Six-Step Motor Drive Commutation to Reduce Current Spikes
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Solution Overview
Problem
Six-step motor drives face challenges in reducing phase current spikes and surges during commutations, particularly when driving low inductance motors with imprecise commutation timing, leading to efficiency losses and reduced motor and drive lifespan.
Innovation Solution
A switching method for six-step motor drives that involves non-simultaneous switching of transistors in the output inverter, monitoring back emf across phase windings to control commutation timing, and using a current source drive with fast regulation to minimize current surges and spikes, especially effective for low inductance air core motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If simultaneous switching of off-going and on-going transistors is used in six-step motor drives, then the control and circuit design is simple, but current spikes and surges occur during commutation
Solution Approach 1:
The patent applies preliminary action by switching off the off-going transistor before switching on the on-going transistor during commutation. This sequential switching approach prevents current spikes by ensuring the off-going transistor has already stopped conducting before the on-going transistor begins conducting, thereby avoiding the harmful simultaneous switching effect while maintaining relatively simple control logic.
2Ease of manufacture
If conventional six-step commutation switching is used, then the implementation is straightforward, but phase current spikes reach twice the normal operating current or higher
Solution Approach 1:
The patent implements preliminary action by advancing the turn-off timing of the off-going transistor relative to the turn-on timing of the on-going transistor. This timing adjustment ensures that the commutation process completes before the next transistor switches on, preventing current spikes from reaching twice the normal operating current while keeping the implementation straightforward.
3Object-generated harmful factors
If precise commutation timing is used for low inductance air core motors, then current spikes are reduced, but the control system complexity increases
Solution Approach 1:
The patent applies preliminary action by introducing a fixed time advance for switching off the off-going transistor before the commanded commutation time. This approach reduces current spikes from back emf shorting in low inductance air core motors without requiring complex real-time timing adjustments, thereby maintaining relatively simple control system architecture.
Solution Approach 2:
The patent changes the timing parameter by introducing a fixed time advance offset for the off-going transistor switch-off event. This parameter modification effectively compensates for the low inductance characteristics of air core motors, reducing current spikes without increasing control system complexity.
4Object-generated harmful factors
If non-simultaneous switching of transistors is implemented, then current surges are reduced, but the switching control becomes more complex
Solution Approach 1:
The patent implements preliminary action with a fixed time advance for switching off the off-going transistor. This approach reduces current surges during commutation while minimizing the increase in switching control complexity by using a simple time offset rather than complex real-time control logic.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method significantly reduces current surges and spikes, enhancing the operating efficiency and lifespan of both the motor drive and motor, while maintaining reliable commutation and reducing the need for precise timing accuracy.
Implementation Method 1
monitoring back emf across phase windings to control commutation timing
Data Source
AI summary
A switching method for six-step motor drive with an output inverter that provides commutation switching of power to the phase windings of a driven motor includes regulating the current to the output inverter and to the motor by a variable bus.switching six transistors of a three phase H-bridge and six associated freewheeling diodes of the output inverter by a pair of two transistors to commutate power to the phase windings conducting during conduction steps, and at each commutation step one off-going transistor is switched off and one on-going transistor is switched onthe switching method further comprising monitoring of the back emf on two legs of the phase windings of the motor for determining commutation timing, and commutating the output inverter through non-simultaneous switching of the off-going transistor with switching of the on-going transistor.