Coordinated Capacitor Voltage Balancing Method for Cascaded H-bridge Inverter with Supercapacitor and DC-DC Stage

Cascaded H-bridge inverter(CHBI) with supercapacitors(SCs) and dc-dc stage shows significant promise for medium to high voltage energy storage applications. This paper investigates the voltage balance of capacitors within the CHBI, including both the dc-link capacitors and SCs. Balance control over the dc-link capacitor voltages is realized by the dcdc stage in each submodule(SM), while a hybrid modulation strategy(HMS) is implemented in the H-bridge to balance the SC voltages among the SMs. Meanwhile, the dc-link voltage fluctuations are analyzed under the HMS. A virtual voltage variable is introduced to coordinate the balancing of dc-link capacitor voltages and SC voltages. Compared to the balancing method that solely considers the SC voltages, the presented method reduces the dc-link voltage fluctuations without affecting the voltage balance of SCs. Finally, both simulation and experimental results verify the effectiveness of the presented method.

Model Predictive Control for Cascaded H-Bridge PV Inverter with Capacitor Voltage Balance

We designed an improved direct-current capacitor voltage balancing control model predictive control(MPC)for single-phase cascaded H-bridge multilevel photovoltaic(PV)inverters.Compared with conventional voltage balanc-ing control methods,the method proposed could make the PV strings of each submodule operate at their maximum power point by independent capacitor voltage control.Besides,the predicted and reference value of the grid-connected current was obtained according to the maximum power output of the maximum power point tracking.A cost function was con-structed to achieve the high-precision grid-connected control of the CHB inverter.Finally,the effectiveness of the proposed control method was verified through a semi-physical simulation platform with three submodules.

A distributed VSG control method for a battery energy storage system with a cascaded H-bridge in a grid-connected mode

With the high penetration of renewable energy,new challenges,such as power fluctuation suppression and inertial support capability,have arisen in the power sector.Battery energy storage systems play an essential role in renewable energy integration.In this paper,a distributed virtual synchronous generator(VSG)control method for a battery energy storage system(BESS)with a cascaded H-bridge converter in a grid-connected mode is proposed.The VSG is developed without communication dependence,and state-of-charge(SOC)balancing control is achieved using the distributed average algorithm.Owing to the low varying speed of SOC,the bandwidth of the distributed communication networks is extremely slow,which decreases the cost.Therefore,the proposed method can simultaneously provide inertial support and accurate SOC balancing.The stability is also proved using root locus analysis.Finally,simulations under different conditions are carried out to verify the effectiveness of the proposed method.

THD Analysis of Cascaded H-Bridge Inverter with Fuzzy Logic Controller

In recent days, the multilevel inverter technology is widely applied to domestic and industrial applications for medium voltage conversion. But, the power quality issues of the multilevel inverter limit the usage of much sensitive equipment like medical instruments. The lower distortion level of the output voltage and current can generate a quality sinusoidal output voltage in inverters and they can be used for many applications. The harmonics can cause major problems in equipments due to the nonlinear loads connected with the power system. So, it is necessary to minimize the losses to raise its overall efficiency. In this paper, a new topology of seven level asymmetrical cascaded H-bridge multilevel inverter with a Fuzzy logic controller had been implemented to reduce the Total Harmonic Distortion (THD) and to improve the overall performance of the inverter. The proposed model is well suited for use with a solar PV application. In this topology, only six IGBT switches are used with three different voltage ratings of PV modules (1:2:4). The lower number of semiconductor switches leads to minimizing overall di/dt ratings and voltage stress on each switches and switching losses. The gate pulses generated by Sinusoidal Pulse Width Modulation (SPWM) technique with a Fuzzy logic controller are also introduced. A buck-boost converter is used to maintain the constant PV voltage level integrated by an MPPT technique followed by Perturb and Observer algorithm is also implemented. The MPPT is used to harness the maximum power of solar radiations under its various climatic conditions. The new topology is evaluated by a Matlab/Simulink model and compared with a hardware model. The results proved that the THD achieved by this topology is 1.66% and realized that it meets the IEEE harmonic standards.

Coordinated Control of Second-order Harmonic Voltage and Current Fluctuations in Cascaded H-bridge Inverter with Supercapacitor and DC-DC Stage at Variable Output Frequencies

In the cascaded H-bridge inverter(CHBI)with supercapacitor and dc-dc stage,inherent second-order harmonic power flows through each submodule(SM),causing fluctuations in both the dc-link voltage and the dc-dc current.There exist limitations in handling these fluctuations at variable output frequencies when employing proportional-integral(PI)control to the dc-dc stage.This paper aims to coordinately control these second-order harmonic voltage and current fluctuations in the CHBI.The presented method configures a specific second-order harmonic voltage reference,equipped with a maximum voltage fluctuation constraint and a suitable phase,for the dc-dc stage.A PI-resonant controller is used to track the configured reference.This allows for regulating the second-order harmonic fluctuation in the average dc-link voltage among the SMs within a certain value.Importantly,the second-order harmonic fluctuation in the dc-dc current can also be reduced.Simulation and experimental results demonstrate the effectiveness of the presented method.

低电容CHB型混合动力中压电机调速系统

针对氢燃料电池大功率电机驱动系统,提出一种以燃料电池为主动力源的轻量化级联H桥(cascadedH-bridge,CHB)型混合动力中压电机调速系统。所提系统由燃料电池/蓄电池/超级电容的混合动力源供电,基于四有源桥(quad activebridge,QAB)与CHB子模块互联的两级变换器(cascaded H-bridges with quad active bridge,CHB-QAB)作为调速变换器。CHB-QAB通过四绕组高频变压器将各子模块进行内部互联,采用单边同步双边移相调制的策略,使得所有子模块呈现开关电容特性,在不依赖复杂控制的前提下,减小子模块电容的容值,提升系统的功率密度。针对三类动力源,采用基于低通滤波(lowpassfilter,LPF)的能量管理策略,保证电机实际运行过程中的有效功率分配,解决燃料电池对电机动态响应缓慢和燃料饥饿现象等问题。最后通过仿真与实验对所提轻量化电机调速系统进行验证。

Neural Network and Fuzzy Control Based 11-Level Cascaded Inverter Operation

This paper presents a combined control and modulation technique to enhance the power quality(PQ)and power reliability(PR)of a hybrid energy system(HES)through a single-phase 11-level cascaded H-bridge inverter(11-CHBI).The controller and inverter specifically regulate the HES and meet the load demand.To track optimum power,a Modified Perturb and Observe(MP&O)technique is used for HES.Ultra-capacitor(UCAP)based energy storage device and a novel current control strategy are proposed to provide additional active power support during both voltage sag and swell conditions.For an improved PQ and PR,a two-way current control strategy such as the main controller(MC)and auxiliary controller(AC)is suggested for the 11-CHBI operation.MC is used to regulate the active current component through the fuzzy controller(FC),and AC is used to regulate the dc-link voltage of CHBI through a neural network-based PI controller(ANN-PI).By tracking the reference signals fromMC and AC,a novel hybrid pulse widthmodulation(HPWM)technique is proposed for the 11-CHBI operation.To justify and analyze the MATLAB/Simulink software-based designed model,the robust controller performance is tested through numerous steady-state and dynamic state case studies.

Simplified Cluster Voltage Balancing Control Based on Zero-sequence Voltage Injection for Star-connected Cascaded H-bridge STATCOM

The cluster DC voltage balancing control adopting zero-sequence voltage injection is appropriate for the starconnected cascaded H-bridge STATCOM because no zerosequence currents are generated in the three-phase three-wire system.However,as the zero-sequence voltage is expressed in trigonometric form,traditional control methods involve many complicated operations,such as the square-root,trigonometric operations,and inverse tangent operations.To simplify cluster voltage balancing control,this paper converts the zero-sequence voltage to the dq frame in a DC representation by introducing a virtually orthogonal variable,and the DC components of the zero-sequence voltage in the dq frame are regulated linearly by proportional integral regulators,rather than being calculated from uneven active powers in traditional controls.This removes all complicated operations.Finally,this paper presents simulation and experimental results for a 400 V±7.5 kvar star-connected STATCOM,in balanced and unbalanced scenarios,thereby verifying the effectiveness of the proposed control.

Capacitor Pattern H-Bridge Multilevel Inverter (CPHMLI) Using Phase Diposition Pulse Width Modulation for Grid Applications

This work presents an implementation of an innovative single phase multilevel inverter using capacitors with reduced switches. The proposed Capacitor pattern H-bridge Multilevel Inverter (CPHMLI) topology consists of a proper number of Capacitor connected with switches and power sources. The advanced switching control supplied by Pulse Width Modulation (PDPWM) to attain mixed staircase switching state. The charging and discharging mode are achieved by calculating the voltage error at the load. Furthermore, to accomplish the higher voltage levels at the output with less number of semiconductors switches and simple commutation designed using CPHMLI topology. To prove the performance and effectiveness of the proposed approach, a set of experiments performed under various load conditions using MATLAB tool.

一种基于磁链估算的单相CHB变流器无锁相环控制策略

为提高并网变流器的控制性能,提出一种新型的无锁相环控制方法,可有效避免锁相环(phase-locked loop,PLL)对动态性能的影响,控制结构得到简化。基于单相级联H桥(cascaded H-bridge,CHB)多电平变流器,首先引入一种增强的观测器,可准确估算出正弦的磁链基波信号;其次,推导了无锁相环控制的实现过程,并给出指令电流的计算公式。然后,针对电网电压谐波干扰的问题,通过建立阻抗模型,分析了系统的谐波抑制能力;并提出一种改进的电流控制器,实现了并网电流无谐波和快速动态响应的控制目标。此外,平衡控制方法使变流器直流侧电压保持稳定。最后,仿真和实验验证结果表明了所提方法的有效性。

一种改进的CHB多电平变换器PWM调制策略

级联H桥CHB(cascaded H-bridge)多电平变换器是中压大功率电机驱动系统最广泛采用的拓扑,传统LS-PWM和PS-PWM不能很好地兼顾输入、输出电流的谐波性能,对比了CHB多电平变换器在这两种调制策略下的输入和输出THD,分析了两种方法下输入、输出波形产生区别的本质原因,进而探讨了一种局部载波移相PWM调制方法。该方法吸收了两种调制方法的优点,发挥PS-PWM调制时模块功率均衡和网侧输入电流谐波低的特点以及LS-PWM输出电能质量好的特点。最后,搭建了三相七电平CHB变换器实验平台,对局部载波移相PWM调制策略进行了验证。

Evaluation of 1.2 kV SiC MOSFETs in Multilevel Cascaded H-bridge Three-phase Inverter for Medium-voltage Grid Applications

A study is conducted to evaluate 1.2 kV silicon-carbide(SiC)MOSFETs in a cascaded H-bridge(CHB)three-phase inverter for medium-voltage applications.The main purpose of this topology is to remove the need for a bulky 60 Hz transformer normally used to step up the output signal of a voltage source inverter to a medium-voltage level.Using SiC devices(1.2-6.5 kV SiC MOSFETs)which have a high breakdown voltage,enables the system to meet and withstand the medium-voltage stress using only a minimal number of cascaded modules.The SiC-based power electronics when used in the presented topology considerably reduce the complexity usually encountered when Si devices are used to meet the medium-voltage level and power scalability.Simulation and preliminary experimental results on a low-voltage prototype verifies the nine-level CHB topology presented in this study.

CHB逆变器3N+1与SVM容错切换

多电平逆变器的开关器件一旦发生故障,会造成输出电压不对称,系统运行负担加剧等不良影响。将3N+1冗余和空间矢量调制(SVM)应用于多电平级联H桥(CHB)逆变器实现开关故障的容错控制,平衡故障引起的直流偏移,稳定逆变器的运行。根据不同开关故障类型的无效空间矢量分布,判断是否需要插入冗余单元以及冗余单元是否发挥直流电压的作用,再选择有效开关状态控制开关器件的通断平衡线电压和负载电压。提出的方案能够提高故障CHB逆变器的最大输出电压和可靠性。仿真和实验结果验证了提出的容错策略的有效性。

Finite-time robust control for transformerless H-bridge cascaded STATCOM with star configuration

This article presents a finite-time robust control(FTRC)of a transformerless STATCOM based on a cascaded multilevel H-bridge converter(CMHC)with star configuration.The FTRC is first proposed for the current loop control of a CMHC-based transformerless STATCOM by using the finite time robust control theory.Taking the parameters,perturbations and external disturbances into account and using coordinate transformation method,the nonlinear dynamic model of the CMHC-based transformerless STATCOM is transformed into a standard nonlinear port-controlled dissipative Hamiltonian(PCDH)structure.Based on the PCDH structure,an FTRC is designed for the CMHC-based transformerless STATCOM to improve the transient stability and oscillation damping of power system.Finally,the simulation results demonstrate that the FTRC has better dynamic performance and strong robustness in comparison with the passivity-based control of the CMHC-based transformerless STATCOM.

基于光储混合配置的级联H桥型光伏逆变器功率平衡策略

级联H桥(cascade H-bridge,CHB)变换器由于其模块化结构,已成为大规模光伏(photovoltaic,PV)并网逆变器的优选方案。然而,在不同光照强度和温度下,不同区域PV组件之间发电功率不同,导致CHB变换器相间输出功率不均衡、不稳定等问题。为此,文中提出一种基于CHB结构的光储混合电能路由,在三相CHB光伏逆变器中配置少量的储能模块,利用光储协同控制,维持CHB内部功率稳定,消除分布式PV在相间产生的不均衡功率,且变换器输出功率能够时刻满足网侧上层功率调度,提高了光伏电站的稳定性。针对系统安全区域,在载波移相调制策略下,全桥子模块传输的功率受到约束,并对光伏和储能模块的配置作详细分析。最后,通过仿真以及实验验证所提拓扑及控制策略的正确性和有效性。

牵引级联变流器低次谐波分析与抑制策略优化

以级联H桥变流器为前级拓扑的电力电子变压器是未来列车牵引的重要发展方向,降低牵引级联变流器的低次谐波对提高电力电子变压器的控制性能具有重要意义。然而,引起级联H桥变流器低次谐波的影响因素与常规四象限变流器存在差异,其机理分析和抑制策略尚未得到深入研究。对此,文章详细探究了电力牵引网侧级联H桥变流器低次电流谐波产生机理,揭示了除直流电压波动、器件死区和管压降外,其低次谐波还与H桥级联的模块数及拓扑结构有关。在此基础上,设计一种兼顾直流电压波动和电路拓扑特性的低次谐波抑制算法。同时,结合功率器件的死区效应与管压降影响,提出级联H桥变流器低次电流谐波综合抑制策略。最后,搭建小功率试验平台进行测试,试验结果验证了理论分析的正确性和优化抑制方案的有效性。

九电平高压级联逆变器及其电压移位脉宽调制技术

介绍了九电平级联H桥逆变器的拓扑结构及其常用的载波调制方式,即相角移位调制和电压移位调制。分析了电压移位调制技术,设计了多电平高压级联H桥逆变器。Matlab／Simulink仿真实验结果表明用电压移位脉宽调制技术设计的九电平级联H桥逆变器在较低的频率下谐波失真小、电压变化率低、在电力系统高压变频及柔性输配电系统等具有较高的实用价值。

单相级联H桥整流电路非线性控制策略

针对电力电子牵引变压器输入级单相级联H桥(CHB)整流电路的非线性及扰动工况,提出一种基于静止坐标系的非线性优化控制策略。根据系统仿射非线性模型及微分几何理论,提出基于部分反馈线性化的零动态设计方案,对其线性部分采用二次型最优方法以确定反馈增益,并引入谐振环节以实现零相差跟踪;对于零动态则采用基于扩张状态观测器的自抗扰控制策略,以提高系统在负载大范围扰动时的控制品质。实验结果表明,该控制策略能提高CHB系统在电网电压及负载扰动时的动态响应速度,保证网侧电流及直流电压快速稳定调节,同时使网侧在单位功率因数下运行,各模块直流电压均衡。

级联H桥型高压变频器中脉冲编解码技术研究

级联H桥型高压变频器在轧钢、冶金、矿井提升、机车牵引以及电力系统有源滤波和无功功率补偿等场合都得到了广泛的应用。在6 k V及以上的工业应用场合,采用级联H桥型技术方案构成的变频器在成本、可靠性、电压谐波质量等方面具有相当的竞争性。在级联H桥型变频器中,各H桥单元的电压处于浮动状态,出于高压隔离的目的,一般采用光纤传输驱动脉冲信号。由于变频器中H桥单元个数众多,驱动脉冲数量庞大,为减少光纤使用数量,降低系统成本,提高系统可靠性,采用一条光纤信号进行脉冲传输成为一种可行的技术方案。分析了对脉冲信号进行编解码的技术方案,并将其成功应用于一台6 k V,600 k W高压变频器中,实验结果验证了所提的脉冲编解码方案的正确性与可行性。

大容量级联式电池储能功率调节系统中多脉冲驱动技术研究

出于高压隔离目的,大容量级联式电池储能系统中,一般采用光纤传输驱动脉冲信号。由于H桥单元个数众多,驱动脉冲数量庞大,为减少光纤使用数量,降低系统成本,提高工作可靠性,采用编解码技术,对多路脉冲驱动信号进行编码后通过一条光纤信号进行串行传输成为一种可行的解决方案。首先分析了PWM脉冲信号的产生算法,在此之上提出针对多路PWM脉冲进行编解码的算法,指定通信协议,采用光纤信号进行串行通信,并将该方案成功应用于一台6 k V,600 k W电池储能功率调节系统(PCS)中,实验结果表明采用该编解码方案使用一条光纤即可完成传统多路光纤传输任务,功率调节系统输出与理论分析一致,电压谐波含量低,并网电流正弦度高,验证了所提的脉冲编解码方案的正确性与可行性。