Current Injection Method Research Articles

Investigation of Torque Production and Torque Ripple Reduction for Six-Stator/Seven-Rotor-Pole Variable Flux Reluctance Machines

This paper investigates the torque production and the torque ripple reduction of a six-stator/seven-rotor-pole (6/7) variable flux reluctance machine (VFRM). As a main advantage, the 6/7 VFRM produces higher torque density, but less torque ripple compared with the 6/4 VFRM. The instantaneous torque equation of the 6/7 VFRM is derived by considering the spectra of the winding inductance and current. Based on the derived equation, the average torque is found to be mainly produced by the mutual inductance between the field and armature windings. The even-order harmonics of self-inductance and odd-order harmonics in mutual inductance between the field and armature windings are eliminated due to the opposite polarity connection of the armature coils in each phase. This results in the elimination of the third harmonic torque ripple, while a multiple of the sixth harmonic torque ripple exists. In order to mitigate the sixth harmonic torque ripple, the harmonic current injection method is implemented into the field winding. The field harmonic current is calculated from the analytical torque ripple equation. The performance of the proposed methods is verified by both finite element analysis (FEA) and experiment.

Analysis of unbalanced clustered voltage and control strategy of clustered voltage balancing for cascaded H-bridge STATCOM

To explore the clustered voltage balancing mechanism of the cascaded H-bridge static synchronous compensator (STATCOM), this paper analyzes the causes of unbalanced clustered voltage. The negative-sequence current caused by the compensation of unbalanced reactive power or detection and control errors and the zero-sequence voltage caused by voltage drift of the STATCOM neutral point contribute to unbalanced clustered voltage. On this basis, this paper proposes a control strategy to inject negative-sequence current and zero-sequence voltage simultaneously. The injection of negative-sequence current may cause current asymmetry in the grid, and the zero-sequence injection has a relatively limited balancing ability in the clustered voltages. The proposed control strategy can not only generate a faster balancing response than the traditional zero-sequence voltage injection method, but also lower the extent of current asymmetry compared with the traditional negative-sequence current injection method. Then, the negative-sequence current and zero-sequence voltage injection are further transformed into the dq frame to establish a unified frame. The effectiveness of the proposed control strategy is verified by the simulation and experimental results.

Compatibility Issues with Irregular Current Injection Islanding Detection Methods and a Solution

Islanding detection methods, based on injecting high-/low-frequency currents or negative sequence fundamental frequency currents and observing the resultant responses, are collectively referred to as irregular current injection methods in this paper. In multi-distributed generation (DG) operation, if there is no restriction to the phase of injected irregular currents, the currents at the same frequency may cancel each other out, and then their convergent current may be too small to cause a detectable response, for which reason islanding detection will be severely affected. Accordingly, this paper raises a compatibility issue, which requires the phase difference between any two injected irregular currents to be within a certain interval. In response to this issue, a solution is proposed. According to this solution, the terminal voltage of DG units is referenced to conduct irregular currents injection, and only certain high-frequency currents are used as injected currents. If this solution is adopted by as many manufacturers as possible, the effect and reliability of such methods will be greatly improved.

Native mass spectrometry provides sufficient ion flux for XFEL single-particle imaging.

The SPB/SFX instrument at the European XFEL provides unique conditions for single-particle imaging (SPI) experiments due to its high brilliance, nano-focus and unique pulse structure. Promising initial results provided by the international LCLS (Linac Coherent Light Source) SPI initiative highlight the potential of SPI. Current available injection methods generally have high sample consumption and do not provide any options for pulsing, selection or orientation of particles, which poses a problem for data evaluation. Aerosol-injector-based sample delivery is the current method of choice for SPI experiments, although, to a lesser extent, electrospray and electrospinning are used. Single particles scatter only a limited number of photons providing a single orientation for data evaluation, hence large datasets are required from particles in multiple orientations in order to reconstruct a structure. Here, a feasibility study demonstrates that nano-electrospray ionization, usually employed in biomolecular mass spectrometry, provides enough ion flux for SPI experiments. A novel instrument setup at the SPB/SFX instrument is proposed, which has the benefit of extremely low background while delivering mass over charge and conformation-selected ions for SPI.

Negative-Sequence Second-Order Circulating Current Injection for Hybrid MMC Under Over-Modulation Conditions

Due to the presence of full-bridge submodules (FBSMs), hybrid modular multilevel converters (HMMCs) consisting of FBSMs and half-bridge submodules (HBSMs) can work under the over-modulation conditions, which means that half of the dc voltage is less than the magnitude of the ac voltage. However, because of the different charging and discharging characteristics of FBSMs and HBSMs under over-modulation conditions, capacitor voltages imbalance may occur if the modulation index exceeds a specific limit. To address this issue, this article first investigates the principles of HMMCs and the energy balance mechanism between the two types of submodules. Based on the theoretical analysis, a negative-sequence second-order circulating current injection method is proposed to keep the capacitor voltage balanced under over-modulation conditions. Finally, the proposed method is validated by both simulation and experimental results.

Torque Ripple Suppression for Open-End Winding Permanent-Magnet Synchronous Machine Drives With Predictive Current Control

In order to suppress the torque ripple of an open-end winding permanent-magnet synchronous machine (OEW-PMSM), a q -axis current injection method is typically employed but the disturbances caused by the third flux linkage parameter mismatch can augment the torque ripple. To solve this problem, in this paper, first, a zero-sequence current (ZSC) and zero-sequence back-EMF observer (ZCBO) are proposed based on an adaptive sliding mode control, which is able to simultaneously estimate ZSC and zero-sequence back EMF under varying conditions. Based on this ZCBO, the estimated ZSC and zero-sequence back EMF could compensate for the one-step control delay and suppress the aforementioned disturbances. Second, although central hexagon modulation is employed in the predictive current control (PCC) scheme, zero-sequence voltage (ZSV) still exists in the zero-sequence path due to the dead time of the inverter, affecting the predictive accuracy of the ZCBO. To accurately establish the ZCBO, the ZSV caused by the dead time of the inverter is considered in the ZCBO. Finally, a comparative study of two types of methods is presented, and simulations established by MATLAB software and experimental confirmations are carried out to verify the effectiveness of the proposed PCC scheme in this paper.

Sensorless Control Scheme of IPMSMs Using HF Orthogonal Square-Wave Voltage Injection Into a Stationary Reference Frame

This paper proposes a new sensorless control scheme of interior permanent magnet synchronous motors (IPMSMs) using high-frequency (HF) orthogonal square-wave voltage injection into a stationary reference frame (SRF). This method is an improvement on the conventional HF rotating sinusoidal voltage injection into the SRF. First, discrete sequences of the HF currents are applied to establish the whole signal process. Then, a position estimation method without low-pass filters is proposed, and the phase shifts caused by high-pass filters are also reduced. Therefore, the proposed sensorless control method would not be adversely affected by digital filters, which can solve the common drawbacks of the current SRF-based injection methods. Furthermore, the digital delay in drive systems is considered, and its negative influence can be eliminated as well. The sensorless control method is verified by experiments on a 2.2-kW IPMSM drive platform.

Capacitor Voltage Balance Control of Hybrid Modular Multilevel Converters With Second- Order Circulating Current Injection

The capacitor voltage imbalance between the full-bridge sub-modules (FBSMs) and half-bridge submodules (HBSMs) may occur in the hybrid modular multilevel converters under the overmodulation operation. In this paper, the sub-module output voltage model under overmodulation is established first to explore the mechanism of capacitor voltage imbalance. With the established sub-module output voltage model, the complementary second-order voltage component in FBSMs and HBSMs is disclosed, which makes the second-order circulating current a novel control freedom to balance the capacitor voltages. With proper design of the magnitude and the phase angle of the injected second-order circulating current, the energy between the FBSMs and HBSMs is transferred and the capacitor voltage imbalance under overmodulation is eliminated. Moreover, the relationship between the sub-module capacitor voltage ripples and injected circulating current is also investigated to optimize the capacitor voltage ripple. Finally, the simulation and experiment results show that the proposed second-order circulating current injection method can not only balance the capacitor voltage but also reduce the voltage ripples of capacitors and current stress of semiconductor devices.

Sensorless Control Strategy for IPMSM to Reduce Audible Noise by Variable Frequency Current Injection

High-frequency (HF) signal injection is widely used in sensorless control schemes to drive interior permanent-magnet synchronous motors at low speeds, acquiring a good dynamic and a steady performance. However, the audible noise created by the injected HF signal is an obvious defect and restricts its application. In this paper, a variable frequency current injection method is proposed to reduce the noise. First, the theoretical basis of the variable frequency signal injection is analyzed and the demand from the injected signal is proposed. Second, a modified resonant controller is applied to realize the variable current injection and provide a zero steady-state control error. A linear active disturbance rejection controller that contains a resonant observer is applied to realize the q -axis current control and acquire rotor position information. Third, a sweep-frequency switching strategy is proposed to disperse harmonic energy. The energy of injected HF current is further extended by the proposed method when compared to the random switching method. Finally, the related experimental results are presented to verify the sensorless control method proposed.

Detection of Ground Insulation Faults in Ungrounded DC Power Supply Systems by Using a DC Current Injection Method

This paper proposes a DC current injection method for detecting ground insulation faults. When the ratio of the voltage of the positive bus to that of the negative bus is lower than a threshold value, the DC current is injected into the ungrounded DC power supply systems. DC power supply systems have essentially some grounded stray and external capacitors, so some of the injected DC current will flow into the grounded capacitor, increasing the voltage of the fault bus and the leakage current. The proposed method increases the leakage current by the injection of DC current, so the current sensor can detect the leakage current from which the insulation resistance can be calculated. Experimental results demonstrate that the DC current injection method can significantly improve the detection of ground insulation faults in ungrounded DC power supply systems.

Islanding Detection Using RT-Lab

As renewable energy is widely used, distributed power generation systems are also used in wide range. However, some problems in renewable power systems have to be addressed. Among these problems, the islanding operation has the most important impact to the safety of utility workers and the service lives of equipment. This paper studies islanding detection for a microgrid system with unbalanced loads and its implementation on a real-time simulator (RT-Lab) to accelerate simulations. The presented islanding detection approach utilizes rate of change of frequency (ROCOF), under/over frequency, and negative sequence current injection methods. Decoupled double synchronous reference frame software phase lock loop (DDSRF-SPLL) is used to synchronize the grid-connected power converter with the utility voltages under unbalanced load conditions. Two cases are tested in real time. The presented approach detects the islanding in 0.09 seconds after the fault occurs, and the voltage at the point of common coupling (PCC) returns stable in 0.1 seconds after the fault occurs, satisfying the IEEE Standard 1547-2003.

Torque Ripple Suppression Method With Reduced Switching Frequency for Open-Winding PMSM Drives With Common DC Bus

Torque ripple caused by zero-sequence current (ZSC) and relatively high switching frequency severely worsens the operating performance of an open-winding permanent-magnet synchronous machine (OW-PMSM) system with common dc bus. In this paper, a novel q -axis current injection method based on the angle-shift-based voltage distribution is proposed for the OW-PMSM system with common dc bus. With the proposed method, torque ripple caused by ZSC can be counteracted by the torque component generated by the injected q -axis current. Meanwhile, the corresponding modulation range is analyzed to investigate the availability of the proposed method. Moreover, in order to reduce the switching frequency, zero vector (111) is no longer necessary to compensate the zero-sequence component and conventional space vector pulsewidth modulation (PWM) with zero vectors (000) and (111) can be simplified. The switching actions in one PWM period can be reduced from 12 to 8. The comparison of losses shows that this strategy can effectively improve the efficiency under both heavy load and high switching frequencies. Finally, the effectiveness of the proposed method is validated through an OW-PMSM experiment with common dc bus.

REALIZING A SINGLE-STAGE HYBRID PV SYSTEM USING BATTERY CURRENTSHARING POWER DECOUPLING METHOD

Conventionally, the single-stage grid-connected PV inverter needs a large PV-side electrolytic capacitor to suppress the doubleline frequency current ripple to keep the PV operating at maximum power point (MPP). However, the short lifetime electrolytic capacitor will reduce the PV inverter’s reliability dramatically. In order to overcome the above problem, a novel battery currentsharing power decoupling (BCSPD) method for hybrid photovoltaic (PV) power systems is proposed in this paper. The proposed BCSPD circuit is parallel-connected with the string PV module to achieve as a single-stage topology. Thus, a high power conversation efficiency can be obtained. The current-injection method is adapted to solve the current ripple problem. Therefore, the required capacitance in PV side can be greatly reduced, so long-life film capacitors can be used instead of electrolytic capacitors. In addition, the battery storage system with the droop control is also used to realize the power regulation function to meet the requirements of actual applications. A 1200 W prototype was designed and implemented to assess the system performance. Experimental results show that the proposed system can track MPP, regulate the load power condition, and reduce current ripple.

Power Flow Control in Distributed Generation System of PFC Rectifier for DC Motor Drive

In this paper is to performance and analysis of grid connected power flow control and power quality improvement in distribution generation (DG) system a new topology of harmonic injection current, connected for a grid mode and DC motor drive. Inherently the system power factor is low and it has high harmonic content in the current. The Swiss rectifier is based on harmonic current injection methods on power flow control and implementation of Power factor correction (PFC), Rectifier, the harmonic mitigating pulse width modulation (PWM) technique have been used to reduce the harmonics for power quality improvement. The renewable sources have been used as DC source and control technique has been used with step up DC-DC converter to regulate DC-link voltage. The second close loop control has been done for voltage source inverter to stabilize its terminal voltage. The DC-AC converter provides the bidirectional power flow between point of common coupling (PCC) and local load. The step up converter regulates the DC link voltage to exchange the power with the three phase feeders, also it is conformed the harmonic current can be satisfied with the proposed method. The simulation Study is performed in MATLAB/ SIMULINK.

A comparative review of different transformer modelling methods in TRV studies in case of transformer limited faults

One of the most serious possible faults in power systems is transformer limited fault (TLF), in which transient recovery voltage (TRV) characteristics is determined by the closest transformer to the circuit breaker and due to the immense variety of transformers; performing experimental tests to determine TRV in all cases is impossible. Therefore, simulation is recommended. Purpose of this paper is to review existing methods for transformers modeling in TRV studies and compare their results with the measurement results. Three different models including impedance model, simplified model and frequency dependent model are studied. All models are obtained using transformer FRA results. Then modelling is done for three separate transformers. Also the application and proposed guidelines of model selection are suggested. Finally, TRV simulations are performed in EMTPWorks using capacitive current injection method. As a result, amplitude factor and TRV frequency are calculated for each model and simulation and measurement results are compared.

Harmonics Current Reduction of a Single-Phase Rectifier Based on Injection Power at Field Side of the DC Motor

The AC electrical distribution systems operate at definite and limited levels of voltages and frequencies. Non-linear loads produce non-sinusoidal currents and voltages in the distribution systems. The controlled and uncontrolled single and three phase rectifiers have been utilized in many applications and different industrial fields. The purpose of these applications is to obtain controlled, systematic and smooth DC currents and voltages. These rectifiers generate harmonics in the supply current that negatively affects at the power quality and efficiency of the system. For this reason, reducing harmonics in the current waveform was under investigation by many research groups. Several methods are suggested for minimizing such harmonics, one of that is the harmonic current injection method, which is considered in this paper. In this paper two injection networks are applied at single phase bridge controlled and uncontrolled rectifier which loaded with DC motor. The first suggested injection network involves back to back thyristor in series with RLC circuit in order to adjust the value and phase of the second harmonic injection current. The second suggested injection network includes a new method to get advantages of using the injection power for supplying a field of DC shunt motor. The obtained results show that the total harmonic distortion is reduced by 79.26% with power factor closed to unity.

Review on FRT solutions for improving transient stability in DFIG‐WTs

Fault-ride-through (FRT) is an imperative capability in wind turbines (WTs) to ensure grid security and transient stability. However, doubly fed induction generator-based WTs (DFIG-WTs) are susceptible to disturbances in grid voltage, and therefore require supplementary protection to ensure nominal operation. The recent amendments in grid code requirements to ensure FRT capability has compelled this study of various FRT solutions. Therefore, for improving FRT capability in pre-installed WTs, re-configuration using external retrofit-based solutions is more suitable and generally adapted. The most relevant external solutions based on retrofitting available are classified as (a) protection circuit and storage-based methods and (b) flexible alternating current transmission system-based reactive power injection methods. However, for new DFIG-WT installations, internal control modification of rotor-side converter (RSC) and grid-side converter (GSC) controls are generally preferred. The solutions based on modifications in RSC and GSC control of DFIG-WT are classified as (a) traditional control techniques and (b) advanced control techniques. This study ensures to curate and compare the FRT solutions available based on external retrofitting-based solutions and internal control modifications. Also, the future trends in FRT augmentation of DFIG-WTs are discussed in this study.

A comparison study between N-Solv method and cyclic hot solvent injection (CHSI) method

Steam injection is one of the major recovery methods to exploit heavy oil reservoirs. Replacing steam with hot solvent is an innovative idea to immensely decrease environmental pollution and energy consumption in steam-based recovery methods. The current hot solvent injection method attracts attention to the vapor solvent extraction (VAPEX) process. In comparison with the VAPEX process, cyclic solvent injection (CSI) process has been acknowledged as a high oil rate method due to the driving force of foamy oil flow. Hot solvent injection method is potentially applicable in the CSI process, which may increase the oil production rate and avoid the disadvantage of the VAPEX method. In this study, two experiments have been conducted to compare the production performance between the hot solvent-based CSI method and the hot solvent-based VAPEX method. The hot solvent-based CSI method is named the cyclic hot solvent injection method (CHSI). The hot solvent-based VAPEX method refers to the N-Solv method. N-solv is a patented method where the solvent is injected at the dew point temperature under the reservoir pressure condition. Due to the temperature difference between the reservoir and injected solvent, the injected solvent will condense in the reservoir and the condensed solvent will generate latent heat that can heat the reservoir chamber and thus reduce the oil viscosity (Nenniger and Gunnewiek, 2009). In this study, the N-Solv method has been studied in a laboratory test for the first time in N-Solv research history (Cao, 2011; Nenniger, 2005; Nenniger and Gunnewiek, 2009).According to experimental results, either of the two methods demonstrates some advantages in comparison with the other method from various aspects. From the production performance point of view, the recovery factor of the CHSI method is nearly 10% higher than that of the N-Solv method. The longer high oil rate period of the CHSI method in contrast with the N-Solv method indicates that the foamy oil behavior is more beneficial to the oil production compared with the gravity drainage and the solvent diffusion effect. In addition, it is shown from the solvent chamber growth difference that the gas flooding effect can enhance oil production in the CHSI process because the oil from gas-flooded area in the reservoir is clearly extracted out. However, according to the production GOR data, CHSI is a solvent-consuming method where a tremendous volume of free gas tends to be trapped in the solvent chamber as a result of gas flooding, which may offset the positive effect of gas flooding due to large consumption of solvent. The phenomenon of free gas trapping has not been found in the N-Solv process.

An Irregular Current Injection Islanding Detection Method Based on an Improved Impedance Measurement Scheme

One class of islanding detection methods, known as impedance measurement-based methods and voltage change monitoring-based methods, are implemented through injecting irregular currents into the network, for which reason they are defined in this paper as irregular current injection methods. This paper indicates that such methods may be affected by distributed generation (DG) unit cut-in events. Although the network impedance change can still be used as a judgment basis for islanding detection, the general impedance measurement scheme cannot separate island events from DG unit cut-in events in multi-DG operation. In view of this, this paper proposes a new islanding detection method based on an improved impedance measurement scheme, i.e., dynamic impedance measurement, which will not be affected by DG unit cut-in events and can further assist some other equipment in islanding detection. The simulations and experiments verify the stated advantages of the new islanding detection method.

A method of thrust ripple suppression for long stator linear synchronous motor

With the advantages of high speed, low noise and high efficiency, the electromagnetic suspension (EMS) type maglev train has a good prospect in railway transportation. It is based on the long stator linear synchronous motor (LSLSM). However, due to cogging effect, end effect and the harmonics in the stator current and flux density distribution around the air-gap, the thrust generated by the LSLSM fluctuates. The thrust ripple brings noise, drop of control accuracy, even causes the resonance of train. In this paper, the thrust ripple produced by the cogging effect and flux linkage harmonics is analyzed. Then a method of harmonic current injection is proposed to compensate cogging force and reduce the thrust ripple, without influence the decoupling control of traction and suspension system. The injected current harmonics are controlled under multiple rotating reference frames independently. Finally, based on voltage equations of harmonics, the decoupled harmonic current controllers with harmonic voltage feedforward are designed, which improve the performance of current harmonics response and thrust ripple suppression. Simulation results on Simulink verify the effectiveness of proposed thrust ripple suppression method for LSLSM.