Aalborg Inverter - A New Type of Buck in Buck, Boost in Boost Grid-Tied Inverter

This paper presents a new family of high efficiency dc/ac grid-tied inverter with a wide variation of input dc voltage. It is a boost in boost, buck in buck inverter, meaning that only one power stage works at high frequency in order to achieve minimum switching loss. The minimum voltage drop of the filtering inductor in the power loop is achieved to reduce the conduction power loss in both boost and buck mode. The principle of operation is demonstrated through the analysis on the equivalent circuits of a half-bridge single-phase inverter. The theoretical analysis shows that when input dc voltage is larger than the magnitude of the ac voltage, it is a voltage-source inverter, and on the contrary it is current-source inverter in the other mode. A 220 V/50 Hz/ 2000 W prototype has been constructed. Simulations and experiments show that it has a good control and system performance.

Active Power and DC Voltage Coordinative Control for Cascaded DCAC Converter With Bidirectional Power ApplicationTwo stage-cascaded converters are widely used in dc-ac hybrid systems to achieve the bidirectional power transmission. The topology of dual active bridge cascaded with inverter (DABCI) is commonly used in this application. This paper proposes a coordinative control method for DABCI and it is able to reduce the dc-link voltage fluctuation between the DAB and inverter, then reduce the stress on the switching devices, as well as improve the system dynamic performance. In the proposed control method, the DAB and inverter are coordinated to control the dc-link voltage and the power, and this responsibility sharing control can effectively suppress the impact of the power variation on the dc-link voltage, without sacrificing stability. The proposed control method is also effective for DABCI in unidirectional power transmission. The effectiveness of the propose control has been validated by both simulations and experiments.

A Three-Phase Isolated Bidirectional AC/DC Converter and its Modified SVPWM Algorithm

This paper proposes a three-phase isolated bidirectional ac/dc converter. The converter achieves buck-boost ac/dc bidirectional conversion, sinusoidal ac current, and high-frequency electrical isolation with single-stage structure. The traditional SVPWM algorithm should be modified to keep the voltage-second balance of the transformer. The circuit derivation, operation principles, and SVPWM algorithm are presented specifically. The solution for shoot-through problem is proposed, which does not need extra dead time. To verify the theoretical analysis, the proposed converter was simulated by MATLAB/SIMULINK and a 3 kW prototype was built in the lab. The simulation and experimental results show the high power factor and the low harmonic distortion characteristics of the circuit.

Practical Application of the Wave-Trap Concept in BatteryCell Equalizers

The use of battery-cell equalizers is mandatory in order to assure that all the cells connected in series are charged to its maximum capacity, even when they present small differences in this parameter due to several factors, such as aging, manufacturing, or temperature. Active equalizers, with a higher efficiency in comparison to passive ones, have the disadvantage of using a considerable number of components. Moreover, in the case of active equalizers with very high performance, this number can be even higher. In this paper, the use of the wave-trap concept, widely used in telecommunication systems, is studied. This concept allows the battery-cell equalizer to use its switching frequency as the control variable that decides which cell is being charged. Hence, it is not necessary to use a complex system based on a high number of controlled switches in order to determine which cell is being charged. In this way, the number of switches (and the corresponding driving signals) can be strongly minimized without reducing the performance of the system. In order to proof the validity of this concept (i.e., wave traps) in the design of battery-cell equalizers, a topology based on a half-bridge structure is also proposed in this paper. It uses only two controlled switches in order to decide which cell is charged. Experimental results are provided for a four-cell equalizer as a proof of concept.

Stochastic Small-Signal Stability of Power Systems With Wind Power Generation

Wind power has had a significant impact on power system stability due to its stochastic nature. In this paper, the impact of stochastic excitation on power-system small-signal stability is investigated based on stochastic differential equation (SDE) theory. The mechanical power input of an asynchronous wind turbine is considered as a stochastic excitation to the system and the system state equation is formulated based on SDE. The mean stability and mean square stability of such a system are demonstrated, and the steady-state expectation and covariance of the system state variables are obtained by mathematical deduction. The numerical simulations are presented on a two-machine infinite bus system and the IEEE 145-bus test system.

Application of Energy-Based Power System Features for Dynamic Security Assessment

This paper presents a novel approach to enable frequent computational cycles in online dynamic security assessment by using the terms of the transient energy function (TEF) as input features to a machine learning algorithm. The aim is to train a single classifier that is capable of classifying stable and unstable operating points independent of the contingency. The network is trained based on the current system topology and the loading conditions. The potential of the proposed approach is demonstrated with the New England 39-bus test power system model using the support vector machine as the machine learning technique. It is shown that the classifier can be trained using a small set of data when the terms of the TEF are used as input features. The prediction accuracy of the proposed scheme was tested under the balanced and unbalanced faults with the presence of voltage sensitive and dynamic loads for different operating points.

PMU-Based Detection of Imbalance in Three-Phase Power SystemsThe problem of imbalance detection in a three-phase power system using a phasor measurement unit (PMU) is considered. A general model for the zero, positive, and negative sequences from a PMU measurement at off-nominal frequencies is presented and a hypothesis testing framework is formulated. The new formulation takes into account the fact that minor degree of imbalance in the system is acceptable and does not indicate subsequent interruptions, failures, or degradation of physical components. A generalized likelihood ratio test (GLRT) is developed and shown to be a function of the negative-sequence phasor estimator and the acceptable level of imbalances for nominal system operations. As a by-product to the proposed detection method, a constrained estimation of the positive and negative phasors and the frequency deviation is obtained for both balanced and unbalanced situations. The theoretical and numerical performance analyses show improved performance over benchmark techniques and robustness to the presence of additional harmonics.

Multi-Polytope-Based Adaptive Robust Damping Control in Power Systems Using CARTAn adaptive damping control scheme based on classification and regression tree (CART) using wide-area signals is proposed in this paper. Different polytopes are chosen using classification trees. Next, a family of robust polytopic controllers is designed off-line. Finally, using regression trees and PMU data, the desired polytopic controller is identified in real time. A 16-generator, 68-bus system is used as the test system. Remote signals obtained from PMUs are employed for control purposes. The simulation results demonstrate that the proposed adaptive control scheme is able to provide adequate damping for the oscillation modes of interest with respect to varying operating conditions without any prior knowledge of the post-disturbance state.

Real-Time Price Based Home Energy Management SchedulerWith the recent development of advanced metering infrastructure, real-time pricing (RTP) scheme is anticipated to be introduced in future retail electricity market. This paper proposes an algorithm for a home energy management scheduler (HEMS) to reduce the cost of energy consumption using RTP. The proposed algorithm works in three subsequent phases namely real-time monitoring (RTM), stochastic scheduling (STS) and real-time control (RTC). In RTM phase, characteristics of available controllable appliances are monitored in real-time and stored in HEMS. In STS phase, HEMS computes an optimal policy using stochastic dynamic programming (SDP) to select a set of appliances to be controlled with an objective of the total cost of energy consumption in a house. Finally, in RTC phase, HEMS initiates the control of the selected appliances. The proposed HEMS is unique as it intrinsically considers uncertainties in RTP and power consumption pattern of various appliances. In RTM phase, appliances are categorized according to their characteristics to ease the control process, thereby minimizing the number of control commands issued by HEMS. Simulation results validate the proposed method for HEMS.