Research on building a new power system framework with new energy as the main body

3. Problems and challenges faced by the power system

(1) Ensuring the supply of electricity

First, the basic theory of ensuring adequate supply is facing challenges. Under the background of global climate change and large-scale development of renewable energy, the renewable energy resource endowment will change significantly in the long-term evolution process. The planning decision of power supply and network is faced with double uncertainty of resource endowment and operation and has obvious path dependence. The above characteristics bring great challenges to the traditional resource endowment assessment and planning theory.

Second, it is difficult to ensure the supply of new energy when it is small. With the rapid development of new energy power generation, the proportion of controllable power sources has declined, the characteristics of new energy "large installed capacity, small power" have become prominent, and the difficulty of ensuring power supply when wind and solar power are small has increased. In the carbon neutral stage, the proportion of thermal power will further decline, the installed scale of new energy will continue to increase, while the load will still maintain a certain growth, real-time power supply and medium - and long-term power supply security difficulties are more prominent.

Third, it is more difficult to ensure supply under rare sky events and extreme weather. Solar eclipse and other rare astronomical phenomena will significantly affect the output of new energy; With the intensification of global warming and climate anomalies, extreme weather events such as hurricanes, snowstorms and freezing, and extremely hot and windless weather are increasing and increasing, exceeding the existing cognition. Rare sky events and extreme weather have the characteristics of small probability, high risk and great harm, which have great influence in the scenario of high proportion of new energy, pushing up the cost of power supply guarantee.

(2) System balance adjustment

First, the basic theory of supply and demand balance is facing challenges. With the continuous increase of the proportion of new energy, both the supply and demand sides and the system regulation resources present a high degree of uncertainty, and the system balance mechanism has changed from "uncertain power generation tracking uncertain load" to "two-way matching between uncertain power generation and uncertain load". The operation characteristics of both sides of supply and demand are highly dependent on external conditions such as climate, so the theory of supply and demand balance established for traditional power systems needs to be developed and perfected.

Second, intra-day adjustment is facing greater difficulties. The random fluctuation of new energy output needs to be offset by the deep adjustment capacity of controllable power supply. The existing adjustment capacity of the power system has been basically tapped out, and more adjustment capacity is still needed in the near future to meet the consumption demand of new energy. After the long-term new energy has become the main power supply, it is difficult to meet the daily consumption demand by relying on the conventional power supply with a declining proportion and the limited load side adjustment capacity.

Third, the demand for long-term seasonal adjustment has increased. There is a seasonal mismatch between new energy power generation and electricity consumption, and the new energy output at the peak of summer and winter power consumption is lower than the average level, while the electricity consumption level at the spring and autumn new energy is at the lowest level throughout the year. The existing energy storage technology can only meet the daily adjustment demand, and the seasonal consumption contradiction will be more prominent under the scenario of a high proportion of new energy.

3. Safe and stable operation

First, the basic theory of stability is facing challenges. The new energy time-varying output leads to the rapid migration of system operating points, and the traditional Lyapunov stability theory based on a given equilibrium point has inadaptability. The synchronous mechanism and dynamic characteristics of new energy power generation are different from those of conventional units, so the classical definition of transient power Angle stability is no longer applicable. The high proportion of power electronic equipment leads to the system dynamic characteristics of multi-time scale interweaving, control strategy dominance, switching and discretization, which makes the corresponding transition process analysis theory and the basic theory of coordination with non-power frequency stability analysis need to be improved.

Second, the basic theory of control needs to be innovated. The control resources of traditional power system are mainly homogenous large capacity equipment such as synchronous generator. In the new power system, a large number of new energy and power electronic devices are connected from various voltage levels, and the control resources are fragmented, heterogeneous, black-box and time-varying, making the traditional model-driven centralized control difficult to adapt, and new basic control theories are needed to effectively implement the aggregation and regulation of various resources.