In this paper a sliding mode observer is designed and applied to the Uniflex-PM structure in order to observe the capacitor voltages. The objective of the Uniflex-PM project is to develop advanced power conversion technique to meet future needs of electricity networks. Uniflex-PM can provide optimized connection of distributed energy resources, integration and management of energy storage, optimized utilization of the transmission/distribution infrastructure, a high quality of supply and coordinated control across the network. The strategic objectives are to secure a clean, sustainable & economic energy supply for the EU and a new modular power conversion architecture for universal applications. The main characteristics that make Uniflex-PM a unique choice for power system applications is the modular structure and the interleaved connection between phases at different ports. Each module comprises two H-bridges connected as an AC/DC converter and a DC/DC converter with a medium frequency transformer isolation. By having interleaved connection between phases, Uniflex-PM is able to operate under unbalanced conditions. In a two-port Uniflex-PM there are nine capacitors whose voltages, are needed in feedback loops of the system controller, which includes the voltage control loop and balancer. This means that nine voltage transducers are required. The use of so many transducers can make the system unreliable, thus it is desirable to observe the capacitor voltages instead of measuring them. The Sliding Mode Observer (SMO) via equivalent control approach has been selected to be applied to the Uniflex-PM because of its robustness against a class of uncertainties in system equations. Simulation results from SABER are used to demonstrate the use of this observer technique.
Smart power supply grids may be required to link future energy production and consumers.Multilevel converters are a building block for smart grids. There are several structures of multilevel converters, for example the Neutral Point Clamped (NPC), the Flying Capacitor Circuit and the Cascaded H-Bridge (CHB) converter. The modular structure of the CHB multilevel converter makes it one of the best options for smart grids. Using modular converter structures reduces production and maintenance costs.Implementation of efficient and fast controllers for multilevel converters requires accurate measurement of the voltages and currents for the system feedback loops. Knowledge of the DC link voltages is necessary to construct voltage control loops. In a typical CHB multilevel converter there are many DC links which means that a lot of voltage transducers maybe required.Voltage transducers at medium voltage are not easy to implement and add to system cost. This thesis presents an efficient way to observe the DC link voltages and hence eliminate the cost associated with voltage transducers. A "Sliding Mode Observer (SMO) using the Equivalent Control Method" has been chosen because of its robustness against system uncertainties.Simulation and practical work has been performed on a three-phase, three-cell multilevel converter to validate the use of this observer.ii
The Multicell converters introduced more than ten years ago. They are capable to handle higher voltage ratings with lower rating switches. Different active control strategies have been introduced to control the state variables of converter. In this paper a new online optimal controller based on the discrete nonlinear model of Multicell inverters will be presented. The optimal feedback will control the state variables in a very fast and efficient manner. The main idea is based on the "Tracking problem" of reference signals by state variables. Simulation results and the theoretical details will be presented in the next sections.
This paper presents considerations on the switching frequency and duty cycle and operating equations of softswitching BUCK chopper. These considerations are discussed and applied to selected soft-switching families such as ZVS-QRC, ZCS-QRC, ZVS-QSW-CV, ZCS-QSW-CC, ZVT-PWM and ZCT-PWM [l]. The limitations on switching frequency and duty cycle are derived in terms of: chopper input voltage (V,), chopper output current (IF), resonant elements values including (C, L,), voltage and current of: filter capacitor and reactor or initial values of capacitor and reactor ( VI, 4).
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