Split DC-Link Multilevel Inverter Control for Capacitor Voltage Balancing
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Solution Overview
Problem
Existing multilevel inverters with split DC links face challenges in balancing DC link capacitor voltages, leading to unequal stress on electrical components and degradation of output waveform quality.
Innovation Solution
A method is introduced to calculate a modulation signal with an even harmonic amplitude based on the actual power difference between DC link capacitors, which is then superimposed onto the setpoint value to generate an adapted reference signal for controlling semiconductor switches, thereby balancing the DC link capacitor voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If additional hardware is added at the split DC link for voltage balancing, then voltage balancing is improved, but device complexity and cost increase
Solution Approach 1:
The invention changes the control parameters by injecting even harmonic signals (2nd, 4th, 6th harmonics) into the reference voltage signals. This modifies the switching patterns of the semiconductor switches to actively balance the DC link capacitor voltages without adding hardware. The harmonic injection changes the temporal distribution of power flow between capacitors, achieving voltage balancing through parameter modification rather than structural addition.
2Ease of manufacture
If proportional gain is used for even harmonic signal control, then implementation is simplified, but control behavior deteriorates with remaining offset error and poor transient behavior
Solution Approach 1:
The invention implements feedback control by continuously monitoring the actual DC link capacitor voltages and using them to dynamically adjust the amplitudes of the injected even harmonic signals. The control system calculates the voltage deviations and modifies the harmonic signal strengths accordingly, creating a closed-loop system that eliminates offset errors and improves transient response. This feedback mechanism ensures accurate voltage balancing while maintaining system stability.
3Device complexity
If even harmonic signal injection is used for voltage balancing, then hardware requirements are reduced, but control precision deteriorates due to poor transient behavior
Solution Approach 1:
The invention makes the control system dynamic by continuously adapting the even harmonic signal amplitudes based on real-time voltage measurements. The control algorithm dynamically adjusts the harmonic injection levels according to the instantaneous voltage deviations, enabling precise control during transient conditions. This dynamic adaptation ensures high control precision without requiring additional hardware, as the system responds adaptively to changing operating conditions.
Data Source
AI summary
To improve voltage balancing at the DC link capacitor voltages of a multi-level inverter with a split DC link a modulation signal with a modulation signal amplitude as even harmonic signal of the output voltage or output current of the inverter is calculated from an actual electric power difference of the actual electric powers at the DC link capacitors and is superimposed onto the setpoint value for setting an output voltage or output current of the inverter.