Jean-Claude Vannier

An optimization-based control strategy for modular multilevel converters: Design and implementation

In this paper we present an optimization-based procedure for designing a reference circulating current which stabilizes the internal dynamics of a modular multilevel converter. This procedure relies on unconstrained convex optimization and it takes into account conflicting performance requirements such as reducing the oscillating components of circulating current and arm voltages. Tracking of such a reference signal is ensured by a robust tracking controller with gains chosen in order to attenuate the measurement noise. Since we were interested in implementation of the control algorithm by using a digital simulator, the design procedure is carried out in the discrete-time domain. Effectiveness of the proposed strategy is confirmed on a prototype of three-phase modular multilevel converter with five sub-modules per arm and RL load.

Wound-rotor synchronous machine dq modeling with saturation for transient analysis

In this paper, a nonlinear dq model is proposed for transient simulations of a salient-pole wound-rotor synchronous machine. Despite the nonlinearity between the flux linkage and the current, it is shown, thanks to a validation based on finite element simulations, that the new model is efficient for saturated transient state of the machine. This method allows obtaining more accurate results than classical linear dq model based on equivalent circuits or inductance matrices. This model is also more convenient than the linear dq model because it is more closely related to a physical model of the machine. Finally, it is far easier and faster to use than the finite element model in simulation and control.

An HVDC experimental platform with MMC and two-level VSC in the back-to-back configuration

In this paper we present the realisation of an HVDC experimental platform with modular multilevel converter and two-level voltage source converter. Local control strategies for both converters are outlined in detail. The experimental platform is configured in such a way that the power-flow is controlled by the modular multilevel converter, while the DC voltage is regulated by the two-level voltage source converter. Local control algorithms are implemented by using OPAL-RT and dSpace platforms for rapid control prototyping. Experimental verification is provided.

Electromagnetic analysis of a wound-field generator with flux-barrier rotor for AC generator sets

This paper proposes a synchronous-reluctance rotor structure for stand-alone power generators. The structure under analysis includes flux-barriers in order to improve saliency, leading to a reduction of the excitation field needed. Different design aspects like the number of barriers and the shape of the poles are discussed. The steady-state performances of the machine and transient parameters are investigated. A comparison with a conventional generator is presented to highlight the benefits and limitations of this rotor structure.

Local and primary controls of a multi-terminal HVDC grid in an experimental setup

This paper focuses on the experimental implementation of local and primary controls for MT-HVDC in a real test bench (Pnom = 6 kW). A local control with two different time scales, one for the current and the other for the voltage, and primary control (droop control), which is responsible to vary the reference voltage when a disturbance appears in the network, are addressed in this paper.

A new control for modular multilevel converters and their use as DC circuit breaker

This paper presents a new modulation for modular multilevel converters (MMC) based on a simple idea, which is very easy to implement. It consists of playing with the relative behaviour of each phase in order to obtain the desired AC voltage. This method also assures that the voltage capacitor in each sub-module remains constant. Moreover, this converter allows the operation of the system under unbalanced conditions, and it can be used intrinsically as a DC circuit-breaker (DC-CB) without the need for additional power electronics and control if full bridge sub-modules are used.

A digital control algorithm for modular multilevel converters

We present a method for designing a stabilizing reference circulating current for modular multilevel converters. To this end, an optimization problem is formulated. This optimization problem takes into account conflicting control requirements such as reducing the oscillating component of the circulating current as well as the oscillating component of the arm voltages. Tracking of the obtained reference signal is ensured by a robust controller with gains chosen in order to attenuate the measurement noise. The control synthesis is carried out in the discrete-time domain. Such an approach yields simpler realtime implementation of the control algorithm. Performances of the proposed method are verified on a grid-connected prototype of modular multilevel converter.