Industrial session: Hardware-in-the-loop demonstration of non-selective protection systems for meshed HVDC grids

FRIDAY 11 SEPTEMBER 2020 | 10:15 – 12:05

Summary:

This session shows the results of a Hardware-in-the-loop demonstration of non-selective protection systems for meshed HVDC grids which was performed within PROMOTioN Project.

The objective of the WP9 of PROMOTioN project is to demonstrate operation of the DC grid protection systems developed in the project using hardware in the loop real-time methods. We integrate results from DC Circuit Breaker (DCCB) modelling and DC protection development including hardware prototype of relay and demonstration of DC Grid protection system interoperability. A plurality of protection methods (or strategies) are tested, to reflect main results of previous studies. Non-selective fault clearing strategies demonstration tests are carried out at the SuperGrid Institute (France), including Converter Breaker Strategy (CBS) and Full-Bridge MMC-based Strategy (FBS).

The specific objectives are:

• To integrate DCCB models, IEDs prototype and protection strategies in real-time simulation environments;
• To develop DC grid benchmark models and test procedures for protection system testing;
• To demonstrate protection system performance using hardware in the loop real-time testing;
• To demonstrate primary and back-up DC Grid protection and system level consequences of protection failure;
• Demonstrate equipment interoperability through the implementation of industrial communication protocol for protection relays, like IEC 61850 standard;
• To demonstrate DC grid restoration performance after protection process thanks to a DC grid control (station and central supervisors) implemented in IEDs (Hardware-In-the-Loop) or into the simulation (Software-In-the-Loop).

The presentation is split into three main parts: an introduction on non-selective fault clearing based strategies for Multi-Terminal DC (MTDC) grids; a technical description of the setup including hardware, software and methodology and finally the Hardware-In-the-Loop demonstration itself including video sequences.

The non-selective protection strategies are presented in order to understand differences with full-selective protection strategies, advantages and disadvantages, particularities, way of working during primary sequence or in case of a protection component failure, i.e. back-up sequences. After this general introduction, a focus is done on the two strategies implemented in this demonstration. The first one is the Converter Breaker Strategy, based on mechanical DC Circuit Breakers at the converter output and able to quickly open the circuit while more line mechanical DCCBs driven by an appropriate algorithm isolate the faulty line. Converter and breakers are all synchronised in order to restore DC voltage and power flow as quickly as possible. The second one is a non-selective based fault clearing strategy employing Full-Bridge MMC converters with fault current control capability. Full-bridge MMC control includes a specific protection algorithm able to rapidly reduce to zero the faulty current at the converter. Line mechanical DCCBs with reduced voltage and breaking current capabilities are opened by a faulty line identification algorithm.

The demonstration implements two test setups, one for each strategy. In addition to the protection strategy validation itself, each experiments has specific objectives. For the Converter Breaker Strategy, the goal is to implement a control and protection supervisor architecture in real controllers, communicating via the IEC 61850 standard protocol. The supervisors are able to start-up the MTDC and to manage voltage and power restoration. Standard IEC61850 is a guarantee of interoperability. For Full-Bridge MMC-based Strategy, the goal is to run in real-time a MTDC grid model, FB MMC control and a specific protection strategy designed and developed by colleagues from RWTH Aachen University. In particular, the protection relay algorithms, first implemented on the real-time simulation tool by Rapid Control Prototyping from a Matlab-Simulink model, are transcript on real IEDs. Communication between real-time simulation and IEDs is designed and added to the initial setup. The FB MMC-based strategy is then validated in this new Hardware-in-the-Loop setup.

Some parts of the setup are common to the two demonstrations and are presented in details:

• the 4-terminals MTDC network;
• relays and supervisor (CBS only) are implemented in Raspberry PI-based IED;
• Communication between real-time simulation and IEDs is based on IEC61850;
• Real-time target and tools.

The Converter Breaker Strategy setup description is focused on:

• the supervisor design and implementation;
• the controller and a communication architecture between the real-time target and 16 IEDs (relays and supervisor);
• the communication IEC61850 implementation.

The Full-Bridge MMC-based protection Strategy setup description is focused on:

• Full-Bridge MMC model;
• the porting of the protection relays algorithm from the real-time simulation to the IEDs;
• the communication IEC61850 implementation.

The last part of the presentation deals with the live demonstration. Pedagogic explanations and video sequences will try to restore the different elements of the validation: supervised start-up of the MTDC, fault-clearing strategies, and voltage and power restoration. To highlights all important parts, video sequences are showing voltages and currents inside the MTDC grid, active and reactive power exchange with the AC areas at each station, breakers and converter status, communication streaming between real-time simulation, relays, station supervisors and central supervisor. In both demonstrations, strategies are validated, showing fault clearing and restoration capabilities in a period perfectly suited to the operation of the networks. Finally, the demonstrations meet the initial objectives of the project: precise component models, realistic MTDC grid and converter controls, implementation in real IEDs, industrial communication protocol fulfilling the interoperability requirements and real-time validation of non-selective protection strategies.

Chairman: Laurent Chédot, SuperGrid Institute, France