Bus Voltage Balancing Research Articles

Increasing System Dependability in CMI-Based STATCOM with Loop-Gain Shaped Control via Per Phase DC Bus Voltage Balancing

Increasing System Dependability in CMI-Based STATCOM with Loop-Gain Shaped Control via Per Phase DC Bus Voltage Balancing

State-of-charge balancing strategy of battery energy storage units with a voltage balance function for a Bipolar DC mircrogrid

For an islanded bipolar DC microgrid, a special problem of making the better compromise between a state-of-charge (SOC) balance among multiple battery energy storage units (MBESUs) in positive and negative polar, and bus voltage balance, should be considered. In order to solve this problem, three kinds of the simplified load equivalent circuits on the different operation status of voltage balancer (VB) are established; based on these equivalent circuits, the SOC unbalance mechanism is analyzed and the rules of SOC deviation and voltage unbalance factor are summarized, which are influenced by micro-source and load changing; then a SOC automatic balancing strategy among MBESUs with a voltage balance function is proposed in this paper. The proposed controlling strategy takes into consideration the energy flow relationship under various working conditions; with the aim of controlling the equilibrium time and energy flow direction of SOC, creates a SOC balancing power bridge with the SOC deviation as the main control variable; adopts the adaptive virtual resistance algorithm for both positive and negative BESUs according to the variation rule of the SOC deviation. When the SOC deviation is significant, according to the net power difference of the system, the values of the virtual resistances can be adaptively adjusted to alter the operation mode of BESUs and the VB control strategy is also adjusted so as to ensure the stable running of the system and accelerate the SOC balancing speed via maximizing the balancing power by VB. In order to decrease the voltage unbalance on SOC balancing, apart from adding bus voltage recovery control to the positive and negative batteries, the virtual resistances are related to the SOC deviation when the SOC deviation is slight. The simulation results demonstrate that the control strategy proposed in this paper can quickly realize SOC balancing when the SOC deviation is significant, has superior equilibrium performance as load and micro-source power varying when the SOC deviation is slight, and is also feasible in decreasing the bus voltage unbalance.

Optimization of hybrid energy storage based on micro grid optical storage and DC in certain regions

It is of great significance to maintain the stability of DC micro grid bus voltage and improve the economic benefits of the micro grid system. A hybrid energy storage form of flywheel and battery is proposed as the energy storage form of the DC micro grid system of the optical storage charging station. The flywheel is used to smooth high-frequency power fluctuation and part of low-frequency power, and the battery is used to balance the reference power to maintain smooth and stable bus voltage. The hierarchical coordinated control strategy of DC bus is designed to achieve the coordinated control of photovoltaic power generation, electric vehicle charging and discharging, and load power demand in the microgrid system. According to the different working conditions of island operation and grid connected operation, the proposed control strategy is simulated and analyzed on the Matlab/Simulink software platform. The simulation results show that under all working conditions, the proposed control strategy can effectively switch the DC bus voltage between different voltage layers, maintain the DC bus voltage balance of the DC microgrid system of the optical storage charging station, and realize the flexible and reliable operation of the entire system. Therefore, the control strategy is feasible and effective.

Design and Analysis of DFIG-STATCOM Coordinated P2P Grid Connected System Using RMSProp

This research work establishes a relationship between STATCOM and DFIG wind turbines in a transmission network for coordinated operation during grid disturbances. A change in wind gust also produces a variable output nonlinearly, thereby making the system unstable. Assuring bus voltage and proper balance of load angle in all the connected generating stations becomes challenging. Therefore, increasing voltage security at all the lines and further enhancing system stability leads to the placement of STATCOM at the proper location in the transmission line. Appropriate coordinated control of STATCOM and DFIG can lead to adequate power flow in the system. This research includes a multi-objective optimization problem for properly tuning the PI- controller. The voltage at the controlled bus, low-frequency oscillating waveforms, and real power available at the bus under pre-fault and post-fault conditions are identified as objective function parameters. To avoid the overgrowth of error inside the search space due to lack of normalization, this method uses the RMSProp algorithm for proper convergence in the state vector. The coordinated control action has been investigated in the different shunt fault conditions. Again, to enhance the system stability, low voltage ride-through capability has been thoroughly verified using Matlab software.

An advanced HBNP multi-level inverter for the performance enhancement with reduced components

ABSTRACT This article proposed an advanced three-phase multilevel inverter called the H-Bridge Neutral Point (HBNP) Inverter, with a minimum number of components. This inverter is designed to generate five-level output voltage using a single solar system in each phase, making it suitable for low-, medium-, and high-power applications like AC drives, grid integration of renewable energy sources, electric vehicles, and high voltage DC and AC transmission systems, etc. The proposed circuit configuration has reduced gate driver circuits, less capacitors, fewer input sources, modularity in structure, and better THD. Furthermore, the hybrid PWM control technique provides switching signals and ensures that all switches have equal conduction intervals. All of the switches have the same temperatures and voltage sharing, indicating a simpler thermal design and DC bus voltage balancing. The proposed and existing topologies are validated using MATLAB Simulink, and the proposed topology prototype is implemented in the laboratory.

Optimal Decision on Current Sharing and Voltage Balancing in DC Microgrids With Feedforward Input

This article is concerned with the issue how to achieve proportional current sharing while realizing bus voltage balancing in DC microgrids, or vice versa. In order to address this issue, proportional current sharing is realized first and then the optimal bus voltage is obtained by using the least square method; Second, assuming that the bus voltage balancing is realized, the optimal current sharing is solved by using Lagrange multiplier method. It can be seen that the results of the two cases are identical. Then a global performance index relating to the generation capacities is presented to make an optimal decision on voltage balancing and current sharing. In order to decrease the communication burden, the distributed control schemes are proposed to replace centralized control strategies. It can be proved that the equilibrium points of distributed schemes are completely identical to the optimal solutions without significantly increasing system complexity. Finally, the effectiveness of the proposed distributed schemes is shown via a simulation example.

DC Voltage Balancing Technique for CMI-Based STATCOM: A Generic Control Approach

This article provides a generic technique for per phase DC bus voltage balancing that might be used in a CMI based STATCOM. The STATCOM system parameter model and the conventional control technique are examined first. A per phase DC bus voltage balancing mechanism is detailed using a dq/abc park transformation and the loop-gain shaped control design technique. This approach aims to maintain a constant DC bus voltage. The dc capacitor may be controlled globally by a proportional resonant controller. A controller that rejects disturbances may be used to regulate clustered loads. By facing a number of challenging tasks at the point of aggregate generally, including balancing the DC voltage and accounting for reactive power. If these problems can be handled, the system’s supremacy could be increased. This article describes the general control arrangement in order to increase the system’s reliability. This system may accomplish reactive power compensation and dc link voltage balancing by using the nine-level cascade multilevel inverter as STATCOM. One particular topic has been emphasised repeatedly throughout the text.

Distributed Electric System Control Strategy Optimization

With the increasing energy crisis and environmental pollution, this paper concentrates on the energy management and power control of DC microgrid due to its advantage in the utilization of renewable energy resources (RES). However, the traditional centralized control relies heavily on communication since the distribution of most RES is scattered, and the communication failures may cause serious control error, therefore, a distributed and cooperative control strategy without communication is proposed for DC microgrid in this paper. The proposed strategy not only maintains the bus voltage and power balance in a cooperative way through the regulation of each micro-sources, but also solves theunbalance problem between ESUs, meanwhile, this method is suitable for DC microgrid with multiple PVs and ESUs since the communication is not necessary, which is benefit for the plug and in of micro-sources. Finally, some simulation models are built on Matlab/Simulink platform, and the performance of suggested solution is verified through a set of simulation experiments, the result turns out to be good and confirms our expectation.

Hierarchical control of DC micro-grid for photovoltaic EV charging station based on flywheel and battery energy storage system

For micro-grid systems dominated by new energy generation, DC micro-grid has become a micro-grid technology research with its advantages. In this paper, the DC micro-grid system of photovoltaic (PV) power generation electric vehicle (EV) charging station is taken as the research object, proposes the hybrid energy storage technology, which includes flywheel energy storage and battery energy storage. Flywheel energy storage is used to stabilize high frequency power fluctuations and some low frequency power. Lithium iron phosphate (LiFePO4) battery is used for balancing the reference power to maintain the DC bus voltage balance. Composition of the DC micro-grid and various operating modes are analyzed, a hierarchical coordinated control based on the power monitoring steps of the 5-layer DC bus voltage is proposed. Finally, simulation analysis is carried out on the MATLAB/Simulink software platform. Under different working states such as PV input power change, AC and DC loads change, EV charging condition change, and battery over-discharge, the proposed control strategy can make the DC bus voltage at different voltage layers effectively switch, and keep the DC bus voltage balance, thus to achieve flexible and reliable operation of the DC micro-grid system.

Development of a Fuzzy-Logic-Based Energy Management System for a Multiport Multioperation Mode Residential Smart Microgrid

In this paper, a grid-tied residential smart microgrid topology is proposed, which integrates energies of a photo-voltaic (PV), a fuel cell, and a battery bank to supply the local loads through a combination of electric and magnetic buses. In contrast to multiple-converter-based microgrids with a common electric bus, using a multiport converter with a common magnetic bus can effectively reduce the number of voltage conversion stages, size, and cost of the renewable energy system and isolates the conversion ports. The resultant topology utilizes a centralized system level control that leads to a faster and more flexible energy management. The proposed microgrid is able to operate in multiple grid-connected and off-grid operation modes. A fuzzy controlled energy management unit (EMU) is designed to select the appropriate operation mode considering both real-time and long-term predicted data of the energy generation and consumption. A mode transition process is designed to smooth the mode variation by using a state transition diagram and bridging modes. To improve the microgrid operation performance, appropriate control techniques, such as synchronized bus-voltage balance, are used. A prototype of the proposed microgrid and the EMU are developed and experimentally tested for three different energy management scenarios. Energy distribution and energy cost analysis are performed for each scenario to validate the proposed control method.

Generation-Storage Coordination for Islanded DC Microgrids Dominated by PV Generators

For the islanded dc microgrids, the photovoltaic (PV) generators and storages are the main components to provide power and maintain the system stability. To avoid the dc bus voltage rise, the overcharge and overdischarge of storages, the coordination between generations and storages is critically important. In this paper, a decentralized control method is proposed to realize the generation-storage coordination based on the dc bus voltage signaling. First, a novel state-of-charge (SOC) based droop control strategy is designed for storages to provide dc bus voltage support and balance their SOCs, which can prevent the overuse of a certain storage. Second, an adaptive power control strategy is applied to PV generators, which can seamlessly regulate the output power of PV generators off maximum power point tracking mode according to the dc bus voltage. Combining these two strategies through the dc bus voltage signaling, the generation-storage coordination can be realized. Furthermore, the stability of the proposed control method is also analyzed. All the conclusions are verified by the real-time hardware-in-loop tests.

A magnetically coupled multi-port, multi-operation-mode micro-grid with a predictive dynamic programming-based energy management for residential applications

This paper presents the development of a residential micro-grid topology based on a combination of common magnetic and electrical buses. The magnetic bus interfaces two low voltage dc buses linking a PV and a fuel cell to a high voltage dc bus connected to a grid-tied single-phase bidirectional inverter. A battery is used to store the surplus energy of the system and stabilise the dc voltage of the fuel cell bus. A synchronised bus voltage balance (SBVB) technique is used to reduce the conduction losses and increase the soft switching operation range of the converters. To improve the maximum power point tracking (MPPT) performance and system efficiency, appropriate control techniques and compensation blocks are designed. The proposed micro-grid is able to operate in multiple grid-connected and off-grid operation modes according to a predictive 2D dynamic programming-based energy management. A mode selection and transition strategy is developed to select the appropriate operation mode and smooth the mode transition. A detailed study of the micro-grid including steady-state operation, small signal modelling, controller design, and energy management is presented. A prototype of the system is developed, and experimental tests are conducted for an energy management scenario.

Electric Vehicle Charging Station With an Energy Storage Stage for Split-DC Bus Voltage Balancing

This paper proposes a novel balancing approach for an electric vehicle bipolar dc charging station at the megawatt level, enabled by a grid-tied neutral-point-clamped converter. The study uses the presence of an energy storage stage with access to both of the dc buses to perform the complementary balance. It proposes a generic balancing structure that can achieve balance regardless the kind of energy storage system (ESS) employed. This is aiming to reduce the hardware requirements of the system and maximize the usage of the ESS, whose main function is to perform the energy management related tasks. To meet this purpose, a three-level dc–dc interface is employed, allowing to compensate the dc currents with a single ESS. Furthermore, in order to prevent the appearance of even-order harmonics in the input current during asymmetrical operation, an alternative switching sequence for the central converter is proposed. Results indicate that, without altering dramatically the charging process of the ESS, it is possible to cover the whole load scenario without the need of a balancing circuit. This allows the use of off-the-shelf products both for the rectifier and the fast chargers. In this paper, simulation and experimental results are presented to validate the proposed balancing strategy.

A DC Bus Voltage Balancing Technique for the Cascaded H-Bridge STATCOM With Improved Reliability Under Grid Faults

As more distributed renewable energy sources are installed in the utility grid, the static synchronous compensators are applied to manage the power factor and the grid voltage in the medium-voltage level of the power system. The cascaded multilevel converter with single-star topology is well applied to this application. The dc-capacitor voltage balancing control is a fundamental issue, and it can be accomplished by negative-sequence current and/or zero sequence voltage injection. Unfortunately, the zero sequence voltage injection increases the risk of over-modulation and the negative-sequence current injection results in high peak current. This paper provides the voltage balancing strategy to manage the peak current or the modulation index. Besides, all the asymmetrical grid voltages are considered in the proposed method to satisfy the grid fault operation. Laboratory test results verify that the proposed method limits the peak current or manages the modulation index during the grid fault operations.

Simulation and Control Strategy of a 5.6 kV 17-level STATCOM Under SVG Condition

To achieve high-voltage reactive power compensation, a 5.6kV 17-level STATCOM under SVG Condition is presented. In this paper, we use a cascaded H-bridge multilevel star-connection converter whose system structure and circuit schematic are described. Then by using the phase-shifted carrier modulation strategy and the activereactive current decoupling method, the STATCOM performs quite well. Moreover modulation strategy of the 17-level STATCOM based on the active disturbance rejection control (ADRC) is presented and the analytical formulas are described. For implementation, control strategy for DC bus voltage balance in cascaded H-bridge multilevel converters, time average distribution method and extreme value offset method are applied in our design. Finally, simulation results demonstrate that the proposed 17-level STATCOM is capable of reactive power compensation, simultaneous controlling and balancing the DC side voltages during the work and verify that high-voltage reactive power can be accurately and effectively compensated.

Stability and Voltage Balance Control of a Modular Converter With Multiwinding High-Frequency Transformer

In this paper, a novel modular cascaded multi-level converter with multiwinding high-frequency (MWHF) transformer is proposed for medium- or high-voltage applications. In the proposed converter, a cascaded H-bridge rectifier (CHBR) is connected directly with the input ac source while the traditional step-down transformer is no longer necessary. Then, an isolated dc-dc converter composed by a group of H-bridge converters and a MWHF transformer with high power density is used to isolate the dc buses produced by the CHBR. The equivalent circuit and mathematical model of the MWHF transformer and the high frequency (HF) converter are obtained firstly in this paper. Then, the voltage stability under unbalanced loads is analyzed and the naturally balance ability is verified. To accelerate the dc bus voltage balancing process, a voltage balance control algorithm based on energy exchange between different transformer windings is proposed that is realized by accomplishing the phase shift adjustment of the terminal voltages on different windings. Simulations and experiments are implemented to verify the performance of the proposed converter and voltage balance algorithm.

Line-to-line Voltage Space Vector Modulation for Neutral-point Clamped Multi-level Converter with DC-link Capacitor Voltage Balancing Using Redundant Vectors

This article presents space vector modulation of line-to-line voltage for the three-phase neutral-point clamped n-level converter with DC-link capacitor voltage balancing using redundant vectors. The developed modulation strategy is based on an equivalent matrix structure of the neutral-point clamped n-level converter. The relation between the 3 × (n – 1) switching functions of the matrix converter and gate signals of transistors of the neutral-point clamped n-level converter is given. A line-to-line space vector modulation strategy for a matrix inverter is used to obtain the switching function. For one switching function, there is more than one combination to produce each output voltage. Thus, redundancies of different switch configurations for generation of intermediate voltages are used to limit the deviation of capacitor voltages. The gate signals of the neutral-point clamped n-level converter can be calculated by inversing the modeling parts. Here, line-to-line voltage space vector modulation for a neutral-point clamped n-level converter is designed without using a Parks transform. Moreover, n × (n – 1) redundant vectors are used for DC bus voltage balancing. To highlight the performances of the developed modulation strategy, simulation results are given for five- and seven-level neutral-point clamped converters. Experimental results are given for a neutral-point clamped three-level converter.

A Novel DC Bus Voltage Balancing of Cascaded H-Bridge Converters in D-SSSC Application

This paper introduces a new scheme to balance the DC bus voltages of a cascaded H-bridge converter which is used as a Distribution Static Synchronous Series Compensator (D-SSSC) in electrical distribution network. The aim of D-SSSC is to control the power flow between two feeders from different substations. As a result of different cell losses and capacitors tolerance the cells DC bus voltage can deviate from their reference values. In the proposed scheme, by individually modifying the reference PWM signal for each cell, an effective balancing procedure is derived. The new balancing procedure needs only the line current sign and is independent of the main control strategy, which controls the total DC bus voltages of cascaded H-bridge. The effect of modulation index variation on the capacitor voltage is analytically derived for the proposed strategy. The proposed method takes advantages of phase shift carrier based modulation and can be applied for a cascaded H-bridge with any number of cells. Also the system is immune to loss of one cell and the presented procedure can keep balancing between the remaining cells. Simulation studies and experimental results validate the effectiveness of the proposed method in the balancing of DC bus voltages.

Modulación Vectorial de Inversores Multinivel con Diodos de Enclavamiento con Balance del Bus de Continua

In this work, a modulation algortihm for the Diode Clamped Multilevel Inverter with DC bus voltage balancing capability is presented. Space Vector modulation technique for the multilevel inverter is described, jointly with a DC bus voltage balancing algorithm that takes advantage from converter's redundancy. The algorithm can be generalized to an arbitrary number of levels and takes into account two important cases: presence or absence of a DC voltage source on the DC bus. The performance of the presented algorithm is evaluated by means of computer simulations.