Capacitor Voltage Balancing Research Articles

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 balancing 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 constructed 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.

Transformer-Less Hybrid Series Static Compensator and its DC Capacitor Voltage Balance Technique Using Zero-Sequence Voltage

Transformer-Less Hybrid Series Static Compensator and its DC Capacitor Voltage Balance Technique Using Zero-Sequence Voltage

Capacitor Voltage Balancing Control of MMC Sub-Module Based on Neural Network Prediction

The issue of sub-module (SM) capacitor voltage unbalance is a hot topic in the current research into the modular multilevel converter (MMC). An excellent strategy comprises mitigating the SM capacitor voltage imbalance by adjusting the SM on time. The traditional capacitor voltage balancing control regulates the speed to maintain accuracy. A unique SM capacitor voltage balancing control strategy is presented in this paper and is based on conventional capacitor voltage balance management and neural network prediction. Firstly, the SM capacitor voltage and arm current are speculated by operating the time series forecasting technique in real time, considering the dynamic changes in the SM capacitor voltage and arm current. Secondly, the SM capacitor voltage distinction between the actual and theoretical value is determined, and a deviation’s mixed Gaussian distribution is established to estimate its compensation voltage. Thirdly, the SM triggering sequence is anticipated by using the neural network along with the pilot values of the SM capacitor voltage, arm current, and the offset compensation value, and the control is executed. Finally, a three-phase, six-leg, eight-module, nine-level MMC model is built to verify the feasibility of the suggested approach.

Output-feedback control of a grid-connected photovoltaic system based on a multilevel flying-capacitor inverter with power smoothing capability

With the large-scale integration of renewable energy systems, the power inertia and voltage support of the grid are low. Using the inverter with temporary storage capabilities cope with shortages and power fluctuations. This paper presents a new sensorless control of a single-phase grid-connected PV system based on a multilevel flying capacitor inverter MFCI) able to smooth out the power produced. The designed controller involves two cascade loops, an outer loop control extracts the maximum power despite climate change, and an inner loop consists of a model predictive control based on the Lyapunov theory for power factor correction and flying capacitor voltage balancing. Furthermore, an interconnected Kalman-like high-gain observer is combined with the predictive control algorithm to estimate the flying capacitor voltages accurately based on the actual grid current. The stability study of the suggested observer in the closed loop has been described. An algorithm that generates reference signals to manage power flows is also developed. The performance of the proposed controller has been verified on the MATLAB/Simulink platform, and the simulation results confirm the effectiveness of the proposed controller over different grid operating modes.

A Discrete-Time Current Control Method for the High-Speed Permanent Magnet Motor Drive Using the Modular Multilevel Converter

High-speed permanent magnet motors (HSPMMs) have received attention in direct drive systems from the industry. Modular multilevel converters (MMCs) have become the most practical solution for HSPMMs in industrial applications due to the advantages of their highly modular structure, high-quality output and high reliability. In this article, the symmetrical discrete-time model of the MMC for the HSPMM drive is presented. Based on this symmetrical discrete-time model, the discrete-time current regulator has been designed. Moreover, the submodel (SM) capacitor energy balance models for MMC have been described, and the energy balance control scheme is introduced. Finally, the simulation and experimental results show that the presented discrete-time current regulator has a strong dynamic response at high speed (15 kr/min), and the SM capacitor voltage balance control is also achieved. Compared with the conventional PI current controller, the proposed discrete-time current regulator improves the current loop dynamic performance at high-speed, and the energy balance control scheme can ensure the SM capacitor voltage balance of the MMC.

A novel switched-capacitor based multilevel voltage boost inverter for EV interface

ABSTRACT Lithium cells are connected in parallel and series to meet the current and voltage requirements in Electric vehicles (EV). Voltage and charge equaliser techniques are employed to protect the lithium cells. These equalisation circuits introduce the loss to the circuit, and the battery pack gets disconnected if any cell is faulty. Switched-capacitor converters have become an alternative to meet the voltage requirement. This article presents a voltage boost multilevel inverter configuration for electric vehicle applications. The proposed MLI features an inherent capacitor self-balancing capability and generates an output with a nine-level range. Algorithms for capacitor voltage balancing or additional sensor circuits are not required because of intrinsic self-balancing. For generating output levels, capacitors with a voltage source with an appropriate charging/discharging pattern are used. The proposed inverter doubles the output voltage for nine levels. A comparison of components, such as the number of semiconductors, diodes, gate driver circuits, and capacitors; system parameters such as voltage gain, blocking voltage, and TSV, is presented to demonstrate the advantages of the proposed MLI over recently developed topologies.

Research on the expansion and optimization control strategy of cascaded rectifier H-bridge

Extensive research on the multi-bridge extension of cascaded rectifier stages is deemed important to meet the requirements of high-voltage and high-power applications. Two control structures for capacitor voltage balancing in cascaded rectifier stages are analyzed in this paper. On this basis, the balance strategy for the multi-bridge extension of single-phase cascaded rectifiers is explored. The balance method of ultra-fast balance modulation trajectories is introduced into single-phase multi-bridge cascaded rectification, and the optimal control strategy is selected through simulation verification and comparative analysis. During the actual experiments, some disturbance factors were introduced into the system, causing an instantaneous unbalanced state. However, through the control strategy proposed in this paper, the system can quickly regain balance. Through simulation validation and analysis of the experimental results, the reliability and innovation of this control strategy have been demonstrated.

Power Losses Reduction of Stacked Multicell Converter Fed Wind Energy Conversion System (WECS) Using Hybrid Methodology

This paper proposes a hybrid method for reduction of power losses of multicell converter in wind energy conversion system (WECS). The proposed methodology is the Artificial Intelligence (AI) based phase disposition pulse width modulation (PD-PWM). The Artificial Intelligence (AI) is the Gradient Boosting Decision Tree algorithm (GBDT). Hence it is named as GBDT-PD-PWM. Gradient boosting is a machine learning system that creates a prediction model in the group of weak prediction models, often called decision trees. The multicell converter is employed as the grid side converter (GSC) of WECS to attenuate harmonics created by nonlinear load. For stacked multicell converters (SMCs), a method of capacitor voltage balance based on PD-PWM approach is proposed.

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.

Circulating current suppression and natural voltage balancing using phase-shifted modulation for modular multilevel converter

The challenge of achieving a balanced capacitor voltage is one of the factors affecting the efficient operation of modular multilevel converters (MMC). This paper investigates this challenge through a proposed method that utilizes a high carrier frequency phase-shifted pulse width modulation (PS-PWM) scheme. This method aims to achieve natural balancing without the need for any additional control mechanisms. Moreover, the number of output voltage levels is affected by the phase shift between the carriers of the upper and lower arms. When there is no phase shift, N<sup>+1</sup> discrete levels are achieved, but when there is a phase shift, the number of discrete levels increases to 2<sup>N+1</sup>. The proportional-resonant (PR) controller and moving average filter (MAF) are employed to decrease the capacitor voltage ripples by suppressing the fourth and second harmonics in the circulating currents. The MMC inverter structure is modeled and simulated in the PLECS and MATLAB/Simulink environments to evaluate the impact of this control scheme on the converter’s performance.

Comprehensive Analysis on Topological Structure of Modular Multilevel Converters

This paper discusses the importance and application of modular multilevel converter (MMC) in the field of power conversion. Firstly, the article starts with the basic concept of MMC and introduces its key role in high-power electrical energy conversion. Subsequently, to address the complexity of MMC, the article describes in detail the common topologies of MMC, including diode-clamped multilevel topology, flyover capacitor topology, H-bridge cascade topology, and switched-capacitor multilevel topology, and also emphasizes the different scenarios in which they are applied to power systems. The last section describes the capacitor voltage balancing strategy in MMC. Several common capacitor voltage balancing strategies, including hardware clamping method, capacitor voltage closed-loop method, and capacitor voltage sequencing method, are comprehensively discussed in this paper, and the principles, advantages, disadvantages, and applicability of each strategy are thoroughly analyzed. Ultimately, this article offers academics and engineers a thorough review of MMC and offers valuable references for further study and real-world applications in the areas of power system conversion and energy management.

Investigation of PWM methods for a 9 level boost inverter using CD-type carriers

The article suggests a new boost inverter topology that uses two switching capacitors and a single dc source to produce an output voltage waveform with nine levels. There are no sensors or other electronics required because the capacitor voltages balance themselves. An input dc boost converter is not necessary when using an inverter because its output voltage is frequently two times greater than its input voltage, especially when the inverter is powered by a natural source. The new modulation techniques that have been proposed for CD-type carrier waves have better efficiency, higher RMS voltage, and less harmonic distortion (THD).The efficacy of the suggested carriers has been confirmed by phase disposition (PD), alternate phase opposition disposition (APOD), and phase opposition disposition (POD) investigations. The effectiveness of each technique described under 9LBI has been evaluated using a MATLAB/Simulink configuration. The operation and dynamic performance of the suggested architecture have been modelled using MATLAB/ SIMULINK.

Zero-sequence controller requirements and comparison for a delta-CHB STATCOM under unbalanced operation

Delta-configured Cascaded H-Bridge (DCHB) topology is a suitable alternative for Static Synchronous Compensator (STATCOM) applications. However, under unbalanced voltage and/or current conditions, zero-sequence current needs to be injected to guarantee dc-link capacitor voltage balancing. The control loop of this zero-sequence current is analyzed in this paper, in order to determine the requirements that the implemented controller must fulfill. Considering these requirements, appropriate transient response and stability margin indicators are defined to quantify and evaluate the performance of different controllers that could be employed —Proportional-Resonant controller (PR), PR controller with delay compensation (PRd), and Vector Proportional-Integral controller (VPI) are proposed and analyzed for this application in this paper. Based on the defined indicators, the VPI is the most appropriate among the studied control techniques. Experimental results validate the analytical model of the controllers and their performance.

Method to Enable Reduced Sensor Capacitor Voltage Estimation in Modular Multilevel Converters

Bulk power applications such as shipping increasingly consider multilevel converter topologies such as modular multilevel converters (MMC), which offers the advantages of scalability, good power quality, and reconfigurability. The internal functioning of MMC requires complete knowledge of the capacitor voltages that make up their submodules meaning a large number of sensors are needed and thus a high number of potential points of failure exist. To increase reliability and reduce investment costs, state estimation techniques such as KALMAN filters have been employed to replace the physical sensors. Analytical techniques based on the knowledge of arm current, arm voltage, and submodule states have also been developed. These techniques exploit the fact that at an insertion index of 1, the arm voltage equals the capacitor voltage on the submodule which permits the estimation algorithm to refresh periodically with measured data thereby increasing the accuracy. This method requires a long refresher time, especially when many submodules are used per arm. In this study, we propose an improved analytical estimation by not only using unity insertion indices, but also exploiting transitions between two successive insertion indices. The study was carried out on a 4 submodule per arm MMC system. The estimated capacitor voltages were then compared with sensor-based voltage measurements confirming the validity of the proposed method. It was then integrated into a complete MMC controller including the inner controls such as circulating current and capacitor voltage balancing.

Analytical Investigation and Optimization of DC Capacitor Voltage Control in the Enhanced Multi-Level STATCOM System

In this paper introduces a novel method for controlling the balance of dc capacitor voltage in a STATCOM, along with a comprehensive logical approach for the balance management system. A balancing control approach has been presented to address the abnormality of the dc capacitor voltage, which is generated by the anomaly of dynamic power absorbed and spent by the chain. This method takes into account the superposition of dynamic voltage vectors. In this approach, a voltage component is added to the output voltage of the append operation in order to modify its inherent power. Furthermore, a thorough scientific approach grounded on vector analysis is introduced. This technique facilitates the deconstruction of the equilibrium control mechanism, including both its stability and boundary constraints. The STATCOM uses a fuzzy logic controller to enhance its aesthetic appeal. A vector analysis-based evaluation is administered to ascertain the optimal approach for equilibrium control. This analysis contrasts the proposed methodology with the other two commonly used methodologies. The findings of this comparison indicate that the suggested strategy for equilibrium control has the benefit of notable stability and a well-defined threshold limit. Reenactments are conducted to illustrate this particular component of the system.

Submodule Capacitor Voltage Balancing through High-Frequency-Side Control for Multiport MMC-Based Solid-State Transformers

Submodule Capacitor Voltage Balancing through High-Frequency-Side Control for Multiport MMC-Based Solid-State Transformers

Staircase Matrix Modulation for the Switched-Capacitor Modular Multilevel Converter With Sensor-Less Capacitor Voltage Balancing

Staircase Matrix Modulation for the Switched-Capacitor Modular Multilevel Converter With Sensor-Less Capacitor Voltage Balancing

Capacitor Voltage Balancing Based on Improved Carrier Overlapping PWM Method for a Five-Level T-NNPC Converter

Capacitor Voltage Balancing Based on Improved Carrier Overlapping PWM Method for a Five-Level T-NNPC Converter

A Novel Sensorless Capacitor Voltage Balancing Method for the Modular Multilevel DC Transformer with Diode-Clamped Circuits

A Novel Sensorless Capacitor Voltage Balancing Method for the Modular Multilevel DC Transformer with Diode-Clamped Circuits

Design and control of modular multilevel matrix converter with symmetrically integrated energy storage for low frequency AC system

AbstractIntegrating energy storage units (ESUs) into part of sub‐modules (SMs) enables the decoupling active power control for the modular multilevel matrix converter (M3C). The low frequency AC (LFAC) system based on M3C with symmetrically integrated energy storage (SI‐AM3C) can provide functions such as renewable power fluctuation smoothing and other power grid auxiliary services, which is attractive in engineering practices. This paper focuses on the design and control of SI‐AM3C. For the converter design, an evaluation method for the number of required active SMs (ASMs) is presented. On this basis, the influences of different system operating conditions on the ASM requirement are analyzed in case studies, and the effects of specific circulating injection strategies are also investigated. The control system targeted at decoupled AC side active power for SI‐AM3C is introduced. A modified inner‐arm capacitor voltage balance strategy is introduced to reduce the capacitor voltage deviation between ASMs and passive SMs (PSMs). The conclusions related to the presented estimation method and converter control strategy are verified by time‐domain simulations in PSCAD/EMTDC.