Virtual Inductance Research Articles

A New Control Method to Reduce the Low-Frequency Output Current Ripple of AC-DC Converters by Using Virtual Inductor

A new concept of virtual inductor XE virtual inductor to reduce the low-frequency dc output ripple of ac-dc converters is introduced in this paper. Virtual inductor is defined as an additional control algorithm that changes the system behavior into the one that has an additional inductor connected on it. The virtual nature of the inductor makes the inductance can be designed without weight and volume restrictions. How to use the virtual inductor to improve the performance of converter XE current controller is discussed in this paper. Several simulated and experimental results are included to show the validity of the proposed concept.

A novel concept for phase noise improvement in monolithic differential LC-VCOs

A novel concept for improvement of phase noise in differential LC-VCOs is proposed. Being based on quality factor (Q) enhancement through conversion of the lossy inductor to a virtual inductor conditionally approaching the ideal lossless limit, the basics of the concept are illustrated and explained. Practical realization of the concept is discussed, and its application in design of a CMOS based Giga Hertz range low phase noise monolithic differential LC-VCO is investigated. Advanced Design System (ADS) simulations using CMOS 0.18 μm TSMC RF design kit are used for evaluation.

An Accurate Power Control Strategy for Power-Electronics-Interfaced Distributed Generation Units Operating in a Low-Voltage Multibus Microgrid

In this paper, a power control strategy is proposed for a low-voltage microgrid, where the mainly resistive line impedance, the unequal impedance among distributed generation (DG) units, and the microgrid load locations make the conventional frequency and voltage droop method unpractical. The proposed power control strategy contains a virtual inductor at the interfacing inverter output and an accurate power control and sharing algorithm with consideration of both impedance voltage drop effect and DG local load effect. Specifically, the virtual inductance can effectively prevent the coupling between the real and reactive powers by introducing a predominantly inductive impedance even in a low-voltage network with resistive line impedances. On the other hand, based on the predominantly inductive impedance, the proposed accurate reactive power sharing algorithm functions by estimating the impedance voltage drops and significantly improves the reactive power control and sharing accuracy. Finally, considering the different locations of loads in a multibus microgrid, the reactive power control accuracy is further improved by employing an online estimated reactive power offset to compensate the effects of DG local load power demands. The proposed power control strategy has been tested in simulation and experimentally on a low-voltage microgrid prototype.

A Dual-Functional Medium Voltage Level DVR to Limit Downstream Fault Currents

The dynamic voltage restorer (DVR) is a modern custom power device used in power distribution networks to protect consumers from sudden sags (and swells) in grid voltage. Implemented at medium voltage level, the DVR can be used to protect a group of medium voltage or low voltage consumers. However, the DVR will therefore be tasked to mitigate even more faults involving downstream loads. Large fault currents would flow through the DVR during a downstream fault before the opening of a circuit breaker. This will cause the voltage at point of common coupling (PCC) to drop, which would affect the loads on the other parallel feeders connected to PCC. Furthermore, if not controlled properly, the DVR might also contribute to this PCC voltage sag in the process of compensating the missing voltage, thus further worsening the fault situation. To limit the flow of large line currents, and therefore restore the PCC voltage as well as protect the DVR system components, a downstream fault limiting function is proposed and integrated in the DVR operation. A flux-charge-model feedback algorithm is implemented so that the DVR would act as a large virtual inductance in series with the distribution feeder in fault situations. Controlling the DVR as a virtual inductor would also ensure zero real power absorption during the DVR compensation and thus minimize the stress in the dc link. Finally, the proposed fault current limiting algorithm has been tested in Matlab/Simulink simulation and experimentally on a medium voltage level laboratory DVR system.

Virtual inductor-based islanding detection method for grid-connected power inverter of distributed power generation system

An islanding detection method is proposed for a distributed power generation system that comprises a DC power source and a grid-connected power inverter connected in parallel to the utility. Besides serving to generate the fundamental real power, the grid-connected power inverter also acts as a virtual inductor when the frequency is slightly higher than the fundamental voltage frequency of the utility. The distributed power generation system is the only source supplying power to the load when the utility is interrupted; consequently, the amplitude or frequency of the load voltage changes because of the operation of the virtual inductor. Hence, the proposed method can immediately detect the islanding operation. A prototype was developed and tested to demonstrate the performance of the proposed islanding detection method. Experimental results show that the proposed method can detect islanding operations effectively.

Power Harvesting Piezoelectric Shunt Damping

Passive shunt damping involves the connection of an electrical shunt network to a structurally attached piezoelectric transducer. Typical shunt networks require inductance values of up to thousands of Henries. Virtual inductors or synthetic networks are required to implement the required impedance. This paper introduces an efficient, light weight, and small-in-size technique for implementing piezoelectric shunt damping circuits. A MOSFET half bridge is used together with a signal processor to synthesize the terminal impedance of a piezoelectric shunt damping circuit. Under certain circumstances, the device is capable of harvesting the real power normally dissipated by resistive network elements.

Optimization and implementation of multimode piezoelectric shunt damping systems

Piezoelectric transducer (PZT) patches can be attached to a structure in order to reduce vibration. The PZT patches essentially convert vibrational mechanical energy into electrical energy. The electrical energy can be dissipated via an electrical impedance. Currently, impedance designs require experimental tuning of resistive circuit elements to provide optimal performance. A systematic method is presented for determining the resistance values by minimizing the H/sub 2/ norm of the damped system. After the design process, shunt circuits are normally implemented using discrete resistors, virtual inductors and Riordian gyrators. The difficulty in constructing the shunt circuits and achieving reasonable performance has been an ongoing and unaddressed problem in shunt damping. A new approach to implementing piezoelectric shunt circuits is presented. A synthetic impedance, consisting of a voltage controlled current source and a digital signal processor system, is used to synthesize the terminal impedance of a shunt network. A two-mode shunt circuit is designed and implemented for an experimental simply supported beam. The second and third structural modes of the beam are reduced in magnitude by 22 and 18 dB.

Fast, accurate and stable simulation of power electronic systems using virtual resistors and capacitors

Simulation of power electronic circuits remains a problem due to the high level of stiffness brought about by the modelling of switches as biresistors i.e. very low turn-on resistance and very high turn-off resistance. The merits and drawbacks of two modelling methods that address this problem are discussed. A modelling solution for ensuring numerically stable, accurate and fast simulation of power electronic systems is proposed. The solution enables easy connectivity between power electronic elements in the simulation model. It involves the modelling of virtual capacitance at switching nodes to soften voltage discontinuity due to the switch current suddenly going to zero. Undesirable ringing effects that may arise due to the interaction between the virtual capacitance and circuit inductance are eliminated by modelling virtual damping resistors in parallel to inductors that are adjacent to switching elements. A midpoint configuration method is also introduced for modelling shunt capacitors. A DC traction system is simulated using this modelling strategy and the results are included. Simulation results obtained using this modelling strategy are validated by comparison with the established mesh analysis technique of modelling. The simulation performance is also compared with the Power System Blockset commercial software.

Transient power characteristics of balanced three‐phase variable inductance

AbstractInductance has a particularly important role in power circuits. The authors have proposed the Variable Active–Passive Reactance (VAPAR), which can produce a virtual variable inductance. In this paper, the transient power characteristics of a balanced three‐phase variable inductance are analyzed using the instantaneous active and reactive power theorem. With an ideal voltage source or an ideal current source connected to a balanced three‐phase variable inductance, the transient power characteristics are analyzed theoretically, and then the results are verified through simulations. In the other cases, it is difficult to solve for the transient power, but it is shown that the transient power characteristics can easily be estimated from the results of simulations in which an ideal voltage source or an ideal current source is connected to a balanced three‐phase variable inductance. Experiments are also carried out to verify the theoretical analysis and simulations. © 2001 Scripta Technica, Electr Eng Jpn, 136(2): 49–57, 2001

A New Instantaneous Power Flow Control Method Using Variable Inductance Realized by Variable Active-Passive Reactance (VAPAR)

Rapid power flow control of power systems is the key concept of Flexible AC Transmission System (FACTS). The power flow is essentially restricted by a line inductance. The authors have previously proposed the Variable Active Passive Reactance (VAPAR)(1) which can generate a virtual variable inductance. In this paper, a new instantaneous power flow control method using variable inductance is proposed. The theoretical analysis shows that the power flow follows in inverse ratio of the line inductance even in a transient state assuming the simple power system with two voltage bus connected by an inductive power line. Simulations and experiments were carried out using the feedfoward-based power controller to verify the effectiveness of this method. Then, the characteristics of the power control were analyzed for different line impedances by simulations. The results show that the power flow can be quickly controlled using variable inductance in the case of a small line resistance, while transient oscillations are observed in the power flow only when a line resistance is rather large.

Transient Power Characteristics of Balanced Three-Phase Variable Inductance

Inductance has a particularly important role in power circuits. The authors have proposed the Variable Active–Passive Reactance (VAPAR), which can produce a virtual variable inductance. In this paper, the transient power characteristics of a balanced three-phase variable inductance are analyzed using the instantaneous active and reactive power theorem. With an ideal voltage source or an ideal current source connected to a balanced three-phase variable inductance, the transient power characteristics are analyzed theoretically, and then the results are verified through simulations. In the other cases, it is difficult to solve for the transient power, but it is shown that the transient power characteristics can easily be estimated from the results of simulations in which an ideal voltage source or an ideal current source is connected to a balanced three-phase variable inductance. Experiments are also carried out to verify the theoretical analysis and simulations. © 2001 Scripta Technica, Electr Eng Jpn, 136(2): 49–57, 2001