JPS62135225A - Power converter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention provides highly reliable protection for overcurrent detection and protection of power converters, which can detect fault current at a low level and furthermore determine which arm of the power converter is abnormally rich. The present invention relates to a power conversion device having a method. [Technical background of the invention and its problems] There are various known power conversion devices similar to the present invention, such as AC-DC converters and DC-AC power converters, such as natural commutation and forced commutation. be. As a protection method for these power converters, for example,
As shown in pages 114 to 117 of the i1 book "New □ Drive Electronics, edited by Naori Ueyama, Denkishoin 1st edition, published July 25, 857," overcurrent protection mainly uses overcurrent detectors and high-speed fuses. It was common to insert it into the circuit to protect it. The third embodiment of this prior art
As shown in the figure. In Fig. 3, 11 is an AC power supply, 12 is a rectifier, and 13 is a rectifier.
14 is a load, 14 is a control circuit, 15 is a reference, 16 is a current detector, 18 is an overcurrent detector, 12. -126 are power conversion elements; 19. ~19. is a high speed fuse. In the power converter configured as shown in FIG. 3, the AC power from the source 11 is converted into DC power by the rectifier 12 to drive the load 13. At this time, the DC power supplied to the load 13 is standard 15
is controlled by the control circuit 14 according to the set value. Six-arm individual power conversion elements 1 constituting a rectifier 12
21 ~] 2. The conventional method of detection and protection when the fuse deteriorates is to use a quick-acting fuse. - 196 is cut off, or the over-11 detector 18 detects whether the current flowing to the rectifier 12 via the current detector 16 is sufficiently larger than the overload current. It was getting worse. The detection and protection system for the power conversion device according to the prior art has the following problems. (1) In the method of protection using the overcurrent detector 18, it is necessary to set the detection level to a value larger than the overload current value of the rectifier 12, and moreover, considering current ripple during overload, etc. The overcurrent detection level must be set to a sufficiently large value relative to the overload tm value. Generally, if the overload capacity is about 225%, the overcurrent detection level is set at a level between 300 and 350 of the rated current. Therefore, there is a problem in that the fault current has increased sufficiently by the time the overcurrent is detected. On the other hand, in a 7-picture conversion device that uses elements with low heat resistance such as power conversion elements,
If we consider that the flow of the accident 'l' flows through other healthy power conversion elements that have not deteriorated (permanently failed), these accident 'iJ! It is clear that it is desirable to detect and protect a fault current when it is as small as possible in order to prevent stress caused by the influence of current from remaining on healthy power conversion elements, but conventional technology has not been able to meet this demand. . (2) Overcurrent detector 18'lf - In the method used, power conversion element 12. ~12. It was not possible to determine which power conversion element had deteriorated among the six arms. For this reason, recent power converters are used in various fields of important plants, but in the unlikely event that the power converter element 12. If any of the power conversion elements deteriorates (permanently fails), the time required to recover from the failure by investigating whether it is a power conversion element, converting the element, and restoring the device will be extremely long, resulting in plant stoppage damage during this time. It also had the disadvantage of being too large. (3) On the other hand, quick acting fuse 19. ~196 rectifier 12
If six wires are inserted into each arm, the fault current will be at least 2
Since the current flows through the fast-blow fuse in the arm, it is not guaranteed that the fast-blow fuse in the part where the power conversion element has deteriorated will blow.
In addition to the above-mentioned drawback (2) remaining, the fast-acting fuse 191
~196 also had to be replaced, but there was a problem that the stress of the electric current remained. [Object of the Invention] The present invention has been made in view of the above-mentioned shortcomings of the prior art, and is capable of detecting and protecting fault current at a lower level than before in overcurrent detection and protection of power conversion equipment. Furthermore, it is an object of the present invention to provide a power converter that is highly reliable and can determine which arm of the power converter is excited, and that can shorten failure recovery time. [Summary of the Invention] The present invention provides a current phase discriminator that compares and discriminates a control timing signal of a control circuit and a current detection signal of a current detector, and compares the magnitude, detection polarity, and timing of the current detection signal. Then, it is determined whether there is a fault current in the rectifier 12 or not. By making this determination, the detection level of the fault '1a flow can be kept within the continuous rated current of the power converter, and fault current detection and protection can be carried out very quickly. Furthermore, if the current phase discriminator is provided corresponding to the cross-current terminal of the power converter, it is possible to determine the presence or absence of a fault current for each arm of the power converter, so it is possible to determine which arm's power converter element has failed. The present invention can provide features that can minimize failure recovery time in the event of an accident. [Embodiment of the Invention] An embodiment of the present invention is shown in FIG. This figure shows an example in which the present invention is implemented in a power conversion device corresponding to FIG. 3, which performs AC-DC conversion by natural commutation. In Figure 1, the third
Circuit components having the same numbers as those in the drawings have the same functions. On the other hand, 17 is a current phase discriminator. In addition, the 11L current flowing to the AC terminal of the rectifier 12 is connected to IN+I
Let s be IT. The operation of the power conversion device in FIG. 1 is the same as that in FIG. do. In FIG. 2, the input AC current waveform of the rectifier 12 is shown as In + Is + IT. These currents IR, Is, and IT flow for a predetermined period with the polarities shown in the figure, which are shown by thick solid lines. That is, if one cycle of the AC power supply 11 is divided into six equal parts every 60 degrees, and the time of each is set as t1 to t, then the input AC current waveforms IR, I will be generated with the polarity and phase relationship shown in the diagram for each period of 120'.
s and ET flow respectively. Further, this waveform can be detected by the current detector 16. On the other hand, in the current phase discriminator [7], the input AC current waveforms Ill, I8 are determined by the control timing signal from the control circuit 14.
．． IT polarity and conduction period can be determined. Therefore, the current phase discriminator 17 is i4 when a current having the polarity of the waveform of the broken line flows during the period shown by the waveform of the broken line in FIG. 2, for example. This different layer is determined by the current phase discriminator 17 and a stop signal is given to the control circuit 14. This function will be explained in detail regarding the input AC current waveform Ia. From time t1, power conversion element 12. is conductive. Therefore, current flows on the positive side during the illustrated period. Time pig 10. At this point, power conversion element 12□ is ignited.At this point, power conversion element 12. deteriorates, AC power supply 11 - power conversion element 12 □ - t voltage conversion element 12 . - An accidental current flows in the loop of the AC power supply 11. The polarity of this accident @ flow appears as a negative polarity at r output from time t to time t4 in FIG. Therefore, if the presence or absence of this negative polarity fault current is determined from time t to time t, -1, the power conversion element 12. The presence or absence of deterioration can be determined. Also, during the period from time 14 to time t6, the power conversion element 124
conducts, so current flows with negative polarity during this period. At time -'power conversion element 12. is ignited, but if the power conversion element 124 deteriorates in the same way, the alternating current (AC) source 11 - power conversion element 124 - power conversion element 12 . - A fault current flows in the loop of the AC power supply 11, and the polarity of this fault current changes at time t6.
It appears with positive polarity during the period up to υ time t. Therefore, it is possible to similarly determine whether or not the power conversion element 124 has deteriorated. Other power conversion elements 12□, 12. . It is clear that 12, , and 126 can be similarly discriminated. Generally power conversion element 12. The probability that deterioration occurs in the power conversion elements 12 and 126 is extremely high before and after the current conduction period, so if it is determined by the method described above, the power conversion elements 12 and 126
It is clear that the presence or absence of deterioration can be determined for each power conversion element. Moreover, the aforementioned time t. Until time t4, or from time t! Since the fault current discrimination level up to , is different in that the current is detected with a predetermined polarity during this period, the current level is set to a current level below the rated continuous current, taking into account the error of the current detector 16, etc. be able to. Therefore, in the present invention, even if the fault current is below the rated continuous current, detection and protection operations can be performed, and even if a power conversion element deteriorates, it is possible to detect which arm the power conversion element belongs to. Current phase discriminator

[Since it can be determined by 7,
It is possible to provide a power conversion device that has the feature that failure recovery time can be significantly shortened. As a modification of the present invention, the detection period of the accident α flow is not particularly limited. This is, for example, the power conversion element 12 in FIG. Speaking of time! , or from load time t4 to time t.
, detects the current flowing through the load 13 during , and calculates the differential flow between this detected current and the current component flowing through the power conversion element 124 during this period, and monitors the time from time t6'! of negative polarity for a predetermined period, it is determined whether the current is at a predetermined level, and the power conversion element 12. The presence or absence of deterioration may also be determined. Further, the fault fourth current detection level of the current phase discriminator 17 is not particularly limited. Further, the configuration and type of the power conversion device to which the present invention is applied is not particularly limited, and the present invention can be applied to forced commutation current source inverter circuits, load commutation inverter circuits, and the like. It is clear that various other embodiments can be provided without changing the gist of the invention. [Effects of the Invention] According to the present invention, it is possible to determine which power conversion element of which arm of the power conversion device has deteriorated, and moreover, the fault current at the time of deterioration of the power conversion device is lower than the continuous rated 14 current of the power conversion device. Detection and protection operations can be performed even at the following levels. Therefore, the power converter according to the present invention has the following features. (1) Since the detection and protection operations are performed at a low level of fault current, the stress of the fault on healthy power conversion elements can be minimized, and the reliability of the device is greatly improved. (2) Which arm's power conversion element has deteriorated?
Since it can be determined using a current phase discriminator, it is possible to immediately begin work on replacing degraded power conversion elements, greatly shortening the failure recovery time, and as a result, reducing plant damage caused by accidents. Stoppage damage can also be minimized. 4. 1? [Brief explanation] Fig. 2 is a diagram of an embodiment in which the present invention is applied to a power converter that converts AC power into DC power; Fig. 2 is a waveform diagram for explaining the operation of Fig. 1; FIG. 3 is a diagram showing an example of a conventional power conversion device corresponding to FIG. 11 AC voltage 12 Rectifier 13 Load 14 ・Control circuit L: 5-2 & quasi
16 paper flow detector t7/current phase discriminator
18...Overcurrent detector 121-126/Four force conversion element 191-196...High speed fuse Figure 1 Figure 2

Claims (1)

[Claims] In a power conversion device for forward converting AC power to DC power or for converting DC power to AC power with a constant direction of DC current, a current detector for detecting the AC current is provided, and a current detector for detecting the AC current is provided, and the power conversion device is Obtain a control timing signal that can determine which arm's power conversion element is conductive.
After the conduction period of each power conversion element in each arm is completed, when a current detection signal of a predetermined level or higher is obtained within a predetermined period with a polarity opposite to the conduction period, the deterioration of the power conversion element in which arm is detected. A power conversion device is characterized in that it performs accident detection and protective operation by determining whether