全桥型MMC用于直流融冰时的控制策略研究

Control of Full-bridge Modular Multilevel Converter for DC Ice-melting Application

冰灾的频繁发生使得直流融冰装置已经成为易覆冰地区电网中的常规设备。现有直流融冰装置采用了晶闸管可控整流技术,在运行中均会消耗一定的无功、产生特征次谐波,对接入交流系统带来一定影响。全桥型模块化多电平换流器具有直流电压、电流双向运行能力,可满足直流融冰对换流器运行工况的要求。将研究基于全桥型模块化多电平换流器(全桥型MMC)的直流融冰装置建模方法。对直流融冰装置主回路拓扑、参数,调制均压、控制策略进行全面研究;充分利用全桥型子模块(FBSM)可输出正、零、负模块电压的特点,研究如何实现输出电流、电压宽范围连续可调,以满足不同类型、长度线路的融冰需求;最后利用PSCAD搭建了全桥型MMC和LCC型直流融冰装置模型,并对二者进行对比分析,验证了全桥型MMC直流融冰装置的优势。仿真结果验证了模型控制和方法的有效性。

Due to the high frequency of the ice disasters,DC ice-melting device has become common equipment in the easy icing areas. The previous thyristor rectifier based on Dc ice-melting device consumed too much reactive power and outputs characteristic harmonics,which further affected the system stability when connecting to AC system. Full-bridge modular multilevel converter（ FBMMC） has the ability of outputting bidirectional DC-link voltages and DC currents.This paper focuses on the control and valve based modulation algorithms of FBMMC for DC ice-melting applications.This paper firstly takes the advantage of the full-bridge sub-module（ FBSM） which can output positive,zero and negative capacitor voltages,trying to make FBMMC output widely ranged and continuous-tuning DC voltages and currents to de-ice the AC conductors of different varieties and length. At the same time,the AC-side voltages of FBMMC remain regulated and almost sinusoidal even when the DC voltage is quite small. Finally electromagnetic transient model of the FBMMC and Line Commutated Converter（ LCC） based DC ice-melting device is simulated on PSCAD / EMTDC and the results have been compared and proved the effectiveness of the proposed control and modeling methods.