A control strategy to compensate for current and voltage measurement errors in three-phase PWM rectifiers

In this paper an approach towards databased fault diagnosis of linear electromagnetic actuators is presented. Time and time-frequency-domain methods were applied to extract fault related features from current and voltage measurements. The resulting features were transformed to enhance class separability using either Principal Component Analysis (PCA) or Optimal Transformation. Feature selection and dimensionality reduction was performed employing a modified Fisher-ratio. Fault detection was carried out using a Support-Vector-Machine classifier trained with randomly selected data subsets. Results showed, that not only the used feature sets (time-domain/time-frequency-domain) are crucial for fault detection and classification, but also feature pre-processing. PCA transformed time-domain features allow fault detection and classification without misclassification, relying on current and voltage measurements making two sensors necessary to generate the data. Optimal transformed time-frequency-domain features allow a misclassification free result as well, but as they are calculated from current measurements only, a dedicated voltage sensor is not necessary. Using those features is a promising alternative even for detecting purely supply voltage related faults.

The servo system of a surface permanent magnet synchronous motor is operated by current sensors to control the motor torque. However, a current sensor has often offset and gain deviation caused by age-related deterioration and thermal variation. These errors lead to d - q axis current ripple and torque ripple, degrading the performance of the servo system. In order to overcome these problems, a new estimation and compensation method for current measurement errors by using a current simulator is proposed. The method aims to decrease torque ripple caused by both offset and gain deviation during current measurement. Experimental results confirm that the proposed method satisfactorily suppresses current ripple and torque ripple caused by current measurement error.

This paper deals with the online parameter estimation of squirrel-cage induction machines using the Gradient Descent Method and coupled stator and rotor flux observers. Stator resistance, rotor resistance and mutual inductance can be estimated simultaneously in real time. For a non-ambiguous parameter tracking, an additional voltage is superimposed. The influence of inverter nonlinearity, current and speed measurement errors is investigated. The presented approach is applicable to a standard industrial drive, including current measurement and motor speed feedback. The concept is verified by experimental tests for open loop V/f control as well as for field-oriented control.

The operation of the smart grid is anticipated to rely profoundly on distributed microprocessor-based control. Therefore, interoperability standards are needed to address the heterogeneous nature of the smart grid data. Since the IEC 61850 emerged as a wide-spread interoperability standard widely accepted by the industry, the Sampled Measured Values method has been used to communicate digitized voltage and current measurements. Realizing that current and voltage measurements (i.e., feedback measurements) are necessary for reliable and secure noperation of the power grid, firstly, this manuscript provides a detailed analysis of the Sampled Measured Values protocol emphasizing its advantages, then, it identifies vulnerabilities in this protocol and explains the cyber threats associated to these vulnerabilities. Secondly, current efforts to mitigate these vulnerabilities are outlined and the feasibility of using neural network forecasters to detect spoofed sampled values is investigated. It was shown that although such forecasters have high spoofed data detection accuracy, they are prone to the accumulation of forecasting error. Accordingly, this paper also proposes an algorithm to detect the accumulation of the forecasting error based on lightweight statistical indicators. The effectiveness of the proposed methods is experimentally verified in a laboratory-scale smart grid testbed.

AC servo motors are operated by current sensors. However, these current sensors often exhibit offsets caused by age-related deterioration and thermal variation. Gain deviation also causes current measurement errors. These errors lead to torque ripples and dq-axis current ripples. This paper proposes a new method of estimating and compensating for gain deviation in current measurement using a current simulator. The method uses dq-axis current ripples arising from sensed current and estimated current. Thus, it can be applied in conjunction with a proposed offset estimation method. In this paper, the methods are tested on a surface-mounted permanent magnet synchronous motor, in which the current sensors are arranged in u-phase and w-phase. Simulation and experimental results confirm that the proposed methods suppress current and torque ripples caused by offset and gain deviation in current sensors.

Due to the unbalanced three-phase currents and the torque ripples and speed fluctuations to the drive caused by the current sampling errors of three-phase current sensors and corresponding signal processing circuits, the estimation on current sampling errors is of great importance to eliminate these adverse effects. The observer-based methods, however, present two defects: first, they could increase the computational burden to the drives, thus limiting their practical applications; second, their high dependence on the system speed or position feedback information might degrade the estimation accuracy. To solve these problems, this article proposed a fixed-point sampling method of lower branch flows and three phase-currents, which adopts the relations between the measured currents, rather than any complex algorithm, to estimate the current sampling errors. To coordinate with the proposed strategy, a fixed-point sampling scheme was accordingly rolled out. Compared with the observer-based methods, as a fixed-point one, much applicable to actual digital controllers, it could reduce the computational burden of the drive. Meanwhile, its effectiveness was verified by experimental results on a 1.5-kW IPMSM prototype, which showed accurate estimated current sampling errors and the effectively eliminated torque ripples and speed fluctuations.

The extension of onshore high-frequency surface wave radar (HFSWR) to shipborne HFSWR has the advantage of extended monitoring area and high application flexibility. However, additional modulation on the echo signal introduced by the forward movement and six-degree-of-freedom (6-DOF) ship motion may increase the surface current measurement error. Considering the radar array position on the ship, six-DOF ship motion, forward movement velocity, first-order Bragg scatter, and background noise, this paper models the backscattered Doppler spectrum of shipborne HFSWR. Based on this model, the performance of surface radial current measurement is analyzed, with the adoption of the MUltiple SIgnal Classification (MUSIC) to estimate the azimuth of the sea patches. Simulation results show that, rotation, sway and forward movement of the ship all have significant impacts on the surface radial current measure error. Nevertheless, if the ship sails at relative low speed and keeps its sailing direction (with small yaw amplitude), shipborne HFSWR may provide a better result than onshore HFSWR.

The errors generated from the current-measurement path are inevitable, and they can be divided into two categories: offset errors and scaling errors. Current data including these errors cause the periodic rotor speed ripples, which are one and two times the fundamental stator current frequency. Since these undesirable ripples can harm the motor drive system, a compensation algorithm must be included in the motor control drive. In this paper, a new compensation algorithm is proposed. The principal feature of the proposed algorithm is the use of the integrator output signal of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$d$</tex> -axis proportional plus integral (PI) current regulator. This output signal is nearly zero or constant because the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$d$</tex> -axis current command is zero or constant, so that the maximum torque or unity power factor can be acquired in the ac drive system. If the stator currents include offset and scaling errors, the integrator output signal of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$d$</tex> -axis PI current regulator ripples in the rotor speed of the same frequency. The proposed compensating algorithm for the current-measurement errors can be easily implemented by subtracting the dc offset value or rescaling the input measurement gain of the stator currents. Therefore, the proposed algorithm has several advantages: it is robust with regard to the variation of the motor parameters; it is applicable to steady and transient states; it is easy to implement; and it requires less computation time. The MATLAB simulation and the experimental results verify the usefulness of the proposed current compensating algorithm.

This paper is concerned with the current ripples which originate from the current measurement errors of a doubly-fed induction generator (DFIG). In this paper, a new compensation algorithm of the current measurement errors is proposed. The main concept of the proposed algorithm is implemented by integrating 3-phase rotor currents in the stationary reference frame to compensate the measured current ripples in DFIG (Doubly Fed Induction Generator). This algorithm has several features: easy implementation, less computation time, and robustness with regard to the variation of the electrical parameters. The experiment results show the effectiveness of the proposed algorithm.

While hysteresis current control offers the benefits of a fast dynamic response and inherent overcurrent protection, its variable switching frequency and inherent two-level switching response make it unsuitable for many applications. This paper presents a new approach for three-level hysteresis control of a single phase grid-connected inverter that overcomes these limitations. The strategy adjusts the hysteresis band magnitude in response to variations in the inverter average output voltage, to achieve constant switching frequency using only one hysteresis comparator and without requiring DC offset compensation or current error zero-crossing measurement. The inverter average voltage is also used to estimate the phase of the incoming grid voltage, to create a current reference for the regulator at any required power factor. The result is a robust sensorless hysteresis current regulator suitable for three-level grid connected applications that operates with a constant switching frequency.

Experimental corroboration of a variety of distinct measurement techniques for determining the voltage and current constituents at a vacuum diode termination of a high power (500 GW) vacuum transmission line operating in a self-magnetic-insulation regime is presented. The inherent difficulties of measuring driver and load parameters with electric field strengths in excess of 106 V/cm and vacuum electron flows comparable with the cathode conduction current have in the past been addressed by single nonverified measurement methods. In this work we perform multiple measurements and find agreement between B-dot and self-integrating Rogowski coil current diagnostics and consistency among the following voltage measurements: an equilibrium flow model calculation based on current flows, a time-resolved Thomson parabola, a resistive voltage monitor, a time-integrating Thomson parabola, and a Rutherford scattering time-of-flight system.

Phasor Measurement Units (PMUs) are becoming widespread in power systems monitoring. Applications relying on synchrophasor measurements ask for models of measurement er-rors that can be integrated to describe the uncertainty of the data. In this paper, an assessment of PMU magnitude and phase-angle errors for current measurements is performed for the first time with the aim to address error distributions. In particular, two commercial PMUs are statistically characterized in a controlled environment to prevent non-stationarity issues. It is proven that Gaussianity appears a valid assumption for magnitude errors of both PMUs, whereas phase-angle errors might be non-Gaussian in an accurate PMU when the contribution of synchronization mechanisms prevails.

This paper is a survey of methods of high-impulse current and voltage measurement. Typically, such measurement techniques must now include capabilities for measuring high-energy impulses having peak powers as high as many megawatts, currents as high as many mega-amperes, or voltages as high as several megavolts, with rise times as short as a fraction of a microsecond (even as short as the subnanosecond range for moderately high-energy impulses). These capabilities had to be attained in recent years to meet the needs of various areas of scientific research employing such high-energy impulses. This represents a significant extension in the state of the art of such measurement techniques beyond their more traditional role in development and testing of high-voltage bulk power system equipment. The three most commonly used methods of high-impulse current measurement are the magnetic probe, current transformer, and "pure" resistive shunt methods. These methods are treated in considerable detail. High-voltage capacitive dividers, resistive dividers, and reflection-type attenuators are covered as the principal methods of high-impulse voltage measurement, with some added discussion of the means of insulating such devices. A brief description is given of schemes involving use of laser light sources to measure high-impulse currents and voltages by means of magnetooptic and electrooptic effects. Diagnosis of the complete properties of high-power pulses is also discussed. The emphasis throughout the paper is on a review directed toward practical measurement considerations and techniques.

This paper presents a topological method for observability analysis of PMU-only systems, using recursive combination of measurement islands, in order to improve the performance of EMS, especially state estimation. Considering potential loss of PMU current measurement, voltage and current measurements are considered separately. First, measurement islands are formed by current phasor measurements. Then, a combination principle for measurement islands are proposed based on equation solvability, and four practical rules for island merging are deduced from it to find the final observable part of the network. The proposed method fully considers the particularity of PMU and the presence of zero injection buses. The creativity of topological rules and little numerical process make the proposed algorithm more competitive in computing time when network is lager. An 17-bus system is studied to illustrate the validity of the proposed method.

Currently, in electrical energy sector, due to the population growth and the increasing energy consumption demand, the electrical grid is becoming more and more complex. This creates new challenges in term of electrical energy management. Our contribution in this area, presented in this paper, consists of the design, implementation and test of a wireless monitoring and control system for household electrical appliances. This system offers to the residential customers a helpful tool to monitor and control the energy consumption of their household appliances. The developed system is composed by a set of components connected to each other using wireless network technologies: the monitoring devices, the gateway and the client devices (with the respective user interface). For the development of this system, we opted to use a hybrid wireless network solution based on Wi-Fi and Bluetooth Low Energy (BLE). We describe the design and the implementation of the monitoring device hardware, as well as the calculation methodologies to obtain the electrical quantities and to reduce as much as possible the measurement errors. This paper describes also the development of the BLE/Wi-Fi gateway and the Graphical User Interface (GUI). The performance of the developed monitoring device was evaluated by means of experimental tests, where we achieved a voltage measurement error below 0.2% and a current measurement error below 0.5%.