JPH0586149B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a protection circuit malfunction detection method for detecting malfunction of a protection circuit of a power conversion device.

[Technical background of the invention and its problems]

Uninterruptible power supplies used as power sources for socially important loads such as banks and airports are required not only to be highly reliable but also to have short failure recovery times. However, the self-excited inverter, which is a main part of the uninterruptible power supply, will fail and stop if the firing order of the thyristors is out of order or if a load current higher than expected flows. For example, if a short circuit occurs on the load side and an excessive load current flows, a self-excited inverter will instantly stop inverter operation when the load current reaches a certain level in order to protect its own switching elements (e.g. GTO). do. This prevents the current flowing through the switching element from exceeding its overcurrent tolerance and destroying the switching element.

Problems with such conventional protection circuits are as follows.

In other words, the problem is that the protection circuit itself may be defective. If the components in the protection circuit deteriorate and the protection circuit is activated by mistake, the self-excited inverter will stop even though the load current is not abnormal.

If the component has completely deteriorated, it is possible to discover a defect in the protection circuit through an investigation after the failure has stopped; however, if it is due to incomplete deterioration, the superficial defect of the component may have returned after the failure has stopped. It may be difficult to detect the defect.

To make matters even more difficult, there are some load abnormalities in which, for example, when a short circuit occurs, the short circuit part melts and the short circuit is canceled, and when the self-excited inverter is restarted, it can be operated as if nothing had happened.

Therefore, whether the cause of the failure is within the protection circuit,
Alternatively, it may be difficult to determine whether an instantaneous short circuit has occurred on the load side, and the cause may ultimately become unknown. In such cases, the waveform recording device is connected to the inverter and one waits for the failure to occur again, but it may take several months to discover and eliminate the true cause of the failure. .

Now, in recent years, the use of microcomputers in the control circuits of power conversion devices has been progressing, but similar problems remain in that case as well. With the introduction of microcomputers for control circuits, protection circuits will naturally be made into software, but there are some parts that cannot be made into software due to system reliability or protection operation speed, and must remain as hardware protection circuits. .

For example, the aforementioned protection circuit for detecting a load short circuit cannot protect a switching element unless it detects and protects the short circuit at a speed of several tens of microseconds. It is difficult to perform such high-speed operation via software.

Therefore, in most microcomputer-controlled power conversion devices, a protection circuit that detects the level using a conventional hardware comparator and a main circuit current/voltage are digitized using an A/D converter, and then level judgment is performed using software. It is conceivable that it will be a two-pronged protection circuit with a protection circuit that protects the
The problem of hardware protection circuit malfunction mentioned earlier remains.

[Purpose of the invention]

The present invention was made in view of the shortcomings of conventional means, and provides a method for detecting malfunction of a protection circuit of a power conversion device, which can diagnose malfunction of a hardware protection circuit and eliminate the cause of the failure in a short time. Its purpose is to.

[Summary of the invention]

For this reason, the present invention digitizes the main circuit current and voltage input to the hardware protection circuit using an A/D converter, sequentially writes this data into the data memory, and detects malfunctions of the protection circuit from the presence or absence of abnormalities in the stored contents. Diagnose.

[Embodiments of the invention]

Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, showing a part of a microcomputerized control circuit.

1 is a self-excited inverter, 2 is a load, and 3 is an A/D converter (ADC) that converts analog quantities into digital quantities.The main circuit current and voltage detected by the detector 10 are thereby digitized. .
4 is a processor circuit (CPU) which is the main control unit of the microcomputer section, 5 is a read-only memory (ROM) in which programs are stored, and 6 is a writable memory (RAM) which serves as the RAM required for normal computer operation. It also serves as a RAM for storing main circuit current and voltage waveforms, which is one of the gist of the present invention. 7 is a digital output circuit which sends a gate cutoff command to the gate circuit 8 according to a command from the CPU 4. A hardware comparator circuit 9 determines the level of the main circuit current and voltage and sends a gate cutoff command to the gate circuit 8 based on the results. The gate circuit 8 normally sends out a gate signal to control on/off of the switching elements of the inverter 1, but when a gate cutoff command is sent from the digital output circuit 7 or the comparator circuit 9, the gate signal is cut off.

The operation of the present invention will be explained with respect to the malfunction of the load short circuit detection protection circuit described above.

In the case of a load short circuit, the rise of the load current is steep, so it is necessary to perform a protective operation within several tens of microseconds after the load current reaches the load short circuit detection level.
It is difficult to do so with protection circuits through software.

Therefore, as shown in Fig. 1, a hardware comparator 9 detects that the load current I _L has reached, for example, 170% of the rated current, and sends a gate cutoff command to the gate circuit 8 to switch off the self-excited inverter. 1
stop instantly.

On the other hand, abnormalities in load 2 include, in addition to the load short circuit described above, overload (for example, 100%) or continued overload (for example, 150% for 10 seconds), but unlike the case of load short circuit, these are instantaneous. There is no need to perform a protection operation, and therefore a software protection circuit can be used.

The protection operation by software in case of continuous overload will be explained.

The A/D converter 3 digitizes the load current I _L , and software determines whether it exceeds 150%. Similarly, when the software detects that the time exceeding 150% continues for 10 seconds, the digital output circuit 7 sends a gate cutoff command to the gate circuit 8 to stop the self-excited inverter 1.

The above is an example of a protection circuit using software, but one gist of the present invention is to sequentially write the data into the RAM 6 after digitizing the load current I _L. Since A/D conversion of the load current I _L is performed at a certain sampling period,
Writing to RAM 6 is also performed at the same cycle.
If you stop writing to RAM6 after a failure occurs,
The data stored in the RAM 6 represents the transition of the load current I _L before and after the failure occurs.

The load current I _L when a load short circuit actually occurs
When the data stored in the RAM 6 is graphed, it becomes as shown in FIG. 2a. This is a three-phase AC waveform that has been full-wave rectified and then digitized and written into the RAM 6, and _t1 is the time of failure detection. obviously point in time
It is detected that an abnormal current flows through load 2 at t ₁ . According to the inventor's experience, it has been found that abnormalities in the load current can be detected by writing to the RAM 6 at a sampling frequency that is about 30 times the output frequency.

On the other hand, FIG. 2b shows the load current I _L when a malfunction of the comparator circuit 9 (at that time t ₁ ) is simulated.
This is a graph of the data stored in the RAM 6, but unlike FIG. 2a, no abnormality is observed.

A diagnostic program for the protection circuit based on the stored data of the load current I _L as described above is shown in FIG.

In other words, a load short circuit is detected (step 32).
When inverter 1 stops, load current I _L RAM
Judge the level of the memory data in 6, for example 170%
Check to see if there is anything that exceeds (Step 33). If there is even one thing that exceeds
It is diagnosed that a load short circuit has actually occurred, and a "load short circuit" fault is displayed (step 34). If none of the stored load current I _L data exceeds 170%, it is diagnosed that the protection circuit has malfunctioned, and a "protection circuit malfunction" fault is displayed (steps 35 and 36). In the latter case, the inverter 1 may be restarted depending on the situation. The diagnostic criterion does not necessarily have to be 170%, which is the level criterion of the comparator circuit 9;
It is better to select a value lower than that and higher than the maximum load current value that can be assumed under normal conditions as the criterion for determination.

Next, another embodiment of the present invention will be described. Diagnosis of malfunction of the protection circuit in the embodiment described above is based on the premise that the A/D converter 3 is normal. If a load short circuit occurs when the A/D converter 3 is abnormal, a "protection circuit malfunction" error message will appear even though a load short circuit has actually occurred, and the cause of the failure will be It may also cause confusion in the pursuit of

Therefore, as an embodiment of the present invention, the A/D shown in FIG.
A reference voltage circuit 1 is connected to the converter 3 as shown in FIG.
2 and a changeover switch 11 are provided. When a load short circuit occurs, the changeover switch 11 switches the input to the A/D converter 3 from the load current _IL to the reference voltage circuit 12. After that, a reference voltage (eg, +5V) is input, digitized, and checked to see if it is within a certain range. If it is outside the range, it is diagnosed that the A/D converter is abnormal, and the protection circuit malfunction is not diagnosed. In this case, "load short circuit" and "A/D
Converter error" will be displayed. The above diagnostic program is shown in a flowchart as shown in FIG.

In the description so far, we have explained the case of a load short circuit in a self-excited inverter as an example, but similar malfunction diagnosis can also be performed for AC overvoltage, AC undervoltage, DC overvoltage, DC undervoltage, and other protection circuits. Furthermore, it goes without saying that the present invention can be similarly applied to not only self-excited inverters but also rectifiers, choppers, separately excited inverters, etc. as power conversion devices.

〔Effect of the invention〕

Thus, according to the present invention, it is possible to immediately detect a malfunction of a protection circuit, which has been difficult in the past, and it is possible to significantly shorten the time required to repair a self-excited inverter, especially in the case of a malfunction due to incomplete deterioration of components, and to improve the reliability of an uninterruptible power supply. This greatly contributes to improving the reliability of the device.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure shows each case when the load is short-circuited and when the protection circuit malfunctions.
FIG. 3 is a diagram showing a graph of stored data in RAM, FIG. 3 is a diagnostic flowchart according to the present invention, FIG. 4 is a configuration diagram showing another embodiment, and FIG. 5 is a diagnostic flowchart in another embodiment. . 1... Self-excited inverter, 2... Load, 3... A/D converter, 4... Processor circuit (CPU), 5... Read only memory (ROM), 6... Writable memory (RAM), 7... Digital output circuit, 8... Gate circuit, 9... Comparator circuit, 10... Detector, 1
1... Selector switch, 12... Reference voltage circuit.

Claims (1)

[Claims] 1. Detecting the current or voltage of each part of the power conversion device and applying it to a comparator circuit, comparing the detected value with a set value in the comparator circuit, and the detected value reaching the set value. Converts the detected value from analog to digital in a protection circuit of the power conversion device that stops the power conversion device or displays an alarm when the power conversion device is activated, and writes the digitized data to a continuously writable memory, and A malfunction of a protection circuit of a power conversion device is characterized in that the writing is stopped after the protection circuit operates, and a malfunction of the protection circuit is detected on the condition that there is no data that has reached the set value among the data. Detection method. 2. Malfunction detection of a protection circuit of a power conversion device according to claim 1, wherein malfunction of a protection circuit is detected on the condition that a circuit that converts the detected value from analog to digital is normal. Method.