CN103884930A - Full bridge uncontrolled rectifier fault diagnosis method based on insulation monitoring - Google Patents

Abstract

The invention provides a rectifier fault diagnosis method based on insulation monitoring. Firstly, the insulation resistance R _t under the normal operation of the system is measured. Connect the positive and negative poles of the IMD injection source based on the DC injection method to the neutral line and the ground respectively, measure the system insulation monitoring value R _f when the IMD is injected in the positive direction, change the direction of the IMD injection signal, and connect the positive pole of the IMD injection source to the ground. , the negative pole is connected to the ground and the neutral line respectively, and the insulation monitoring value R _r when the IMD is reversely injected can be measured. If R _f or R _r is not equal to R _t , the system enters the fault diagnosis process, and uses the collected R _f and R _r , calculate the real insulation resistance R _m of the system, and then compare it with the insulation resistance value R _t under the normal operation of the system to find out whether the change of insulation resistance is caused by the fault of the rectifier.

Description

A Fault Diagnosis Method for Full-Bridge Uncontrolled Rectifier Based on Insulation Monitoring

technical field

The invention relates to a fault diagnosis method for an uncontrolled rectifier in an IT power distribution system, in particular to a fault diagnosis method for a full-bridge uncontrolled rectifier based on insulation monitoring.

Background technique

The failure of the rectifier mainly refers to the failure of the diode in the rectifier bridge. The reverse breakdown of the diode itself or the destruction of the insulating layer of the bridge arm will cause a short circuit of the diode, resulting in a rapid rise in current and a steep drop in conduction voltage drop. In severe cases, the equipment will be damaged and the system will be paralyzed; Poor wiring or over-current burning will cause the diode to open circuit, which may cause the current of other diodes to exceed the limit, the output DC voltage ripple will increase, and affect the normal operation of the device; these are the most common faults of the rectifier and harm.

Normally, the formation of a rectifier fault is a process of continuous deterioration, which is manifested in the conduction voltage drop of the diode. When the conduction voltage drop rises or decreases to a certain limit, the open circuit or short circuit fault of the diode occurs. Therefore, if the fault can be found in the early stage of the fault, that is, before the faulty rectifier causes great harm, the probability of accidents can be reduced and the maintenance of the system can be facilitated. At present, the main methods used to diagnose rectifier faults at home and abroad are: 1. Spectrum analysis method; 2. Direct detection method; 3. Dictionary database diagnosis method; 4. Expert system method; 5. Neural network fault diagnosis and other methods.

The spectrum analysis method is to extract the time domain signal of the fault. Usually, the Fourier transform is used to change the time domain signal of the fault into the frequency domain for analysis. However, this method does not consider the process of the gradual deterioration of the diode, and only directly opens and shorts the diode. analysis; the direct detection method judges whether the diode is faulty by detecting the voltage at both ends of the diode or the current of the rectifier bridge arm, but this method requires more voltage and current sensors, which virtually increases the cost and complexity of the system, resulting in The system may have to pay a higher price for the fault of the sensor; the dictionary diagnosis method needs a large number of numerical simulations and experiments to obtain the fault value and eigenvalue, which is difficult to realize in the actual system; the expert system method and the neural network fault diagnosis method are both The method has strong calculation ability and artificial intelligence simulation ability, but its shortcomings such as difficult to obtain training samples, weak diagnostic ability, and vague network weight expression form limit the practical application range of this method.

The application of the IT system needs to rely on the insulation monitoring device (IMD), whose main purpose is to monitor the first ground fault in the system and issue an audible and visual alarm; if the IMD installed in the IT system itself can be used to monitor the diode fault Deterioration, the rectifier can be maintained before the extreme fault (short-circuit fault, open-circuit fault) of the rectifier, so as to eliminate hidden dangers and prevent accidents without the need for additional measuring instruments. Especially for small, low-power rectifiers, it is of little significance to indicate the range of faulty diodes, because low-power diodes are cheap, and the rectifier bridge is made modular, and there is no need to disassemble and replace the diodes; but once the diodes are short-circuited or The harm caused by an open-circuit fault is far higher than the cost of the rectifier. Therefore, within the scope of the IT system, if you can use its own IMD to diagnose the faulty rectifier and remind the maintenance personnel to deal with the rectifier in time, it will be possible for the rectifier. The convenience of maintenance work is also very important for ensuring the safety and power quality of the entire system.

Contents of the invention

The purpose of the present invention is to propose a rectifier fault diagnosis method based on insulation monitoring. Use the IMD installed in the IT system itself to monitor the diode fault degradation process, and maintain the rectifier before the extreme fault (short circuit fault, open circuit fault) occurs in the rectifier to achieve the purpose of eliminating hidden dangers and preventing accidents without the need for additional measuring instruments . Using its own IMD to diagnose faulty rectifiers and remind maintenance personnel to deal with rectifiers in time can bring convenience to rectifier maintenance and is also very important for ensuring the safety and power quality of the entire system.

The technical solution of the present invention is: a method for fault diagnosis of a full-bridge uncontrolled rectifier based on insulation monitoring, the specific steps are as follows:

a) Measure the insulation resistance R _t under normal operation of the system;

b) Connect the positive and negative poles of the IMD injection source of the insulation monitoring device based on the DC injection method to the neutral line and the ground of the IT system with a full-bridge uncontrolled rectifier circuit respectively. In the entire path, the DC side acts as an "excitation power supply" role , the AC side acts as a "load". For the DC side, the AC side can be equivalent to a DC resistance network. From the perspective of the equivalent DC network port on the AC side, it is equivalent to bear the role of a DC voltage source;

The simplified DC impedance equivalent network is as follows: including IMD injection source voltage U _s , sampling resistance R _s , interference source voltage U _c , interference source equivalent internal resistance R _c , AC line-to-ground equivalent insulation resistance R; R The signal at one end _{of s} is connected to R and R _c , the signal at one end is connected to one end of U _s , and the other end of U _s is grounded; the signal at one end of R is connected to R _s and R _c , and one end is grounded; the signal at one end of R _c is connected to R and R _s , and the other end is grounded. The signal is connected to the U _c positive terminal, and the U _c negative terminal is grounded;

c) Using the IMD positive injection signal, that is, the positive terminal of the IMD injection source voltage U _s is connected to the signal of the sampling resistor R _s , and the negative terminal is grounded. The measured insulation resistance is recorded as R _f ; the specific steps are as follows:

Using the principle of superposition, I _c is the current value flowing through the sampling resistor R _s under the action of U _c alone, and I _s is the current flowing through the sampling resistor under the action of U _s alone:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

d) Use IMD to reverse the direction of the injection signal, that is, the negative terminal of the IMD injection source voltage U _s is connected to the signal of the sampling resistor R _s , and the positive terminal is grounded. The measured insulation resistance is recorded as R _r ; the specific steps are as follows :

Using the principle of superposition, I _c is the current value flowing through the sampling resistor R _s under the action of U _c alone, and I _s is the current flowing through the sampling resistor under the action of U _s alone:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

e) Combine formula (1) and formula (2) to get the real insulation resistance value R _m of the system:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}}{\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

f) The rectifier fault diagnosis method in the system, the specific steps are as follows:

1) The monitoring value of the insulation monitoring device IMD changes;

2) If the R _f measured in step c) is not equal to the R _t measured in step a), or the R _r measured in step d) is not equal to the R _t measured in step a), then judge There is a problem with the system at this time;

3) Compare the real value R _m of the insulation resistance measured in step e) with the R _t measured in step a), if R _m = R _t , it is diagnosed that the rectifier in the system is faulty.

Further, the system problems described in step f) include rectifier failures, changes in the insulation resistance of the system itself, or external DC interference sources in the system

Further, in step f), if R _m ≠ R _t , it is diagnosed that the insulation resistance of the system itself changes, or there is an external DC interference source in the system.

The fault diagnosis principle of the rectifier in the system is as follows: when the system is in normal operation, that is, when there is no insulation fault in the system and there is no external DC interference source in the system, the insulation resistance of the DC side line of the rectifier to the ground is equal, and the factors that affect the voltage of the midpoint to the ground There is only the power supply voltage of each bridge arm, and the power supply voltage of each bridge arm is only related to the conduction voltage of the diode of the rectifier bridge arm. Insulation resistance is injected into the ground and into the neutral point of the AC side, which affects the insulation monitoring of the IMD. If the detection value of the IMD of the insulation monitoring device changes, it is diagnosed as a fault in the rectifier in the system.

This kind of rectifier fault diagnosis method first needs to measure the insulation resistance value under the normal operation of the system, as a reference value, collect the insulation resistance value measured during the two injections of IMD forward and reverse, and obtain the required system insulation resistance after processing The actual value is compared with the benchmark value measured under normal system operation to obtain the reason for the change of the IMD monitoring value.

The beneficial effects of the present invention are: the insulation monitoring function of the IMD that comes with the IT system is used to diagnose the rectifier fault in the system, and the rectifier fault is diagnosed by using the idea based on insulation monitoring described in the present invention. When the diode deteriorates, that is When a short circuit or open circuit fault has not yet formed, the fault is found, and the principle is simple and operable, mainly due to the following characteristics:

1) The method adopted in the present invention avoids the possibility of adding rectifier fault diagnosis devices to increase the complexity of the system, and can accurately diagnose faults.

2) The present invention can diagnose the fault degradation process of the rectifier, and promptly remind the maintenance personnel to repair and replace the rectifier, so as to prevent the damage to the system caused by the extreme fault of the rectifier (short circuit fault, open circuit fault).

3) The present invention aims at the shortcomings of the existing rectifier fault diagnosis method being complex and unable to diagnose the deterioration process of the switching tube. After analysis, firstly determine the reason that affects the change of the IMD monitoring value, and obtain that the insulation drop of the rectifier bridge diode and the cable is the cause of the IMD monitoring value. reason for the change. The insulation resistance monitoring values of IMD forward and reverse injection are collected respectively, and after processing, the real insulation resistance value of the system is obtained. When the real insulation resistance value is inconsistent with the reference value, it is diagnosed as a rectifier failure.

4) For small, low-power rectifiers, it is not meaningful to indicate the range of faulty diodes, because low-power diodes are cheap to manufacture, and the rectifier bridge is made modular, so there is no need to disassemble and replace the diodes; but once the diodes are short-circuited or The harm caused by the open circuit fault is far higher than the cost of the rectifier, so the present invention uses its own IMD to diagnose the faulty rectifier and remind the maintenance personnel to deal with the rectifier in time, which can bring convenience to the maintenance work of the rectifier. It is also very important to ensure the safety and power quality of the entire system.

Description of drawings

Figure 1 is a circuit diagram of an IT system with a three-phase bridge uncontrolled rectifier;

Figure 2 is a simplified circuit model of the system with a three-phase bridge uncontrolled rectifier;

Fig. 3 is a graph showing the variation of the midpoint voltage with the turn-on voltage of the common cathode diode;

Fig. 4 is a graph showing the variation of the midpoint voltage with the turn-on voltage of the common anode diode;

Figure 5 is a simplified circuit diagram of the IMD insulation monitoring affected by the midpoint voltage during the forward injection of the IMD;

Figure 6 is a simplified circuit diagram of the IMD insulation monitoring affected by the midpoint voltage during IMD reverse injection;

Figure 7 is a schematic diagram for calculating insulation resistance.

Detailed ways

As shown in Figure 1, it is a circuit diagram of an IT system with a three-phase bridge uncontrolled rectifier. According to the switching function of the uncontrolled rectifier, the common cathode or common anode diodes are respectively turned on in a cycle, and each diode The on-duty cycle is one-third of the period. Using this feature, the three common cathode diodes can be equivalent to one diode, and the common anode diode is also equivalent to one diode. At the same time, the three The phase power supply is equivalent in the upper and lower bridge arms, which are E _p and E _n respectively. Finally, the three triangle-connected resistors R _h , R ₊ , R _- are transformed by △-Y to become R _p , R The resistance of the Y-type connection composed of _n and R _l .

As shown in Figure 2, _Du is the equivalent common-cathode diode, and D _d is the equivalent common-anode diode. The equivalent resistance and equivalent power supply in the figure are: R _n =R _h R _- /(R _h + R ₊ +R _- ), R _p =R _h R ₊ /(R _h +R ₊ +R _- ), R _l =R _- R ₊ /(R _h +R ₊ +R _- ), E _p = max{E _a , E _b , E _c }, E _n =min{E _a , E _b , E _c }. Using loop current method to analyze the circuit model shown in Figure 2, the mid-point voltage U _m =i ₀ ·R _l is obtained. As long as U _m is not 0, there is a direct current flowing into the neutral point, and the following is carried out calculate:

$\left\{\begin{array}{c}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="i"\; filenames="HDA0000472385850000013.png"\; state="\{\{state\}\}">i</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}\\ <span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="i"\; filenames="HDA0000472385850000013.png"\; state="\{\{state\}\}">i</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Eliminate i ₁ to get i ₀ , and then bring i ₀ into the midpoint voltage expression to get

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Generally speaking, the insulation resistance of the DC side of the rectifier to the ground is equal, that is, R _p = R _n , and the factors that affect U _m are only E _p and E _n . From the expressions of E _p and E _n , it can be seen that their magnitude is only related to the rectifier It is related to the conduction voltage U _f of the bridge arm diode. Establish the circuit model of the IT system with a three-phase bridge uncontrolled rectifier in the MATLAB/Simulink simulation software, and take the three-phase voltages as E _a =220∠0°, E _b =220∠-120°, E _c =220∠ 120°, the forward conduction voltage of the diode is 0.8V, C is 3000μF, R _h is 10Ω, R ₊ and R _- are 20MΩ and 20MΩ respectively, and R _g is 100kΩ. Effect of the conduction condition of the ediode on U _m . Other conditions remain the same, only change the U _f value of _D1 tube, from 0.5V to 1.1V, the step size is 0.05V, record the change of U _m , as shown in Figure 3; only change the U _f value of _D6 tube, by Change from 0.5V to 1.1V with a step size of 0.05V, and record the change of U _m , as shown in Figure 4.

After the midpoint voltage U _m is unbalanced, the rectified DC current is injected into the ground through the insulation resistance of the DC line to the ground, and enters the neutral point of the AC side, which affects the insulation monitoring of the IMD. In the entire path, the DC current The AC side acts as an "excitation power source", and the AC side acts as a "load". For the DC side, the AC side can be equivalent to a DC resistance network. From the perspective of the equivalent DC network port on the AC side, it can be considered to bear a The action of a DC voltage source. According to the principle of IMD and the mechanism of the midpoint voltage _Um , the whole system can be simplified as the equivalent network of DC resistance shown in Figures 5 and 6, where Us _is the IMD injection source voltage, _Rs is the sampling resistor, and _Uc is the interference source voltage, R _c is the equivalent internal resistance of the interference source, and R is the equivalent insulation resistance of the AC line to the ground.

Use the insulation monitoring device of the IT system itself to diagnose rectifier faults. The insulation resistance measured according to the direction (forward direction) of the IMD injection signal shown in Figure 5 is denoted as R _f , mainly using the superposition principle, as shown in Figure 7, _Ic is _Uc flowing through the sampling resistance R under the action of Uc alone The current value of _s , I _s is the current flowing through the sampling resistor under the action of U _s alone:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Change the signal injection direction of the IMD, and inject the DC signal shown in Figure 5 into the positive and negative poles of the power supply U _S reversed, that is, the upper negative and the lower positive (reverse), as shown in Figure 6, record the insulation resistance value at this time , recorded as R _r , using the principle of superposition, as shown in Figure 7, I _c is the current value flowing through the sampling resistor R _s under the action of U _c alone, and I _s is the current flowing through the sampling resistor under the action of U _s alone:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Simultaneous formula (3) and formula (4), the real insulation resistance value R of the system can be obtained:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}}{\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

It can be seen from formulas (3), (4) and (5) that if the insulation resistance is measured by only using the IMD to inject a signal in the forward or reverse direction, the influence of interference may not be ruled out, that is, when the insulation resistance measured by the IMD changes, it may be Because the insulation resistance of the system itself changes, it may also be that there is a DC interference source in the system. Based on the analysis of the midpoint voltage, it can be seen that when the midpoint power supply is unbalanced to the ground voltage, it will interfere with the IMD as a "DC excitation source", and the diode of the rectifier bridge is the only factor affecting the midpoint voltage. Generally speaking, there is no external DC interference source in the system. Therefore, if the reason for the change of IMD insulation monitoring can be ruled out as the change of the insulation resistance of the system itself, it can be diagnosed as a rectifier failure.

For different systems, the corresponding insulation resistance values under normal operation are different, so it is necessary to measure the safe insulation resistance of the system on site, and take it as R _t (generally 20-80kΩ), if the measured R _f or R _r If it is not equal to R _t , it is considered that there is a system insulation change or there is a rectifier fault at this time, and the system enters the diagnosis process, and R _r and R _f are brought into the insulation resistance calculation formula (5) to obtain the real value of the system insulation resistance R _m , compare R _m and R _t , if R _m ≠ R _t , it is diagnosed that the insulation resistance of the system itself has changed (increased or decreased), and corresponding measures can be taken for the system; if R _m = R _t , the diagnosis is The rectifier in the system has failed.

The rectifier fault diagnosis scheme based on insulation monitoring is used to diagnose the change of rectifier diode conduction voltage in the IT system. According to the idea of rectifier fault diagnosis provided by the present invention, the insulation monitoring function of IMD itself is used to diagnose rectifier faults. Extraction, in the process of rectifier failure or failure deterioration, it can be diagnosed quickly and convenient for system maintenance.

The key to the solution of the present invention is to analyze the reason for the change of the IMD measurement value, and design a fault feature extraction scheme to eliminate the change of the IMD measurement value caused by the insulation drop of the system itself, so as to determine the fault of the rectifier.

The present invention has been disclosed above with preferred embodiments, but it is not intended to limit the present invention. Those skilled in the art of the present invention can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be defined by the claims.

Claims (3)

1. a not control rectifier method for diagnosing faults of the full-bridge based on insulating monitoring, is characterized in that: concrete steps are as follows:

A), measure the insulation resistance R under system normal operation _t;

B) positive and negative electrode that, insulation monitoring and warning device IMD based on DC injection method is injected to source respectively with IT system band full-bridge not the neutral line of controlled rectifier circuit be connected with the earth, in whole path, DC side is served as " excitation power supply " role, AC serves as " load " role, for DC side driving source, AC can equivalence be a direct current resistance network, and from the equivalent DC network port of AC, the effect of bearing a direct voltage source is thought in equivalence;

Direct current resistance equivalent network after simplification is specific as follows: comprise that IMD injects source voltage U _s, sampling resistor R _s, interference source voltage U _c, interference source equivalent internal resistance R _c, alternating current circuit equivalent insulation resistance R over the ground; R _sone end signal is connected to R and R _c, an end signal is connected to U _sone end, U _sother end ground connection; R mono-end signal is connected to R _sand R _c, one end ground connection; R _cone end signal is connected to R and R _s, an end signal is connected to U _cpositive terminal, U _cthe sub-ground connection of negative terminals;

C), utilize IMD forward Injection Signal, i.e. IMD injection source voltage U _spositive terminal and sampling resistor R _ssignal connects, negative terminals ground connection, and the measured insulation resistance obtaining is designated as R _f; Concrete steps are as follows:

Utilize superposition principle, I _cfor U _cthe dirty over-sampling resistance R of independent role _scurrent value, I _sfor U _sthe electric current of the dirty over-sampling resistance of independent role:

$R_f=\frac{U_s}{I_s-I_c}-R_s---\left(1\right)$

D), utilize the direction of IMD inverse injection signal, IMD injects source voltage U _snegative terminals and sampling resistor R _ssignal connects, positive terminal ground connection, and the measured insulation resistance obtaining is designated as R _r; Concrete steps are as follows:

Utilize superposition principle, I _cfor U _cthe dirty over-sampling resistance R of independent role _scurrent value, I _sfor U _sthe electric current of the dirty over-sampling resistance of independent role:

$R_r=\frac{U_s}{I_s+I_c}-R_s---\left(2\right)$

E), simultaneous formula (1) and formula (2), the real insulating resistance value R of the system that obtains _m:

$R_m=\frac{U_s}{I_s}-R_s=\frac{2}{\frac{1}{R_f+R_s}+\frac{1}{R_r+R_s}}-R_s---\left(3\right)$

F), rectifier method for diagnosing faults in system, concrete steps are as follows:

1) monitor value of insulation monitoring and warning device IMD changes;

2) if the R measuring in step c) _fwith the R measuring in step a) _tthe R measuring in unequal or step d) _rwith the R measuring in step a) _tunequal, judge now system existing problems;

3) by the insulation resistance actual value R measuring in step e) _mwith the R measuring in step a) _trelatively, if R _m=R _t, be diagnosed as rectifier in system and break down.

2. not control rectifier method for diagnosing faults of a kind of full-bridge based on insulating monitoring according to claim 1, is characterized in that: system described in step f) existing problems comprise that rectifier breaks down, the insulation resistance of system itself changes or Installed System Memory at external dc interference source.

3. not control rectifier method for diagnosing faults of a kind of full-bridge based on insulating monitoring according to claim 1 and 2, is characterized in that: in step f), if R _m≠ R _t, the insulation resistance that is diagnosed as system itself change or Installed System Memory at external dc interference source.

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