A new converter fault discrimination method for a 12-pulse high-voltage direct current system based on wavelet transform and Hidden Markov Models

Abstract

The progressive development in high-voltage direct current (HVDC) transmission enhances the need to implement an efficient protection scheme to distinguish the minimum faulty part of the system and to relieve the stressed equipment. This paper proposes a new classification method based on Hidden Markov Models and wavelet transform to discriminate HVDC converter faults. In the proposed technique, probabilistic characteristics of signals discriminate fault signals without any deterministic index, so more flexible classification in different system conditions is achieved. Based on this method, high-speed protection decisions with small computational time could be performed in approximately 5 ms for severe system faults, and in 12.5 ms for faults that are restricted by protective control decision. PSCAD/EMTDC software simulations demonstrate suitable performance of this scheme for different fault types and system conditions in the International Council for Large Electric Systems (CIGRE) HVDC benchmark. All simulation results validate the stability and robustness of proposed scheme in different conditions, such as noisy systems.

Flyback-Based Multiple Output dc-dc Converter with Independent Voltage Regulation

“…In this time interval, channel 1 is compensated by its series buck converter and channel 2 is regulated by the flyback converter. The operation of the proposed SIMO power supply during this time interval is similar to that during time Interval 1 and the corresponding time spans t 11 , t 12 , t 13 , t 14 and t 15 . All presented equations and timing scheme for channel 1's flyback converter and channel 2's buck converter within time interval 1, can be adapted for channel 2's flyback converter and channel 1's buck converter, respectively.…”

“…The magnetizing inductance of the flyback transformer is preferred to be designed for CCM operation, since it has lower peak current and consequently lower output voltage spikes. According to [15], minimum L m can be designed for the minimum output voltage, which is 15V, as follow: The switching frequency of the buck converters is the same as that of the flyback converter to avoid EMI issue. The inductor of buck converter is designed as 2μH for CCM operation to minimize current spike and to limit the output voltage ripple.…”

“…Note that diode D L1 has been adopted to avoid unintentional current draw from MOSFET Q L1 's body diode. In steady state, we have [15]:…”

“…The magnetizing inductance of the flyback transformer is preferred to be designed for CCM operation, since it has lower peak current and consequently lower output voltage spikes. According to [15], minimum L m can be designed for the minimum output voltage, which is 15V, as follow:…”

“…However, leakage inductance and saturated inductance still affect the boundary lines and a minimum load is required to maintain the regulation. Further efforts have been devoted in [13][14][15][16][17][18] to mitigate the cross regulation, where the need for multiple linear regulators at high load current and high frequency would deteriorate the efficiency and increase the control complexity.…”