JP3740937B2 - Capacitor overvoltage suppression circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a capacitor overvoltage suppression circuit capable of detecting an abnormality of the switch when the capacitor overvoltage is suppressed by a discharge circuit composed of a resistor and a switch connected in series.
[0002]
[Prior art]
FIG. 3 is a connection diagram showing a conventional example of a power conversion apparatus including a rectifier, an inverter, and a smoothing capacitor connected to a DC intermediate circuit that couples both. In FIG. 3, the single-phase AC power from the AC power source 1 is converted into DC power by a rectifier 2 having a diode bridge connection and output to a DC intermediate circuit. The smoothing capacitor 3 connected to the DC intermediate circuit. Removes the pulsation of this DC power. The smoothed DC power is converted into AC power having a desired voltage and frequency by the VVVF inverter 4 composed of a transistor and a diode. The induction motor 5 drives the load 6 at a desired rotational speed by the variable voltage / variable frequency AC power output from the VVVF inverter 4.
[0003]
When the load 6 is a cargo handling machine, for example, when the cargo is raised, the induction motor 5 is rotated by the output power of the VVVF inverter 4, but when the cargo is lowered, the mass of the cargo rotates the induction motor 5. The induction motor 5 serves as an induction generator and generates AC power. The VVVF inverter 4 converts the DC power into DC power and sends it to the DC intermediate circuit to charge the smoothing capacitor 3 connected to the DC intermediate circuit. . If the voltage of the smoothing capacitor 3 becomes excessive due to charging, not only the smoothing capacitor 3 but also each device connected to the DC intermediate circuit, in particular, the semiconductor element may be destroyed.
[0004]
Therefore, a series circuit of a discharge resistor 11 and a discharge transistor 12 as a circuit switch is connected in parallel to the smoothing capacitor 3, and a capacitor voltage detector 14 for detecting the terminal voltage is connected to the smoothing capacitor 3, When it is detected that the capacitor voltage has become excessive, the capacitor voltage detector 14 sends an operation signal to the base drive circuit 13 as a switch driver to turn on the discharge transistor 12. As a result, the electric charge accumulated in the smoothing capacitor 3 is consumed by the discharge resistor 11 to reduce the voltage of the smoothing capacitor 3. When the capacitor voltage falls to a separately defined lower limit value, the capacitor voltage detector 14 gives an off signal to the discharge transistor 12 via the base drive circuit 13 to stop the discharge.
[0005]
[Problems to be solved by the invention]
By the way, even if the discharge circuit consisting of the discharge resistor 11 and the discharge transistor 12 connected in series does not operate normally, for example, even if the capacitor voltage detector 14 detects an overvoltage and issues an ON command to the base drive circuit 13, When an abnormality occurs such that the base drive circuit 13 is inoperative, the discharge circuit operates even when the power generated when the cargo handling machine lowers the cargo causes the smoothing capacitor 3 to be excessively charged. Therefore, the voltage of the smoothing capacitor 3 rises abnormally and damages the device connected to the smoothing capacitor 3 and the DC intermediate circuit. Therefore, it becomes necessary to detect whether or not the operation of the discharge circuit is normal.
[0006]
FIG. 4 is a circuit diagram showing a first conventional example for detecting whether or not a discharge circuit connected in parallel with a capacitor operates normally. In order to avoid the circuit diagram becoming complicated, a DC intermediate circuit is shown. Only the part is shown. The names, applications, and functions of the smoothing capacitor 3, the discharge resistor 11, the discharge transistor 12 as a circuit switch, the base drive circuit 13 as a switch driver, and the capacitor voltage detector 14 are the same as those described in FIG. Since this is the same as the conventional circuit of the converter, the description thereof is omitted. In FIG. 4, a series circuit of a voltage dividing resistor 15 and a DC voltage detector 16 is connected in parallel to the discharge transistor 12, and the presence or absence of the collector-emitter voltage of the discharge transistor 12 is detected by the DC voltage detector 16. By providing this detection result to the base drive circuit 13, the base drive circuit 13 discriminates an abnormality in the discharge circuit.
[0007]
FIG. 5 is a circuit diagram showing a second conventional example for detecting whether or not the discharge circuit connected in parallel with the capacitor operates normally. In order to avoid the circuit diagram becoming complicated, a DC intermediate circuit is shown. Only the part is shown. The names, applications, and functions of the smoothing capacitor 3, the discharge resistor 11, the discharge transistor 12 as a circuit switch, the base drive circuit 13 as a switch driver, and the capacitor voltage detector 14 are the same as those described in FIG. Since this is the same as the conventional circuit of the converter, the description thereof is omitted. In FIG. 5, a DC current transformer 17 is inserted into the discharge circuit, the presence or absence of collector current flowing through the discharge transistor 12 is detected by the DC current transformer 17, and the detection result is given to the base drive circuit 13. In this configuration, circuit abnormality is discriminated by the base drive circuit 13.
[0008]
However, the first conventional circuit shown in FIG. 4 and the second conventional circuit shown in FIG. 5 require a DC voltage detector 16 or a DC current transformer 17 separately. These devices are expensive and have drawbacks such as an increase in the number of parts of the device.
Accordingly, an object of the present invention is to make it possible to easily detect that an abnormality has occurred in a discharge circuit of a capacitor without using an expensive DC voltage detector or DC current transformer.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an overvoltage suppression circuit for a capacitor according to the present invention comprises:
A series circuit of a discharge resistor and a circuit switch is connected in parallel to a capacitor. When the capacitor voltage exceeds a first set voltage, a closing signal is given to the switch driver for driving the circuit switch, and the capacitor voltage is In a conventional circuit that gives an open circuit signal to the switch driver if it falls below a second set voltage lower than the first set voltage,
A switch voltage detector that detects the presence / absence of a voltage across the circuit switch, and the presence / absence of a voltage across the switch and a switch signal to the switch driver are input to operate the circuit switch normally. A logic circuit for determining whether or not.
[0010]
The switch voltage detector has a configuration in which resistors are connected to both ends of the switch.
The logic circuit determines that if there is a voltage across the switch when a closing signal is given to the switch driver, it is abnormal if there is a voltage across the switch, and is normal if there is no voltage across the switch, and opens the circuit to the switch driver. When there is a voltage across the switch when a signal is applied, it is determined to be normal, and when there is no voltage across the switch, it is determined to be abnormal.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a circuit diagram showing a first embodiment of the present invention. In FIG. 1, a discharge circuit formed by connecting a discharge resistor 11 and a discharge transistor 12 as a circuit switch in series, a smoothing capacitor 3 and a capacitor voltage detector 14 are connected to a positive side and a negative side of a DC intermediate circuit. Are connected in the same manner as the first conventional circuit of FIG. 4 and the second conventional example of FIG.
[0012]
In the present invention, a series circuit of the voltage dividing resistor 22 and the voltage dividing resistor 23 is connected between the collector and the emitter of the discharge transistor 12, and both ends of the voltage dividing resistor 23 are connected to the logic circuit 21. That is, when the discharge transistor 12 is on, a zero voltage appearing at both ends of the voltage dividing resistor 23 is input to the logic circuit 21, and when the discharge transistor 12 is off, the discharge resistor 11, the voltage dividing resistor 22, and the voltage dividing resistor 23 The divided DC intermediate circuit voltage is input to the logic circuit 21. On the other hand, an ON command issued when the capacitor voltage detector 14 detects that the first set voltage has been exceeded, or an OFF command issued when it has been detected that the voltage has fallen below the second set voltage is also logical. Input to the circuit 21.
[0013]
The base drive circuit 20 including the logic circuit 21 turns on or off the discharge transistor 12 in response to the above-described on command or off command. Whether or not the discharge transistor 12 is operating according to this command. Is checked, and if the operation is not performed as instructed, an abnormality is alarmed.
[0014]
FIG. 2 is a flowchart showing a second embodiment of the present invention. In this flowchart, it is determined whether to output an ON command or an OFF command to the discharge transistor 12 from the voltage of the smoothing capacitor 3 detected by the capacitor voltage detector 14 (process 31), and the command is ON or OFF. Is determined (determination 41). On the other hand, the voltage across the discharge transistor 12 is detected from the voltage dividing resistor 23 (process 32), and the presence or absence of the voltage is determined (determination 42). Four combinations are obtained from the two results of decision 41 and the two results of decision 42.
[0015]
That is, when the ON command is issued and the voltage across the discharge transistor 12 is zero (indicating the ON state), it is determined that the path is normal through the AND element 51 → OR element 61 → processing 33. When an off command is issued and the voltage across the discharge transistor 12 is present (indicating an off state), it is determined that this is also normal through the path of the AND element 52 → OR element 61 → processing 33. However, when the ON command is issued and the voltage across the discharge transistor 12 is present (indicating the OFF state), it is determined that there is an abnormality in the path of the AND element 53 → OR element 62 → process 34, and an alarm is issued (process 35). Is done. When an off command is issued and the voltage across the discharge transistor 12 is zero (indicating an on state), this is also determined to be abnormal in the path of the AND element 54 → OR element 62 → process 34, and an alarm is issued (process 35). )
[0016]
【The invention's effect】
Since it is clear that various problems will occur if the capacitor voltage becomes excessive, in order to prevent overvoltage, a discharge circuit consisting of a series connection of a discharge resistor and a circuit switch is connected in parallel to the capacitor, and if necessary, this Although the discharge circuit is operated, a DC voltage detector or a DC current transformer has conventionally been installed in case the discharge circuit is abnormal and an appropriate operation cannot be obtained. However, they have the disadvantages of being expensive and complicating the circuit. On the other hand, in the present invention, the on / off operation of the circuit switch forming the discharge circuit is detected based on the presence / absence of the voltage of the voltage dividing resistor, and whether the on / off operation command for the discharge circuit is reliably executed. Is detected by a logic circuit. At this time, the on / off state is detected only by the resistor and the logic circuit has a simple configuration, so that an effect of easily and surely detecting the presence or absence of abnormality in the discharge circuit can be obtained.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a first embodiment of the present invention. FIG. 2 is a flowchart showing a second embodiment of the present invention. FIG. 3 is a rectifier, an inverter, and a DC intermediate circuit in which both are coupled. FIG. 4 is a circuit diagram showing a first conventional example for detecting whether or not a discharge circuit connected in parallel with a capacitor operates normally. FIG. 5 is a circuit diagram showing a second conventional example for detecting whether or not a discharge circuit connected in parallel with a capacitor operates normally.
DESCRIPTION OF SYMBOLS 1 AC power source 2 Rectifier 3 Smoothing capacitor 4 VVVF inverter 5 Induction motor 6 Load 11 Discharge resistor 12 Discharge transistor 13 as circuit switch, 20 Base drive circuit as switch driver 14 Capacitor voltage detector 15, 22, 23 minutes Voltage resistor 16 DC voltage detector 17 DC current transformer 21 Logic circuits 31 to 35 Processing 41 and 42 Determination 51 to 54 AND elements 61 and 62 OR element

Claims (2)

A series circuit of a discharge resistor and a circuit switch is connected in parallel to a capacitor, a capacitor voltage detector is connected to both ends of the capacitor, and if it is detected that the voltage of the capacitor exceeds the first set voltage, the circuit A closing signal is given to a switch driver for driving the switch, and when it is detected that the capacitor voltage is lower than a second set voltage set lower than the first set voltage, an open circuit signal is sent to the switch driver. In the capacitor overvoltage suppression circuit
A switch voltage detector that detects the presence / absence of a voltage across the circuit switch, and a determination that the voltage across the switch is abnormal when the switch drive signal is given and is normal if there is no voltage across the switch And an overvoltage suppression circuit for a capacitor, comprising: a logic circuit that determines that if there is a voltage across the switch when there is an open circuit signal to the switch driver, it is normal if there is no voltage across the switch . The capacitor overvoltage suppression circuit according to claim 1,
The overvoltage suppression circuit for a capacitor, wherein the switch voltage detector is configured by connecting resistors to both ends of the switch.

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