PWM Controller DC Braking Current Limiting
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Solution Overview
Problem
Existing methods for stopping permanent magnet synchronous motors, such as regenerative braking, DC braking, and reversed phase braking, face issues like excessive current generation leading to demagnetization, switching element failure, and instability, especially at high speeds, and lack control over braking power and torque.
Innovation Solution
A power converter device with a switching circuit, PWM controller, current detection means, and DC braking maximum current setup, which alternates between PWM all-phases cutoff and zero vector output to manage current flow and achieve stable braking power without external speed detection or braking means.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If DC braking is applied to a permanent magnet synchronous motor rotating at high speed, then braking force is generated, but excessive current is generated causing demagnetization, burning of motor, or breakage of switching elements
Solution Approach 1:
The patent applies periodic action by alternating between DC braking mode and PWM all-phases cutoff mode. The controller switches between these two modes periodically, allowing DC braking to provide stopping force while PWM cutoff periods prevent excessive current from causing demagnetization or damage to switching elements. This periodic switching resolves the contradiction by enabling braking force generation without sustained excessive current exposure.
Solution Approach 2:
The patent employs feedback by detecting the actual current flowing through the motor during DC braking and comparing it against a predetermined threshold value. When the detected current exceeds the threshold, the controller automatically switches to PWM all-phases cutoff mode. This closed-loop feedback mechanism ensures braking force is maintained when needed while preventing excessive current damage, thus resolving the contradiction between generating braking force and avoiding harmful current effects.
2Device complexity
If power supply is cut off to stop the permanent magnet synchronous motor, then no external braking means are required, but braking power is insufficient and stoppage takes a long time
Solution Approach 1:
The patent applies self-service by utilizing the motor's own electromagnetic system to generate braking force through DC braking mode, without requiring external mechanical brakes or additional stopping devices. The motor controller itself provides the braking function by controlling current flow during the deceleration phase, thereby reducing stoppage time while avoiding increased device complexity.
Solution Approach 2:
The patent uses periodic action by alternating between DC braking mode (which provides strong braking force to reduce stoppage time) and PWM all-phases cutoff mode (which prevents excessive current). This periodic switching enables the system to achieve fast stopping without requiring external braking means, as the motor's own electromagnetic system is dynamically controlled to provide both braking force and current protection.
3Power
If regenerative braking is used to decelerate the permanent magnet synchronous motor, then braking power can be obtained, but control means for decelerating and stopping must be provided separately and loss of synchronization may occur
Solution Approach 1:
The patent applies universality by making the single PWM controller perform multiple functions: it controls both the deceleration phase (generating braking power) and the stopping phase (executing DC braking), without requiring separate control means. The controller dynamically switches between different operating modes (PWM all-phases cutoff, DC braking, and normal operation) based on motor speed and current conditions, thereby providing both braking power and simplified control architecture.
Solution Approach 2:
The patent uses periodic action by having the controller switch between regenerative braking mode and DC braking mode at different stages of the stopping process. This periodic switching between different braking mechanisms within a single control system provides continuous braking power while avoiding the need for separate control means, and prevents loss of synchronization by maintaining active control throughout the entire deceleration and stopping sequence.
4Speed
If DC braking is applied when the motor is rotating at low speed, then stopping can be achieved, but braking force is in shortage and it takes a long time to decelerate to desired speed
Solution Approach 1:
The patent applies periodic action by switching between PWM all-phases cutoff mode and DC braking mode based on motor speed. At higher speeds, PWM cutoff is used to rapidly reduce speed. As the motor approaches lower speeds, the controller transitions to DC braking mode to provide the necessary braking force for final stopping. This speed-dependent periodic switching between modes ensures adequate braking force is available at each speed range without requiring extended stopping time.
Solution Approach 2:
The patent employs dynamics by dynamically adjusting the braking mode based on real-time motor speed conditions. The controller continuously monitors motor speed and automatically switches between different braking strategies (PWM all-phases cutoff at high speeds, DC braking at lower speeds) to optimize braking force availability throughout the entire deceleration process, thereby preventing both excessive current at high speeds and insufficient braking force at low speeds.
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
Enables stable and controlled braking power at high and low speeds, preventing demagnetization and switching element failure, while ensuring desired stopping torque without external assistance.
Implementation Method 1
a switching circuit (4), and a PWM controller means (5), which controls ON or OFF of the switching circuit (4)
Implementation Method 2
a permanent magnet synchronous motor (9)
Implementation Method 3
when running DC current to the permanent magnet synchronous motor (9), so as to execute DC braking
Data Source
Figure 1
Figure 2~3
AI summary
A power converter device for achieving a stable braking operation, preventing excessive current to flow therein, when conducting DC braking on a permanent synchronous motor, comprises: a switching circuit for converting DC to AC; a PWM controller means, for controlling ON or OFF of said switching circuit; a means for detecting or estimating current flowing through a permanent magnet synchronous motor; and a means for executing DC braking of said permanent magnet synchronous motor, wherein there are provided a DC braking maximum current setup value, which is determined from an outside or is determined in advance within an inside, and a PWM all-phases cutoff function and a zero vector output function within said PWM controller means, within said PWM controller means, whereby the PWM all-phases cutoff and the zero vector output are repeated within said PWM controller means, if a current value, which is obtained by said means for detecting or estimating the current, exceeds said DC braking maximum current setup value, when running DC current to the permanent magnet synchronous motor, so as to execute DC braking for obtaining a braking power.