Lampros Papangelis

On the modeling of MMC for use in large scale dynamic simulations

This paper focuses on simplified models of the Modular Multilevel Converter suitable for large-scale dynamic studies, in particular simulations under the phasor approximation. Compared to the existing literature, this paper does not a priori adopt the modeling approach followed for the original two-level or three-level Voltage Source Converter. On the contrary, a model is derived following a physical analysis that preserves its average internal dynamic behavior. An equivalent control structure is proposed and various alternatives are highlighted. The proposed model with its controllers has been implemented in a phasor simulation software and its response has been validated against a detailed Electromagnetic Transient model. Finally, an illustrative example is presented with the application of the proposed model on a large grid consisting of AC areas interconnected with a multi-terminal DC grid.

Coordinated Supervisory Control of Multi-Terminal HVDC Grids: A Model Predictive Control Approach

A coordinated supervisory control scheme for future multi-terminal high-voltage direct-current (HVDC) grids is proposed. The purpose is to supervise the grid and take appropriate actions to ensure power balance and prevent or remove voltage or current limit violations. First, using DC current and voltage measurements, the power references of the various Voltage Source Converters are updated according to participation factors. Next, the setpoints of the converters are smoothly adjusted to track those power references, while avoiding or correcting limit violations. The latter function resorts to model predictive control and a sensitivity model of the system. The efficiency of the proposed scheme has been tested through dynamic simulations of a five-terminal HVDC grid interconnecting two asynchronous AC areas and a wind farm.

Local control of AC/DC converters for frequency support between asynchronous AC areas

This paper proposes a novel control scheme for frequency support among asynchronous AC areas through HVDC grids. It is based on local controllers, each acting on a voltage source converter, using locally available measurements only, and supporting frequency of the adjacent AC area after a significant disturbance. The controller is combined with the existing DC voltage droop technique and is inspired of Model Predictive Control, taking into account various constraints. The coordination of the proposed control scheme with the existing secondary frequency control of an AC area is also discussed. Examples obtained from a test system with a five-terminal DC network connecting two asynchronous areas demonstrate the effectiveness of the proposed control scheme.

Modular modelling of combined AC and DC systems in dynamic simulations

A formulation is proposed in which an AC-DC system is modeled as a combination of AC grids, DC grids, injectors, AC two-ports and AC/DC converters, respectively. This modular modelling facilitates the dynamic simulation of future complex AC/DC systems. Furthermore, it can be exploited by the solver, which performs less operations on components with lower dynamic activity, and offers parallel processing of the time simulation. This approach is illustrated on a test system in which a multi-terminal DC grid connects two asynchronous AC systems, allows frequency support between them, and acts as emergency control against AC voltage instability.

A dynamic simulation approach to identify additional reactive reserves against long-term voltage instability

A simple method is proposed to identify additional reactive reserves enabling to counteract long-term voltage instability after a large disturbance. In contrast to the many references based on power flow calculations, the method resorts to dynamic simulation. The post-disturbance system evolution is simulated in the presence of time-varying shunt susceptances with specified rate of change. This allows to deal with dynamic issues such as the required speed of the additional reactive power sources, or the onset of unstable electromechanical oscillations. Furthermore, a compromise is sought between the speed of action and the volume of additional compensation. The method is demonstrated on a detailed model of the Nordic test system.