From the perspective of skills alone, the control method of the low-voltage inverter also indicates its skill portal to a certain extent. Here, we've broken down the following manipulation methods:
1. Sinusoidal pulse width modulation
Sinusoidal Pulse Width Modulation (SPWM) is characterized by simple control circuit structure, low cost, good mechanical hardness, and can meet the requirements of smooth speed regulation of general transmission, and has been widely used in various fields of industry.
However, at low frequencies, 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 band effect at low speed, and the stability deteriorates.
2. Voltage Space Vector (SVPWM)
Voltage Space Vector (SVPWM) It is based on the premise of the overall generation of the three-phase waveform, with the intention of forcing the ideal circular rotating magnetic field orbit of the motor air gap, generating a three-phase modulated waveform at one time, and controlling it by the method of inscribed polygon imminent circle.
After practical use, 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 to improve the accuracy and stability of the dynamics.
3. Direct torque control (DTC) method
Direct Torque Manipulation (DTC) Method 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 applied to the high-power communication transmission of 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, thus eliminating many complex calculations in vector rotation conversion; It does not need to mimic the operation of a DC motor, nor does it need to simplify the mathematical model of the communication motor for decoupling.
4. Matrix cross-hand control method
The matrix alternating and alternating control methods VVVF frequency conversion, vector control frequency conversion, and direct torque control frequency conversion are all one of the AC-DC-AC frequency conversion. One of the defects 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 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, and then eliminates the large and expensive electrolytic capacitors.
Because the matrix AC-AC frequency conversion eliminates the intermediate DC link, and then eliminates 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. This skill is not experienced now, and its essence is not to indirectly manipulate the amount of current, flux, etc., but to complete the torque directly as the amount to be manipulated.
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Let's start with Schneider Masterpact, which is a structural circuit breaker. The current rating of the structure varies from 800A ---- 6300A. The Masterpact series is divided into M series and MT series. The M series has been on the market since 1986 and was screened and delisted in 2002.
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