Voltage Balancing Research Articles

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.

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.

Model Predictive Control With Reduced Common-Mode Voltage Based on Optimal Switching Sequences for Nested Neutral Point Clamped Inverter

This paper proposes a new model predictive control strategy with reduced common-mode voltage (CMV) based on optimal switching sequences (OSS-MPC) for a three-phase (3PH) four-level nested neutral point clamped (4L-NNPC) inverter. The proposed method controls load current, mitigates the voltage fluctuations of flying capacitors (FCs) in the entire operating frequency range, and provides a constant inverter switching frequency. In this work, the switching sequences (SSs) are configured so that the peak CMV is limited to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$V_{dc}/6$</tex-math></inline-formula> . By involving time in the optimization process, the balance of FCs voltages is realized in the entire operating frequency, especially in low-frequency operating mode. Also, the voltage fluctuations of FCs are further mitigated through a mathematical-logic technique. To implement the proposed method on the digital signal processor, the deadbeat control technique is also used to reduce the search space and thus, computation burden. The performance of the proposed method is verified in MATLAB/SIMULINK. The experimental results are carried out based on a scaled-down hardware prototype validating the theoretical claims.

P-f Stability of 2030 Nordic Power System due to Non-Synchronous Generation

The Nordic Power System is undergoing significant transformation and development in the coming years. A driving factor for this is the increased dependency on renewable energy sources and high voltage direct current transmission (HVDC). Various stability challenges due to the dynamics of reactive power - voltage (Q-V) balancing and active power - frequency (P-f) balancing seep into the system with such rise of non-synchronous generation (NSG). This paper investigates the projected impact of NSGs on the P-f dynamic performance of Nordic power system in 2030. As NSGs are systems with low inertia, power discrepancies lead to larger oscillations, higher Rate of Change of Frequency (RoCoF) and bigger maximum frequency deviation (MFD) values. To address these issues, Emulated Inertia (EI) control for wind turbines and Synthetic Inertia (SI) control for VSC-HVDC links are proposed in this paper. The simulation is carried out using DIgSILENT PowerFactory 2022 SP1 simulation software. The results obtained confirm the Effectiveness of the proposed EI and SI methods to enhance frequency response and mitigate deviations.

Voltage and Current Balancing of a Faulty Photovoltaic System Connected to Cascaded H‐Bridge Multilevel Inverter

A healthy operation of photovoltaic installations (similar to all electrical systems) is always limited by breakdown, degradation due to aging, or imbalance caused by weather conditions. In this context, producing the maximum energy possible with an acceptable form factor is a significant challenge for autonomous systems, especially those connected to the grid. In this paper, we have two main issues to address. The first is determining the maximum power point of an unbalanced photovoltaic field (due to a defect or nonuniform weather conditions affecting the photovoltaic generators). For such a system, the particle swarm optimization (PSO) algorithm remains highly effective because it can easily handle the existence of multiple maxima simultaneously to provide the best possible solution. The second challenge is managing the imbalance between the three phases of the photovoltaic system. In this context, the results of conducted studies propose two approaches to balance and maximize the power supplied by the photovoltaic generator and converters. In addition, the presence of a battery storage system plays dual roles: firstly, compensating the power fluctuations due to nonuniform operating conditions between phases, and secondly, ensuring system power supply during periods of no sunlight exposure. The proposed approaches take into account the constraints imposed on DC voltages and currents to ensure optimal integration with the multilevel inverter stage (cascaded H‐bridge multilevel inverters). This is achieved through selective harmonic elimination control without the need for a filtering system. A comparative study between these two approaches will be conducted to assess their advantages and disadvantages. The battery‐based storage system efficiently absorbs excess energy and provides energy during deficits, thanks to a flexible control mechanism that allows easy switching between different battery groups and phases.

A Novel Voltage Judgment Component Injection Scheme for Balanced and Unbalanced DC-link Voltages in Three-Phase Vienna Rectifiers

A Novel Voltage Judgment Component Injection Scheme for Balanced and Unbalanced DC-link Voltages in Three-Phase Vienna Rectifiers

Evaluating a Scheduling Fractional-Order Controller in an AC/AC Matrix Converter Driving a PMSM Model

This paper discusses a fractional-order controller applied to an AC/AC matrix converter when it is driving a Permanent Magnet Synchronous Motor (PMSM). The process of design and simulation of the controller is shown. A numerical simulator composed of detailed models of the main components AC/AC Matrix Converter, PMSM, power electronics and control system are employed to probe the performance of the controller. The simulation was carried out in MATLAB/Simulink. Simulation results show the effectiveness of the controller to reduce current and voltage harmonics of the AC/AC matrix converter. These simulations were performed using changes on velocity and also with balanced and unbalanced input voltages.

Maximum Reactive Power Generation Method Based on Limitation of Output Capacity for Star-Connected Cascaded H-Bridge STATCOM Under Voltage Sag

Star-connected cascaded H-bridge (SCHB) STATCOM is being widely used in medium and high voltage to support grid by injecting positive and negative sequence current. Under balanced conditions, the rated reactive power is usually utilized to calculate the required reactive current reference based on instantaneous power theory. However, under grid voltage sag, the rated reactive power changes due to the introduced negative sequence current and extra zero sequence voltage for cluster voltage balancing, which may increase overcurrent and overmodulation risk. Therefore, how to derive the maximum compensable reactive power is required for SCHB STATCOM under the grid voltage sag. In this paper, the quantitative relationship between the imbalanced degree of grid voltages and reactive power reference is fully explored. On this basis, the maximum reactive power is calculated under voltage sags by considering current and voltage limitation. In this calculation, a new geometrical analysis method is proposed, which makes the calculation speed faster for online calculation. Therefore, a new grid support control strategy is proposed for the SCHB STATCOM under grid voltage sag, which can effectively support the grid with the maximum output reactive power. Finally, the proposed method is verified by experimental results on a 400V/7.5kVar SCHB STATCOM prototype.

Overview of Voltage Balancing Schemes in Bipolar DC Microgrids

Overview of Voltage Balancing Schemes in Bipolar DC Microgrids