Micro generator platform for water and wind energy

Description

Project describes the development of an open brushless controller platform dedicated for low power energy conversion applications.

Platform is based on a well-known VESC Project, which provides a good starting point for projects related to motor control. Modifications to the embedded and PC software as well as hardware will be presented which will allow for standalone generator operation.

Goal of the project is to provide and inspire new open solutions in the field of energy conversion, either in the form of the whole system, control strategy, firmware, hardware or development/testing concept.

Details

Controller is being designed with three specific operating topologies in mind.

Current state:

We have a working software for the 1.) and 3.) topology. Next, custom HW design and software support for 2.) topology is planned.

1.) Generator is connected to a battery

Motor controller shall run a MPPT algorithm, control charging, reduce power consumption when energy conversion is not possible.

2.) Generator is connected to a grid tied micro inverter
Motor controller shall emulate a U/I load that is compatible with micro inverter MPPT algorithms.

3.) Generator is supplying a low voltage grid
Motor controller shall regulate voltage on the DC voltage grid.

Embedded SW for motor controller:
Controller can operate in different modes according to the above requirements. For motor/parameter setup existing VESC capabilities and documentation can be used.

MODE 1: MPPT + battery charging
Simple and predictable MPPT scanning algorithm was developed. Parameters can be adjusted to fit different applications (scanning time, current/torque step, maximum current, MPP timeout, starting speed etc.).

Based on the battery voltage charging current is derated at full state of charge (with adjustable voltage gap and full battery voltage).

MODE 2: Voltage regulation to support U/I curves

Voltage on the output of the motor controller is regulated by constantly adjusting motor torque. Output voltage/current curve can be parametrized to support external MPPT tracking from the grid tied inverter.
U/I curve can also be parametrized to support a constant DC voltage source within the capabilities of the mechanical energy source.

MODE 3: Simulation of rotational energy source

A simple mechanical energy source is modeled that reduces rotational speed with increasing torque (with adjustable coefficients). This mode can be used to test different generation algorithms on a back-to-back setup (two motors and controllers mechanically coupled with a coupling).

SW for PC GUI application:
Generator mode is integrated into the existing VESC GUI application. Different generation modes and parameters of the controller can be configured.

Hardware design:
A variation of low power (<50 V 1000 W) motor controller and mechanical enclosure will be proposed with improved thermal and environmental performance. A contactor on the DC link will be added to reduce current leakage when motor is not generating power. Software will still be fully compatible with existing VESC based motor controllers.

System sizing instructions:
Template for motor/controller sizing based on the system requirements will be prepared.

Project Logs

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DC supply voltage control

Mitja Breznik • 05/12/2019 at 12:44 • 0 comments

I have decided to first develop a simple DC supply voltage controller that will be the basis for two configurations described in the introduction (controller acting as a voltage source for the self sustained DC "grid"; controller connected to the grid-tied inverter).

Controller is a simple PI regulator that determines the motor torque based on DC voltage reference and measured DC voltage:

Parameters are currently set with experimentation, but there should be a simple way of defining the coefficients based on system parameters (capacitance, torque constant, rotational speed).

For the "proof of concept" test I used a simple power resistor as a load for DC supply:

Voltage reference was set at 15 V (voltage controller running at 1kHz), while resistor was connected and disconnected multiple times. Voltage remained constant while the motor current changed according the the DC supply energy demand:

Here is a video of the multimeter and power resistor connected to the controller DC terminals:

After some additional testing I will add the support of the new mode and parameters to the PC GUI.

MPPT scanning algorithm test

Mitja Breznik • 05/05/2019 at 09:24 • 0 comments

Simplest way for me to test different energy conversion functionalities is to build a back-to-back setup. I have coupled two brushless outrunners enclosed in a plexiglass tube for protection. It is not the optimum solution for long term testing, due to heat build-up, but it will suffice for SW testing.