Inverter Control Preventing Overvoltage in AC Electric Systems
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Solution Overview
Problem
In alternating current electric systems, when the power converter is stopped, electromagnetic energy from the reactance component flows into the power converter, causing overvoltage and overcurrent issues, which can damage components like capacitors and batteries, and existing solutions increase cost and volume or are uneconomical.
Innovation Solution
A control method for an alternating current electric system that acquires current information to determine when current reaches zero and strategically turns off semiconductor switching elements, short-circuits electric terminals using reflux diodes, and manages arm switching states to prevent electromagnetic energy flow into the power converter during converter transition periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power converter is stopped, then the power converter can be protected from overvoltage and overcurrent, but electromagnetic energy from the reactance component flows into the power converter causing damage
Solution Approach 1:
The control device determines whether to stop the power converter in advance before electromagnetic energy can cause damage. By evaluating the state of the alternating current electric machine and predicting potential energy flow issues, the system prepares the converter for safe stopping, preventing the harmful effect before it occurs.
Solution Approach 2:
The control device continuously monitors the state of the alternating current electric machine and uses this feedback information to determine the appropriate timing for stopping the power converter. This closed-loop control ensures that the converter is stopped at the optimal moment to prevent electromagnetic energy from flowing into it while causing overvoltage or overcurrent.
2Reliability
If countermeasures such as increasing capacitance or breakdown voltage are taken, then component destruction is avoided, but cost and volume increase
Solution Approach 1:
The alternating current electric machine itself serves to prevent the harmful effect. By controlling when the power converter is stopped based on the machine's state, the system uses the machine's operational characteristics to protect the converter, eliminating the need for additional protective components like larger capacitors or higher voltage-rated parts.
Solution Approach 2:
The invention changes the operational parameters of the power converter dynamically based on the state of the alternating current electric machine. By adjusting the stopping timing according to real-time machine conditions, the system prevents electromagnetic energy from causing damage without requiring hardware changes that would increase volume or cost.
3Reliability
If a dynamic braking circuit is added, then voltage rise of the main capacitor is suppressed, but cost and volume increase significantly
Solution Approach 1:
The invention extracts and eliminates the need for the dynamic braking circuit by using an alternative approach. Instead of adding a separate braking circuit to suppress voltage rise, the system uses intelligent control of the power converter stopping timing based on the alternating current electric machine's state, removing the harmful effect without additional complex circuitry.
Solution Approach 2:
The control system uses information from the alternating current electric machine's own operation to protect the main capacitor. By monitoring the machine's state and determining the optimal stopping moment, the system prevents voltage rise in the main capacitor without requiring a separate dynamic braking circuit, thereby reducing device complexity.
4Speed
If the drive of the power converter is stopped immediately, then response time is reduced, but electromagnetic energy causes overvoltage and overcurrent
Solution Approach 1:
The control device performs preliminary evaluation of the alternating current electric machine's state before stopping the power converter. By assessing potential electromagnetic energy issues in advance, the system can stop the converter quickly when safe to do so, achieving both fast response and system safety.
Solution Approach 2:
The system uses real-time feedback from the alternating current electric machine to dynamically determine the stopping timing of the power converter. This feedback mechanism enables the converter to stop as quickly as possible while ensuring that electromagnetic energy will not cause overvoltage or overcurrent, thus achieving both speed and reliability.
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 method effectively prevents overvoltage and overcurrent, protecting the power converter and power supply, thereby increasing the safety and efficiency of the alternating current electric system without significant cost or volume increases.
Implementation Method 1
electromagnetic energy having the previously described reactance component flows into the power converter 10
Implementation Method 2
when the direction of the current flowing through each electric terminal is a forward direction from the power converter toward the alternating current electric machine
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
When the current flowing through each electric terminal of an alternating current motor 21 reaches the vicinity of zero, an operation putting the electric terminals of the alternating current motor 21 into an opened state, or putting an electric terminal into a conductive state via a reflux diode inside an inverter 11, is carried out. Herein, as an operation such that the current flowing through each electric terminal reaches the vicinity of zero, the electric terminals are short-circuited by all upper arm or lower arm switching elements of the inverter 11 being turned on. By so doing, a flow of electromagnetic energy of a reactance component of the alternating current motor 21, or the like, from the alternating current motor 21 into the inverter 11 side when the drive of the inverter 11 is stopped is prevented or suppressed. As a result of this, the occurrence of an overvoltage or overcurrent is prevented, thus protecting the inverter 11, a main capacitor 50, and a power supply, and increasing the safety of an alternating current electric system.