Multi-terminal flexible direct current system droop control method comprising secondary adjustment of voltage and frequency

Abstract

The invention discloses a multi-terminal flexible direct current system droop control method comprising secondary adjustment of voltage and frequency. The method includes specific steps: presetting aninitial reference value; measuring a direct current voltage Udc, an active power P and a frequency f of an alternating current power grid at the beginning of a control period; calculating a deviation[delta]Udc of the direct current voltage Udc deviated from a set value; calculating an active power added value [delta]Pdc required by secondary adjustment of the direct current voltage; calculatinga required active power added value [delta]Pf; calculating a droop deviation er between the direct current voltage and the active power; calculating a d-axis reference current idref required by an inner ring current controller; transmitting the d-axis reference current idref to the inner ring current controller to calculate a modulation pulse required by a direct current converter station; and waiting for the next control period and repeating the above steps. According to the control method, the power distribution characteristic and the frequency adjusting capability of the conventional methodare maintained, the direct current voltage is slowed to the set value after the end of a transition process, and the reliable operation capability of a multi-terminal flexible direct current system is enhanced.

Description

Technical field [0001] The invention relates to the technical field of power electronics, in particular to a droop control method for a multi-terminal flexible direct current system with secondary regulation of voltage and frequency. Background technique [0002] Flexible DC technology is a brand-new power transmission and distribution technology, which realizes the change from AC to DC through a voltage source converter. Since the voltage source converter uses fully controlled power electronic devices such as IGBT and pulse width modulation technology, it can accurately and quickly control the voltage amplitude and phase of the AC side of the voltage source converter. Therefore, from the perspective of the AC system, the voltage source converter The current generator can be equivalent to a motor or generator with no moment of inertia, which can realize independent control of active power and reactive power in the four quadrants of PQ almost instantaneously. Based on this featur...

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Problems solved by technology

[0004] However, the working principle of the above method determines that when the steady state is reached, the DC voltage deviates from its rated value. When the frequency disturbance is large or the DC load changes drastically, the DC voltage deviates too much from the rated value, interrupting the normal operation of the flexible DC transmission system.

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