Voltage Balancing Research Articles

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.

Decentralized Control for Multi-Terminal Cascaded Medium-Voltage Converters Considering Multiple Crossovers

Decentralized control with multiple droop characteristics can significantly improve the accuracy of power flow in medium-voltage direct-current (MVdc) networks. However, multiple crossovers caused by different control characteristics can lead to the drifts of power and voltage and instability issues. When this type of control is implemented in the cascaded three-level neutral-point-clamped (C3L-NPC) converters, on one hand, the mechanism of such the power and voltage drifts was not investigated. On the other hand, power control accuracy, dc voltage balancing across submodules (SMs) and multiple crossovers should all be considered, which requires suitable control methods. To address the challenges, firstly, the mechanism behind the power and dc voltage drifts is analyzed. Secondly, a control scheme is presented to improve the power control accuracy and dc voltage balancing and concurrently, to avoid the multiple crossovers. This is achieved by suitable droop gain design and adding a secondary power compensator. The presented control scheme is verified in MATLAB/Simulink simulation and experimentally validated in a three-terminal MVdc testbed. Results show that the accuracy of steady-state power flow is improved by 15% due to the elimination of multiple crossovers, while the power accuracy at dynamics improved by 13% with the secondary power compensator.

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.

Comprehensive Analysis of Vienna Rectifiers for Renewable Resources

The issue of energy has emerged as a significant subject of concern in contemporary discourse. The significance of the advancement of novel energy sources is progressively growing. Relevant strategies should aid in the advancement of power electronics. The rectifier is a commonly used electronic component that finds application in many circuits involving electronic equipment. Its primary function is to convert alternating current into direct current, which is then supplied to the load. The Vienna rectifier is a widely used rectifier that has garnered significant attention and scrutiny from professionals in the field of power electronics on a global scale. This article begins by illustrating the use of power electronics technology, specifically focusing on the charging pile circuit. It proceeds to discuss the classification and current research status of rectifiers. Subsequently, the article provides an overview of the circuit layout and operational principles of the Vienna rectifier circuit. This section provides an overview of the approaches and features used to optimize the operating performance of Vienna rectifiers in four key areas: current control, voltage control, neutral point voltage balance management, and harmonic stability control. This research will ultimately provide a forecast about the future development trend of Vienna rectifiers, together with a comprehensive overview of all improvement attempts.

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.

Static Series Compensator for the compensation of voltage-quality disturbances based on particle swarm optimization techniques

Static Series Compensator (SSC) is a power electronic based device that provides three-phase controllable voltage source to restore the load voltage to pre-sag conditions within few milliseconds. This paper proposes a new control technique based on an adaptive tunning PI controller that uses a selective controller to describe the effectiveness of SSC for mitigating voltage sags in power distribution systems at critical loads. The integral of time multiply squared error (ITSE) index is minimized to reach the optimal tuning of PI controllers based on particle swarm optimization (PSO) technique to determine whether the best fitting solution is achieved. The controller is designed in a synchronously-rotating reference frame. Independent (homopolar component, d-axis component and qaxis component) controllers are used to tackle balanced and unbalanced voltage supplies. Simulation is done using Simulink “SimPowerSystem” Toolbox to illustrate the principle and performance of an SSC operation in load voltage compensation

Harmonics Cancelation in 3-Phase 4-Wire System using Modified Reference Frame

In this paper, A modified synchronous reference frame (SRF) or (d-q theory) with Self-Tuning Filter (STF) for the three-phase four wires system is presented to control of 4-legs shunt active power filter (SAPF) under balanced supply voltages. The main goal of the paper is to apply this control method using unit vector generation with STF instead of PLL circuit. In utility power system, it has been observed that harmonics build a major role in reducing the power quality. These harmonics caused by nonlinear loads. Many consumers appliances demand quality of power continuously for their operation. The performance of the end user equipment is heavily dependent on the quality of power supplied to it. This power is affected by various external and internal factors. They are like voltage and frequency variations, faults, outages etc. The solution to overcome these problems is to filter out these harmonics. For this purpose, there are many filters' topologies and control methods are proposed and studied in the literature to eliminate harmonics currents. In our study, 4-legs shunt active power filter is proposed and controlled by d-q method with modified unit vector generation. The SAPF is proposed to solve problems of line harmonic currents and neutral line currents of three phase 4-wire power distribution system. The use of STF in the modified control method can optimize the performance of this topology regarding to classical one (high pass and low pass filters). The proposed control strategy is simulated in MATLAB Simulink and the results are presented.

Power quality improvement using renewable energy

This paper presents a three-phase Active Power Conditioner to improve power quality in microgrids based on renewable energy. Three hysteresis controllers are used to control the six IGBT bridge. In a microgrid which is a weak electrical grid the disturbances can be very important. The Active Power Conditioner (APC) presented in this paper acts as an interface between renewable energy sources and the AC bus of microgrid. The improved control strategy used offer the possibility to inject electrical energy from the renewable sources and on the other hand to improve the power quality in the same microgrid. This control strategy named Extended Indirect Control Strategy is capable to achieve better values for the following power quality indicators: THDI (Total Harmonic Distortion), PF (Power Factor), current and voltage balancing. Simulation results show the validity of the innovative control strategy

Arm‐current sensorless model predictive control for grid‐interfacing modular multilevel converter with reduced switching frequency

AbstractModel predictive control (MPC) emerges as an attractive alternative for the control of modular multilevel converters (MMCs) owing to its superior dynamic performance and ease of implementation. Nevertheless, conventional MPC's performance could be further improved by reducing dependence on weighting factors, switching frequency, and computational burden. To achieve these objectives, an arm‐current sensorless MPC is developed for a grid‐interfacing MMC in this article. The MPC is integrated with an arm‐current sensorless reduced switching frequency voltage balance algorithm that requires only switching vectors (where number of submodules per arm) to optimize the cost function. This method does not require knowledge of arm‐current direction to decide the charging and discharging state of the submodule capacitors. The developed control not only reduces the switching frequency of devices but also eliminates the need to sense the arm currents. As a result, it reduces the system's cost, complexity, computational burden, switching losses and provides a more reliable control method for MMCs with superior dynamic performance. Further, the effect of parameter mismatch on the developed MPC's dynamic performance and stability is studied. The developed MPC's effectiveness is validated through both simulation and experimental results and also compared with existing methods under different conditions.

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.

A comprehensive circuit and modulation design of mixed frequency conversion cascaded power electronic transformer

The power electronic transformer (PET) is one of the promising equipment of the energy Internet. In a distributed network, cascaded (cascaded full-bridge, CFB)-type PETs can withstand high-voltage stress and contain a low-voltage DC (LVDC) port, which provides access for distributed generation (DG). However, the hardware cost of the traditional CFB-type topologies remains high, and structure compactness can still be improved. The recently presented mixed-frequency conversion cascade PET (MFCC-PET) is one of the promising solutions. In this study, a comprehensive circuit design of MFCC-PET, a low-voltage distortion nearest-level pulse width modulation (NL-PWM), and a sub-module (SM) voltage balancing strategy for the proposed modulation method under mixed-frequency conversion are presented. A 100 V/2,000 W MFCC-PET prototype is built based on the above analysis and successfully placed into operation.

Development and testing midpoint voltage balance algorithms of three-level inverters

Nowadays, the use of inverters is increasing inmore and more applications. Environmental awareness is becom-ing a trend, so more and more people install solar energy systemson their houses, which also require the use of inverters. Higherpower levels have led to the emergence of three-level inverterswhich has opened up new challenges, such as the issue of mid-point voltage balancing. This paper discusses voltage balancingand voltage ripple reduction techniques for three-level inverterswith Neutral-Point Clamped (NPC) topology. The balancing isbased on injecting zero-sequence voltage component in carrier-based modulation. The viability of the modulation techniques areverified by computer simulation and then tested on hardware.

Performance Analysis of Direct Power Controlled PWM Rectifier under Disturbed AC Line Voltage.

Voltage and current source inverter are widely used in electrical motor drives. In this drives, DC voltage (or current) are usually provided from phase control or line commutation rectifiers. Because of disadvantage & limitation of this converter, some new topologies are presented in advanced drive such as PWM rectifier. Thanks to well known capabilities of PWM rectifier, classical converter’s problem can be overcome. There are several PWM rectifier control strategies. In this paper these control methods are introduced. At first, performance of the Direct Power Control (DPC) PWM rectifier is studied under balanced voltage condition. As line voltage disturbance are often considerable in industrial applications, rectifier performance under disturbed line voltage is investigated. For this purpose a DPC method is implemented in MATLAB/SIMULINK environment. Based on simulation results, DPC-PWM rectifier performances under unbalance and voltage sag is discussed.

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.

Voltage Equalizing Strategy for Cascaded Constant Current Power Supply

In order to detect the underground medium with large depth, the transmitter of electromagnetic sounding instrument has higher and higher power and voltage. A novel voltage equalizing strategy for cascaded constant current power supply using in electromagnetic transmitter was proposed in this paper. The cascaded topology of the transmitter has two isolated full‐bridge AC/DC converters, which had same input source and were connected in series on the output side. The mathematical model based on state space average method was analyzed. After simplifying the circuit, the state space equation was used to describe the circuit model. The stability and frequency characteristics of the system were analyzed. Aiming at the constant current output and the output voltage balance of the two converters, the system coupling model was established. The constant current controller and voltage equalizing controller were designed with decoupling method. A 300 W prototype was built and the experimental results verified the performance of the proposed method. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Multi-objective cooperative controller design for rapid state-of-charge balancing and flexible bus voltage regulation in shipboard DC microgrids

In this paper, a multi-objective cooperative (MOC) controller based on average consensus algorithm is designed to achieve rapid State-of-Charge (SoC) balancing, proportional load current sharing, and flexible DC bus voltage regulation for parallel battery storage units (BSUs) in shipboard DC microgrids. Different from the conventional secondary controllers, the designed MOC controller can simultaneously achieve the above three control objectives with a fully distributed manner without requiring multiple controllers, thereby effectively improving the system stability and reducing the communication burden. Furthermore, an optimized convergence factor is designed to accelerate SoC balancing, and pinning control is introduced to obtain flexible and accurate DC bus voltage regulation. The process of SoC balancing and current sharing analysis, SoC convergence performance analysis, large-signal stability analysis, and global steady-state analysis verifies the rationality and stability of the MOC controller. Finally, the Matlab/Simulink simulation and StarSim HIL experimental results demonstrate the effectiveness and robustness of the designed MOC controller in a shipboard DC microgrid under various testing scenarios.

Control strategies for active power filters

In this paper a comparison between strategies for extracting the three-phase reference currents for active power filters is shown. The performance of these strategies will be evaluated under different source and load conditions. The study has been applied to a three-phase four-wire system in order to include imbalance. It will be shown that under balanced and sinusoidal voltages, harmonic cancellation and reactive power compensation can be achieved by all the methods. However, when the voltages are distorted and/or unbalanced, the compensation capabilities are not equivalent. It will be proved that some strategies do not offer an adequate solution when the mains are not ideal, including harmonics or imbalance.

Notice of Violation of IEEE Publication Principles: Washout Filter-Based Distributed Resilient Current Control for Cyber-Physical Microgrids

Notice of Violation of IEEE Publication Principles: <br><br>“Washout Filter-Based Distributed Resilient Current Control for Cyber-Physical Microgrids," <br>by X. Lu and J. Lai, <br> in IEEE Systems Journal, Early Access <br><br>After careful and considered review of the content and authorship of this paper by a duly constituted expert committee, this paper has been found to be in violation of IEEE’s Publication Principles. <br><br>This paper contains significant portions of original text from the paper cited below. The original text was copied without attribution (including appropriate references to the original author(s) and/or paper title) and without permission. <br><br>"A Combined Distributed Cooperative Method and Washout Filter-Based Method for Power Sharing and Voltage Balancing in Bipolar DC Microgrids" <br> by Ramin Babazadeh-Dizaji, Mohsen Hamzeh, Nima Mahdian Dehkordi, <br>submitted to IEEE Transactions on Energy Conversion, August 2020. <br><br> <br/> This article proposes a washout filter-based distributed resilient current control scheme that can achieve current sharing of distributed generations (DG) and voltage restoration of dc bus almost surely under communication channel noise interferences. Since the cyber channels are exposed to inherent noise interferences, the stability and reliability of cyber-physical dc microgrids may terribly be reduced. To dispel the adverse influences of noise interferences, a novel discrete time washout filter is developed. Accordingly, a discrete-time-distributed noise-resiliency control algorithm is developed for dc microgrids based on washout filters, in which only the current state variable is allowed to exchange among DGs with the local decentralized voltage controller. This makes the proposed control mode different from the conventional parallel mode usually requiring a leader–follower consensus-based voltage control by exchanging two state variables (i.e., terminal voltage and current output). Thus, the proposed control mode decreases the complexity to the formulation and enhances the robustness to the leader communication failure. By introducing stochastic theory and Lyapunov stability function, the sufficient conditions considering noise interferences is derived to ensure the stability operation of the whole closed-loop dc network. The obtained results show the effectiveness of the proposed strategy by a tested dc microgrid in OPAL-RT real-time simulator.

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.