Dynamic Braking Control for Synchronous Motor Drives
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Solution Overview
Problem
Existing motor drive apparatuses face challenges in reducing dynamic braking time and extending the service life of mechanical contacts used for short-circuiting synchronous motor windings during emergency stops, as they either suffer from increased cost and complexity or prolonged braking times due to the use of mechanical contacts or semiconductor switches.
Innovation Solution
A motor drive apparatus with a dynamic braking control unit that utilizes a full-bridge inverter with semiconductor switching devices and a selector switch to short-circuit synchronous motor windings, controlling the semiconductor switching devices to minimize voltage across mechanical contacts and prevent sparking, thereby extending contact life and reducing braking time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical contacts are used to short-circuit motor windings for dynamic braking, then the braking function can be achieved, but the contact service life is reduced due to sparking and voltage stress
Solution Approach 1:
The semiconductor switching devices are turned on before the mechanical contacts close to pre-establish a low-impedance path. This preliminary action ensures that when the contacts close, the voltage across them is already minimized, preventing sparking and extending contact life
Solution Approach 2:
Semiconductor switching devices are introduced as an intermediary between the power supply and motor windings. These devices handle the high-voltage switching before the mechanical contacts engage, protecting the contacts from voltage stress and sparking
2Reliability
If semiconductor switching devices are used for dynamic braking, then contact service life is extended, but the braking time increases
Solution Approach 1:
The system merges the advantages of both semiconductor switching devices (contact protection) and mechanical contacts (fast braking). The semiconductor devices handle preliminary switching while mechanical contacts provide the final low-impedance short-circuit path for rapid energy dissipation
Solution Approach 2:
The braking process continues through multiple stages: semiconductor devices initially manage the switching, then mechanical contacts close to maintain continuous braking action. The semiconductor devices remain active to ensure continuous protection while the contacts provide sustained low-impedance path
3Ease of manufacture
If dynamic braking is applied by turning off all semiconductor switching devices, then the motor acts as a generator, but the braking time is prolonged due to insufficient damping
Solution Approach 1:
The system dynamically adjusts the braking impedance by first using semiconductor switching devices for initial deceleration, then closing mechanical contacts to provide a low-impedance path for rapid energy dissipation. This dynamic adjustment optimizes braking speed throughout the process
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 solution effectively shortens dynamic braking time and extends the service life of mechanical contacts by minimizing voltage across contacts and preventing sparking, while maintaining a low-cost and simple apparatus design.
Implementation Method 1
a full-bridge inverter with semiconductor switching devices... the semiconductor switching devices are controlled on and off to convert DC to AC
Implementation Method 2
dynamic braking that produces a dynamic braking force by short-circuiting the motor windings... the rotational energy of the synchronous motor can be quickly converted into Joule heat and dissipated through the dynamic braking resistor
Implementation Method 3
free-wheeling diodes connected in reverse parallel with respective ones of the plurality of semiconductor switching devices
Data Source
AI summary
A motor drive apparatus includes an inverter which has an upper and lower arms each provided with a plurality of semiconductor switching devices and free-wheeling diodes connected in reverse parallel with respective ones of the plurality of semiconductor switching devices, wherein the semiconductor switching devices are controlled on and off to convert DC to AC, a short-circuiting unit which includes a selector switch between motor phase windings of a synchronous motor, the selector switch being opened and closed under the control of a command, and a dynamic braking control unit which, upon reception of a dynamic braking start command, performs control so as to turn on all of the semiconductor switching devices provided in either one of the upper and lower arms and to turn off all of the semiconductor switching devices provided in the other arm, and thereafter controls the short-circuiting unit so that the selector switch is closed.