Start-up Control Research Articles

A Lightweight Artificial Neural Network Start-Up Controller for CLLC Resonant Converters

A Lightweight Artificial Neural Network Start-Up Controller for <i>CLLC</i> Resonant Converters

Non-linear cascade control with gain-scheduling and startup control strategy study for thermionic space reactor TOPAZ-II

The TOPAZ-II thermionic space reactor system, which was designed by the Soviet Union, is characterized by its high degree of nonlinearity and positive temperature reactivity feedback. The thermionic space reactor exhibits characteristics of high inertia and significant delay in controlling its electrical power and outlet temperature. The simple PID controller is difficult to achieve good performance. To carry out controller design for thermionic space reactor, the simulation platform for thermionic space reactor is developed based on coupling between reactor system thermal-hydraulic code RESYS and control system simulator in this study. After that, based on the cascade control strategy and gain-scheduling, the reactor thermal controller, electric power controller, outlet temperature controller applicable for the full power range is designed with transfer function model and frequency domain analysis method. To validate the nonlinear electric power controller performance, the continuous minor step disturbances, major step disturbances, and ramp variation of electric power setpoint is simulated. The performance of outlet temperature controller is verified with the simulation result of step and ramp variation of outlet temperature setpoint. Thereafter, the start-up process of the thermionic space reactor TOPAZ-II is simulated and analyzed. The simulation result reveals that the controller designed in this paper can overcome the nonlinearity of the thermionic space reactor system and has good performance throughout the entire power range. Compared to traditional simple PID controller, the cascade controller has better performance and can achieve good control performance even in situations where simple PID controllers cannot function properly.

Start-up and Transient Support Control of AC-DC Hybrid Distribution Networks with Distributed PV Access

Abstract For AC-DC hybrid distribution networks, a large number of interconnecting converters connected to DC micro-sources and DC distribution networks in the distribution network provide a powerful aid for restoring power supply to the loads in the lost area after an accident by using the local power supply of the system, and at the same time, the power synchronisation control strategy provides a friendly power supply mode for the power supply of the interconnecting converters to the passive network. This paper analyses the start-up control of AC-DC hybrid distribution networks with distributed photovoltaic (PV) access under the scenario of interconnecting converter multi-machine co-operation in transferring power to a load area without a superordinate power supply; and puts forward a power synchronous control of interconnecting converter multi-machine co-operation to suppress power-frequency oscillation under faults of a distribution network without a superordinate power supply.

Fast Start-Up Control of Both-Side Current Without Overshoot Focusing on Rectification Timing for Dynamic Wireless Power Transfer Systems

The paper proposes a method to improve the tran- sient characteristics of current overshoot and oscillation at the start of power transmission for a dynamic wireless power transfer system. The system is important to reduce the settling time as short as possible without current overshoots for a stable power supply. However, conventional methods to suppress current overshoot have a slow response on the secondary side. This paper proposes the superposition of primary and secondary responses. The proposed method controls the secondary voltage by comparing the steady-state current with the current value on the secondary side. The method can effectively suppress the oscillations in the transient response by applying the secondary voltage at the appropriate timing. This paper also studied the ro- bustness of constraints based on model analysis and experimental verification. In the experiments, the proposed method reduces the current overshoot and the settling time of the secondary current, and maximizes the receiving energy.

Minimum water level in surge tank and control methodology under the combination condition of load acceptance after rejection

This paper aims to guide the control of hydropower stations by obtaining the most dangerous instant of surge superposition to improve the extreme value in surge tanks under the combination conditions of load acceptance after rejection. Firstly, the theoretical formula for calculating the most dangerous superposition instant of the minimum surge in the surge tank under the combined conditions is derived. Then, the dynamic mechanism is expounded. Finally, the concept of ’ the time span ’ and the calculation process are proposed, which should be avoided under the start-up control in hydropower stations. The results indicate that the most dangerous superposition instant occurs when the change rate of the surge tank water level with the tunnel flow in the front condition is the same as that in the post condition. This study proposes the theoretical formula with high precision and explains the mechanism from the perspective of energy. It suggests that hydropower stations can reduce the cross-sectional area of surge tanks by controlling the start-up far away from ’ the time span ’, which can not only effectively reduce the project cost, but also enhance the understanding of surge superposition in surge tanks.

A Novel Saturated Differential Inductance-Based Position Estimation and Sensorless Startup Control of Non-Salient DC Vernier Reluctance Machine

A Novel Saturated Differential Inductance-Based Position Estimation and Sensorless Startup Control of Non-Salient DC Vernier Reluctance Machine

Model-free adaptive optimal control for fast and safe start-up of pumped storage hydropower units

Pumped storage unit (PSU) is a special kind of hydropower unit, that undertakes the task of power generation, and performs the function of energy storage. Due to its unique advantages, pumped storage power stations have been extensively developed in China in recent years and play an important role that is difficult to be performed by other energy sources. Although many studies have been carried out on the control of PSUs, most of the control algorithms are based on object models, which results in the control performance depending on the model accuracy to a large extent, limiting the practical application of these algorithms. For this reason, a preliminary application of model-free adaptive control in PSUs is investigated in this paper. Firstly, a refined nonlinear model of PSU is established, secondly, the model-free adaptive controller of PSU and its parameter optimization strategy are designed, and finally, verification is carried out by simulation studies for four different start-up conditions, and a comprehensive comparison is made with control strategies such as proportional-integral-derivative (PID), fractional-order PID, and nonlinear generalized predictive control. The results show that the proposed method has significant improvement in both speed and head control performance compared with other methods, with the regulation time being on average at least 5.53 s faster and the overshoot being on average at least 2.85 % lower. It proves the effectiveness and superiority of the method. In addition, the proposed method reduces energy consumption in the regulation process, and the computational cost meets the real-time control requirements, which has a wide range of application prospects.

Improvement on Thrust Control for Start-Up and Piston Motion of Free-Piston Linear Generator

Free-piston linear generators (FPLGs) without a crank mechanism are promising to be used in hybrid vehicles due to their unique operation characteristics. However, the FPLG currently still faces challenges in the start-up and piston control. In this paper, the start-up and operation process of FPLG are analyzed deeply and the improved thrust control strategies for the linear electric machine (LEM) are presented accordingly. First, the mechanism that the vibration center shifts under the general constant thrust resonance starting method is revealed, considering the asymmetric potential energy caused by non-linear compression spring effect in the combustion chamber. Then, a compensation thrust iteratively adjusted by the vibration offset is added to stabilize the swing center during start-up. Next, the coupling effect between the dead centers under single-stroke independent thrust control method is analyzed, by modeling the piston motion from the aspect of energy flow. Accordingly, an improved thrust control method for coupling suppression is presented to enhance the accuracy and robustness of piston motion. Finally, the performance of the proposed method is verified by controlling a permanent- magnet linear synchronous machine (PMLSM) in experiments and simulations.

Study on start-up characteristics of a heat pipe cooled reactor coupled with a supercritical CO2 Brayton cycle

The new megawatt nuclear power system coupling a heat pipe cooled reactor with a supercritical CO2 Brayton cycle is considered one of the most promising energy conversion systems for large Unmanned Undersea Vehicles (UUVs). This system combines the characteristics of a heat pipe cooled reactor and a S-CO2 Brayton cycle, such as heat pipe start-up limitations and significant thermal inertia. It is unclear whether existing start-up control strategies for either heat pipe cooled reactors or S-CO2 Brayton cycle are suitable for this new system. Therefore, the start-up characteristics and the control strategies of the new megawatt nuclear power system are investigated in this study. A simulation code is developed for the study of the start-up characteristics of this system, which includes models for the reactor, heat pipes, and the S-CO2 Brayton cycle. The validation of the code is conducted based on the experiments as well as the design values. Good agreement between the calculation results and the experimental values or the design values are obtained. And then, the control scheme and start-up strategy of the new system are proposed. The start-up process is divided into four sub-stages, that is, core start-up from cold to critical state, heat pipes start-up, compressor start-up and turbine preheating, and branch switching. Different control strategies are applied to each sub-stage. The results show that the shaft raising rate of 2000 rpm/min is effective in overcoming expansion resistance without causing excessive overshoot in mass flowrate. This control strategy can achieve stable start-up of the new system without exceeding a temperature change rate of 10 K/min. This research may serve as a reference for the conceptual design of this new megawatt nuclear power system.

Research on the Numerical Method of Pollutant Emission during Gas Turbine Start-up

It was of great research value and significance to predict the pollutant emission from the gas turbine start-up process by numerical method, which could improve the operation and regulation of gas turbines. In the paper, the computational fluid dynamics(CFD)-chemical reaction network (CRN) method was used to study the pollutant emission of gas turbines. According to the control process of the start-up control module, the start-up process had been divided into 12 states, and the CFD numerical analysis was carried out. Based on the data of Damkohler number (Da), temperature and velocity obtained by CFD, the chemical reaction network model of each state point was established. The research showed that the design parameter value of the state point was the basis of compiling the calculation process and source code; The basic data and partition basis for the chemical reaction network could been provided by the results of CFD analysis, which was an important guarantee for accurate prediction of NOx; The method of CFD-CRN could accurately predict NOx emission of gas engine during start-up, and provided reasonable and reliable research means and mathematical methods.

I–f closed‐loop starting strategy of high‐speed PMSM based on current vector adaptive regulation

AbstractConventional I–f startup control algorithms often lead to significant speed fluctuations, extended convergence times, and sluggish dynamic responses when the motor is working at the acceleration process. To address these challenges, the article constructs a discrete kinetic model of the motor, extracts and summarizes the change law of the motor torque angle fluctuation amplitude and frequency with the motor parameters and the reference current vector during I–f starting process based on the Runge–Kutta method, reveals the fundamental mechanism of the pole slipping of the I–f control. On this basis, the article proposes a closed‐loop I–f starting control strategy for high‐speed permanent magnet motors based on current vector adaptive regulation, The strategy notably improves speed tracking performance and current dynamic response to I–f startup control. Experimental results validate the efficacy of the proposed algorithm.

Dual-adaptive energy management strategy design for fast start-up and thermal balance control of multi-stack solid oxide fuel cell combined heat and power system

Solid oxide fuel cell (SOFC) hybrid system offers several advantages, including rapid start-up, effectively mitigating thermal stress and system stability. In this study, a multi-stack SOFC battery hybrid (SBH) Combined Heat and Power (CHP) system is designed. A dual-adaptive control strategy for this multi-stack system is proposed. The assembly of each power generation module (PGM) in parallel is implemented and the reliability of the system is verified. The dynamic characteristics of the multi-stack SBH-CHP system and the effect of temperature on the system are investigated. The results show that the multi-stack system can achieve stability within 80 s. The transient current observed in the system reaches up to 40 A, which accounts for at least 25% of the current generated by the SOFC. The system exhibits robust and prompt dynamic response characteristics, which ultimately contribute to an extended operational lifespan. The proposed adaptive control method and adaptive energy management strategy have been proven to be effective approaches for addressing the issues associated with rapid start-up and over-temperature within the multi-stack SBH-CHP system.

Start-up control strategy of high-power motor based on H-MMC

Hexagonal modular multilevel converter (H-MMC), as a direct AC/AC converter, is particularly well suited to the field of high-power motor drives. This paper proposes a start-up control strategy of high-power motor drive system based on H-MMC. The motor side current is traditionally limited to the rated current during the start-up process, while the grid side current is far less than its rated current. Thus, H-MMC is not operating at the rated condition for the arm current being mainly composed of phase current on motor and grid, which results in reduced start-up torque and slower start-up speed. Combined with the dead-beat control method, the static-free tracking of the arm current can be realized without complicated parameter tuning. Finally, the motor stator current and torque increase during the start-up process, and the start-up time is shortened. Both simulation and RT-LAB experiments prove the effectiveness and superiority of the presented start-up control strategy. The findings demonstrate that the presented start-up control strategy enhances the dynamic performance of the system and enables rapid motor start-up.

Improved startup control of aero doubly salient electromagnetic starter generator based on optimised currents distribution with advanced angle commutation

AbstractDoubly salient electromagnetic machine (DSEM) can constitute a competitive rugged starter generator (SG) system. But under the traditional startup control method, the field current is set to the rated value regardless of speed or load torque conditions, and the phase currents are controlled with standard angle commutation, bringing in large power loss as well as non‐negligible torque ripple. To overcome these shortcomings, based on the established DSEM power loss calculation model, a currents distribution strategy is proposed according to the obtained quantitative relationship between DSEM power loss and field current under multiple speed and load torque conditions. Then, to identify the load torque for practical implementation, a novel torque observer is designed based on back propagation (BP) neural network algorithm. Afterwards, to further improve the startup torque performance, currents distribution with advanced angle commutation (AAC) strategy is put forward, where the optimal advanced angle is selected from a 3‐D lookup table to achieve the minimal commutation torque ripple. Under the proposed control strategies, DSEM power loss as well as the output torque ripple are desired to be decreased, the simulation and experimental results on a 12/8‐pole DSEM prototype verify the correctness and feasibility of the proposed strategies under multiple operating conditions.

Revisiting Mobile Paste Reactor Fuel

In April 1961, Atomic Power Development Associates (APDA) produced the “Summary of the APDA Fuel Development Programs.” Chapter XVII described a paste fuel concept. The report noted that there are “advantages inherent in a mobile-fueled reactor.” Patent number 3,169,117, entitled “Nuclear Reactor Paste Fuel Composition,” was issued on May 9, 1961. In May 1964, Argonne National Laboratory produced the “Catalog of Nuclear Reactor Concepts.” The chapter concerning paste fuels concluded: “The few paste-fuel concepts developed to date and the present early stages of such developments show that considerably more work probably will be required before the paste-fuel concept can be considered for commercial development.” This monograph enlarges upon and quantifies the APDA concept, which appears not to have been pursued. Additional passive safety concepts that might also eliminate the need for control assemblies are described. Several important consequences of continuously processed fuel that are not discussed in the APDA report are described in this paper, in particular, that the “iodine pit” startup control instability can be eliminated.

Parameter optimization strategy of LLC converter soft start-up process based on a simplified numerical calculation model

High-frequency start-up strategy is usually used to limit the current overshoot in the resonant tank of LLC converter. However, the strong coupling among start-up frequency, initial duty cycle, and current limit increases the design complexity of parameters. This paper proposes a parameter optimization strategy of the LLC converter soft start-up process based on the numerical calculation method. With this strategy, the initial switching frequency and duty cycle are determined adaptively according to the given maximum current requirements during the start-up process. The current overshoot is suppressed and soft switching is achieved in the whole process. After the second switching period, 50% duty cycle operation occurs without oscillation. Furthermore, exponential frequency reduction is used in the process, and the current overshoot limiting condition in the initial period is discussed. Finally, a 240 W LLC converter prototype is built to verify the correctness of the theoretical analysis in this paper. In terms of current limiting, soft switching, and initial switching frequency, the comprehensive performance of the soft start-up control strategy proposed in this paper is better. Compared to the traditional control strategy, the current overshoot is reduced by 45.6%. The theoretical calculation, simulation, and experimental results are consistent.

Automated power-following control for nuclear thermal propulsion startup and shutdown using MOOSE-based applications

This paper describes an investigation of various automated control strategies applied to a full-core multiphysics Griffin/Bison/RELAP-7 model of a prototypical nuclear thermal propulsion system. In all cases, control is achieved by actuating control drums based on the demanded power and predicted quantities from the numerical model. One key finding is that hybrid proportional integral derivative controllers – a novel type of controller that uses both power and reactivity predicted signals – can demonstrate a level of performance rivaling that of period-generated control. The former requires parameter tuning, while the latter mostly necessitates providing reactivity coefficients and temperature rates of change, which could be very challenging to accurately measure in real-time.In addition, decay heat plays an important role in determining cooling requirements during cooldown phases. A decay heat model, accounting for burn time and throttling, was derived, and is incorporated within the model to simulate the steady-state and shutdown phases and satisfyingly follow the power demand. However, temperature overshoots and non-constant specific impulse during throttling will necessitate further improvements.

Study on the start-up control strategy of DFIG wind farm via MMC-HVDC grid connection

The flexible DC transmission technology proposed in recent years has significant technical advantages over other transmission methods for long-distance grid-connected transmission of large-capacity wind farms. However, as the scale of wind farms continues to expand, new problems have emerged, mainly in the form of start-up control as the basis for the reliable grid-connected operation of wind turbines. In this paper, a start-up control strategy for DFIG wind farms connected to the grid via MMC-HVDC is proposed for DFIG wind farms via flexible DC outgoing transmission scenarios, mainly including MMC-HVDC controlled rectifier start-up control and single DFIG start-up control. Finally, the correctness and feasibility of the proposed control strategy are verified by simulation.

Internal and Startup Controls of the Solutions of Boundary-Value Problem for Parabolic Equations with Degenerations

For a second-order parabolic equation with degenerations, we construct the solution of the problem of optimal control for systems described by the first boundary-value problem with internal and startup controls. The coefficients of parabolic equation have power singularities of any order in time and space variables on a certain set of points.

Hybrid bipolar VSC-DRU HVdc connection for offshore wind farms

This paper presents a hybrid bipolar high voltage direct current (HVdc) link for offshore wind farms (OWFs) connection. Voltage source converter (VSC) technology is used in one of the offshore poles, using a diode rectifier unit (DRU) in the other one. Therefore, economic and power-loss advantages of the DRU over the VSC are leveraged by changing one of the HVdc poles conventional technology. In the proposed control strategy, VSC reactive power is used to control OWF ac grid frequency, allowing the DRU commutation and active power transfer. VSC active power is used for OWF ac grid start-up and hybrid bipolar HVdc link power flow control. OWF ac grid voltage magnitude is controlled while the DRU pole is blocked, and it is automatically accommodated to the required value when the DRU is conducting. Moreover, VSC is also used as an active filter for the main DRU current harmonic components, thus removing the huge passive ac filters from the offshore platform. Poles balanced and unbalanced power flow control strategies are proposed for the hybrid bipolar HVdc, considering both bipolar with neutral return and rigid bipolar configurations. Simulation results validate the proposal which aims reducing cost and size of the OWF HVdc connection.