Working Principle of Vector Frequency Converter
The principle of vector frequency converter is that vector control technology uses coordinate transformation to equivalently transform the three-phase system into an M-T two-phase system, converting the AC The motor stator current vector is decomposed into two DC components to achieve the purpose of controlling the magnetic flux and torque of the AC motor respectively. Therefore, the same control effect as the DC speed control system can be obtained.
The vector operator is used to generate the magnetic field oriented stator current component, the given value and the slip angular frequency given value and the measured motor speed. After integral operation, the rotor flux position angle θ can be obtained, and Sent to the rotation transformation stage.
The system composition of the vector inverter: The inverter of the three-phase cage asynchronous motor drive system based on dual DSP vector control adopts an AC-AC voltage structure and SVPWM pulse width modulation method. The vector frequency converter system consists of a three-phase rectifier, filter capacitor, voltage inverter, inverter drive circuit, three-phase cage asynchronous motor and dual DSP control system. The dual DSP control system consists of three parts: VC33 subsystem, F240 subsystem and data exchange unit. Vector control uses the VC33 chip as the core to complete the vector control core algorithm and two-phase current detection.
The difference between vector inverters and ordinary inverters
There are general-purpose inverters There are two types of inverters: vector inverters. However, although both types of inverters can be used, there are still differences between the two inverters. After reading the following analysis, you will understand why the price of vector inverters is higher than that of general-purpose inverters.
There are two main differences between vector frequency converters and ordinary frequency converters: One is high control accuracy, and the other is large output torque at low speed. It can output 150%-200% of the rated torque. Because vector frequency conversion decomposes the motor current into D-axis current and Q-axis current, where the D-axis current is the excitation current and the Q-axis current is the torque current. By controlling D and Q separately, the motor can obtain greater starting torque. Generally used in heavy load startup situations. For example, high-power long belts, elevators, etc. At this time, if the ordinary frequency converter is used, the load at startup is too heavy and the output torque is not enough, which will cause the motor to fail to start, and a fault such as motor stall or frequency converter overcurrent will be reported.
For the control of ordinary water pumps, you can choose the fan-pump-specific or universal type. There is no need to choose vector, which is expensive. The parameter settings are similar. Nothing importantthe difference.
Using the analogy of driving a car, everyone knows: vector control is also called ‘speed control’, and you can see a few differences literally.
V/F control method: Just like when driving, the accelerator opening of your foot remains unchanged, but the speed of the car is definitely changing! Because the road the car is traveling on is uneven, the resistance of the road is also changing. The speed will slow down when going uphill, and the speed will speed up when going downhill. For the inverter, your frequency setting value at this time is equivalent to the opening of the accelerator with your foot when driving. The accelerator opening is fixed during V/F control.
Vector control method: It can control the vehicle to keep the vehicle speed as constant as possible and improve the speed control accuracy under changing road conditions, resistance changes, uphill, downhill and other changes. Then, in order to keep the vehicle speed stable regardless of uphill or downhill slopes or changes in road resistance, the throttle opening must be adjusted at any time.
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