为改善半桥-全桥混合型子模块数量较少的模块化多电平换洗器(modular multilevel converter, MMC)运行性能,推进其在直流配电网等中低压领域的应用,提出了一种全电平逼近调制策略(full level modulation,FLM)。所提FLM利用全桥子模块(full bridge submodule,FBSM)的全电平输出能力,控制桥臂中某一FBSM运行于“脉宽调制(pulse width modulation, PWM)模式”,将所得全电平PWM波与原阶梯波叠加以进一步逼近正弦调制波。子模块工作模式由电容电压排序结果确定,相单元中任意时刻均有两个FBSM运行于“PWM模式”,输出互补的全电平PWM波。基于Matlab/Simulink的仿真结果和物理实验结果表明,在所提FLM调制策略下,交流侧电压电流质量远高于传统最近电平逼近调制策略,运行损耗、控制复杂度及循环电流均优于传统载波移相脉冲宽度调制,满足中低压领域的调制要求。

In order to improve the operating performance of half bridge - full bridge hybrid modular multi-level converter (MMC) with small quantities of submodules and promote its application in medium and low voltage fields such as DC distribution grids, a novel full-level modulation (FLM) strategy is proposed in this paper. The full-level output capability of full-bridge submodule (FBSM) is utilized in the proposed FLM, where a selected FBSM in arm operates in the “PWM mode”. The obtained full-level PWM wave is superimposed with the original step wave to further approximate the sine modulation wave. The operating mode of submodules is determined by the voltage sorting result, and at any time, there are two FBSMs in the phase unit operating in the “PWM mode”, outputting complementary full-level PWM waves. The results of simulation based on Matlab/Simulink and physical experiment reveal that the quality of voltage and current on AC side under FLM is much higher than that of the conventional nearest level modulation strategy. Compared with the carrier phase-shifted pulse width modulation, FLM performs better in terms of operating loss, control complexity and circulating current, which can satisfy the modulation requirements of medium and low voltage fields.

结合东莞松山湖地区中压配电网的实际问题和工程示范规划,对中压柔性直流互联在该地区中压配电网中的应用方案进行研究。对系统的主接线方式、联接变压器配置和接地方式进行了论证;对系统中模块化多电平换流器和电力电子直流变压器进行了初步设计,确定了关键设备主要技术要求;仿真分析了系统过电流和过电压特性,提出了系统的过流耐受和绝缘配合要求;设计了系统总体控制架构和保护配置,明确了系统的控制保护策略。文章对示范工程所采用的新型主回路拓扑进行了论证,提出并采用了高纹波紧凑化的设备设计方案,提出了交流故障协调响应策略,并对这些新技术进行了论证和仿真验证,可为后续相关研究和工程实践提供参考。

Combined with the actual problems of the medium-voltage (MV) AC distribution network in Songshan Lake area of Dongguan, the technical scheme of an MVAC distribution network project for demonstration with HVDC-flexible interconnection is studied. The main wiring mode, connection transformer configuration and grounding mode are demonstrated. The modular multi-level converter and power electronic DC transformer in the system are preliminarily designed, and the technical requirements for key equipment are determined. The system overcurrent and overvoltage characteristics are analyzed by simulation, thus overcurrent tolerance and insulation coordination requirements being put forward. The overall control architecture and protection configuration of the system are designed, and the control and protection strategy of the system is defined. The new main connection topology proposed in this article is used in a practical demonstration project. The scheme of high-ripple design for compact equipment is adopted and the AC fault coordination response strategy is proposed. All those new technologies are demonstrated and verified with simulation, which provide reference for follow-up related research and engineering practice.

动态特性是电力电子变换器在面对启动、扰动和参数突变等情况下非常重要的一种基本性能，这种性能直接决定了变换器能否胜任实际应用场景。对于双有源桥（DAB）变换器，现有的控制方法普遍存在动态响应慢，鲁棒性不强等特点。为了实现对DAB变换器动态特性的有效控制，本文针对DAB的阶跃响应提出了一种基于动态矩阵控制（DMC）的模型预测控制方法。与传统的控制方法相比，DMC不仅有误差反馈校正环节，而且具有模型预测功能和滚动优化功能。因此，DMC控制具有更好的动态响应，在抑制超调、减小稳态误差等方面有着更强的控制性能。仿真和实验均验证了上述性能。

The dynamic characteristic is a very important and basic performance of power electronic converter when suffering from situation such as startup, disturbance and the mutation of parameter, and the dynamic characteristic directly determines whether the converter is qualified for practical application scenarios. However, existing control methods always have the slow dynamic response and weak robustness for the Dual Active Bridge (DAB) converter. In order to improve the effective control of dynamic response for DAB converter, Dynamic Matrix Control (DMC) of model predictive control is introduced, which can boost the speed of the dynamic response for DAB. Compared with the traditional control, DMC not only has the error feedback compensation, but also has the function of model prediction and rolling optimization. Thus, DMC has better control performance, including: faster dynamic response, overshoot suppression and static error reduction. Both of the simulation and experiment proves the performance.