This paper first summarizes the working principle and advantages and disadvantages of cascaded H-bridge, NPC and FC multi-level inverters, and the seven levels are simulated as examples have verified the characteristics of devices switching frequency, device voltage stress, output harmonic content. . The working principle and control strategy of the tight multi-level inverter is then studied. The main research content includes main circuit topologies, operation principles, control policies, modulation policies, etc., and conducts the number of devices in various topologies. Incident summary, forming mathematical expressions. The loss model of traditional two-level, diode clamp three, tight seven-level inverter is established, respectively, calculated the size of the loss value at a switching frequency of 10 kHz, 20 kHz and 50 kHz. Through the control mode of the voltage outer loop current, the simulation model of single-phase tight seven level inverter in the island is established. Finally, the single-phase tight seven-level inverter is established when the grid is operated. Simulation model.
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After the study of this article, it is obtained by following:
(1) The electromagnetic interference of the traditional two-level inverter is large, the DU / DT is large, the equipment is large, the switching frequency is high, the inverter is low, and it is not suitable for high pressure systems. It can be effective in using multi-level inverters. solve these problems.
(2) The control of the H-bridge multi-level inverter is relatively simple, but the number of independent DC voltage sources is more; the NPC multi-level inverter is controlled simple, no additional independent DC power supply, but there is more Quantity clamping diode; FC multi-level inverter's switch status combination, more flexible, more complicated, requires problems such as flying cross-capacitor voltage imbalance.
(3) Since the number of devices of the tight seven-level inverter is greater than the two levels and three levels, the total conduction loss of the power device is large. When the switching frequency is low, the conduction loss is the main loss, so the loss of the tight seven-level inverter is large, and the advantage is not obvious. However, as the switching frequency increases, the switching loss becomes a major loss, and the loss of the tight seven-level inverter is the smallest, and the advantage is obvious.
(4) Compared with the traditional multi-level inverter, the number of devices used in the tight multi-level inverter is the least, the switch status is unique, the control is simple, and the device is small.
(5) The control strategy of the voltage outer ring current inner ring is used to operate at a single-phase tight seven-level inverter, which can output voltage and frequencies in accordance with a given voltage and frequency reference value; The seven-level inverter is simultaneously simulated, which proves its feasibility and reliability when it is grunnet.
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1.1 Next Work Outlook
This paper achieves a certain results by learning existing seven-level inverters and new tight seven-level inverters. However, there are still many work to be further studied due to limited time and the author level. Specific description is as follows:
(1) Learning and simulation of traditional multi-level inverters simulates the simulation of current single closing loop in part, so it can only learn the number of devices, device withstand voltage, and device switching frequency. At the same time, since the flying across capacitor inverter cannot be controlled by conventional carrier laminated mode, it is possible to further study the control method of improving the type carrier laminated method or the learning space voltage vector control, and is used to control the flying cross-capacitor inverter.
(2) The more the number of inverter levels, the smaller the output harmonic content, the smaller the filter inductance required, and the smaller the loss caused by the filter inductance. Therefore, in the loss model, the loss of filtering inductance can also be established. This can more highlight the efficiency advantage of the multi-level inverter. At the same time, when the loss is compared, the loss model of other seven level inverters can be also established to compare the tight seven-level inverter.
(3) In the current simulation, the model is only established to establish a direct source as an ideal voltage source and access to the rectifier bridge, and the model when the tight seven-level inverter is connected to the photovoltaic system should be used to apply it to Photovoltaic grid system. , Reading the full text, the technology area
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