This paper proposes a hybrid control scheme that combines fractional-order sliding-mode control (FOSMC) with radial basis function neural network adaptive damping passivity-based control (RBFPBC) for modular multilevel converters (MMC) under non-ideal operating conditions. According to the passive control theory, we establish the Euler–Lagrange (EL) models of positive and negative sequences based on the unbalanced grid. A passivity-based controller that satisfies the energy dissipation law is designed. To enable rapid convergence of the system energy storage function, a radial basis function neural network (RBFNN) is introduced to adjust the injection damping adaptively. Additionally, a fractional-order sliding-mode controller (FOSMC) is designed. The fractional-order sliding mode surface used can improve tracking performance, and effectively suppressed the undesirable chattering phenomenon compared to the traditional sliding-mode control (SMC). Finally, combining the two control methods can effectively solve the issue of passivity-based control (PBC) being too dependent on parameters. The proposed hybrid control scheme enhances the ability of the system to resist disturbances, and improves its overall robustness. Simulation results demonstrate the feasibility and effectiveness of this control method.

In recent years, the power electronic transformer (PET) used as the wind energy conversion system at the grid interface has attracted widespread attention for its ability to effectively suppress voltage fluctuations caused by the transient characteristics of wind energy without the need for additional reactive compensation devices. However, the conventional PET structure poses control challenges during grid faults, making it difficult to manage unbalanced grid conditions and compromising system dynamic performance. To enhance dynamic performance and fault tolerance, this paper proposes a novel wind energy conversion system based on the modular multilevel converter (MMC) power electronic transformer, along with its structural design and control strategy. Firstly, a fault-switching control strategy based on passive sliding mode control is designed to handle system operation during faults, incorporating sub-modules with fault protection features to dissipate fault power. Secondly, extensive simulation studies are conducted under various operating conditions using software simulation and semi-physical simulation platforms. Finally, comparative experiments between the proposed wind power generation system and traditional wind power systems validate the advantages of the novel system structure using the proposed control strategy, including reactive power compensation, effective limitation of submodule voltage rise during faults, and improvement in power quality. The results demonstrate the outstanding fault crossing capabilities of the proposed system in meeting the latest requirements for grid operation under fault conditions.

The low-frequency transmission system (LFTS) for offshore wind power is a promising integrated solution. Hexverter, as a topology derived from the Modular Multilevel Matrix Converter (M3C), exhibits certain advantages in low-frequency transmission. However, its application in offshore wind power faces challenges due to the stochastic nature and nonlinear characteristics of renewable energy, making linear PID control less effective. In contrast, the Lyapunov control strategy has shown better performance in controlling nonlinear systems than PID control. Therefore, this paper proposes a Lyapunov control strategy for Hexverter. Firstly, the global asymptotic stability of the Lyapunov control strategy for Hexverter is analyzed. Then, based on the topology of Hexverter, the control laws for bilateral Lyapunov control of Hexverter are derived, and the parameter selection problem for Lyapunov control is discussed. Subsequently, a Lyapunov control system for Hexverter is established using Simulink and RT-LAB platforms. The operating results under various conditions are simulated, and the feasibility and effectiveness of the proposed Lyapunov control strategy are validated by comparing the simulation results with PID control.

The low-frequency transmission system for offshore wind power is a promising integrated solution. Hexverter, as a topology derived from the modular multilevel matrix converter (M3C), exhibits certain advantages in low-frequency transmission. However, its application in offshore wind power faces challenges due to the stochastic and nonlinear characteristics of renewable energy, making linear PID control less effective. In contrast, the Lyapunov control strategy has shown better performance in controlling nonlinear systems than PID control. Therefore, this paper proposes a Lyapunov control strategy for Hexverter. Firstly, the global asymptotic stability of the Lyapunov control strategy for Hexverter is analyzed. Then, based on the topology of Hexverter, the control laws for bilateral Lyapunov control of Hexverter are derived, and the parameter selection problem for Lyapunov control is discussed. Subsequently, a Lyapunov control system for Hexverter is established on MATLAB/Simulink and RT-LAB platform. The operating results under various conditions are simulated, and the feasibility and effectiveness of the proposed Lyapunov control strategy are validated by comparing the simulation results with PID control.

In order to solve the problems of traditional modulated model predictive control (M2PC) in three-level indirect matrix converter-permanent magnet synchronous motor (TLIMC-PMSM) system, such as inaccurate sector selection and duty ratio calculation of M2PC. An improved modulated model predictive control based on virtual vector prediction (VVP-M2PC) is proposed and applied to TLIMC-PMSM system. Compared with the traditional M2PC, VVP-M2PC re-partitions the sectors of the three-level inverter stage and constructs a new virtual vector to reduce the current control error. In addition, the feasibility of this method is discussed from two aspects: computational complexity and theoretical error analysis. Finally, compared with MPC and traditional M2PC, the simulation and experiment results show that the algorithm can improve the speed and torque ripple of PMSM, and improve the quality and robustness of input and output waveforms of the system.

To settle the problems of three-phase voltage source rectifier VSR (Voltage Source Rectifier), which adopts dual closed-loop control systems based on proportional integral (PI) control, such as large startup overshoot voltage, slow dynamic response speed and high current harmonic content, an improved double closed loop Sliding mode control scheme is adopted, that is, the voltage outer loop adopts global fast terminal Sliding mode control, the current inner loop adopts Sliding mode control based on exponential reaching law. Firstly, establishing a mathematical model of three-phase VSR in d-q rotating coordinate system, and then the design process of dual loop Sliding mode control system is introduced at length, finally, simulation comparison results prove the effectiveness of the dual Sliding mode control scheme, and provides a theoretical basis for industrial applications.

The three-level direct matrix converter（TLDMC） has attracted wide attention in the fields of motor drive,distributed power generation, and renewable energy because of its advantages of high power density, high efficiency, and low common mode voltage. However, in unbalanced grid voltage conditions, the current distortion on the input side of the TLDMC will affect the power factor and power quality of the output side, and reduce the reliability of the system. The existing TLDMC input closed-loop control strategy cannot meet the requirements of high dynamic response and robustness. To this end, a TLDMC nonlinear control strategy is proposed based on back-stepping sliding-mode control（BS-SMC） which is suitable for balanced and unbalanced grid voltage conditions without positive and negative sequence separation. A dynamic modulation index is used to suppress the ripple of the active power double frequency in unbalanced conditions. The input reactive power is controlled by eliminating the nonlinear term in the Lyapunov derivative function and applying a sliding mode surface as a virtual error. After theoretical analysis and comparative experiments, the results show that compared with the traditional control strategies, the response speed of the back-stepping sliding-mode control is increased, and the THD is reduced. The method proposed provides a reference for the input control strategy of matrix converters.

模块化多电平换流器(modular multilevel converter,MMC)-并联式有源滤波器(shunt active power filter,SAPF)能够补偿大电压时电能中的电流质量,但若采用单一控制方法难以很好地对电流质量进行补偿.为此,提出了无源性控制(passivity-based control,PBC)与滑模控制(sliding mode control,SMC)相结合的无源性滑模控制补偿方法,用以提升电流质量.首先,推导出不平衡电网下MMC-SAPF的数学模型,并对电压和电流进行正负序分离;然后,针对单一控制方法存在的问题,提出了基于MMC-SAPF的无源性滑模控制方法;最后,搭建了 MMC-SAPF系统实验平台,将无源性滑模控制与PID和PBC2种控制方法进行比较,结果表明无源性滑模控制的精度更高、鲁棒性更强、响应更快,且能够快速、准确地补偿电流.

由于模块化多电平变流器(modular multilevel converter,MMC)电力电子变压器(power electronic transformer,PET)使用传统的控制策略难以保证系统运行时的动态性能,在电网处于不平衡时使得控制难度进一步增加.为了提高系统的动态性能,提出了一种非线性的反馈线性化滑模复合控制策略.该复合控制策略将反馈线性化控制(feedback linearization control,FLC)和滑模控制(sliding mode control,SMC)的优势结合在一起实现优势互补.首先,建立了MMC-PET整体仿真模型;其次,通过数学模型建立反馈线性化滑模控制的控制模型;最后,利用仿真与实验平台进行仿真对比实验,将所提复合控制策略与单一的反馈线性化控制、滑模控制以及常用的PI控制作了仿真对比,以验证所提控制策略可以在外部扰动时具有良好的动态性能和较好的鲁棒性等优势.

针对模块化多电平变流器(MMC)-统一潮流控制器(UPFC)潮流跟踪性能优化问题,提出了一种基于MMC-UPFC的反演滑模控制(BSC-SMC)非线性策略,它既保留了滑模控制(SMC)的抗干扰能力强等性能,也兼具反演控制(BSC)响应速度快等优点.首先,根据MMC-UPFC的拓扑结构,建立数学模型,分析它的内部特性;其次,详细论述了BSC控制的原理和设计过程,结合SMC控制,当系统参数变化时可提高系统的稳定性;然后,经过子模块均压控制,通过载波移相调制将信号传送给MMC;最后,搭建MMC-UPFC仿真系统进行仿真验证,将所提BSC-SMC控制策略与BSC控制、SMC控制、PID控制控制策略进行比较,验证了在2种不同工况下MMC-UPFC的BSC-SMC控制策略的有效性和优越性.

Power electronic transformer（PET） is widely used in power transmission and distribution system due to the advantages of small volume, harmonic control, power control, and electrical isolation. The combination of modular multilevel converter（MMC） and PET can solve the problem of power quality effectively in medium-and high-voltage distribution network. However, there are many unexpected interference factors in the transmission and distribution process, which lead to system instability and affect the power quality of transmission and distribution. In order to improve the reliability and dynamic response of the system under non-ideal conditions, the passivity-based control-sliding-mode control（PBC-SMC） based on MMC-PET is proposed. Firstly, the PBC controller based on Euler-Lagrange（EL） model of MMC is applied to the inner loop current control, and then the sliding mode control is introduced, which can effectively solve the problem that PBC control is excessively dependent on system parameters, so that the control system has stronger anti-interference ability and faster response speed. The output DC voltage of intermediate isolation stage is stabilized by phase shift voltage regulation control, and the PBC controller of output stage inverter is designed. Finally, the MMC-PET simulation system is built for experimental verification. The results show that the PBC-SMC control method of MMC-PET is effective and superior under non-ideal conditions.

模块化多电平矩阵变换器(MMMC)应用于新能源海上风电直接AC/AC变换时,由于新能源发电的随机性及本身的非线性特性,在三相电压不平衡下MMMC输入、输出双侧电流常用的PID控制策略难以达到理想的控制效果,基于Lyapunov函数控制方法的控制器数量、控制复杂程度和控制效果都优于PID控制,提出了三相电压不平衡下MMMC的输入、输出双侧采用Lyapunov控制策略.根据MMMC的数学拓扑结构建立三相电压不平衡下MMMC双侧Lyapunov的数学模型,证明了其具有全局渐进稳定性,讨论了控制不精确以及参数选择问题.最后通过仿真平台对提出的Lyapunov控制策略与PID控制策略进行仿真比较,验证了所提控制方法的正确性与优越性.所提Lyapunov控制方法相较于PID控制稳定速度更快,总谐波畸变量(THD)更低,且具有强鲁棒性,对参数的变化不敏感.

The MMC-UPQC system formed by unified power quality controller（UPQC） and modular multi-level converter（MMC） can be used for the compensation control of current and voltage at medium and high voltage and high power. However, at present, the MMC-UPQC generally adopts PID linear control methods to carry out the compensation control of current and voltage. The MMC-UPQC is a nonlinear and multivariable object, thus linear control methods such as PID are difficult to obtain satisfactory compensation quality. Therefore, this paper proposes a nonlinear Lyapunov function control method for compensation control of MMC-UPQC current and voltage under unbalanced grid voltages.First, mathematically model for MMC-UPQC under unbalanced power grid is established; next, the positive and negative sequences of electrical quantities on series and parallel sides of MMC-UPQC under unbalanced grid are separated; the Lyapunov function control method is used for power quality compensation of MMC-UPQC under unbalanced grid voltage, the stability of Lyapunov function control system is proved, and the stable range of Lyapunov function control gain is introduced. Finally, the two methods of Lyapunov function control and traditional PID control are compared on the simulation system platform. The simulation results verify that the Lyapunov function control method can be adopted to better compensate the power quality of MMC-UPQC current and voltage.

Existing modulation and control strategies of direct matrix converter (DMC) cannot take both fast response and waveform quality into account, and there is also a lack of research on its application to complex scenarios such as power systems. In this paper, a mathematical model of DMC-UPFC is established based on the characteristics of DMC and the principle of unified power flow controller (UPFC), then a novel modulated model predictive control algorithm is proposed by combining the advantages of space vector modulation and model predictive control. In order to deal with the unbalanced conditions which is common in the power system, a compensation strategy is adopted as well. Simulation and experimental results verify that adequate dynamic performance and considerable waveform quality is achieved by using the proposed method. It can maintain power stability and current sinusoidal even under unbalanced conditions, which further verifies the feasibility of the scheme.

The Y-type modular multilevel converter (Y-MMC) has high reliability due to its high modularity. It can promise AC/AC conversion for high-voltage and large-capacity fractional frequency transmission systems (FFTS). The Y-MMC under linear control has a poor ability to adapt to changing working conditions, resulting in unstable transmission, slow response, and large harmonics and overshoot. The Robustness Improvement Model Predictive Control strategy (RI-MPC) for Y-MMC under nonideal conditions is presented in this paper to enhance robustness under unbalanced conditions and adaptability to load changes. It points out that the conventional MPC has low robustness when Y-MMC encounters parameters difference due to faulty line, designs an improved outer-loop PI control to enhance robustness to provide an excellent reference value for the inner-loop current, combines the Luenberger observer with MPC and limits the parameters with Jury criterion to improve stability, and uses a two-step prediction to compensate for delay and reduce harmonics. Through software simulation and hardware experiments, it is proved that compared with the traditional PI and MPC method, the RI-MPC method is more robust, faster, and has application value.

A new direct torque control method for three-level direct matrix converter permanent magnet synchronous motor (TLDMC-PMSM) based on the modulation coefficient optimization method (MCOM) is proposed to address the problems of large torque chain pulsation, amplitude disorder and weak system robustness in matrix converter permanent magnet synchronous motor system (MC-PMSM) using direct torque control (DTC). In the paper, firstly, the principle of MC-PMSM-DTC system is described; secondly, the two-level MC is replaced by TLDMC, the speed loop is cascade spiral sliding mode control, the torque magnetic chain loop is super twisting sliding mode control-direct torque control to replace the traditional PI control, and the modulation coefficient optimal method is introduced to reduce the drawback of gradually increasing motor torque fluctuation, and then the accurate control of PMSM is realized; finally, the feasibility and superiority of the proposed method are verified by MATLAB/Simulink simulation software and hardware experiments.

配电台区应用过程中,使用低压配电台区的用户占大多数.低压配电台区的走向和线路具有一定复杂性,如果低压配电台区运行时间过长,或者相关部门对低压配电台区缺乏维护,就极容易造成低压配电台区漏电故障,为供电企业带来严重的经济损失.文章针对低压配电台区漏电故障进行分析,讨论低压配电台区漏电故障排查要点,以供参考.

To ensure the robustness of the fractional frequency transmission system (FFTS), the ability of Y-type modular multilevel converters (Y-MMC) to operate under unbalanced operating conditions is essential. The Y-MMC controlled by traditional linear strategy has low robustness, high harmonics, low accuracy, and other disadvantages. In order to solve those problems, a passive sliding mode control strategy is proposed for Y-MMC in this paper. First, design a passivity-based controller based on the Euler–Lagrange (EL) model of Y-MMC, prove its stability using Lyapunov's theorem, combine the passivity-based controller with the sliding mode controller to derive a mathematical expression for the passive sliding mode control so that can enhance the robustness. Then, the modules of control target design, reactive power distribution, and modulation degree allocation are described. Finally, extensive MATLAB/Simulink platform simulation and RT-LAB platform experiments were conducted in different scenarios to verify the feasibility of the proposed method. This strategy improves the power quality indices under non-ideal conditions. It has better advantages than the traditional PI controller and passivity-based control in the accuracy and robustness of power transmission.

The control structure of modular multilevel matrix converter（M3C） is complicated when the dual αβ coordinate transformation is applied,the controlled variables are still AC components,and the control effect of the nonlinear M3C with linear proportional integral differential（PID） control is unsatisfactory. It is proposed to use the double dq coordinate transformation with simpler control system structure to convert all controlled variables in the M3C control system to DC components and adopt the nonlinear passivitybased control（PBC） strategy. Based on the PBC theory,the passivity and stability of the M3C object are analyzed,and the PBC strategy of M3C is designed and derived. The M3C PBC simulation system based on double dq coordinate transformation is built by MATLAB/Simulink to simulate the system operation under three operating conditions. The simulative results show that compared with PID control,the proposed PBC strategy has fewer control parameters,faster response speed,lower harmonic content and better overall control effect.