Independent engineering · Motor & power-electronics control
Control the current.
Make the machine work.
I’m Joshua. I develop control for three-phase brushless motors and power converters, such as dual-active-bridge (DAB) systems.
Good control starts with understanding the hardware. I like connecting the equations to what’s happening on the bench—and making that connection clear.
01 / Work with me
From a control problem
to a practical solution.
Bring me the system you’re building, the behavior you’re trying to improve, or the question you haven’t resolved yet. We’ll define the engineering work around what your project needs.
Three-phase
brushless motors
Field-oriented control, current regulation, rotor-position feedback, and operation across the motor’s speed and load range.
Control beyond
the motor
Control for power-electronics systems, such as dual-active-bridge (DAB) converters. Switching, sensing, and regulation considered together.
Understand.
Implement. Refine.
Discuss a focused design question, an implementation challenge, or support for a broader development effort.
02 / The person behind the work
Hi, I’m Joshua.
Engineer. Builder. Always curious.
I run 3 Phase Control LLC, a contract engineering business focused on motor and power-electronics control.
I’ve been working in electric motor control since 2014. My experience in control engineering spans nearly two decades, beginning with internal-combustion engine control before moving into electric motors.
I enjoy taking a difficult control problem apart until the behavior makes sense. These notes are a place to explain that thinking—with pictures, equations, and a connection back to the hardware.
03 / Engineering notes
A picture first.
Then the details.
Short explanations of the ideas behind the control. Open a note below to take a closer look.
01Why use a rotating reference frame?Three phase currents → two quantities that are easier to regulate.
Change the viewpoint.
The phase currents in a running motor keep changing. That is what we expect: the current pattern must move with the rotor. But regulating those changing waveforms directly is not the only way to approach the problem.
The Clarke transform describes the three-phase system using two stationary axes. The Park transform then turns those axes with the rotor’s electrical angle. For balanced sinusoidal steady-state operation, currents that oscillate in the phase frame become steady d- and q-axis quantities.
With the d-axis aligned to the permanent-magnet flux, the q-axis current is associated with torque production. The d-axis current also matters: its role depends on motor saliency and operating region. Two current regulators can work in this rotating frame, then transform their requested voltages back for the inverter.
The practical connection: the angle used by the transform is part of the control system. An error in that angle changes what the controller sees as d and q.
Illustration is conceptual.
02What does field weakening actually change?Speed, available voltage, and the current budget.
More speed needs voltage headroom.
As a permanent-magnet motor turns faster, its back-EMF rises. Eventually the inverter’s available voltage becomes a constraint. Adding more torque-producing current alone does not remove that constraint.
Negative d-axis current can reduce the effective flux linkage and make higher-speed operation possible within the voltage limit. That current still uses part of the motor and inverter current budget. The allowable operating point must satisfy both current and voltage constraints.
The practical connection: field weakening is an operating-region decision, not free extra speed. Current limits, motor parameters, magnet limits, and the required torque all matter. Surface-PM and interior-PM machines need different treatment.
Diagram shows current components, not a particular motor’s operating envelope.
03How does a dual-active bridge move power?Two bridges, an isolated link, and a timing difference.
Timing controls the transfer.
A dual-active bridge connects two DC ports through actively switched bridges and a transformer. The transformer provides isolation; the link inductance is central to how current changes during each switching interval.
In single-phase-shift operation, the bridges produce square-wave voltages. Their relative timing creates a voltage across the transfer inductance, changing the link current. Adjusting the phase shift controls average transferred power; reversing which bridge leads reverses the direction of transfer under the usual operating assumptions.
The practical connection: equal transferred power does not always mean equal device stress. Voltage ratio, modulation, circulating current, and soft-switching conditions affect how well a converter operates across its range.
Topology drawn in CircuitLab. Ls represents the total transfer inductance, including transformer leakage and any external series inductance. Gate drives, sensing, and protection are omitted; this is an explanatory schematic, not a simulation model.
04 / Start a conversation
What are you working on?
Tell me a little about the motor or converter, where the project stands, and what you need help with. A short email is a good place to start.
You’ll be talking directly with me.