Inverter Shutdown Control Under Open Contactor and Motor Rotation
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Solution Overview
Problem
Existing inverter control devices face challenges in appropriately stopping the operation of an inverter when contactors are open and a rotating electrical machine is in a rotating state, leading to increased heat generation and voltage issues due to continuous current flow.
Innovation Solution
The inverter control device performs full active short circuit control by bringing both upper-stage-side and lower-stage-side switching elements into an on state for at least one phase, allowing current to flow back between the rotating electrical machine and the inverter, thereby distributing the current flow and reducing temperature increase, and transitions to shutdown control when the rotational speed is within a defined limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If active short circuit control is performed with conventional switching element configuration, then current can flow back between the rotating electrical machine and inverter, but large current continuously flows through the inverter causing increased heat generation
Solution Approach 1:
The inverter is divided into multiple phases (three-phase system), and the active short circuit control is applied selectively to only one phase while other phases operate normally or are shutdown. This segmentation allows the return current to be distributed and limited to specific pathways, reducing overall heat generation in the inverter components.
Solution Approach 2:
The control strategy applies different operating states to different phases: one phase performs active short circuit control to enable current recirculation, while other phases may be in shutdown or normal operation mode. This local differentiation optimizes heat distribution and allows targeted current management to minimize thermal buildup.
2Ease of operation
If charge/discharge control and mixed-loop control are performed, then the inverter can be stopped, but when the rotating electrical machine rotates at relatively high speed, it becomes difficult to stop the inverter and transition to shutdown control
Solution Approach 1:
The control strategy dynamically adapts based on rotational speed conditions. At high speeds where counter-electromotive voltage is high, active short circuit control is enabled to facilitate inverter stopping. As speed decreases and conditions become favorable, the system transitions to shutdown control. This dynamic adaptation allows effective inverter stopping across a wide speed range.
Solution Approach 2:
The control mode changes based on operational parameters, specifically rotational speed and counter-electromotive voltage levels. The system transitions between charge/discharge control, mixed-loop control, active short circuit control, and shutdown control depending on the current operating state, allowing flexible adaptation to high-speed conditions.
3Ease of operation
If all switching elements are brought into off state for shutdown control, then the inverter stops operation, but when counter-electromotive voltage is higher than direct-current side voltage, shutdown control cannot be performed
Solution Approach 1:
Before attempting shutdown control, the system checks voltage conditions. When counter-electromotive voltage exceeds direct-current side voltage, active short circuit control is performed first to equalize or reverse the voltage relationship. This preliminary action creates favorable conditions for subsequent shutdown control execution.
Solution Approach 2:
The control sequence is structured to perform active short circuit control as a preliminary step under high-speed conditions, which prepares the electrical state for eventual shutdown. This staged approach ensures that shutdown control can be safely executed once voltage conditions are appropriate.
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 configuration effectively suppresses the increase in direct-current link voltage and reduces heat generation, allowing for safe and efficient stopping of the inverter operation even when the rotating electrical machine is at high speed.
Implementation Method 1
large current continuously flows through the inverter (10), and thus, heat generation by the current may increase
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
When contactors (9) are in an open state and a rotating electrical machine (80) is in a rotating state, an inverter (10) is controlled to appropriately stop operation of the inverter (10). An inverter control device (20) that controls the inverter (10) of a rotating electrical machine driving device (2) including: the inverter (10) connected to a direct-current power supply (11) through contactors (9) and connected to the alternating-current rotating electrical machine (80); and a smoothing capacitor (4) performs, when the contactors (9) are in an open state and the rotating electrical machine (80) is in a rotating state, full active short circuit control that brings an upper-stage-side switching element (31) and a lower-stage-side switching element (32) for at least one phase among switching elements (3) for a plurality of phases in the inverter (10) into an on state to allow current to flow back between the rotating electrical machine (80) and the inverter (10).