I. Overview
“An AC/DC hybrid power grid combines both AC and DC transmission and distribution systems, making it easier to integrate renewable energy sources such as wind and solar power into the electrical grid. By connecting AC and DC systems through power electronics devices, such as converters, power can be transferred seamlessly between the two systems. This hybrid approach can improve efficiency, reduce the cost of energy transmission, and provide greater system stability. The use of an AC/DC hybrid power grid can also facilitate the integration of energy storage systems, improving the reliability and resilience of the electrical grid and supporting the integration of renewable energy sources.”
Topics of AC-DC hybrid power grid control
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Interlinking inverter/converter control
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Unbalance Compensation Control
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Harmonic compensation
My research focus on developing AC-DC hybrid grid control algorithm based on power system analysis theory (Refer to AC-DC hybrid grid analysis ), linear/nonlinear control thory. From this research, I anticiapte the enhancement of power grid resillience, power system stability enhancement, low carbon emission (i.e., net zero).
AC-DC hybrid grid analysis ), linear/nonlinear control thory. From this research, I anticiapte the enhancement of power grid resillience, power system stability enhancement, low carbon emission (i.e., net zero).II. Interlinking Inverter/Converter Control
“Development of bi-directional power conversion control system technology based on renewable energy such as photovoltaic power generation and wind power generation requires efficient energy balance control technology in accordance with changes in energy supply sources, load conditions, and user-required power demands for stable power supply”
- Kwangki Kim
Topics of optimal control approaches to inverter/converter are as follows:
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Using the basis of Pontryagin maximum principle
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Model predictive control
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Lyapunov methods
Flowchart of the optimal trajectory generation using Pontryagin’s principle (Dissanayake and Ekneligoda, 2019)
Overall MPC controller for the DG inverter with E/KF denoting the exogenous Kalman filter and P/KF denoting the plant Kalman filter (Tan.et.al., 2013)
Block diagram of the proposed control scheme for traditional single-phase voltage-source grid-connected inverter based Lyapunov method (Zhang and Liu, 2020)
III. Unbalance Compensation Control
“Three-phase distribution feeders are umblanced because of conductor spacing and the unbalanced loads served. Because of this, the line-to-line voltages serving an induction motor will be unbalanced. When a motor operates with unbalanced voltages, it will overheat and draw unbalanced currents that may exceed the rated current of motor”
- Kersting, Distribution System Modeling and Analysis, Fourth Edition, 2018
Topics of load/voltage unbalance control are as follows:
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Unbalance compensation using power electronics
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Unbalnace compensation using droop control
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Unbalance compensation using STATCOM
Schematic diagram of voltage unbalance compensation using droop control on local level (Savaghebi.et.al., 2012)
STATCOM voltage regulation using separate regulation loops for positive and negative sequence components. (Hochgraf and Lasseter, 1998)
IV. Harmonic compensation
“The harmonics probelm in power system is not a new problem. (…) Since power system harmonic distortion is mainly caused by non-linear loads and power electronics used in the electrical power system, the presence of non-linear loads and the increasing number of distributed generation power systems in electrical grids contributes to changing the characteristics of voltage and waveforms in the power systems”
- Lu.et.al., Harmonic Balance Finite Element Method: Applications in Nonlinear Electromagnetics and Power Systems, Wiley & Sons, 2016
Topics of harmonic compensation are as follows:
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Harmonic compensation using converter control
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Harmonic compensation using filter control
Conventional harmonic compensation strategies (Maganti and Padhy, 2022)
(a) Current controlled converter with feed-forward harmonic voltage
(b) Voltage-controlled converter with feed-forward harmonic current
(c) Voltage-controlled converter with harmonic voltage feedback
