Cascaded H-bridge Converter Research Articles

Multisampling with Sigma-Delta ADCs for Medium-Voltage Cascaded H-Bridge Converters

The control of medium-voltage cascaded H-bridge (CHB) converters demands precise, high-bandwidth, low-latency, and isolated measurements. Traditional analog-to-digital converters (ADCs) can facilitate multisampling methods to meet these requirements but do not provide the high-voltage galvanic isolation that may be necessary in a system operating at medium voltage. Sigma-Delta ADCs (SD-ADCs) present a promising alternative due to their superior noise rejection capabilities and direct integration with the optical fiber interface. However, the inherent latency associated with SD-ADCs, stemming from their operating principles, poses challenges when integrating them with multisampling methods. This paper analyzes the integration of multisampling techniques with SD-ADCs for medium-voltage CHB converter control. First, the impact of SD-ADC-induced delays on the control system is elucidated from the passivity perspective. Second, the practical implementation of multisampling with SD-ADCs is discussed in detail. Finally, experimental results from a 2400 Vrms medium-voltage CHB converter are presented to validate the analysis and illustrate the effectiveness of the proposed implementation.

Zero Sequence Injection in Delta-CHB STATCOM: Towards Optimum Silicon Area Through Typical Power IGBT/diode Model

This work quantifies the impact of third harmonic circulating current injection (THCCI) in a Cascaded H-bridge converter in delta configuration (Delta-CHB) for Static Synchronous Compensator (STATCOM) application. The analyses consist of evaluating the impact of THCCI on the silicon area of semiconductor devices. To achieve this objective, this work develops a typical IGBT/Diode model to determine the nominal current of the devices for a given maximum junction temperature. Commercial devices in the voltage classes of 1700 V, 3300 V, 4500 V, and 6500 V were considered, with nominal currents ranging from 150 A to 3600 A. A hybrid approach based on physical-oriented scaling laws and black-box modeling allows to reach a coefficient of determination higher than 79\% for all modeled variables. The results showed an increase of 43.8\% in the active area of the IGBT and 30.87\% in the active area of the diode when the peak cluster current increased by 62\% due to THCCI.

Passivity-based adaptive current control loop of cascaded H-bridge multilevel converter for grid-tied photovoltaic system

This paper proposes an algorithm to passivity-based control (PBC) for the current control loop of the cascaded H-bridge converter (CHB) connecting the grid-connected PV system with the space vector modulation (SVM) algorithm using the law of expanding any number of voltage levels. The algorithm SVM in this paper is suitable for CHB converters. It can create a number of high levels of alternating voltage that other methods cannot do. Passivity-based control (PBC) algorithm aims to create a flexible controller that can change its structure or parameters to adapt to changes in the system, ensuring stable system quality, reducing switching losses and gaining energy conversion efficiency. It enhances the capability of accurately delivering power on demand to the grid with the CHB inverter in situations in which the grid demands the mobilization of maximum power from the photovoltaics (PV) system. The simulation results of the 9-level CHB system performed by MATLAB/Simulink software have proved the feasibility of the proposed algorithm.

Extremely Low Frequency PS-PWM Based Technique for Cascaded H-Bridge Converters With Grid Voltage Compensation Capability

Cascaded H-Bridge Converters (CHB) are good candidates for many industrial applications. Among the modulation techniques that can be applied to CHB converters, the Phase-shifted PWM method (PS-PWM) provides very good harmonic quality being the most popular modulation technique at the expense of presenting high switching losses. On the contrary Block Switching technique as well as Selective Harmonic elimination/mitigation (SHE/SHM) techniques provides lower switching frequency and losses with a lower harmonic quality. Additionally with these techniques the converter operation becomes stiff. In this work a modification of PS-PWM based on an extremely low frequency carrier is proposed with the objective of achieving both low switching losses and an acceptable harmonic quality, simultaneously. The main advantage of the proposed solution is the capability of adjusting the phase-shift angle among the carriers to compensate for harmonic grid voltage disturbance. Several experimental results have been reported to demonstrate the good performance of the proposed modulation technique.

Unified Switching Frequency Minimized Harmonic Mitigation Technique for Asymmetric Cascaded H-Bridge Converters

Unified Switching Frequency Minimized Harmonic Mitigation Technique for Asymmetric Cascaded H-Bridge Converters

Improved Sequential Model Predictive Control of Cascaded H‐Bridge Multilevel Converter

The cascaded H‐bridge (CHB) converter can achieve rich functions, such as active rectification, active power filtering, distributed energy storage, etc. The control of the CHB converter is a multiobjective optimization problem. Finite control set model predictive control (FCS‐MPC) is an effective method developed in recent years to solve this problem. However, because of the large amount of calculation, traditional FCS‐MPC cannot be directly used to control the multilevel CHB converter. It is also difficult to tune the weighting factors in traditional FCS‐MPC. To solve these problems, this paper proposes an improved sequential MPC (IS‐MPC) method for the CHB converter. The proposed method divides the control objectives of the CHB converter into different layers according to their priorities and the control degrees of freedom of each layer can be adjusted according to the system state. Simulation and hardware‐in‐the‐loop (HIL) implementation on a three‐phase 7‐level CHB converter shows that the proposed method can effectively control the ac current and submodule voltage of the CHB converter and reduce the switching loss. Moreover, it significantly reduced the calculation burden of traditional FCS‐MPC, and the use of the weighting factors is also avoided. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Optimal Decoupled Discontinuous Modulation for StatComs Based on the Cascaded H-Bridge Converter

Conventional discontinuous pulse width modulation (DPWM) strategies for cascaded H-bridge static compensators suffer from poor inter-phase capacitor voltage balance control during unbalanced grid voltage conditions. Specifically, the logic-based algorithm that calculates the zero-sequence voltage (ZSV) for discontinuous operation interacts with the closed-loop capacitor voltage control. This paper proposes an optimal DPWM strategy based on a finite-set optimization that chooses the best ZSV candidate that minimizes the control interactions while clamping a converter voltage. Furthermore, the effect of the different ZSV candidates on the switching loss is also considered within the optimization. Extensive experimental study is provided to demonstrate the effectiveness of the proposed approach.

A Hybrid Modulation Technique for Operating Medium-Voltage High-Power CHB Converters Under Grid Voltage Disturbances

Power converters, and particularly multilevel converters, are key elements in the current energy scenario. Among them, Cascaded H-Bridge Converters (CHB) are a popular and versatile solution for many industrial applications. Technical literature provides multiple modulation techniques for its operation. Among them, hybrid-PWM modulation techniques provide a good trade-off between switching loss and output voltage quality. In this work a hybrid modulation technique is presented which allows not only the fundamental block switching operation of some power cells but also a harmonic control over a specific harmonic distortion present in the grid. To validate the operation of the proposal, several experimental results have been reported to demonstrated the good behaviour of the proposed modulation technique.

Dual-Stage MPC for SoC Balancing in Second-Life Battery Energy Storage Systems Based on Delta-Connected Cascaded H-Bridge Converters

Dual-Stage MPC for SoC Balancing in Second-Life Battery Energy Storage Systems Based on Delta-Connected Cascaded H-Bridge Converters

Dual-Layer Modulated Model Predictive Control Scheme for the Cascaded H-Bridge Converter

To simultaneously achieve fast dynamics and fixed switching frequency, a dual-layer modulated model predictive control scheme is proposed for the cascaded H-bridge (CHB) converter in this article. For the output current control layer, firstly, each phase cluster is considered as a whole, and only six nonzero vectors are evaluated for output current prediction. Then, two optimal vectors are selected, and their dwell times are calculated based on the current prediction results. As a result, fast output current dynamics can be obtained with a greatly reduced number of evaluated control options. For the cluster voltage balancing control layer, instead of fundamental-frequency zero-sequence voltage (ZSV), the adaptive ZSV is injected according to the predicted cluster voltage differences. As a result, the active power flows are adjusted in each control period, and the cluster voltage balancing speed can be significantly improved. By the proposed scheme, complicated weight factor design is avoided, and fixed switching frequency is obtained through the integration of pulsewidth modulation. Experimental results verify that the proposed scheme can achieve fast output current and cluster voltage balancing dynamics with fixed switching frequency.

A model-based power switch fault diagnosis strategy for cascaded H-Bridge converter

Cascaded H-Bridge (CHB) converter is a promising solution in medium-voltage high-power application, such as railway traction, grid-connected photovoltaic (PV) system. However, the large number of power switches involved in the topology is a potential reliability risk since the power switch is the most vulnerable component in a power electronic system. To achieve a fast and accurate power switch fault diagnosis (FD) in CHB, this paper proposes a model-based hierarchical FD strategy, consisting of phase-level and cell-level fault detection. There is no need of extra sensors or high computational burden. The effectiveness of the method is verified by simulation and experiment.

Neural Network Model-Predictive Control for CHB Converters With FPGA Implementation

Finite Control Set Model Predictive Control appears an interesting and effective control technique for Cascaded H-Bridge converters but, because of its computational complexity, becomes impractical when the number of levels of the converter increases. This paper proposes a Neural Network-based approach capable of overcoming the computational burden of conventional predictive control algorithms. The proposed control is then applied to a Cascaded H-Bridge Static Synchronous Compensator using FPGA and tested via hardware in the loop. Results and analysis demonstrate that optimal control of multilevel converters with many levels can be obtained with low computational effort.

Virtual Inertia Control for CHB-STATCOM in a Power Electronics Dominated Grid

Integration of renewable energy sources (RESs) leads the power system to be a low inertia system, resulting in frequency deviation in the grid. This paper presents a cascaded H-bridge (CHB) converter-based static synchronous compensator (STATCOM) providing virtual synchronous inertial support. This topology achieves two functionalities. 1. It reduces the system frequency deviation in a power electronics dominated grid (PEDG) following the updated grid codes. 2. Without disturbing the normal operation of CHB-STATCOM, it provides reactive power support. This topology uses the cumulative stored energy in the distributed DC-bus capacitors of CHB-STATCOM to improve the frequency nadir/zenith and the rate of change of frequency (RoCoF), preventing frequency instability. A closed- loop control algorithm is developed, which injects an adequate amount of stored energy to prevent frequency variation. It also facilitates re-energizing the capacitors in a smooth fashion, so that subsequent frequency events can be taken care of. For this, a high-pass-filter (HPF) is designed for autonomous DC- link voltage restoration for CHB converter. Relationship between frequency variation and inertial energy support by CHB is analyzed in depth. Finally, the viability of the proposed theory is verified in OPAL-RT test bench for step-up and step-down load change.

Flexible Power Control for Extending Operating Range of PV–Battery Hybrid Cascaded H-Bridge Converters Under Unbalanced Power Conditions

Due to the nonuniform solar irradiance, different temperature and inconsistent module features, the output power among each photovoltaic (PV) module in a single-phase cascaded H-bridge (CHB) inverter is unequal. The H-bridge module with higher power generation faces the risk of overmodulation. To further extending the operating range of the CHB PV inverter under unity power factor condition, a battery module is connected with the system in series to form a PV-battery hybrid CHB converter in this paper. Meanwhile, the corresponding flexible power control strategy is proposed. The injected power of the battery module is controlled adaptively according to the maximum modulation index (MI) of all PV modules. With the proposed approach, all PV modules are free from overmodulation even with severe power imbalance and thus more energy are harvested. The effectiveness of the proposed control method is verified by experimental results.

Balanced Charging Algorithm for CHB in an EV Powertrain

The scientific literature acknowledges cascaded H-bridge (CHB) converters as a viable alternative to two-level inverters in electric vehicle (EV) powertrain applications. In the context of an electric vehicle engine connected to a DC charger, this study introduces a state of charge (SOC)-governed method for charging li-ion battery modules using a cascaded H-bridge converter. The key strength of this algorithm lies in its ability to achieve balanced charging of battery modules across all three-phase submodules while simultaneously controlling the DC charger, eliminating the need for an additional intermediate converter. Moreover, the algorithm is highly customizable, allowing adaptation to various configurations involving different numbers of submodules per phase. Simulative and experimental results are presented to demonstrate the effectiveness of the proposed charging algorithm, validating its practical application.

A New Active Front-End Control for Regenerative Cascaded H-Bridge Motor Drives With Filter- Less Interfacing Capability

This paper proposes a new active-front-end (AFE) control method for regenerative Cascaded H-bridge (CHB) motor drives. Conventional CHB converters have dominated the market for the medium-voltage industrial motor drives. However, conventional CHB converters cannot provide regenerative capability. To enable regeneration; diode-front-ends (DFEs) in power cells are replaced with IGBT-based PWM AFEs. Despite the appealing dynamic performance of PWM AFEs, their integration to the CHB converters is not optimal. First, they introduce more semiconductor losses due to the high frequency switching. Second, they introduce switching harmonics that are not cancelled by phase-shifting transformers. Therefore, they require additional harmonic filtering solutions to comply with grid harmonic standards. To resolve these challenges, this paper proposes a new AFE control for regenerative CHB converters based on fundamental frequency switching (FFE) to reduce switching frequency and thus power losses. The operation of FFEs at nominal and sag voltage conditions is presented, in addition to the capability of filter-less interfacing to the transformer. Finally, the performance of the proposed control is validated experimentally on a seven-level regenerative CHB drive.

Optimal Components Selection for a DAB Model of CHB Converter

This paper proposes a sizing procedure for the cascaded H-bridge (CHB) converters integrating the battery energy storage system at the submodule level through a dual active bridge (DAB) converter. The suggested methodology considers different parameters, such as the adopted modulation strategies and the topology of the DAB converter employed. Three possible DAB configurations are considered: the one using only full-bridges (for both sides), the one using only half-bridges (for both sides) or a mixed configuration using half-bridge on one side and full-bridge on the other side. After determining the system parameters, the solution capable of reaching the required efficiency target at the minimum cost is obtained. The cost analysis and the efficiency evaluation are carried out considering a dataset containing almost 1000 semiconductor devices whose datasheets have been taken from the manufacturers' websites. The procedure has been developed in the framework of a collaboration with NHOA Energy and its effectiveness is demonstrated by sizing a 1 MW-CHB converter combined with energy storage systems at 11 kV.

Inverter Operation Mode of a PhotoVoltaic Cascaded H-Bridge Battery Charger

The paper deals with a grid-connected single-phase battery charger integrated with photovoltaic generators (PVGs). The circuit topology consists of a multilevel architecture based on a Cascaded H-Bridge (CHB) rectifier. Its main task is to charge the batteries, primarily from the PVGs, by also assuring to keep their state-of-charge (SOC) balanced. Nevertheless, when the battery SOC overcomes a predefined upper limit, beyond which the charging process could be interrupted, the available PV power can no longer be transferred to the batteries. Therefore, to avoid an undesired curtailment of PV power production, this latter can be supplied to the grid by inverting the system operation. The paper shows how to achieve this result by implementing a dedicated control action based on a multi-step procedure. Numerical investigations are carried out on a 19-level CHB converter implemented in the PLECS environment to validate the feasibility and effectiveness of the proposed control technique.

An improvement of stability and dynamic response in hybrid AC-DC microgrids using optimal power control management

Microgrid topologies enable more effective use of renewable resources as well as the autonomous process. Microgrids are effective frameworks for managing dispersed assets such as renewable structures with small-scale distributed generator supplies. Smart grids are adaptable electricity networks that have arisen as a result of the introduction of new technologies and features. It is suggested that a three-terminal AC/DC hybrid microgrid with DC two and AC one terminal be used. A two dual active bridge (DAB) with cascaded H-bridge (CHB) converter with AC grid link-based interactions that connect isolated two DC buses are included in the suggested structure. To minimise the energy generation stages and power devices, the DAB converters are intrinsically linked to the CHB of DC rails based on the structure-specific requirements. To present the unnecessary grid currents and DC rail voltage issues exist by this revised structure topology by simply two power alteration stages, a better solution is suggested that employs zero-sequence voltage (ZSV) injection in the CHB converters. The impacts of managed settings on structure stability and dynamic responsiveness are investigated in order to reduce conflicts among ZSV injection by structure voltage/current regulation. This paper compares the performance of a PI and a PR for DC voltage regulation. A comparison of simulation results for both control approaches is provided. The major difficulty is to normalise the system model in order to identify the appropriate controller settings for robust control. The findings are confirmed and compared to the conventional regulator PI. The suggested 3-Φ AC current and DC rail voltage regulating approach's universal efficacy is proved by MATLAB/Simulink analytical model from the three and five-terminal hybrid AC/DC power structures.

Transmission of Digital Data to Cascaded H-Bridge Converters Through the Power Line

Power line communication (PLC) technologies enable the point-to-point linking between distributed power production and consumption units, thus overlaying enhanced monitoring and control capabilities to the overall power system. A novel PLC method for cascaded H-bridge converters is presented in this article, which enables the transmission of digital data by a remote terminal computer to the individual power modules synthesizing a cascaded H-bridge power converter through their power circuits. The proposed PLC method comprises an integrated framework of a digital data transmitter, receiver, and communication protocol, without using additional coupling circuits, which is suitable for cascaded H-bridge power converters with either a dc or an ac output. Its operation was tested using an experimental prototype consisting of a two-module cascaded H-bridge inverter and a field-programmable gate array device hosting the digital transmitter and receiver units. The experimental results verified the successful transmission of digital parameterization commands from a central terminal computer to the individual power modules of the cascaded H-bridge converter, along with the simultaneous transmission of ac or dc power to the load over the common power cable.