| In order to improve the atmospheric environment,the converter used in the field of new energy development is a truly "green" power converter.According to the output characteristics of the converter,it can be divided into the voltage source converter and the current source converter.The current source converter has the advantages of wide output voltage range,direct control of output current,inherent short-circuit protection capability and fast dynamic response.It is mainly used in electric vehicles in the transportation field,uninterruptible power supply in the field of power supply,and high-voltage power transmission and low-voltage power distribution in the field of power systems.In this thesis,the modulation strategy and control strategy of the three-phase current source converter are mainly studied as follows.Firstly,the working principle and switching state of the three-phase current source converter are described in detail.And based on the switch state,the generation principle of several types of conventional modulation strategies for the three-phase current source converter and the advantages and disadvantages of each of the modulation strategies are respectively compared and analyzed in detail.In order to improve the shortcomings of low DC current utilization and high switching loss in traditional carrier modulation strategies,a new carrier modulation strategy is proposed in chapter 2.The new carrier modulation strategy not only has the advantages of improving the DC current utilization rate by 15.5%,reducing the switching loss by 1/3 and the complicated process without any logic operation,but also provides a theoretical basis for the control process using DSP alone.Secondly,in order to carry out a series of systematic theoretical research on the three-phase current source converter,the mathematical model of the three-phase current source converter in the two-phase rotating dq coordinate system is established.Based on the mathematical model,the parameter design of the AC side LC filter is completed.Since the LC filter alone will cause the system to resonate,a large number of harmonics are generated,which seriously affects the current quality.Generally,a scheme of series-parallel damping resistors for passive inductors or passive capacitors is adopted toachieve the purpose of increasing system damping,and the conventional scheme has the advantages of simple implementation and high reliability.Based on the passive damping scheme of the traditional inductive shunt resistor,this thesis proposes a novel passive damping scheme for split inductors,which not only achieve the same damping effect as the traditional damping scheme but also solve the disadvantage that the traditional damping scheme has large damping power consumption.At the same time,based on the mathematical model proposed in this thesis,the AC current closed-loop control strategy of the three-phase current source converter is systematically designed.The closed-loop design not only ensures that the system is in unity power factor operation,but also effectively reduces the low harmonic content of the AC current.The simulation verification of the proposed scheme is realized by using MATLAB,and the correctness of the proposed scheme is verified.Finally,the experimental platform of three-phase current source converter with TMS320F28335 DSP and XC3S400 FPGA as control system is designed and built.Through the experimental platform,the experimental comparison between the traditional scheme and the proposed scheme verifies the feasibility and correctness of the proposed scheme. |
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