Dual Inverter Current Recirculation to Prevent Battery Short Circuits
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Solution Overview
Problem
Existing dual inverter systems face challenges in shifting from single or dual mode to active short circuit control without causing a short circuit of the battery.
Innovation Solution
A dual inverter system with a controller that executes upper and lower short circuit controls to recirculate current through the stator coil, avoiding battery short circuits by managing the switching elements and connection switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If active short circuit control is executed by closing switching elements to recirculate current, then current is effectively consumed and motor voltage is protected, but battery short circuit may occur causing system failure
Solution Approach 1:
The patent divides the protection control into two independent parts: (1) opening the connection switch to disconnect the battery, and (2) closing switching elements to recirculate current. This segmentation ensures that current recirculation cannot cause battery short circuit because the battery is already disconnected, thus resolving the technical contradiction between protection reliability and battery safety.
Solution Approach 2:
The connection switch is opened before closing the switching elements for current recirculation. This preliminary action of disconnecting the battery eliminates the risk of battery short circuit before the current recirculation path is established, allowing safe execution of protection control.
2Object-affected harmful factors
If connection switch is opened to disconnect second inverter from battery, then battery short circuit is prevented, but system cannot execute dual mode operation
Solution Approach 1:
The connection switch dynamically changes state based on operational requirements: closed during dual mode operation to enable both inverters to drive the motor, and opened during protection control to prevent battery short circuit. This dynamic switching resolves the contradiction between maintaining operational versatility and preventing harmful effects.
Solution Approach 2:
The connection switch serves multiple functions: (1) enabling dual mode operation by connecting the second inverter to the battery, and (2) preventing battery short circuit by disconnecting the second inverter during protection control. This multi-functionality allows a single component to address both operational versatility and safety requirements.
3Speed
If switching elements are closed to recirculate current rapidly, then current attenuation speed increases protecting components, but switching element load increases causing overheating
Solution Approach 1:
The patent employs periodic action by alternately closing upper and lower switching elements in different phases. During upper phase recirculation, upper switching elements conduct current; during lower phase recirculation, lower switching elements conduct current. This periodic alternation allows each switching element to cool down during its off-period, resolving the contradiction between rapid current attenuation and thermal management.
Solution Approach 2:
The patent recovers thermal management capability by utilizing the off-period of each switching element as a cooling interval. During this recovery period, heat generated during the previous conduction phase dissipates, preventing cumulative overheating while maintaining rapid current attenuation capability when needed.
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 recirculates current to the stator coil, preventing battery short circuits and reducing power loss, while maintaining high torque output.
Implementation Method 1
a current generated by an induced electromotive force of the stator coil is recirculated
Implementation Method 2
When a voltage of a direct current (DC) end of the inverter exceeds a predetermined threshold voltage
Data Source
AI summary
The dual inverter system includes a first inverter connected to one end of a stator coil of the motor and a second inverter connected to the other end. The controller can execute a dual mode in which the motor is driven by two inverters and a single mode in which the motor is driven by only one inverter. The controller closes the upper SW elements of all of the first and second inverters, opens all the lower SW elements, and closes the connection switch when the voltage at the DC end of the first inverter exceeds the threshold voltage. Alternatively, the controllers close all the lower SW elements of the first and second inverters to open all the upper SW elements and close the connection switches.