Capacitor Discharge via Homopolar Current in Electric Stator Windings
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Solution Overview
Problem
Existing methods for discharging capacitors in electric circuits of rotating electrical machines, particularly in hybrid or electric vehicles, are costly and complex, as they often require additional components and can cause undesired motor torque.
Innovation Solution
A method involving a switching system with controllable switching cells that transforms discharge current into homopolar current, allowing each coil of the stator winding to be traversed by a zero-sequence current, thereby discharging the capacitor without creating torque and without using additional resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If discharge resistors are connected to the electrical circuit to discharge capacitors, then the capacitor discharge function is achieved, but the number of components increases and cost increases
Solution Approach 1:
The switching system normally used to control the rotating electrical machine is made to perform an additional function: discharging capacitors. By controlling the switching cells during a braking phase, the system discharges capacitors without requiring dedicated discharge resistors, thus achieving multi-functionality with existing components
Solution Approach 2:
The electrical circuit uses its own switching system and stator winding to discharge the capacitors, rather than relying on external discharge resistors. The system serves itself by utilizing its inherent components for the discharge function, eliminating the need for separate discharge components
2Reliability
If discharge current is passed through the electric stator winding, then capacitor discharge is achieved, but undesired motor torque is created
Solution Approach 1:
The switching cells are controlled in a periodic manner with a switching period, creating alternating current phases that cancel out torque production. The periodic switching ensures that while discharge current flows through the stator winding, the net torque over each cycle is zero, eliminating undesired motor torque
Solution Approach 2:
The control system adjusts the switching parameters of the switching cells to transform the discharge current into homopolar current with zero-sequence components. By changing the current distribution parameters across the phases, the system achieves capacitor discharge while maintaining zero net torque
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 efficiently discharges capacitors in a simple and cost-effective manner, ensuring no torque is applied to the rotor and allowing for safe discharge without increasing the number of components in the electrical circuit.
Implementation Method 1
the switching cells being controlled so that the electric stator winding is traversed by the homopolar electric current
Implementation Method 2
the discharge current of this or these capacitor(s) is transformed by the switching system into homopolar current... Each coil can only be traversed by the zero-sequence current iM0 during this discharge of the capacitor(s)
Implementation Method 3
the electric stator winding is electrically energized by currents which each create a rotating field and the combination of these fields does not create an overall rotating field in the air gap of the machine, so that no torque is exerted on the rotor thereof
Data Source
Figure 1~3
AI summary
The invention relates to a method for discharging at least one capacitor (2) of an electric circuit (1), said electric circuit (1) also comprising: an electric stator winding (4) of a polyphase rotary electric machine, said winding (4) comprising a plurality of coils (6) which each form a stator phase and which are not being coupled to one another; and a switching system (5) disposed between the capacitor (2) and the electric stator winding (4) and comprising a plurality of controllable switching cells (10). According to the method of the invention, the coils (6) are electrically powered by the capacitor (2) by means of the switching system (5), of which the switching cells (10) are controlled such that the homopolar electric current passes through the electric stator winding (4).