Differential Equation Model Computation Of The Pwm Dc/Ac Circuit And The Ac Steady-state Characteristics Analysis

The new power system into some new element including new energy power generation、 DC transmission project、flexible electricity load and so on, these newly emerging industries combination of the traditional power system mainly depends on the power conversion technologies. Rapid development of the high power gate turn-off switch prompt power conversion Core technology-SPWM inverter also becoming increasingly high-performance, analysis of the SPWM inverter work process of the physical will provide a strong theoretical basis for design and manufacturing、research of control methods、comprehensive evaluation.The foreign and domestic research of the working principle and mathematical model of the SPWM inverter are built on specific research objectives and requirements, functionally equivalent mathematical models tend to ignore some of the physical phenomena in the modeling process, leading to the existence of one-sidedness and limitations of the analysis results. Differential equation solver should be able to reflect the physical nature of the circuit analysis methods, but the initial value which difficult to determine become obstacles when it applications in power electronics. This paper inspired by the role of the diode freewheeling in SPWM inverter circuit, proposed a differential equation modeling approach of SPWM inverter circuit, then get the ac steady-state physical characteristics of circuit.SPWM theory is based on inertia theorem which require a higher DC voltage、have large switching losses and low DC voltage utilization, on this basis, the physical process of the inverter circuit is divided into two stages:First, control current that flow through the IGBT is based on target conditions by controlling starting and the pulse width of the SPWM; Second, feedback current that flow through the diode is utilized back-emf of inductor stored energy, it has constituted a continuous ac current. The inverter circuit under SPWM series pulse control presented the dynamic characteristics of repetitive transition process. This paper mapped circuit structure change to power source change in a conventional port circuit, has been steady state current form of the repetitive transition process by the methods of classical differential equation solver, used Overlay items to solve the problem that initial value is difficulty to determine in series of differential equation solver. On the basis of analysis of control current pulse and the phasor diagram of power frequency component under four typical state which including rectifier, inverter, absorb reactive, generate reactive.The paper establish a differential equation steady-state model of the SWPM inverter circuit by considering diode continued to the DC side, using the superposition of the transition process to solve the problem that transition process circuit can not be used differential equation to solve. Finally, we get the power frequency steady-state components and operating characteristics in inverter circuit output current, provides a new theoretical basis for design, manufacture, study of control method.