Xinjie inverter control mode

The output voltage of low-voltage general frequency conversion is 380-650V, the output power is 0.75-400kW, and the working frequency is 0-400Hz. Its control methods have gone through the following four generations.

1U/f=C sinusoidal pulse width modulation (SPWM) control method

It is characterized by a simple structure of the control circuit, low cost, good hardness of mechanical characteristics, and can meet the requirements of smooth speed regulation of general transmission, and has been widely used in various fields of industry. However, in this control method, at low frequencies, the torque is significantly affected by the voltage drop of the stator resistance due to the low output voltage, so that the maximum output torque is reduced.

In addition, its mechanical characteristics are not as hard as DC motors after all, the dynamic torque ability and static speed regulation function are not satisfactory, and the system function is not high, the control curve will change with the change of load, the torque should be 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 developed vector control frequency conversion speed regulation.

Xinjie inverter control mode

Voltage Space Vector (SVPWM) control method

It is based on the condition of the whole generation of the three-phase waveform, with the intention of pressing the aspiring circular rotating magnetic field orbit of the motor air gap, and the three-phase modulation waveform is generated at one time, and is controlled by the method of inscribed polygon imminent circle.

After practical application, it has been improved, that is, the introduction of frequency compensation, which can eliminate the error of speed control; By reacting the reaction to estimate the flux amplitude, the influence of stator resistance at low speed is eliminated. The output voltage and current are closed in a closed loop to advance the accuracy and stability of the dynamics. However, there are many links in the control circuit, and the scheduling of torque is not introduced, so the function of the system has not been fundamentally improved.

Vector control (VC) method

The method of vector control frequency conversion speed regulation is to convert the stator current Ia, Ib, Ic of the asynchronous motor in the three-phase coordinate system into the alternating current Ia1Ib1 under the two-phase stop coordinate system through the three-phase - two-phase conversion, and then through the directional rotation conversion according to the rotor magnetic field, it is equivalent to the DC 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 reverse conversion.

Its essence is to equivalence the AC motor to the DC motor, and the two components of speed and magnetic field are independently controlled. By controlling the rotor flux, and then decomposing the stator current, the two components of torque and magnetic field are obtained, and the orthogonal or decoupled control is completed through coordinate conversion. The vector control method is of epoch-making significance. However, in practice, because the rotor flux is difficult to observe accurately, the system characteristics are greatly affected by the motor parameters, and the vector rotation conversion used in the control process of the equivalent DC motor is messy, which makes it difficult to achieve the results of aspiration analysis in the control of the actual operation.

Direct Torque Control (DTC) method

In 1985, Professor DePenbrock of the Ruhr University in Germany first proposed direct torque control frequency conversion technology. This technology has dealt with the lack of vector control to a large extent, and has been rapidly developed with novel control thinking, concise and clear system structure, and excellent dynamic and static functions.

At present, this technology has been successfully applied to high-power AC drives for electric locomotive traction. Direct torque control directly analyzes the mathematical model of the AC motor under the stator coordinate system, and controls the flux and torque of the motor. It does not require the AC motor to be equivalent to a DC motor, so it eliminates a lot of messy accounting in vector rotation conversion; It does not require the control of a DC motor to be mimicked, nor does it require a mathematical model of the AC motor to be simplified for decoupling.

Matrix alternating and interlocuting control method

VVVF frequency conversion, vector control frequency conversion, and direct torque control frequency conversion are all one of the AC-DC-AC frequency conversion. Another disadvantage is 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 power grid, that is, it cannot carry out four-quadrant operation.

For this reason, matrix alternating frequency-alternating frequency came into being. Because the matrix AC-AC frequency conversion eliminates the intermediate DC link, the large and expensive electrolytic capacitor is eliminated. 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 the technology is not yet sophisticated, it still attracts many scholars to study it in depth. Its essence is not to directly control the current and flux equals, but to directly treat the torque as the controlled quantity.

--Here's how:

The stator flux is controlled and the stator flux observer is introduced to complete the velocity sensorless method.

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.;

End Band-Band ControlBand-Band control generates PWM signals according to the Band-Band control of flux and torque, and controls the inverter switching status.

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

Xinjie inverter control mode

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