I am in a small hydro power generation project. According to best known system the turbine has mechanical gear boxes and belt/pully system to get controlled range of frequency, voltage and current from the generator.

The system implementation cost is high because of mechanical system. I have a rough idea for use solar inverter to get stable frequency/voltage and current. I have a small 3 phase generator and output of that will feed to a rectifier. (This rectifier system also has voltage stabilization system that suitable for solar inverter). Then rectified output will feed to the solar inverter.

How to make the rectifier for this? It should be contain voltage stabilization system also. What parameter should I consider for make such rectifier/stabilizer?


Generator s 2kW induction motor.

Simple block diagram Simple block diagram

Questions are,

Is it possible to interface below "Rectifier and stabilizer" between solar inverter and 3 phase generator? If not what are the reasons? What are the considerable parameters when designing/selecting this rectifier and stabilizer system?

  • 1
    \$\begingroup\$ Hydro and solar use different algorithms. In hydro you set the output torque to k * w^2. (k is a constant, and w is the rotational speed of the impeller or whatever it is called). In solar MPPT you discover and track the maximum power voltage by varying the output. I don't think an MPPT solar inverter will work well when matched with a hydro generator. If that is not what you are talking about, then maybe you should draw a system diagram to explain a bit better what components you have and how they will be put together. \$\endgroup\$
    – user57037
    Commented Oct 25, 2022 at 7:23
  • \$\begingroup\$ Could you give an approximate power sizing for your system? One person's small is another person's huge! \$\endgroup\$
    – jonathanjo
    Commented Oct 25, 2022 at 8:39
  • \$\begingroup\$ @mkeith I have updated the question. \$\endgroup\$
    – user_fs10
    Commented Oct 25, 2022 at 9:15
  • 1
    \$\begingroup\$ OK, well, keeping the induction generator generating could prove difficult. Induction generators typically are connected to a live grid and work well in that application. But without the grid, the field collapses and they stop generating. They can be kept generating by the use of capacitors or something like that but it is a finicky business that would work best if the load never changes. \$\endgroup\$
    – user57037
    Commented Oct 25, 2022 at 19:42
  • 1
    \$\begingroup\$ electronics.stackexchange.com/questions/156968/… \$\endgroup\$
    – user57037
    Commented Oct 25, 2022 at 19:48

1 Answer 1


I don't have any experience with hydro. I don't see any reason why you couldn't use rectifiers to make DC from the three-phase output of your generator. That is a proven principle. Mainly you need to select rectifiers that can sustain the average current you expect, and have a reverse voltage at least as large as the maximum peak output voltage. Both ratings should be generously larger than the expected values for a robust design.

Maybe it would then be necessary to put a DC-DC converter between the rectified output of the generator and the inverter input. I am not sure.

What I am much less certain about is whether the overall setup will work and respond to load changes the way you would want it to. For example, if the electrical load on the inverter is reduced, then ultimately, the electrical load on the generator will also be reduced. This will lead to reduced torque or increased speed or both. Will that cause problems for the system? I don't know.

The other issue is that induction generators require an AC voltage to be present at their output in order to function. When you tie an induction motor or generator to the grid, and mechanically overhaul it, it will naturally start generating. But if there is no grid to get it excited in the first place, it may not work properly. I have seen videos online where people succeeded in making induction motors into generators, usually using capacitors to change the power factor. My impression is that this could be a finicky process and may be subject to unexpected collapse. If you already have that issue sorted out then that is great. If not, consider this a warning.

Here is a discussion of induction generators that may be useful for you. https://acim.nidec.com/motors/usmotors/TechDocs/ProFacts/Induction-Generator


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