Connecting varaible DC to PV input of Solar MPPT inverter

Question

I have a synchronous alternator with output of 170~220 VAC and 40~60 Hz (1200-1800 RPM). I am designing a system to stabilize my output to 220 VAC and 50 Hz. So I am working on AC-DC converter that can handle my output, but my question: Can I take the converted DC (70 VDC~120 VDC) and connect it to the PV input of solar inverter? Will the inverter accept this? Here is the inverter I intend to use https://goo.gl/Vb2ybG My load will be 4 KW max. Thank you.

Summary of Specs:

Inputs:

• Alternator 170~220 VAC and 40~60 Hz, hydraulic oil motor control input, response time and power out (12 KW).
• AC-DC Converter output 70 VDC~120 VDC, Max power ( 5KW )

Outputs:

• Load 4kW max for Converter, Current, max( unknown), Pulse load max( unknown), kVAR load max ( unknown )
• %load regulation (unknown)
• % speed and phase regulation of alternator ( unknown)
• Power factor ( 0.85 )

Answer 1

This project of yours may work, but I highly doubt that it will fulfill your expectations.

Here's why:

Solar PV inverter will search for MPPT, and, assume the source has a V-I curve of a solar panel. Now, your generators VI graph and MPPT point is much different than that. Because of that, the inverter will never catch the MPPT. Its output will fluctuate. So if there is an option to shut off MPPT, please do so.

Secondly, how will you rectify 4kW of AC power to DC? Just using diodes and capacitors? You'll need huge capacitors and the level of harmonics in the DC side will probably cause the solar inverter to go insane. The inverter probably will have a modulated output.

I think you'll be better of with a pure sine inverter and batteries instead of capacitors.

Answer 2

You cannot begin to design anything until you explicitly define all the Specs.

This includes all inputs, outputs, functions and operating conditions.

It includes the functions of every power and signal I/O, signal feedback , signal conditioner and control mechanism with the transfer function, fault detection and protection limits.

When you can do this , one can say you understand the requirements and have parameters to test for design verification, corrections and changes until it satisfies all the requirements.

Until then , time is better spent , learning what specs are needed and avoid implementation thoughts at all costs. It's also essential to become familiar with component specs for switches, chokes, caps for the limits and non-ideal parameters like ESR, DCR, SRF, RdsOn, PIV, SOA limits.

Once you perfect this way of thinking, you will think like a professional designer, the technical problems and solutions become easy and with experience, even trivial.

My best hint, is to learn to analyze s parameters and z parameters which is the ratio of inputs and outputs. We often talk about ESR and Load regulation which is inversely related. By understanding the impedance of your grid and the problems and your solutions, you will learn the Law of Conjugate Impedance matching and how to predict performance based on knowing the impedance of everything including your PV under varying Solar Conditions. So if you understand the Impedance of every component and can find linear and non-linear properties, you can simply apply Ohm's Law where the range is linear for complex functions, such as MPT. So in short study impedance both linear and nonlinear with DC and Z(f). Then you will find the field of Spectroscopy and Control Systems Engineering, much easier.

Others may not know these parameters yet have simple GTI's that work some of the time, but not know when they will fail.

e.g. By understanding the specs and response mechanisms and impedance to impulses, steady line frequency and switched surge voltages or step load power with inertial mass (or lack of ) on the alternator, control systems are then more successful with defined transfer functions.

In short; you have much more to learn.