Closed-loop Technique Research Articles

Is It Possible to Obtain Benefits by Reducing the Contribution of the Digital Signal Processing Techniques to the Control of the Active Power Filter?

This paper presents a simple yet efficient control method for active power filters that can be used to improve power quality. Applying this method can open the way towards limiting the hardware and computational expenditure, which are needed for control of the active filter, while maintaining its required performance. The method is based on the indirect approach of obtaining reference signals combined with the closed-loop current control technique. Monitoring of changes of energy stored in reactance elements of the active filter is the base for obtaining reference signals for compensation. The active filter can perform classical compensation and, additionally, can perform some extra functionality for managing of active power in the system. In particular, it can stabilize the supplying source power, enable energy exchange between loads connected on DC and AC sides of the active filter, and—in a case of generating loads—enable their energy storage and redistribution amongst consuming loads. The presented method can be useful for voltage-source as current-source inverter based active filters, and for DC systems as well as for AC single- or three-phase ones.

Towards Safe and Robust Closed-Loop Artificial Pancreas Using Improved PID-Based Control Strategies

Artificial pancreas enhances the life experience for diabetic patients by allowing them to live normally with their glucose levels controlled automatically with minimal or no intervention. For closed-loop glucose controllers to be approved for clinical practice, they have to prove safety under all potential scenarios. One of the biggest challenges of closed-loop glucose control is to handle the distortion caused by meal intake. This challenge becomes more problematic when taking into account the imperfections and limitations of glucose sensors. In this article, we propose new Proportional-Integral-Derivative (PID)-based control strategies for robust glucose control under varying meal conditions. The proposed approaches aim at counteracting the challenges imposed by the large delays incurred in glucose sensing and insulin action. Statistical model checking was utilized to analyze the performance figures and safety properties as compared with existing closed-loop techniques. The results have shown that one of the proposed approaches provide substantial enhancements towards safe and robust glucose control especially under sensor noise. Where, under a typical relative meal size between 75 and 125 (g/100Kg), the proposed approach can satisfy hypoglycemia safety property for 90% of the patients compared to lower than 50% of the patients for the other investigated techniques. These enhancements can be achieved without additional personalized tuning beyond the standard PID control.

A Closed Loop Delay Compensation Technique to Mitigate the Common Mode Conducted Emissions of Bipolar PWM Switched Circuits

This article presents the design of a new closed loop technique that reduces the common mode conducted emission. It can be applied to any kind of switching circuit in which couples of outputs are modulated by a bipolar PWM signal. It is based on the compensation of the delay between complementary output switching edges, using a simple sensing circuit and a low computational effort software algorithm, which is implemented in a microcontroller driving the switching circuit. One of the main advantages of the proposed solution is the reduction of the disturbance energy, without affecting the system efficiency. The technique is practical to implement, and the measurements performed on a power inverter prototype confirm the theoretical analysis outcomes about the reduction of the conducted emission in the lower-to-medium frequency range.

Active Gate Driver and Management of the Switching Speed of GaN Transistors during Turn-On and Turn-Off

The paper investigates the management of drain voltage and current slew rates (i.e., dv/dt and di/dt) of high-speed GaN-based power switches during the transitions. An active gate voltage control (AGVC) is considered for improving the safe operation of a switching cell. In an application of open-loop AGVC, the switching speeds vary significantly with the operating point of the GaN HEMT on either or both current and temperature. A closed-loop AGVC is proposed to operate the switches at a constant speed over different operating points. In order to evaluate the reduction in the electromagnetic disturbances, the common mode currents in the system were compared using the active and a standard gate voltage control (SGVC). The closed-loop analysis carried out in this paper has shown that discrete component-based design can introduce limitations to fully resolve the problem of high switching speeds. To ensure effective control of the switching operations, a response time fewer than 10 ns is required for this uncomplex closed-loop technique despite an increase in switching losses.

Linearized active circuits: transfer functions and stability

<abstract><p>We study the properties of electronic circuits after linearization around a fixed operating point in the context of closed-loop stability analysis. When distributed elements, like transmission lines, are present in the circuit it is known that unstable circuits can be created without poles in the complex right half-plane. This undermines existing closed-loop stability analysis techniques that determine stability by looking for right half-plane poles. We observed that the problematic circuits rely on unrealistic elements with an infinite bandwidth. In this paper, we therefore define a class of realistic linearized components and show that a circuit composed of realistic elements is only unstable with poles in the complex right half-plane. Furthermore, we show that the amount of right half-plane poles in a realistic circuit is finite, even when distributed elements are present. In the second part of the paper, we provide examples of component models that are realistic and show that the class includes many existing models, including ones for passive devices, active devices and transmission lines.</p></abstract>

CLoSES: A platform for closed-loop intracranial stimulation in humans

Targeted interrogation of brain networks through invasive brain stimulation has become an increasingly important research tool as well as therapeutic modality. The majority of work with this emerging capability has been focused on open-loop approaches. Closed-loop techniques, however, could improve neuromodulatory therapies and research investigations by optimizing stimulation approaches using neurally informed, personalized targets. Implementing closed-loop systems is challenging particularly with regard to applying consistent strategies considering inter-individual variability. In particular, during intracranial epilepsy monitoring, where much of this research is currently progressing, electrodes are implanted exclusively for clinical reasons. Thus, detection and stimulation sites must be participant- and task-specific. The system must run in parallel with clinical systems, integrate seamlessly with existing setups, and ensure safety features are in place. In other words, a robust, yet flexible platform is required to perform different tests with a single participant and to comply with clinical requirements.In order to investigate closed-loop stimulation for research and therapeutic use, we developed a Closed-Loop System for Electrical Stimulation (CLoSES) that computes neural features which are then used in a decision algorithm to trigger stimulation in near real-time. To summarize CLoSES, intracranial electroencephalography (iEEG) signals are acquired, band-pass filtered, and local and network features are continuously computed. If target features are detected (e.g. above a preset threshold for a certain duration), stimulation is triggered. Not only could the system trigger stimulation while detecting real-time neural features, but we incorporated a pipeline wherein we used an encoder/decoder model to estimate a hidden cognitive state from the neural features.CLoSES provides a flexible platform to implement a variety of closed-loop experimental paradigms in humans. CLoSES has been successfully used with twelve patients implanted with depth electrodes in the epilepsy monitoring unit. During cognitive tasks (N=5), stimulation in closed loop modified a cognitive hidden state on a trial by trial basis. Sleep spindle oscillations (N=6) and sharp transient epileptic activity (N=9) were detected in near real-time, and stimulation was applied during the event or at specified delays (N=3). In addition, we measured the capabilities of the CLoSES system. Total latency was related to the characteristics of the event being detected, with tens of milliseconds for epileptic activity and hundreds of milliseconds for spindle detection. Stepwise latency, the actual duration of each continuous step, was within the specified fixed-step duration and increased linearly with the number of channels and features.We anticipate that probing neural dynamics and interaction between brain states and stimulation responses with CLoSES will lead to novel insights into the mechanism of normal and pathological brain activity, the discovery and evaluation of potential electrographic biomarkers of neurological and psychiatric disorders, and the development and testing of patient-specific stimulation targets and control signals before implanting a therapeutic device.

Closed-Loop Elastic Demand Control under Dynamic Pricing Program in Smart Microgrid Using Super Twisting Sliding Mode Controller.

Electricity demand is rising due to industrialisation, population growth and economic development. To meet this rising electricity demand, towns are renovated by smart cities, where the internet of things enabled devices, communication technologies, dynamic pricing servers and renewable energy sources are integrated. Internet of things (IoT) refers to scenarios where network connectivity and computing capability is extended to objects, sensors and other items not normally considered computers. IoT allows these devices to generate, exchange and consume data without or with minimum human intervention. This integrated environment of smart cities maintains a balance between demand and supply. In this work, we proposed a closed-loop super twisting sliding mode controller (STSMC) to handle the uncertain and fluctuating load to maintain the balance between demand and supply persistently. Demand-side load management (DSLM) consists of agents-based demand response (DR) programs that are designed to control, change and shift the load usage pattern according to the price of the energy of a smart grid community. In smart grids, evolved DR programs are implemented which facilitate controlling of consumer demand by effective regulation services. The DSLM under price-based DR programs perform load shifting, peak clipping and valley filling to maintain the balance between demand and supply. We demonstrate a theoretical control approach for persistent demand control by dynamic price-based closed-loop STSMC. A renewable energy integrated microgrid scenario is discussed numerically to show that the demand of consumers can be controlled through STSMC, which regulates the electricity price to the DSLM agents of the smart grid community. The overall demand elasticity of the current study is represented by a first-order dynamic price generation model having a piece-wise linear price-based DR program. The simulation environment for this whole scenario is developed in MATLAB/Simulink. The simulations validate that the closed-loop price-based elastic demand control technique can trace down the generation of a renewable energy integrated microgrid.

Multitechnique Concise Robust Control for the Insulation Containment Space Pressure Control of LNG Carrier

In this note, a novel multitechnique concise robust control scheme, based on the mirror mapping technique (MMT), closed-loop gain shaping algorithm (CGSA), Smith predictor (SP), and nonlinear feedback technique (NFT), is proposed for the pressure control of the liquefied natural gas (LNG) carrier insulation containment space. Firstly, a kind of integral unstable time-delay model is obtained by linearizing the nonlinear model of the pressure maintenance system around its equilibrium. By using the MMT and CGSA, one acquires the corresponding stable mirror mapping model of the unstable linear model and the designed controller. And the SP is introduced to tackle the time-delay problem. In addition, for the purpose of energy saving, the NFT is added into the control scheme. Finally, a set of experiments has been employed to illustrate the control effects, and the results show that it can achieve satisfying performance in aspects of disturbance rejection and energy saving.

Tracking a Reference Damping Force in a Magneto-Rheological Damper for Automotive Applications

Magneto-rheological dampers are gaining a lot of attention in the automotive industry and they show many advantages over their hydraulic counterpart. However, they are characterised by a highly nonlinear damping characteristics which may not be desired. In this paper, the authors present a control scheme which gives the possibility to track any reference damping force in a magneto-rheological damper. The main assumption of this research is the actual force exerted by the damper is not available for measurement, since such a sensor could not be installed onto a commercial vehicle. The control of this device is particularly challenging because of a singularity point in the origin which has significant repercussions on performance if not considered. The authors propose a novel closed-loop technique which is compared against an industrial solution based on an open-loop scheme, proving the former to be superior via a qualitative and quantitative analysis.

A Modified Closed-Loop Voltage Model Observer Based on Adaptive Direct Flux Magnitude Estimation in Sensorless Predictive Direct Voltage Control of an Induction Motor

Voltage model observer is a simple and economical technique for flux estimation in induction motor sensorless drives. However, it shows poor performance in low-speed regions. Therefore, in most cases, the use of this observer is limited. On the other hand, using a simple but accurate estimator is important when the control method is sophisticated and requires heavy computation. This issue will be important in predictive control more than the other methods because the accuracy of the prediction is dependent on the flux estimation. In this paper, a modified closed-loop technique based on voltage model observer is proposed for flux estimation. The feedback loop is supported by the proposed model reference adaptive system direct flux magnitude estimation technique. The dependence of the feedback loop on the stator resistance is eliminated. Therefore, the drift error will be avoided. This will allow the method to withstand the high stator resistance error even at low speeds. Also, a new Lyapunov-based technique for the stator resistance estimation via reduced-order model is proposed. By using the proposed observer, the predictive direct voltage control technique is used as the control method in order to achieve a control method that requires low computation. The proposed method is validated through the experimental results.

Fault Waveform Regenerator and Its Digital Closed-Loop Modification Technique

In order to provide a novel and more effective alternative to the commonly used relay protection testing device that outputs only the sinusoidal testing signals, the concept of fault waveform regenerator is proposed in this paper, together with its hardware structure and software flow chart. Fault waveform regenerator mainly depends on its power amplifiers (PAs) to regenerate the fault waveforms recorded by digital fault recorder (DFR). To counteract the PA’s inherent nonlinear distortions, a digital closed-loop modification technique that is different from the predistortion technique is conceived. And the experimental results verify the effectiveness of the fault waveform regenerator based on the digital closed-loop modification technique.

Quantitative comparison of closed-loop and dual harmonic Kelvin probe force microscopy techniques.

Kelvin probe force microscopy (KPFM) is a widely used technique to map surface potentials at the nanometer scale. In traditional KPFM, a feedback loop regulates the DC bias applied between a sharp conductive probe and a sample to nullify the electrostatic force (closed-loop operation). In comparison, open-loop techniques such as dual harmonic KPFM (DH-KPFM) are simpler to implement, are less sensitive to artefacts, offer the unique ability to probe voltage sensitive materials, and operate in liquid environments. Here, we directly compare the two techniques in terms of their bandwidth and sensitivity to instrumentation artefacts. Furthermore, we introduce a new correction for traditional KPFM termed "setpoint correction," which allows us to obtain agreement between open and closed-loop techniques within 1%. Quantitative validation of DH-KPFM may lead to a wider adoption of open-loop KPFM techniques by the scanning probe community.

Robust desynchronization of Parkinson's disease pathological oscillations by frequency modulation of delayed feedback deep brain stimulation.

The hyperkinetic symptoms of Parkinson’s Disease (PD) are associated with the ensembles of interacting oscillators that cause excess or abnormal synchronous behavior within the Basal Ganglia (BG) circuitry. Delayed feedback stimulation is a closed loop technique shown to suppress this synchronous oscillatory activity. Deep Brain Stimulation (DBS) via delayed feedback is known to destabilize the complex intermittent synchronous states. Computational models of the BG network are often introduced to investigate the effect of delayed feedback high frequency stimulation on partially synchronized dynamics. In this study, we develop a reduced order model of four interacting nuclei of the BG as well as considering the Thalamo-Cortical local effects on the oscillatory dynamics. This model is able to capture the emergence of 34 Hz beta band oscillations seen in the Local Field Potential (LFP) recordings of the PD state. Train of high frequency pulses in a delayed feedback stimulation has shown deficiencies such as strengthening the synchronization in case of highly fluctuating neuronal activities, increasing the energy consumed as well as the incapability of activating all neurons in a large-scale network. To overcome these drawbacks, we propose a new feedback control variable based on the filtered and linearly delayed LFP recordings. The proposed control variable is then used to modulate the frequency of the stimulation signal rather than its amplitude. In strongly coupled networks, oscillations reoccur as soon as the amplitude of the stimulus signal declines. Therefore, we show that maintaining a fixed amplitude and modulating the frequency might ameliorate the desynchronization process, increase the battery lifespan and activate substantial regions of the administered DBS electrode. The charge balanced stimulus pulse itself is embedded with a delay period between its charges to grant robust desynchronization with lower amplitudes needed. The efficiency of the proposed Frequency Adjustment Stimulation (FAS) protocol in a delayed feedback method might contribute to further investigation of DBS modulations aspired to address a wide range of abnormal oscillatory behavior observed in neurological disorders.

Synthesis of 3-PRS Manipulator Using Exact Method

This paper presents dimensional synthesis of 3-PRS manipulator which is based on physical constraints of the manipulator. The synthesis of the manipulator involves determination of dimensional parameters of manipulator so as to determine the directions and location of revolute joints and location of spherical joints by considering the physical constraints such that a point on the mobile platform passes through a prescribed set of positions in space. The dimensions of the manipulator are determined by considering physical constraints of the manipulator and are carried out using optimized exact method. The result of exact method approach shows that the maximum error in occupied (obtained) position $$\left( {p_{xi} , p_{yi} , p_{zi} } \right)$$ of mobile platform is $$\left| { \pm \,4.5 \times 10^{ - 8} } \right|$$ m and the maximum percentage of positional error is $$\left| { \pm \,4.83 \times 10^{ - 2} } \right|\%$$, the maximum error in occupied (obtained) orientation $$\left( {\psi_{i} , \theta_{i} , \phi_{i} } \right)$$ of mobile platform is $$\left| { \pm \,1.01 \times 10^{ - 6} } \right|$$ degrees and the maximum percentage of error in orientation is $$\left| { \pm \,3.16 \times 10^{ - 3} } \right|\% .$$ The actuator positions are calculated by inverse kinematics by closed-loop technique and the obtained (occupied) positions, and orientations of the manipulator are determined by direct position kinematics by vector technique. The resulting nonlinear equations are solved by using MATLAB. The numerical example for the synthesis with five positions is presented to demonstrate the synthesis procedure. The 3-PRS manipulator is used for alignment applications where tip, tilt and position motions are significant.

Innovative Hybrid Pile Oscillator Technique in the Minerve Reactor: Open Loop Versus Closed Loop

Pile oscillator techniques are powerful methods to measure small reactivity worth of isotopes of interest for nuclear data improvement. This kind of experiment has long been implemented in the Minerve experimental reactor, operated by CEA Cadarache, Saint-Paul-les-Durance, France. A hybrid technique mixing reactivity worth and flux variations surrounding the oscillator is presented here. It was made possible after developing high-sensitivity miniature fission chambers introduced next to the irradiation channel. A test campaign, called MAESTRO-SL, took place in 2015. Its objective was to assess the feasibility of the hybrid method and investigate the separation of mixed neutron effects, such as fission and capture or scattering and capture. The experimental results are presented and discussed in this paper, which focus on comparing two measurement setups, one using a power control system (closed-loop technique) and another one in which reactor power is free to drift (open-loop technique). First, it is demonstrated that the open loop is equivalent to the closed loop, and both techniques bring similar results. It is shown that measuring the flux change around oscillated samples provides valuable information on partial neutron cross sections. Second, uncertainty management and methods’ reproducibility are discussed. As expected, both techniques can achieve similar performances. In this paper, uncertainty as low as 0.007 pcm for samples’ reactivity worth and $1.2 \times 10^{-4}$ for local flux change were achieved.

Three Degree of Freedom Spatial Parallel Manipulator Inverse Kinematic Position Analysis

This paper presents inverse kinematic position analysis of three degree of freedom spatial parallel manipulator, which has three similar kinematic closed loops. Each loop consist of an actuated sliding linkage- rotational joint and spherical joint. The actuated sliding linkage is coupled to inclined limb of fixed base platform and rotational joints are integrated to the linear sliding actuators. The limbs are connected from rotational joints to moving platform by spherical joints. The degree of freedom of a manipulator is obtained by spatial kutzbach criterion. The inverse kinematic position analysis problem solved by using closed loop technique is applied to 3-coupled trigonometric equations which are obtained with side and behaviour constraints of a parallel manipulator. By using MATLAB the three non-linear coupled algebraic equations are solved. The inverse kinematic position analysis procedure is used in the development process of spatial parallel manipulator. The part of kinematic analysis is used to check the required positions-orientations and after kinematic process the obtained positions-orientations of the moving platform of the developed spatial parallel manipulator.

Abstract: A Retrospective Comparison of Two Techniques of Fat Grafting in Breast Reconstruction: Outcomes over 5 Years

BACKGROUND: Autologous fat grafting (AFG) has become a common method of contour modulation of breasts after post-mastectomy implant reconstruction since the lift of the ASPS ban in 2009. Standard methods involve multiple tedious steps: harvesting, collection (with various possible manipulations) and finally reinfusion to the recipient site, most frequently via manual syringe.1,2 We developed a novel technique condensing these steps into one closed-loop system. In this innovative method3,4 we used a continuous flow pump to reinfuse fat to the breast. Del Vecchio also recently showed safety and efficiency with this method.5 METHODS: We conducted a retrospective cohort review of patients receiving AFG for breast contouring either by the syringe or closed-loop method by a single surgeon. Time to infuse fat, complications, and outcomes were analyzed. The cohort included 19 syringe AFG procedures (34 breasts) and 25 closed-loop procedures (41 breasts) between 2013 and 2018. Both short term (infection, explant) and long-term complications (granulomas, cysts, biopsy) were analyzed. RESULTS: Average infusion time was 15 minutes (4–30) for the closed-loop technique. Clinical follow-up times ranged from 28 to 161 weeks (mean=88) for syringe and 0 to 130 weeks (mean=32) for the closed-loop method. There were 2 major and 6 minor complications out of 34 breasts in the syringe method (5.5%, 16.6%, overall 23.5%) versus 1 major and 5 minor complications out of 41 breasts in the closed-loop method (2.4%, 12.1%, overall 14.6%) [p-value major=0.49, minor=0.58, overall=0.33]. Syringe complications included 2 granulomas and 1 cyst (8.8%) while the closed-loop complications included 2 granulomas (4.9%) [p-value=0.50]. Average total volume transferred was 262cc (60–850) for syringe, and 334cc (80–795) for closed-loop method. Infusion rate for the closed-loop method ranged from 100 to 250 mL/min, most consistently at 125 ml/min. CONCLUSION: The study suggests the closed-loop technique significantly decreases time of fat transfer to an average of 15 minutes, a trend towards decreased overall complications, though not statistically significant, and good subjective fat retention beyond 12 months. This suggests the closed-loop method is safe, effective, and significantly decreases operating time. We continue to collect patients in the closed-loop cohort and are also analyzing variation in adipocyte viability between the two methods. REFERENCES: 1. Coleman SR, Saboeiro AP. Fat Grafting to the Breast Revisited: Safety and Efficacy. Plastic and Reconstructive Surgery. 2007;119(3):775–785. doi:10.1097/01.prs.0000252001.59162.c9. 2. Delay E, Garson S, Tousson G, Sinna R. Fat Injection to the Breast: Technique, Results, and Indications Based on 880 Procedures Over 10 Years. Aesthetic Surgery Journal. 2009;29(5):360–376. doi:10.1016/j.asj.2009.08.010. 3. Hayssen H, Hagarty SE. A Novel Closed-Loop Autologous Fat Grafting Technique for Breast Reconstruction. Annals of Plastic Surgery. Vol 78, April 2017. 4. US and International Patent Applications. (US20170312403) Simple Closed Loop System for Direct Harvest and Transfer for High Volume Fat GraftingApril 2016 and (WO2017189918) A CLOSED LOOP SYSTEM FOR DIRECT HARVEST AND TRANSFER FOR HIGH VOLUME FAT GRAFTING, PCT Patent Applications April 2016, April 2017. 5. Del Vecchio D, Wall S Jr., Expansion Vibration Lipofilling: A New Technique in Large-Volume Fat Transplantation. Plastic and Reconstructive Surgery. 2018 May;141(5):639e-649e. doi:10.1097/PRS.

A dual-loop tracking control approach to precise nanopositioning

Nanopositioners are mechanical devices that can accurately move with a resolution in the nanometer scale. Due to their mechanical construction and the piezoelectric actuators popularly employed in nanopositioners, these devices have severe performance limitations due to resonance, hysteresis and creep. A number of techniques to control nanopositioners, both in open-loop and closed-loop, have been reported in the literature. Closed-loop techniques clearly outperform open-loop techniques due to several desirable characteristics, such as robustness, high-bandwidth, absence of the need for tuning and high stability, along with others. The most popular closed-loop control technique reported is one where a damping controller is first employed in an inner loop to damp the mechanical resonance of the nanopositioner, thereby increasing achievable bandwidth. Consequently, a tracking controller, typically an Integral controller or a proportional–integral controller, is implemented in the outer loop to enforce tracking of the reference signal, thereby reducing the positioning errors due to hysteresis and creep dynamics of the employed actuator. The most popular trajectory a nanopositioner is forced to track is a raster scan, which is generated by making one axis of the nanopositioner follow a triangular trajectory and the other follow a slow ramp or staircase. It is quite clear that a triangle wave (a finite velocity, zero acceleration signal) cannot be perfectly tracked by a first-order integrator and a double integrator is necessary to deliver error-free tracking. However, due to the phase profile of the damped closed-loop system, implementing a double integrator is difficult. This paper proposes a method by which to implement two integrators focused on the tracking performance. Criteria for gain selection, stability analysis, error analysis, simulations, and experimental results are provided. These demonstrate a reduction in positioning error by 50%, when compared to the traditional damping plus first-order integral tracking approach.

A Versatile Mass-Sensing Platform With Tunable Nonlinear Self-Excited Microcantilevers

A versatile mass-sensing platform based on the nonlinear dynamical response of a microcantilever embedded in a self-excitation feedback loop is proposed. It is experimentally shown that the delay imposed in the feedback loop by an adjustable phase-shifter can be used to finely tune this system to work in three different modalities, according to the desired mass sensing application: 1) as a continuous mass sensor, where the oscillation frequency smoothly responds to changes in the mass added to the resonator; 2) as a threshold sensor, where a sudden change in the oscillation frequency is triggered by an arbitrarily small change of mass added to the cantilever; and 3) as a stable microresonator, whose oscillation frequency is almost not affected by environmental conditions, such as changes in added mass, or in density/viscosity of the surrounding fluid. This variety of dynamical responses was registered for a wide range of added masses, in the form of beads individually attached to the cantilever. A complete analytical model to explain the observed experimental results is derived and shows a strong agreement with the measured data. The high resolution and signal-to-noise ratio, as well as the threshold and stable sensing modalities obtained with this closed-loop technique, are not available in the current open-loop microcantilever-based mass sensors.

Investigation of production forecast biases of simulation models in a benchmark case

Reservoir management decisions are often based on simulation models and probabilistic approaches. Thus, the response of the model must be sufficiently accurate to base sound decisions on and fast enough to be practical for methodologies requiring many simulation runs. However, simulation models often forecast production rates different to real production rates for various reasons. Two possible causes of these deviations are (1) upscaling (a technique to reduce the computational time of simulation models by reducing the number of grid blocks) and (2) uncertainties (the values established to attributes are different from real values caused by lack of knowledge of real reservoir). Morosov and Schiozer [(2016) applied a closed-loop technique in a benchmark case where decisions taken using the simulation models are applied to a reference case. The optimized production strategy, using simulations models, increased the expected monetary value of the project by about 29%, but the Net Present Value (NPV), calculated using a reference case, decreased by 2%. The real NPV was outside the expected range and revealed that the set of models did not fully represent the real field, even for high-quality history-matched models. The objective of this study is to identify the causes of these discrepancies. To reach this goal, we investigate and analyze both the impact of the upscaling and the uncertainty on production and economic indicators. We use a set of representative models of benchmark UNISIM-I (Avansi and Schiozer, 2015) to consider the effects of uncertainty and upscaling. Our main concern was the uncertainties in the distribution of petrophysical properties that strongly influence the productivity and injectivity of wells, noted by Morosov and Schiozer (2016) as being the main cause for differences among models. Furthermore, to verify the isolated effects of the possible causes of deviation, we use a single model to show only the effects of upscaling, and another set of models showing only the uncertainty. The results showed that the impact of the uncertainties was higher than the upscaling for the studied case. The upscaling generated an optimistic bias for production and economic indicators, but well-correlated with the reference case. The uncertainties significantly affected the production forecasts for this study. This happened because the response of the wells is highly dependent on the petrophysical properties of the model, which varies widely between the different models representing uncertainties and was not adequately depicted by the representative models.