PMSM And BLDC Inverter Braking With Multi-State Current Recirculation
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Solution Overview
Problem
Conventional braking techniques for electric motors, such as BLDC and PMSM, fail to provide rapid and controlled deceleration to a non-zero motor speed, leading to inefficiencies and potential damage due to uncontrolled current surges and voltage fluctuations.
Innovation Solution
A motor control system that implements a multi-state deceleration sequence, including a braking state, bottom-side recirculation state, regeneration state, and top-side recirculation state, to manage motor winding current and decelerate the motor in a controlled manner, preventing regenerative energy pump-back and maintaining safe current limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional braking techniques are used, then the motor can be decelerated, but the deceleration is not rapid enough and causes uncontrolled current surges and voltage fluctuations
Solution Approach 1:
The braking process is divided into multiple distinct states (first braking state, first recirculation state, second braking state, second recirculation state) that are executed in sequence. Each state performs a specific function: the braking states apply reverse voltage for rapid deceleration, while the recirculation states allow current to circulate safely through the inverter switches, preventing uncontrolled current surges and voltage fluctuations.
Solution Approach 2:
The multi-state braking sequence is implemented as a periodic cycle that repeats until the motor reaches the target speed. The controller alternates between braking states (for rapid deceleration) and recirculation states (for current management), creating a periodic action pattern that achieves both rapid deceleration and controlled current behavior.
2Loss of time
If rapid deceleration is implemented, then deceleration time is reduced, but uncontrolled current surges occur
Solution Approach 1:
The patent converts the potentially harmful back-EMF and inductive energy that would normally cause uncontrolled current surges into a beneficial recirculating current. During the recirculation states, the controller activates diagonal switches to create current circulation paths through the inverter switches, transforming the harmful energy into a controlled recirculation process that prevents voltage fluctuations and current damage while enabling rapid deceleration.
Solution Approach 2:
The recirculation states act as intermediary steps between the braking states. Instead of directly transitioning from one braking state to another (which would cause current surges), the controller introduces recirculation states as intermediaries that safely manage the current transition, allowing rapid deceleration without harmful current spikes.
3Reliability
If multi-state deceleration sequence is used, then controlled deceleration is achieved, but the control complexity increases
Solution Approach 1:
The controller dynamically transitions between different braking and recirculation states based on real-time motor conditions. The system adapts the braking sequence by monitoring current levels and adjusting the timing and duration of each state, enabling controlled deceleration while managing complexity through dynamic rather than static control.
Solution Approach 2:
The control system uses feedback from current sensors and motor speed measurements to determine when to transition between states. The controller monitors phase currents during braking and recirculation, using this feedback to timing the state transitions appropriately, which manages the complexity through intelligent control rather than fixed timing.
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 multi-state deceleration sequence enables rapid and controlled deceleration of electric motors, preventing uncontrolled current surges and voltage fluctuations, thus ensuring motor safety and efficiency while meeting stringent deceleration requirements.
Implementation Method 1
Sensor-less BLDC motors often rely on back electromotive force (BEMF) detection to determine the angular position of the permanent magnet rotor
Implementation Method 2
The braking state generates a motor winding current of a polarity that is opposite to the back-EMF voltage to create a negative, or decelerating, torque
Data Source
AI summary
A motor control system operable to control a motor includes a motor control circuit and an inverter circuit connected to the motor control circuit and configured to connect to the motor at phase output terminals. The inverter circuit, in response to one or more output control signals indicating a deceleration instruction from the motor control circuit, implements a multi-state deceleration sequence for at least one commutation state of a commutation scheme of the motor.