RU2124801C1 - Frequency converter - Google Patents

Abstract

FIELD: conversion equipment, A C electric motor drives, sources of secondary electric power supply. SUBSTANCE: given frequency converter has intermediate D.C. element and power unit presenting bridge circuit built up on transistor keys. There is inserted protection of these keys against failure with emergence of through current in arm of bridge and during transition processes initiated by cut-off of converter. First one of these protections is realized by insertion of limiting resistor shunted by diode in series with capacitor of supply filter and second one - by feed of permission signal of converter from secondary winding of network transformer. Radiator with transistor keys is used as vertical wall of frame of converter. EFFECT: improved thermal characteristics, decreased mass and dimensions of converter. 1 dwg

Description

 The invention relates to a conversion technique and is intended for use in AC electric drives and secondary power sources.

 In famous converters / patent Japan. N 4-49348, H 02 M 7/48, "Method and device for protecting the PWM inverter against current overload", US patent N5175676, H 02 M 7/122, "Advanced short circuit protection for DC / AC converters" / To protect power keys from current overload and short circuits, a current sensor and threshold devices are used that either turn off the converter or put it into current limiting mode. However, in transistor power switches in bridge circuits, due to the high slew rate, current sensors and threshold devices do not provide protection against failure of transistors on one arm, if for some reason they turn out to be open. The installation of limiting resistors and chokes in the shoulders of the bridge reduces the efficiency and increases the size.

 When the converter is turned on and off, transients occurring in the reactive elements can disable power switches. In the known device / application N 92014590/07, H 02 M 3/335, Palagutin A.N. "Single-cycle self-generating voltage converter" / a circuit is presented that delays the onset of the conversion mode after turning on the device until the end of transients in the supply circuit. However, this does not exclude the failure of power switches when the converter is turned on.

 In the known device / patent N 2042256, H 02 M 7/00, H 01 L 25/03, Ryabovsky S.V., Ekimov V.V., Trokhalin V.P. "Rectifier unit" / design of a power unit with improved thermal characteristics is proposed by attaching radiators with power elements through electrically insulating heat-conducting gaskets to the vertical walls of the housing. However, the housing walls have a small specific heat sink area and this leads to the need to increase the overall dimensions of the device.

 The closest in technical essence to the proposed device is a rectified network voltage converter, which contains a network rectifier, an RC filter, the capacitor of which is connected to the input of a half-bridge transistor inverter, and a control unit powered by a separate rectifier / a.s. N 951600, H 02 M 5/458, H 02 M 7/537 Gals B.K., Uzberg N.P., Bulyk V.M. "Converter of rectified mains voltage".

 In this device, the half-bridge inverter transistors open alternately. However, it is possible that both transistors are simultaneously in the open state as a result of interference or during transients when the inverter is turned off, since in this case the device operates in an abnormal mode. When both half-bridge transistors are in the open state, the discharge current of the filter capacitor disables them.

 The claimed technical solution is aimed at improving the reliability of the Converter and reducing its size.

 To do this, in a frequency converter containing a network rectifier consisting of a series-connected transformer and a diode bridge, a U-shaped CLC filter, a three-phase inverter consisting of transistor switches connected in a bridge circuit with reverse diodes, sensors, a load and a control and protection unit, the inputs and outputs of which are connected to a three-phase inverter, a resistor shunted by a diode is switched on in series with the second capacitor of the CLC filter, and when the capacitor of the CLC filter is discharged, it becomes non-conductive , a threshold device is connected to the secondary winding part of the transformer of the network rectifier, the output of which is connected to the enable enable switch in the control and protection unit, and the inverter transistor switches are located on one of the vertical walls of the converter housing and are insulated from it.

 The drawing shows the proposed frequency converter. It consists of a transformer 1, the primary winding of which is connected to the mains. A rectifier 3 connected to the U-shaped CLC filter 4, consisting of the first capacitor 5, inductor 6 and second capacitor 7, is connected to the secondary winding 2. Resistor 8 shunted by diode 9 is connected in series with capacitor 7. The polarity of diode 9 is such that discharge of the capacitor 7, it is locked.

 An inverter 10 is connected to the output of the filter 4, consisting of transistor power switches connected in a bridge circuit. The inverter also contains reverse diodes, sensors of the load current and current consumption / not shown /.

 The transistor power switches are controlled, the set frequencies are provided, the sensor signals are processed by the control and protection unit 11, the outputs and inputs of which are connected to the inverter 10.

 A threshold device 12 is connected to part of the secondary winding 2, the output of which is connected to the conversion enable input of block 11.

 The load 13 of the inverter 10 may be, for example, an induction motor or a rectifier.

 Transistor switches are mounted on the radiator and insulated from it. The radiator is used as one of the vertical walls of the housing.

 In the process of operation of the converter, transistors in each arm of the bridge of the inverter 10 open alternately. Moreover, the control unit 11 provides the opening of one of the transistors only when the second transistor is closed. However, there is a possibility that if the control unit fails, both transistors can be simultaneously open for a while and the capacitor 7 is short-circuited. In this case, there is a rapid increase in current in the shoulder. The short circuit protection circuit available in the control unit 11 has a certain delay in operation, and therefore the likelihood that the transistors of the inverter 10 will fail. The resistor 8 limits the discharge current of the capacitor 7 to a value that does not cause failure of the transistors until the short circuit protection circuit operates. Since the protection response time is usually units and fractions of microseconds, the permissible current of the inverter transistor 10 is significantly higher than the nominal one and the value of resistor 8 is such that during normal operation of the converter it does not affect its parameters and the power losses on it are negligible. Diode 9 is necessary to eliminate overvoltage impulses that occur, for example, when the motor speed, which is the load of the converter, decreases rapidly.

 When the converter is turned off, the transistors of the inverter 10 must be closed before the supply voltage decreases to the value at which the control and protection fail. The inclusion of the threshold device 12 between the part of the secondary winding of the transformer 1 and the enable input of the transformations of the block 11 allows you to get the minimum time from the moment the converter is turned off until the transistors are locked.

 Unlike diodes and thyristors, installing transistors in a bridge circuit on separate radiators in groups is not effective. In addition, it is desirable to arrange both transistors of one arm at the minimum allowable distance. Currently, transistor modules with an electrically insulated housing are becoming more widespread. Therefore, all key transistors are mounted on one radiator. This radiator is a vertical wall of the housing. This ensures optimal heat dissipation and minimum weight and dimensions of the converter.

Claims (1)

 A frequency converter containing a network rectifier, consisting of a transformer and a diode bridge, while the primary winding of the transformer is connected to the network, and the secondary winding through a diode bridge, a U-shaped CLC filter and a three-phase inverter consisting of transistor switches connected in a bridge circuit with reverse diodes, and sensors of the load current and current consumption, is connected to the load, as well as a control and protection unit, characterized in that a resistor shunted across the second CLC filter capacitor is connected a threshold device is connected to the parts of the secondary winding of the transformer of the network rectifier, the output of which is connected to the enable input of the conversion of the control and protection unit, which controls transistor switches and processes the signals of the load current sensors and current consumption.