Flying Capacitor PWM Edge Modulation for Voltage Balancing
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Solution Overview
Problem
Multilevel converters face challenges in balancing flying capacitor voltages due to sensitivity to gate drive circuitry mismatches and other circuit imperfections, leading to higher voltage stress and subharmonic oscillations.
Innovation Solution
A method of balancing flying capacitor voltages in multilevel power converters using pulse width modulated (PWM) control signals with phase/timing shifts between pairs of switches. The method involves modifying the widths of PWM pulses by changing the timing of their edges to balance the capacitor voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If interleaved operation of switching pairs is used, then voltage stress is reduced and ripple frequency is increased, but flying capacitor voltage balancing becomes sensitive to gate drive circuitry mismatches
Solution Approach 1:
The patent implements active feedback control by monitoring the actual voltages on flying capacitors and dynamically adjusting the PWM duty cycles of switching pairs. The controller compares measured capacitor voltages with reference values and generates correction signals to maintain voltage balance, thereby compensating for gate drive mismatches and circuit imperfections that would otherwise cause voltage stress and instability.
Solution Approach 2:
The patent dynamically changes the duty cycle parameters of PWM control signals based on real-time flying capacitor voltage measurements. By adjusting the pulse widths of complementary switching pairs in response to detected voltage imbalances, the system maintains optimal operating conditions and eliminates the sensitivity to gate drive mismatches that would otherwise occur in conventional interleaved operation.
2Reliability
If active balancing control is implemented, then voltage balancing is improved, but control complexity increases
Solution Approach 1:
The patent implements a self-service control mechanism where the system monitors its own flying capacitor voltages and automatically adjusts switching pair duty cycles without external intervention. The controller uses built-in voltage sensing and comparison circuits to detect imbalances and generates appropriate correction signals, enabling the converter to self-correct voltage mismatches and maintain balanced operation through intrinsic feedback loops.
3Reliability
If PWM pulse widths are modified by edge modulation, then flying capacitor voltage balancing is achieved, but subharmonic oscillations may occur
Solution Approach 1:
The patent applies periodic modulation to the PWM control signals, introducing a controlled oscillating component at a frequency related to the switching frequency. This periodic action in the duty cycle adjustment helps to counteract subharmonic oscillations that may arise from edge modulation, maintaining system stability while achieving voltage balancing through the interplay of periodic control actions and feedback mechanisms.
Data Source
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AI summary
A method of balancing voltages on flying capacitors in a multilevel power converter is provided (along with an associated controller). The power converter includes one or more flying capacitors. Pairs of switches in the power converter are controlled by pulse width modulated (PWM) control signals. The different pairs of switches are controlled by PWM control signals having a phase/timing shift between them. To balance the voltage on the one or more flying capacitors, one set of pulses can be widened or narrowed while another set is widened or narrowed. To change their widths, one edge of each pulse is modulated, while the other edge is unchanged. More specifically, the leading edge of one set of pulses is modulated, while the trailing edge of the other set of pulses is modulated.