A Structural-Algorithmic and Parametric Synthesis of Single-Phase Voltage Source Inverters for Increased Power Capacity

The recent interest of developers of new technology in studying a structural and algorithmic synthesis (SAS) of voltage source inverters (VSI) for solar power plants (SPP) is stemming from a growing need to solve problems in connection with the revealed new possibilities of converting energy flow (from DC to AC) with better energy efficiency by reducing the depth of its pulse modulation. This problem is solved by using more rational structural and algorithmic solutions. It is shown that for SPPs for a capacity of about 1 MW and more, it is more expedient to construct inverters based on the energy flow multichannel conversion principle. Given a limited power capacity of the transistor components, the application of this principle allows the problem to be solved in fact without using an output filter. The output voltage waveform is shaped using the energy flow pulse-amplitude modulation (PAM), and its M parts are summed in the output circuit by out using M winding transfilters (M-TF). The proposed method for carrying out combined SAS of single-phase voltage source inverters with multichannel conversion is considered, which consists in using an N-level single-phase VSI (N-SPVSI) in each of the M channels with the voltage levels optimized in terms of the minimum total harmonic distortion (THD). The resulting voltage of this class of single-phase inverters, designated as MxN-SPVSI, is formed by the corresponding phase shift of the channel voltages followed by summing the channel currents by M-TF. It is shown that the resulting output voltage levels are also close to their values optimized with respect to the minimum of the THD indicator. The results from a comparative analysis of two options — a single-channel 8-level inverter and a four-channel 8-level inverter are given. For the second option, only one intermediate voltage tap in the solar battery is required (instead of seven taps in the first option) along with modern transistor components that are available for practical implementation. In both options, the THD value less than 5% is obtained with almost no need of using an output filter. The presented results provide a certain information and methodological support for system designing of single-phase voltage source inverters as applied to the specific features of solar power plants. Three-phase inverters can be built on the basis of three single-phase inverters with galvanic isolation of the power sources for each phase.