Inverter EMC Filter Capacitor Discharge via Rectified DC Link
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Solution Overview
Problem
Existing inverters face power loss due to continuous conversion of electrical energy into heat through discharge resistors when discharging EMC filter capacitances, which is inefficient and increases with the amount of capacitance, and there is a need for a method to discharge these capacitances quickly without converting energy into heat.
Innovation Solution
A method involving a grid connect switch and a switching power supply unit that rectifies the voltage across the EMC filter capacitance to charge a DC voltage link and discharge it using a clocked switch, eliminating the need for discharge resistors and preventing power loss by using the electrical energy to recharge the power supply unit instead of converting it to heat.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If discharge resistors are connected in parallel with EMC filter capacitances to discharge them quickly, then the discharge time is reduced and safety requirements are met, but continuous power loss increases due to conversion of electrical energy into heat
Solution Approach 1:
The patent converts the harmful effect of stored electrical energy in EMC filter capacitances (which normally would be dissipated as heat through discharge resistors) into a beneficial resource by using it to charge the DC voltage link of the power supply unit. This transforms waste energy into useful energy that powers the inverter's control and communication systems, eliminating continuous power loss while maintaining fast discharge capability when needed.
Solution Approach 2:
The DC voltage link serves multiple functions: it acts as an energy storage element for the power supply unit, a discharge path for EMC filter capacitances, and a buffer that can supply power during grid detachment. This multi-functionality eliminates the need for dedicated discharge resistors, reducing continuous power loss while maintaining safety discharge capabilities when required.
2Reliability
If discharge resistors are used to discharge EMC filter capacitances, then the capacitances are discharged within the requisite time, but electrical energy is continuously converted into heat causing power loss even when the inverter is not feeding energy into the AC grid
Solution Approach 1:
The patent transforms the potentially harmful stored energy in EMC filter capacitances into a beneficial resource by routing it through the rectifier to charge the DC voltage link, which then powers the power supply unit. This eliminates continuous heat generation through discharge resistors while ensuring reliable discharge capability when safety requires it.
Solution Approach 2:
The power supply unit serves itself by using the energy from EMC filter capacitances to charge its own DC voltage link, creating a self-sustaining system that eliminates the need for external discharge resistors and their associated continuous power losses.
3Reliability
If the sum of EMC filter capacitances at the output of the inverter is increased, then EMC filter performance is improved, but the power loss increases due to the amount of current needed to flow through the discharge resistors
Solution Approach 1:
The patent converts the increased energy storage capacity of higher EMC filter capacitances into a benefit rather than a burden. Instead of requiring larger discharge resistors that would increase continuous power loss, the system uses the stored energy to charge the DC voltage link, transforming what would be waste energy into useful power for the inverter's auxiliary systems.
Solution Approach 2:
The DC voltage link serves as both an energy storage element and a discharge path for multiple EMC filter capacitances simultaneously. This multi-functional approach allows the system to handle larger total capacitance values without proportionally increasing power loss, as the energy from all capacitances is consolidated and reused to power the power supply unit.
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 approach allows for rapid discharge of EMC filter capacitances without converting electrical energy into heat, reducing power loss and maintaining the functionality of the power supply unit even at low voltage levels, thus meeting safety standards and optimizing energy usage.
Implementation Method 1
rectifying any voltage applied across the capacitance independently of its polarity to provide a rectified voltage of fixed polarity
Implementation Method 2
discharging the DC voltage link via a clocked switch of the switching power supply unit
Data Source
Figure 1~2
Figure 3
AI summary
To discharge an filter capacity (7, 8) at the output of an inverter (1) for feeding electrical power from a generation unit into a grid via a grid connect switch (11) having a generation unit side and a grid side and via AC grid terminals (L1, L2, L3) on the grid side of the grid connect switch (11), the filter capacity (7, 8) being connected to at least one of the AC grid terminals, any voltage applied across the filter capacity (7, 8) is rectified independently of its polarity to provide a rectified voltage of fixed polarity, and a DC voltage link (13) of a power supply unit (14) for operating circuitry of the inverter (1) is charged with this rectified voltage.