Optimal pressure equalizing control method of modular multilevel converter type direct current transmission system

A DC transmission system, modular multi-level technology, applied in the direction of converting AC power input to DC power output, without intermediate conversion to AC conversion equipment, electrical components, etc., can solve the large delay of trigger control and reduce the multi-level modularization The efficiency of the level converter type DC transmission system, reducing the speed of the converter tracking modulation wave, etc., to achieve the effect of reducing the frequency of switching

CN101860203BInactive Publication Date: 2012-06-27ZHEJIANG UNIV
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Patent Information

Authority / Receiving Office
CN · China
Patent Type
Patents(China)
Current Assignee / Owner
Publication Date
2012-06-27
Estimated Expiration
Not applicable · inactive patent

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Abstract

The invention discloses an optimal pressure equalizing control method of a modular multilevel converter type direct current transmission system. By setting an upper limit and a lower limit on voltage, the pressure equalizing control is mainly carried out on submodules with out-of-limit capacitor voltage, and capacitor voltage sequencing for submodules with no out-of-limit capacitor voltage is processed by combing the charging / discharging conditions of bridge arm current so as to increase the probability of maintaining an original switching state for the submodules with no out-of-limit capacitor voltage when the next action is in triggering control and lower the switching frequency of devices. The introduction of the pressure equalizing control can not lower the working frequency of triggering control and the tracking speed of a converter by using submodule capacitor voltage sequencing and triggering control to work at different frequencies. The optimal pressure equalizing control method of the invention can greatly lower the switching frequency of the devices on the premise of having no obvious increment on submodule capacitor voltage fluctuation.
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Description

technical field

[0001] The invention relates to the technical field of multilevel converter capacitor voltage equalization control, in particular to an optimized voltage equalization control method for a modular multilevel converter type direct current transmission system. Background technique

[0002] The modular multilevel converter is a relatively new multilevel voltage source converter, and its structure is as follows figure 1 shown. Based on modular design and manufacture, the converter can reach a very high level number, and is suitable for high-voltage and high-power DC transmission fields.

[0003] The sub-module capacitances of the modular multilevel converter are independent of each other. The difference in charge and discharge, loss and capacitance value of each sub-module will make the capacitor voltage unbalanced, which will endanger the normal operation of the converter. When the sub-module capacitor is connected to the bridge arm, it is said that the sub-mo...

Examples

Embodiment

[0022] The optimal voltage equalization control method for the modular multilevel converter type DC transmission system is: set the upper and lower limits of two sets of voltages, the upper and lower limits of the capacitor voltage in mode 1 are 21V and 19V respectively, and the capacitor voltage in mode 2 , The lower limit is 22V and 18V respectively. Combined with the charge and discharge of the bridge arm current, the capacitor voltage sorting of the sub-modules whose capacitor voltage does not exceed the limit is processed to increase the probability that the sub-modules whose capacitor voltage does not exceed the limit will maintain the original switching state when triggering the next action of the control, and reduce the device The switching frequency, the specific processing is as follows:

[0023] If the bridge arm current charges the sub-module, when the trigger control next action tends to input the sub-module with low capacitor voltage, the capacitor voltage of the...