This article provides a systematic overview of the basics of talkative power conversion (TPC). TPC is an emerging technique for simultaneous information and power transmission, in which data modulation is integrated into a switched-mode power converter. The data sequence is embedded in the ripple voltage, which is superimposing the output voltage of the converter. In contrast to conventional power line communication (PLC), TPC can be used universally, not only in grid applications. Aspects of power electronics (PE) and digital communication are presented in a structured form, including new perspectives such as multiple-input multiple-output (MIMO) techniques applied to TPC, adaptive modulation and channel coding, and advanced receiver design with adaptive channel and load estimation. The new aspects aim to mitigate the inherent shortcomings of TPC.

Talkative power conversion (TPC), which embeds information into the switching ripple to achieve the simultaneous transmission of power and data without installation of additional hardware, can reduce the additional communication infrastructure in cyber-physical systems of smart grid and renewable power plants. The TPC in DC/DC converters has been the subject of numerous investigations, but comparatively few studies have focused on the DC/AC converters. In this paper, the space-vector pulse width modulation (SVPWM)-based TPC techniques including both variable zero vector width modulation (VZVWM) and variable zero vector position modulation (VZVPM) for three-phase DC/AC converters are proposed. The DC/AC converters can transmit information to the receiver, crossing the LCL filter and power cable, with a good power quality. The sliding FFT method is employed for demodulation, and the bit rate is analyzed. Finally, simulations and experiments prove the viability of the SVPWM-based three-phase DC/AC talkative power converters with a bit rate of 100 bps and 1-blt length time delay.

Talkative power conversion (TPC), which can simultaneously transfer the energy and data by the power electronics converters and avoid using extra communication infrastructures, is an emerging technique for the digital power and digitalization of power system. In this paper, the TPC technology is used in the dual-active bridge (DAB) converter, in which the switching frequency and common phase are used as the degrees of control freedom respectively to modulate the data and power simultaneously. The transient performances of the DAB converters modulated by the PWM-frequency shift keying (PWM-FSK), which is a simple and effective technique for the TPC. The constraints on carrier frequency are derived, and the influence of data communication on power conversion is analyzed. The demodulation strategy based on the fast Fourier transform (FFT) algorithm is used to acquire the sent data. The simulation and experimental results clearly validate the effectiveness and correctness of the theoretical analysis.

Constructing the prediction intervals (PIs) for electric vehicle (EV) charging demand based on traffic flow information is crucial for the efficient operation of EV charging stations. However, due to the volatile nature of traffic flow, obtaining long-term traffic flow information (e.g., one week in advance) is challenging, particularly for multiple neighbored sites. To address this issue, this work establishes a deep learning prediction framework called Spatiotemporal Periodic Network (STPNet), which utilizes an encoder-decoder architecture. The STPNet incorporates a spatiotemporal and periodic pattern learning technique, and leverages the advantages of convolutional long short-term memory units (ConvLSTM) to quantify the uncertainty of traffic flow. Furthermore, to improve the performance of traffic flow prediction, a spatiotemporal series decomposition strategy based on Seasonal and Trend decomposition using Loess (STL) is employed, and a spatiotemporal PI performance-based loss function is creatively developed in this work. Then, the PIs of the EV charging demand are obtained based on the predicted traffic flow information and an M/M/C/K queuing model. Validated using a real-world dataset, the proposed model has been demonstrated to exhibit effectiveness in generating high-quality EV charging demand PIs for multiple locations.

In distribution networks integrated distributed generation, the forward and reverse power of power electronic transformers may be unequal. For this regard, this paper proposes a bidirectional asymmetric-power-flow isolated DC/DC (BAI-DC/DC) converter topology, which not only meets the requirements of bidirectional asymmetric power transmission, but also reduces the active device rating and increases the number of power paths, which can decrease system cost and improve system reliability. Simulation and preliminary experimental results verify the feasibility of the proposed topology.

The stringent regulations on the power quality declared in the standard IEEE 519-2014 push the companies and the power producers to install active filters to compensate the voltage harmonics distortion in the point of common coupling (PCC). However, in the case of a Photovoltaic (PV) park, the cost for an additional active filter converter can be saved by using the PV converters themselves as active filter. This solution is very attractive, but reserves several challenges. In fact, the harmonic current injection by the PV converters can generate ripples in the DC link which increases the stress on the converter components and affects the MPPT. Moreover, the overcurrent protection of the PV converter must be taken into account. In this paper a centralized optimized strategy to share the harmonic current injection among all the converters in a PV park is investigated. The optimization is formulated as a quadratic programming (QP) problem: the active power consumed by the PV park for the active filtering and the DC link ripple of the PV converters caused by the harmonic currents injection are minimized. The limit on the maximum injectable harmonic current by each PV converter are respected.

The quasi discontinuous conduction mode (QDCM) of the double active bridge (DAB) is addressed in this paper. The DAB converter usually is operated turning on always two semiconductors per bridge, and this leads to a continuous inductor current: However, a similar operation to dc/dc converters can be implemented, for this, less than two switches are turned on, at certain time, in one of the bridges; this leads to the quasi-DCM. With this mode of operation, a natural soft-switching is performed during the whole range of operation, but also low current stress is performed compared to the square modulation, not only at low power range. The modulation is relatively simple compared to other techniques. The proposed technique is described, analyzed, numerically simulated, and experimentally tested.

A modular Solid-State- Transformer (SST), typically consisting of cascaded H-Bridge (CHB) cells and isolated dc-dc converters, is considered as one of the most promising candidates for grid integration of large-scale PV systems (from MW to GW). However, the power imbalance among different modules and phases limits the operation range of SST. In this paper, a new common-dc-bus SST architecture, which consists of boost dc-de converters, isolated dc-dc converters and cascaded H-bridge cells, is proposed to solve the power imbalance issue. Power losses in the conventional and proposed common-dc-bus SST architectures are compared. Considering the characteristics of the proposed architecture, Zero Voltage Switching (ZVS) and the reactive current ratio of the isolated dc-dc converters are studied in detail. Simulation results of a three-phase 7-level large-scale PV system verify the effectiveness and feasibility of the proposed architecture.

The power electronics-based Smart Transformer (ST) can increase the hosting capacity of Distributed Generators (DGs) as well as electric vehicle charging stations and potentially reduce the reinforcements in the distribution grid by providing the DC connectivities and optimizing the capability in the secondary substations. Due to the asynchronous behaviour between the power generation in DGs and load consumption, the ST will operate in asymmetrically bidirectional power flow conditions. The power electronics in the ST can be fully used under the forward power flow condition, while only be partially used under the reverse power flow condition. This paper proposes a Bidirectional-Asymmetrical DC/DC converter in ST to reduce the cost of the power semiconductors and to satisfy the ST operating in bidirectional requirement. Under forward operation mode, the power sharing between two paralleled full bridge rectifiers in the secondary side of the proposed converter is studied and then the output impedance reshaping solution is presented to improve the dynamic performance of the output voltage under load disturbances. The simulation results clearly validate the effectiveness and feasibility of the proposed converter.

The increasing penetration of Distributed Generators (DG) in the modern electric distribution network poses high priority on the problem of the stability. In this article the Harmonic Stability of a Smart Transformer-fed microgrid is investigated under different control strategies. The considered microgrid is composed by a Smart Transformer and three Distributed Generators, considering the bandwidth of the DGs unknown. The robustness is evaluated analysing the eigenvalues as a consequence of a variation of the DGs bandwidth. The system is modelled as a Multi Input Multi Output System (MIMO); the eigenvalue based analysis is carried out to assess the stability and compare the robustness of the traditional double-loop PI and a state-feedback (SF) integral controller. The results show that the SF controller ensures a higher robustness than the traditional PI controller with respect to increasing bandwidths of the DGs.

Considering the increase in renewable generation and the consequent reduction in power system inertia, the Virtual Synchronous Machine (VSM) control method has been proposed to control power converters to emulate the inertia and other the characteristics of the synchronous machine. However, to achieve the function of VSM control, an extra energy base, typically storage, is required to connect to the controlled converter. In this work we investigate the application of the VSM control to the distribution system demand through the use of a VSM controlled smart transformer. Through control of the demand in this way, the demand itself can be used to emulate inertia and provide frequency support. This paper presents the details of the flexible demand control applied to a smart transformer supplying a low voltage distribution grid. The operation of the control is validated on scaled hardware using real time simulation with hardware in the loop. Simulations on a 400 kVA, 400 V distribution network are used to quantify the demand flexible. IEEE 39 bus is used to verify the benefit of the proposed control in terms of voltage and frequency in the power system.

The converter on the low voltage side of a Smart Transformer often has to supply unbalanced loads. The consequent neutral current flows through the DC link electrolytic capacitors in a DC-split configuration and hence represents the main cause of their overheating and of their premature failure. Since this kind of unbalanced operation is a very frequent condition to be faced, one way to extend the capacitor lifetime and the system reliability is to limit the neutral current through a zero-sequence current control. Nevertheless, this technique produces a large deviation of the PCC voltages, which no longer meet the limits set by the standards. To this purpose, the present paper proposes a zero-sequence injection technique that can achieve the best trade-off between the capacitor lifetime extension and the quality of the voltages at the PCC.

Unlike the conventional Uninterruptible Power Supply (UPS), which generally is connected to the scheduled critical loads (data centers, chemical plants and hospitals), the Smart Transformer (ST) experiences a complicated distribution grid with high penetration of Distributed Generator (DG) and nonlinear loads, leading to ST-fed distribution grid suffering from more power quality issues, due to harmonic interaction among DG, nonlinear loads and ST. Based on the CIGRE LV 50Hz distribution grid model, this paper systematically studies the impact of distribution grid integrated with DGs and nonlinear loads on grid voltage power quality by comparing various voltage FeedForward (FF) (reference and measured voltage FF), various current FeedBack (FB) (filter inductor and capacitor current FB), and various current controller (proportional and proportional plus resonant controller). In order to satisfy the standard EN50160 requirement on voltage quality, an improved voltage control strategy is proposed to improve grid voltage quality. The simulation results based on the CIGRE model clearly validate the effectiveness and feasibility of the proposed voltage control strategy.

Harmonics and load unbalance create several adverse issues in power distribution system, which are generally mitigated by bulky shunt active power filter (SAPF). This paper explores load compensation features of smart transformer (ST) in a two-feeder city center, where conventional power transformer (CPT) in one feeder is replaced by the ST whereas other feeder is continued to be supplied through the CPT. The ST is controlled not only to supply its own loads connected at the low voltage side, but also to compensate reactive, unbalance and nonlinear loads of the other feeder. This makes total MV grid currents of the combined city center balanced, sinusoidal, and in unity power factor at the point of common coupling (PCC) voltage. Therefore, in addition to providing continuous and reliable support to the ST based loads, the ST eliminates need of bulky SAPF and isolation transformer from the city center which are used for achieving reactive and harmonic current compensation. A switching model of the system is developed in power system computer aided design (PSCAD) software and implemented on a developed experimental prototype to show the capability of the ST.

Cascaded H-bridge (CHB) multilevel converters are promising candidates for large-scale grid-connected photovoltaic (PV) systems. In this paper, a new topology concept is introduced based on CHB multilevel converters and three-port dc-dc converters with isolation. This topology can handle the inherent power imbalances through the use of a single dc bus made up of ports in dc-dc converters. Simulation results of a 7-level CHB PV system are presented as a preliminary validation of the proposed topology.

Distribution grids unbalance challenges the DC-link of the Smart Transformer leading to higher ripples and then the lifetime of the DC aluminium electrolytic capacitors (AEC) is reduced. Additionally, dead time and nonlinearity characteristic of IGBT also may introduce ripple current in DC link, potentially decreasing the lifetime of AEC. Based on physical characteristic of AEC, the lifetime estimation of AEC is investigated considering aforementioned impacts. To suppress these impacts, an improved voltage control strategy that can reduce AEC current ripple and then preserve AEC lifetime is proposed. The theoretical analysis has been demonstrated by the simulation results.

This paper deals with a doubly-fed induction generator-based (DFIG) wind turbine system under grid fault conditions such as: unbalanced grid voltage, three-phase grid fault, using a high order sliding mode control (SMC). A second order sliding mode controller, which is robust with respect to matched internal or external disturbances, fast transient response and finite reaching time, is employed to reduce chattering phenomenon caused by high frequency switching of SMC, which serious exists in lower order SMC, and to overcome parameter dependence of traditional proportional integral (PI) control. In order to improve control performance of the overall system, electromagnetic power and active power oscillations elimination strategies are proposed respectively. Lastly, the effective of the proposed control strategy is verified by the simulation results of a 2 MW DFIG system.