Balance Control Strategy Research Articles

Third-order current harmonic suppression and neutral-point voltage balance control strategy for single-phase three-level NPC inverter

The imbalance of capacitor voltage on the DC side of the inverter will cause the third-order current harmonics and the device will be damaged greatly with the increase of voltage stress. The mechanism of imbalance capacitors voltage and the third-order current harmonics generated by the double frequency fluctuation are analyzed. This paper presents a feedforward capacitor differential pressure control strategy based on PR controller, which is aimed at the single-phase three-level NPC inverter and considers the cause of double modulation wave. The PR controller is used in the current loop to suppress the third-order harmonic by static-free tracking of the AC signal, and the voltage balance is realized by the feedforward DC-link capacitor voltage difference to offset the DC component of the output side. The simulation model and 1kW prototype driven by the control strategy have been established to demonstrate that the capacitor voltage of the inverter is balanced and the third-order harmonic is suppressed efficiently.

A battery balancing control strategy for industrial applications

Abstract The voltage-based equalization strategy is very simple, and it is widely used in industrial applications, however, for the traditional control strategy, while the battery voltages are equal, the battery management system (BMS) will stop balancing, due to the complex composition of the battery voltage, the battery cell is not well balanced. This paper proposed a battery balancing control strategy for industrial applications, which adds ohmic voltage compensation based on the traditional equalization control strategy, by increasing the compensation and prolonging the equalization time of the battery cell, a better equalization effect can be achieved. Compared with the traditional equalization strategy, the only parameters required are equalization current and battery internal resistance, these parameters are very easy to obtain without any burden, and are very suitable for industrial applications. This paper analyzes in detail the reasons why the traditional equilibrium strategy is insufficient, introduces the principle and error of the proposed strategy, and compares it with the traditional equilibrium strategy. The experimental results show that the error of the equalization strategy proposed in this paper is about 3 mV (discharge) and 2 mV (idle), while the traditional strategy is 10 mV and 8 mV, respectively.

An Internal Model Direct Power Control With Improved Voltage Balancing Strategy for Single-Phase Cascaded H-Bridge Rectifiers

Single-phase cascaded H-bridge rectifiers (CHBR) are widely studied for vehicular power electronic transformers. In this article, an internal model direct power control (IM-DPC) with a voltage balancing strategy is proposed to improve the control performance of CHBR. First, a modified power control structure is built by the relationship of coordinate transformation. On this basis, the IM-DPC method is presented to obtain a straightforward design for the inner-loop. This approach can be implemented without phase-locked loop, and coordinate transformation is not necessary as well. Then, a first-order transfer function between the difference of dc-side voltage square and that of power is constructed. Further, a novel calculation structure for the compensation duty cycle is proposed. Through the proposed voltage balancing control scheme, the dynamic performance of the dc-side voltage is improved when load unbalancing occurs. The coupling effect between the overall control for the CHBR is also eliminated. Finally, experimental prototype tests are conducted to verify the effectiveness of the proposed method.

Strategy for compensation of unbalanced powers in LV residential distribution networks using distributed single-phase battery systems

Unbalanced powers, due to high penetration of single-phase PV rooftop systems and loads into a low voltage residential distribution system, can result in large neutral current and neutral to ground voltage rise. This paper proposes a distributed cooperative dynamic power balancing control strategy to mitigate the unbalanced powers using single-phase battery storage systems distributed in the low voltage residential distribution system. First, a distributed clustering algorithm is used to aggregate the battery storage systems connected to the same phase into the same cluster. Within each cluster, a distributed average grid power calculation algorithm calculates the average grid power exchanged with the corresponding phase. Then, the proposed distributed cooperative dynamic power balancing control strategy is applied to balance the unbalanced powers using the single-phase battery systems at the given bus while minimizing the power exchanged with the grid. The battery systems’ charge/discharge constraints, power constraints and willingness of the battery systems’ owners to participate in the power balancing control strategy are considered. Performance of the proposed strategy is verified using Real-Time Digital Simulator (RTDS).

Simple and high‐performance cell balancing control strategy

AbstractThe basis for judging whether the battery pack is balanced is generally whether the voltage of the battery cell is consistent because the voltage of the battery cell is very easy to obtain. However, when the voltage of battery cells is the same and the battery management system (BMS) turns off the equalization, it will get poor balance performance. In this paper, a new balancing strategy is proposed, while the calculated state of charge (SOC) difference between the battery cells instead of the voltage reaches the set value, the BMS turns on or off, and the difference in the SOC between battery cells is obtained by adding a small amount of calculation to the difference in voltage between battery cells, due to the long balancing time of the battery, the battery will enter a steady state at the end of balancing, based on the voltage difference of battery cell, the voltage drop generated by the balancing current on the ohmic resistance and polarization resistance is added, combined with the open circuit voltage (OCV)‐SOC curve, the difference in battery voltage can be indirectly converted into a difference in SOC. This strategy will appropriately delay the battery balancing time to make up for the drop in the voltage of the balanced battery cell after the BMS turns off the balancing. In this paper, the proposed strategy and performance are analyzed in detail, the experimental platform is designed to verify, and the battery pack is tested under static and discharge conditions. Although the equalization goal is the same voltage between battery cells, using the voltage‐based equalization strategy, the voltage difference between the battery cells is 8 and 6 mV, respectively, while the strategy proposed in this paper is 2 and 3 mV, which has better performance.

Machine Learning Strategies for Low-Cost Insole-Based Prediction of Center of Gravity during Gait in Healthy Males.

Whole-body center of gravity (CG) movements in relation to the center of pressure (COP) offer insights into the balance control strategies of the human body. Existing CG measurement methods using expensive measurement equipment fixed in a laboratory environment are not intended for continuous monitoring. The development of wireless sensing technology makes it possible to expand the measurement in daily life. The insole system is a wearable device that can evaluate human balance ability by measuring pressure distribution on the ground. In this study, a novel protocol (data preparation and model training) for estimating the 3-axis CG trajectory from vertical plantar pressures was proposed and its performance was evaluated. Input and target data were obtained through gait experiments conducted on 15 adult and 15 elderly males using a self-made insole prototype and optical motion capture system. One gait cycle was divided into four semantic phases. Features specified for each phase were extracted and the CG trajectory was predicted using a bi-directional long short-term memory (Bi-LSTM) network. The performance of the proposed CG prediction model was evaluated by a comparative study with four prediction models having no gait phase segmentation. The CG trajectory calculated with the optoelectronic system was used as a golden standard. The relative root mean square error of the proposed model on the 3-axis of anterior/posterior, medial/lateral, and proximal/distal showed the best prediction performance, with 2.12%, 12.97%, and 12.47%. Biomechanical analysis of two healthy male groups was conducted. A statistically significant difference between CG trajectories of the two groups was shown in the proposed model. Large CG sway of the medial/lateral axis trajectory and CG fall of the proximal/distal axis trajectory is shown in the old group. The protocol proposed in this study is a basic step to have gait analysis in daily life. It is expected to be utilized as a key element for clinical applications.

A novel control strategy of resonant converter with modular rectifier based on SiC switching device

The resonant converter with modular rectifier (RMR) is a promising topology for DC grid applications. This paper studies the control strategy of RMR based SiC switching device including the output voltage and submodule (SM) capacitor voltage balancing control strategy. Firstly, different working modes of the RMR converter are analyzed, and the Critical Mode with the highest efficiency is introduced. A control method is proposed to guarantee the RMR operating the Critical Mode. The control parameters design is detailed. Secondly, the charging and discharging principles of SM capacitor voltages are introduced, then a balancing method is proposed: the SM capacitor voltages are sorted, then assign gate signals with smaller pulse width to SMs with lower capacitor voltages, and vice versa. The proposed control methods are verified by experimental results on a 300 V/1200 V 8 kW RMR prototype based SiC switching device. According to the experimental results, the RMR operates at the Critical Mode under different load and gain conditions. The SM capacitor voltages are well balanced. The peak efficiency is 98.2%.

Energy Balance Control for Improving Transient Performance of DC Bus Voltage in Power Electronic Transformer for the Voltage-Sensitive Loads

The power electronic transformer (PET), as a main topology for the energy router in the energy internet, consists of the rectifiers, the dual active bridge (DAB), and the inverter, and these three parts are connected by two dc buses. So, the performance of the dc bus voltages is very important because it can totally affect the output waveforms of the dc and ac voltage, especially for the voltage-sensitive loads. Compared with the proportion integration (PI) control scheme, the energy control method utilizes the energy as the control variable, and the control strategy derived from the energy relationship, including the passive elements and all the interfaces, is more direct and explicit. In this paper, considering the energy between the dc bus capacitors and the input inductor and the load and the source in the PET topology, the energy balance control (EBC) strategy is proposed. For the two dc bus voltages, the energy balance relationship of the different time scales is used to decouple the interaction in the control scheme. The EBC strategy can obviously reduce the fluctuation and the transient time of the two dc bus voltages when the load power or voltage reference is changed. Thus, under the limited voltage fluctuation, the EBC strategy can reduce the dc bus capacitance in order to reduce the volume and weight of the converter and enhance the reliability. The simulation and experimental results verify the effectiveness of the proposed control strategy.

Three-Layer Double-Vector Model Predictive Control Strategy for Current Harmonic Reduction and Neutral-Point Voltage Balance in Vienna Rectifier

Vienna rectifier, which is a nongenerative-boost-type rectifier, is widely employed in electric vehicle charging systems. Nevertheless, the Vienna rectifier faces the challenge of current distortion elimination, current ripple mitigation, and neutral-point (NP) voltage balance. As these problems are mutually coupled, the conventional finite control set model predictive control (FCS-MPC) methods cannot solve these problems properly. To address these issues, a three-layer double-vector FCS-MPC method is proposed. In the first layer of the proposed FCS-MPC method, the sectors are divided and the candidate vectors are selected to reduce the current distortion. In the second layer of the proposed FCS-MPC method, the double vectors with optimal duty cycles are adopted to reduce the current ripples. In the third layer of the proposed FCS-MPC method, the NP voltage is balanced by selecting the redundant p-type small vector or n-type small vector. Through the proposed method, the current distortion elimination, current ripple mitigation, and NP voltage balancing are realized at the same time. The effectiveness of the proposed method has been verified by simulation and experiment.

Synergistic balancing control for low-inertia power systems with high PV penetration: Tibet as a case study

This paper proposes a novel synergistic balancing control scheme for low-inertia power systems with high photovoltaic (PV) penetration in Tibet power grid (TPG). The mechanism and dispatching principle of choosing the suitable area control error (ACE) control mode for TPG are analyzed., An adaptive control mode switching method is proposed to meet the different control demands for the dynamically changing topologies. Then, we propose a new coordinated control scheme to dispatch hydropower generators and PV power stations. A set of optimum control objectives considering balancing control performance, regulation mileage of conventional generators, and power curtailment of PV are first presented. The control objectives are decomposed and simplified by step-by-step approximation and linearization, which are easily extended to be applied to real-world automatic generation control (AGC) systems. The simulation results show the effectiveness of the proposed solutions for synergistic balancing control by using the equivalent TPG test system. The equivalent system includes 63 generators with total power equal to 1618.5 MW and 51 PV power stations over 1100 MW. In addition, the actual operation cases present that the coordinated control between conventional and renewable generation dispatched by AGC has the basic conditions in the actual operation of the power grids, which will play a more significant role with the rapid increase of renewable generation sources in the future.

Research on balance control strategy of lithium-ion battery energy storage system

Abstract Lithium-ion batteries are widely used in grid energy storage, electric vehicles and other occasions because of their excellent performance. Passive equalization is widely used because of its high performance, but traditional passive equalization control strategies do not perform well. This paper proposes a new control strategy, which divides the battery pack into three state of charge (SOC) ranges according to the different SOC of the battery pack and different performance requirements. When the SOC of the battery pack is high, the maximum rechargeable capacity needs to be considered and the battery balancing should be realized in advance; and when the SOC of the battery is low, the maximum discharge capacity needs to be considered, the battery balancing should be delayed and, in other areas, it is the same as the traditional balancing control strategy. Moreover, the balance control strategy proposed in this paper keeps the high-performance battery at a lower voltage and the low-performance battery at a higher voltage; the low-performance battery works with more favorable conditions, so that the battery pack is in a more balanced state. The experimental results show that the battery pack consisting of four cells in series can be almost fully charged and the battery pack voltage is ~16.788 V; during the discharge process, the equalization system hardly operates to ensure its maximum discharge capacity. The strategy proposed in this paper is simple and easy to implement and has better performance.

Variable Voltage Variable Frequency Modular Multilevel AC/AC Converter With High-Frequency Harmonics Filtering Capability

This article proposes a variable voltage variable frequency modular multilevel ac/ac converter (VVVF-MMC) with a high-frequency isolation link, which can realize voltage and frequency conversion simultaneously with insulated-gate bipolar transistors (IGBTs) of the same rated voltage and current level. The parallel connection of multiple modules is realized by coupling reactors, which can realize large-scale voltage and current transformation and save volume. It combines parallel multiplexing and serial multiplexing technology of submodules (SMs) to increase the equivalent switching frequency, thereby canceling nonzero sequence high-frequency voltage and current harmonics, so it has good power quality in the steady-state. Under the improved carrier phase-shifted pulsewidth modulation (CPS-PWM) strategy, the pulse flip circuit can realize soft switching operation, thereby improving energy conversion efficiency. Furthermore, dc capacitor voltage balancing and parallel SM current balancing control strategies are designed. With the strong filtering ability, the proposed ac/ac converter can be used as the onshore converter station of fractional frequency offshore wind power system. Due to the advantages of small size and high efficiency, it also has broad application prospects in distribution networks and electric drive. Simulation and experimental results validate the effectiveness of the proposed converter topology.

An Optimal Adaptive Control Strategy for Energy Balancing in Smart Microgrid Using Dynamic Pricing

Energy balancing in smart microgrid plays a vital role to improve the reliability and resolves the load shedding problem to ensure consistent energy supply. However, energy balancing is challenging due to uncertain and intermittent nature of renewable energy integrated in smart microgrid. To solve such problems, dynamic energy pricing mechanism is developed that maintain energy balance for overcoming the gap between demand and supply. Thus, the particle swarm optimization based super twisting sliding mode controller (PSO-STSMC) is developed which uses dynamic energy pricing to control renewable energy resources’ generation according to the consumers’ demand for real time closed loop energy balancing in an energy market. The proposed PSO-STSMC based model is compared with existing models like proportional integral derivative (PID) controller, proportional integral (PI) controller, proportional derivative (PD) controller, and fractional order proportional derivative (FO-PD) controller and the optimized models of the particle swarm optimization based proportional integral (PSO-PI) controller and particle swarm optimization based proportional integral derivative (PSO-PID) controller. Simulations results demonstrate that energy price regulation by PSO-STSMC consistently controls the elastic demand for real time energy balancing.

Implementation of Power Balance Control Scheme for a Cascaded Matrix-Based Dual-Active-Bridge (CMB-DAB) MVAC-LVDC Converter

Though the merits of matrix-based dual-active-bridge (MB-DAB) ac–dc converter as a submodule for grid-connected multilevel medium-voltage ac (MVac)–low-voltage dc (LVdc) conversion have been presented in recent literature, its operational challenges in the cascaded configuration have not been explored. The objective of this article is to present the inevitable challenge of unequal power routing through the submodules of cascaded matrix-based dual-active-bridge (CMB-DAB) and its mitigation. The detailed and simplified small-signal model of the CMB-DAB converter along with the proposed power balance control (PBC) strategy required to eliminate the power imbalance issue are explained comprehensively. The simulation results for a 3-cell 52.65-kVA CMB-DAB converter along with scaled-down 5.85 kVA experimental results are presented, to demonstrate the unavoidable power imbalance issue and the proposed PBC strategy as a mitigation technique. The proposed scheme is observed to perform seamlessly with the conventional LVdc bus voltage control and remediate power-routing imbalance issue during the steady-state, load-change and hot plug-in/hot plug-out operations.

A power balance control strategy for stand alone wind energy conversion systems

Supplying off-grid areas with stand-alone wind energy conversion systems required a battery charge controller for energy storage. Furthermore, to cope with the stochastic wind nature, the frequent variations of the load demand, together with ensuring a proper battery charging process, based on the available wind power, the battery status, and the load power demand, a multi-mode control strategy is proposed, which can instantly balance the wind power flow delivered to the DC load and the battery. The control system entails three operating modes, namely, maximum power point tracking (MPPT) charging mode, constant current (CC) charging mode, constant voltage (CV) charging mode. Thereafter, a new battery energy management algorithm is also developed, to ensure a smooth switching from one operating mode to another. The controller performances are theoretically analyzed, then are tested through MATLAB/SIMULINK/SIMPOWER environment. The obtained simulation results prove that the proposed controller meets its objectives under various weather conditions and load demand.

Branch Voltage Balancing Control Strategy Based on the Transfer Power Model by Zero-Sequence Circulating Current for the Hexverter

This paper proposes a novel branch voltage-balancing control strategy for a hexagonal converter (Hexverter). First, the state-space model based on the double- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> transformation is analyzed in-depth along with the necessary basic mathematical derivation, and the active/reactive power control model in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> reference frame for the Hexverter is proposed. Second, a zero-sequence double-loop network consisting of a Y-loop and a Hex-loop circulating current was established. This study proposes a method to suppress the Y-loop circulating current by connecting a capacitor at the neutral point. We then establish a novel branch voltage-balancing control strategy based on the transfer power model. The essence of the proposed control strategy is to control the charging and discharging states of each submodule via the zero-sequence voltages and the Hex-loop circulating current to regulate the power transfer between adjacent submodules and branches, thereby effectively ensuring the dynamic balance of the DC voltages of the submodules. The branch voltage-balancing control model and power control model proposed in this paper are based on zero-sequence and positive-sequence networks, respectively. The relative independence of the positive- and zero-sequence networks leads to decoupling of the branch voltage-balancing control model and the power control model; thus, the respective control objectives can be achieved by adjusting the respective control variables independently. It has a stronger adaptability to diverse power grid operating parameters. Finally, the validity and correctness of the mathematical model and control strategy proposed in this study are verified using MATLAB/Simulink.

Design of energy balancing circuit for battery cells connected in series based on modifying the bidirectional CuK converter

&lt;abstract&gt; &lt;p&gt;This paper proposes a design of energy balance circuit for two adjacent Lithium-ion battery cells in the cell string based on the modifying of the bidirectional CuK converter principle. This design only uses one MOSFET to transfer energy between two cells in a direction controlled by the first relay, second relay controls the cutting energy balance circuit off the cells when they have the same energy level. The control command sent by the management battery system (BMS) to the energy balance circuit via an RS485 communication protocol controls the direction of transferring energy, the amplitude of the balance current, the frequency and duty of PWM, the PWM signal applied to MOSFET is programmed by a microprocessor PIC18F2685. This design overcomes some disadvantages caused by applying the principle of bidirectional CuK converter to design the energy balancing circuit, these are the need for a multiple level DC source to open MOSFETs and issue of the energy loss on the elements of energy balance circuit. This design is also easy to expand for the battery string with a large number of cells. The energy balance control strategy can be implemented directly by each the energy balance circuit or remotely by BMS using RS485 communication. The experimental results of online optimal energy balance control based on state of charge (SoC) feedback for 07 SAMSUNG 22P battery cells connected in series are presented to prove the efficiency of the energy balance circuit design for two adjacent cells proposed in this paper.&lt;/p&gt; &lt;/abstract&gt;

Power Balance Control Strategy of Permanent Magnet Synchronous Motor of Belt Conveyor

Aiming at the problem of multi-machine power balance control of long distance belt conveyor with double drum and three permanent magnet synchronous motor, the control method of speed and torque of master and slave motors of belt conveyor driven by multiple motors is analyzed. According to the properties of coaxial rigid connection and flexible connection of three motors of double drum, The power balance strategy based on fuzzy Active Disturbance Rejection Controller (ADRC) is proposed to achieve the purpose of disturbance rejection and improve the stability of the system. The simulation results show that the proposed method can solve the power imbalance problem of the system motor. Compared with the traditional PID control method, the corresponding speed of fuzzy ADRC control method is less than 300ms, the power deviation of rigid connected motor is less than 0.1kW, and the power deviation of flexible connected motor is less than 0.3kW. This method can effectively reduce the synchronization error of each motor, and has good robustness, and realize the power balance distribution among multiple motors.

Stability and Control Analysis for Series-Input/Parallel-Output Cell Balancing System for Electric Vehicle Battery Packs

Battery management implement cell balancing algorithms to equalize state of charge of series-connected cells in a battery pack. Balancing strategies range from passive, where a simple resistive circuit is used to drain current from the battery cell, to active, where sophisticated control schemes and advanced circuitry may be employed. Recent development of active balancing control strategies for a modular cell-balancing architecture utilize low-voltage bypass DC-DC converters and a shared low-voltage dc bus. Although these systems show promise in preliminary experiments, questions remain over the inherent stability properties of the architecture. This letter presents a stability analysis for an N-cell battery module and provides insight for design of embedded controllers.

A Fast and Energy Efficient Nonnegative Least Square-Based Optimal Active Battery Balancing Control Strategy for Electric Vehicle Application

A Fast and Energy Efficient Nonnegative Least Square-Based Optimal Active Battery Balancing Control Strategy for Electric Vehicle Application