Power Converter Control Circuit Ripple Reduction

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Solution Overview

Problem

Control circuits for power converters face challenges in reducing ripple-induced distortion in AC input current due to voltage control loop ripple, which can lead to low power factor and high total harmonic distortion, and also experience output voltage undershoot during transient load conditions.

Innovation Solution

A control circuit configuration that includes a voltage control loop and a current control loop, where a parameter of the voltage control loop is sampled only once per full cycle of the AC reference signal to generate a sinusoidal reference for the current control loop, and a detector is used to update the voltage control loop parameter at a higher frequency during transient load conditions to minimize output voltage undershoot.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the bandwidth of the voltage control loop is reduced to reduce ripple, then ripple-induced distortion in AC input current is reduced, but the dynamic response to transient load conditions deteriorates causing output voltage undershoot

Engineering Contradiction:

Improveripple reductionVSAvoiddynamic response speed

Core Design Contradiction:

Manufacturing precisionVSSpeed

Solution Approach 1:

The control circuit dynamically adjusts the sampling frequency of the voltage control loop parameter based on operating conditions. During normal operation, it samples at a low frequency (once per AC cycle) to minimize ripple. During transient load conditions, it automatically increases the sampling frequency to maintain fast dynamic response, thus resolving the contradiction between ripple reduction and dynamic response speed.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The invention changes the sampling frequency parameter of the voltage control loop based on detected load conditions. By transitioning between low sampling frequency (for ripple reduction) and high sampling frequency (for fast response), the system optimizes both ripple performance and dynamic response without requiring a fixed bandwidth reduction.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If the bandwidth of the voltage control loop is reduced to reduce ripple, then distortion in AC input current is reduced, but power factor deteriorates

Engineering Contradiction:

Improvecurrent distortion reductionVSAvoidpower factor

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The control circuit uses dynamic sampling frequency adjustment to maintain high power factor. By sampling the voltage control loop parameter at optimal moments (when ripple content is minimal) rather than continuously at reduced bandwidth, the system generates accurate sinusoidal current references that maintain unity power factor while still reducing ripple-induced distortion.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control circuit proactively samples the voltage control loop parameter at predetermined optimal points in the AC cycle (once per full cycle) to generate clean sinusoidal references. This preliminary sampling approach ensures current waveform quality and maintains power factor without requiring continuous high-bandwidth voltage control.

Inventive Principle:

Principle #10Preliminary action

3Manufacturing precision

If the voltage control loop parameter is sampled at low frequency to reduce ripple, then ripple-induced distortion is reduced, but measurement precision of voltage variations deteriorates

Engineering Contradiction:

Improveripple reductionVSAvoidvoltage variation detection

Core Design Contradiction:

Manufacturing precisionVSMeasurement precision

Solution Approach 1:

The system dynamically adjusts sampling frequency based on detected transient conditions. During normal operation, low-frequency sampling (once per AC cycle) suffices for ripple reduction. During transients, the detector triggers high-frequency sampling to precisely measure voltage variations, thus resolving the contradiction between ripple reduction and measurement precision.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control circuit uses feedback from a transient detector to adjust sampling frequency. The detector monitors for voltage variations exceeding a threshold and triggers high-frequency sampling when needed, ensuring precise measurement of voltage variations only when necessary, while maintaining low ripple during normal operation.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS9065325B2Control circuits for power converters

Publication Date: 2015.06.23 AES GLOBAL HLDG PTE LTD

AI summary

A control circuit for controlling one or more power switches of a power converter includes a voltage control loop and a current control loop. The control circuit is configured to generate a current reference for the current control loop using the voltage control loop and an AC reference signal. The control circuit is configured to operate in at least a first mode in which a parameter of the voltage control loop is sampled only at every other zero crossing of the AC reference signal and the sampled parameter is used to generate the current reference for the current control loop. The power converter may be an AC-DC converter or a DC-AC converter (i.e., inverter). Alternatively, the voltage control loop may be sampled at every zero crossing of the AC reference signal, and/or more frequently during transient load conditions.