Ts Doorn

Module-Level DC/DC Conversion for Photovoltaic Systems: The Delta-Conversion Concept

Photovoltaic (PV) systems are increasingly used to generate electrical energy from solar irradiation incident on PV modules. PV modules are formed by placing many PV cells in series. The PV system is then formed by placing a number of PV modules in series in a string. In practical cases, differences will exist between output powers of the PV cells in the various PV modules, e.g., due to (part of) the modules being temporarily shaded or pollution on one or more PV cells. Due to the current-source-type behavior of PV cells and their series connection, these differences will lead to a relatively large drop in PV-system output power. This paper addresses this problem by adding dc/dc converters on PV-module level. The so-called delta-conversion concept is introduced that aims at averaging out differences in output power between groups of PV cells within modules and between modules inside the PV system. All groups of PV cells can then output their maximum available power, such that a drop in output power of the total system is prevented. This paper describes implementation details, compares the delta-conversion concept with other state-of-the-art module-level power-conversion concepts, and presents first measurement results obtained with a demonstrator system.

A Cell-Level Differential Power Processing IC for Concentrating-PV Systems With Bidirectional Hysteretic Current-Mode Control and Closed-Loop Frequency Regulation

This paper describes an integrated power management IC with bidirectional current capability, aimed at compensating differences in output current between series-connected cells in concentrating photovoltaic (CPV) systems. The integrated 3.6-MHz power stage allows building a small-form-factor converter per cell. A hysteretic current-mode controller regulates the bidirectional converters current to equalize neighboring cell voltages. A phase-locked loop controls the inductor current ripple around the average value to stabilize the switching frequency. The use of hysteretic current-mode control with a novel bidirectional senseFET scheme provides inherent current protection and high reliability. The converter can operate from an input voltage as low as 1.8 V and with an inductor current up to ±1.5 A, while achieving a system efficiency above 90% for current mismatches between cells up to 60%. Measurement results show that the converter maximizes the output power of series-connected CPV cells with mismatched output currents.

A cell-level power management IC in BCD-SOI for partial power processing in Concentrating-PV systems

This work presents a power management IC used to mitigate the effects of mismatch in Concentrating-Photovoltaic (CPV) systems. The IC contains a bi-directional dc-dc converter, an auxiliary boost converter to generate the internal 10 V power supply, as well as protection and monitoring circuits. The main power converter, with a maximum current rating of 1.5 A, is designed to equalize the voltage between neighbouring CPV cells by using the Δ-converter approach. Due to partial power processing, the converters power rating and efficiency requirements are relaxed, leading to a more cost-effective solution with a high switching frequency of 3.6 MHz. An on-chip, mixed-signal controller regulates the main converter using a digital voltage loop and an analog hysteretic current-mode loop. The IC has several advanced features to reduce the light-load power consumption, including burst-mode operation in both the auxiliary and main-stage converters, as well as an input supply switching scheme for the internal linear voltage regulators.

A driver IC for photovoltaic module-integrated DC/DC converters

Photovoltaic (PV) installations suffer from a disproportional decrease in output power in case irradiance differences are present in the system. The Delta converter improves the output power in such cases by routing current differences around the shaded substring or module. This paper presents a driver IC for the Delta converter that simultaneously reduces its cost and improves its reliability. The driver IC integrates the complete control loop, power supplies, protections and references. The driver IC demonstrated trouble-free operation for 3 months under real-life conditions in a PV installation with different shading patterns. Depending on the shading pattern the Delta converter energy gain was 8%-18%.

Robust low power embedded SRAM design: from system to memory cell

Low power memories continue to be an important topic for low power digital design, especially in light of the recent focus on green products. Voltage scaling for some time was a natural part of technology scaling, which automatically resulted in power reduction. For sub-100nm technologies it has been difficult to reduce active power consumption for SRAMs, because the amount of memory in digital ICs is still increasing and the memory bit cell does not allow a lower supply voltage without a severe area penalty. However, voltage scaling is not a goal in itself, and a variety of techniques exist to achieve low power. This paper gives an overview of the trends in technology scaling and its impact on low power memory design. The most important techniques that are used to make low power SRAM are discussed, and system level considerations are given, including trade-offs on the selection of SRAM and DRAM. For advanced technologies, SRAM variability is an important topic. Lowering the supply voltage to save power increases the sensitivity of SRAM to variability and reduces its robustness. Simulation approaches used to guarantee high yield even for large amounts of SRAM are discussed. A combination of these methods and techniques helps to achieve low power, yet robust systems.