Research On Closed-loop Dynamic Phasor Model Of DC System Considering Phase-locked Loop And Commutation Failure

In order to meet the objective needs of economic and social development,HVDC transmission technology has developed rapidly in China.At this stage,the power grid of China has become the world’s largest AC/DC hybrid power grid with the highest voltage level.The continuous construction of DC lines also brings new challenges to system simulation.In order to solve the problem that the transient response of AC/DC hybrid system is difficult to calculate quickly and accurately,a detailed modeling of the entire LCC-HVDC system is carried out based on the dynamic phasor method in this thesis.On this basis,a complete closed-loop dynamic phasor model of the DC system is established.Firstly,the HVDC converter is analyzed in this thesis and the dynamic phasor model of converter with phase-locked loop(PLL)is established.The existing switching function is also improved in this process,so that it can reflect the working process of converter under AC asymmetry condition.By combining the output of PLL with improved switching function,the time-domain signal calculation method is used to replace the frequency-domain convolution of the traditional dynamic phasor,which further improves the calculation speed and accuracy.At the same time,for commutation failure that is easy to occur on the inverter side,a composite criterion and a switching function modification method are proposed to judge and process it quickly,which expands the applicability of the model.After establishing the dynamic phasor model of converter,this thesis further models the DC line,DC control system and converter transformer.Then on the basis of clarifying the connection and interaction modes of each part of the DC system,the closed-loop simulation process of the DC system is finally formed.Appling the model built in this thesis to the CIGRE BENCHMARK standard system,the simulation results under multiple fault types further prove its advantages over traditional dynamic phasor models.Based on the consideration of phase-locked loop and commutation failure,this thesis conducts the research of closed-loop dynamic phasor model on DC system,and this further expands the application of dynamic phasor theory in power system simulation.It also provides the possibility for accurate real-time simulation of modern power system in the future.