Hierarchical Modeling Scheme for High-Speed Electromagnetic Transient (EMT) Simulations of Power Electronic Transformers
Abstract : The extensive application of the power electronic transformers (PET) in power systems poses a challenge as the accurate and high-speed electromagnetic transient (EMT) simulation of PET has been a critical issue. The computational time of the detailed EMT simulation of PET on EMT programs is unacceptable, due to the large electrical node count, microsecond-range simulation steps, high switching frequency of the devices and transformers. This paper proposes a hierarchical modeling scheme for PET. Unlike the existing modeling methods, the proposed technique recursively decreases the dimension order of the admittance matrix to obtain the generalized Norton equivalent of each phase leg. The final admittance matrix overlaid onto the external system admittance matrix has a dimension order of magnitude remarkably smaller than that of the unreduced structure. By comparison with a detailed EMT model of a medium-voltage dc (MVDC) system, the performance of the proposed scheme has been assessed in PSCAD/EMTDC under various working conditions. With negligible loss of accuracy, approximately one to two orders of magnitude speedup over a straightforward EMT program is achieved.
? A challenge is to obtain these data since they are not provided by the existing phasor-domain cases in the literature, and hence need to be estimated.
? An approach is to assume a typical wave propagation velocity of, e.g., 0.97(the speed of light) and calculate the per-unit-length impedance and length of the line.
? In response to the inability of performing harmonic calculation and analysis of power system dynamics due to a GMD in existing GMD test cases, a GMD version of IEEE-118 which incorporates supplementary modelling details for time-domain simulation of a GMD within an EMT-type package is developed in this work.
? The converter transient response is governed by the natural time constants of the and numerical approaches for such problems may be found in , which also examines the modeling and simulation of more exotic phenomena such as chaos in power electronics.
? Simulation of these topologies remains a key tool in comparing topologies for an application, discovering problems in a new circuit or control approach, trying out variations to overcome each successively discovered hurdle, and then refining the circuit or controller to meet performance requirements.
? Although general-purpose circuit simulators such as SPICE are increasingly being used for power electronics simulation, they are still beset with problems when used to simulated detailed device behavior.
• A number of the proposed test cases have been developed from phasor-domain versions by supplementing/modifying the original case data to enable time-domain simulations.
• All proposed test cases of this paper assume a continuouslytransposed line, and hence, the FD line model is sufficient, and the WB model is not needed, but can be also selected and unbalanced lines can be created from given data.
• Load-flow solution should converge and be feasible, and voltage amplitudes should be typically between 0.95- 1.05pu. The proposed test cases of this paper meet this criterion.
• In this version, the transmission lines are modelled by their more detailed FD representation whose model is generated from the proposed line data.
? After the components have been selected and the designer has gone through the physical realization process, usually via a board layout, predict circuit performance under abnormal conditions.
? Usually, auxiliary circuits such as over-voltage, over-current, and over-temperature detection and shutdown are incorporated into the circuit.
? In addition, conducted and radiated EMI performance also must be assessed for conformance to regulatory requirements; this is typically determined today by exhaustive experimental testing.
? Many of the methods described above can be folded into a framework that assesses circuit performance with variation of circuit parameters or operating conditions.
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