1. U/f=C sinusoidal pulse width modulation (SPWM) control mode is characterized by simple control structure, low cost, good mechanical properties and hardness, which can meet the requirements of smooth speed regulation of general transmission, and has been in the industry. Various fields are widely used. However, in this mode of control, at low frequencies, the torque is affected by the voltage drop of the stator resistance due to the lower output voltage, which reduces the maximum output torque. In addition, its mechanical characteristics do not have DC motor hard, dynamic torque capability and static speed regulation performance are not satisfactory, and the system performance is not high, the control curve will change with the load change, the torque response is slow, the motor turns The moment utilization rate is not high, and the performance is degraded due to the existence of the stator resistance and the dead zone effect of the inverter at a low speed, and the stability is deteriorated. Therefore, people have also studied vector control frequency control.
2. Voltage space vector (SVPWM) control mode It is based on the premise of the three-phase waveform overall generation effect, aiming at the ideal circular rotating magnetic field trajectory close to the motor air gap, generating a three-phase modulation waveform at a time, and approximating the circle with the inscribed polygon Way to control. After practice, it has been improved, that is, the introduction of frequency compensation can eliminate the error of speed control; estimate the magnitude of the flux linkage through feedback to eliminate the influence of stator resistance at low speed; close the output voltage and current to improve the dynamic accuracy and stability. However, there are many control circuit links and no torque adjustment is introduced, so the system performance has not been fundamentally improved.
3. Vector control (VC) mode vector control The principle of variable frequency speed regulation is to make the stator currents Ia, Ib, Ic of the asynchronous motor in the three-phase coordinate system pass the three-phase-two-phase transformation, which is equivalent to the two-phase stationary coordinate system. The lower alternating current Ia1Ib1 is equivalent to the direct current Im1, It1 in the synchronous rotating coordinate system by the rotational transformation of the rotor field, which is equivalent to the exciting current of the direct current motor; It1 is equivalent to the armature proportional to the torque. Current), then imitate the control method of the DC motor, obtain the control quantity of the DC motor, and realize the control of the asynchronous motor through the inverse transformation of the corresponding coordinates. The essence is that the AC motor is equivalent to a DC motor, and the two components of speed and magnetic field are independently controlled. By controlling the rotor flux linkage and then decomposing the stator current to obtain two components of torque and magnetic field, coordinate transformation is used to realize orthogonal or decoupling control. The proposed vector control method has epoch-making significance. However, in practical applications, because the rotor flux linkage is difficult to accurately observe, the system characteristics are greatly affected by the motor parameters, and the vector rotation transformation used in the equivalent DC motor control process is complicated, making the actual control effect difficult to achieve the ideal analysis. result.
Lithium-Silicon Alloy
Lithium-boron Alloy is a composite material composed of a brittle Li7B6 matrix phase with a porous structure and a ductile Li filling phase. The density is 0.88±0.04g/cm3. The appearance is silver-white metal. It is extremely unstable. It is easily deteriorated when exposed to air and reacts with water. severe. Lithium-boron alloy is mainly used as anode material for lithium-based thermal batteries. It has outstanding advantages such as high specific energy, high specific power and low polarization, electrochemical potential similar to that of pure lithium, and solid state above 600℃. It is a new type of lithium-based thermal battery. The excellent negative electrode material. Compared with the currently widely used lithium-silicon alloy, the unit cell assembled with the lithium-boron alloy as the negative electrode material has better performance in both the highest voltage and the discharge working time.
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