Guillaume Gateau

Flying Capacitor MultiCell Converters with Reduced Stored Energy

Flying capacitor multilevel converters (FC) have been introduced in the 90s and have given a certain number of industrial converters. Most of these products use the three-cell four-level configuration, then come the two-cell and to a lesser extent the four-cell, but although the principle can be extended to any number of cells there is not a single application using five cells or more. There is however a need for converter with five semiconductors in series or more, but today the number, size and cost of the flying capacitors limits the use of this topology to four-cell maximum. In a first section, modified topologies with less capacitors but producing the same waveforms as FC converters will be presented and classified. In a second section, topologies with a lower component count and providing a priori a lower harmonic performance are listed and compared to the previous topologies.

Stacked multicell converter (SMC): reconstruction of flying capacitor voltages

We present in this paper a new method for the observation of the flying capacitor voltages dedicated to stacked multicell converters (SMC). Unlike the imbricated-cell converter, the new SMC topology allows increasing the input voltage level while decreasing the energy stored in the converter. This consists of a hybrid association of commutation cells, which enables to share the voltage constraint on several switches. During normal operation, the flying capacitor voltages have to be kept constant by the control strategy. Due to high voltage/high power applications, it is difficult and expensive to measure the flying capacitor voltages. Therefore, a new method has been developed to estimate those voltages. After an introduction and a brief reminder on the SMC topology, we will present a new strategy to estimate the capacitor voltages based on the determination of an image of those ones regarding the control signals and the chopped voltage. The influence of the measurement noise on our new technique has also been studied carefully and appropriate strategies have been developed. The last part will be devoted to conclusions and perspectives

Neutral point control in multi level converters applying novel modulation schemes

This paper investigates the behavior of the neutral point (NP) voltage and current for generalized multilevel converters introduced in recent years (ANPC: active neutral point clamped converter, SMC: stacked multicell converter). The unified approach introduced in this paper shows that all considered topologies have the same NP current properties when applying standard modulation schemes. A simple graphical representation is used to explain how the NP currents of the different phases combine in a multiphase converter. New modulation schemes are proposed and their impact in the NP current is demonstrated. The current that can be injected when needed is maximized. A new NP control scheme without using the common mode (CM) voltage is introduced. Experiments confirm that the NP voltage can be controlled by the dynamic application of the different modulation types, even if there is a static CM applied to the output voltage. A 5-level SMC converter is used for the experimental verification of the NP current characteristics and the new NP control strategy.

Stacked multicell converter (SMC): estimation of flying capacitor voltages

This paper introduces a new estimation technique of the flying capacitor voltages dedicated to stacked multicell converters (SMC). Those voltages have to remain constant during the operation of the converter so as to ensure the proper repartition of the voltage constraints over the commutation cells. This objective can be achieved by implementing an active control of the capacitor voltages, which requires the knowledge of those quantities at each time. However it is both difficult and expensive to measure them because of the high voltage/power range of applications. Thus we move toward the development of an estimation of those quantities. After an introduction and a succinct reminder on the SMC topology, the first part describes the new strategy for the estimation of the capacitor voltages. It is based on a real-time simulation of the state-space model of the system. To prevent this emulator from drifting away, an update should be included in the estimation procedure by the use of an extra voltage measurement. The second main part is devoted to the influence of the current or the voltage sensing noise on our approach and the development of appropriate strategies to counter those phenomena

Stacked Multicell Converter: Sliding Mode Observation of Flying Capacitor Voltages

This paper introduces a new observation strategy of the flying capacitor voltages dedicated to stacked multicell converters (SMC). The proper operation of this particular converter relies on the equal repartition of the voltage constraints over the semiconductors. This objective is achieved providing the capacitor voltages remain constant. The intermediate voltages can be actively controlled so as to ensure this requirement but this procedure necessitates the knowledge of those quantities at each time. It is both difficult and expensive to measure them considering the voltage levels, which motivates the actual research scope. The solution presented in this paper is based on a sliding mode observation of the flying capacitor voltages by means of phase current measurements

Stacked Multicell Converter: Digital Sliding Mode Observation of Flying Capacitor Voltages

This paper details the digital implementation of a new observation strategy of the flying capacitor voltages dedicated to stacked multicell converters (SMC). This particular topology relies on the use of flying capacitors so as to equally share the voltage constraint on several semiconductors and increase the number of output levels. However the SMC appropriate operation is guaranteed by the stability of the flying capacitor voltage levels and the current flow creates variations of those quantities. The idea is therefore to develop an accurate estimation technique that avoids the utilization of differential measurements and allows the active control of the intermediate voltages. The actual research scope thus focuses on the sliding mode observation of the flying capacitor voltages by means of phase current measurements. This paper does not describe the observability requirements as well as the observer design, but rather detail the algorithm digitizing and performances

Digital emulator and observer of multicell converter

This article presents the design of a digital real-time emulator dedicated to the simulation of four-level multicell converter. The design has been made using a new tool: the co-simulation. Co-simulation results are presented in this paper and an experimental setup has been realised on a FPGA1 in order to validate this new tool. In the final part, we present the test of an observation loop using this emulator.