Neutral point potential balance control method for direct current side in NPC three-level structure

A potential balance and control method technology, which is applied in the direction of converting AC power input to DC power output, photovoltaic power generation, electrical components, etc., can solve the problems of midpoint potential imbalance, adverse performance and safety of inverters, and inaccurate calculation of zero-sequence voltage. Accurate and other issues, to achieve the elimination of DC bias and low frequency fluctuations, the control algorithm is simple and easy, and the effect of improving the quality of output current

Active Publication Date: 2013-11-27

XIAN LONTEN RENEWABLE ENERGY TECH

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AI-Extracted Technical Summary

Problems solved by technology

Due to the inflow and outflow of current at the midpoint of the DC side, it is easy to cause the imbalance of the midpoint potential, which will have a very adverse impact on the performance and safety of the inverter. Therefore, the midpoint potential imbalance must be eliminated through appropriate control.

At present, the research on software control algorithms is relatively extensive. Some control the midpoint potential to fluctuate within a certain range by performing hysteresis comparison on the midpoint. This method is simple and easy to implement, but it does not completel...

Abstract

The invention relates to a neutral point potential balance control method for a direct current side in an NPC three-level structure. A neutral point clamping type three-level inverter circuit is adopted in a photovoltaic grid-connected inverter, so that neutral point potential imbalance is prone to being caused; a software control algorithm, namely, a control method conducting hysteresis comparison on a neutral point cannot not completely eliminate low frequency fluctuation of neutral point potential; a control algorithm for injecting zero sequence voltage is relatively complex. The neutral point potential balance control method for the direct current side in the NPC three-level structure is characterized in that the difference value of one half of busbar voltage on the direct current side of a photovoltaic inverter and neutral-point voltage, the current value which needs to be injected into the neutral point in a present switching period is obtained by a PI regulator, the acting time of redundant small vectors in each sector in space vector pulse width modulation is used as a modulation method, and the allocation proportion of the redundant small vectors in one switching period is computed. The neutral point potential balance control method for the direct current side in the NPC three-level structure eliminates direct current bias and low frequency fluctuation of the neutral-point potential of a diode clamping type three-level inverter on the existing hardware condition, and neutral-point balance is achieved.

Application Domain

Ac-dc conversionPhotovoltaic energy generation

Technology Topic

DC biasBus voltage +14

Image

Examples

Experimental program(1)

Example Embodiment

[0037] Examples:

[0038] See figure 1 、After connecting the photovoltaic inverter, the control chip will obtain the three-phase inductor current through the sampling circuit , , , And calculate the small vector that can affect the midpoint potential , Sum vector The action time is , with , The currents corresponding to the midpoint when they act are respectively , with. You can do the following operations, see image 3 :

[0039] If , The reference voltage is located in the small triangle 1 of the first sector:

[0040] (1) If , Then select As a redundant small vector for regulation, according to the required current at the midpoint , Calculate the distribution coefficient of the redundant small vector;

[0041] (2) If , Then select As a redundant small vector for regulation, according to the required current at the midpoint , Calculate the distribution coefficient of the redundant small vector.

[0042] If , The reference voltage is located in the small triangle 3 of the first sector:

[0043] (1) If , Then select As a redundant small vector for regulation, according to the required current at the midpoint , Calculate the distribution coefficient of the redundant small vector;

[0044] (2) If , Then select As a redundant small vector for regulation, according to the required current at the midpoint , Calculate the distribution coefficient of the redundant small vector.

[0045] There is only a pair of redundant small vectors in the small triangles 2 and 4, so there is no selection problem.

[0046] Judgment basis and distribution coefficient of the A and C triangle area switching synthesis mode of each sector as follows:

[0047] 1. According to the above method, the judgment basis for the switching and synthesis mode of the triangular area A and C of the first sector is as follows:

[0048] Table 1 Criterion for switching vector synthesis mode of triangle area A and C in sector I

[0049]

[0050] Distribution coefficient of each area as follows:

[0051] Table 2 Proportion of small vector distribution in sector I

[0052]

[0053] 2. According to the above method, the judgment basis for the switching and synthesis mode of the triangle area A and C of the second sector is as follows:

[0054] Table 3 Criterion for switching vector synthesis mode of triangle area A and C in the second sector

[0055]

[0056] Distribution coefficient of each area as follows:

[0057] Table 4 Proportion of small vector distribution in sector II

[0058]

[0059] 3. According to the above method, the judgment basis for switching the synthesis mode of the triangle area A and C of the third sector is as follows:

[0060] Table 5 Criterion for switching vector synthesis mode of triangle area A and C in the third sector

[0061]

[0062] Distribution coefficient of each area as follows:

[0063] Table 6 Distribution ratio of small vector in sector III

[0064]

[0065] 4. According to the above method, the judgment basis for the switching and synthesis mode of the triangular area A and C of sector IV is as follows:

[0066] Table 7 Criterion for switching vector synthesis mode of triangle A and C in sector IV

[0067]

[0068] Distribution coefficient of each area as follows:

[0069] Table 8 Proportion of small vector distribution in sector IV

[0070]

[0071] 5. According to the above method, the judgment basis for switching the synthesis mode of the triangular area A and C in the V area is as follows:

[0072] Table 9 Criterion for switching vector synthesis mode of triangle area A and C in sector

[0073]

[0074] Distribution coefficient of each area as follows:

[0075] Table 10 Distribution ratio of small vector in sector V

[0076]

[0077] 6. According to the above method, the judgment basis for the switching synthesis mode of the triangle area A and C in the VI sector is as follows: Table 11 The criterion for the switching vector synthesis mode of the triangle area A and C in the VI sector

[0078]

[0079] Distribution coefficient of each area as follows:

[0080] Table 12 Distribution ratio of small vector in sector VI

[0081]

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Description & Claims & Application Information

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Classification and recommendation of technical efficacy words

Eliminates DC bias

Control method of bidirectional full-bridge DC/DC converter circuit and suppression magnetic biasing

InactiveCN109450255AEliminates DC biasBias suppression

Owner:HEFEI KEWELL POWER SYST CO LTD

Neutral point potential balance control method for direct current side in NPC three-level structure

AI-Extracted Technical Summary

Problems solved by technology

Abstract

Image

Examples

Example Embodiment

PUM

Description & Claims & Application Information

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