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Model predictive control (MPC) is a control method that involves determining the input to a dynamical system as the solution to an optimization problem that is solved online. In the wind turbine research literature, MPC has received considerable attention for its ability to handle both actuator constraints and preview disturbance information about the oncoming wind, which can be provided by a lidar scanner. However, while many studies simulate the wind turbine response under MPC, very few physical tests have been carried out, likely due in part to the difficulties associated with solving the MPC problem in real time. In this work, we implement MPC on an experimental, scaled wind turbine operating in a wind tunnel testbed, using an active grid to create reproducible wind sequences and a hot-wire anemometer to generate upstream wind measurements. To our knowledge, this work presents the first physical test of MPC for blade pitch control of a scaled wind turbine. We compare two MPC strategies: one including preview disturbance information and one without. Our results provide further evidence that feedforward control can improve wind turbine performance in transition and above-rated conditions without increasing actuation requirements, which we hope will encourage industry experimentation and uptake of feedforward control methods. We also provide a high-level analysis and interpretation of the computational performance of the chosen approach. This work builds upon the results of an earlier study, which considered unconstrained optimal blade pitch control.

In this article, the authors present a test of wake steering at a commercial wind farm. A single fixed yaw offset, rather than an optimized offset schedule, is alternately applied to an upstream wind turbine and the effect on downstream turbines is analyzed. This experimental design allows for comparison with engineering wake models independent of the controller's ability to track a varying offset and correctly measure wind direction. Additionally, by applying the same offset in beneficial and detrimental conditions, we are able to collect important data for assessing second-order wake model predictions. Results of the article from collected data show good agreement with the FLOw Redirection and Induction in Steady State (FLORIS) engineering model and offer support for the asymmetry of wake steering predicted by newer models, such as the Gauss-curl hybrid model.

Gradient flows provide a means for a networked formation system to reach and stabilize at a target configuration. However, the decentralization constraints and the geometry of the state space make the appearance of stable but undesired configurations inevitable. The presence of these undesired stable configurations precludes global convergence to the target configuration. In this article, we address the issue by considering a controlled formation system on special orthogonal groups over a directed graph. Agents of the system are tasked with stabilizing from others at target relative attitudes. The nominal dynamics of the agents are gradient flows of certain potential functions. These functions are parameter dependent, pretuned by the controller. To prevent the formation system from being trapped at an undesired configuration, we formulate and address the problem of whether the controller can steer the system from any configuration to any other configuration by retuning, on the fly, the parameters of the potential functions. We show that the answer is affirmative provided that the underlying graph is rooted with a single root node being fully actuated. We formulate the result as a main theorem and provide a complete proof of the result.

With the development of lidar technology for measuring wind disturbances ahead of a wind turbine, various feedforward control techniques have been proposed to utilize preview disturbance information for rotor speed regulation. Among these is model predictive control (MPC), which generates an optimal control trajectory subject to system constraints, but very few physical tests have been conducted using MPC for wind turbines presumably due to the challenges involved in solving an optimization problem online. In this paper, we test an optimal feedback/feedforward control algorithm that maintains the clear disturbance inclusion of MPC but results in a linear control law that can be implemented easily. On the other hand, the proposed controller is not able to handle physical system constraints explicitly—full MPC is the subject of future work. A scaled wind turbine model in a wind tunnel is used for testing.

In the search for a lower levelized cost of wind energy, one approach is to increase the accuracy of wind turbine measurements such as wind speed and wind direction. The sensors available on wind turbines are susceptible to local turbulence and measurement bias, which can result in suboptimal turbine performance. As an alternative, recent research has considered using the sensor measurements in a coordinated manner. With such a cooperative approach, the local wind conditions can be estimated more accurately and reliably without the need for additional measurement equipment. In this paper, a novel wind field estimation approach is presented that estimates the local wind conditions based on turbine measurements using Gaussian processes. We show that the estimation framework is able to improve the accuracy of the wind direction estimate both in an offline and online manner, as well as identify possible biases in the sensors and reduce unnecessary wind turbine yaw activity.

Wake steering is a wind farm control strategy in which upstream turbines operate with a yaw misalignment to deflect their wakes away from downstream turbines, yielding a net power gain for the wind plant. But the inability of wake-steering controllers to perfectly track the wind direction leads to suboptimal performance. In this paper, we propose the use of preview wind direction measurements upstream of the turbine to improve controller performance by anticipating wind direction changes. Further, data from an operational wind plant are used to determine realistic preview measurement accuracy. Using the FLOw Redirection and Induction in Steady State (FLORIS) engineering wind farm control tool, we compare the performance of standard and preview-enabled baseline and wake-steering control for a two-turbine array during below-rated operation. Assuming perfect preview information, preview-based wake steering increases energy production by the equivalent of 8.9% of the baseline wake losses, compared to a wake loss recovery of 5.8% with standard wake steering. However, when realistic measurement accuracy is included, the preview-based controller provides no advantage over standard control, motivating the need for more sophisticated control and wind direction forecasting strategies.

This paper focuses on the design of wind-based hybrid power plants that operate at different timescales ranging from seconds to days. Traditionally, renewable power plants have been designed to maximize the amount of energy produced. As the energy system transitions to higher amounts of renewables, hybrid power plants may be asked to provide baseload or peaking plant services that have been traditionally been serviced by coal and natural gas power plants. This paper demonstrates that considering these types of plants and their corresponding objects, that operate at different timescales, result in different solutions and should be considered in the design phase of hybrid power plant development.

As the wind energy industry continues to push for increased power production and lower cost of energy, the focus of research has expanded from individual turbines to entire wind farms. Among a host of interesting problems to be solved when considering the wind farm as a whole, we consider the challenge of scalar field estimation, based on information already collected at the individual turbine level. We aim to estimate the large-scale, low-frequency characteristics of the wind field, such as the mean wind direction and the overall decrease in wind speed across the farm, and employ a Kalman filter that models the wind field using a polynomial function. We compare the proposed method's performance to both a simple averaging technique and filtering of individual turbine measurements. The method presented is not limited to wind turbines and is applicable in other situations where multiple remote agents are used to estimate a scalar field.

While a growing body of research into model predictive control (MPC) for wind turbines shows that MPC can outperform baseline controllers, literature comparing various MPC formulations is scarce. In this paper, we compare MPC based on numerical linear time-invariant (LTI) and linear parameter-varying (LPV) models with differing prediction horizons. Our MPC formulation includes constraints on the turbine control inputs and explicitly handles preview disturbance and scheduling parameter information provided by lidar. Unsurprisingly, when simulated on a nonlinear model of a wind turbine, the LPV-based controller generally performs better than its LTI counterpart. Further, longer prediction horizons lead to improved performance in the LTI case. However, we find that for the LPV-based MPC, there is no clear improvement in performance with horizon length, with short horizons performing similarly (and in some metrics better) than long horizons. We discuss potential takeaways from this surprising result and its implications for the use of lidar-enabled MPC for wind turbines.

As wind energy plays a growing role in the energy sector, new methods for controlling wind turbines and wind farms to maximize performance are garnering industry interest. A developing body of research treats the entire wind farm as a control system, with individual turbines acting as agents in a network, allowing farm-level objectives to be considered. Two promising developments in this research are wake steering control, which seeks to increase the power generated at a wind farm by directing the wakes of upstream turbines away from downstream ones, and communication-based spatial filtering, which seeks to improve the quality of information used by turbine- and farm-level controllers by combining measurements of the wind field collected at the individual turbines. The latter method has been shown to improve the estimates of wind direction at the turbines; however, the resulting potential for increased power capture warrants further investigation. With this paper, we begin to address this gap by combining wake steering with wind direction spatial filtering. To do so, we present a preliminary method for assessing the power capture of dynamic controllers using wind farm codes designed for time-averaged simulation. This allows us to generate results much more rapidly than would be possible using high-fidelity wind farm simulators and may be useful in many wind farm control design applications.

Disturbance accommodating control has received considerable interest in the wind turbine research community for its ability to explicitly account for disturbances in the incoming wind field. Early work was based around estimating the disturbance from feedback information, while more recent research into disturbance accommodating control (as well as other feedforward control laws) has considered disturbance measurements produced by lidar. This work compares the two methods (estimating and measuring the disturbance) while keeping all other aspects of the controller the same. By doing so, we shed light on the performance improvements that can be attained using preview disturbance measurements of the wind.

This study aimed to develop and test a prostate cancer educational program, as well as an electronic keypad survey procedure, among African-Americans. A 1 h seminar and 12-item knowledge questionnaire were reviewed by both professional and lay consultants and then tested among African-American men and women recruited from the city of Chicago. Eight free presentations were delivered to a total of 63 attendees. Mean percent correct rose from 20% pre-program to 57% post-program (P0.001) and there was an increase on all individual questions. This feasibility study demonstrated: (a) there is a general lack of information about prostate cancer among African-Americans; (b) know-ledge can be significantly increased by means of an hour-long seminar; and (c) electronic keypads provide an easy, acceptable means of collecting data. Finally, the study underscored the need for the development of active and creative recruitment strategies to increase attendance. Such efforts are currently underway.

Objectives As the incidence of prostate cancer in the United States exceeds 330,000 in 1997, increasingly more men are faced with treatment choices for which there is no clear approach. At every stage of disease, these treatment choices may involve clinically equivalent modalities that differ in side effects and impact upon quality of life (QOL). Comprehensive, yet efficient, questionnaires are needed to measure QOL in patients with prostate cancer. Methods Developed as a disease-specific adjunct to the Functional Assessment of Cancer Therapy (FACT) measurement system, a 12-item prostate cancer subscale (PCS) was developed and tested in three independent samples: a subscale development sample (n = 43), validity sample 1 (n = 34), and validity sample 2 (n = 96). The 12 items ask about symptoms and problems specific to prostate cancer. These questions are added to the general (FACT-G) instrument, thereby comprising a 47-item questionnaire. Results Internal consistency of the PCS ranged from 0.65 to 0.69, with coefficients for FACT-G subscales and aggregated scores ranging from 0.61 to 0.90. Concurrent validity was confirmed by the ability to discriminate patients by disease stage, performance status, and baseline prostate-specific antigen (PSA) level. Sensitivity to change in performance status and PSA score over a 2-month period suggested that some subscales of the FACT-Prostate (P) (including the PCS) are sensitive to meaningful clinical change. Conclusions Our findings support use of the FACT-P as a meaningful component of QOL evaluation in men undergoing therapy for prostate cancer.

Thermomyces lanuginosus, isolated from self-heated jute stacks in Bangladesh, was studied for production of high level of cellulase-free thermostable xylanase at 50°C using xylan. Optimization of the medium composition was carried out on shake-flask level using Graeco-Latin square technique. This increased xylanase production from 527 nkat ml−1 in the original medium to 9168–9502 nkat ml−1 in the optimized medium under optimized culture conditions e.g. initial medium pH (6.0–6.5), culture temperature (50°C) and time (5–6 d). The lag phase was very much shorter in the laboratory reactor compared to which existed in the shake cultures and 7111 nkat of xylanase activity were obtained per ml of culture filtrate at 60 h of cultivation. With a 15 min reaction time, the optimal pH and temperature for the xylanase activity were at 6.5 and 65°C, respectively. The enzyme was almost stable over a broad range of pH 3–9 at 20°C, with an optimum stability at pH 6.5. After 51 h heating at 50°C the enzyme retained 60%, 100% and 90% activity at pH 5.0, 6.5 and 8.0, respectively. The crude enzyme could hydrolyse xylan effectively and in only 6 h 67.3%, 54.0% and 49.2% saccharifications were achieved for 2%, 5% and 10% substrate levels, respectively. The principal product of hydrolysis was xylobiose together with smaller amounts of xylooligosaccharides (degree of polymerization 3–7) and xylose.

Cultural conditions for the production of thermostable xylanase (EC 3.2.1.8) by the thermophilic fungus Thermomyceslanuginosus were investigated in both submerged and solid-state culture. Under submerged growth conditions in shake flasks, the C and N sources mainly influenced the enzyme yield. The xylanase of T. lanuginosus was found to be inducible by xylan containing C sources as well as by xylose. The enzyme spectrum in culture filtrates after growth on different C-sources was compared by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A central composite design was used to optimize the fermentation medium with respect to medium components. The medium for the optimal production (31.2 g l−1 corn cobs, 30.2 g l−1 yeast extract, and 5.0 g l−1 KH2PO4) yielded 36,200 nkat ml−1 within 7 days of cultivation. The production of other lignocellulolytic enzymes (β-xylosidase, β-glucosidase, acetyl esterase, and α-arabinofuranosidase) using the optimized medium was very low. The optimal pH values of all enzymes were determined. Filter paper cellulase, CMCase, β-mannosidase, and mannanase activities were absent. Solid-state cultures using corn cobs as C source were carried out with a water content of 70% and with yeast extract between 1.4 and 9.6% (w/w). The optimized medium containing 1.75% yeast extract yielded 125,000 nkat ml−1 xylanase activity (337,000 nkat g−1 dry solid) within 9 days of cultivation.

Thermomyces lanuginosus, isolated from self-heated jute stacks in Bangladesh, was able to produce a very high level of cellulase-free xylanase in shake cultures using inexpensive lignocellulosic biomass. Of the nine lignocellulosic substrates tested, corn cobs were found to be the best inducer of xylanase activity. The laboratory results of xylanase production have been successfully scaled up to VABIO (Voest-Alpine Biomass Technology Center) scale using a 15-m3 fermentor for industrial production and application of xylanase. In addition, some properties of the enzyme in crude culture filtrate produced on corn cobs are presented. The enzyme exhibited very satisfactory storage stability at 4–30°C either as crude culture filtrate or as spray- or freeze-dried powder. The crude enzyme was active over a broad range of pH and had activity optima at pH 6.5 and 70–75°C. The enzyme was almost thermostable (91–92%) at pH 6.5 and 9.0 after 41 h preincubation at 55°C and lost only 20–33% activity after 188 h. In contrast, it was much less thermostable at pH 5.0 and 11.0. Xylanases produced on different lignocellulosic substrates exhibited differences in thermostability at 55°C and pH 6.5.

To determine whether an education program on prostate cancer could improve awareness and knowledge among African-American men. African-American men have the world's highest incidence of prostate cancer and more than twice the mortality compared with white men. Screening programs for prostate cancer have not been successful in attracting African-American participation. One explanation is a poor awareness and knowledge about the disease among this high-risk population.We surveyed 900 African-American adults attending prostate cancer education seminars in community settings throughout Illinois between March 1998 and January 2001. Participants were asked to complete a multiple-choice questionnaire on topics related to prostate cancer. The main outcome measures were a change in awareness and knowledge of prostate cancer after the 1-hour educational seminar.The mean survey score improved from 26.0% before the seminar to 73.3% after it (P0.0001). Every multiple-choice question was answered correctly more often after the seminar than before it. Increasing levels of education and income were associated with higher before and after scores (P0.001). Men achieved a significantly greater score improvement (mean 48.1%) compared with women (mean 41.1%; P = 0.006). Previous screening for prostate cancer was reported by 23% of the participants. Using logistic regression analyses, higher levels of education and income correlated with higher rates of screening. After the seminar, 63.1% stated the intention to undergo screening.Our results demonstrate that prostate cancer awareness and knowledge can improve dramatically after a 1-hour seminar on the topic. Additional studies to evaluate the long-term retention of knowledge and impact on behavior are warranted.

Objectives. Changes in health care economics have prompted new clinical pathways for radical prostatectomy to reduce length of hospitalization after surgery to 1 day. We evaluated satisfaction, outcomes, and short-term morbidity in 187 consecutive patients with overnight hospitalization after radical retropubic prostatectomy (RRP). Methods. In 1995, we initiated a critical pathway for RRP that included epidural anesthesia with or without spinal anesthesia and postoperative methadone, acetaminophen, and ibuprofen for pain control. Patients were discharged when they were afebrile, tolerating a regular diet, ambulating without assistance, and using oral medications for analgesia. An 18-item satisfaction survey was mailed to each patient 3 weeks after discharge. Responses to the postoperative survey, morbidity, blood loss, and use of transfusions were recorded. Results. Of 252 patients who underwent RRP, 187 (74.2%) were discharged 1 day after surgery. The mean age of patients was 61.4 years (range 42 to 73). A pelvic lymphadenectomy was performed in addition to the RRP in 32 men (17%). Epidural anesthesia with or without spinal anesthesia was used for all but 3 patients. The mean estimated blood loss was 1166 mL, and 24 patients (12.8%) required transfusion, with a mean of 1.9 U (range 1 to 6) of packed red blood cells. The postoperative complication rate was 11.8%, of which 2.1% (n = 4) were definitely or probably related to our protocol. These complications included clot retention (n = 2), gastrointestinal bleeding (n = 1), and spinal headache (n = 1). Three of 187 patients were readmitted to the hospital within 30 days but only one (0.5%) required admission because of our protocol. The survey response rate was 91.4%. No patient was dissatisfied with his overall care, and only 10.5% of patients would have preferred to stay in the hospital longer. Conclusions. One-day hospitalization after RRP is associated with minimal postoperative morbidity and high patient satisfaction. Similar data are needed for RRP from other centers before policy decisions regarding the length of stay after this procedure are made.

Objectives Cryosurgical ablation of the prostate represents a possibly efficacious method of treating prostate carcinoma in men failing radiation therapy. In addition to eradicating the disease, cryosurgery has the potential to avoid some of the morbidity associated with other treatment modalities. Therefore, a prospective Phase II trial was conducted to determine the safety and efficacy of cryosurgery following radiation therapy in men with local recurrence. Methods Cryosurgical ablation of the prostate was performed in men with prostate cancer previously treated by radiation therapy. All patients had biopsy-proven recurrent disease and no evidence of metastases. Initial follow-up occurred at approximately 3 months and included repeat biopsy and serum prostate-specific antigen (PSA) determinations. Biochemical disease-free survival defined as a PSA value less than 0.3 ng/mL was assessed using the Kaplan-Meier method. Results Thus far, 23 patients have been treated with cryosurgery with follow-up ranging between 12 and 23 months. Approximately 3 months after treatment, sextant biopsies revealed no cancer in 19 of 22 (86%) of the specimens; however, 10 of 22 (45%) showed small amounts of benign glandular tissue. The PSA at 3 months postoperatively declined in 18 of 22 (82%) patients but reached female levels in only 8 men (36%). Nineteen of 22 (86%) patients followed up a minimum of 1 year after cryotherapy have a PSA level equal to or greater than 0.3 ng/mL Complications occurred in 100% of the patients with 12 of 22 (55%) requiring at least one transurethral resection of sloughed, necrotic tissue. Conclusions Our preliminary results suggest that the current Cryosurgical technique used in men failing radiation therapy has a low probability of biochemical cure and a high complication rate. Until more data are available, cryosurgery for men with locally recurrent disease after radiation therapy should be considered strictly experimental.