Asymmetric Full Bridge Switching Device for Synchronous Machine EMC
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Solution Overview
Problem
Existing control methods for separately excited synchronous machines in hybrid or electric vehicles suffer from high-frequency interfering currents due to parasitic capacitance charging and discharging, leading to electromagnetic compatibility (EMC) issues and potential bearing damage, which known EMC filters cannot fully mitigate.
Innovation Solution
A new short-circuit branch is introduced in parallel with the bridge branch, where switches T1 and T2 are switched synchronously, and a diode or switchable semiconductor element is used to ensure continuous current flow, compensating for parasitic capacitance effects and reducing EMC issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If asymmetric full bridge control is used with one switch permanently on, then current regulation is simple and reliable, but high-frequency interfering currents occur due to parasitic capacitance charging and discharging
Solution Approach 1:
The patent converts the harmful high-frequency interfering currents generated by parasitic capacitance into a beneficial effect by using them to charge a capacitor during the short-circuit phase. This stored energy is then used to suppress bearing currents and reduce electromagnetic interference, transforming a harmful phenomenon into a protective mechanism.
Solution Approach 2:
The patent introduces a capacitor as an intermediary element that stores energy during the short-circuit phase and releases it during the excitation phase. This capacitor acts as a mediator that decouples the harmful high-frequency currents from the power electronics and on-board network, preventing their propagation while maintaining current regulation functionality.
2Object-generated harmful factors
If symmetric operation with both switches switched simultaneously is used, then parasitic capacitance effects are compensated, but rotor current ripple increases and control accuracy reduces
Solution Approach 1:
The patent employs asymmetric switching where one switch (T1) is permanently on while the other switch (T2) is pulse-width modulated. This asymmetric configuration prevents simultaneous switching of both switches, thereby avoiding the strong rotor current ripple that would result from symmetric operation, while still compensating for parasitic capacitance effects through controlled short-circuiting.
Solution Approach 2:
The patent uses periodic pulse-width modulation of switch T2 at a frequency of 10 kHz, alternating between excitation and short-circuit states. This periodic action allows controlled charging and discharging of parasitic capacitances without causing the harmful simultaneous switching effects, maintaining both parasitic capacitance compensation and control accuracy.
3Measurement precision
If PWM frequency of 10 kHz is used for current regulation, then good overall regulation is achieved, but bearing currents increase due to parasitic capacitance charging and discharging
Solution Approach 1:
The patent converts the harmful bearing currents caused by parasitic capacitance charging and discharging into a beneficial effect by using the same charging/discharging process to charge a capacitor that subsequently suppresses bearing currents. The high-frequency switching necessary for good current regulation thus becomes part of the solution rather than just the problem.
Solution Approach 2:
The patent introduces a capacitor as an intermediary that absorbs the high-frequency charging and discharging currents during PWM operation. This capacitor mediates between the parasitic capacitances and the bearing, preventing harmful bearing currents while allowing the PWM regulation to function effectively at 10 kHz.
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 solution significantly reduces EMC problems by canceling out interfering currents and maintaining continuous current flow, thereby minimizing bearing damage and electromagnetic compatibility issues while maintaining control accuracy and reducing acoustic radiation.
Implementation Method 1
The charging and discharging of the parasitic capacitances necessarily present in any SSM is, however, disadvantageous for this type of asymmetric control.
Implementation Method 2
The polarity of the parasitic capacitances in the region of the rotor of the SSM are here inverted in opposite senses. The interfering current with respect to a ground potential is thus essentially canceled out.
Data Source
AI summary
A control method and a switching device are provided for a separately excited synchronous machine as a drive in a hybrid or electric vehicle. The switching device converts and/or distributes electrical energy within the vehicle, in particular the hybrid or electric vehicle, wherein an asymmetric full bridge is provided, in the bridge branch of which a rotor of an SSM is arranged. Switches are provided in the asymmetric full bridge in order to provide a pulse width modulation corresponding to a desired motor rotational speed and power of the SSM. The device is characterized in that it has a short-circuit branch extending in parallel with the bridge branch of the asymmetric full bridge, by which short-circuit branch the rotor of the SSM is able to be short-circuited.