JPH1127853A - Protective circuit for main circuit power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure protection by detecting a current flowing through an element connected in series with the output of a converter based on the voltage between the input and output of the element and limiting the output current from the converter when the detected current exceeds a predetermined level thereby limiting the input current to a load even in case of abnormal load, failure of the main circuit, etc. SOLUTION: An A/D converter 104 detects the voltage VD between the input and output of a diode 102 connected in series with the output of a converter 101 and a microprocessor 105 detects the output current ID from the converter 101 based on the detection current VD. When the current VD exceeds a predetermined level, a thyristor in the converter 101 is controlled through a driver 106 to limit the output current ID. According to the arrangement, input current to a load 110 is limited even when an overcurrent flows due to abnormality of the load 110 or failure of the main circuit resulting in reliable protection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for a main circuit power supply of a servo control device or an inverter control device provided with a converter for converting an alternating current to a direct current using a switching element, and more particularly to an abnormality of a load or the like. The present invention relates to a protection circuit for a main circuit power supply capable of reliably protecting the main circuit power supply by simply and inexpensively adding a circuit even when an excessive current flows to a load input due to a failure of the main circuit power supply.

[0002]

2. Description of the Related Art As a main circuit power supply of a conventional servo control device or inverter control device, for example, there is one shown in FIG. In FIG. 3, a main circuit power supply according to the conventional example includes a converter 101 for converting three-phase alternating current to direct current using a thyristor, and a leakage current prevention for detecting R-phase, S-phase, and T-phase AC inputs. The configuration includes a diode 102 and a main capacitor 103 for smoothing, and supplies a direct current to a load 110 which is a servo control device or an inverter control device. In such a conventional main circuit power supply, the load 11
If 0 is large and the input current to the load 110 is large, an overcurrent or an overload in the load 110 is detected to determine an abnormality, and the power supply to the load 110 from the main circuit power supply is cut off. Was.

[0003]

However, in the above-mentioned conventional main circuit power supply, when the load 110 is short-circuited for some reason or an excessive current flows to the power supply input due to a failure of the main circuit or the like. There was a problem that it could not be protected. The present invention has been made in view of the above-described conventional problems. Even when an excessive current flows through an input due to an abnormality in a load or a failure in a main circuit, the current can be easily added by a low-cost circuit. An object of the present invention is to provide a protection circuit for a main circuit power supply that can be reliably protected by limiting.

[0004]

In order to solve the above problems, a protection circuit for a main circuit power supply according to claim 1 of the present invention comprises:
In a protection circuit for a main circuit power supply including a converter for converting an alternating current to a direct current using a switching element, an element connected in series to an output of the converter, and a voltage detecting means for detecting a voltage between input and output of the element And detecting a current flowing through the element based on the voltage detected by the voltage detecting means, and if the current exceeds a predetermined value, controls the switching element to turn off to limit the output current of the converter. Control means. In addition, the protection circuit for the main circuit power supply according to the second aspect is the first aspect.
Wherein the control means corrects the detected current value based on an ambient temperature of the element. In the protection circuit for the main circuit power supply according to claim 1 of the present invention, the voltage between the input and the output of the element connected in series to the output of the converter is detected by the voltage detection means, and the voltage is detected by the control means. A current flowing through the element is detected based on the voltage, and when the current exceeds a predetermined value, the switching element of the converter is turned off to limit the output current of the converter. As a result, even when an excessive current flows through the input due to an abnormality in the load, a failure in the main circuit, or the like, the input current to the load can be limited to ensure protection. Further, the diode is used for preventing leakage current when detecting an AC input, the voltage detecting means is controlled by an A / D converter which detects the input and output voltages of the converter, and the control means is controlled to turn off / off the switching element of the converter. If each of the components is configured by a microprocessor to perform, the protection circuit of the main circuit power supply of the present invention can be realized by diverting components already added to realize other functions such as the main circuit power supply circuit, and the like. It can be realized by adding a low-cost circuit. Further, in the protection circuit for the main circuit power supply according to claim 2,
The control means corrects the detected current value based on the ambient temperature of the element. As a result, even when an element whose current-voltage characteristic changes depending on the ambient temperature is used, accurate current detection is possible, and overcurrent to the load can be limited to reliably protect the load.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the protection circuit for a main circuit power supply according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram of a protection circuit for a main circuit power supply according to an embodiment of the present invention. FIG. 3 (conventional example)
The same reference numerals are given to portions overlapping with. In FIG. 1, a protection circuit for a main circuit power supply according to the present embodiment is a converter 10 for converting three-phase AC of R, S, and T phases to DC of P and N phases using a thyristor as a switching element.
1, a diode 102 as an element for preventing leakage current when detecting R-phase, S-phase, and T-phase AC inputs, and as an element connected in series to the output of the converter; a main capacitor 103 for smoothing; A / D converter 10 as voltage detecting means for detecting the input / output voltage of 102
4 and the voltage V detected by the A / D converter 104.
A current ID flowing through the diode 102 is detected based on D. If the current ID exceeds a predetermined value, the thyristor is turned off (extinguished) and the output current I
Microprocessor (C as control means for limiting D)
PU) 105 and a thyristor driver 106 that drives a thyristor of the converter circuit 101, and is configured to supply a direct current to a load 110, such as a servo control device or an inverter control device. However, converter 101 may be directly driven by microprocessor (CPU) 105, in which case thyristor driver 106 may not be required. The operation of the main circuit power supply protection circuit of the present embodiment having the above-described configuration will be described below. First, in order to turn on the main circuit power, the thyristor driver 106 is driven and controlled based on the control of the microprocessor 105, and sequentially.
Build up DC voltage by performing thyristor firing control. As a result, the R-phase, S-phase, and T-phase three-phase AC voltages are rectified, the main capacitor 103 is charged, and P-phase and N-phase DC voltages are generated at both ends thereof. Supplied to At this time, the diode 10
2, the output current ID of the converter 101 flows.
2 has a current-voltage characteristic as shown in FIG. In the protection circuit for the main circuit power supply of the present embodiment, the converter 10
1 is detected. That is, in the A / D converter 104, the input terminal voltage V
1 and the value (digital value) of the output terminal voltage V2,
This is supplied to the microprocessor 105. The microprocessor 105 detects the input / output voltage VD of the diode 102 as a difference voltage (V1-V2) between the input terminal voltage V1 and the output terminal voltage V2, and detects the current ID of the diode 102 stored in advance as a characteristic table. And detecting the output current ID of the converter 101 from the detected input / output voltage VD based on the relationship between the input / output voltage VD. When the detected value of the output current ID of the converter 101 exceeds a predetermined threshold value, the microprocessor 105 determines that the input current to the load 110 is excessive, and controls the thyristor driver 106 to shut off. Then, the thyristor of the converter 101 is turned off (extinguished), and the output current ID of the converter 101 is limited to be equal to or less than the threshold value. As described above, in the protection circuit for the main circuit power supply of the present embodiment, the input-output voltage V of the diode 102 connected in series to the output of the converter 101
D is detected by the A / D converter 104, and the microprocessor 105 detects the output current ID of the converter 101 based on the detected voltage VD,
Exceeds a predetermined value, the thyristor of the converter 101 is turned off to limit the output current ID of the converter 101. Therefore, even if an excessive current flows to the input due to an abnormality in the load 110, a failure in the main circuit, or the like, The input current to the load 110 can be limited to ensure protection. The diode 102 is an existing diode for preventing a leakage current when detecting an AC input.
The A / D converter 104, the microprocessor 105, and the thyristor driver 106 are also disclosed in JP-A-8-7.
If the circuit for turning on the main circuit power is used as described in the "Main circuit power-on circuit of the servo control device" disclosed in Japanese Patent No. 0576, protection of the main circuit power supply can be achieved simply and at low cost by adding a circuit. A circuit can be realized. If the characteristic of the current ID and the input / output voltage VD of the diode 102 held in the microprocessor 105 is a value obtained by temperature-compensating the ambient temperature, the voltage of the diode 102 depends not only on the current but also on the temperature. Therefore, accurate current detection is possible, and overcurrent to the load can be reliably limited and protected. Further, in the above embodiment, the output current I
In order to detect D, the voltage drop due to the on-resistance of the diode 102 is detected. However, the diode 102 may be an element having another voltage drop. The effect of can be obtained.

[0006]

As described above, according to the main circuit power supply protection circuit of the present invention, the voltage between the input and output of the element connected in series to the output of the converter is detected by the voltage detection means, and the control means The current flowing through the element is detected based on the voltage detected by the voltage detection means, and when the current exceeds a predetermined value, the switching element of the converter is turned off to limit the output current of the converter. Therefore, even when an excessive current flows through the input due to a load abnormality or a failure of the main circuit, etc., a protection circuit for a main circuit power supply capable of reliably protecting the current by providing a simple and low-cost circuit is provided. be able to. Further, in the protection circuit for the main circuit power supply of the present invention, the control means corrects the detected current value based on the ambient temperature of the element, so that an element whose current-voltage characteristic changes with the ambient temperature is used. Even in such a case, it is possible to provide a protection circuit for the main circuit power supply that can accurately detect current and can reliably protect the load by limiting overcurrent to the load.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a protection circuit for a main circuit power supply according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating current-voltage characteristics of the diode according to the embodiment.

FIG. 3 is a configuration diagram of a main circuit power supply of a conventional servo control device or inverter control device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Converter 102 Diode (element) for preventing leakage current 103 Main capacitor for smoothing 104 A / D converter (voltage detecting means) 105 Microprocessor (CPU) (control means) 106 Thyristor driver 110 Load Current flowing through ID diode VD Diode Input / output voltage

Claims (2)

[Claims] 1. A protection circuit for a main circuit power supply comprising a converter for converting an alternating current into a direct current using a switching element, wherein a voltage between an element connected in series to an output of the converter and an input / output of the element is determined. A voltage detecting means for detecting, a current flowing through the element based on the voltage detected by the voltage detecting means, and when the current exceeds a predetermined value, the switching element is turned off to control the converter. A protection circuit for a main circuit power supply, comprising: control means for limiting an output current. 2. The protection circuit for a main circuit power supply according to claim 1, wherein the control means corrects the detected current value based on an ambient temperature of the element.