What is the structure of the variable frequency power supply system and its function?
The main circuit input of the IDEALPLUSING variable frequency power supply system is the three-phase AC power introduced from the mains. After rectification and filtering, it becomes a stable DC power and supplies it to the power conversion device. The three-phase AC current drives the AC motor. The power conversion device adopts a highly integrated intelligent power module, which integrates power conversion, gate control and protection circuits, and has system protection functions such as driving voltage, overcurrent, bridge arm short circuit and overheating.
The control circuit is the core of the entire variable frequency system. All control circuits only need to use the three-phase SPWM waveform generator chip to realize SPWM signal output, system protection and other functions. The system circuit structure is simple, the control adjustment is convenient, and the degree of intelligence is high. Next, let's understand the SPWM circuit, how the bridge rectifier and the filtering link work?
Bridge rectifier: The term rectifier is the unidirectional conduction principle of the diode that completes the work. Usually, the diode is forward-conducting and reverse-disconnected, which means that the diode only allows its positive pole to enter the positive pole and its negative pole to enter the negative pole. The diode only allows current to flow in one direction. When connected to an AC circuit, the current in the circuit can only flow in one direction. The so-called "rectification" involves winding the four diodes of the rectifier bridge together and driving only four wires. pin. Below the four pins, the two DC output connections are marked with + or -, and the two AC input connections are marked with ~.
Filtering: When the current through the inductor changes, the induced electromotive force generated in the inductor coil prevents the current from changing. As the current flowing through the inductor coil increases, the self-induced electromotive force generated by the inductor coil is opposite to the direction of the current, which prevents the increase in current while converting part of the electrical energy into magnetic energy. Magnetic field energy and stored in the inductor:
When the current through the inductor coil decreases, the self-induced electromotive force is in the same direction as the current, which prevents the current from decreasing while releasing the stored energy to compensate for the current drop. Therefore, after the inductor filtering, not only the load current and load pulsation are reduced, but also the waveform becomes smooth, and the conduction angle of the rectifier diode increases. Filtering is an important concept in signal processing. Filtering is divided into classical filtering and modern filtering.
SPWM circuit: When pulse width modulation is performed, the pulse duty cycle of a series of pulses is arranged according to the sine law. When the sine value is the maximum, the pulse width is also the largest, and the interval between pulses is the smallest. On the other hand, when the sine value is small, the pulse width is also small, and the interval between pulses is large. Such a voltage pulse sequence can greatly reduce the high-order harmonic components in the load current (called sinusoidal pulse width modulation).
It is said that SPWM changes the modulation pulse mode based on PWM, and the duty cycle of the pulse duration is arranged according to the sine law, so that the output waveform can be a waveform output sine wave after proper filtering. It is widely used in DC-AC (DC-AC) inverters, and more advanced UPS is an example. Three-phase SPWM uses SPWM to simulate the three-phase output of the power grid.
Guangzhou IDEALPLUSING Company is professionally committed to the research and development and application of power electronic conversion technology, specializing in the production of variable frequency power supplies, DC power supplies, adjustable power supplies, high voltage power supplies, DC converters, battery chargers and automated test systems. Products and solutions manufacturers are domestic power supply industry and test system core technology automation high-tech enterprises.
