Research On Speed Sensorless And Direct Flux Oriented Vector Control System’s Control Strategy

In some low cost applications, an alternative method is avoiding making using of speed sensor. The using of speed sensor reduces the overall performance of the motor control system and even leads to the robustness of system becoming worse. Speed sensor totally can’t fit in some situations. Speed sensorless vector control system becomes a research hot spot.Speed sensorless vector control system avoids the bad effect of speed sensor to the robustness and reliability of the system. The core issue of Vector control is flux-oriented and there are three directional method(stator flux oriented, gap flux oriented and rotor flux oriented) to choose from. The rotor flux oriented manner with respect to the other two directional methods allows the motor’s performance closing to its mechanical characteristics and high hardness.Flux calculation model including current model, voltage model and voltage-current hybrid model, the current model sensitive to motor parameters(magnetizing inductance and rotor time constant).Voltage model based on the integration of back EMF voltage and calculation of integration will accumulate DC offset resulting in saturation. At low speed the stator’s resistance has a heavy impact on the result of calculation. Hybrid model combines the advantages of both model, current model is used to compensate for voltage model, improving directional precision of motor control system at the cost of increasing calculation complexity.Hybrid model has been studied by many scholars. But the integrated approach and the role of the characteristics of the two models is simply a linear superposition and theoretical analysis, not given a detailed explanation of the running law from low frequencies to high frequencies. This paper uses a closed-loop calibration method to integrate voltage model and current model. Firstly introducing design guidelines of closed loop regulator and the problem of convergence with modern control theory; second, through non-linear model of rotor flux observer to simplify the design of calibration parameters and analyze its characteristics.Based on analysis of flux observer, there exits problem of system performance’s degradation at low speeds. The reason for this phenomenon is inverter’s non-linear voltage drop, which leading to the motor’s voltage drop accuracy become worsen, and the voltage are closely related to flux orientation. After the inverter nonlinear voltage drop detailed analysis, to fix the given voltage of motor and improve accuracy with voltage second principle theory.Use MATLAB / SIMULINK for speed sensorless vector control simulation to verify the flux observer and dead-time compensation theoretical analysis’ s rightness. Dead-time compensation reduces current harmonics and improves the angle accuracy of flux-oriented. The error of closed loop rotor flux observer is small at stable operation and the dynamic adjustment process convergences fast. Satisfy the requirement of the motor control system’s orientation.Experimental platform based on Texas Instruments digital signal processor 28035 and asynchronous motors with rated power 3KW. Design the above algorithm, debugger for experimental verification. Experimental results consistent with theory analysis and simulation waveforms. Also it verifies that closed loop rotor flux observer meets the requirements of vector control system at wide speed area and the usefulness of dead time compensation.