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Standards Development
This technical specification addresses the generic electromagnetic transient (EMT) simulation models of converter-based power plants(CBPPs) for power system dynamic analysis. The scope of the standard covers the grid-connected CBPPs for photovoltaic power stations, wind power plants, energy storage systems, etc.
The models specified in this standard can be primarily used for power system dynamic simulation analysis in the electromagnetic time scale.
The specifications in this standard includes definitions, specification of the EMT model for CBPPs, and specification of a validation procedure.
The EMT model for CBPPs includes specification of converter -based power units(CBPUs), specification of multiplication of CBPUs and specification of aggregation of CBPPs.
The specification of CBPUs not only covers generic models but also inputs and outputs of black -box models.
The validation dimensions of EMT models specified in this standard includes both frequency domain and time domain.
The validation procedure provides quantitative measures for the model accuracy based on comparison of model outputs to measured values.
The global energy transition has witnessed accelerating integration of renewable energy (RE) generation into modern power systems, with RE generation now constituting 50.3% of worldwide installed electricity capacity, surpassing fossil fuel-based generation capacity for the first time. Since RE power generation is typically integrated into the grid through power electronic converter, the operation of power system has undergone profound changes. New stability issues, such as broadband oscillation and transie nt overvoltage, have emerged. From 2014 to now, multiple oscillations between Hz~kHz occurred worldwide, such as 250~350Hz oscillations occurred at an offshore farm in the North Sea, 23/77Hz oscillations occurred in Xinjiang, China. There is also transient overvoltage occurred at the sending end power plants of HVDC. These problems have resulted in tripping-off accidents in large-scale renewable energy plants, seriously affecting the safe and stable operation of power system worldwide.
New stability issues such as broadband oscillation and transient overvoltage involve the interaction between CBPPs and the AC power grid or the HVDC transmission system. The frequency can cover from Hz ~ kHz, and the time scale is within 15 ms. In this cas e, RMS model is no longer applicable. EMT models for CBPPs are urgently needed for system dynamic analysis. Now, with the cross -border export of converter-based devices, various countries have put forward modeling and verification requirements for them. EM T models of converter-based devices are requested by grid operators to conduct the stability analysis in converter - based power systems, and RE plants developers are requested to provide EMT models to obtain grid integration access. In order to ensure that consistent and compatible models can be shared among different manufacturers, research institutions, and users in power system analysis, it is necessary to standardize the EMT model internationally to reduce investment in time and cost.
Currently, the widely adopted EMT modeling method is the black -box model based on 'code encapsulation', which primarily focuses on the external dynamic characteristics of RE units, and is usually provided by RE manufacturers. However, users encounter the f ollowing limitations during implementation:1) Each model contains functional code coupled with redundant components, causing inefficient utilization of computational resources during simulations. 2) Software version updates require repetitive encapsulation work, which severely degrades modeling efficiency. 3) The model control structure and parameters are unknown to users, making key control loops and parameters unobservable and unmodifiable during system simulations, fundamentally limiting adaptability to grid integration studies.
Another EMT modeling method is the generic modeling based on control structure and parameter identification. This method utilizes field-tested steady-state and transient response data, including impedance characteristics and fault ride-through responses, to systematically identify the control structures and control parameters of RE units. Through coordinated integration of primary power circuit with the identified control systems, RE units can be modeled in different types and versions of software using uni fied variable definitions. And the model accuracy can be validated by comparing its steady -state and transient dynamic response to the testing results. This generic modeling method achieves unified definition of variables, compatibility across different types and versions of software. Both control structures and parameters of generic models are observable, measurable and modifiable to users. The limitations of black - box models can be avoided.
Although IEC 61400-27-3 and IEC 61400-27-4 have specified the frequency-domain models and time-domain EMT models for converter-based units respectively. The specifications are mainly for black box EMT models of converter-based units. In addition, due to the various operating points and various locations of different power units in a power plant, simple power plant model aggregated by same power units cannot accurately simulate the dynamic characteristics.There is a lack of EMT models for dynamic analysis at system level. Furthermore, in order to ensure the accurate dynamic response during the steady state and transient state, the EMT models for converter-based units contained in the plant need to be validated from both frequency and time domains. In this respect, the generic EMT models for CBPPs need further standardization.
IEC SC 8A mainly focuses on the impact of high penetrations of RE on modern power grids. WG8 aims at modeling of renewable energy generation for power system dynamic analysis. It includes experts from universities, research institutes and manufacturers wit h most advanced experience on modeling of converter-based units and plants. It has launched the project IEC TS 63406 ED1, which aims at RMS modelling for power system dynamic analysis and has passed DTS voting with a 93% in favour rate. Following IEC TS 63406 ED1, WG8 has also done a lot of work on EMT mode lling. This proposed technical specification will be the second standard of WG8. It is primarily focused on EMT modelling, which is of global significance and requires immediate attention.
During the joint meeting (JWG4 & WG8 & AHG3) in Zurich, Switzerland in June 2024, the proposal of EMT modelling for power system dynamic analysis was presented. The working groups had a sufficient communication and exchanged ideas internally. After that, w e have made modifications and improvements according to experts’ comments. In the SC 8A plenary meeting held in Saclay, France, Sep. 2024, the revised proposal was presented again. A common agreement was reached that it was necessary to launch the EMT modelling work of converter-based power plants. After the meeting, further modifications were made, and now this proposal is being presented here.
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