The Research On Reactive Power Optimization Of Hybrid AC-DC Power System

With the expansion of power system and the opening of power market, safe and economic operation of the power system were more and more greatly considered. Reactive power optimization for power grid by reasonable and systematic means of reactive power regulation can not only effectively ensure the voltage quality, but also improve power system stability and security, reduce power consumption, give full play to the economic benefits of electricity.With the development of HVDC, DC transmission has been widely used in large capacity power transmission system in recent years because of its outstanding advantages of economic and operating characteristics. Used of DC transmission and AC transmission complement each other for AC-DC hybrid transmission has become one of the main transmission way of the regional power grid interconnection. In the AC-DC transmission system, how to control the DC variable and AC variable in reason for optimal operation is the important issues of concern in the study.Reactive power optimization of this article is based on AC-DC hybrid transmission system model above, considering the common operation mode DC transmission. The AC-DC transmission system achieve the purpose of the minimum active power loss by reasonable schedule the DC voltage, the DC current, the transmission power, the control angel of inverter of DC part and the generator terminal voltage, the adjustable transformer tap, reactive compensation capacity of AC part, while making the voltage of each node, the reactive power output of generator node and so in a reasonable range.On this basis, this thesis proposed hybrid optimization strategy of interior point method combined with PSO through researching on the classical algorithms, artificial intelligence algorithms and hybrid algorithms of reactive power optimization. Interior point method particularly the predictor-corrector primal-dual interior point method has the fast searching speed and the size of the system is not sensitive, the benefit especially prominent when calculating the large-scale planning issues, but it is more difficult to deal with discrete variables. As a new swarm optimization algorithm, PSO has a faster speed and a simpler operation than the similar artificial intelligence algorithms, moreover, it is easy to handle discrete variables, but it easily fall into partial optimum because of the lack of diversity of particle when dealing with the large-scale problems. Optimization strategy of this paper decompose reactive power optimization into consecutive and discrete optimization sub-problems, alternating with two methods to solve. Examples show that the hybrid optimization algorithms has better convergence and faster searching speed, it is easily handle discrete variables. Moreover, the PSO has been solved the discrete optimization sub-problem, this equivalent of reducing the scale of the optimization problem, the particles easier to find the global optimum.Examples also show that the optimization result is different when it use different DC operating mode. Such as using rectifier constant current control-inverter constant extinction angle control, the economy of the system is better, that is, the loss of active power is less. But the same system using rectifier constant trigger angle control-inverter constant current control, the security of the system is better, that is, the node voltage is higher. So in the actual system, it need to select reasonable control mode of HVDC according to the demand of the system.In short, with the development of grid scale and application of DC power transmission, the research on reactive power optimization of hybrid AC-DC power system has a positive meaning for the system's security and economy. But reactive power optimization is a complex nonlinear optimization problem with a large number of variables and constraints. With the continuous development of HVDC technology and the application of the new algorithm, many issues of reactive power optimization of hybrid AC-DC power system need further study.