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.

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.

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.

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.

基于级联H桥换流器的APF-STATCOM的控制与调制

有源滤波器(APF)和静止同步补偿器(STATCOM)在电力系统应用中都是独立开来,分别进行谐波抑制和无功补偿。将APF和STATCOM功能结合起来,以级联H桥换流器构成APF-STATCOM装置,同时实现无功补偿和谐波抑制。在分析级联H桥APF-STATCOM拓扑及其工作原理的基础上,提出了一种简单有效的控制策略;针对级联H桥换流器各子模块间的电容电压均衡问题,采用最近电平逼近调制(NLM)并提出了一种适用于级联H桥换流器的电容电压均衡控制策略。利用PSCAD/EMTDC对36级联H桥APF-STATCOM进行了建模仿真,结果验证了该控制策略和电容电压均衡控制策略的可行性和有效性,并表明所提出的电容电压均衡策略能有效避免H桥模块IGBT不必要的频繁开关,减少器件的开关频率。

基于级联H桥五电平变流器SAPF的应用研究

提出了基于级联H桥型五电平变流器的并联型有源电力滤波器,详细介绍了基于无差拍控制的交流侧电流控制和直流侧总电压闭环电压控制的原理。仿真和实验结果表明了SAPF系统在低开关频率情况下,能够准确有效地补偿谐波和无功电流,性能良好。

基于H桥级联型逆变器的APF直流侧均压和稳压控制策略研究

针对H桥级联型逆变器直流侧电压不均衡、不稳定的现象,深入研究了一种两级式的均压和稳压控制策略。上级稳压控制维持各相直流侧总电压的稳定,控制装置与电网间的能量交换;下级均压控制维持相内各单元直流侧稳定,按需求分配从电网吸收的功率。从能量的角度分析了直流侧电容电压的波动规律和均压、稳压的控制原理。最后通过Simulink进行仿真,验证了基于H桥级联型逆变器APF的均压、稳压控制策略的可行性。

级联H桥APF软启动方式的研究

针对级联H桥多电平有源滤波器APF(active power filter)在投入电网启动过程直流侧电容电压上升对级联APF的冲击问题,在不改变级联拓扑结构的前提下,提出一种适用于级联APF的软启动方式。整个软启动过程包括预充电阶段、升压充电阶段和切除充电电阻阶段,可以有效地将级联APF的电容电压充电至设定值,不会对APF造成冲击。级联H桥七电平仿真和实验验证了所提方法的正确性和可行性。

基于Luenberger观测器的链式APF控制策略研究

为了克服传统无差拍控制和基于两拍采样的预测电流控制方法在控制延时情况下稳定裕度低、鲁棒性差等缺点,提出基于Luenberger观测器的鲁棒预测电流控制器设计方法,该方法有效补偿电流跟踪的时滞效应,显著地改善电流环的高频特性,提高控制精度、改善系统的稳定裕度和鲁棒性。动模实验表明,链式APF对于各种非线性负载均具有良好的补偿精度和动态响应速度,能够实现各H桥直流母线电压自均衡控制。

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.

单相级联H桥APF载波相移梯形波脉宽调制与电容电压平衡控制方法

针对电气化铁路谐波污染的电能质量问题,将载波相移梯形波脉宽调制CPS-TPWM(carrier phase-shifted trapezoidal wave pulse width modulation)策略引入到单相级联H桥多电平有源电力滤波器APF(active power fil?ter)中,同时在单相级联多电平有源电力滤波器直流侧电容电压控制上采用内外层控制策略,以提高直流侧电压的均衡性和稳定性。结合数学分析,搭建3个单元模块的单相级联H桥多电平APF主电路和控制系统进行仿真验证。结果表明:所提方法能够有效抑制电气化铁路中的谐波电流,并且能提高各单元模块直流侧电容电压的稳定性和均衡性。

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.

一种高性能的谐波检测数字低通滤波器

谐波检测的准确性和实时性是影响有源电力滤波器的重要因素。文中采用指数平均低通滤波器,并利用级联技术,解决了数字信号处理器有限字长与谐波提取的准确性和实时性之间的矛盾。将其用于串联混合型有源电力滤波器中,实现了高性能的谐波检测。实验结果证明了所提出的理论的正确性。

载波带频率变化的PWM(VFCB-PWM)在级联有源电力滤波器中的应用

分析了级联H桥型变换器的工况,讨论了载波带频率变化的PWM(VFCB-PWM)技术,提出了基于VFCB-PWM技术的级联H桥型多电平变换器。利用瞬时无功功率理论,将其应用在并联型有源电力滤波器(APF)中。仿真结果表明,该并联型APF系统能够有效地补偿非线性负载引起的谐波和无功电流,性能良好。

相移SPWM多电平变流器有源滤波器的仿真

通过仿真研究了级联型CPS—SPWM多电平变流器在电力有源滤波器中的应用问题。在并联有源滤波器的应用系统中,由于直流侧不需要提供有功功率,级联型多电平变流器的优势得到了充分的发挥;而CPS—SPWM技术良好的谐波传输特性也得到了良好的利用。

CPS-SPWM在级联型有源电力滤波器中的应用

提出了基于载波相移-正弦脉宽调制(CPS-SPWM)技术的级联H桥型多电平变流器,它是CPS-SPWM技术与级联H桥型变流器拓扑结构的结合,同时具备二者的优点,在大功率变流器领域具有很好的应用前景。文中给出了载波相移技术在级联H桥型变流器上的具体实现方法,并将其应用在并联型有源电力滤波器(APF)中,对直流侧总电压闭环电压控制的原理进行了验证。仿真和实验结果表明,该并联型APF系统在低开关频率情况下能够准确有效地补偿谐波和无功电流,性能良好。