JP2000078760A - Fault detector circuit for charger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect and protect a short-circuiting fault of a charging circuit in a short time, by comparing a voltage specified value changing according to a time from starting charging with a detected voltage of a DC circuit of a power converter, and deciding the fault if the detected value is lower. SOLUTION: A DC voltage detected value Vdc of a DC circuit detected by a voltage detector 10 is compared with a voltage specified value VL (an output of a voltage specified value generator 2) by a DC voltage discriminator 1. If Vdc<VL, a fault of a charging circuit is decided. For example, if the DC circuit is short-circuited so that the DC voltage detected value is a waveform like Vdc2, Vdc<VL is obtained at a time T2, and the fault can be detected. Since the value VL at a time T1 after a sufficient time is elapsed from ON of a main switch 5 is a detected value V1, wherein T1 is about several times as large as a charging time constant 0 and V1 is a detected value of the lowest DC voltage allowable at the time of establishing the DC voltage, when the DC voltage is not established, the fault can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure detection circuit for a charging circuit for initially charging a DC circuit in a power converter such as an inverter or a converter.

[0002]

2. Description of the Related Art Generally, a power converter connected to an AC power supply such as an inverter or a converter generally initializes a DC circuit from a AC power supply by a charging circuit such as a diode rectifier before starting and turning off a main switching element. It is necessary to charge and establish a DC voltage. If the charging circuit is faulty, initial charging cannot be performed and a DC voltage cannot be established. Therefore, it is necessary to detect a fault in the charging circuit at startup. FIG. 5 is a circuit block diagram showing a conventional example of a failure detection circuit for a charging circuit of an inverter, and FIG. 6 is a waveform diagram for explaining the operation. In FIG. 5, a diode rectifier 7 is connected to an AC power supply 4 through a main switch 5 and a charging resistor 6, an electrolytic capacitor 8 is connected to its DC side, and a DC voltage detection value Vd obtained by detecting a DC voltage with a voltage detector 9.
c is input to the failure detection circuit 51. However, components not related to the present invention are omitted in the drawings.
The failure detection circuit 51 determines whether or not the DC voltage detection value Vdc after a lapse of a predetermined time T1 since the main switch 5 is turned on is equal to or less than a specified value V1. It is assumed that the DC voltage has not been established and that the charging circuit has failed.

[0005] The conventional operation will be described below with reference to FIGS. When the main switch 5 is turned on, a charging current flows to the electrolytic capacitor 8 through the charging resistor 6 and the diode rectifier 7, and the DC circuit starts charging with a charging time constant τ0 determined by the charging resistance value and the electrolytic capacitor capacity. As an example,
It is assumed that the time T1 is set to be about several times the charging time constant τ0, and V1 is set to be a detection value of the lowest allowable DC voltage when DC voltage is established.

[0004] The DC voltage detection value when the charging circuit is normal is:
The waveform becomes like Vdc1 in FIG. However, main switch 5
Is turned on at time 0. As can be seen from FIG. 6, when there is no failure in the charging circuit, the main switch 5 is turned off.
The DC voltage detection value at time T1, which is a sufficient time after N has passed, becomes larger than the specified value V1, which is the minimum allowable DC voltage detection value. Therefore, it can be determined that the DC voltage has been established.

If there is any abnormality in the charging circuit, the DC voltage is not established even if a sufficient time has elapsed since the main switch 5 was turned on. Therefore, the DC voltage detection value at time T1 becomes Vdc2, The value becomes equal to or less than the value V1, and the failure is detected by the failure detection circuit 51, and the failure of the charging circuit is determined.

[0006]

The above-described fault detection circuit has the following problems. When the DC circuit is short-circuited and hardly charged, failure detection in a short time is required to protect the circuit. The DC voltage detection value at this time is as shown by Vdc2 in FIG.
A failure is detected. Therefore, a short-circuit current flows through the charging resistor 6 and the diode rectifier 7 for several times the charging time constant τ0. For this reason, there is a problem that the charging resistor 6 and the diode rectifier 7 must have large capacities so as not to burn or break.

In order to speed up fault detection, time T1
If is set to a value of about the charging time constant τ0, as will be understood from FIG. 6, a failure is detected even in a normal state, so that V1 does not need to be set lower than the minimum allowable DC voltage detection value when DC voltage is established. Will not be. Then, this time, there is a problem that it is not possible to confirm whether the DC voltage value after a sufficient time has elapsed since the main switch 5 was turned on has reached the allowable minimum DC voltage value. The present invention has been made in view of the above points, and an object of the present invention is to provide a failure detection circuit for a charging circuit that solves these disadvantages.

[0008]

In order to achieve the above object, the present invention provides a voltage-specified-value generating section for outputting a voltage-specified value which varies with time from the time when charging is started. And a DC voltage that determines a failure when the DC voltage detection value is smaller by comparing a DC voltage detection value that is an output of a voltage detector that detects a voltage of a DC circuit of the power conversion device with the specified voltage value. And a determination unit.

In a preferred embodiment of the present invention, a first specified voltage value generator for outputting a first specified voltage value that changes with time from the time when charging is started, and a first specified voltage value smaller than the first specified voltage value. A second voltage specified value generating unit that outputs a second voltage specified value, and a DC voltage detection value that is an output of a voltage detector that detects a voltage of a DC circuit of the power conversion device, is a first voltage. A DC voltage determination unit that determines that a failure has occurred if the value is not between the specified value and the second voltage specified value. Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit block diagram showing a case where a first embodiment of the fault detection circuit according to the first embodiment of the present invention is applied to an inverter. FIG. 2 shows the operation of the first embodiment. FIG. 4 is a waveform diagram for explaining. In FIG. 1, reference numeral 1 denotes a DC voltage determination unit, 2 denotes a specified voltage value generation unit, and 1 and 2 constitute a failure detection circuit 3. Reference numeral 10 denotes a voltage detector which is a voltage detector, and the components having the same reference numerals as those in FIG.

In such a circuit, the voltage of the DC circuit of the inverter is detected by the voltage detector 10 and output to the DC voltage determination unit 1 as a DC voltage detection value Vdc. The DC voltage determination unit 1 includes a DC voltage detection value Vdc and a specified voltage value generation unit 2.
Is compared with the specified voltage value VL which is the output of
In the following case, it is determined that the charging circuit has failed, and the comparison operation is started immediately after the main switch 5 is turned on.

The specified voltage generator 2 includes a main switch 5.
Assuming that the moment when is turned on is time 0, a voltage regulation value VL as shown in FIG. 2 is generated. Here, as an example, T1 in FIG. 2 is several times the charging time constant τ0, and V1 is the detected value of the minimum allowable DC voltage when the DC voltage is established. Next, the operation will be described with reference to FIG.
Under normal conditions, the DC voltage detection value is like Vdc1, which is always larger than VL, so that no failure is detected.

Next, consider the case where the DC circuit is short-circuited and the DC voltage detection value has a waveform like Vdc2. At this time, at time T2, Vdc2 becomes smaller than VL, and a failure can be detected. When T1 and V1 are set to the values described above, the value of the voltage regulation value VL at time T1, which is a sufficient time after the main switch 5 is turned on, becomes the minimum allowable DC voltage when the DC voltage is established. Since the detected value V1 is the voltage, the failure can be detected when the DC voltage is not established. The same effect can be obtained even if the voltage regulation value VL is set to a waveform like VL1. If the value of VL at each time gives a lower limit of the DC voltage detection value at each time, the same effect can be obtained with other waveforms, and the setting of T1 and V1 can be obtained. The method is not limited to this embodiment.

FIG. 3 is a circuit block diagram showing a second embodiment of the present invention, and FIG. 4 is a waveform diagram for explaining the operation of the second embodiment. In FIG. 3, 1 is a DC voltage determination unit, 31 and 32 are voltage specified value generation units,
32 constitutes the failure detection circuit 3. The DC voltage determination unit 1 includes a DC voltage detection value Vdc and a specified voltage value generation unit 31,
32 is compared with the specified voltage values VH and VL,
If dc is equal to or lower than VL or equal to or higher than VH, a failure of the charging circuit is determined, and the comparison operation is started immediately after the main switch 5 is turned on.

The specified voltage value generators 31 and 32 generate the specified voltage values VH and VL as shown in FIG. 4 when the moment when the main switch is turned on is time 0. VL is always higher than VH. Is also small. Here, as an example, T1 in FIG. 4 is several times the charging time constant τ0, and V1 is the detected value of the minimum allowable DC voltage when the DC voltage is established.

Next, the operation will be described with reference to FIG. In a normal state, the DC voltage detection value becomes like Vdc1, and is always VH
And VL, the failure is not detected. Next, consider a case where the DC circuit is short-circuited and the DC voltage detection value is like Vdc2. At this time, at time T3, Vdc2 becomes smaller than VL, and a failure can be detected. When T1 and V1 are set to the above values, the voltage regulation value V at time T1 after a sufficient time has elapsed since the main switch 5 was turned on.
Since the value of L is the detection value V1 of the minimum allowable DC voltage when the DC voltage is established, the failure can be detected when the DC voltage is not established.

Further, if the charging time constant τ0 changes due to an abnormality in the constant of the charging resistor or the electrolytic capacitor, and the DC voltage detection value becomes a waveform like Vdc3, Vdc3 becomes larger than VH at time T4 and a failure occurs. Can be detected. That is, it is possible to detect a constant abnormality of the charging resistor or the electrolytic capacitor. VL at each time
Is a waveform that gives the lower limit of the DC voltage detection value at each time, and the value of VH at each time is
As long as the waveform gives the upper limit of the DC voltage detection value at each time, the same effect can be obtained even if the VH and VL of the output of the specified voltage generation unit are other than those shown here. The method of setting T1 and V1 is not limited to this embodiment. Although the example in which the present invention is applied to the charging circuit of the inverter has been described above, the same effect can be obtained by applying the present invention to a power conversion device having another charging circuit.

[0018]

As described above, according to the fault detection circuit of the present invention, a fault such as a short circuit of a DC circuit of a charging circuit can be detected and protected in a short time. Therefore, the charging resistance and the capacity of the diode rectifier can be reduced. It is also possible to detect an abnormality that the DC voltage has not yet been established after a sufficient time has elapsed from the start of charging.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing an embodiment according to claim 1 of the present invention.

FIG. 2 is a waveform chart for explaining the operation of the embodiment of FIG.

FIG. 3 is a circuit block diagram showing an embodiment according to claim 2 of the present invention.

FIG. 4 is a waveform chart for explaining the operation of the embodiment of FIG. 2;

FIG. 5 is a circuit block diagram showing a conventional example.

FIG. 6 is a waveform chart for explaining the operation of the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC voltage determination part 2 Voltage specified value generation part 3 Failure detection circuit 4 AC power supply 5 Main switch 6 Charging resistance 7 Diode rectifier 8 Electrolytic capacitor 9 Voltage detector 10 Voltage detection part 31 Voltage specified value generation part 32 Voltage specified value generation part 51 Failure detection circuit

Claims (2)

[Claims] 1. A failure detection circuit for a charging circuit that charges a DC circuit of a power conversion device, a voltage specification value generation unit that outputs a voltage specification value that changes with time from the time when charging is started, A voltage detection unit that detects a voltage, and a DC voltage determination unit that compares the DC voltage detection value output from the voltage detection unit with the specified voltage value and determines that a failure has occurred when the DC voltage detection value is smaller. A failure detection circuit for a charging device, comprising: 2. A failure detection circuit for a charging circuit for charging a DC circuit of a power conversion device, wherein a first voltage regulation value that changes with time from the time when charging is started is output.
A specified voltage generation unit, a second specified voltage value generation unit that outputs a second specified voltage value smaller than the first specified voltage value, and a voltage detection unit that detects a voltage of the DC circuit And a DC voltage determination unit that determines that a failure has occurred when a DC voltage detection value output from the voltage detection unit is not a value between the first voltage specification value and the second voltage specification value. A failure detection circuit for a charging device, comprising: