UPS Leakage Current Control via Variable Gate Resistance
Solution Overview
Problem
Conventional uninterruptible power supplies (UPS) suffer from excessive and uncontrollable leakage current, which can cause noise, ground loop currents, and malfunctions in sensitive electronic equipment, particularly in medical applications.
Innovation Solution
A UPS circuit with a gate drive circuit that controls the switching speed (dV/dt rate) of the output switch in response to leakage current, reducing it to maintain leakage current below a maximum value by adjusting gate resistance or voltage, thereby minimizing undesirable high-frequency components that couple to external components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional PWM switching is used in the inverter circuit, then power conversion efficiency is improved, but leakage current increases excessively
Solution Approach 1:
The patent applies dynamics by making the gate resistance variable rather than fixed. The gate drive circuit dynamically adjusts the gate resistance value based on operating conditions to control the dV/dt rate of the output switch. This dynamic adjustment allows the system to maintain optimal power conversion efficiency while reducing leakage current through controlled switching speed modulation.
Solution Approach 2:
The patent changes the parameter of gate resistance to control the switching characteristics of the output switch. By varying the gate resistance value, the dV/dt rate during switching transitions is controlled, which directly affects leakage current generation. This parameter change enables the system to reduce harmful leakage current while maintaining acceptable power conversion efficiency.
2Object-generated harmful factors
If the dV/dt rate of the output switch is reduced to decrease leakage current, then leakage current is reduced, but switching speed decreases
Solution Approach 1:
The system uses dynamic control of gate resistance to adjust switching speed in real-time. During conditions where leakage current is problematic, the gate resistance is increased to reduce dV/dt rate and thus reduce leakage current. During conditions where power conversion efficiency is prioritized, the gate resistance is decreased to improve switching speed. This dynamic adaptation resolves the contradiction by allowing both parameters to be optimized at different times based on system needs.
Solution Approach 2:
The gate resistance parameter is varied to control the trade-off between leakage current and switching speed. By changing this parameter, the system can shift the operating point along the performance curve, reducing dV/dt rate when leakage current control is critical, and improving switching speed when power conversion efficiency is the primary concern.
3Object-generated harmful factors
If gate resistance is increased to reduce dV/dt rate and leakage current, then leakage current is reduced, but power losses increase
Solution Approach 1:
The gate resistance is dynamically adjusted rather than kept constantly high. The control system monitors operating conditions and only increases gate resistance when leakage current becomes problematic. During normal operation where leakage current is acceptable, the gate resistance remains at optimal values for power conversion efficiency. This dynamic approach minimizes unnecessary power losses while still achieving leakage current reduction when needed.
Solution Approach 2:
The system changes the gate resistance parameter selectively based on operating conditions. Rather than maintaining a consistently high gate resistance that would cause excessive power losses, the parameter is adjusted upward only when leakage current exceeds acceptable thresholds. This conditional parameter change achieves leakage current control while minimizing the impact on power conversion efficiency and reducing overall power losses.
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 solution effectively reduces leakage current to a controlled level, maintaining it constant despite variations in output power, improving the reliability and safety of sensitive equipment by minimizing noise and ground loop currents, while potentially increasing energy efficiency.
Implementation Method 1
the gate drive circuit controls the switching speed (i.e., dV/dt rate) of the output switch such that a dV/dt rate of the output switch is reduced in response to increasing leakage current
Data Source
AI summary
An uninterruptible power supply having a controllable leakage current is disclosed. The leakage current is controlled by adjusting a switching speed (i.e., dV/dt rate) of switches in the output inverter (i.e. DC-AC converter stage). Leakage current can be reduced by reducing the switching speed (dV/dt rate) of the output inverter switches. In one embodiment, leakage current is held constant or moderated as output power decreases by reducing the switching speed (responsive to leakage current) as output power decreases. The switching speed can be adjusted by adjusting the gate resistance or gate voltage. Increasing the gate resistance or decreasing the gate voltage will cause a reduction in the switching speed, and increase in leakage current. Conversely, reducing the gate resistance, or decreasing the gate voltage will cause an increase in switching speed, and increase in leakage current. The present invention is applicable to any uninterruptible power supply having output inverter switches.