Sinusoidal mains inverter is so simple to design? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: December 31, 2022, 01:07:02 pm
content: Hi,Why is the sinusoidal mains inverter said to be so difficult to design?The attached LTspice does it no problem..There is no need even to adjust the amplitude of the reference sine wave.If you change the load on the output, it automatically changes the sinusoidal current to suit it...and puts the same sine voltage across it.All open loop!Why is this said to be so difficult?(Not Grid_tied here, of course)Generating the ref sine signal....i'd say this is best done by a mini LLC converter, wouldnt you agree?....tap off the sine with a current transformer, and use that as the ref sine? Big L and C values for 50Hz sine, but low current. AYK, its a train of half-sines thats actually needed (rectified sine)As you know, when the load is purely a resistor of constant value, then the simple inverter principle above applies, but when there is rapid load changing , or non linear loads, then we need a control algorithm to be added.Though the below appears to be the only chipset available to do this quickly. Do you know of any others?https://www.ti.com/lit/ug/tiduay6e/...185&ref_url=https%3A%2F%2Fwww.edaboard.com%2F

author: SeanB
author_rank: Super Contributor
timestamp: December 31, 2022, 02:02:25 pm
content: Comes down to the cost of the magnetics to filter, and also peak current in the switching devices, and thus the losses in them. Yes you can do it, but the inductors and capacitors ramp up with power in a non linear manner, so that doubling the power output needs magnetics with around quadruple the volume, and around triple the mass of copper in them. As well you need to switch the power devices rather hard, and also this means you need high power in the driver, and high losses in the devices as well.You see this in inverter generators, where the pure sine version is around three to four times the cost of the same size regular generator, just so you can have an output with dfixed frequency and voltage, and so you can still have full voltage at reduced load, with reduced engine RPM and thus reduced fuel use.

author: Faringdon
author_rank: Super Contributor
timestamp: January 01, 2023, 03:53:10 pm
content: Thanks, Generating the ref sine signal....i'd say this is best done by a mini LLC converter, wouldnt you agree?....tap off the sine with a current transformer, and use that as the ref sine? Big L and C values for 50Hz sine, but low current. AYK, its a train of half-sines thats actually needed (rectified sine)

author: langwadt
author_rank: Super Contributor
timestamp: January 01, 2023, 10:33:37 pm
content: Quote from: Faringdon on January 01, 2023, 03:53:10 pmwhy? just use an MCU

author: David Hess
author_rank: Super Contributor
timestamp: January 02, 2023, 02:23:29 pm
content: Take a look at how class-D audio amplifiers work.

author: Faringdon
author_rank: Super Contributor
timestamp: January 02, 2023, 04:46:56 pm
content: Thanks, i agree, as such the class D audio amp is essentially how a 50Hz inverter operates.It needs the 50Hz sine ref as you know...only other (analog) way to make a 50Hz sine signal i can see at the moment is to rc filter a 50Hz square wave, and then amplify it back up? Plus ideal diode rectification because we only want a train of positive haversines....of about 1V peak.

author: langwadt
author_rank: Super Contributor
timestamp: January 02, 2023, 04:50:58 pm
content: Quote from: Faringdon on January 02, 2023, 04:46:56 pmhttps://en.wikipedia.org/wiki/Rube_Goldberg_machine

author: schmitt trigger
author_rank: Super Contributor
timestamp: January 02, 2023, 04:57:38 pm
content: The difficulty with the design of a *reliable* power converter of any kind, is the operation and protection of the device during overload and out of bounds operation.Adverse conditions are many: short circuit, overloads, low power factor loads, nonlinear loads, back-emf, the list is long.