Voltage-Offset Resistive Control for Photovoltaics

This thesis introduces voltage-offset resistive control (VRC) for photovoltaic (PV) applications that exhibits low sensitivity to solar irradiance changes. Although there are numerous control schemes and maximum power point tracking (MPPT) methods for PVs, few focus on maintaining low sensitivity to irradiance transients. Daily PV electrical characteristics are observed to identify trends in the maximum power point (MPP) movement. Analysis shows that VRC has inherently low sensitivity to irradiance changes and is an effective inner-loop control method to maintain operation at the MPP. For the buck and boost dc-dc converter, simple control equations that represent the ideal VRC equilibrium are examined for stability. Small- and large-signal analyses show that one control equation for the boost converter is stable over the intended operation range???with some limitations based on component values. VRC is implemented using a digital controller on a boost converter PV module. Steady-state stability is verified, and irradiance and control parameter step responses are observed through simulated and experimental results. VRC exhibits stability and fast transient response; it is promising as an effective inner-loop control scheme. A number of MPPT methods that utilize VRC for low irradiance sensitivity are introduced. These methods take measurements and adjust the control periodically; control parameters are held constant between measurements. This sample-and-hold control approach reduces controller computation requirements and power consumption. Traditional and VRC MPPT methods that utilize sample-and-hold operation are compared through simulation. The fractional open-circuit voltage VRC and MPP-current-based VRC methods are identified as effective and simple control solutions for PV systems that maintain high efficiency under irradiance transients