Current Injection Control Research Articles

Impact of a power converter virtual impedance based fast fault current injection control strategy on distance protection

Impact of a power converter virtual impedance based fast fault current injection control strategy on distance protection

A Sinusoidal Doubly Salient Electromagnetic Machine Drive Fed by Third-Harmonic Injection Two-Stage Matrix Converter With Integrated Injection Inductor

This manuscript studies a sinusoidal doubly salient electromagnetic machine (SDSEM) drive fed by third-harmonic injection two-stage matrix converter (3TSMC) with integrated injection inductor to improve the power density of the whole system. First, compared with the conventional matrix converter (MC), the 3TSMC suffers from larger volume due to the inductor in the harmonic current injection circuit. In the proposed system, the harmonic injection current is synthesized by the field current of SDSEM and the injection inductor is removed. Then, the control strategy is proposed to decouple the current injection control and field current control, which means that the harmonic current and the field current can be regulated flexibly. Finally, a prototype is built to evaluate the proposed system and control strategy. Furthermore, the proposed 3TSMC-fed drive with the corresponding control strategy is also suitable for the other DC-excited three-phase sinusoidal AC machines, such as wound rotor synchronous machines.

Harmonic Current Injection Control Algorithm for Narrowing the Switching Frequency Range in CrM Totem-Pole PFC

Harmonic Current Injection Control Algorithm for Narrowing the Switching Frequency Range in CrM Totem-Pole PFC

Fault Location and Phase Selection Method of Distribution Network Containing IIDG Based on Online Active Detection

This paper proposes a fault location and phase selection method for the distribution network containing IIDG based on online active detection, utilizing online active detection. In this method, the characteristic harmonic current injection control strategy based on d- and q-axis control is obtained by analyzing the structure, control strategy, and short-circuit current of IIDG. During a fault, the distributed power supply injects characteristic harmonic current into line, adapting its magnitude with the short-circuit current’s size. By detecting the difference in harmonic current content rate for both ends of the fault point, the method achieves online location and line selection of fault points. A 10 kV IIDG distribution network model is simulated by using PSCAD to validate the feasibility and accuracy of the proposed fault location and phase selection method.

Smart Sag Detection and Reactive Current Injection Control for a PV Microgrid under Voltage Faults

Low-power photovoltaic distributed generators are increasing rapidly in number by the grids of the modern era, but they also bring up the concern of grid stability. To maintain grid stability, it is essential for the network operators to update the grid codes at regular intervals due to the case of highly penetrated grid-connected photovoltaic systems (GCPVs). Integration of large-scale electrical grids with renewable energy sources, one being photovoltaic systems, faces the challenge of riding through low-voltage (LVRT) phases. As compared to the previous grid codes for power generation, recent advances require distributed generation resources to provide for such capabilities under grid faults. This work contributes to the ongoing investigation of this specified and destabilizing fault condition. Various simulations of a PV microgrid system are carried out with the ability to ride through low-voltage faults, with the help of a DC-chopper circuit to absorb DC-link over-voltage, and the current is also maintained within acceptable limits according to the required standards. The fundamental contribution of this research is a proposed neural network (NN) control framework. This framework effectively detects voltage sags, comprehends their characteristics, and provides support to the system by injecting reactive current in accordance with the demands imposed by designated grid codes. This NN control model has been systematically developed utilizing data gathered from a vast array of testing simulations conducted under different and dynamic conditions. The proposed strategy, on the other hand, is compared with the RMS fault detection method in combination with the conventional LVRT algorithm. The NN control approach showed better results as compared to the conventional methods in terms of accuracy and robustness, especially when confronted with difficult sag situations.

Peak Arm Current Minimization of Modular Multilevel Converter Using Multiple Circulating Current Injection

Conventional circulating current (CC) control schemes of the modular multilevel converters (MMC) typically suppress the CC to zero to reduce the system loss. However, the non-zero CC can also bring additional benefits. In this paper, a peak arm current minimization method of the MMC using multiple circulating current injection control (MCCIC) is studied. Specifically, the second-order CC (SOCC) and the fourth-order CC (FOCC) are used to achieve this purpose. Firstly, the amplitude and phase angle of the SOCC are determined to shape the arm current into a saddle wave. Next, the amplitude and the phase angle of the FOCC are studied to further cut flat the crest of the saddle wave to minimize the peak arm current. The feasibility boundary for the proposed strategy is discussed quantitatively. Moreover, a decoupling circulating current control strategy is developed for precise control of the SOCC and FOCC. In the end, the proposed techniques are verified via both PSCAD/EMTDC simulation and RTLAB&RTU-BOX hardware-in-the-loop experiment. The results show that the peak arm current of the MMC operating with high power factors can be reduced by about 23% and its power handling capacity can be increased by about 30%.

Third-Harmonic Current Injection Control of Five-Phase Permanent-Magnet Synchronous Motor Based on Third-Harmonic Current Reference Online Identification

The ratio of torque to copper loss can be increased by injecting third-harmonic current into five-phase permanent-magnetic synchronous motor (PMSM). Accurate flux linkage information is indispensable in the process of calculating third-harmonic current reference corresponding to the maximum torque/copper loss ratio. In harsh working environments, the flux linkage will deviate from the initial measured value, resulting in the deviation between the third-harmonic current and the maximum torque/copper working point. Therefore, a third-harmonic current injection control strategy of five-phase PMSM based on third-harmonic current reference online identification is proposed in this paper. The key of this strategy is to transform the steady-state voltage equations into an equation containing only voltages and currents. The transformed equation has a characteristic that it is equal to 0 when the motor operates at the maximum torque/copper loss ratio working point. Meanwhile, an observer is designed to estimate the third-harmonic current reference by using the characteristic. Finally, the observer is applied in third-harmonic current injection control of five-phase PMSM. Compared with previous methods, the proposed strategy is simple, no need of flux linkage information and not affected by the change of flux linkage. The experimental results demonstrate the robustness of the proposed strategy.

Effective spin injection into the organic semiconductor PTCDA evaluated by a normalization method

Studies of spin current injection, transport, and interface control have drawn attention recently for efficient organic spintronic devices. In this study, we apply both spin pumping (SP) and the longitudinal spin Seebeck effect (LSSE) to inject spin currents into a π-conjugated organic semiconductor, perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), and characterize injection and transport by measuring inverse spin Hall voltage VISHE in spin detectors. A normalization factor introduced to SP analysis eliminates a contribution provoked by deviation of spin sources and leads to a more accurate determination of the spin diffusion length in PTCDA. While SP with Permalloy as a spin source is effective in generating detectable VISHE, the LSSE from yttrium iron garnet shows no convincing sign of spin injection. In addition, spin-flip scattering induced by hybrid states undermining electrical spin injection is negligible in SP. These results are attributed to interfaces between spin sources and PTCDA, indicative of the importance of injection methods and material choices.

Optimization of speed response of super-high-speed electric air compressor for hydrogen fuel cell vehicle considering the transient current

A super-high-speed electric air compressor for a hydrogen fuel cell vehicle must have a wide speed range and high-speed regulation response capacity. However, due to the distortion of the air gaps magnetic field of the super-high-speed permanent magnet synchronous motor (SHSPMSM) in the super-high-speed domain, the motor's output torque capacity is reduced. Then its speed regulation response capacity is weakened. To solve this problem, firstly, we analyze the effect of transient current on the speed regulation response of the super-high-speed PMSM. Secondly, we proposed a new speed regulation control method, the transient current injection (TCI) control method. Finally, simulation analysis and experimental results demonstrate the effectiveness of the proposed control method. Under target speed of 151,703 rpm, the average electromagnetic torque of SHSPMSM using the TCI control method is increased by 3%. Furthermore, the speed regulation response time decreased by about 0.49s.

Improved Comprehensive Control of Modular Multilevel Converter under AC/DC Grid Faults and Harmonic Operation Conditions

Recent applications of modular multilevel converter (MMC) have posed various problems such as ac/dc grid faults, asymmetric operation conditions, ac grid voltage excessive harmonics, and ac circulating currents, which deteriorate the system's performance and also threaten the safe operation. In this article, an improved comprehensive control architecture of MMC is proposed to maintain a stable voltage control, eliminate harmonics in ac-side and circulating currents, and dc-bus voltage ripple under ac/dc grid faults and harmonic operation conditions. The proposed comprehensive control consists of improved hierarchical voltage control and repetitive controller-based arm current control. The improved hierarchical voltage control, including a novel negative-sequence current injection and dc-circulating current injection-based leg-averaging control and their seamlessly switching handling, enables the MMC to operate under various operating conditions, thereby producing the arm current reference for inner-loop control. The proposed repetitive controller-based arm current control can recognize the control of multifrequency components of arm current without separating positive-, negative- and zero-sequence current components of ac-side currents and circulating currents. Finally, the simulation and experimental studies of the three-phase MMC were carried out in detail, and the findings demonstrate the efficiency and merits of the proposed control method.

Maximum Torque per Ampere Control for IPMSM Traction System Based on Current Angle Signal Injection Method

Rail transportation interior permanent magnet synchronous motor traction control system (IPMSM TCS) requires high torque output capability. Traditional algorithms used to find the maximum torque per ampere (MTPA) operating point in TCS have strong dependence on motor parameters. Because the algorithm is less robust to motor parameters, there will be deviation between the MTPA operating point and the actual value when the parameters change, so that it is difficult to guarantee the torque output capability of the traction system under different working conditions. This paper introduces a current angle signal injection control method (CASIM) to solve this problem. The proposed method tracks the MTPA operating point and generates d-axis current command according injecting an angle signal to current and making the partial derivative of torque to current angle equal to zero. At the same time, less motor parameters are needed to calculate the torque in this method. Consequently, in the process of looking for MTPA operating point, the accuracy is less affected by the variation of motor parameters. And also it does not inject any real signal to IPMSM, so that it does not increase copper and iron losses. Moreover, it is robust to speed mutation and torque disturbances. The effectiveness of CASIM proposed in this paper is proved by simulation and experiment results on an IPMSM TCS platform.

Torque Ripple Suppression of Permanent Magnet Synchronous Motor Based On Robust Current Injection

In order to improve the performance of permanent magnet synchronous motor (PMSM) servo system and suppress the influence of torque ripple on the control system, a robust current injection control method combining active disturbance rejection controller (ADRC) and current injection is proposed. We designed a current injection module to suppress the torque ripple of the motor and proposed an ADRC to improve the anti-disturbance performance of the system, which ensures the strong robustness and rapidity of the system. The simulation results show that compared with the conventional PI control and PI superimposed current injection, the proposed method can more effectively suppress the torque ripple, while improving the robustness and dynamic response of the system.

Active Power Control of New Energy System of Large Power Grid With UPFC

FACTS equipment based on power electronics and control technology has made great help to the optimization of power systems. The Unified Power Flow Controller (UPFC) is the most promising FACTS device due to its flexible regulation and complete functions. This paper analyzes the basic composition and working principle of UPFC, studies the idea of voltage injection control and current injection control, and presents the building of relevant control loops.

A Novel Reactive Current Injection (RCI) Control for Microgrid Protection with Inverter Based Distributed Generation (IBDG)

As the development of renewable distributed generations (DGs) is growing rapidly, the autonomous self-healing microgrid had emerged as an effective solution for integrating renewable DGs in the distribution networks. However, before the autonomous self-healing microgrid can be realized, one of the main issues that needs to be resolved is the ability to utilize the most cost-effective protection system—overcurrent relays—to achieve the goal. However, the overcurrent relay is insensitive to the limited fault current contributed by the inverter-based distributed generation (IBDG). Therefore, this paper will propose a novel inverter fault current control with a reactive current injection (RCI) that injects the correct fault current vector, albeit with a limited magnitude, for detection by the cost-effective directional overcurrent relay. This paper will also evaluate the performances of the different RCI controls in delivering an efficient self-healing microgrid protection based on a directional overcurrent relay. The proposed self-healing protection scheme is tested with both a simple distribution test network and also the IEEE 16 bus test system, considering random system parameters like variations in IBDG location, fault location, load capacity and load power factor. Moreover, the performance of the proposed inverter RCI control is also tested under changing weather conditions.

Parallel current‐controlled synchronverters for voltage and frequency regulation in weak grids

The emulation of synchronous machines is becoming an attractive solution to provide virtual inertia and voltage support to weak grids and microgrids, representing an alternative to conventional current-injection control strategies. However, synchronverters operate as voltage sources and this makes it difficult to limit the current when an event like voltage sag takes place. Here, a method to limit the output current of synchronverters in parallel connection is proposed. First of all, a fictitious reference current is generated, and its value is then followed by an internal current controller. A method to avoid the loss of synchronism when the current saturates is proposed and studied in detail. Also, the implementation of the controller is addressed carefully. All the control system improvements are tested on a prototype consisting of two 15 kVA synchronverters connected in parallel to a configurable weak grid.

PI‐based controller for low‐power distributed inverters to maximise reactive current injection while avoiding over voltage during voltage sags

In the recently deregulated power system scenario, the growing number of distributed generation sources should be considered as an opportunity to improve stability and power quality along the grid. To make progress in this direction, this work proposes a reactive current injection control scheme for distributed inverters under voltage sags. During the sag, the inverter injects, at least, the minimum amount of reactive current required by the grid code. The flexible reactive power injection ensures that one phase current is maintained at its maximum rated value, providing maximum support to the most faulted phase voltage. In addition, active power curtailment occurs only to satisfy the grid code reactive current requirements. As well as, a voltage control loop is implemented to avoid overvoltage in non-faulty phases, which otherwise would probably occur due to the injection of reactive current into an inductive grid. The controller is proposed for low-power rating distributed inverters where conventional voltage support provided by large power plants is not available. The implementation of the controller provides a low computational burden because conventional PI-based control loops may apply. Selected experimental results are reported in order to validate the effectiveness of the proposed control scheme.

Enhanced AC voltage and frequency control of offshore MMC station for wind farm connection

Connecting large offshore wind farms using high-voltage direct current (HVDC) transmission systems based on the modular multilevel converter (MMC), the offshore alternating current (AC) voltage and frequency are regulated by the offshore MMC station and are important for the stable wind power generation and transmission. This study proposes an enhanced AC voltage and frequency control strategy of the offshore MMC for wind farm integration, where an additional frequency loop is used to improve its AC voltage and frequency controllability. A fault current injection control is also proposed, where the offshore MMC station actively provides fault currents during an offshore AC fault to enable overcurrent protection for the network. To ride-through onshore AC faults, a direct current (DC) voltage-dependent AC voltage controller is introduced to actively reduce the offshore AC voltage during an onshore AC fault to alleviate the DC overvoltage of the HVDC system. Simulation results in normal operation and during offshore and onshore faults confirm the feasibility of the proposed control scheme.

Three‐phase current injection method for mitigating turn‐to‐turn short‐circuit fault in concentrated‐winding permanent magnet aircraft starter generator

Fractional-slot concentrated-winding (FSCW) permanent magnet synchronous machines, which are characterised with high power density, fault tolerance and wide constant-power speed range, are gaining more and more attention in the aircraft starter generator (SG) systems. Nevertheless, the short-circuit (SC) fault, especially the turn-to-turn SC fault, is the obstruct crux in aviation applications. This study is aimed to demonstrate the feasibility of FSCW permanent magnet SG (PMSG) in dealing with turn-to-turn SC fault. The law of FSCW-PMSG SC fault is analysed and verified by finite-element analysis (FEA), including the influence on turn-to-turn SC current by the number of the shorted turns and the coil position in the slot. The three-phase current injection control is employed to mitigate the SC fault in PMSG when a turn-to-turn SC fault occurs. A 24-slot, 16-pole FSCW-PMSG with spoke-type rotor topology is designed to confirm the ability of inhibiting turn-to-turn SC current without the risk of irreversible demagnetisation. Both FEA and experimental results are presented, verifying the effectiveness of the three-phase current injection control in restraining the turn-to-turn SC current for FSCW PMSG in an acceptable range.

Parallel Resonance Detection and Selective Compensation Control for SAPF With Square-Wave Current Active Injection

Due to capacitor elements and inductive line impedance in power system, parallel resonance could be triggered in the presence of harmonic currents from nonlinear load, whose frequency may shift resulting from intermittent switching of the capacitor devices. So it is difficult for shunt active power filter (SAPF) to damp parallel resonance. This paper investigates parallel resonance detection with square-wave current active injection and selective compensation control with closed-loop regulation of point of common coupling (PCC) voltage for SAPF. The principles of parallel resonance and its frequency detection are analyzed by means of equivalent circuit. Through injecting given square-wave current lasting for 0.5 s, SAPF could fast detect parallel resonance with the help of spectrum analysis of resonance power index. In order to improve power quality of both PCC voltage and grid current, SAPF is controlled to suppress specified harmonic currents from nonlinear load and selectively damp parallel resonance at the same time. In addition, ordinary proportional-integral plus advanced repetitive controller in parallel is used to improve current tracking performance. Experiment test results are provided to verify the validity of proposed detection and control methods.

New Control of Wind Turbines Ensuring Stable and Secure Operation Following Islanding of Wind Farms

This paper first presents the phenomena of the offshore wind farm (OWF) experience following the blocking of the high voltage direct current converter used for connecting the wind farm (WF) to the main onshore grid. Measurements in real large WFs show that the voltage will rise by approximately 30% within 50–100 ms in the ensuing island operation. The process is superimposed by transients caused by short but repetitive periods of saturation of the transformers. Based on the analysis of common wind turbine (WT) control concepts, it has been found that the reason for the voltage rise is the integral characteristic of the classical current controller. Generally, it seems that the current injection control, as it is used in almost all WT controls, is not suitable in grids dominated by converter in-feed like in OWF. The authors are suggesting a new WT control concept that is characterized by voltage injection instead of the usage of an explicit current controller. Simulation results show that the voltage rise following islanding can be avoided, whereas the fault ride-through response to grid short circuits remains almost the same as before.