Inverter control method - Reynolds

The output voltage of low-voltage general frequency conversion is 380-650V, the output power is 0.75-400kW, and the operating frequency is 0-400Hz. Its control methods have gone through the following four generations. The 1U/f=C sinusoidal pulse width modulation (SPWM) control method is characterized by simple control circuit structure, low cost, and good hardness of mechanical characteristics, which can meet the smooth speed regulation requirements of general transmission, and has been widely used in various fields of the industry. However, at low frequency, because the output voltage is low, the torque is significantly affected by the voltage drop of the stator resistance, so that the maximum output torque is reduced.

In addition, its mechanical characteristics are not as hard as DC motors, dynamic torque capabilities and static speed regulation functions are not satisfactory, and the system function is not high, the control curve will change with the change of load, the torque echo is slow, the motor torque utilization rate is not high, and the function decreases due to the existence of stator resistance and inverter dead zone effect at low speed, and the stability becomes poor. Therefore, people have studied vector control frequency conversion speed regulation. The Voltage Space Vector (SVPWM) manipulation method is based on the condition of the whole generation of the three-phase waveform, with the intention of the aspiring circular rotating magnetic field orbit of the motor air gap, and the three-phase modulation waveform is generated at one time, and the method of the inscribed polygon imminent circle is controlled.

Inverter control method - Reynolds

After practical use, it has been improved, that is, the introduction of frequency compensation, which can eliminate the error of speed control; The flux amplitude is estimated by the reaction, and the influence of stator resistance at low speed is eliminated. The output voltage and current are closed loop to improve the accuracy and stability of the dynamics. However, there are many links in the control circuit, and there is no torque adjustment, so the function of the system has not been fundamentally improved. Vector control (VC) method vector control frequency conversion speed regulation method is to convert the stator current Ia, Ib, Ic of the asynchronous motor in the three-phase coordinate system through three-phase - two-phase change, equivalent to the communication current Ia1Ib1 in the two-phase static coordinate system, and then after directional rotation and replacement according to the rotor magnetic field, it is equivalent to the direct current Im1 and It1 under the synchronous rotation coordinate system (Im1 is equivalent to the excitation current of the DC motor; IT1 is equivalent to the armature current proportional to the torque), and then imitate the control method of the DC motor, obtain the control quantity of the DC motor, and complete the control of the asynchronous motor through the corresponding coordinate reversal.

Its essence is to equivalence the communication motor to the DC motor, and the speed and magnetic field weight are controlled independently. After manipulating the rotor flux, and then decomposing the stator current to obtain the two weights of torque and magnetic field, the coordinates are changed to complete the orthogonal or decoupling control. The vector manipulation method is of epoch-making significance. However, in practice, because the rotor flux is difficult to observe accurately, the characteristics of the system are greatly affected by the motor parameters, and the vector rotation change used in the operation process of the equivalent DC motor is messy, which makes it difficult to achieve the results of ambition analysis in practice.

Direct Torque Manipulation (DTC) method

In 1985, Professor DePenbrock of the Ruhr University in Germany first proposed the direct torque control frequency conversion technology. This skill has largely dealt with the shortcomings of the above-mentioned vector manipulation, and has been rapidly developed with novel manipulation thinking, concise and clear architecture, and excellent dynamic and static functions.

Now, this skill has been successfully used in high-power communication transmissions for electric locomotive traction. Direct torque manipulationDirectly analyze the mathematical model of the communication motor under the stator coordinate system, and control the flux and torque of the motor. It does not need to equate the AC motor to a DC motor, so it eliminates a lot of messy calculations in vector rotation reversal; It does not need to be modeled after the operation of a DC motor, nor does it need to simplify the mathematical model of the communication motor for decoupling. Matrix alternating - alternating control method VVVF frequency conversion, vector control frequency conversion, direct torque control frequency conversion are one of the AC-DC-AC frequency conversion. Its common disadvantages are that the input power factor is low, the harmonic current is large, the DC circuit requires a large energy storage capacitor, and the regenerative energy cannot be reflected back to the grid, that is, it cannot carry out four-quadrant operation.

For this reason, matrix alternating frequency-alternating frequency came into being. Because matrix AC-AC frequency conversion eliminates the central DC link, thus eliminating the large and expensive electrolytic capacitors. It can complete the power factor of L, the input current is sinusoidal and can operate in four quadrants, and the power density of the system is large. Although this skill is not sophisticated now, it still attracts many scholars to study it in depth. Its essence is not to directly manipulate the current and flux equals, but to directly use the torque as the quantity to be manipulated.

Here's how:

Control the stator flux to introduce the stator flux observer to complete the method without speed sensor;

Automatic identification (ID) relies on the accurate mathematical model of the motor to automatically identify the motor parameters;

The practical value is calculated and the actual torque, stator flux, and rotor speed are calculated for real-time control corresponding to stator impedance, mutual inductance, magnetic full element, inertia, etc.;

Complete Band-Band control: PWM signal is generated by Band-Band control of flux and torque, and the inverter switching state is controlled.

Matrix alternating frequency conversion has fast torque response (<2ms), high speed accuracy (±2%, no PG reaction), and high torque accuracy (<+3%). Together, it also has high starting torque and high torque accuracy, especially at low speed (including 0 speed), it can output 150%-200% torque.

Inverter control method - Reynolds

Sections viewed

Contact

working hours