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| Inverter control way |
| General low-voltage inverter output voltage is 380 ~ 650V, output power of 0.75 ~ 400kW, the operating frequency is 0 ~ 400Hz, its main circuit adopts AC-DC-AC circuit. The control mode has experienced four generations.
Sinusoidal pulse width modulation (SPWM) control mode of 1U/f=C:
It is characterized in that the control circuit of simple structure, low cost, good mechanical properties of hardness, can meet the general requirements of smooth speed regulation drive, has been widely used in various fields of industry. However, this control method in low frequency, the output voltage is low, the torque is affected by the voltage of stator resistance is significant, so that the maximum output torque is reduced. In addition, the mechanical characteristics of DC motor will not hard, dynamic torque capacity and static performance is not just as one wishes, and the system performance is not high, the control curve will vary with the change of load, the torque response is slow, the motor torque utilization rate is not high, low speed because of the stator resistance and the inverter dead-time effect in the presence of performance degradation worse, stability. So people research the vector control variable frequency speed regulating.
Voltage space vector (SVPWM) control method:
It is based on the overall effect of three-phase waveform as the premise, to approximate the ideal air-gap circular rotating magnetic track for the purpose, a generation phase modulation waveform, in order to control the inscribed polygon approximation round way. The practical use and improved, namely introducing frequency compensation, can eliminate the error of speed control; through the feedback to estimate the flux amplitude, eliminate the influence of the stator resistance at low speed; the output voltage, current loop, in order to improve the dynamic accuracy and stability. But the control circuit more links, and no regulation into torque, so the performance of the system has not been fundamentally improved.
Vector control (VC) mode:
Method of vector control variable frequency speed regulating is in three-phase asynchronous motor coordinate of stator current Ia, Ib, Ic, through the three-phase - phase transformation, equivalent to the current Ia1Ib1 two-phase stationary coordinate system, then based on the rotor field orientation rotation transformation, equivalent to the synchronous rotating coordinate system, the DC current Im1 It1 (Im1 excitation current; equivalent to the DC motor It1 is equivalent to the armature current is proportional to the torque), then control method of DC motor control quantity of imitation, the DC motor, after the corresponding coordinates transformation, control of the asynchronous motor. Its essence is the AC motor is equivalent to the DC motor speed, respectively, independent control of two components of the magnetic field. Through the control of rotor flux, and the decomposition of the stator current and torque and the two components of the magnetic field, the coordinate transformation, achieve orthogonal or decoupling control. The vector control method has the epoch-making significance. However in the practical application, because the rotor flux can not be accurately observed, affect the system performance by motor parameter is larger, and the equivalent DC motor control in the process of rotation vector transform is more complex, the actual control effect is difficult to achieve ideal results.
Direct torque control (DTC) mode:
In 1985, Professor DePenbrock University Ruhr in Germany first proposed the direct torque control technique. The technology solves the defects of the vector control to a large extent, and the novel strategy, simple system structure, excellent dynamic and static performance has been the rapid development. At present, the technology has been successfully applied to high-power AC drive electric locomotive traction in the. Direct torque control analysis of mathematical model of AC motor directly in the stator coordinate, control motor flux and torque. It does not need to be equivalent to the DC motor, AC motor, thus eliminating the many complex computing vector rotation transformation; it does not need to control DC motor mathematical model to imitate, also do not need to simplify the decoupling of AC motor.
Matrix AC-AC control mode:
VVVF variable frequency, vector control, direct torque control inverter are delivered a DC-AC inverter. The common defect is low input power factor, harmonic current, DC circuit requires a large energy storage capacitor, the regenerative energy cannot be fed back to the supply, that can not be four quadrant operation. Therefore, matrix AC-AC frequency conversion emerge as the times require. Because the matrix AC - alternating frequency no intermediate DC link, thereby eliminating the need for electrolytic capacitor of large volume, the price of your. It can realize the power factor is l, the input current in the four quadrant operation, the power density of the large system. The technology is not yet mature, but still attracted many scholars to study. In fact, not the indirect current control flux equal, but to be controlled to achieve volume as direct torque. The specific method is:
1, control of the stator flux into the stator flux observer, speed sensorless mode;
2, automatic identification (ID) depends on the motor mathematical model, automatic identification of motor parameters;
3, to calculate the actual value corresponding to stator resistance, inductance, magnetic saturation, inertia factors. The actual torque, stator, rotor speed for real-time control;
4, implementation of Band - Band control PWM signal generated by the flux and torque of the Band - Band control, control of the inverter switching state.
Matrix AC - alternating frequency with fast torque response (<2ms), very high speed precision (± 2%, no PG feedback), high precision torque (<+3%); also has a high starting torque and high torque accuracy, especially at low speed (0 speed), can output 150% ~ 200% torque. | | | author: Published at: 2013/4/28 15:42:23 |  |
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