| Different from AC power network,there is no frequency fluctuation and angular swing in DC power distribution network.However,with the continuous improvement of distributed power supply and load capacity,the negative impedance characteristic of constant power load(CPL)after short-term disturbance has a more significant impact on weakening DC voltage damping.In addition,voltage mutations due to low inertia of the DC system also increase the risk of stable operation of the system.Therefore,improving the dynamic stability of DC voltage has become a new challenge for the stable operation of DC di stribution network.The main work and achievements of this paper are as follows.(1)The mathematical model of DC distribution network is established to analyze the voltage stability characteristics of the system.The mathematical model of DC distribution network with wind turbines,photovoltaic(PV),storage and CPL is established,and the voltage state differential equation of DC bus is established to analyze the damping characteristics of DC distribution network.The volt-ampere characteristic curve of the DC distribution network is drawn to analyze the moving trajectory and stable operation conditions of the system operating points when the load changes.(2)A voltage stability evaluation method based on electric quantity is proposed.Based on the analysis of power system model derived from the equation of state,transient power converter equipment prepared on either side of the effect the stable operation of the system mechanism,and combined with stable operation condition,is put forward based on the power of the DC power distribution network dynamic stability margin and criterion,qualitative change of voltage stability,at the same time,the strength of the quantitative characterization of voltage stability.(3)The damping control strategy and the additional electric quantity control strategy are put forward from damping and electric quantity.By introducing the variation of the DC bus voltage and dynamically adjusting the droop coefficient,a damping control strategy is proposed to enhance the DC voltage damping.Although the damping ability of the DC voltage is enhanced,the strategy leads to the aggravation of the bus voltage offset,which cannot fully represent the voltage stability of the system." Principle of electric quantity equality" based on DC power distribution network,with the introduction of DC bus voltage and its change rate,improve energy storage side converter droop control,put forward to expand the additional power system dynamic stability margin control strategy,the strategy not only enhances the system damping characteristics,more from the macroscopic level to enhance the system voltage stability.(4)Simulation verifies the theoretical analysis results and the effectiveness of the proposed stability evaluation method and control strategy.The simulation system of multi-terminal DC distribution network is built to verify the influence of CPL,control coefficients and system parameters on voltage stability,and the rationality of stability criterion based on electric quantity.From the two aspects of frequency domain and time domain,the effect of the traditional droop control strategy and the two proposed control strategies on the voltage stability is compared and verified,and it is proved that the additional electric quantity has a good support ability to the voltage stability of the DC distribution network. |
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