Time Constant Of Low-pass Filter Research Articles

Solar PV and BESS Plant-Level Voltage Control and Interactions: Experiments and Analysis

In real world operation, low-frequency oscillations associated with plant-level voltage control of inverter-based resources (IBRs) have been a concern of grid operators. This research aims to demonstrate and analyze the effect of plant-level voltage control on system stability and potential interactions among IBRs. The experiment results of a 13.2-kV system interconnected with two IBRs—a 1-MW battery energy storage system (BESS) and a 430-kW solar photovoltaic (PV) plant—are presented. Both 0.5-Hz and 3-Hz oscillations become visible at certain conditions. The phenomenon is further explained by use of a feedback system consisting of the plant-level droop control and the effect of reactive power or var injection on voltage. The main components of the block diagram are obtained via frequency scan measurements. The analysis offers an understanding of the main contributors and other influencing factors of the 3-Hz and 0.5-Hz modes. It also reveals the role of the volt-var droop gain, the low-pass filter time constant, and the system impedance in stability.

Series PIDA Controller Design for IPDT Processes

This paper discusses optimal design of the series proportional–integral–derivative–accelerative (PIDA) controller for integral-plus-dead-time (IPDT) plants. The article starts with the design of disturbance reconstruction and compensation based on proportional-derivative-accelerative (PDA) stabilizing controllers. It shows that by introducing positive feedback by a low-pass filter from the (limited) output of the stabilizing PDA controller, one gets disturbance observer (DOB) for the reconstruction and compensation of input disturbances. Thereby, the DOB functionality is based on evaluating steady-state controller output. This DOB interpretation is in full agreement with the results of the analysis of the optimal setting of the stabilizing PDA controller and of its expanded PIDA version with positive feedback from the controller output. By using the multiple real dominant pole (MRDP) method, it confirms that the low-pass filter time constant in positive feedback must be much longer than the dominant time constant of the stabilized loop. This paper also shows that the constrained PIDA controller with the MRDP setting leads to transient responses with input and output overshoots. Experimentally, such a constrained series PIDA controller can be shown as equivalent to a constrained MRDP tuned parallel PIDA controller in anti-windup connection using conditional integration. Next, the article explores the possibility of removing overshoots of the output and input of the process achieved for MRDP tuning by interchanging the parameters of the controller transfer function, which was proven as very effective in the case of the series PID controller. It shows that such a modification of the controller can only be implemented approximately, when the factorization of the controller numerator, which gives complex conjugate zeros, will be replaced by a double real zero. Neglecting the imaginary part and specifying the feedback time constant with a smaller approximative time constant results in the removal of overshoots, but the resulting dynamics will not be faster than for the previously mentioned solutions. A significant improvement in the closed-loop performance can finally be achieved by the optimal setting of the constrained series PIDA controller calculated using the performance portrait method. This article also points out the terminologically incorrect designation of the proposed structure as series PIDA controller, because it does not contain any explicit integral action. Instead, it proposes a more thorough revision of the interpretation of controllers based on automatic reset from the controller output, which do not contain any integrator, but at the same time represent the core of the most used industrial automation. In the end, constrained structures using automatic reset of the stabilizing controller output can ensure a higher performance of transient responses than the usually preferred solutions based on parallel controllers with integral action that, in order to respect the control signal limitation, must be supplemented with anti-windup circuitry. The excellent properties of the constrained series PIDA controller are demonstrated by an example of controlling a thermal process and proven by the circle criterion of absolute stability.

Enhanced Dynamic Behaviour of Grid Connected Wind Farms in Load Participation and Frequency Regulation

The control of grid frequency in power systems due to the penetration of wind turbines is vital to maintaining the stability of power grids, based on recent grid requirements. In this paper, the dynamic behaviour of a wind farm connected to an existing grid is presented. The existing grid is made up of steam turbines, while the wind farm is based on squirrel cage induction generators. An energy capacitor system is used to stabilize the wind farm during periods of wind speed change. Loads with various capacities were connected to the grid to test the robustness of the controllers of the energy capacitor system employed. Furthermore, the effect of varying the time constant of the in-built DC-DC chopper of the energy capacitor system was investigated, considering load participation in the grid. One of the targets of this paper is the stabilization of the grid frequency of the network, despite the load capacity and the nature of the wind speed in the wind farm. The system performance was evaluated using Power System Computer Design and Electromagnetic Transient Including DC (PSCAD/EMTDC). The same conditions of operation were used to investigate the various scenarios considered in this study, to ensure an effective comparison. The natural wind speed employed was the same for all the considered scenarios. The presented results show that small load capacity with a high value low pass filter time constant, provided better response for the grid frequency and the entire variables of the power network.

A Practical Secondary Frequency Control Strategy for Virtual Synchronous Generator

A practical secondary frequency control (SFC) strategy for virtual synchronous generator (VSG) with predictable rotor frequency response is proposed in this letter. The relationship between rotor inertia, damping factor, integral coefficient and the time constant of low-pass filter is revealed, moreover, the complexity of parameter design is reduced obviously. Finally, the proposed concept is verified by Simulation results.

Hydrogen production using variable and fixed speed wind farm topologies in a utility grid

This paper presents hydrogen production in a utility grid that is composed of variable and fixed speed wind farms. The variable speed wind farm is made of Doubly Fed Induction Generator (DFIG) wind turbines, while the fixed speed wind farm is composed of only Induction Generator wind turbines. To achieve smoothening of the wind farm terminals, Flexible AC Transmission System devices of an Energy Capacitor System with a DC chopper type and Static Synchronous Compensator were used to stabilize the fixed speed wind farms. The power converters of the DFIGs were used to provide reactive power during dynamic periods to achieve stability of the variable speed wind farm. Since the amount of wind energy required producing hydrogen is insignificant and also by taking advantage of the smoothed terminal of the wind farms, a hydrogen generator composed of a rectifier and electrolyzer is connected to the wind farms to produce hydrogen. The produced hydrogen gas thereby acts as a means of transportation to power fuel cell cars. The cooperative control strategies of the system were developed in the visual simulation Power System Computer Aided Design/Electromagnetic Transient Including DC environment. The results obtained show that it is more cost effective to use the variable speed wind farm topology in hydrogen gas production. The effect of the low pass filter time constant in the electrolyzer circuitry was also investigated in the production of hydrogen gas. On the basis of the same grid energy in the utility network, the average time required to fill the hydrogen tanks using high pass filter time constant is shorter.

Impact of edge localized mode on photo-elastic-modulator based motional Stark effect polarimetry

Intermittent increase in background light induced by edge localized mode (ELM) in high confinement mode (H-mode) plasma gives disturbances to polarization angle of incident light measured by motional Stark effect (MSE) polarimeter using photo-elastic modulator (PEM), even if the background light is not polarized. The error in the polarization angle γPEM determined by the light intensity at the frequency modulated by the PEM originates in a broadband frequency spectrum of the intermittent background light and applies to PEM based polarimeter in general. The impact of the background light induced by the ELM on the error in γPEM is numerically investigated in terms of the polarization angle of incident light γ, the peak intensity of background light normalized by the intensity of beam emission XELM, ELM frequency fELM, ELM decay time τELM and the time constant of low-pass filter (LPF) per single stage τLPF. The error increases almost proportionally with γ between ±22.5° when inphase spectral amplitude is used in γPEM calculation. The error becomes quite large for γ approaching to the direction of PEM axis (±22.5°), when absolute spectral amplitude is used. The error increases with XELM but does not depend on τELM. When the ELM frequency is sufficiently lower than a critical ELM frequency that is given by inverse of an effective LPF time constant (τLPF times the number of LPF stages), the error has its peak, the height of which is independent of fELM, soon after the ELM and vanishes between subsequent ELMs. However, when fELM is higher than the critical ELM frequency, errors induced by subsequent ELMs pile up and the error increases with fELM. In case of no pileup, the maximum error becomes larger for smaller τLPF, because impact of ELM temporally concentrates in a shorter period just after the ELM. The error induced by ELMs is roughly estimated to be ∼0.002° in a type-I ELMy H-mode JT-60U discharge, which is much smaller than other errors coming from calibrations (about 0.1–0.2°) and temporal fluctuation (less than about 0.05°), mainly since the background light induced by ELMs is weak compared to the beam emission XELM ∼0.07 in JT-60U. However, MSE diagnostics experiencing large background light (XELM) should take this kind of error into account.