As the name suggests, is the power converter, a frequency conversion to another frequency of the power supply control device is mainly realized by power semiconductor devices, the current mainstream technology of frequency conversion is the power frequency AC power into DC power rectifier, inverter technology through the DC power supply inverter for AC power needs.
The inverter is mainly composed of rectifier (AC DC), filter, inverter (DC AC), brake unit, drive unit, detection and control unit.
1, rectifier unit
The rectifier unit is mainly 50HZ AC power into DC, in the past, there is no controlled rectifier rectifier and two main rectifier, in view of many shortcomings such as controllable rectifier, power factor and low harmonic content, complex control, has already been eliminated, the current mainstream mode is not controlled rectifier, through the diode or consists of thyristor rectifier, rectifier realization.
2, filter unit
Take the voltage type inverter as an example, the filter unit uses the capacitor to carry on the filter, the DC voltage waveform is quite straight, under the ideal condition is a constant voltage source.
3, inverter unit
The inverter unit is composed of IGBT module, which controls the on-off of the IGBT through the control signal of the drive unit to change the frequency of the output power.
4, brake unit
The brake unit is composed of IGBT and energy resistance, when the motor is turned into braking, motor generator produces electrical energy consumption in a DC circuit in the DC circuit, and intermediary into energy resistance will generate electricity consumption, realize brake.
5, drive unit
The drive unit is driven by the control unit according to the control requirements to drive the IGBT.
6, detection unit
The control system to collect field signal acquisition circuit, mainly in the current and voltage signals, signals can accurate and effective acquisition system to a certain extent determines the quality control of inverter.
The current commonly used sampling technique with series resistance method of current transformer, sampling method, Holzer sensor method, sampling voltage by a resistor divider, voltage transformer, voltage sensor Holzer method and linear optocoupler method.
7, control unit
At present, the control unit of the frequency conversion speed regulation is mainly using the single chip microcomputer or DSP as the control core, and the sampling signal and the control signal of the external user are operated by logic to output the control signal.