Adjustable discontinuous modulation method of modular multilevel topology based on double buck sub-modules
A modular multi-level, modulation method technology, applied in the direction of climate sustainability, electrical components, high-efficiency power electronic conversion, etc., can solve the problems of large current stress of switching tubes, distortion of port output current, and low utilization of inductors. Achieve the effects of improving power conversion rate, reducing switching loss, and improving output power quality and efficiency
Active Publication Date: 2020-03-31
NANJING NORMAL UNIVERSITY
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[0003] The existing continuous modulation strategy means that the two switch tubes work in a high-frequency state at the same time within one switching cycle, and the inductor current is in a continuous conduction mode. At this time, the sub-module will generate a circulating current. Large, low inductance utilization, high switching loss
The existing discontinuous modulation strategy makes the two switches of the dual-step-down sub-module conduct complementary conduction within one switching cycle, which can reduce switching losses and improve the utilization of the inductor; however, due to the inductance of the dual-step-down inverter unit Due to the unidirectional conduction characteristics of the current, the port output current (that is, the bridge arm current of the modular multi-level topology based on the dual-step-down sub-module) will produce distortion at the moment of zero crossing, which may reduce the power quality
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[0025] Such as figure 1 , as known in the prior art, the modular multilevel topology based on the double buck sub-module has two upper and lower bridge arms, and the midpoint of the upper and lower bridge arms is passed through the resistor R g , inductance L g and AC power U g Back grounding; the head end of the upper bridge arm and the tail end of the lower bridge arm respectively pass the DC power supply U dc back to ground. Each of the upper and lower bridge arms includes N series-connected dual step-down sub-modules SM jn , and the respective output currents are equal to the arm current i of the modular multilevel topology j , the output current of the entire modular multilevel topology is i o , j={u,l}, n={1,2,...,N}, the subscripts u and l respectively represent the upper bridge arm and the lower bridge arm of the topology where the corresponding submodule is located, and N is a positive integer. Each sub-module has two dual-buck inverters connected in series. Wh...
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The invention discloses an adjustable discontinuous modulation method of modular multilevel topology based on double buck sub-modules, and the method enables the negative half cycle of the phase arm inductive current of sub-modules to be cut off through the alternate conduction of two switching tubes of the sub-modules in one switching period. The objective of the invention is to overcome the problem of bridge arm current zero-crossing distortion caused by the existence of the topological loop current under half-cycle modulation. One half of the maximum bridge arm current ripple is used as a threshold value through theoretical analysis and is compared with a bridge arm current sampling value to obtain an enable signal; and a switching signal is obtained through a logic AND gate together with the bipolar PWM modulation signal, so that a minimum switching signal overlapping channel can be formed near a bridge arm current zero crossing point for simultaneously switching on or switching off a switching tube. According to the invention, the conversion efficiency and the power density of the inverter are improved, the topological reliability is improved, the switching loss of the sub-modules is reduced by adjustable discontinuous modulation, the current zero-crossing distortion is eliminated, and the quality of output electric energy is improved.
Description
technical field [0001] The invention belongs to the technical field of high-voltage and high-power power electronics, and mainly relates to an adjustable discontinuous modulation method based on a modular multi-level topology of double-buck sub-modules. Background technique [0002] The existing dual-buck inverter as a sub-module modular multi-level topology overcomes the output distortion caused by the direct and dead zone of the traditional modular multi-level inverter with a half-bridge structure as a sub-module problem, improving power quality and power conversion efficiency as well as operational reliability. Modulation strategies commonly used in modular multilevel converters based on double-buck inverters include continuous modulation strategies and discontinuous modulation strategies. [0003] The existing continuous modulation strategy means that the two switch tubes work in a high-frequency state at the same time within one switching cycle, and the inductor curren...
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IPC IPC(8): H02M7/5387H02M1/088
CPCH02M7/53871H02M1/083H02M1/088H02M1/0038H02M1/0054Y02B70/10
Inventor 孙毅超吕丹丁楠木王琦
Owner NANJING NORMAL UNIVERSITY