Eiichi Ikawa

Parallel connection of grid-connected LCL inverters for MW-scaled photovoltaic Systems

This paper deals with the parallel connection of photovoltaic inverters in a large scale photovoltaic generation system. 250kW grid-connected LCL inverters are evaluated in order to achieve parallel operation of two, three, and four units, reaching a total capacity of 1MW when four units are operating. The concept is to treat these four parallel connected units as one equipment, being able to operate jointly or separately as required. Several operation conditions such as operation at different DC voltage and at different input power are tested. Results show the feasibility of the parallel connection keeping the same characteristics as a single unit, achieving a satisfactory performance for two, three and four parallel connected units.

Design and development of a 500kW utility-interactive switch-clamped three-level photovoltaic inverter

This paper introduces the development of a switch-clamped utility-interactive photovoltaic inverter intended for very large scale photovoltaic (PV) power generation. The switch-clamped inverter proposed is superior to the diode-clamped inverter in terms of converter losses and harmonic distortion, thus a high efficiency of 98.5% was achieved by applying a switch-clamped three-level inverter and latest 6th generation IGBTs. The adoption of a three level configuration, supported by CAD design tools made possible to achieve a considerable reduction in size. Factory test results are presented to confirm the inverter performance and suitability for large-scaled photovoltaic applications.

Development of a 250kW PV PCS and adaptive MPPT method

This paper presents the hardware configuration of a developed 250kW photovoltaic (PV) power conditioning system (PCS) and shows the efficiency curve both with transformer and without transformer. Also, adaptive maximum power point tracking (MPPT) method is proposed and it tracks the accurate maximum power point (MPP) during the fast changing environmental conditions. The proposed method is verified through simulations and a scaled-down experiment.

Relevant aspects in designing a photovoltaic inverter for industrial and commercial applications

This paper presents design considerations for grid connected photovoltaic inverters intended for use in industrial and commercial applications. Important aspects such as efficiency, reliability, construction constraints, control, standards and grid codes compliance are discussed. On the other hand, characteristics of a 600 V system based on Japanese standards and a 900 V system based on IEC standards are compared and discussed. Experimental data for a 2 kW down-scaled prototype are presented along with test data for 250 kW isolated and transformerless units built under Japanese standards and IEC standards.

MW-range PCS for efficient operation of large PV plants — High efficiency and less maintenance works

The paper introduces development of the high power inverters for the Power Conditioning System (PCS) for the large scale Photo Voltaic (PV) power plants. At first, the paper introduces a 500kW PCS with very high efficiency of 98.5%. The PCS also offers wide operation range in DC voltage and current. The wide operation range enhances the performance of the Maximum Power Point Tracking (MPPT) control to draw out the power from the PV cells as much as possible. Thus, the 500kW PCS maximizes the PV plant system efficiency. The key factors are the latest power semiconductor technology and circuit topology applied to the 500kW PCS. Then, secondly, the paper introduces a 100kW PCS cooled only by natural convection. This is the world first PCS eliminating the cooling fans, in this capacity range, realized by two key factors, loss reduction and sophisticated cooling design. This technology greatly reduces the maintenance works during the PV PCS life cycle and thus contributes efficient operation of PV plants. The cooling design and evaluation results are introduced in the paper. The 500kW and 100kW PCSs are expected to contribute highly efficient operation of large scale PV plants for its life cycle.

Development of grid interaction features for a utility-interactive photovoltaic inverter

This paper presents grid interaction features implemented in a utility-scaled photovoltaic inverter. The aim is to provide grid support according to applicable standards and grid codes. Islanding detection, voltage ride-through, reactive power control and active power control algorithms were developed and implemented in a 500kW and a 630kW photovoltaic inverter. Adjustable settings are provided to comply with several standards and local grid codes. Test results performed with a down-scaled inverter are presented for anti-islanding, voltage ride-through, reactive power control and other features demonstrating compliance with most relevant standards and grid codes.

Beam acceleration experiment with developed 10 MW class high-precision power supply for accelerator electromagnets

A 10 MW-class high-precision power supply was developed for the electromagnets of a large proton accelerator (J-PARC). This power supply consists of an advanced self-commutated current-source type converter (ACSC) using IEGTs and a hybrid filter. The current ripple was less than 1×10−6, and the tracking error was less than ±0.5×104. With this power supply, the proton beam was successfully accelerated to 30 GeV, which is the target energy of the first stage of J-PARC.

Consideration on self-commutated converter characteristics for DC power supply

A new DC power supply system is proposed based on the advanced current source type self-commutated convertor (ACSC). The ACSC is a network-friendly convertor and expected to achieve the high accuracy of 10/sup -5/ to 10/sup -6/ range of the DC current and required in the accelerator electromagnet application. The ACSC system performance is studied through digital simulation with the EMTDC (Electro Magnetic Transients program for Direct Currents transmission) and two control methods are discussed. A system consisting of the voltage source self-commutated convertor (VSC) and the choppers is also evaluated. Furthermore, characteristics of power conversion systems are discussed especially on the coordination between the convertor and the AC network. It is indicated that the convertor selection needs careful consideration on both the DC power quality requirements and the AC network conditions.