Nobuyuki Hattori

Controller design of a grid-tie inverter bypassing DQ transformation

This paper proposes a novel approach for the controller design of a three-phase grid-tie inverter. First, the paper analyzes the input-output map of the system consisting of the cascade connection of a diagonal transfer function pre- and post-multiplied by DQ (direct-quadrature) and inverse DQ transformations which are prevalently used as a controller for systems with a rotating axis. It shows that the input-output map is time invariant when the angular velocity of DQ transformation is constant and derives the transfer function. It extends the result when the angular velocity is not constant, and derives an LPV state-space representation of the input-output map. Second, the paper analyzes the input-output map in terms of the positive and negative phase sequence components. Finally, the paper applies the analysis to the controller design for a grid-tie inverter bypassing DQ transformation. The efficacy of the proposed method is verified by a simulation and an experiment.

Decentralized Voltage Regulation for PV Generation Plants Using Real-Time Pricing Strategy

Photovoltaic (PV) generation may cause a voltage rise at the interconnection point due to reverse power flows, and it is recognized as a critical issue for keeping power quality. This paper investigates a decentralized management problem of power conditioning systems (PCSs), which are used to interconnect the PV system into the power grid. We consider a real-time pricing strategy of the operator, a management office of a PV generation plant, and each PCS determines own set points of the active and reactive power injections by solving an individual small-size optimization problem that includes the conceptual price provided by the operator. This feedback interaction between the operator and PCSs eventually suppresses the voltage deviation. The effectiveness of the proposed real-time pricing and distributed decision-making methodology is evaluated through the numerical experiments, as well as the real physical experiments.

Distributed active and reactive-power flow management for grid voltage maintenance using real-time pricing strategy

This paper investigates the distributed voltage control problem of a distribution power grid in which a voltage rise occurs due to reverse load flow from distributed generators. A centralized operation to regulate the grid voltage becomes difficult, since the number of distributed generators involved is large. This paper considers a real-time pricing strategy and distributed optimization by each distributed generator. An independent entity or community manager called a utility, who maintains the grid voltage, tries to determine and provide an additional price, which conceptually represents tax or subsidy to each distributed generator. The distributed generator decides its desired output by solving an individual optimization problem including the provided price. This feedback interaction between the utility and distributed generators eventually maintains the grid voltage. The effectiveness of the proposed real-time pricing and distributed decision making methodology is evaluated through a numerical experiment.

Decentralized control of inverter networks for PV generation plants using real-time pricing strategy

Global warming and the depletion of fossil fuels encourage installing a large scale PV (photovoltaic) system. The large scale PV system may cause a issue of the voltage rise at an interconnection point due to the reverse power flow. This paper investigates the distributed management problem of PCSs (power conditioning systems) which are used to interconnect the PV system to the power gird. We consider the real-time pricing strategy of the utility, a management office of the PV systems, and each PCS determines own reference input of the reactive power flow by solving the optimization problem including the provided price. This feedback interaction of the utility and PCSs suppresses the voltage deviation. The effectiveness of the proposed distributed management methodology is evaluated through the real physical experiments.

Decentralized active and reactive power control for PV generation plants using real-time pricing strategy

PV (photovoltaic) generation may cause voltage rise at the interconnection point due to reverse power flow, which is recognized as a critical issue for keeping power quality. This paper investigates a decentralized management problem of PCSs (Power Conditioning Systems) which are used to interconnect the PV system into the power grid. We consider a real-time pricing strategy of the operator who plays the role of a management office of a PV generation plant. Each PCS determines own set-points of the active and reactive power injections by solving an individual small size optimization problem that includes the conceptual price provided by the operator. This feedback interaction between the operator and PCSs eventually suppresses the voltage deviation. The effectiveness of the proposed methodology is evaluated through the numerical and real physical experiments.

High efficiency of 3-level inverter embedding neutral point voltage shifting control

Recently renewable energy has attracted a lot of attention and solar power generation systems and wind power generation systems are widely used as public eco-awareness increases. Generally inverters are used in such power generation systems. They need high efficiency. Multi-level technique improves efficiency of inverters. We proposed neutral point voltage shifting control.(1)(2) for 2-level inverters to achieve high efficiency of the inverters before. It is difficult to apply our neutral point voltage shifting control to 3-level inverters. In this paper, we propose a new neutral point voltage shifting control for 3-level inverters.

Stabilization techniques of power hardware-in-the-loop simulation with time delay compensation

In power electronics, Power Hardware-in-the-loop Simulation (PHILS) which consists of Hardware part and Digital Simulator part has attracted attention. This is the very useful tool to shorten development time and to simplify verification under complicated condition. However, it is known that instability is caused by the time delay between Digital Simulator and Hardware. This paper applies two methods to manage instability. One is model-base Smith method, and the other is the model-free Fictitious Reference Iterative Tuning (FRIT) method. Experimental results indicate that two methods are effective in compensating the time delay and stabilizing PHILS system.

Fast and high-precision phase detection of positive phase sequence component by three phase PLL with complex coefficient filter

A power grid connected inverter is operated in synchronized with reference ac voltage at the point of common coupling. The robust phase detection is indispensable for inverter operation in harsh condition. The phase detection system is required to be immune to unbalance and distortion of ac voltage waveform. A complex coefficient filter can discriminate positive and negative frequency component in input signal, which cannot be attained for conventional real coefficient filter. This paper studies the applicability of infinite impulse response digital filter with complex coefficient to a phase detection system by phase locked loop (PLL) for three phase ac system. The frequency characteristics and dynamic response of the filter is assessed, and series connection of band pass and notch filter is evaluated to satisfy both required performance. The phase detection system is implemented in the digital processor hardware and the applicability of the complex coefficient filter is experimentally evaluated.