Search

Fast frequency response (FFR) of battery energy storage system (BESS) is an effective way to mitigate the system frequency deviation induced by the fluctuation of power generation from the increased renewable energy resources and the impact of reduced system inertia caused by decreased synchronous generators. However, existing standards referring to technical requirements for the frequency measurement do not sufficiently consider abnormal grid conditions, such as voltage unbalance, frequency sweep, and dynamic voltage step. This article shows the impact of frequency measurement logic on the FFR performance of BESS in grid disturbance conditions by control hardware-in-the-loop (CHIL) testing and proposes improved frequency measurement logic based on a phase-locked loop (PLL). A benchmarking of the proposed PLL was conducted against existing PLL and discrete Fourier transformation-based frequency measurement logics. Finally, the FFR performance of BESS with each frequency measurement logic has been tested in CHIL simulation. This CHIL comprises the actual power plant controller, the actual bidirectional inverter control board, and a real-time simulator. In the CHIL experiments, several system disturbance situations likely to happen in existing power systems were considered as test cases and showed that the frequency measurement accuracy and latency were violated in some frequency measurement logics. Furthermore, this article reveals the effects of frequency measurement accuracy and latency on the FFR performance of BESS by a closed-loop power control simulation with a CHIL environment. In conclusion, considerations for the frequency measurement method used for FFR are proposed. [ABSTRACT FROM AUTHOR]

This article presents a 40-channel high-resolution automotive LiDAR system-on-chip (SoC), which utilizes the world’s first dual-data converter (DDC). The proposed DDC consolidates the functions of ADC and TDC into a single circuitry and achieves acquisition of both high-precision time and voltage data from the input, realizing a 5 $\times $ smaller analog front-end (AFE) area than prior arts. Such innovations lead us to a 40-channel AFE integration of the SoC without silicon cost increase, which characterizes our LiDAR system with 2 $\times $ higher pixel resolution. To enhance the ADC’s signal-to-noise and distortion ratio (SNDR) without sacrificing the area efficiency, a calibration-free and variation-tolerant voltage-controlled oscillator (VCO)-based ADC with a multiphase pulse density modulator (MP-PDM)-based feedback is proposed. Our proof-of-concept LiDAR system achieves a measurement range of 225 m at 70-klx direct sunlight, with a resolution of 240 $\times $ 192 pixels at 10 frames per second (FPS). To quantitatively measure the effect of the resolution improvement of our LiDAR, we evaluate the LiDAR’s detection accuracy of small targets 75 m away. Due to the 2 $\times $ higher vertical pixel resolution, our LiDAR can detect targets with 2 $\times $ smaller height. The 3-D point cloud of the LiDAR captured outdoor in the wild is presented. [ABSTRACT FROM AUTHOR]

We develop an algorithm for synthesizing a spatial pattern of charging/discharging operations of in-vehicle batteries for provision of ancillary service (AS) in power distribution grids. The algorithm is based on the ordinary differential equation (ODE) model of the distribution voltage that has been recently introduced. In this paper, first, we derive analytical solutions of the ODE model for a single straight-line feeder through a partial linearization, thereby providing a physical insight to the impact of spatial electric vehicle (EV) charging/discharging to the distribution voltage. Second, based on the analytical solutions, we propose an algorithm for determining the values of charging/discharging power (active and reactive) by in-vehicle batteries in the single feeder grid, so that the power demanded as AS (e.g., a regulation signal to the distribution system operator for the primary frequency control reserve) is provided by EVs, and the deviation of the distribution voltage from a nominal value is reduced in the grid. Effectiveness of the algorithm is established with numerical simulations on the single feeder grid and on a realistic feeder grid with multiple bifurcations. [ABSTRACT FROM AUTHOR]

Sales of electric vehicle are rapidly growing worldwide. Vehicle grid integration is important for mitigating impact of charging demand on the distribution feeders, realizing renewable powered charging from the rooftop photovoltaic and wind power generation, and contributing to the Vehicle‐to‐Grid ancillary services for the power systems. This article reviews current trends of the vehicle grid integration R&D. Future prospective is also pointed out on the key issues such as an electrical interface, multiple services integration, and the electric vehicle living demonstration for open innovation. [ABSTRACT FROM AUTHOR]

This paper presents a time-to-digital converter/analog-to-digital-converter (TDC/ADC) hybrid LiDAR system-on-chip (SoC) to realize reliable self-driving systems. The smart accumulation technique (SAT) is proposed to achieve both 200-m and high-pixel-resolution range imaging, which was untrodden with conventional LiDARs. The “smart” accumulation is realized by a simple object recognition strategy with small circuit overhead. When compared to conventional accumulations, the LiDAR range is enhanced without degrading the pixel resolution. Moreover, a TDC/ADC hybrid architecture is proposed to achieve a wide-distance-range LiDAR with a small silicon area and short-range precision. To minimize the ADC cost, a residue-quantizing noise-shaping (RQNS) SAR ADC is proposed. The prototype LiDAR SoC is fabricated in the 28-nm CMOS technology and integrated into the silicon photomultiplier (SiPM)-based LiDAR system. LiDAR measured with 240 $\times$ 96 pixels at 10 frames/s achieves a measurement range of 200 m with a 70-klx direct sunlight: the measurement range is 2 $\times$ longer than conventional designs. Furthermore, our LiDAR achieves 4 $\times$ higher effective pixel resolution compared to conventional designs using simple accumulation. A 3-D point-cloud image acquired with a real-life environment is presented. [ABSTRACT FROM AUTHOR]

Electric vehicles (EV) and photovoltaic (PV) generation are widely recognized around the world. Most EV owners in the major Chinese cities are forced to charge their EV batteries at the workplace during the daytime due to the limited space near their homes, which will increase the peak load during the daytime. On the other hand, the PV output is most likely to have a peak at around noon, which means, PVs could have a potential capability to compensate the EV charging load. An EV owner-friendly charging strategy based on PV utilization which alleviates both the EV charging constraints and the negative impact of the EV charging load on the grid is proposed. The PV utilization for compensating the unconstrained EV charging load is maximized to derive the maximum number of EVs with unconstrained charging. If the actual number of EVs exceeds the maximum number, a portion of EVs have to be charged only from the grid. Then, the line loss is introduced as the optimization objective in which the charging states are regulated. The case study shows that the proposed strategy can successfully increase the number of EVs with unconstrained charging, and reduce the peak-to-peak of the load curve. [ABSTRACT FROM AUTHOR]

The large integration of photovoltaic (PV) power generation systems into power systems causes deterioration in power system stability. In our previous work, we showed that reactive power control using the inverters of PV systems, known as dynamic voltage support (DVS) capability, is a promising approach to improve the short-term voltage stability in power systems. In this paper, we propose a novel DVS capability as a function of PV inverters. In contrast to the conventional DVS capability, the proposed method uses both active and reactive power injection to improve the short-term voltage stability. Numerical examples show that the proposed DVS capability further improves the short-term voltage stability compared with the conventional DVS capability. Furthermore, the proposed method can alleviate a frequency drop after a fault caused by interruption in PV systems. [ABSTRACT FROM AUTHOR]

SUMMARY Because of global warming, attention to photovoltaic (PV) generation has increased, and considerable PV generation capacity will be installed in the power system. In Japan, most PV generation will be connected to the distribution system, which will cause changes in power flow in the power system. Forward power flow (flow from the higher voltage system to the lower voltage system) will be reduced and reverse power flow may occur. Because of the change in power flow, the voltage characteristics will also be changed. Consequently, it is expected that the penetration of PV generation will have some impact on voltage stability. In previous studies, the voltage characteristics in a simple power system model consisting of one infinite bus, one load, and one PV power source, have been investigated. It was found that there is not only a forward power flow limit but also a reverse power flow limit (the left nose in the PV curve), and that when the output power from PV generation is very large, the left nose sometimes has some impact on voltage stability. In this paper, the voltage stability in a simple power system model considering the dynamics of an induction motor is discussed. [ABSTRACT FROM AUTHOR]

SUMMARY This paper presents a novel system reduction method which makes it possible to consider the impact of photovoltaic (PV) penetration on transient stability precisely. The object system for system reduction can be aggregated into a simple equivalent circuit by using the proposed method. The equivalent circuit consists of a lumped load model, a lumped PV model, and three equivalent impedances. Using the equivalent circuit, power flow into the object system when the system voltage changes can be analyzed without repeated power flow calculation of the original system. In order to verify the proposed method, this paper presents a numerical example of transient stability analysis with a one-generator-to-infinite-bus system model. The results of analysis indicate that transient stability considering PV penetration can be analyzed with high accuracy with the proposed method. [ABSTRACT FROM AUTHOR]

To integrate large scale renewable energy sources in the power grid, the battery energy storage performs an important role for smoothing their natural intermittency and ensuring grid-wide frequency stability. Electric vehicles have not only large introduction potential but also much available time for control because they are almost plugged in the home outlets as distributed battery energy storages. Therefore, vehicle-to-grid (V2G) is expected to be one of the key technologies in smart grid strategies. This paper proposes an autonomous distributed V2G control scheme. A grid-connected electric vehicle supplies a distributed spinning reserve according to the frequency deviation at the plug-in terminal, which is a signal of supply and demand imbalance in the power grid. As a style of EV utilization, it is assumed that vehicle use set next plug-out timing in advance. In such assumption, user convenience is satisfied by performing a scheduled charging for the plug-out, and plug-in idle time is available for the V2G control. Therefore a smart charging control is considered in the proposed scheme. Satisfaction of vehicle user convenience and effect to the load frequency control is evaluated through a simulation by using a typical two area interconnected power grid model and an automotive lithium-ion battery model. [ABSTRACT FROM PUBLISHER]

SOC (State of Charge) estimation-based battery management is essential for HEV (Hybrid Electric Vehicle) applications. The SOC can be estimated by the relationship between the OCV (Open Circuit Voltage) and SOC, which is based on the Nernst equation, in combination with Coulomb counting. However, voltage hysteresis and relaxation make measurement of the OCV difficult. The OCV measured after charge (discharge) is higher (lower) than the OCV estimated by the Nernst equation, and relaxes slowly with a time constant from a few minutes to a few hours. In this paper, to express voltage hysteresis and relaxation, a three-layer model for nickel active materials is proposed. A voltage gap between the surface and inside of the nickel active material is introduced, and voltage hysteresis is modeled with the surface partial battery governing the OCV of the whole battery. Voltage relaxation is also expressed as equalization between the surface layer and the relaxation layer with a higher internal resistance. The static and dynamic behavior of the proposed model is confirmed through experiments with a 7.2-V 6.5-Ah NiMH battery module. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(1): 1-7, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21102 [ABSTRACT FROM AUTHOR]

In recent years, the PMU (Phasor Measurement Unit) has received a great deal of attention as a synchronized measurement system of power systems. Synchronized phasor angles obtained by the PMU provide valuable information for evaluating the stability of a bulk power system. The aspect of instability phenomena during midterm tends to be more complicated, and the stability analysis using the synchronized phasor measurements is effective in order to keep a complicated power system stable. This paper proposes a midterm stability evaluation method for the wide-area power system using synchronized phasor measurements. By clustering the power system to some coherent groups, step-out is predicted on the basis of an aggregated two-machine equivalent power system. The midterm stability of a longitudinal power system model of Japan's 60-Hz systems constructed by a hybrid-type power system simulator is practically evaluated using the proposed method. [ABSTRACT FROM AUTHOR]

We examined electrocochleogram (ECochG) and transiently evoked otoacoustic emission (TEOAE) on five cases of sudden sensorineural hearing loss which had no abnormalities detected on diagnostic imagings and showed complete recovery of hearing. At the initial examination, three cases showed a broadened wave I with prolonged latency in the auditory brainstem response (ABR) at 90 dB HL. The ECochG AP showed a broad waveform, low amplitude, and high threshold. CM threshold, although increased, was relatively well preserved compared with hearing threshold measured with conventional pure-tone audiometry. The thresholds in TEOAE examination were similar to those for CM and preserved better when compared with pure-tone audiometric thresholds. These findings suggest that the location of the disorder in these three cases involved not only the cochlea but also the retrocochlear auditory pathway. The other two cases showed normal ABR waveforms at 90 dB HL at the initial examinations. ECochG examination showed that a normal AP in one case and a smaller amplitude AP, an elevated threshold, and normal waveform of AP in the other ear. CM thresholds coincided with the conventional audiometry thresholds. These findings suggest that hearing loss in these two cases involved primarily the sensory hair cells. [ABSTRACT FROM AUTHOR]