Three-Level Power Conversion Apparatus Neutral Point Control
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Solution Overview
Problem
Existing power conversion systems face challenges in reducing size and weight while maintaining balance control over DC capacitors without adding special circuits, particularly in uninterruptible power supply systems where harmonic filtering and voltage balancing are critical.
Innovation Solution
A power conversion apparatus utilizing a three-level circuit configuration for both the converter and inverter, along with a control device to manage neutral point potential fluctuations, allows for reduced size and weight by using smaller reactors and capacitors, and achieves balance control without additional circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the number of turns of a coil is increased to increase inductance of the reactor, then the harmonic filtering capability is improved, but the volume and weight of the reactor increase
Solution Approach 1:
The patent changes the circuit topology from a conventional two-level inverter to a three-level inverter configuration. This fundamental parameter change in the circuit structure allows for reduced reactor inductance requirements while maintaining effective harmonic filtering, thereby reducing reactor volume and weight without compromising harmonic suppression performance
2Object-generated harmful factors
If a multi-level circuit is used in the inverter, then the voltage output quality is improved, but the device complexity increases due to additional capacitors and wiring
Solution Approach 1:
The patent makes the neutral point wiring serve multiple functions: it provides the necessary connection for the three-level circuit operation and simultaneously acts as a pathway for balance control current to equalize DC voltages across the series-connected capacitors. This multi-functionality eliminates the need for separate balance control circuits, reducing overall device complexity while maintaining voltage output quality
Solution Approach 2:
The patent combines the neutral point connection function with the capacitor voltage balance control function into a single wiring structure. The neutral point wiring is used both for circuit operation and for implementing balance control by allowing current flow that equalizes capacitor voltages, thereby merging two functions into one structural element
3Stability of the object's composition
If wiring is added from the multi-level circuit to the neutral point for balance control, then the capacitor voltage balance is improved, but the device complexity and potential fluctuation at the neutral point increase
Solution Approach 1:
The patent enables the neutral point wiring to automatically perform balance control function by allowing current to flow through it during normal three-level circuit operation. The system self-regulates the capacitor voltages through the inherent current paths provided by the neutral point connection, without requiring external control circuits or additional active components, thereby achieving voltage balance while minimizing added complexity
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 configuration effectively reduces the size and weight of the power conversion system, enhances operational efficiency by minimizing harmonic distortion and potential fluctuations, and maintains balanced DC capacitor voltages without the need for special balance control circuits.
Implementation Method 1
The filter includes a reactor and a capacitor and removes a harmonic generated by the first conversion device
Implementation Method 2
a capacitor for smoothing DC voltage input to the inverter
Data Source
AI summary
A power conversion apparatus includes an inverter for converting DC power to AC power for supply to a load, a converter for converting AC power from an AC power supply to DC power for supply to the inverter, and a DC voltage converter for converting a voltage value of power stored in a storage battery and supplying DC power from the storage battery to the inverter when power supply by the AC power supply is abnormal. The converter includes a first three-level circuit which is a multi-level circuit. Similarly, the DC voltage converter includes a second three-level circuit. A control device controls the first and second multi-level circuits to suppress potential fluctuation at a neutral point between first and second capacitors.