High-reliability medium voltage frequency converter adopting redundancy design

Abstract

The invention discloses a frequency converter, which comprises power units, isolating transformers, bypassing contactors and high voltage switches, wherein the number of the power units is N; the number of the bypassing contactors is X; the number of the high voltage switches is X; N, X and N / X are all positive integers, and X is more than 1; the bypassing contactors are used for bypassing N / X power units; the two ends of each of the N / X power units are connected with the bypassing contactor respectively; when the power units of each group or a corresponding isolating transformer works normally, the bypassing contactors are in an off state; and when the power units of a certain group or the corresponding isolating transformer fails, the bypassing contactors are switched on, and simultaneously the high voltage switch between the corresponding isolating transformer and a high voltage bus is switched off to switch a main loop on. By the frequency converter and a method provided by the invention, the acceptable failure rate of the whole system is greatly increased; moreover, the full-load running of the system can be realized without derating in a failure.

Description

technical field [0001] The invention relates to the field of industrial electrical transmission, in particular to a frequency converter and a control method for the frequency converter. Background technique [0002] In the current field of industrial electrical drives, the structure of high-voltage inverters is mostly based on unit series, because this type of topology can greatly improve the output waveform and achieve perfect harmonic-free output. [0003] Such as figure 1 As shown, take a system in which six power units (A1-A6, B1-B6, C1-C6) are connected in series for each phase as an example. ) of the bus connection, so each phase can get thirteen different voltage levels, and use pulse width modulation to realize the superposition output of the power unit. The "Y" connection method is adopted between the three-phase power units, and the neutral point of the "Y" connection is grounded, so as to obtain a variable-frequency three-phase high-voltage power supply. [000...

AI Technical Summary

Problems solved by technology

[0005] However, there is a problem in the frequency converter with this structure: when a certain power unit fails or the isolation transformer 202 fails, the frequency converter will immediately stop running as a whole, causing the motor 203 to lose power and stop, which will have an impact on the entire system. very big

[0007] However, "unit bypass" cannot meet the reliability requirements of the hoist system. The problem lies in:

Because the frequency converter is in the state of derating operation, the magnetic density will decrease, which will cause the motor to heat up, so the above solution cannot be used as a long-term operation mode, and the fault needs to be solved after stopping

In practical applications, none of the equipment can operate in bypass mode for a long time;

[0009] 2. In some cases, the power unit cannot be successfully bypassed

For example: the power supply of the circuit board of the power unit takes the two-phase AC power of A and C through the transformer, but if the fuse of the two phases of A and C fails, the circuit board of the power unit cannot receive power supply, and the SCR cannot be controlled at this time. Bypass

Similarly, for example, if the IGBT, capacitor and other devices with conductive materials inside the power unit fail, the circuit board of the power unit may also be damaged at this time, so that the completion of the bypass cannot be guaranteed

[0010] In addition, "unit bypass" itself also has disadvantages: the unit inverter link (ie image 3 The inverter bridge DI1-DI6, Q1~Q4) is a long-term and bypass link (ie image 3 The part of the silicon controlled rectifier component) is operated in parallel at the same time, so it is very likely that the failure of the inverter bridge will be caused by the damage of the silicon controlled silicon device, thus making the entire power unit "paralyzed". Frequency-based design, so the thyristor cannot withstand long-term high-frequency voltage erosion

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