Research Of Discrete Frequency Soft Starter Based On DSP

Soft Start of three-phase asynchronous motor is an important research topic. The traditional soft is by changing the thyristor firing angle to reduce the size of the input voltage of the motor so that the motor starting current is reduced, but limits the size of the starting torque, heavy-duty starter can not be achieved. Starter motor with inverter has invested too much cost. So for these contradictions, we use thyristors chopping technique, we propose a new scheme, namely the classification frequency soft start technology, the software we have different power frequency half-wave-off combined control, in order to achieve VVVF, so that we can not increase the cost to meet the original motor for starting current and torque requirements.In this paper, a hierarchical frequency as the theoretical basis, we use mathematical analysis methods for the classification of sub-frequency inverter system in-depth study to determine the phase angle between sub-level frequency and the original signal. Through theoretical and simulation analysis, we can find the best combination of phase angle and various sub-optimal firing angle frequency of maximum electromagnetic torque. In this paper, the traditional motor soft starter main circuit structure has been improved, and made four starting points classification frequency regulator in the form of soft start, to ensure that the sub-optimal frequency levels can be achieved positive sequence voltage combinations, in order to determine the starting torque moments maximized. This paper also analyzes the causes of the current oscillations generated by the motor soft start regulating the process and made a classification variable frequency motor soft start controller imply the motor power factor angle view of closed- loop control during the second frequency to the power frequency, the method can make the electromagnetic torque and current ripple significantly suppressed in the process of starting.By classification variable frequency soft starter modeling and simulation, comparing with the tradition soft start, we validated that the classification variable frequency soft starter has the advantage in terms of heavy-duty starter. According to the results of theoretical analysis and simulation, we develop a classification variable frequency soft sarter prototype. The experiment results show that the classification variable frequency soft starter can reduce the starting current and in crease the starting torque, and the control effect is very good. According to this, we verify the correctness of the design of the circuit and feasibility.