Abstract By analyzing the causes of failures in general-purpose frequency converters and their troubleshooting methods, it is of practical significance for mastering the correct use and maintenance of frequency converters. Keywords : general-purpose frequency converter; troubleshooting methods 1 Introduction Although the reliability of the new generation of frequency converters is already very high, if the equipment is used or maintained improperly or over time, it may still fail or operate poorly, shortening the service life of the equipment and inevitably causing losses. Therefore, troubleshooting frequency converters is very important. 2 Causes of failures in general-purpose frequency converters 2.1 Analysis of the causes of overcurrent tripping (1) When restarting, the circuit breaker trips as soon as the speed is increased, which is a very serious overcurrent. The main causes are: 1) short circuit on the load side; 2) mechanical jamming; 3) inverter tube damage; 4) the starting torque of the motor is too small, and the drive system cannot turn. (2) When restarting, the circuit breaker does not trip immediately, but trips during operation. Possible reasons: 1) The acceleration time is set too short; 2) The deceleration time is set too short; 3) The torque compensation setting is too large, causing excessive no-load current at low frequencies; 4) The electronic thermal relay is improperly set, and the operating current is set too small, causing malfunction. 2.2 Reasons for overvoltage and undervoltage tripping (1) Voltage tripping, the main reasons are: 1) The power supply voltage is too high; 2) The deceleration time is set too short; 3) During the deceleration process, the regenerative braking discharge unit does not work ideally. (2) Undervoltage trip, possible causes: 1) Power supply voltage is too low; 2) Power supply phase loss; 3) Rectifier bridge failure; 2.3 Analysis of the reasons why the motor does not turn (1) Improper function preset, for example: 1) The upper limit frequency and the highest frequency or the basic frequency and the highest frequency are contradictory. The preset value of the highest frequency must be greater than the preset values ​​of the upper limit frequency and the basic frequency; 2) When using external setpoint, the selection of "keyboard setpoint/external setpoint" is not preset; 3) Other unreasonable presets; 4) When using external setpoint mode, there is no "start" signal: When using external setpoint signal, it must be controlled by the start button or other contacts. If it is not necessary to control by the start button or other contacts, the RUN (or FWD) and COM terminals should be shorted. (2) Other possible causes include: 1) Mechanical jamming phenomenon; 2) Insufficient starting torque of the motor; 3) Circuit failure of the frequency converter. 3 Troubleshooting and Maintenance Methods for Frequency Converters 3.1 Frequency Converter with Fault Diagnosis Display Data When a frequency converter malfunctions, if it displays fault diagnosis data, the solution is to find the relevant information in the frequency converter's instruction manual indicating the cause of the fault, locate the faulty component, and the user should focus on checking the relevant part according to the instruction manual to eliminate the faulty component. 3.2 Frequency Converter without Fault Diagnosis Display Data When a frequency converter malfunctions but there is no fault display, it should not be powered on rashly to avoid causing further damage. In this case, after power is cut off, resistance characteristic parameter tests should be performed to preliminarily locate the problem. (1) Inspection of the main circuit: Taking the SANKEN VVVF frequency converter as an example, open the frequency converter end cover and remove all external leads of the terminals. Check the continuity and resistance characteristic parameters between all terminals such as N, P, Rl, TI, R, 5, T, U, V, W, etc. The connection between these terminals and the main circuit is shown in Figure 1. Set the pointer-type multimeter to the 1Ω or 10Ω range. The test results are shown in Table 1. [align=center]Figure 1 Connection between terminals and main circuit[/align] The following table shows continuity, meaning the resistance is a few ohms to tens of ohms; no continuity indicates a very high resistance, above tens of thousands of ohms. [align=center]Table 1[/align] When measuring the same component, if inconsistent or significantly different test results are found, it indicates a problem with a certain component. For example, when measuring Q[sub]vP[/sub], if continuity is observed between P and V using both the black and red probes regardless of the measurement method, it indicates that the GTR is faulty and should be further investigated. The following situations should be noted: If, during inspection, it is found that RP, SP, and TP of D[sub]rp[/sub], D[sub]sp[/sub], and D[sub]tp[/sub] do not conduct when measured with the red and black probes reversed, it can be determined that the rectifier bridge is damaged or the charging resistor RI is burnt out; during the testing of Q[sub]up[/sub], Q[sub]vp[/sub], and Q[sub]w[/sub], if P[sub]u[/sub], P[sub]v[/sub], and P[sub]w[/sub] do not conduct when measured with the black and red probes reversed, it can be determined that the GTR is damaged or the FusE is burnt out; when testing Q[sub]UN[/sub], Q[sub]VN[/sub], and Q[sub]wN[/sub], if the above situation occurs, in addition to the possibility that the GTR is damaged, the resistor R may also be burnt out. After the above checks, further judgment should be made. The control board should be removed and the resistance of the main circuit R should be measured to be tens of ohms to 100. If it is conductive, it means that R1 is short-circuited or the relay is stuck. The components that are initially judged to be damaged should be removed and checked separately. If they are damaged, they need to be replaced. 75kVA and above frequency converters CTR are generally used in parallel and should be checked one by one. (2) Check the drive circuit: After the main circuit is repaired, connect the control board, unplug the socket of the GTR base, connect the external connection, and power on to observe whether the digital display is normal and whether the CHARGE light is on. When there is no display, check whether 380V voltage is applied between R1 and T1. If there is voltage between R1 and T1, check whether the 3052 voltage regulator has SV voltage. If there is no voltage, it may be that the transformer is damaged or the voltage regulator is damaged. When the CHARGE light is not on, it may be that the main circuit is not powered. Check whether the voltage between NP is 540V. If it is 540V, then the CHARGE light may be damaged or there is a problem with the CHARGE light circuit. After the digital display is normal, set U/f to 0 and increase the frequency to 50Hz. Measure the waveforms of B[sub]u1[/sub], B[sub]v1[/sub], B[sub]w1[/sub] and B[sub]u2[/sub], B[sub]v2[/sub], B[sub]w2[/sub]. The oscilloscope probe test is shown in Table 2. The standard waveform is shown in Figure 2, and its voltage is a reference value. The voltage amplitude is also different for different frequency converters. The oscilloscope probe test points are shown in Table 2: [align=center]Table 2[/align] If the waveform is abnormal, it indicates that there is a problem with the tested drive circuit. The drive transistor, the components in the drive circuit, and the voltage of the power supply section should be carefully checked. [align=center]Figure 2 GTR drive waveform[/align] (3) Simple measurement of high-power transistor (GTR): If a problem with the high-power transistor GTR is suspected, a multimeter can be used for simple testing if there is no GTR testing equipment. The inspection steps are as follows: 1) Turn off the input power and ensure that the CHARGE light is off. Then disconnect the R, 5, T, V, U, and W terminals. 2) Remove the connectors on the control circuit board and remove the circuit board and accessory board from the equipment. 3) If the modules are used in parallel, disconnect the parallel terminals in modules BZ, E: and BZx, EZx and then test each module as shown in Figures 3, 4, and 5. [align=center] Figure 3 Schematic diagram of GTR module[/align] Note: The resistance is infinite when not conducting and several ohms to tens of ohms when conducting. This method can be used to preliminarily determine whether the selected GTR is usable. [align=center] Figure 6[/align] (4) Replacement of high power transistor (GTR): If a damaged GTR is found, the damaged GTR module can be replaced according to the following steps. 1) Disconnect the main circuit wiring on the damaged module; 2) Unplug the base control signal line from the damaged module (hold the terminal plug and do not pull the wire); 3) Unscrew the screws securing the module and remove the damaged module; 4) First, select a component with the same parameters as the GTR to be replaced, and after measurement and verification, apply a small amount of conductive silicone to the bottom of the GTR, spreading it evenly to cover the bottom; 5) Clean the inverter base plate, place the silicone-coated GTR in the replacement position, and tighten the fixing screws, applying even force when tightening the four screws; 6) Insert the base signal line pin into the base of the GTR. During the entire component replacement process, do not touch any parts marked "Do Not Touch with Hands." First, touch a grounded metal part with your hand before handling those components; 7) Restore the control circuit and main circuit wiring; 8) After wiring, use a multimeter to check the resistance between the P-N terminals and between each output line to confirm there are no short circuits.