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This tutorial provides a comprehensive overview of the challenges and solutions for protection in DC microgrids. DC microgrids present unique protection requirements that differ fundamentally from traditional AC systems, including non-standardized fault characteristics, fast fault currents, and the absence of natural zero-crossings for conventional protection coordination. Key topics include the short-circuit behavior of power electronic converters, grounding schemes, the application of solid-state circuit breakers, and measurements from short-circuit tests, providing participants with both theoretical understanding and practical industrial insights.

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This presentation will focus on the industrial implementation of DC technology within the new power system, sharing practical insights from Taikai's self-developed all-DC demonstration project in its smart park. It will highlight a data center solution integrating photovoltaics, storage, DC power, and flexible resources based on silicon carbide solid-state transformers, and elaborate on the cross-scenario application value of source-grid-load-storage integrated DC microgrids from the perspective of direct green power connection.

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As large-capacity power electronic interface, HVDC systems are increasingly expected to act as active parts of the power grid, rather than just passive connections for transmitting electricity. This presentation aims to offer a way to improve and make use of the ability of HVDC systems to support the power grid. The focus will be on new converter designs, control methods, and ways to integrate these systems so that HVDC can actively help keep the power grid stable and resilient.

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With the rapid development of new power systems, the integration of large-scale renewable energy and MMC-HVDC transmission into receiving-end power grids has become a defining trend in China. This presentation investigates the active frequency support control methods for large-scale renewable energy MMC-HVDC systems. It systematically analyzes the factors limiting frequency support capabilities, focusing on both the energy sources available (such as sending-end power, energy storage, and submodule capacitance) and the energy transmission pathways (overload capability of DC converters). The efficacy of frequency support is quantified considering technical constraints, such as inertia emulation duration and power margin. A comparative study of phase-locked loop (PLL) and virtual synchronous control strategies is presented, revealing that while virtual synchronous control offers quicker frequency response, the robustness of PLL makes it more adaptable to practical grid conditions. Furthermore, two main frequency signal transmission strategies (communication based and DC voltage based) are evaluated. Results indicate that communication based approaches provide greater flexibility and stability, with minimal frequency support degradation due to communication delays, which can be compensated by energy management measures. The proposed control and transmission strategies have been validated through simulation, demonstrating their effectiveness in enhancing the frequency stability of receiving-end power grids dominated by renewable energy and MMC-HVDC systems.

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The transition from a predominantly fossil fuel-based power generation towards renewable power sources, predominantly wind turbines and photovoltaic systems, inevitably leads towards an energy supply system that greatly depends on power electronics to feed the energy in the electrical grid. As all power electronic driven systems are intrinsically DC sources or loads, DC transmission and distribution systems become evident, not only because it is more efficient and cost effective, but also increases the ampacity of cables. Similar to AC distribution grids, which are configured in single- or three-phase systems, the DC distribution grids can be configured in monopole or bipolar structures. Compared to monopole systems, bipolar DC distribution grids are with numerous benefits, e.g., multiple available voltage levels and resilience of power delivery in case of a wire failure. This tutorial will present recent advancements in power conversion technologies for bipolar LVDC and MVDC distribution systems. Several novel converter topologies of multi-level AC-DC and DC-DC converters for LVDC and MVDC applications will be addressed, which are inherently capable of bipolar operation. These topologies are based on the concept of topological integration of voltage balancers, which are required individually in classic approaches for maintaining voltage balance of bipolar DC grids. This is exploited by provision of zero-sequence current path via grid interface transformers, which are designed intrinsically tolerant of DC winding current. These innovations equip converter stations with critical ancillary functionalities without sacrificing footprint or incurring extra hardware costs.

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Switched-capacitor Converter (SC) belongs to a branch of power electronics converters, which comprises capacitors and switches without the participation of inductors. In the first part, a family of switched capacitors is introduced, featuring simple circuit, interleaved operation, continuous input current, and systematic expandability, suitable for renewable power conversion from low voltage to high voltage, for connecting battery to high-voltage DC to perform charging and discharging, and also for micro-grid operation with distributed DC sources, batteries, and loads. The circuit can be implemented in the form of discrete circuit for high-power applications or in the form of integrated circuit for low-power applications. In the second part, a new family of Hybrid Boost Converter (HBC) is introduced on top of the first part, which features a symmetrical configuration, low component voltage rating, small output voltage ripple, and expandable structure. The topology integrates inductive switching cores of various functionalities and control strategies with Bipolar Voltage Multiplier (BVM) to form the new HBC including the Basic, Symmetrical, Isolated, and Tapped-inductor collections. Additionally, all of the collections can be extended for bidirectional power delivery, 3D structure for high power delivery, and half-bridge micro-inverter configuration for DC/AC applications. The proposed HBC family is suitable in DC Micro-grid system such as fossil fuel cell energy conversion, front-end photovoltaic energy system, and energy storage systems.

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The rapid development of Solid-State Transformers (SST) enables a future for microgrids that features the connection of various sources, loads, and storage elements to a common MVDC bus. The simulation of such systems presents various challenges due to their growing complexity caused by the large number of connected power converters and the diversification of sources and loads. Quick benchmarking in booming MVDC areas requires simulation models that feature superior speed with a dynamic response that fits real hardware. This tutorial provides an accessible overview of MVDC distribution grids and the system-level modelling approach used to simulate them. Starting from DC grid fundamentals and emerging standards, it introduces the concept of average models for elementary SST cells built with controlled current/voltage sources embodying the dynamic behaviour of real SST systems. Modular configurations and their implications on the DC bus are discussed, and representative simulation examples illustrate the approach in practical MVDC scenarios. The presentation is supported by industrial experience and academic insight. Outline: 1) Introduction to MVDC grids: DC grid fundamentals: topology, strengths, and typical disturbances, Overview of emerging DC standards; 2) System-level modelling of SST for MVDC: Average model of an elementary SST cell, Paralleling and modularity of SSTs, Modelling of the DC bus and peripheral elements (sources, loads, storage); 3) Simulation examples: Walkthrough of a representative MVDC grid model for renewable energy systems, Discussion of dynamic responses and failure scenarios; 4) Conclusions and outlook: Prospects for MVDC grids and open discussion.

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In microgrids, master-slave control strategy is commonly used. However, it is only suitable for islanded system with small load capacity and large power supply. The peer control strategy will lead to power angle and frequency stability problems particularly in an ac microgrid. To deal with these drawbacks and improve the operational stability of microgrids, a synchronous current source equivalence control technique is proposed. This novel control strategy can convert an AC system with multiple converters into a DC-equivalent form. In this tutorial, the control principle, control architecture, and engineering implementation will be addressed in detail. Based on a fixed frequency, the method enables power sharing among distributed generators and fast response to load fluctuations. Its prominent simple control logic and strong adaptability, makes it suitable for both medium-voltage microgrids and low-voltage microgrid scenarios.