The dynamic characteristics of the power grids in the future are discussed. Starting from the basic principle of AC power grid operation，this paper describes three technical challenges faced by power grids with high proportion of non-synchronous machine sources. The three technical challenges are： the new form of synchronous stability-generalized synchronous stability； the inapplicability of electromechanical transient analysis method in analyzing the generalized synchronous stability； and the wide-band resonance instability caused by negative resistance of power electronic equipment. It is pointed out that the non-synchronous machine source must rely on the control means to realize the synchronization with other sources in the power grid； and the decisive factor is the phase-locked loop （PLL）. The lock failure of the PLL means that the non-synchronous machine source is out of step with other sources in the power grid. Therefore，the concept of the generalized synchronous stability is proposed. It is difficult to simulate the PLL characteristics accurately by the electromechanical transient analysis method based on the positive sequence fundamental phasor. Therefore，the countermeasure to study the generalized synchronous stability of the high proportion non-synchronous machine power grids by the electromagnetic transient analysis method is proposed. It is pointed out that the essence of the problem of the wide-band resonance instability caused by negative resistance of power electronic equipment is the attenuation characteristics of the free components with natural resonance frequency in response to power grid disturbances，and the s-domain nodal admittance matrix method is proposed to study the problem.

Nowadays，the Chinese power grid exhibits a new architecture of multi-infeed HVDC transmission with large-scale wind and photovoltaic new power generation interconnection. The complex structure and new component characteristics of hybrid power grid make the stability of AC/DC systems more vulnerable after large disturbance. This paper mainly reviews the research progress of large disturbance stability analysis and divides the analysis methods into five classes： the step-by-step integration，the asymptotic expansion，functional approximation，direct method and other methods. Several common large-disturbance stability analysis methods are introduced. The advantages and disadvantages of the methods are discussed in this paper，which are thought to be useful for further study on large-disturbance stability in the future.

Due to the randomness and volatility of new energy data，data quality problems such as lack of data，repetition，abnormality and uneven distribution of grid-connected data have become more and more prominent. Studies on data quality evaluation and governance have important and positive significance for the development of new energy. Traditional data quality research methods are not suitable for solving new energy data quality problems，while artificial intelligence algorithms have incomparable advantages in dealing with this problem. Generative adversarial networks （GAN） is one of the hottest research directions in the field of artificial intelligence in recent years，and its excellent data generation ability has attracted wide attention. Firstly，this paper introduces the framework，advantages，disadvantages and improvement of classic GAN. Then，the application of GAN in new energy，the research literature of new energy data quality and GAN applying in new energy data quality are reviewed. Finally，this paper summarizes the paper and looks forward to the possible application of GAN in new energy.

Modal resonance could reveal the mechanism of some low-frequency power oscillation cases in large scale power systems，which could not be well explained by traditional damping torque analysis method. The progress of research and practice on modal resonance studies in the past few decades are reviewed. Firstly，the discovery of modal resonance phenomenon are recalled. Then the theory and experiments of modal-resonance-caused low-frequency power oscillation are concluded. Secondly，the mechanism and hearsay evidence of near strong modal resonance causing low-frequency power oscillation are introduced，including the improvement of the mathematical analysis tools and the suppression measures of the system resonance. Then the engineering examples of resonance in the past decade over the world are given，with the effectiveness of the above mechanism with actual cases. Finally，its theoretic progress，measure improvement and possible application prospect are concluded.

Recently，deep learning method has become the focus of academic research because of its achievement in areas such as image recognition. On this basis，this paper studies the feasibility of applying deep learning to the convergence criterion of power flow calculation，which is one of the fundamental calculation task in power systems. Compared with image recognition，the specificity of power flow calculation and the difficulty of applying deep learning in it are firstly discussed. After that，the network structure and training process of deep neural network（DNN） are presented as well as the method to solve the overfitting problem. Then according to the characters of power systems，feature vectors applied to the DNN model are constructed，including basic feature vectors，index set of reactive power adjustment capability and index set of power factor level. Finally，based on IEEE 14 system，1.6 million samples are generated and setting rules of hyper parameters are introduced，and calculation results show that high prediction accuracy can be achieved via the model and the feature vectors proposed in this paper.

Large-scale integration to renewable energy in the power system promotes the energy structure optimization，while at the same time，it brings uncertainties to the power system operation. In order to improve the stability of power systems with renewable energy integration，it is necessary to study the power system analysis method considering uncertainties，and identify the key uncertainties which have large impacts on the small signal stability of power systems accurately and quickly. This paper focuses on the small signal stability of power systems in the background of large-scale integration to renewable energy. A small signal stability model with wind power integration is established and three sensitivity analysis methods，including the one-at-a-time method，the trajectory method and the global method are compared to determine the key uncertainty in the eigenvalue of the status matrix. In addition，the sparse polynomial chaos expansion （SPCE） method is used to improve the efficiency of the global sensitivity analysis. A 14-bus system is used to test the accuracy and efficiency of sensitivity analysis methods mentioned in this paper，and the effectiveness of the global sensitivity analysis method is verified.

Under the new format and business model of integrated energy services，basic research on integrated energy system modeling and physical mechanism analysis is particularly important. This paper first analyzes the domestic and international research status and development trends of the integrated energy system in terms of modeling and analysis，and then expounds the research system of energy network theory and method for modeling and analysis of integrated energy systems，including “unified modeling of integrated energy systems theory” and “analysis of dynamic behavior of energy and helium in integrated energy systems”，and analyzes the key scientific issues，and then gives specific research plans，and puts forward the core method of “modeling and physical mechanism analysis”. In the end，the research on energy network theory elaborates on how to establish a perfect energy network theory，realizes unified modeling of multi-energy systems，and introduces exergy and entransy to describe the characteristics of integrated energy systems. The challenges faced are analyzed and the prospect is presented.

An electromagnetic transient model of transformer is proposed based on the J-A（Jiles-Atherton）model simulating its hysteresis characteristics. Differentiation is used to obtain the discrete model. The J-A hysteresis model is implemented by injecting extra current source to the transformer model. By thorough analysis of the numerical characteristics of the J-A model in different simulation step length，the computation efficiency is improved through the use of multi-rate simulation schema. By comparing multiple test cases，the proposed model is validated. The improvement of efficiency is also verified through the comparison of consumed times. It provides an efficient and reliable implementation method for transformer hysteresis simulation based on J-A model in electromagnetic transient simulation programs.

Multi-terminal HVDC system has attracted much attention due to its flexible structure and high economic efficiency. Because the operation mode of multi-terminal HVDC system is flexible，the selection of key equipment parameters and the calculation of the main circuit state need to consider more factors. Firstly，the operating conditions of the multi-terminal DC system，the operation mode and control mode of the multi-terminal DC system are analyzed. Then，the limiting factors of the key equipment parameters are analyzed，and the computation method for the key parameters of the multi-terminal HVDC are proposed. The power flow calculation equation of the DC network is constructed，and the adjustment method of constraint conditions is proposed. Finally，the validity of the proposed method is verified by design examples. The method proposed in this paper provides technological means and support for the design of multi-terminal HVDC systems.

HVDC breaker is an important device for realizing DC networking. Taking ±535 kV hybrid DC breaker of Zhangbei HVDC grid project as the research object，its insulation structure is mainly analyzed and designed in this paper. The trend of voltage distribution for the DC breaker is calculated with wide-band circuit model by PSCAD. Combined with the overall insulation requirements of the DC breaker，the withstand voltage levels for the key components are proposed. Based on the overall layout of the DC breaker，the equipotential design and insulation coordination are carried out，considering the operating environment，voltage waveforms and electrode types. Under typical operating conditions，the electric field distribution of the whole three-dimension DC breaker is calculated and evaluated by the finite element simulation software. The insulation tests of the DC breaker are carried out. Through the research of this paper，one suitable design method for the insulation structure of DC breaker is proposed，which is modular，sub-regional，layered and single-point nearby potential fixed. The maximum electric field strength on the surface of DC breaker fittings is 27.7 kV/cm under the lightning impulse withstand voltage，and 19 kV/cm during the fault current breaking process. No flashover or breakdown occurs during the type tests，satisfying the requirements of engineering applications. The research results can provide reference for the insulation structure design of high-voltage equipment.