Single phase grid connected converters suffer from the well-known pulsation of power at twice the fundamental frequency. This ripple affects the current in the three-phase AC system through the DC link voltage control, leading to inefficiencies and potential reliability concerns. An improved DC link voltage control algorithm, based on the small signal approach, is proposed in this paper, in order to ensure constant input power on the three-phase side despite the pulsating single-phase output power. This algorithm theoretically eliminates the twice ripple effect on 3ϕ quantities, optimising harmonic content and system performance. Simulation results validate the effectiveness of the method, with experimental validation planned for a same scale power conversion system. These results will be detailed in an extended version of this paper. Compared to conventional solutions, this approach significantly improves three-phase side ripple mitigation, increasing the performance and reliability of the power conversion system without the need for additional equipment.

The usage of an Auxiliary Resonant Commutated Pole (ARCP) circuit with an 11-level Cascaded H-Bridge (CHB) converter as an option for feeding high-power Wireless Power Transfer (WPT) track-pads in traction applications is proposed in this research. By utilizing a mathematical model to obtain the switching pulses of the ARCP circuit, a reduction in the conduction losses of the involved inductance can be achieved. Moreover, an optimization routine is developed to reduce the MOSFETs' root mean square current by finding each module's phase shift angles. The study uses the SAE J2954 standard to restrict the Electromagnetic Interference (EMI) in the frequency band between$400\ kHz$and$30\ MHz$. The success of the suggested technique is displayed by simulation results showing that it is possible to operate the CHB with Zero Voltage Switching in all modules of the power converter. Inductive Power Transfer applications applied in railways can benefit from this contribution due to the use of multilevel converters.

High Voltage Direct Current (HVDC) grids are becoming a preferred option for the expansion of the traditional electrical networks as a result of their potential economic, technical and environmental benefits. Developing HVDC grids includes the linking of existing HVDC buses which may be implemented with different voltage levels, different HVDC technology and various grounding schemes. Interconnecting these HVDC systems will require DC-DC converters to provide voltage matching, isolation and a means for splitting the HVDC grid into sub systems. This paper presents a modified trapezoidal operation of MMC-DC-DC converter, MTrMMC-DC-DC, with high semiconductor device utilization and lower device current rating in addition to an increase of converter’s energy density. Better utilization of the semiconductor devices results from conducting the current through the arms of the TrMMC-DC-DC converter continuously. The reduction of the energy storage requirements is achieved through careful design of the submodule (SM) capacitors and arm inductors to achieve resonance between the effective equivalent capacitor of each arm and the arm inductor at a frequency below twice the fundamental operating frequency. The circuit parameter design is validated for an 800MW, 400kV HVDC-based system through PLECS simulations.

Isolated DC/DC modular multilevel converters (MMC) consisting of two MMCs isolated by a transformer are one of the converter topologies being considered used for DC/DC conversion in HVDC transmission. Two level modulation can be used to obtain different voltage levels by inserting/bypassing a specific number of sub-modules (SM) in the converter circuit. However, it does not take into account the SM's voltage when elevation factors need to be readjusted, which results in either higher or lower output voltage than the reference. This paper proposes a finite control set model predictive control (FCS-MPC) for output voltage regulation to the reference value. A cost function comprising the output voltages is defined and a mathematical equation is formed to calculate the one step ahead value of output voltage. The number of SMs which minimize the cost function is applied to the converter circuit. Voltage balancing amongst the sub-module cells has been achieved by using a sorting algorithm. The performance of the proposed control strategy is evaluated and verified.

Hybrid Voltage Source Converters (VSC), that combine the conventional three-level VSCs and Modular Multilevel Chain-Links (CLs), offer a promising solution for future HVDC stations, achieving reduced footprint with respect to the MMC while maintaining high power quality and low loss. This paper introduces a new hybrid solution named `Parallel Connected Unfolding Bridge Modular Multilevel Converter' (PCUB) which uses a parallel connection of phases on the DC side and comprises of wave shaping Chain-Links and unfolding H-bridges. This paper presents the operating principle and basic mathematical model of the PCUB and also details an optimisation of the transformers turn ratio for the minimisation of the energy requirements in the CLs. PLECS simulation results for the proposed topology operating at 20kV DC - 11kV AC and 20MW are also presented to demonstrate its performance.

This paper presents a novel hybrid modular multilevel voltage source converter suitable for grid applications. The proposed converter retains the advantages of other modular multilevel topologies and can be made more compact making it attractive for offshore stations and other footprint critical applications like city in feeds. In this paper, the basic operating principle and design criteria for the converter implementation are presented. The submodule capacitor requirements which have significant influence on the size of a converter station are also evaluated and compared to the MMC. The performance of the converter is supported by simulation results from a representative medium voltage scaled demonstrator.

Tolerance and component aging can cause significant differences in the capacitance values of the submodules (SMs) in a modular multilevel converter (MMC). Depending on the modulation technique, capacitance mismatches may produce uneven switching transitions of the SMs, hence imbalances in the power losses that can lead to reliability problems. In this paper, a new algorithm that helps to achieve evenly distributed switching and conduction losses within the converter SMs is presented. The proposed algorithm is based on a modification of the common voltage balancing algorithms, balancing a weighted function of voltage and losses. Even distribution of power losses is achieved at the cost of slightly increasing the capacitor voltage ripples. The effectiveness of the strategy has been demonstrated by simulation results of a high-power grid-connected MMC.

This paper analyses the behaviour of grid connected modular multilevel converter, under pulsed load at the DC side. The goal is to achieve minimum AC power fluctuation despite high power fluctuation on the DC side. Pulsed load causes imbalances of cell capacitor voltages, and this effect is analytically described. The control methodology, together with an algorithm for capacitor voltage balancing is presented. The simulation proves the success of the algorithm in the majority of the cases, but its operation is dependant on the pulse position with respect to grid voltages. The limitations of the algorithm are analysed in detail.

Multilevel Converters are known to have many advantages for electricity network applications. In particular Cascaded H-Bridge Converters are attractive because of their inherent modularity and scalability. Predictive control for power converters is advantageous as a result of its applicability to discrete system and fast response. In this paper a novel control technique, named Modulated Model Predictive Control, is introduced with the aim to increase the performances of the Predictive control. The proposed controller is described in detail and validated through simulation and experimental testing, in comparison with Dead-Beat and Model Predictive Control.