Modulation method of multilevel inverter without common mode voltage
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A multi-level inverter and common-mode voltage technology, which is applied to electrical components, photovoltaic power generation, circuit devices, etc., can solve the problems of increased common-mode voltage amplitude, increased voltage vector number, and poor versatility. Achieve the effect of eliminating common mode voltage, reducing the amount of calculation, and strong versatility
Active Publication Date: 2020-09-22
BEIJING JIAOTONG UNIV
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[0003] The existing multi-level inverter modulation technology is mainly divided into two types: space vector modulation (SVPWM) and sinusoidal pulse width modulation (SPWM). SVPWM is relatively mature for two-level and three-level applications. When the number of levels increases to five Level and above, the voltage vector number increases greatly, and the calculation becomes extremely complicated, and SVPWM will increase the amplitude of the common-mode voltage as the number of levels increases.
SPWM is relatively mature in the traditional topology with a specific correspondence between the carrier and the switch tube. It is not very versatile for non-traditional topologies. Its common-mode voltage is reduced compared with SVPWM, but the higher output frequency makes the parasitic capacitance on The voltage changes at high frequency, and it is still necessary to add a common-mode filter in the subsequent stage to suppress the leakage current
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Embodiment 1
[0057] Such as figure 1 As shown, the embodiment of the present invention provides a modulation method for a multi-level inverter without common-mode voltage, including the following process steps:
[0058] For an n-level inverter, the electric level step is E, and its DC side voltage is V dc , the technical scheme adopted in the present invention comprises the following steps:
[0059] Step (1), the three-phase modulation wave u shown in formula (1) A , u B , u C Decomposed into u shown in formula (2) 1 , u 2 , u 3 , after decomposition, u A with u 1 -u 2 Same phase, equal amplitude, u B with u 2 -u 3 Same phase, equal amplitude, u C with u 3 -u 1 With the same phase and equal amplitude, the transformation matrix is shown in formula (3).
[0060] u A =Msin(ωt)
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[0065]
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[0067] In the formula, M is the amplitude of the modulation wave, which can be set artificially and does not exceed half of t...
Embodiment 2
[0083] In the second embodiment of the present invention, a seven-level inverter based on switched capacitors with complex charging and discharging conditions is selected as an example topology. figure 2 As shown, it is the topological structure diagram of phase A, phase B and C are the same as phase A, and the three phases of A, B, and C are connected together. dc Equal to 375V.
[0084] A, B, C three-phase modulation wave u A , u B , u C As in formula (1), u can be obtained by matrix transformation of formula (2) 1 , u 2 , u 3 .
[0085] u A =180sin(ωt)
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[0087]
[0088]
[0089] u 1 , u 2 , u 3 Five-level one-dimensional space vector modulation is required, and five voltage vectors divide the one-dimensional space into four sectors: 0~E, 0~-E, E~2E, and -E~-2E. image 3 shown. A sawtooth carrier with a period of 50s and a uniformly increasing amplitude from 0 to E is used. u 1 , u 2 , u 3 Flip and fold to get u′ 1 , u' 2 , u' 3 , so th...
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Abstract
The invention provides a modulation method of a multi-level inverter without common-mode voltage, belonging to the technical field of multi-level inverter modulation. The modulation method comprises the steps that modulating wave is decomposed, and every two phases of the decomposed modulating wave are subtracted from each other to obtain original modulating wave; the decomposed modulating wave issubjected to one-dimensional space vector modulation to obtain the action vector for synthesizing the modulating wave and the corresponding action time of the vector; by being compared with the sawtooth carrier, the vector with small modulus in one carrier period of the positive half period is output first, and the vector with large modulus in the negative half period is output first to obtain intermediate PWM signals; a three-phase PWM signal is obtained by subtracting every two phases of the intermediate PWM signals; and redundant vectors are selected according to the actual needs of different topologies. The modulation method eliminates the common mode voltage, eliminates the influence of the leakage current on the grid-connected current, and improves the waveform quality. Compared with the traditional SVPWM modulation strategy, two-dimensional simplification is changed to one-dimensional simplification, sector judgment and vector action time are simplified, without trigonometric function operation, and the computational effort is small. The method has high versatility for different inverter topologies.
Description
technical field [0001] The invention relates to the technical field of modulation of multilevel inverters, in particular to a modulation method of multilevel inverters without common mode voltage. Background technique [0002] In recent years, photovoltaic power generation has been widely concerned by countries all over the world because of its clean and renewable, abundant resources and huge development potential. Compared with the traditional photovoltaic grid-connected inverter with isolation transformer, the non-isolated photovoltaic grid-connected inverter has a much smaller volume, lower cost and higher efficiency. However, the photovoltaic panels of non-isolated photovoltaic grid-connected inverters are directly connected to the grid, generating leakage current, which will cause electromagnetic interference, grid-connected current distortion, and increased power loss, and may even endanger the safety of equipment and personnel. The multi-level inverter can reduce the...
Claims
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