Actively Controlled DC Bus for Electric Drive Resonance
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Solution Overview
Problem
Existing electric drive systems with multiple power inverters experience resonance currents due to capacitive and inductive interactions, leading to inefficiencies and heat issues, and lack active control for bi-directional power flow and DC link resonance management.
Innovation Solution
An electric drive system with a positive DC bus connecting two power inverters, equipped with switches and a control unit that selectively allows or interrupts current flow based on power characteristics, using thyristors or IGBTs to actively control and eliminate oscillation currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple power inverters are connected via DC link cables, then power flow between systems is enabled, but resonance currents oscillate between cable inductance and inverter capacitance causing energy loss and heat issues
Solution Approach 1:
A current control device with controllable switches (IGBTs or thyristors) is introduced as an intermediary between the power inverters on the DC bus. This intermediary actively monitors and controls current flow, enabling bi-directional power transfer while preventing resonance currents from developing between the inverters, thus resolving the contradiction between enabling power flow and preventing energy loss.
2Loss of energy
If diode rectifier systems or diodes are inserted to isolate traction motors, then resonance currents are reduced, but bi-directional power flow is prevented
Solution Approach 1:
The patent replaces static isolation devices (diodes) with dynamic controllable switches (IGBTs or thyristors) in the current control device. These switches can dynamically change their state based on system requirements, allowing the system to enable bi-directional power flow when needed while actively preventing resonance currents, thus resolving the contradiction between isolation and adaptability.
Solution Approach 2:
The current control device incorporates feedback control by monitoring power characteristics (voltage, current) at different locations and using this information to selectively control the switches. This feedback mechanism enables the system to maintain isolation when resonance is detected while allowing bi-directional power flow when conditions are favorable, resolving the contradiction between energy loss reduction and power flow versatility.
3Device complexity
If DC link resonance is left uncontrolled, then system simplicity is maintained, but operational stability and diagnosability deteriorate
Solution Approach 1:
The control unit continuously monitors power characteristics at multiple locations and uses this feedback to actively control the switches in the current control device. This feedback control stabilizes DC bus currents by preventing resonance and enables better fault isolation, improving operational stability and diagnosability while adding manageable complexity to the system.
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
The system effectively reduces or eliminates resonance currents, enhances power efficiency, and allows bi-directional power flow, improving the operational stability and diagnosability of the drive system by actively managing DC bus currents.
Implementation Method 1
The first switch may be a first insulated gate bipolar transistor (IGBT) circuit, and the second switch may be a second IGBT circuit. The first IGBT circuit and the second IGBT circuit may be selectively turned on and off to control the flow of current between the first inverter and the second inverter.
Implementation Method 2
Because each of the power inverters contains one or more capacitors, a resonating current may arise that oscillates between the inductance of the interconnections in the DC link cables and the capacitance of each inverter. Resonating circuits of this type are often called 'tank' circuits, due to the 'sloshing' effect of current as it resonates between the capacitors.
Implementation Method 3
The method may further include monitoring the passing of power between the first and second locations, and removing an oscillation current between the first and second locations.
Data Source
AI summary
The present disclosure is directed to an electric drive. The electric drive may include a first power inverter, a second power inverter, and a positive DC bus connecting the first power inverter and the second power inverter. The electric drive may also include a first switch connected to the positive DC bus between the first power inverter and the second power inverter. The electric drive may include a second switch connected to the positive DC bus between the first power inverter and the second power inverter. The electric drive may further include a control unit connected to the first switch and to the second switch. The control unit may be configured to selectively allow current to pass through the first switch and the second switch.