Current Compensation Methods Research Articles

Partial Current Harmonic Compensation in Dual Three-Phase PMSMs Considering the Limited Available Voltage

Multiphase electric machines are known to have problems with stator current harmonics. The harmonics can be eliminated by various current harmonic compensation methods. However, using the active harmonic compensation can increase the required output voltage of the inverter supplying the machine. Because the maximum voltage is limited, complete elimination of the current harmonics may not always be possible. For such cases, this paper introduces a strategy for a partial compensation of the current harmonics. The aim of the proposed strategy is to provide a maximum reduction in the magnitude of the harmonics when the available voltage is limited. The strategy is verified by experimental results.

Dynamic time warping: Compensating for temperature variations

Guided wave structural health monitoring has the potential to monitor large structural areas. Yet, temperature variations are known to misalign measurement data and cause false alarms. Current popular temperature compensation methods include the optimal signal stretch method and interpolation method. While these methods perform well for small temperature changes, they fail in large temperature variations. In this paper, dynamic time warping is used to realign signal responses that have been distorted by temperature. Baseline subtraction between the realigned signal and the baseline can then be used to detect and identify damage responses. We demonstrate dynamic time warping with guided wave measurements taken from an aluminum plate that is heated in cycles from roughly 75°F to 125°F. Dynamic time warping achieves a correlation between the chosen baseline and the pre-damage measurements greater than 90%. Applying no temperature compensation or more traditional methods, such as optimal signal stretch, demonstrate correlations of 0% and 30%, respectively. This shows that dynamic time warping removes temperature effects more accurately than other current approaches.

Versatile Control of Unidirectional AC–DC Boost Converters for Power Quality Mitigation

This paper introduces a versatile control scheme for unidirectional ac–dc boost converters for the purpose of mitigating grid power quality. Since most power factor correction circuits available in the commercial market utilize unidirectional ac–dc boost converter topologies, this is an almost no-cost solution for compensating harmonic current and reactive power in residential applications. Harmonic current and reactive power compensation methods in the unidirectional ac–dc boost converter are investigated. The additional focus of this paper is to quantify the input current distortions by the unidirectional ac–dc boost converter used for supplying not only active power to the load but also reactive power. Due to input current distortions, the amount of reactive power injected from an individual converter to the grid should be restricted. Experimental results are presented to validate the effectiveness of the proposed control method.

Radial force dynamic current compensation method of single winding bearingless flywheel motor

The position of rotor and stator in switched reluctance motor is exchanged to obtain the single winding bearingless flywheel motor (SWBFM), which is more useful for flywheel energy storage with outer rotor. Compared with the switched reluctance motor, bearingless flywheel motor has obvious advantages in cost savings and consumption reducing. The radial force and torque are produced by single windings and the outer rotor could directly drive the flywheel with less mechanical transmission. In this study, a mathematical model of SWBFM is established based on Maxwell tensor method, in addition, the correction factor is present to obtain an accurate mathematical model based on finite element. In energy storage keeping state, the flywheel energy storage system could run on rated speed without the power input. Considering the relationship between the angle and the radial force coefficient, and the difference of radial force coefficient with each tooth pole, radial force dynamic current compensation methods of without β direction constraint and β direction constraint are present to ensure the SWBFM stable suspension under the condition of winding open-circuit fault. The results show that the proposed compensation methods are feasible and have high precision.

Significantly enhanced ferroelectricity and magnetic properties in (Sr0.5Ca0.5)TiO3-modified BiFeO3 ceramics

BiFeO3 multiferroic ceramics were modified by introducing (Sr0.5Ca0.5)TiO3 to form solid solutions. The single phase structure was easy to be obtained in Bi1−x(Sr0.5Ca0.5)xFe1−xTixO3 (x = 0.2, 0.25, 0.3, and 0.4) solid solutions. Rietveld refinement of X-ray diffraction data revealed a transition from rhombohedral R3c (x = 0.2, 0.25, and 0.3) to orthorhombic Pnma (x = 0.4). Current density-field (J-E) characteristics indicated that the leakage current density was reduced by three orders of magnitude in Bi1−x(Sr0.5Ca0.5)xFe1−xTixO3 ceramics. Both the ferroelectricity and magnetic properties were significantly enhanced in the present solid solutions. P-E hysteresis loop measurements with dynamic leakage current compensation methods showed the significantly enhanced ferroelectric properties for x = 0.25 and 0.3 and the paraelectric behavior for x = 0.4. The best ferromagnetic characteristics were achieved in the composition of x = 0.25, where the saturated M-H loop was determined with Mr = 34.8 emu/mol. The improvement of ferroelectricity was mainly due to the suppressed leakage current, and the enhanced magnetism originated from the partial substitution of Fe3+ by Ti4+, which destroyed its previous spiral structure to allow the appearance of a macroscopic magnetization.

Unifying the Theory of Mutual Coupling Compensation in Antenna Arrays

i»?The limitations of current mutual coupling compensation methods in antenna arrays are thoroughly reviewed. The theory of mutual coupling compensation is unified in such a way that efficient methods can be employed for calibrating both transmit and receive systems having arbitrary geometries. The theory leads to methods that can evaluate mutual coupling using either theoretical or experimental means. Reciprocity is studied through the careful comparison of receive and transmit analytical formulations. Examples involving various applications are presented for the validation of the theory. This theory has numerous applications and contributes to the areas of antenna theory, mutual coupling analysis, complex structure modeling, and antenna measurements.

Impacts on the utilization degree of canal water caused by agricultural water reallocation: a case study from China

Our study area in the People's Victory Canal Irrigation District (PVCID), which is downstream of the Yellow River in China, has been undergoing agricultural water transfer to the city for municipal uses. Water supply condition data from PVCID are used to analyze the impacts of water reallocation on agricultural water supply quality, and field survey data in PVCID are used to examine the impacts of agricultural water supply quality on the utilization degree of canal water. Several issues on the current compensation methods are also discussed. Results show that the amount of irrigation water and the number of days for irrigation are affected by water reallocation, especially when the amount of water diversion significantly decreases. Regression results show that timeliness and adequacy of canal water are important factors affecting the utilization degree of canal water. Several factors reveal significant association with the utilization degree of canal water, such as the water price of canal water, water fee charge methods, soil texture of the largest cropland, precipitation, and age of farm household head. Current compensation methods can hardly compensate for the decrease in canal water reliability. Some recommendations are put forward to compensate for the adverse effects of agricultural water transfer.

A new framework for robust speech recognition in complex channel environments

Channel distortion is one of the major factors which degrade the performances of automatic speech recognition (ASR) systems. Current compensation methods are generally based on the assumption that the channel distortion is a constant or slowly varying bias in an utterance or globally. However, this assumption is not sustained in a more complex circumstance, when the speech records being recognized are from many different unknown channels and have parts of the spectrum completely removed (e.g. band-limited speech). On the one hand, different channels may cause different distortions; on the other, the distortion caused by a given channel varies over the speech frames when parts of the speech spectrum are removed completely. As a result, the performance of the current methods is limited in complex environments. To solve this problem, we propose a unified framework in which the channel distortion is first divided into two subproblems, namely, spectrum missing and magnitude changing. Next, the two types of distortions are compensated with different techniques in two steps. In the first step, the speech bandwidth is detected for each utterance and the acoustic models are synthesized with clean models to compensate for spectrum missing. In the second step, the constant term of the distortion is estimated via the expectation-maximization (EM) algorithm and subtracted from the means of the synthesized model to further compensate for magnitude changing. Several databases are chosen to evaluate the proposed framework. The speech in these databases is recorded in different channels, including various microphones and band-limited channels. Moreover, to simulate more types of spectrum missing, various low-pass and band-pass filters are used to process the speech from the chosen databases. Although these databases and their filtered versions make the channel conditions more challenging for recognition, experimental results show that the proposed framework can substantially improve the performance of ASR systems in complex channel environments.

Gaussian Specific Compensation for Channel Distortion in Speech Recognition

Channel distortion is one of the major factors degrading the performance of automatic speech recognition (ASR) systems. Most of the current compensation methods rely on the assumption that the channel distortion remains unchanged within an utterance or globally. However, we show in this letter that the distortion varies over speech frames even if the channel response is unchanged. To address this problem, we relax the above-mentioned assumption and propose a new method to compensate the channel distortion for each Gaussian of the acoustic models. Firstly, we derive the relationship between the clean and distorted models, and then estimate the channel magnitude response with the expectation-maximization (EM) algorithm. Finally, we obtain the matched models with the estimated magnitude response and the clean models. Experiments were conducted on the TIMIT/NTIMIT databases and the results confirmed the effectiveness of the proposed method.

Information Cost, Broker Compensation, And Collusion In Insurance Markets

We examine the impact of intermediation on insurance market transparency and performance. in a differentiated insurance market under imperfect information, consumers can gain information about product suitability by consulting an intermediary. We analyze current broker compensation methods: commissions and fees. although insurers’ equilibrium profits are equivalent under both systems, social welfare is always higher under a fee-for-advice system than under a commission system. Both systems offer the opportunity to increase profits via collusion. under a commission system, collusion enables insurers to separate consumers into groups purchasing different contracts. insurers may then extract additional rents from some consumers. this advantage can explain why brokers tend to be compensated by insurers.

Evaluating passively shielded gradient coil configurations for optimal eddy current compensation

In magnetic resonance imaging, rapidly switching magnetic fields are used to spatially encode the signal. The temporal change of these fields induces eddy currents in nearby conducting structures of the scanner. These eddy currents, in turn, generate a secondary magnetic field that opposes and distorts the desired gradient field. Eddy current compensation methods are generally applied assuming that the primary and secondary magnetic field gradients possess similar spatial characteristics in the imaging volume (field matching). In this work an optimization method is used to deform the shape of the coil support and/or a highly conductive passive shield in order to improve the field matching and reduce the inductive coupling between the gradient coil and the passive shield. Using the residual field after eddy current compensation as the objective function, the coil support and/or conducting surfaces were deformed to obtain passively shielded x- and z-gradient coils with improved field matching and eddy current compensation. Assuming a single frequency, quasi-static simulation, it was demonstrated that the residual field was reduced up to 24 times by reshaping the coil and passive shield surfaces due to the improved field matching. However, using transient analyses we showed that in the case of the passively shielded x-gradient coil the residual field may only be reduced by five times from a cylindrical coil configuration. A bulge shape is created in the conducting surface as a mechanism of matching the field and at the same time reducing the mutual inductive coupling between the coil and the passive shield. An actively shielded coil with control over the magnetic field produced by the induced current was used as a reference coil that produces the minimal residual field. The actively shielded gradient coil produces minimal residual field for short and long pulses in the transient analyses.

A method for improving the resolution of active and passive balancing schemes for disc drives

Some of the current imbalance compensation methods used in hard disk drives are based on using fixed compensating masses that are placed at uniformly spaced angular positions. Several masses of predefined fixed weights are placed at predefined angular positions and algorithms are used to choose the best combination of masses and their locations in order to compensate the imbalance. The main disadvantage of using uniformly distributed locations for the placement of compensating masses is that some of the possible combinations may be overlapping and the distribution of all resulting compensations is not uniform. This reduces the resolution of the balancing algorithms. This article proposes a novel method for finding the optimal angular distribution of locations that are used for the placement of compensating masses. The method finds such a distribution of the locations that there are minimum overlapping combinations and hence almost all possible compensations are utilized. Furthermore, it optimizes the distribution of all possible compensations and thus results in significant improvement in the resolution of balancing algorithms.