Frequency Controlled Power Converter Characterization
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Solution Overview
Problem
Frequency-controlled power converters face challenges in determining the power stage transfer function due to complex behavior and interactions of energy storage components, making it difficult to maintain a constant output voltage under varying load conditions and noise.
Innovation Solution
A method is introduced to characterize the frequency response of a power stage by opening the feedback control loop and using a sinusoidal perturbation waveform to measure the frequency response, which involves generating a set of discrete frequency deviation control values and cross-correlating them with the output voltage samples using a dual discrete Fourier transform to build a transfer function table.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional feedback control methods are used to maintain constant output voltage, then the converter can operate under varying load conditions, but the complex behavior and interactions of energy storage components make it difficult to determine the power stage transfer function and achieve effective compensation
Solution Approach 1:
The patent changes the operating parameters by opening the feedback loop and applying sinusoidal perturbations at various frequencies to the control input. This allows measurement of the power stage frequency response across different operating points, enabling accurate determination of transfer function parameters without dealing with the complexity of closed-loop interactions
Solution Approach 2:
The patent introduces an intermediary measurement system that uses sinusoidal perturbations and cross-correlation techniques to extract transfer function information. This intermediary approach separates the measurement process from the normal control operation, allowing accurate characterization without interfering with the converter's primary function
2Measurement precision
If the feedback control loop is opened to measure frequency response, then accurate transfer function characterization can be achieved, but the converter cannot maintain constant output voltage during measurement
Solution Approach 1:
The patent applies periodic sinusoidal perturbations to the control input while the feedback loop is open. These periodic excitations allow measurement of the power stage frequency response at specific frequencies without requiring the feedback loop to be closed, thus achieving accurate measurement while accepting temporary loss of voltage regulation
Solution Approach 2:
The patent performs frequency response measurements as a preliminary characterization step before normal closed-loop operation. The transfer function information obtained from these preliminary open-loop measurements is then used to design appropriate compensation for subsequent closed-loop operation, separating the measurement phase from the control phase
Data Source
AI summary
A frequency-controlled power converter includes a power stage frequency response characterization circuit. A PWM input control value F_OL_CTL generates a PWM output control signal to drive the converter to a selected output voltage. F_OL_CTL is added to each of a set of periodic, incrementally time-sequenced discrete frequency deviation control values F_DEV(t) having a periodicity of F_RESP corresponding to a frequency at which a response of the power stage is to be measured. A resulting set of perturbed PWM input control values F_CTL_PTB(t) frequency-modulate the PWM output control signal and perturb the converter output voltage. A corresponding set of perturbed converter output voltage samples V_OUT_PTB(t) is cross-correlated to the set of F_CTL_PTB(t) to generate correlation components of V_OUT_PTB(t) and F_CTL_PTB(t). Real and imaginary components of a frequency response of the converter power stage are determined from the correlation components for each F_RESP and together form the power stage transfer function.