Inverter Protection Control for Head Capacitor Surge Suppression
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Solution Overview
Problem
Existing electric compressors face issues with inappropriate control of current flow into the head capacitor due to lack of direct information about the switch state, leading to potential switching element failure from voltage surges.
Innovation Solution
A control device with an electricity detection unit and protection control unit that monitors changes in electrical quantities to control the inverter switching elements, preventing current flow into the head capacitor by estimating the switch state based on voltage or current slope changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the head capacitor is reduced in size to reduce the electric compressor size, then the capacitance of the head capacitor decreases, but the voltage across the head capacitor decreases instantly when power is cut off, causing rapid voltage increase that may exceed switching element withstand voltage
Solution Approach 1:
The control device performs preliminary action by detecting the voltage across the head capacitor before power cutoff and predicting its behavior. When the switch is opened, the control device proactively controls switching elements to prevent current flow into the head capacitor, avoiding voltage surge before it can damage the switching elements.
Solution Approach 2:
The control device implements feedback by continuously monitoring the voltage across the head capacitor and using this information to adjust switching element control. The detection unit measures voltage, and the control device uses this feedback to determine when to activate protection mode, creating a closed-loop control system that responds to actual capacitor voltage conditions.
2Reliability
If the control device controls switching elements to prevent current flow into the head capacitor, then switching element failure is prevented, but the control device needs direct information about switch state which is not provided by the vehicle-side system
Solution Approach 1:
The control device practices self-service by autonomously determining switch state without external information. Instead of relying on the vehicle-side system to provide switch state data, the control device independently monitors voltage across the head capacitor and infers switch state from voltage characteristics, making the system self-sufficient for protection control.
Solution Approach 2:
The voltage across the head capacitor serves as an intermediary that indirectly provides information about switch state. Since direct switch state information is unavailable, the control device uses voltage measurements as a mediator to infer whether the switch is open or closed, enabling control decisions without direct communication from the vehicle-side system.
3Productivity
If the switch is opened during electric compressor operation to cut off power supply, then power management is achieved, but voltage across the head capacitor decreases instantly causing rapid voltage increase that may exceed switching element withstand voltage
Solution Approach 1:
The control device applies preliminary anti-action by preparing protection measures before voltage surge occurs. When the switch is opened, the control device immediately detects the voltage change and activates control to prevent current flow into the head capacitor, counteracting the harmful voltage surge effect before it can damage switching elements.
Solution Approach 2:
The control device converts the harmful effect of voltage decrease into a beneficial detection signal. The instant voltage decrease when the switch opens is normally harmful, but the control device uses this voltage change as a useful signal to detect switch state and activate appropriate protection control, turning a harmful event into a useful control trigger.
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 effective suppression of current flow into the head capacitor even without direct information about the switch state, thereby preventing switching element failure.
Implementation Method 1
a head capacitor that is provided to suppress a surge voltage caused by the operation of the switching elements or to smooth the direct voltage
Implementation Method 2
The inverter is equipped with a plurality of switching elements that convert a direct voltage into an alternating voltage to supply an alternating current to a stator winding of the motor
Implementation Method 3
a motor that rotates the compressor
Data Source
AI summary
A control device that includes an electric detection unit which detects an electric physical quantity relating to a head capacitor provided between a DC power supply and an inverter switching element; and a protection control unit which controls the inverter switching element in accordance with a change in the electric physical quantity so that no electric current flows to the head capacitor.