Research On Power Theory Of Multiphase Circuit

Power theory is developed to meet the requirements of two aspects of theorization and practicality.Although power theory has been gradually improved,there are still a lot of problems to be solved in the field.One of the problems is the method of reference point selection.On the one hand,there are a variety of reference point selection methods,and we need to find a better one.On the other hand,both the instantaneous apparent power and instantaneous reactive power in instantaneous power theory and apparent power and reactive power in average power theory will be affected by the selection of reference points.Therefore,it is necessary to describe its function relationship mathematically.In order to select a better method from the existing reference point selection methods,many current methods in power theory are summarized and compared in the thesis,and it is obtained that selecting virtual neutral point as a reference point is a more advantageous reference point selection method.In this thesis,the method of selecting virtual neutral point is deduced,the compatibility of the reference point selection method with the existing methods is analyzed,and the uniqueness of the virtual neutral point is also proved.Various kinds of instantaneous power theories are compared,it is obtained that generalized instantaneous power theory is the best one in the existing instantaneous power theory.It can not only include the instantaneous power theory of three-phase circuit,but also can be directly applied to multiphase circuit.The theory is deduced by using the method of conditional variation,then the current and power are decomposed from the point of current detection,and the block diagram of current detection based on generalized instantaneous power theory is also obtained.Finally,the current detection method is simulated,and the simulation results show the feasibility of the current detection method based on generalized instantaneous power theory.When reference point is selected arbitrarily in the system,instantaneous apparent power and instantaneous reactive power of generalized instantaneous power theory are affected by reference point selection.The functional relationship between two power quantities and the reference potential is described,and it is found that instantaneous apparent power and instantaneous reactive power have a quadratic functional relationship with the reference point potential,and the relationship can explain mathematically the reason why instantaneous apparent power and instantaneous reactive power are affected by reference point selection.Various existing average power theories are also compared,and it is obtained that the power theory based on periodic function space has a wide scope of application and a simple analysis of current and power.Therefore,it is helpful to describe the relationship between power and reference point selection.The power theory based on periodic function space ismathematically derived by using circuit optimization method of conditional variation.The thesis focuses on the current decomposition and power definition,and it is found that the definition of active power in the theory has unidirectional transfer characteristic and reactive power has cyclic transfer characteristic.When reference point is selected arbitrarily in the system,apparent power and reactive power are both affected by reference point selection.By describing the relationship between apparent power and reactive power and reference point potential,it is found that apparent power and reactive power present a quadratic functional relationship with the effective value of reference point potential,the relationship can also explain mathematically the reason why apparent power and reactive power are affected by reference point selection.In order to analyze the relationship between generalized instantaneous power theory and the power theory based on periodic function space,power definition processes of two theories are analyzed.It is concluded that the processes of mathematical definitions of two theories are exactly the same,only the inner products introduced are in different forms.It is because of this difference in mathematical form of inner products,power quantities of instantaneous power theory are given by one theory,while power quantities of average power theory are given by another.