Power Balance Control Research Articles

Power-Linked Predictive Control Strategy for Power Electronic Traction Transformer

Power electronic traction transformer (PETT) is a module-cascaded converter with high-frequency-link technology to realize high-power conversion. A typical structure of PETT contains a single-phase cascaded H-bridge rectifier in the first stage and several dual active full-bridge (DAB) dc-dc converters in the second stage. For PETT adopting such a complex topological structure, the control strategy also becomes complicated and should be carefully designed. In this article, a power-linked predictive control (PLPC) strategy for PETT is proposed based on the predictive controls of the H-bridge rectifier and DAB dc-dc converter. A power link is brought into the control strategy to connect the H-bridge rectifier with a dc-dc converter, through which the input power of PETT can match the output power. Moreover, the voltage balance control and power balance control are also combined with predictive control by the PLPC strategy. Using such a strategy, the fluctuation of the H-bridge rectifier dc voltage is suppressed, the circumfluence among modules is reduced, and the dynamic and steady-state performances are both improved compared with traditional strategy. Simulation and experimentation platforms with both resistance load and motor load are built to show the effectiveness and correctness of the PLPC strategy.

Beat Phenomenon Suppression for Reduced DC-Link Capacitance IPMSM Drives With Fluctuated Load Torque

Beat phenomenon is an important concern in the reduced dc-link capacitance motor drive system. In previous research works, the topic is mainly concentrated on the beat phenomenon caused by the interaction of the fluctuated dc-link voltage and the motor phase voltage. In this paper, another form of the beat phenomenon generated by the fluctuated dc-link voltage and the severely fluctuated load torque is investigated. The effect of the beat phenomenon on the grid current and the motor speed is analyzed, which fluctuate with the low-frequency oscillation. In order to improve the drive system performance, a power balancing controller is proposed to suppress the grid current fluctuation, and a resonant controller is utilized to regulate the periodic power signals. Meanwhile, the applied fluctuated torque suppression method could improve the performance of the motor speed, which is only sensitive to the frequency of the fluctuated load torque. Experimental results are provided to verify the effectiveness of the proposed method.

Coordinated power flow control of DC microgrid consisting of distributed generations and energy storage system

In this paper, to operate DC microgrid in a flexible and reliable way, a coordinated power flow control strategy of DC microgrid and control methodology of power electronic converters are presented in both the grid-tied mode or islanded mode. For this purpose, the operation algorithm and power flow of DC microgrid are selected based on the distributed generation power, load demand, and energy storage system (ESS) status. The effectiveness of the system power balance and power flow control method are verified during operation mode transition through the simulation studies based on the PSIM software.

Communication-Independent Power Balance Control for Solid State Transformer Interfaced Multiple Power Conversion Systems

A coordinated power balance control strategy independent of communication is proposed in this article, which includes autonomous modes transition control methods for photovoltaic converter, battery energy storage system and their cooperation with solid state transformer. The synthesized multiple power conversion systems contain an internal dc point-of-common coupling (PCC) and an external ac PCC, which form a dc microgrid and an ac microgrid, respectively. In grid-connected mode, the system is able to operate in power regulation pattern corresponding to grid-side response, or secondary dc bus voltage regulation pattern corresponding to local loads response, and switch between them on demand. Grid-connected and islanded/standalone modes can be transferred seamlessly, without the need of control structure reconfiguration through communication links. Moreover, control-related real-time communication is no longer necessary in this scheme, thus improving the reliability and reducing the total costs accordingly. Experimental results are provided to validate the effectiveness of the proposed control scheme.

A unified power quality conditioner for power quality improvement in distributed generation network using adaptive distributed power balanced control (ADPBC)

Power quality improvement is one of the central and critical needs in all types of power-driven industries for perfect utilization of sources. However, fundamental inconveniences in power quality have been recognized, for instance, sags, swells, harmonic distortions and different blocks. Among those, sags and swells are overwhelmingly uncovered, and each influences the electrical gadgets or electrical machines and this requires to be compensated with an advancement to ensure any mal-operation or disappointment. To settle these troubles, custom power gadgets are used like unified power quality conditioner (UPQC), dynamic voltage restorer (DVR) and Distributed Static Compensator (DSTATCOM). This work aims to update the power quality in both single-phase and three-phase system using UPQC. The capacity of UPQC to mitigate voltage sag, voltage swell, responsive power remuneration, load balancing, zero voltage direction, and power factor redress and Total Harmonics Distortion (THD) in the appropriation framework is done by utilizing adaptive distributed power balanced control (ADPBC) method. This investigation works on the single-phase UPQC design to utilize two H-connect setups with eight switches and the three-phase UPQC arrangement to use four legs and three-phase four wire course of action. The overall function of the UPQC with distributed generation (DG) system will be able to compensate for the offset voltage and current disturbances with all the compensated data being collected and verified in Internet of Things (IoT) based on conditional Random Fields (CRFs).

A Comprehensive Harmonic Analysis and Control Strategy for Improved Input Power Quality in a Cascaded Modular Solid State Transformer

In a three-stage cascaded modular solid state transformer (CMSST), unbalanced dc bus voltages at the output of cascaded multilevel rectifier is a common issue due to inevitable parameter mismatch in stage-2. To balance the dc bus voltages, either voltage balance control (VBC) in stage-1 or power balance control (PBC) in stage-2 is necessary. In this paper, an in-depth theoretical analysis to investigate the input power quality of the CMSST in the presence of voltage and PBC schemes is presented. The grid-side multilevel voltage of the CMSST is analyzed to highlight the limitation of using VBC in stage-1. It is then mathematically proven that the switching frequency based harmonics in the grid current are significantly reduced by using the PBC in stage-2. Simulation studies of a 3.3-kV, 50-kVA CMSST are carried out using the PLECS software to substantiate the proposed analysis. Experimental verifications are performed on a 750-VA single-phase CMSST laboratory prototype for a 20% parameter mismatch in stage-2. It is found that the grid current total harmonic distortion (THD) is reduced from 6.65% to 3.8% at 50% load by using PBC in stage-2. This paper provides guidelines for the designer to choose appropriate balance controllers for the CMSST.

Power Control and Fault Ride-Through Capability Analysis of Cascaded Star-Connected SVG under Asymmetrical Voltage Conditions

The cascaded H-bridge static var generator (SVG) has been employed to provide reactive power and regulate grid voltages for many years because of its good modularity, easy scalability, and improved harmonic performance. A novel cluster-balancing power control method combining negative-sequence currents and zero-sequence voltage is proposed to redistribute the unbalanced active powers and eliminate the power oscillation under asymmetrical conditions. Simultaneously, the dynamic performance of the SVG power balance control can be improved under asymmetrical conditions with the zero-sequence voltage expression derived in this paper. On the basis of the proposed method, the fault ride through capability of star-connected SVG under asymmetrical conditions is compared among active power oscillation elimination (APOE), reactive power oscillation elimination (RPOE), and balanced positive sequence current (BPSC) injection references calculation strategies from the perspective of the zero-sequence voltage, maximum phase voltage, and maximum phase current. The method provides the theoretical reference for power control under asymmetric conditions and the analysis results show that under asymmetrical conditions, the current of BPSC is minimal and symmetrical, while the RPOE has the least voltage and no zero- sequence voltage needs to be injected. Finally, the results of simulation and experiment have been given to verify the theoretical studies.

Automatic Coordination of Internet-Connected Thermostats for Power Balancing and Frequency Control in Smart Microgrids

This paper proposes a novel feedback control strategy, so-called clock-like controller (CLC), to balance power supply and demand in smart microgrids by adjusting the setpoint temperatures of air conditioning (AC) loads. In the CLC algorithm, the grid operator communicates with the individual thermostats via the Internet and adjusts their setpoints by discrete temperature intervals (e.g., ±0.5 °C). Numerical simulations indicate that the proposed algorithm is able to deliver a smooth controllability of the aggregate AC power despite discrete temperature offsets. It can also be used for peak load shedding to mitigate the power generation cost. The CLC algorithm is then integrated into the grid frequency control problem, in which both power generators and loads in the network attempt to regulate the frequency of the system despite disturbances from demand, renewable sources, and local weather conditions. An autonomous microgrid model including a steam and a hydro generator, a solar energy source, and a large number of thermostatic loads is developed to evaluate and demonstrate the proposed method. Simulation results indicate that the AC loads with CLC algorithm can help maintain the power system frequency during extreme events when demand exceeds the maximum generation capacity available to the network. Under normal conditions, the contribution of demand-side control is marginalized by the fast responding generators, because of time delays in the frequency measurement and internet communication network.

Flexible Modern Power System: Real-Time Power Balancing through Load and Wind Power

Increasing large-scale integration of renewables in conventional power system has led to an increase in reserve power requirement owing to the forecasting error. Innovative operating strategies are required for maintaining balance between load and generation in real time, while keeping the reserve power requirement at its minimum. This research work proposes a control strategy for active power balance control without compromising power system security, emphasizing the integration of wind power and flexible load in automatic generation control. Simulations were performed in DIgSILENT for forecasting the modern Danish power system with bulk wind power integration. A high wind day of year 2020 was selected for analysis when wind power plants were contributing 76.7% of the total electricity production. Conventional power plants and power exchange with interconnected power systems utilize an hour-ahead power regulation schedule, while real-time series are used for wind power plants and load demand. Analysis showed that flexible load units along with wind power plants can actively help in reducing real-time power imbalances introduced due to large-scale integration of wind power, thus increasing power system reliability without enhancing the reserve power requirement from conventional power plants.

Interference Balance Power Control for Uplink Non-Orthogonal Multiple Access

In this letter, an interference balance power control (IBPC) scheme is proposed for uplink non-orthogonal multiple access. Compared with fixed signal-to-noise ratio (SNR) difference scheme in the 3rd Generation Partnership Project, the proposed scheme could effectively suppress the residual interferences of the prior decoding user equipments (UEs) and decrease the error propagation. Moreover, the transmit power of UEs can be changed by the instantaneous or static channel state information. The exact outage probability expressions for IBPC scheme are derived and Monte Carlo simulation results verify the accuracy of the theoretical results. Simulation results show that the proposed scheme performs better than that of fixed SNR difference scheme on outage performance and sum data rate, especially in lower SNR region.

基于平均功率平衡控制的磁悬浮分子泵电力失效补偿

基于平均功率平衡控制的磁悬浮分子泵电力失效补偿

Average power balance method for power failure compensation control of high‐speed turbo molecular pump with AMB system

High-speed permanent magnet motors supported by an active magnetic bearing (AMB) have been widely used in the industrial field. However, the AMB-rotor system will lose its magnetic force if the mains power fails, and high-speed rotor will crash the stator severely and bring a fatal damage to the system. To solve this problem, a power failure compensation control method based on the average power balance control was proposed. Firstly, a motor energy feedback model was proposed. Secondly, a non-linear controller with double closed loops was designed. And the Lyapunov function was built and analysed to ensure the system stability. Finally, a series of experiments based on the high-speed magnetically suspended vacuum turbo molecular pump was carried out. The experiment results verified the validity and feasibility of the proposed method, and the safety of the AMB system was improved greatly.

Synchronization and Reactive Current Support of PMSG-Based Wind Farm During Severe Grid Fault

Grid codes require wind farm to remain on-grid and inject specific reactive current when grid fault occurs. To satisfy the requirements, reactive power devices, such as the static synchronous compensator (STATCOM), are usually used in modern wind farms. In order to produce reactive currents, the wind energy generation system (WECS) and the STATCOM are normally controlled with the phase-locked loop (PLL) oriented vector control methods. Due to the active power imbalance between the generation and consumption, the wind farm has the risk of losing synchronization with the grid under severe fault conditions. This paper analyzes the dynamic synchronization mechanism and stability criteria of the wind farm and proposes a coordinated current control scheme for the WECS and the STATCOM during severe grid-fault period. The synchronization stability of both the WECS and the STATCOM is remained by the active power balancing control of the wind farm. The control objectives of the generator- and grid-side converters for the WECS are swapped to avoid the interaction between the dc-link voltage control loop and the synchronization loop. The synchronized STATCOM produces additional reactive currents to help the wind farm meet the requirements of the grid code. Effectiveness of the theoretical analyses and the proposed control method is verified by simulations.

Hybrid Modulated Model Predictive Control in a Modular Multilevel Converter for Multi-Terminal Direct Current Systems

In this paper a hybrid modulated model predictive control (HM2PC) strategy for modular-multilevel-converter (MMC) multi-terminal direct current (MTDC) systems is proposed for supplying power to passive networks or weak AC systems, with the control objectives of maintaining the DC voltage, voltage stability and power balance of the proposed system. The proposed strategy preserves the desired characteristics of conventional model predictive control method based on finite control set (FCS-MPC) methods, but deals with high switching frequency, circulating current and steady-state error in a superior way by introducing the calculation of the optimal output voltage level in each bridge arm and the specific duty cycle in each Sub-Module (SM), both of which are well-suited for the control of the MMC system. In addition, an improved multi-point DC voltage control strategy based on active power balanced control is proposed for an MMC-MTDC system supplying power to passive networks or weak AC systems, with the control objective of coordinating the power balance between different stations. An MMC-HVDC simulation model including four stations has been established on MATLAB/Simulink (r2014b MathWorks, Natick, MA, USA). Simulations were performed to validate the feasibility of the proposed control strategy under both steady and transient states. The simulation results prove that the strategy can suppress oscillations in the MMC-MTDC system caused by AC side faults, and that the system can continue functioning if any one of the converters are tripped from the MMC-MTDC network.

A Comprehensive Strategy for Accurate Reactive Power Distribution, Stability Improvement, and Harmonic Suppression of Multi-Inverter-Based Micro-Grid

Among the issues of accurate power distribution, stability improvement, and harmonic suppression in micro-grid, each has been well studied as an individual, and most of the strategies about these issues aim at one inverter-based micro-grid, hence there is a need to establish a model to achieve these functions as a whole, aiming at a multi-inverter-based micro-grid. This paper proposes a comprehensive strategy which achieves this goal successfully; since the output voltage and frequency of micro-grid all consist of fundamental and harmonic components, the strategy contains two parts accordingly. On one hand, a fundamental control strategy is proposed upon the conventional droop control. The virtual impedance is introduced to solve the problem of accurate allocation of reactive power between inverters. Meanwhile, a secondary power balance controller is added to improve the stability of voltage and frequency while considering the aggravating problem of stability because of introducing virtual impedance. On the other hand, the fractional frequency harmonic control strategy is proposed. It can solve the influence of nonlinear loads, micro-grid inverters, and the distribution network on output voltage of inverters, which is focused on eliminating specific harmonics caused by the nonlinear loads, micro-grid converters, and the distribution network so that the power quality of micro-grid can be improved effectively. Finally, small signal analysis is used to analyze the stability of the multi-converter parallel system after introducing the whole control strategy. The simulation results show that the strategy proposed in this paper has a great performance on distributing reactive power, regulating and stabilizing output voltage of inverters and frequency, eliminating harmonic components, and improving the power quality of multi-inverter-based micro-grid.

Modified hybrid modulation strategy with power balance control for H‐bridge hybrid cascaded seven‐level inverter

Compared with the traditional cascaded H-bridge multi-level inverters, the hybrid cascaded multi-level inverters have been receiving attention because they can generate more levels with the same number of power cells. However, with the general hybrid pulse width modulation (PWM), the output power distribution between the high-voltage and low-voltage H-bridge cells is extremely uneven in low amplitude modulation, and it may appear that the high-voltage cell feeds power into the low-voltage cell in some modulation ratio intervals causing the low-voltage cell capacitor voltage boost. To avoid this problem, a method of a modified hybrid PWM strategy with power balance control is proposed. It has achieved the output power balance of H-bridge cells in full amplitude modulation, the occurrence of the phenomena of extremely uneven output power distribution between the high- and low-voltage cells in low amplitude modulation is avoided, and the performance of the inverter is improved. Simulation and experimental results verify the correctness and feasibility of the proposed strategy.

A study on power balance control strategies of mining variable speed magnetic coupling based on fuzzy self-adaptive PID

This paper studied fuzzy self-adaptive PID control strategies that are applicable to mining variable speed magnetic coupling based on analysis on the magnetic coupling mathematical model fitted by a large number of data simulation and calculation by combining traditional PID control strategies and fuzzy control methods and then carried out experiments for further verification. It can be proved by experimental analysis that such control strategy can not only solve multi-motor driving power balance problems effectively, but also adapt to working condition changes and revise control parameters automatically, which can provide theoretical support for project practices.

A Comprehensive Strategy for Power Quality Improvement of Multi-Inverter-Based Microgrid With Mixed Loads

In order to solve the influence of nonlinear and unbalanced mixed loads on output voltage of microsource inverters in microgrid, this paper proposes a comprehensive strategy which can be used to accurate power distribution, harmonic suppression, negative-sequence voltage component suppression, and stability improvement. On one hand, a fundamental control strategy is proposed upon the conventional droop control; the problem of accurate reactive power distribution is solved by introducing virtual impedance to inverters, while considering the aggravating problem of stability because of introducing virtual impedance, a secondary power balance controller is added to improve the stability of voltage and frequency. On the other hand, the fractional frequency harmonic control strategy and negative-sequence voltage control strategy are proposed to solve the influence of mixed loads, which focus on eliminating specific harmonics caused by the nonlinear loads and the negative sequence component of the voltage. The power quality of microgrid can be improved effectively. Finally, small signal analysis is used to analyze the stability of the multiconverter parallel system after introducing the whole control strategy. The simulation results show that the strategy proposed in this paper has a great performance on distributing reactive power, regulating and eliminating harmonic components, eliminating negative-sequence components and stabilizing output voltage of inverters and frequency, and improving the power quality of multiinverter-based microgrid.

A study on power balance control strategies of mining variable speed magnetic coupling based on fuzzy self-adaptive PID

A study on power balance control strategies of mining variable speed magnetic coupling based on fuzzy self-adaptive PID

A Method for Autonomous Power Balance of DC Microgrid with Photovoltaic and Storage System

DC microgrid with photovoltaic and energy storage has been attracted widespread attention due to its high reliability and flexibility. In order to solve the problem that the power of DC microgrid cannot be self balanced due to the no uniformity and uncertainty of the output of photovoltaic power in the photovoltaic DC storage microgrid. In this paper, a power balance control method based on the DC bus voltage signal autonomous switching mode is proposed, this method can effectively stabilize the power fluctuation and maintain the power balance in the network, and enhance the safe and reliable operation ability of the optical storage DC microgrid. Finally, the feasibility and effectiveness of the proposed control method are verified by experiments.