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A Predictive Control Method for Modular Multilevel Inverter
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A modular multi-level, predictive control technology, applied in electrical components, output power conversion devices, AC power input into DC power output and other directions, can solve problems such as poor dynamic and static performance, and achieve adaptive performance Good, fixed switching frequency, fast tracking effect
Active Publication Date: 2017-07-21
SHANDONG UNIV
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[0004] The traditional control strategy of the modular multilevel converter is that the feedback signal is adjusted by PI adjustment or other adjustment methods and then sent to SPWM to generate the driving signal or other control strategies to realize the rectification or inverter function. The traditional modulation strategy is in the working process of the inverter. It needs a lot of calculations to meet the output requirements, so the system needs a long time and complex calculations to output the current and voltage waveforms that meet the requirements, so the dynamic and static performance of the traditional modulation method is not good
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Embodiment 1
[0079] (1) Topological analysis:
[0080] The topology and internal model of the modular multilevel converter are shown in the attached figure 1 , the present invention is suitable for modular multilevel converters, and has been verified on the system simulation of half-bridge module quantity n=4 by figure 1 It can be seen that (where i=a, b, c, I=A, B, C) Since there is an inductance L in the upper and lower bridge arms of each phase in the three phases arm So its single-phase equivalent circuit is as figure 2 Shown:
[0081] Therefore, the above formula can be transformed into: By transforming the three-phase voltage and current into the αβ coordinate system through 3-2, we can get
[0083] Since i(k+1) cannot be obtained by measurement, it needs to be predicted to obtain the value it should take in the next step. Here, it is approximated by using the Lagrange quadratic interpolation theorem: i(k+1)=3i( k)-3i(k-1)+i(k-2), therefore...
Embodiment 2
[0114] When n=6, there are 2n=12 sub-modules in each phase, since the number of sub-modules in each phase is always n=6, so there are seven combinations of the number of sub-modules in the upper and lower bridge arms of each phase: 6, 0; 5, 1; 4, 2; 3, 3; 2, 4; 1, 5; 0, 6; Let the capacitor voltage in the module be U c , then the phase output voltages in these seven cases are: 6U c , 4U c , 2U c , 0, -2U c 、-4U c 、-6U c ; By controlling these seven combinations, the output waveform can be sine wave. Let the DC bus voltage be U dc , so the MMC three-phase inverter has five output voltages for each phase: 0, And the three phases can output 7*7*7=343 voltage states in total.
[0115] Each of the upper and lower bridge arms has 6 sub-modules, and the capacitor voltage and current direction of each sub-module at a certain time. Assuming that it is calculated from the control strategy above, the upper bridge arm needs to invest in 2 sub-modules, and the lower bridge ar...
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Abstract
The invention discloses a prediction control method for a modularized multi-level inverter. According to the control method, prediction control is adopted on the basis of a traditional capacitance and voltage sequencing principle of various submodules, wherein the prediction control has the advantages of high tracking speed, small harmonics, fixed switching frequency and the like. According to a traditional modulation method, a sampling current needs to be transformed into a dq coordinate system and generates a modulation wave through a PI (proportional-integral) link, the modulation wave is compared with a triangular wave to form an SPWM (Sinusoidal Pulse Width Modulation) wave, and a large amount of calculations are needed in the transformation process. The prediction control method disclosed by the invention has the advantages of relatively small calculated amount, high tracking speed, small harmonics, fixed switching frequency and the like.
Description
technical field [0001] The invention relates to a predictive control method for a modular multilevel inverter. Background technique [0002] With the country's increasing emphasis on new energy, the photovoltaic industry has developed very rapidly in recent years. Improving power quality, reducing harmonicpollution, and improving the efficiency and power of power generation systems are important parameters for various inverters. In recent years, high-voltagepower transmission technology has become more and more popular, and high-voltagepower transmission has become a general trend. The traditional method to improve the system withstand voltage is to select a high-voltage resistant device as the switch tube of the converter. Although this can increase the system withstand voltage, the improvement space is limited, and it is easy to cause system instability. Therefore, other methods are selected to increase the system withstand voltage abnormally. important. [0003] The ...
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