Research findings indicate that in multi-unit systems experiencing subsynchronous oscillations(SSO),the units tend to exhibit similar torsional vibration frequencies.Therefore,an analysis was conducted on the interac-tive effects among shaft systems of units with similar frequencies,as well as the mechanisms of system series com-pensation,electrical distances between units.Additionally,the paper delved into the mechanisms through which system series compensation,electrical distances between units,and similar torsional vibration frequencies impact the SSO.Firstly,based on characteristic matrices,the expression for the complex torque coefficients of two parallel thermal power units in the system was derived.Subsequently,the simplified complex torque coefficient method for a single unit was extended to encompass multi-unit systems,resulting in a streamlined expression for the electrical damping of dual thermal power units.The analysis further examined the influence of other units on the damping of the target unit,revealing that series compensation,electrical distances between units,and similar torsional vibra-tion frequencies all exert an influence on system damping and stability.Finally,the mechanisms through which in-fluencing factors affect the subsynchronous stability of the system were validated through numerical examples.
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