A pre-charging circuit and pre-charging method of a low-voltage inverter

Abstract

The invention discloses a pre-charging circuit and a pre-charging method of a low-voltage frequency converter. The pre-charging circuit is connected between the rectification circuit and the inverter circuit of the low-voltage frequency converter. The pre-charging circuit includes a main control module and more than three groups of pre-charging modules , each pre-charging module is connected in series in turn and connected to the main control module respectively; The charging control switch is turned off to connect or bypass the corresponding pre-charging resistor; the pre-charging method is an implementation method using the above-mentioned pre-charging circuit. The invention can greatly reduce the inrush current at the moment of power-on of the low-voltage frequency converter, and at the same time take into account the pre-charging time, has the advantages of a structural unit, low cost, and can intelligently realize the advantages of small charging current, short pre-charging time and stable charging process.

Description

technical field [0001] The invention relates to the technical field of low-voltage frequency converters, in particular to a pre-charging circuit and a pre-charging method for low-voltage frequency converters. Background technique [0002] The pre-charging circuit is an important part of the voltage source AC inverter. Its main function is to pre-charge the energy storage capacitor of the DC link when the system is powered on, so as to avoid burning out the power due to the strong impact current when powering on. module, and the damage to the DC capacitor will shorten the life of the DC capacitor and reduce the performance. [0003] Such as figure 1 As shown, the current pre-charging circuit (current-limiting part) used in low-voltage inverters is generally composed of a charging resistor connected to the contact of the main circuit relay to complete the pre-charging, but this type of pre-charging circuit has the following defects: [0004] 1) It is difficult to choose a pr...

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Problems solved by technology

[0004] 1) It is difficult to choose a pre-charging resistor with a suitable resistance value. If the charging time is considered to be short, the charging current will often be too large, and if the charging current is considered to be small, the charging time will be slow, and it is impossible to balance the charging current and charging time. Achieving a balance on this problem has always been a difficult problem in this type of pre-charging circuit;

[0005] 2) Since this type of pre-charging circuit is a single charging resistor, during the charging process, the heating value of the charging resistor will be large, which will cause the overall temperature of the inverter to be too high, which will reduce the safety of the inverter and reduce the frequency conversion. service life of the device;

[0006] 3) The performance requirements of the charging resistor are high, and the overload capacity of the resistor is usually required to be dozens to hundreds of times, so the required cost is high and the volume is large;

[0007] 4) Since the charging resistor is easily damaged, and when the charging resistor is damaged, the inverter cannot operate normally, which will further increase the maintenance cost

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