Washing Machine Motor Braking with Ramped DC Injection
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Solution Overview
Problem
Conventional washing machines face challenges in braking the spin basket from operational speed to zero speed efficiently, as existing methods like dynamic and regenerative braking are costly and lead to reduced motor life due to current spikes, while DC injection braking is not suitable for full operational loads and speeds.
Innovation Solution
The method involves collapsing the motor's rotating magnetic fields for a predefined time and then applying DC braking voltage at a controlled ramp rate to generate a fixed amplitude braking torque, applicable to synchronous or asynchronous motors, including three-phase AC induction motors, to ensure safe and controlled stopping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If DC injection braking is applied to synchronous or asynchronous motors in washing machines, then braking cost is reduced and simplicity is improved, but large induced current spikes and thermal stresses are generated at higher loads and speeds, reducing motor life
Solution Approach 1:
The patent applies preliminary action by collapsing the rotating magnetic field before applying DC braking voltage. The controller disables the inverter bridge for a predetermined time period (e.g., 100-200 milliseconds) to allow the magnetic field to collapse, which prevents large induced current spikes when DC voltage is subsequently applied. This preliminary magnetic field collapse prepares the motor for safe DC braking without thermal stress damage.
Solution Approach 2:
The patent implements periodic action through the cyclic alternation between inverter operation and DC braking. The controller periodically switches between disabling the inverter (allowing magnetic field collapse) and applying DC braking voltage, creating a rhythmic braking pattern that effectively stops the motor while preventing continuous current spikes. This periodic on-off cycling of the braking mechanism protects the motor from thermal stress.
2Power
If dynamic braking is used to control power to the motor, then braking torque is proportional to kinetic energy, but braking torque decreases as load diminishes, requiring additional mechanical brake hardware
Solution Approach 1:
The patent extracts the need for additional mechanical brake hardware by using DC injection braking on the motor windings themselves. Instead of relying on dynamic braking followed by mechanical brakes, the DC voltage applied directly to the stator windings creates a stationary magnetic field that provides sufficient braking torque across all load conditions, eliminating the need for separate mechanical braking components.
Solution Approach 2:
The patent replaces the mechanical brake system with an electrical braking solution. By applying DC voltage to the motor windings, an electromagnetic braking force is generated that substitutes for mechanical friction brakes. This electrical substitution eliminates mechanical wear components and simplifies the overall braking system while maintaining effective braking torque.
3Reliability
If mechanical braking systems with brake pads or shoes are used, then reliable stopping is achieved, but cost and maintenance requirements increase due to limited design life and wear
Solution Approach 1:
The patent replaces the mechanical brake pad and shoe system with an electrical DC injection braking system. By applying DC voltage to the motor windings, electromagnetic forces create the braking effect without mechanical contact. This substitution eliminates wear-prone mechanical components, reducing maintenance needs and system cost while maintaining reliable stopping capability.
Solution Approach 2:
The motor windings themselves serve the dual function of both driving the motor during operation and providing the braking mechanism when DC voltage is applied. The existing motor structure performs the braking function without requiring separate brake components, making the system self-sufficient and eliminating the need for external mechanical braking parts that would wear and require replacement.
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
This approach reduces the drawbacks of DC braking, such as current spikes and motor wear, while ensuring compliance with safety standards like UL standards, providing a cost-effective and reliable braking method for washing machines.
Implementation Method 1
DC injection braking is a method for braking synchronous or asynchronous motors wherein DC voltage is applied to the stator windings to produce a stationary magnetic field. The spinning rotor is magnetically drawn to this stationary magnetic field, which acts as a drag (i.e., a braking force) on the rotor
Data Source
AI summary
A method of braking a washing machine from an operational speed to a zero speed is provided (as well as a washing machine incorporating the method) for a washing machine driven by one of a synchronous or asynchronous motor. Upon receipt of a stop signal, collapsing the motor rotating magnetic fields are collapsed for a predefined time period. After the predefined time period, DC braking voltage is applied to the motor stator windings at a controlled ramp-up rate to a fixed amplitude to generate a controlled ramped braking torque on the motor. The braking torque is applied until the motor is stopped.