The study of five-level inverters with the various PWM
The energy indicators of multilevel voltage converters are analyzed. The relevance of the research is indicated by the increasing demands of technological processes for the economic use of electric energy, the reduction in power consumed by semiconductor converters, and also to the level of regulated reactive power. The converter considered is a five-level voltage inverter. As the topology of the converter, the structure of the inverter on H-bridges is considered. The article presents two-stage three-phase circuits with the connection of inverter cells to wye. Possible states of electronic keys and their corresponding operating modes are described. The voltage of constant voltage sources is 535 V. In the article algorithms for the formation of pulse-width modulation (PWM) are considered: Phase Opposition Disposition, Alternative Phase Opposition Disposition and Hybrid methods with zero sequence sinusoidal shape of the modulate voltage or with triangular shape of the modulate voltage. As a criterion for evaluating the quality of the inverter's output voltage, total harmonic distortion and line-to-line voltage were adopted. A harmonic voltage spectrum is developed for various control methods of the converter. Possible ways of reducing the harmonic coefficient, as well as increasing the amplitude modulation factor, are shown, by using various methods of forming the pulse-width modulation.
Analysis of power losses in multilevel pulse-width modulation inverters
The paper describes the types of multilevel pulse-width modulation, as well as methods for obtaining control signals for the inverter power switches for each of the types. The dependence of the harmonic composition of the output voltage of the inverter on the number of levels and the switching frequency of the keys of each level is analyzed. By modeling, the dependences of the transistor junction temperature on the number of voltage levels, switching frequency and load power are determined. The power switching system of an inverter with phase-shifted pulse-width modulation in high-frequency mode is analyzed, the dependence of switching losses on inductance is investigated. The ways of solving or improving the control systems of the conductivity losses of the converter flowing through the primary winding of a high-frequency transformer during the free-running period are formulated. The importance of this direction for the technological development of the economy, where efficiency improvements can lower individual utility bills, create jobs, and help stabilize electricity prices and volatility is shown. The most important stage of inverter design is called structural synthesis stage – the choice of topology and modulation algorithm that will ensure the greatest efficiency of the device. In addition, since the efficiency and reliability of inverters depend on the efficiency and reliability of secondary electricity consumers, the task of optimizing inverter circuits is a cornerstone for the effective development of technology and economy. The maximum dynamic power loss at a PWM frequency of 1 kHz reaches only 80 watts compared to the static power loss value of 800 watts
Numerical tools applied to power reactor noise analysis
In order to be able to calculate the space- and frequency-dependent neutron noise in real inhomogeneous systems in two-group theory, a code was developed for the calculation of the Green's function (dynamic transfer function) of such systems. This paper reports on the development as well as the test and application of the numerical tools employed. The code that was developed yields the space-dependence of the fluctuations of the neutron flux induced by fluctuating properties of the medium in the two-group diffusion approximation and in a two-dimensional representation of heterogeneous systems, for both critical systems and non-critical systems with an external source. Some applications of these tools to power reactor noise analysis are then described, including the unfolding of the parameters of the noise source from the induced neutron noise, measured at a few discrete locations throughout the core. Other concrete applications concern the study of the space-dependence of the Decay Ratio in Boiling Water Reactors, the noise-based estimation of the Moderator Temperature Coefficient of reactivity in Pressurized Water Reactors, the modeling of the beam- and shell-mode core-barrel vibrations in Pressurized Water Reactors, and the investigation of the validity of the point-kinetic approximation in subcritical systems driven by an external source. In most of these applications, calculations performed using the code are compared with at-power plant measurements. Power reactor noise analysis applications of the above type, i.e. core monitoring without disturbing plant operation, is of particular interest in the framework of the extensive program of power uprates worldwide.