Renewable energy sources are one key enabler to decrease greenhouse gas emissions and to cope with the anthropogenic climate change. Their intermittent behavior and limited storage capabilities present a new challenge to power system operators to maintain power quality and reliability. Additional technical complexity arises from the large number of small distributed generation units and their allocation within the power system. Market liberalization and changing regulatory framework lead to additional organizational complexity. As a result, the design and operation of the future electric energy system have to be redefined. Sophisticated information and communication architectures, automation concepts, and control approaches are necessary in order to manage the higher complexity of so-called smart grids. This paper provides an overview of the state of the art and recent developments enabling higher intelligence in future smart grids. The integration of renewable sources and storage systems into the power grids is analyzed. Energy management and demand response methods and important automation paradigms and domain standards are also reviewed.

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A Review of Architectures and Concepts for Intelligence in Future Electric Energy Systems

This paper presents a practical approach to eliminating both bearing current and ground leakage current from an inverter-driven motor rated at 400 V and 3.7 kW. When the shaft voltage with respect to the motor frame exceeds the dielectric breakdown voltage of thin lubricating grease films in two metal bearings at the drive and non-drive ends, an electrical discharge machining (EDM) current flows through the bearings. A passive electromagnetic interference (EMI) filter can keep the shaft voltage in check, as a result of having eliminated high-frequency common-mode voltage from the motor terminals. Hence, no dielectric breakdown occurs in the grease films, so that no EDM current flows in the bearings. Experimental results verify the viability and effectiveness of the passive EMI filter designed in this paper

A Passive EMI Filter for Eliminating Both Bearing Current and Ground Leakage Current From an Inverter-Driven Motor

This paper deals with improving the voltage quality of sensitive loads from voltage sags using a dynamic voltage restorer (DVR). The higher active power requirement associated with voltage phase jump compensation has caused a substantial rise in size and cost of the dc link energy storage system of DVR. The existing control strategies either mitigate the phase jump or improve the utilization of dc link energy by the following: 1) reducing the amplitude of the injected voltage or 2) optimizing the dc bus energy support. In this paper, an enhanced sag compensation strategy is proposed, which mitigates the phase jump in the load voltage while improving the overall sag compensation time. An analytical study shows that the proposed method significantly increases the DVR sag support time (more than 50%) compared with the existing phase jump compensation methods. This enhancement can also be seen as a considerable reduction in dc link capacitor size for new installation. The performance of the proposed method is evaluated using simulation study and finally verified experimentally on a scaled laboratory prototype.

An Enhanced Voltage Sag Compensation Scheme for Dynamic Voltage Restorer

Shape memory alloys (SMA), in particular nickel–titanium alloy (or nitinol), have been used as actuators in some astronautic, aeronautic and industrial applications. The future will see more SMA application if less energy is required for actuation. This paper presents the design and experimental results of control of an SMA actuator using pulse width modulation (PWM) to reduce the energy consumption by the SMA actuator. A SMA wire test stand is used in this research. Open-loop testing of the SMA wire actuator is conducted to study the effect of the PWM parameters. Based on test results and parameter analysis of the pulse width (PW) modulator, a PW modulator is designed to modulate a proportional plus derivative (PD) controller. Experiments demonstrate that control of the SMA actuator using PWM effectively saves actuation energy while maintaining the same control accuracy as compared to continuous PD control. PWM also demonstrates robustness to external disturbances. A comparison with a pulse width pulse frequency modulator is also presented.

https://iopscience.iop.org/article/10.1088/0964-1726/12/5/007/pdf

Control of shape memory alloy actuator using pulse width modulation

A complete digital audio amplifier has been developed, implemented and tested. The process is entirely computational, and the output load and filter are the only analog components in the system. The process makes use of digital signal processing and a switching power stage to provide both high fidelity and high efficiency, beginning with a digital audio data stream. The advantages of naturally-sampled pulse-width modulation (PWM) are discussed in depth, including spectral analysis and comparisons to uniformly-sampled PWM. It is shown that natural PWM does not introduce audible distortion at switching frequencies consistent with power electronics practice. Interpolation methods for sample data conversion to natural PWM are discussed, and error analysis is presented based on Lagrange's Expansion Theorem. Noise-shaping processes are used to support high fidelity with practical values of time resolution. A counter conversion process enforces switching dead time in the inverter gate signals. The experimental full-bridge inverter implementation demonstrates that miniaturization is possible. A complete test system delivered more than 50 W into an 8 /spl Omega/ load with an efficiency of 80% and total harmonic distortion plus noise of 0.02%.

High-fidelity PWM inverter for digital audio amplification: Spectral analysis, real-time DSP implementation, and results

The parameters of electrical energy such as voltage amplitude are very important, particularly from the viewpoint of the final consumer and sensitive loads connected to the grid. The dynamic states in the power grid-deep voltage sags and swells-might cause faults and defects in sensitive loads. This paper deals with a three-phase hybrid transformer (HT) without dc energy storage to compensate voltage sags and swells and to protect sensitive loads against the rapid and extensive changes in supply voltage amplitude. The analyzed HT contains two main units: the first one is the conventional electromagnetic transformer, realizing an electromagnetic coupling, and the second one is the buck-boost matrix-reactance chopper, realizing an electrical coupling in the HT unit. In the presented solution, output voltage is transformed in two ways-electromagnetically and electrically. This paper presents an operational description, the theoretical analysis, and the experimental test results from a 2-kVA laboratory model. On the basis of the authors' research, it can be stated that the HT makes it possible to compensate deep voltage sags (deeper than 50% of nominal source voltage) and overvoltages (up to 140% of nominal source voltage) while maintaining good dynamic properties. The main advantages of the proposed solution, in comparison to other conventional solutions, are the ability to control the output voltage in the range of 0.66-3.5 US, good dynamics (transient state during source voltage uS amplitude change is shorter than 10 ms), and galvanic separation between source and load (such as in the case of the conventional electromagnetic transformer).

AC Voltage Sag/Swell Compensator Based on Three-Phase Hybrid Transformer With Buck-Boost Matrix-Reactance Chopper

This paper deals with the AC voltage transformation circuits, which contain matrix or matrix-reactance PWM AC fine conditioners. These circuits can be treated as PWM AC/AC semiconductor transformers. In this paper the review of single-phase topologies are presented. The review covers both nonisolated and isolated ones as well as single or two-quadrant structure. Furthermore there are shown the averaged models, their four terminal chain parameters and some exemplary applications are outlined of presented AC voltage transformation circuits as well.

Single-phase PWM AC/AC semiconductor transformer topologies and applications

This paper deals with three-phase direct matrix- reactance frequency converters (MRFC) based on unipolar PWM AC matrix-reactance choppers (MRC). The topologies of the proposed MRFC are based on a three- phase unipolar MRC structure. Each MRC with conventional topology has two synchronous-connected switches [SCS] sets. In the MRFC, unlike the MRC topology, one of SCS sets is replaced by a matrix-connected switches (MCS) set in order to make possible of the load voltage frequency change. Six new topologies of the MRFC based on MRC boost, buck-boost, Cuk, Zeta or SEPIC structures are presented. Through the generation concept of the proposed converters both the description of above- mentioned converter topologies and general description of the control strategies are presented. The structure of the proposed MRFC contains a three-phase matrix converter (MC), which is introduced instead of the source or load SCS used in unipolar MRC. The step-down or step-up of the MC set is dependent on the input and output voltage or current source configurations. Analysis determining the location where the MC should be introduced is realized by means of the one-cycle switched models with suitable voltage and current sources introduced instead of the capacitors and inductors respectively. Furthermore, exemplary results of the simplified theoretical analysis, based on the averaged state space method, as well as simulation test results obtained for a classical Venturini control strategy of MC, are also presented as an initial verification of the properties of the proposed converters.

Generation of matrix-reactance frequency converters based on unipolar PWM AC matrix-reactance choppers

In this paper, the authors present quantitative experimental results of the amplitude and rate of bearing current pulses emerging in common use PWM drives configurations. Based on measurement data and a simulation model, it has been shown that a whole path of bearing currents is closed inside of the motor and that these currents do not flow to a grounding arrangement as had been suggested in previous works.

Bearing current path and pulse rate in PWM-inverter-fed induction

This paper deals with three-phase direct matrix-reactance frequency converters (MRFC) based on unipolar PWM AC matrix-reactance choppers (MRC). The topologies of the proposed MRFC are based on a three-phase unipolar MRC structure. Each MRC with conventional topology has two synchronous-connected switches (SCS) sets. In the MRFC, unlike the MRC topology, one of SCS sets is replaced by a matrix-connected switches (MCS) set in order to make possible of the load voltage frequency change. Six new topologies of the MRFC based on MRC boost, buck-boost, Cuk, Zeta or SEPIC structures are presented. Through the generation concept of the proposed converters both the description of above-mentioned converter topologies and general description of the control strategies are presented. The structure of the proposed MRFC contains a three-phase matrix converter (MC), which is introduced instead of the source or load SCS used in unipolar MRC. The step-down or step-up of the MC set is dependent on the input and output voltage or current source configurations. Analysis determining the location where the MC should be introduced is realized by means of the one-cycle switched models with suitable voltage and current sources introduced instead of the capacitors and inductors respectively. Furthermore, exemplary results of the simplified theoretical analysis, based on the averaged state space method, as well as simulation test results obtained for a classical Venturini control strategy of MC, are also presented as an initial verification of the properties of the proposed converters.

Zbigniew Fedyczak

Papers

AC Voltage Sag/Swell Compensator Based on Three-Phase Hybrid Transformer With Buck-Boost Matrix-Reactance Chopper

Single-phase PWM AC/AC semiconductor transformer topologies and applications

Generation of matrix-reactance frequency converters based on unipolar PWM AC matrix-reactance choppers

Bearing current path and pulse rate in PWM-inverter-fed induction

New family of matrix-reactance frequency converters based on unipolar PWM AC matrix-reactance choppers