Measured Phase Currents Research Articles

Sensorless control of the high-speed switched reluctance generator of the micro power plant

Introduction. In the distributed and autonomous generation systems using renewable energy sources, low-power generating units (not more than 100-200 kW) based on microturbines function. Microturbines operate most efficiently at high rotational speeds. In this regard, the generator running with a microturbine must also be a high-speed one. A generator is a switched reluctance electric machine (EM) that needs information on the rotor position. It is difficult to use a position sensor in such mechanisms at high speeds. This paper discusses the issues of sensorless control of a high-speed switched reluctance electric generator in conjunction with a steam microturbine.Materials and Methods. So, it is required to evaluate the proof-of-principle developed to control a high-speed switched reluctance EM. For this purpose, a mathematical model has been created including models of the investigated EM, an electric power converter, and a control system. For the EM under consideration, the active resistance is determined, as well as the dependence of the phase flux linkage on the current flowing through it and the position of the moving element. The method used involves probing the idle phase of an electric machine with short voltage pulses of equal duration, and measuring the current in this phase. If the voltage pulse length is much shorter than the phase time constant, then the current pulse amplitude is inversely proportional to the inductance. Thus, registering the maximum current pulse amplitude, it is possible to determine the rotor passage through an uncoordinated position for the probed phase. This information is used to form control actions by other phases. Moreover, the length of the test voltage pulses, required to obtain current pulses sufficient for measuring the value, is of significance versus the duration of the pulsing time. Hence, with an increase in the rotational speed, the number of test pulses is insufficient for measuring the position with the accuracy required for the control goals. This reduces drastically the precision of determining the rotor position; therefore, at high speeds, the application of this method is limited without further refinement of the rotor position. In this case, to increase the precision of measurements, it is necessary to evaluate the rate of current rise when applying the basic voltage pulse or the voltage pulse rate forming the phase current before switching to a single-pulse control mode. Research Results. Two conclusions important for correcting the estimation of the rotor position in a single-pulse operation mode of a reluctance EM are proved. The first conclusion is on the efficiency of the proposed technique of filtering phase current measurement data, the second one concerns the applicability of the identified information criteria. The analysis results of the processes in the switched reluctance EM using sensorless control that implements the described principles for determining the rotor position are presented.Discussion and Conclusions. To correct the estimation of the rotor position, the following information criteria can be used: the presence of a pause between the excitation pulse and the start of the generation process; the decrease in current by the time the generation begins. To refine the estimate, the following fact can be used: on the generation interval, the current curve knee corresponding to the maximum phase inductance is observed at the same rotor position.

Measurement of the PMSM Current with a Current Transducer with DSP and FPGA

In the present work, two approaches for the phase current measurement of a permanent magnet synchronous motor (PMSM) were compared. The measured phase current was distorted by glitches, and a software method to eliminate these glitches was necessary. An averaging of samples was carried out, and the experimental results indicated that averaging was essential for further calculations. Moreover, the PMSM operated smoothly, and the difference between the set point and the actual speed was reduced for the full range of loads from the free run up to a full load. The increasing popularity of field-programmable gate array (FPGA) devices has encouraged developments in PMSM controllers using a direct hardware approach and the classic software approach utilizing a digital signal processor unit. In this study, the selected performance of TMS320F2812 and Spartan-3E were compared. This paper proposes an original adaptive correction method for a current transducer.

MTPA Control Strategy Based on Signal Injection for V/f Scalar-Controlled Surface Permanent Magnet Synchronous Machine Drives

In this paper, a new maximum torque per ampere (MTPA) control method for surface permanent magnet synchronous motors (SPMSMs) controlled by the scalar control (v/f) method is proposed. The scalar control is a sensorless method that controls only the magnitude and the frequency of the stator voltage vector without the information of the rotor position. This method suggests the injection of the high frequency voltage signal in the stator current vector reference frame, which can be calculated from the measured phase currents, to avoid the use of rotor position information. In addition, this method adjusts only the magnitude of the stator voltage to minimize the stator current based on the calculated input power. Another merit of this method is the robustness of the MTPA control to machine parameter errors or variations. With this proposed method, the stator current can be minimized in the whole speed-torque range and the drive efficiency can be improved. Simulation and experimental results are provided to verify the performance of this control strategy.

Identification of line status changes using phasor measurements in transient states through deep learning networks

The problem of detecting changes in a topology of an electrical network in real time is solved. This paper proposes a line state detection method based on a convolutional neural network (CNN) classifier using phasor measurements of bus voltages and currents in transient states.

A Rotating Restart Method for Scalar (v/f) Controlled Synchronous Reluctance Machine Drives Using a Single DC-Link Current Sensor

This paper presents a rotating restart method for $v/f$ scalar controlled Synchronous Reluctance Machines (SynRMs) using a single DC -link current sensor. In such a case, the initial rotor position and speed are required to restart the machine due to the absence of a position sensor. The method proposes to inject three active voltage vectors in the stationary reference frame to induce the phase currents required for estimating the rotor position and speed. In addition, the phase current reconstruction method is proposed to reduce the distortion of the measured phase currents caused by adopting a single DC -link current sensor and to consequently enhance the rotor position estimation accuracy. With the proposed method, the appropriate voltage vector can be applied to the machine, thus minimizing the inrush current during the restart. Furthermore, the proposed method only requires the machine parameters on the nameplate, and it does not require any additional machine-specific tuning processes. This paper proposes a simple restart method suitable for scalar-controlled SynRM drives with a single DC -link current sensor. The effectiveness of the proposed restart scheme is validated through the simulation and experimental results.

GPS spoofing detection for the power grid network using a multireceiver hierarchical framework architecture

In the future, the modernized power grid, or smart grid, will utilize devices called phasor measurement units (PMUs) to continuously monitor the power grid state in real time. These devices utilize GPS to synchronize the voltage and current phasor measurements across the continental network; however, because the civilian GPS signals are unencrypted, PMUs are susceptible to GPS spoofing attacks. We propose a spoofing detection algorithm using a wide-area, hierarchical architecture. In the network, each PMU transmits conditioned signal fragments containing the military P(Y) signal, which serves as an encrypted signature in the background of all authentic GPS signals. This signature is then verified among a subnetwork consisting of a select number of well-dispersed receivers. We subsequently compare representative signals generated for each subnetwork in order to detect coordinated attacks against the subnetwork receiver collection. Using real-world data recorded during a government-sponsored, live-sky spoofing event, we demonstrate that our algorithm successfully evaluates the authenticity of a widely dispersed receiver network.

Fault-Tolerant Control of Primary Permanent-Magnet Linear Motors With Single Phase Current Sensor for Subway Applications

Because both magnets and windings can be mounted in the mover, the primary permanent-magnet linear motor (PPMLM) has a low-cost advantage for subway applications. In this paper, a fault-tolerant control (FTC) with single phase current sensor is proposed for PPMLM traction system in subway applications. In the proposed FTC, d - and q -axis currents are estimated from the reference synchronous currents and the surviving measured phase current. The estimation is robust since no machine parameters are required. In steady-state operation, the estimated current errors are half the actual ones. As a result, the current response is slowed but the current command can be achieved. However, the achievement of control target depends on the current tracking accuracy, which is enhanced by the voltage decoupler. Compared with existed FTC schemes, the proposed one is robust and has better transient-state performances. The effectiveness of the proposed FTC is verified by theoretical analysis and experimental results.

Residual current-based method for open phase detection in radial and multi-source power systems

Open phase conditions typically result in very low fault currents which makes their detection using the existing conventional protective relaying schemes very difficult. This paper proposes a new current-only Open Phase Detection (OPD) scheme suitable for effectively grounded distribution networks. The proposed OPD approach is based on the prevailing current imbalance in the network. Reference phase currents are calculated (predicted) online using Residual Current Multiplying Factors (RCMFs), and are afterwards compared with the measured phase currents. A mismatch between the predicted reference phase currents and the measured phase currents is used as an indication of an open conductor event.Extensive studies were performed using a distribution network modelled in RSCAD software. The performance of the proposed protection scheme was validated using the Real-Time Digital Simulator (RTDS) for various open phase events and non-open phase conditions. The experimental results obtained validate the effectiveness of the proposed OPD scheme.

PMU based line outage identification using comparison of current phasor measurement technique

In this paper, a novel algorithm for identification of multiple line outage based on comparison of current phasor measurement (CCPM) technique is presented. A least square norm minimization model has been developed considering bad data due to faulty phasor measurement unit (PMU). In this proposed algorithm, the line current phasors obtained from load flow simulation for several outage cases are stored. On occurrence of actual outage, PMU provided current phasors are compared with the stored simulated current phasors using least square norm minimization approach. Moreover, random Gaussian noise with zero mean and standard deviation from 1% to 5% is introduced in the proposed model to check the feasibility in real power network. The performance of the proposed algorithm is evaluated by introducing two novel indices i.e., estimation accuracy including critical cases (EAICC) and estimation accuracy excluding critical cases (EAECC). Moreover, another new performance index i.e., success rate with repeated trial (SRWRT) is proposed to verify the noise independency of the test results with repeated number of trials. Performance of the algorithm is tested on IEEE 5-bus, 14-bus, 30-bus, 57-bus, and 118-bus systems. Numerical results show the reliability and viability of the proposed methodology for identification of multiple line outages.

Uncertainty Bounds of Transmission Line Parameters Estimated From Synchronized Measurements

The parameters of the transmission lines are used in several monitoring and control tools of the power system control center. An accurate knowledge of the power system model (including transmission lines impedances) impacts positively the situational awareness of the power system operators. It also improves the protection and corrective measures that may be applied in case of a disturbance. Nevertheless, line parameters that are stored in the control center database are typically subjected to errors, and therefore it is necessary to regularly refine them. The presence of a phasor measurement unit (PMU) at both ends of the transmission line allows the calculation of the transmission line parameters using synchronized current and voltage phasor measurements. Although the use of PMU measurements is a straightforward way to calculate the transmission line parameters, the uncertainty of the synchronized phasor measurements should be incorporated to the calculated transmission line parameter values. In this paper, an analytical expression for the bounds of the calculated transmission line parameters from PMU measurements is derived, considering both instrument transformers and PMU errors. The calculated bounds of uncertainty are evaluated through Monte Carlo simulations, while the importance of knowing the bounds of the calculated line parameters is underlined through the derivation of power–voltage curves considering the lower and upper bounds of the parameters. The simulation results are obtained using the IEEE 14-bus system.

Application of artificial neural networks for transistor open‐circuit fault diagnosis in three‐phase rectifiers

This study deals with the transistor open-circuit fault diagnosis technique based on the grid current processing. In accordance with the proposed method, in the first stage, the defect of the power electronics converter is recognised. For this purpose, the zero current periods are registered in each converter phase circuits. The faulty transistors are identified calculating the average values of differences between predicted and measured phase currents. The novelty of the presented technique is an application of a neural network for the grid current prediction in the active rectifier. In fact, the transistor open-circuit faults do not affect the predicted grid currents immediately as soon as the transistor defects happen. Therefore, the differences between the predicted currents and the measured ones increase which are used for the faulty transistors identification. In the comparison to the switch open-circuit fault diagnostic techniques, which are known from the scientific literature survey, the method presented in this study is insensitive to load changes no matter a direction of the energy flow in the power conversion system.

Minimal Current Sensing Strategy for Switched Reluctance Machine Control With Enhanced Fault-Detection Capability

This paper focuses on a minimal current sensing strategy and fault detection of switched reluctance machines (SRMs). In order to reduce the number of required current sensors in multiphase motor drives, the optimal selection and location of current sensors is presented in consideration of the precise actual phase current measurement, open- and short-circuit fault detection. The proposed scheme requires two current sensors to replace the phase current sensors placed in each phase without any additional devices for multiphase SRMs to achieve a more compact and low-cost drive. Different current regulation methods are employed for single phase conducting region and commutation region. To obtain the phase currents from the proposed approach, different settings of the pulsewidth modulation signals for adjacent phases during the commutation region are implemented. The simulation and experiments on a four-phase 8/6 pole SRM are carried out to verify the effectiveness of this approach in the healthy and faulty cases.

A Simplified Indirect Technique for the Measurement of Mechanical Power in Three-Phase Asynchronous Motors

Abstract This paper presents an indirect method for measuring the mechanical power produced by three-phase induction motors. The proposed technique is based on the hypothesis that three-phase induction motors are balanced systems that transform electrical power into mechanical one. The measurement of a single phase current is used to estimate the mechanical power generated at the axis. The relationship between electric current and mechanical power is generally non-linear. By expressing the quantities in p.u., this trend is approximated with a second order polynomial. From the analysis of the mechanical power characteristics related to 13 motors we obtained the parameters of the interpolating parabolic curves of motors from 1.1 kW to 75 kW rated power. The proposed technique can be easily adopted in order to monitor the mechanical power of three phase induction motors using only one phase current transducer. Starting from the motor nameplate no experimental measurement or other data are necessary to estimate the mechanical power. This technique can be widely used in low cost multipoint measurement system able to monitor the mechanical power where no other transducer or voltage divider are necessary.

Three-Level NPC Inverter Incipient Fault Detection and Classification using Output Current Statistical Analysis

This paper deals with open switch Fault Detection and Diagnosis (FDD) in three-level Neutral Point Clamped (NPC) inverter for electrical drives. The approach is based on the already available phase current time series measurements for different operating conditions (motor speed, load, and environment noise). Both fault detection and classification are studied and the efficiency performances of the proposed selected features are shown. For the fault detection, we focus on the first four statistical moments and the extracted features and then the Cumulative Sum (CUSUM) algorithm as the feature analysis technique to improve the performances. For the classification study, we propose to couple the knowledge on the faulty system brought by the statistical moments and the Kullback-Leibler divergence particularly suitable for the detection of incipient changes. The Principal Component Analysis (PCA) is then used to perform the classification. A 2D framework is obtained, which allows the faults to be classified efficiently within the considered operating conditions for all the selected fault durations.

Line Impedance Estimation Based on Synchrophasor Measurements for Power Distribution Systems

Effective monitoring and management applications on modern distribution networks (DNs) require a sound network model and the knowledge of line parameters. Network line impedances are used, among other things, for state estimation and protection relay setting. Phasor measurement units (PMUs) give synchronized voltage and current phasor measurements, referred to a common time reference (coordinated universal time). All synchrophasor measurements can thus be temporally aligned and coordinated across the network. This feature, along with high accuracy and reporting rates, could make PMUs useful for the evaluation of network parameters. However, instrument transformer behavior strongly affects the parameter estimation accuracy. In this paper, a new PMU-based iterative line parameter estimation algorithm for DNs, which includes in the estimation model systematic measurement errors, is presented. This method exploits the simultaneous measurements given by PMUs on different nodes and branches of the network. A complete analysis of uncertainty sources is also performed, allowing the evaluation of estimation uncertainty. Issues related to operating conditions, topology, and measurement uncertainty are thoroughly discussed and referenced to a realistic model of a DN to show how a full network estimator is possible.

A Robust Method for Induction Motor Magnetizing Curve Identification at Standstill

Modern electric drives use a self-commissioning procedure to precisely identify motor parameters for achieving high-performance control. Typically, the induction motor magnetizing curve is identified using no-load rotational test. However, some applications necessitate the electric drive to identify the magnetizing curve at standstill conditions. As one of the well-known standstill approaches, the traditional flux integration exhibits several practical problems. Any imperfection in measured current, estimated stator resistance, and dead-time compensation directly affects the accuracy of the estimated magnetizing curve because of error accumulation in open-loop integration. This paper proposes a robust yet simple solution against those practical concerns. It can identify the magnetizing curve without using any dead-time compensation and stator resistance. Only industry-standard dc-link voltage and phase current measurements are used. Its superior features are experimentally verified on a number of motors and the results are confirmed by no-load rotational test results. Its robustness against current offset and extra longer integration duration is also proved.

Short switch fault diagnosis method for power converter using a model‐based approach in switched reluctance motor drives

Switched reluctance motor (SRM) is a competitive solution for aircraft and automotive applications due to its fault-tolerant capabilities and robust configuration. Power converter is a key component in SRM drives, but it prone to faults. In this study, a new and fast diagnosis method for short-circuit fault of the SRM converter is proposed based on the mixed logical dynamic (MLD) model and residual generation. Effects of short-circuit fault on SRM drives are analysed in detail. The MLD model of an asymmetrical half-bridge converter of SRM drives is presented to evaluate the currents of the power converter. The short-circuit faulty switch is identified by analysing the system residual, achieved by comparing the outputs of the MLD model and the sensor measurements. In contrast to other methods, the presented method requires no additional hardware but only measured phase currents and command signals, which are available in the control system. Simulation results confirm the effectiveness of the proposed diagnosis method. It is shown that such diagnosis method can identify the faulty switch of the power converter in a few milliseconds, which is important to avoid catastrophic consequences. It is fast, reliable and easy for industrial applications due the low-computational requirement.

IGBT Junction Temperature Estimation via Gate Voltage Plateau Sensing

A method for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> high-bandwidth junction temperature estimation of insulated-gate bipolar transistors is introduced in this paper. The method is based on the acquisition of the gate voltage plateau during turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> . It can be related to the junction temperature at any known device current, that can be effectively approximated using existing phase current measurements. This allows fast overtemperature protection of the power device or even active thermal cycle reduction via thermal control. This paper discusses, first, the physical mechanisms leading to the temperature sensitivity of the gate voltage plateau. Second, a rigorous sensitivity analysis of the gate voltage plateau is conducted. It allows to determine the maximal estimation error and provides information about the suitability of this method for various devices and applications. Finally, a sensing circuitry is presented, which allows accurate gate voltage plateau sensing every switching period as well as an easy integration into the gate driver. The performance of the proposed method is experimentally demonstrated with the sensing circuitry on a double pulse test bench over a wide operation range.

Electromagnetic Field Characteristic Analysis and Comparison of Slotless Permanent Magnet Synchronous Generators with Grid Connection

This paper deals with the characteristic analysis of permanent magnet (PM) wind power generators according to stator winding topology to compare the machine performance, and the experimentally measured current with grid connection is employed for the investigation. The analysis models dealt with in this study have the slotless structure in their stator core to eliminate the cogging torque with the identical PM rotor, and three coil winding types according to coil pitch and winding types are addressed for their comparison. One of the analysis models is manufactured to be integrated with a grid-connected power converter, and the measured phase current of the generator is applied to investigate their flux density, resulting radial force and power loss characteristics of each analysis model. For the reasonable comparison, the generators have very similar equivalent circuit parameters, such as induced voltage and resistance, so the load voltage and current characteristics are almost identical. From the results dealt with in this study, one of the analysis models is proposed to be applied for the small-scale wind power generation systems.

Demodulation Approach for Slowly Sampled Sensorless Field-Oriented Control Systems Enabling Multiple-Frequency Injections

This paper describes a demodulation approach based on the least squares method for a saliency-based position estimation in slowly sampled field-oriented control systems. The proposed approach focuses on the sensorless control of electrical drives in which the sample rate of the control task chosen is slower than both the maximum possible update rate of the phase voltages and the maximum possible sample rate of the phase current measurement by a multiple. Under those conditions, it is possible to inject multiple-frequency carrier signals between two successive control sampling instances without affecting the control. Furthermore, a combined demodulation of these signals is enabled by exploiting the constant manipulated variables of the field-oriented control system during the injection sequence. With the proposed method, the signal-to-noise-ratio of the calculated rotor position as well as the acoustic noise produced by signal injections can be optimized. The approach is implemented in a field-oriented control for permanent magnet synchronous machines and is verified in experiments.