This paper proposes a new field bus protocol based on the IEEE 802.3 Ethernet standard. The protocol enables fast data exchange between the modules and synchronised control in the modules of modular power electronic systems. With increasing switching frequency, a highly accurate synchronisation of the different modules is a necessary requirement for a control bus. The proposed field bus protocol provides a stable and efficient scheme including a novel data frame structure and allows the realisation of a synchronisation accuracy of ±4 ns based on the 1 GBit Ethernet standard. For validation of the new protocol, a prototype system was developed and the measurement results are reported herein. The results show that the implementation satisfies the specifications. Finally, different use-cases and the achievable data rates for the given implementation were derived.

Excellent control performance is a prerequisite to operate compact modular multilevel converter (MMC) designs that employ very small module capacitance values. This paper presents a novel model predictive control (MPC) scheme featuring a linear and accurate prediction model to overcome the drawbacks of comparable control schemes. The MPC is based on a modulator that determines the switching states of the individual modules to guarantee scalability of the algorithm also for MMCs with a high number of modules. The control performance of the proposed MPC scheme is evaluated with simulations and compared to a classic cascaded PI-controller scheme.

Recently, modular multilevel conterters (MMC) are also considered for medium voltage (MV) applications, where the number of modules and the switching frequency are relatively low compared to high voltage (HV) applications. In this context, standard modulation methods can cause relatively large output voltage errors. This effect is amplified even more, if the value of the module capacitances is decreased to reduce cost and volume of the MMC. Large output voltage errors disturb the higher level closed loop control of the MMC significantly, such that control targets (e.g. keeping the circulating current zero) could not be met anymore. This paper analyses the output voltage error induced by the standard level shifted PWM method and proposes three approaches to reduce the error. All four methods are compared with respect to the error for different switching frequencies and arm currents. The effects on the closed loop performance of a current controller are investigated with time domain simulations.

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In this paper, a novel feedback controller concept for grid-connected Modular Multilevel Converters (MMC) is proposed. The controller is based on the Linear Quadratic Regulator (LQR) method and shows outstanding control performance since it is a multi-input multi-output (MIMO) controller. The proposed controller achieves efficient energy balancing control with high bandwidth, such that the required margin for the module capacitance value for dynamic control is reduced and an excellent transient behavior can be accomplished. Alternatively, compact MMC designs can be realized with a reduced capacitance value by sacrificing some transient performance. The implementation requires a relatively low computational effort, and the simple control structure enables a straightforward tuning and time-delay compensation.