A Novel Unbalanced Coordinate Transformation System And Application

With the increasing demand for energy and the large-scale exploitation of renewable energy,the capacity of the modern power grid is larger and larger.Today's grid is different,and no longer consists of single synchronous generators,but access to more and more power electronic converters interfacing renewable energy power generation.But these power electronic converters do not have hard characteristics as synchronous generators due to the deficiency of control performance,thus causing the three-phase unbalance existence in the grid system commonly.So the controlling of power electronic converters under unbalanced three-phase grid has become particularly important.As a result of the existence of negative sequence component,the traditional control of power electronic converters under unbalanced three-phase grid will introduce second harmonic problem,while the introduction of filter will affect the system dynamic performance.Aiming at the above problem,a new Tan-Sun coordinate transformation system is established from the perspective of coordinate transformation novelly.Under the Tan-Sun coordinate transformation system,unbalanced three-phase ac quantity can be transformed into two-phase dc quantity directly,and not containing the second harmonic component,avoiding the use of filter in the control system,thus improving the control performance of the power electronic converter especially dynamic performance.Power definition method and adaptive phase-locked loop(PLL)technique based on the above Tan-Sun coordinate transformation system are also proposed.Because of the benefit of no using filter in the above Tan-Sun coordinate transformation system,and avoiding three-phase unbalanced voltage and current phase sequence component extraction meanwhile,the power calculation and PLL also have the advantage of real-time and high accuracy,thus providing a basis for better control performance for three-phase unbalanced systems.Finally,the three-phase PWM rectifier simulation and experiment platform has been set up,and the power definition and PLL technology based on Tan-Sun coordinate transformation system will be applied to the platform,to verify the correctness and practicality of the Tan-Sun coordinate transformation system and its application.