Multilevel Power Converter Precharge for Semiconductor Overvoltage
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Solution Overview
Problem
Existing power conversion devices face overvoltage issues during initial charging when the power supply is turned on, which can damage low-withstanding-voltage semiconductor elements, affecting efficiency and increasing costs.
Innovation Solution
A power conversion device is designed with a rectification circuit, leg circuit comprising series-connected semiconductor elements, balance resistors, charge/discharge capacitors, smoothing capacitors, and an inrush preventing circuit with a current limiting resistor to control charging speeds and suppress overvoltage by adjusting resistance values and capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a power conversion device uses a multilevel converter configuration with charge/discharge capacitors, then DC power output efficiency is improved, but overvoltage is applied to semiconductor elements during initial charging when the power supply is turned on
Solution Approach 1:
The patent applies preliminary action by introducing a pre-charging circuit that charges the charge/discharge capacitor before the main switching operation begins. This pre-charging process prevents overvoltage spikes during initial power-on by establishing a controlled voltage gradient, allowing the semiconductor elements to be gradually exposed to operating voltage levels without sudden stress.
Solution Approach 2:
The patent uses an intermediary approach by inserting a pre-charging circuit between the power supply and the main converter circuit. This intermediary circuit acts as a buffer that mediates the voltage transfer, controlling the charging current and preventing direct overvoltage application to the semiconductor elements while still enabling efficient power conversion.
2Object-affected harmful factors
If balance resistors are connected in parallel to switching elements and diodes, then overvoltage is suppressed in stopped state, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the pre-charging circuit to serve multiple functions: it suppresses overvoltage during initial charging, balances capacitor voltages during operation, and maintains voltage equilibrium in stopped state. This multi-functional approach eliminates the need for separate balance resistors connected in parallel to each switching element, reducing overall device complexity while maintaining overvoltage suppression capabilities.
Solution Approach 2:
The patent merges the functions of overvoltage suppression and voltage balancing into a single pre-charging circuit rather than using separate balance resistors for each component. This consolidation reduces the total number of passive components and simplifies the circuit architecture while achieving comprehensive overvoltage protection across all operating states.
3Ease of manufacture
If low-withstanding-voltage semiconductor elements are used to improve efficiency and reduce costs, then device cost and efficiency are improved, but overvoltage during initial charging damages these elements
Solution Approach 1:
The patent applies preliminary action by implementing a pre-charging sequence that prepares the circuit conditions before main operation begins. This pre-charging phase establishes safe voltage levels on the charge/discharge capacitor, ensuring that when low-withstanding-voltage semiconductor elements are activated, they are not subjected to damaging overvoltage spikes, thereby protecting reliability while enabling cost-effective component selection.
Solution Approach 2:
The patent uses beforehand cushioning by introducing a pre-charging circuit that acts as a protective buffer before the main power conversion operation. This cushioning mechanism absorbs and controls the initial voltage surge, creating a protected environment that allows fragile, low-withstanding-voltage semiconductor elements to operate reliably without exposure to damaging overvoltage conditions.
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 suppresses overvoltage during initial charging, allowing the use of lower-withstanding-voltage semiconductor elements, reducing costs and improving efficiency by prolonging charging times and balancing capacitor voltages.
Implementation Method 1
an inrush preventing circuit provided between the AC power supply and the leg circuit, and including a current limiting resistor
Implementation Method 2
at least one charge/discharge capacitor connected between a connection point of the semiconductor elements in the upper leg and a connection point of the semiconductor elements in the lower leg
Data Source
AI summary
This power conversion device includes a rectification circuit which rectifies input voltage from the AC power supply; a leg circuit having an upper leg composed of semiconductor elements connected in series and a lower leg composed of semiconductor elements connected in series, the upper leg and the lower leg being connected in series, at least the semiconductor elements in the lower leg being switching elements; a balance resistor connected in parallel to the semiconductor elements; at least one charge/discharge capacitor connected between a connection point of the semiconductor elements in the upper leg and a connection point of the semiconductor elements in the lower leg; a smoothing capacitor connected to an output of the leg circuit; and an inrush preventing circuit provided between the AC power supply and the leg circuit, and including a current limiting resistor.