Mauricio Espinoza

Model Predictive Control of Modular Multilevel Matrix Converter

This paper presents a new and simple Finite Control Set Model Predictive Control (FCS-MPC) strategy of the Modular Multilevel Matrix Converter (M3C). This converter is one of the direct AC/AC power converters suitable for medium-voltage high-power machine drives with regenerative capacity. One of the main feature of this converter is that does not need external dc-voltage supplies and thus, all capacitor voltages have to be regulated to the desired value. Therefore, this paper provides a cost function that considers error terms related to the output current and capacitor voltages. Moreover, a compensation input current is presented in order to improve the dynamics response of the capacitor voltage average value. Simulation results illustrate that the proposed algorithm is capable to achieving good performance, even in critical operation point of the M3C.

Control of Wind Energy Conversion Systems Based on the Modular Multilevel Matrix Converter

The nominal power of single wind energy conversion systems (WECS) has been steadily increasing, now reaching power ratings close to 10 MW. In the power conversion stage, medium-voltage power converters are replacing the conventional low-voltage back-to-back topology. Modular multilevel converters have appeared as a promising solution for multi-MW WECSs, due to their modularity and the capability to reach high nominal voltages. This paper discusses the application of the modular multilevel matrix converter to drive multi-MW WECSs. The modeling and control systems required for this application are extensively analyzed and discussed in this paper. The proposed control strategies enable decoupled operation of the converter, provide maximum power point tracking capability at the generator side, grid code compliance at the grid side (including low-voltage ride-through control) and good steady state and dynamic performance for balancing the capacitor voltages in all the clusters. Finally, the effectiveness of the proposed control strategy is validated using simulation and through experimental results obtained with a 27-power-cell prototype.

Improved control strategy of the modular multilevel converter for high power drive applications in low frequency operation

Modular Multilevel Converters (M2C) are considered an attractive solution for high power drives. However, its operation at low rotational speeds can produce undesired voltage fluctuations in the M2C capacitors. In this paper, two methodologies to improve the converter performance in this speed range are analysed and tested. The first strategy proposes the control of the inner converter currents combining a synchronous dq rotating frame and resonant controllers to improve the current tracking and to reduce the voltage fluctuations. The second strategy achieves the reduction of the voltage fluctuations by adjusting the DC Port voltage as a function of the machine frequency. Both methods are validated by simulation and experimental work, where a 18 cell M2C prototype is applied to drive an induction machine.

Modelling and control of the Modular Multilevel Matrix Converter and its application to Wind Energy Conversion Systems

In the last past years, some countries are enforcing stringent grid codes to regulate the connection of Wind Energy Conversion Systems (WECSs) to the electrical network, mainly because of the high penetration of electric power from this renewable source. Additionally, the trend of wind turbines has shown an ongoing power rating growth, reaching sizes up to 10 MW. Multilevel converters have appeared as a solution for large WECSs, due to its high reliability, controllability and the capability to reach high power ratings. This paper presents a control strategy for the application of the Modular Multilevel Matrix Converter in Multimegawatts Wind Turbines. Extensive computer simulations and a downscaled laboratory prototype, with twenty-seven power cells, are presented to validate the effectiveness of the proposed control system.

Closed loop vector control of the modular multilevel matrix converter for equal input-output operating frequencies

The Modular Multilevel Matrix Converter (M3 C) is an AC-to-AC Modular Multilevel Converter composed of H-Bridge Power Cells connected to flying capacitors. This converter has been proposed as a solution to high-power drive applications due to its characteristics such as high power quality, medium or high voltage operation and control flexibility. However, the energy balancing of this converter is complex when the Input Port has a frequency close to the Output Port frequency because large voltage fluctuations can appear in the flying capacitors. Consequently, this paper proposes a novel Closed-Loop Vector Control Strategy, which is implemented in dq synchronous frames, to allow the operation of the converter in a broad range of operating frequencies. Extensive discussion of the model and control of the M3C is presented. The effectiveness of the proposed Control Strategy is validated through simulations and experimental results obtained with a 27 power-cells prototype.

The application of the modular multilevel matrix converter in high-power wind turbines

The trend in wind turbines has shown an ongoing power rating growth, reaching sizes up to 10 MW. Multilevel converters have therefore become a favourable solution for Multi-MW Wind Energy Conversion Systems (WECSs), due to high efficiency, reliability, controllability and the ability to reach high power/voltage ratings. Moreover, stringent grid codes to regulate the connection of WECSs to the electrical networks have been developed in countries with a high penetration of wind energy. In this context, this paper introduces the novel application of the Modular Multilevel Matrix Converter for interfacing Multi-MW Wind Turbines to provide decoupled input-output regulation, variable speed operation and fulfilment of modern grid codes.

Active power oscillation elimination in 4-leg grid-connected converters under unbalanced network conditions

In this paper a new methodology to compensate double-frequency power oscillations in unbalanced 4-leg distribution networks is presented. The zero sequence components in the voltages and currents are used to provide an extra degree of freedom to compensate reactive and active power pulsations. A novel closed-loop algorithm for the compensation of fluctuations in the converter side, instead of the grid side is presented in this work. Simulation results are discussed, validating the proposed control system.

Modelling and control of the modular multilevel converter in back to back configuration for high power induction machine drives

Drives based on modular multilevel topologies are the next generation of high-power/voltage converters. In this paper, the Modular Multilevel Converter model is extended to the Back to Back scheme, allowing its control as an unique system, instead two separated converters. Additionally, the proposed control strategy is able to regulate the ac ports and to perform the voltage balancing in both converters by using circulating currents and common mode voltage, providing independence between the converters and the ac ports. Extensive computer simulation and a laboratory prototype of a Modular Multilevel Converter with eighteen power cells feeding an induction machine validate the effectiveness of the presented control algorithm.