Research On Digital Control Technique Of 25Hz Railway Signal Power Supply And Its Parallel Operation

25Hz railway signal power supply is an AC two-phase inverter for phase-sensitive rail circuit. It can be operated in parallel mode in order to expand capacity for different scale railway stations. The power supply’s reliable operation can guarantee that phase-sensitive rail circuit obtains the information of rails occupancy, which is very important for safety management of railway operation. The research and discussion of digital control technique for 25Hz railway signal power supply and its parallel operation were presented in this dissertation.A novel deadbeat control scheme for PWM inverters with multi-loop structure is proposed, which is a full digital control scheme and making inverter achieve excellent dynamic response and steady-state behavior. In this scheme one-beat lag of PWM output is considered as z-1 unit which is treated as a part of plant and digital controllers of current-loop and voltage-loop are designed in Z domain. Compared to the traditional PID control scheme, the proposed scheme can obtain better control performance, more convenient implementation, which is not dependent on the empirical selection of control bandwidth; compared to the single voltage loop deadbeat control, this scheme can obtain better stability and reliability. In order to deal with the problem of parameter sensitivity in deadbeat control, stability analysis is presented which based on root locus method, MATLAB simulation model is constructed for aided design. The presented control scheme of inverter has excellent performance:two-beat track performance of current-loop as well as three-beat track performance of voltage-loop. By utilizing this feature, dead-time compensation can be done so as to improve output voltage, which isn’t affected by one-beat lag of PWM output. To reduce the error of digital feedforward compensation of load current and save hardware cost, design of predictive observer is analyzed and simulation results found first-order model than the zero-order model of load current observer has better prediction.Related issues about parallel operating inverters of voltage source are analyzed. Because the resolution of DA and AD conversion is always limited, circulation current among parallel inverters is inevitable. Design’s goal of inverter parallel is to control circulation current in acceptable range. Considering applications of parallel inverter, mainstream data networks are analyzes and compared related with real-time performance and media access control (MAC). An auto-master-slave parallel scheme of inverters based on CAN bus communication is presented. This parallel logic via CAN bus can not only assigns master/slave status to parallel inverters automatically, but also realizes carrier synchronization of parallel inverters. By overclocking CAN bus to 2MHz, real-time control data’s transmission in each carrier cycle is obtained. This parallel scheme can suppress fundamental circulation, as well as harmonic circulation, which guarantee the same output voltage quality with independent operation mode.The experiments of two 25Hz railway signal power supply validate the digital control schemes of inverter and its parallel proposed in this dissertation.