A frequency converter is a power exchange device that transforms a fixed-frequency, fixed-voltage power supply into a variable-frequency, variable-voltage power supply, thereby completing VF conversion to control an asynchronous motor. The motor designed here is a dedicated frequency converter motor, which can achieve different speeds and torques under the drive of the frequency converter to adapt to changes in load requirements.
I. Overview of Frequency Converters
Inverters are mainly divided into two categories: voltage type, which converts DC voltage from a voltage source to AC voltage, and its DC circuit is filtered by capacitors.
The output voltage waveform is a rectangular wave, and the current waveform is approximately sinusoidal. Deep negative feedback is generally required for stabilization. In a current-type converter, the DC current source is transformed into AC, with the DC circuit filtered by an inductor. The current waveform is a rectangular wave, and the voltage waveform is approximately sinusoidal. Positive feedback is generally used for gain.
Modern frequency converters mainly use VVVF frequency conversion or vector control frequency conversion, which means that the mains frequency AC power is first converted through a rectifier.
It converts the power to DC, and then converts the DC power to AC power with controllable frequency and voltage to supply the motor. However, the disadvantages of VVVF are that the input power factor is relatively low, the harmonic current is large, and the DC circuit requires a large energy storage capacitor.
The main circuit of a frequency converter consists of: power input—rectifier bridge—starting resistor—bus capacitor—braking unit (braking resistor)—inverter bridge—power output. The main circuit is the power conversion section that provides voltage and frequency adjustable power to the asynchronous motor; it consists of three parts:
1. Rectifier circuit: Converts mains frequency power to DC;
2. Smoothing circuit: Absorbs voltage ripples generated in the converter and inverter;
3. Inverter circuit: Converts DC into AC with adjustable frequency.
II. Measurement of Main Parameters
The operating system mainly consists of two parts: a frequency converter and a frequency converter motor. Common faults of frequency converter motors include overcurrent, overvoltage, undervoltage, overheating, output imbalance, and overload. Frequency converters are commonly used in motor control systems, requiring measurements of the frequency converter's input and output signals, as well as system characteristics such as motor torque and speed.
Input and output parameters: voltage, main measurement parameters include: rated current and power, rated input capacity, output...
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