Frequency conversion optimization control method for modular multilevel DC transformers
A modular multi-level, DC transformer technology, applied in the direction of converting DC power input to DC power output, adjusting electrical variables, control/regulating systems, etc., can solve the problem of high operating frequency, affecting circuit stability, large dv/dt and other problems, to achieve the effect of increasing transmission power, simple control, and suppressing backflow power
Active Publication Date: 2020-07-24
SOUTHEAST UNIV
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However, the current control strategy of this topology is to use multiple or all sub-modules to be turned on at the same time, and the operating frequency is high, which is easy to generate a large dv / dt, which affects the stability of the circuit
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[0034] The technical solutions and beneficial effects of the present invention will be described in detail below in conjunction with the accompanying drawings.
[0035] The average power transmitted in half a cycle of the DC transformer is defined as the transmission power P, and the negative transmission power is defined as the backflow power Q.
[0036] Such as figure 1 As shown, in the DC transformer constructed by the present invention, the primary side adopts the MMC bridge arm, and the secondary side still adopts the H-bridge topology to form the MMC-H bridge topology. Considering that the MMC bridge arm structure in the DC transformer is the same and the two phases / three phases are symmetrical, now take the phase a as an example for analysis, point p1 and point p2 can be regarded as equipotential, so the two points are short-circuited in phase a so that Simplify analysis.
[0037] Similarly, when the secondary side is an H-bridge, it can be obtained figure 2 Simplif...
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The invention discloses a frequency conversion optimization control method suitable for a modular multi-level DC transformer. The MMC-H bridge type DC transformer consists of an MMC bridge arm and anH bridge. The nearest level modulation strategy is set for the MMC side, and square wave modulation is set for the H bridge side and the operation characteristics of the direct current transformer isanalyzed; According to the topology and operation characteristics of DC transformer, the expressions of transmission power and return power of DC transformer based on the nearest-neighbor approximation modulation strategy are derived. For the derived power expression, the distribution of power with parameters is analyzed, the factors affecting the reflux power are summarized, the optimal configuration of voltage regulation ratio is discussed, and the boundary conditions of zero reflux power are scoured to obtain the zero reflux power region. According to the derived power expression, the operating frequency is inversely proportional to the transmission power, and the DC transformer adjusts the shift ratio to fall into the zero-return power region through the change of the operating frequency, so as to realize the suppression of the DC transformer return power. This method can reduce the reflux power and current stress.
Description
technical field [0001] The invention belongs to the fields of modular multilevel converters and direct current conversion, in particular to a modular multilevel MMC direct current transformer, and belongs to the field of modular multilevel converters and direct current conversion. Background technique [0002] Renewable energy power generation has the characteristics of random fluctuations, and when a large number of them are connected to the AC grid, it will seriously affect the reliability and stability of its power supply, including frequency fluctuations, reactive power compensation and other issues. The above-mentioned problems do not exist in the DC distribution network. At the same time, with the development of power electronics technology, the advantages of the DC distribution network in terms of new energy generation access, power quality, and transmission loss have become increasingly prominent. [0003] Unlike the AC grid, the DC grid must rely on power electronic...
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IPC IPC(8): H02M3/335
CPCH02M3/33576
Inventor 梅军管州丁然葛锐范光耀何梦雪吴夕纯王冰冰
Owner SOUTHEAST UNIV