Motor Control Apparatus Discharge Smoothing Capacitor Charge
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Solution Overview
Problem
Existing motor control apparatuses face issues with current flow through motor windings due to timing deviations and resistance variations in switching elements, leading to potential electric shock and motor rotation, even after the DC power source is disconnected.
Innovation Solution
A motor control apparatus with a control circuit that sets both switching elements of a single switching circuit in the conducting state to discharge the smoothing capacitor's residual charge, while setting all other switching elements in the non-conducting state, ensuring no current flows through the motor windings, and optionally using a DC-to-DC converter circuit for additional discharge paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If all switching elements are set in the on state to discharge the smoothing capacitor, then the stored charge is discharged effectively, but timing deviations cause momentary high current flow through motor windings
Solution Approach 1:
The patent segments the discharge process by dividing the switching elements into two distinct groups: a first group (connected to positive terminal) and a second group (connected to negative terminal). This segmentation allows independent control of each group, enabling sequential discharge operations that prevent simultaneous conduction paths through motor windings, thereby eliminating the risk of momentary high current flow while still achieving effective charge discharge.
Solution Approach 2:
The patent applies preliminary action by first setting the switching elements of the first group to the on state to initiate discharge, and only after this is established does it set the switching elements of the second group to the on state. This sequential preliminary action ensures that discharge current flows through controlled paths without creating unintended current loops through motor windings, preventing electric shock hazards before they can occur.
2Reliability
If switching elements have different on-state resistance, then discharge current flows through motor windings, but uniform resistance control is difficult
Solution Approach 1:
The patent segments the switching elements into two independently controllable groups based on their terminal connections. This segmentation allows the control apparatus to manage discharge current paths separately for each group, compensating for resistance variations by controlling which group is active at any given time, thereby maintaining reliable discharge control despite device characteristic variations.
Solution Approach 2:
The patent implements dynamic control by sequentially switching between different groups of switching elements rather than activating all simultaneously. This dynamic approach allows the system to adapt to resistance variations in real-time, selecting optimal discharge paths that maintain reliability while accounting for individual element characteristics.
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
Effectively prevents electric shock and current flow through motor windings by controlled discharge of the smoothing capacitor's charge, ensuring safe operation and preventing damage to switching elements.
Implementation Method 1
a smoothing capacitor CN for smoothing a DC voltage from a DC voltage source PW
Implementation Method 2
the control apparatus applies control whereby both of the switching elements of a single switching circuit are set in an on state
Data Source
AI summary
A motor control apparatus has a plurality of DC-to-AC inverter circuits which supply respective electric motors, each inverter circuit formed of a plurality of switching circuits, all of the switching circuits being connected in parallel with a smoothing capacitor which smoothes a DC voltage. A charge which remains in the smoothing capacitor, after the source of the DC voltage has become disconnected, is discharged through a single switching circuit in each of the inverter circuits, with all other switching circuits of each inverter circuit being held in a non-conducting state, thereby preventing a flow of discharge current through any of the motors.