 9 and sends a control signal to turn on the thyristor (step S8). As a result, the second switch 5 is opened, while the first switch 4 is closed, and this time AC power is supplied to the load 11 through the first switch 4. Usually, since the maximum rated current of the thyristor is considerably larger than that of the MOSFET, even a current that exceeds a predetermined value in step S7 may be within the maximum rated current of the thyristor.

  Even after performing the switch switching control in step S8, the control unit 8 returns to step S6 and continues to monitor the detected current value. As described above, when the state in which the output current is equal to or higher than the predetermined value is very temporary, the current detection value is less than the predetermined value without passing time after the transition to the power feeding through the first switch 4. Return to. In that case, the process returns from step S7 to S5, the first switch 4 is switched to the non-conductive state, the second switch 5 is switched to the conductive state, and the power supply through the second switch 5, that is, the MOSFET is restored.

  On the other hand, when the state where the output current is equal to or greater than the predetermined value continues for a certain extent, the fuse 2 is blown by an excessive current, and the power itself supplied from the single-phase AC power supply 10 to the AC switch 3 is cut off. The Since the fuse needs to be blown before the thyristor breaks, the characteristics of the fuse are selected according to the maximum rated current of the thyristor. That is, the fuse 2 is blown before the situation where the thyristor is damaged even if the abnormal state cannot be quickly resolved after the power supply through the second switch 5 is shifted to the power supply through the first switch 4 due to the occurrence of the abnormal state. As a result, the AC switch 3 is not damaged. Therefore, even if the user accidentally shorts the load, it is only necessary to replace the blown fuse 2 with a new one, and the maintenance of the apparatus is very easy.

  Further, in a normal state where no abnormality occurs as described above, AC power is supplied through the MOSFET of the second switch 5, and since the MOSFET has a small voltage drop between the source terminal and the drain terminal when conducting, the power loss Can be suppressed. In addition, the control unit 8 can stop the power supply by interrupting the second switch 5 at an arbitrary time by a control signal sent to the gate terminal of the MOSFET.

  It should be noted that the above embodiment is merely an example of the present invention, and it is obvious that any modification, correction, or addition that is appropriately made within the scope of the present invention is included in the scope of the claims of the present application.

The block diagram of the principal part of the alternating current power adjustment apparatus by one Example of this invention. The schematic block diagram of the conventional alternating current power adjusting device. The control flowchart for demonstrating operation | movement of the alternating current power adjustment apparatus of a present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b ... Input terminal 2 ... Fuse 3 ... AC switch 4 ... 1st switch 5 ... 2nd switch 6 ... Current transformer 7a, 7b ... Output terminal 8 ... Control part 9 ... Drive circuit 10 ... Single phase AC power supply 11 ... load

Claims (2)

In the AC power adjustment device for opening and closing the AC power supplied to the load,
a) an AC switch comprising a first switch using a thyristor as a switching element and a second switch using a MOSFET, which are inserted in the power supply line and connected in parallel;
with said current when started to supply an alternating current to a load through b) said AC switch to determine whether it is greater than a predetermined value, said current when that supplies alternating current to the load through the AC switch Current determination means for determining whether or not is greater than or equal to a predetermined value;
c) A means for controlling conduction / non-conduction of the first and second switches, wherein at the start of energization, the second switch is controlled to be non-conduction and the first switch is conducted, and the current determination means When it is determined that the current is less than the predetermined value, the second switch is turned on and the first switch is turned off. In the normal state, the first switch is turned off and the second switch is turned on. Control means for switching the first switch to be conductive and the second switch to be non-conductive when the current determination means determines that the current is greater than or equal to a predetermined value;
An AC power adjusting device comprising:   2. The AC power adjustment apparatus according to claim 1, wherein a fuse is inserted in a power supply line in front of the AC switch.

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