Thursday, November 27, 2014

Solar/Mains SSR-Switched Electrical System Design, Version 1 - Off-Topic Electrical System Design Idea Nr 4234

The following represents a second draft of my own written response to a discussion forum item, this evening. The initial question was, essentially, to illustrate an application of a comparator element, within an electrical circuit -- as in a context near to a discussion of op-amps, though of course a comparator is not essentially an op-amp.

Sure, the initial question sort of  asks for a response that would require a respondent to pull a design out of thin air. Having tried to find any sort of an interesting, practical application of this particular kind of electronic systems component to respond about, then, I had thought - at first - that a comparator could be used for a switched power supply. That's really a stretch, I know -- moreover, an instance of confusing a comparator with a switch -- but at least it fits the requirement of providing a practical example of a comparator, insofar as at least illustrating a hypothetical application of that one of many different types of electrical circuit element.

Proceeding as to refine the design I proposed in my response, I've been able to sketch up at least a high-level block diagram for ... some electrical things and stuff -- nothing competitive, but insofar as it would involve a circuit onto AC mains, nothing I'll share unless it was a thoroughly tested design.

The following is now my note's page for such a thing, which here I'll share for later reference.

A comparator may be applied as a voltage switch, perhaps in designing a circuit for a switched power supply of two possible voltage sources, wherein at least one voltage source may provide a varying voltage over duration of time. A single comparator would provide an output for a single voltage source providing an input of a higher voltage.  (Ed. Note: This is where I began confuse a comparator with a switch)

If a power supply would need to switch between more than two voltage sources, and only comparators would be available, then perhaps multiple comparators could be cascaded, with or without additional solid-state circuit elements in the cascade design.

Candidly, this may present an essentially crude design description. With some further refinement in the design, perhaps a comparator element could be of use for a battery switching circuit, such as in a solar electrical system -- namely as to provide a continuous output voltage and output current, across the output cycle of the solar cells and the charge cycle of any number of batteries. 

Alternately, a digital switching circuit could be applied, together with a programmed AVR microcontroller -- as in the Instructables items, below --implementing a PWM controlled charging model between the solar cells and the batteries, along with additional control and display functionality, in the solar/battery/load electrical system.

(Ed Note: The following paragraph represents, essentially, an instance of confusing a comparator with a switch)
Alternately, perhaps a comaprator circuit may be applied in a switching model for a combined grid/off-grid electrical system -- as for switching onto AC residential mains, outside the system's inverter, in case of battery under-voltage or other solar system failure, to the reference point of the inverter's output. In such an application -- in a simple view, albeit -- perhaps an AC coupled comparator would be applied, if having an input frequency range compatible with AC mains current. Perhaps a relay-driven switch with a solid state relay might be more readily applicable, for switching the input at a point beyond the inverter, in such a system.

Works Consulted:

[1] Op-Amp Comparator Circuit
[2] Op-Amp Schmitt Trigger Circuit 
[3] Instructables.  Arduino Solar Charge Controller (Version-1)
[4] Instructables. DIY Off-Grid Solar System 
[5] Texas Instruments.  AC Coupled Comparator Reference Design  (60 Hz not within input frequency range, component probably not designed for application on AC residential mains)
[6] Phidgets. Solid-State Relay Primer

DPDT solid state relay: Charter Electronics 38.21 

Residential/Household Electrical - Concepts and Standards
Comparators - Additional Reources: