A ground breaking ‘transformerless’ central inverter system for utility scale photovoltaic power plants is set to maximise investor returns  through optimised  availability, efficiency and yield. Control Techniques’ SPV is constructed using 145kWp, 176kWp and multiple 176kWp parallel connected inverter modules to produce any desired power rating up to 1760kWp.

The inverter modules are based on a mature design that is well-proven in thousands of demanding industrial applications Worldwide including the booming PV industry.  Control Techniques is now introducing a unique control methodology that enables the modular inverters to switch between standby and active states to match the instantaneous power available from the solar array; this significantly enhances both efficiency and plant availability.

The SPV inverter design focuses on reliability.  Each inverter is constructed from one or more, easy to handle, compact modules that are  mass produced  ensuring inherent quality, short delivery times and minimised spares holding. The active / standby sequence of the inverter modules rotates daily ensuring that all modules are exercised equally with the added benefit that individual modules accrue fewer operational hours per year than the alternative “bulk inverter” solution commonly found in the market. As a consequence the CT modular solution offers longer service life. Critically the SPV is extremely fault tolerant; in the event of the loss of an inverter module the system automatically isolates the single module and continues to operate efficiently and with re-optimised capacity. Often there is no reduction in output if the prevailing meteorological conditions aren’t at the optimum.  The SPV can also be oversized if required, to provide redundancy for critical installations or additional reactive power capability without additional thermal losses.

Control Techniques’ SPV inverter achieves Euro and CEC weighted efficiencies of 97.6%. However, the real gains are in the SPV’s very flat load / efficiency curve and its ability to maximise energy yield in low to medium light conditions.  The alternative to Control Techniques modular inverters are large single bulk inverters whose efficiency tumbles below 20% of rated power. The SPV sequentially energises power modules in response to varying solar irradiation eliminating the large fixed switching losses associated with bulk inverters. Regardless of power rating, SPV can turn on / off at an exceptionally low power threshold of only 900W effectively extending the length of the operational day.  The benefit of increased yield under low light conditions may not be accurately reflected by the traditional efficiency weighting methodology, particularly in less temperate zones such as northern Europe, and can have major impact on investment returns.

The energy yield of the SPV inverter is further enhanced by Control Techniques’  second generation Maximum Power Point Tracking (MPPT) algorithm.  The software is designed to track transient changes in irradiation whilst accurately determining the optimum condition across the operating temperature range of the PV plant. The MPPT range of the SPV is 400 to 800VDC, with the planned UL version operating from 300-600VDC.

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