Bidirectional AC-DC Converter Ripple Control With Auxiliary Loop
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Solution Overview
Problem
Conventional bi-directional AC-DC power converters face challenges in controlling power flow in both inverter and rectifier modes with reduced ripple and component count, often leading to increased capacitance, reduced power density, and complex control strategies.
Innovation Solution
A single simplified control scheme using a main controller and an auxiliary controller with bandpass filters to generate a converter control signal, attenuating frequencies around the ripple frequency, allowing for reduced ripple and component count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If capacitance on the DC bus is increased to reduce ripple, then ripple is reduced, but power density of the converter decreases
Solution Approach 1:
The control system is segmented into a main controller for overall power flow management and an auxiliary controller specifically for ripple reduction. This segmentation allows independent optimization of each control function without requiring increased capacitance, thereby maintaining power density while reducing ripple.
Solution Approach 2:
An auxiliary controller acts as an intermediary between the main controller and the converter stages. It processes ripple signals and generates corrective control signals that are combined with the main control signal, enabling ripple reduction without modifying the physical capacitance of the DC bus.
2Device complexity
If a single simplified control scheme is used to control bi-directional power flow, then device complexity is reduced, but control precision for both inverter and rectifier modes becomes more difficult to achieve
Solution Approach 1:
The control scheme is divided into a main controller that handles overall power flow and an auxiliary controller that specializes in ripple reduction. This segmentation maintains simplicity in the main control path while adding precision where needed through the auxiliary controller, achieving both bi-directional control and high precision without excessive complexity.
Solution Approach 2:
The auxiliary controller is designed to universally handle ripple reduction in both inverter and rectifier modes through a unified control architecture. This multi-functionality allows a single auxiliary controller to improve control precision across different operating modes without requiring mode-specific control circuits.
3Adaptability or versatility
If conventional control strategies are used to control bi-directional power flow, then power flow control is achieved, but component count increases
Solution Approach 1:
The main controller and auxiliary controller are merged into a unified control system that shares common signal processing resources and output stages. This merging allows bi-directional power flow control with ripple reduction functionality while minimizing the total component count by eliminating redundant elements.
Solution Approach 2:
The control system is designed with universal components that can operate in both inverter and rectifier modes. The auxiliary controller uses the same signal processing chain for ripple reduction regardless of operating mode, reducing the need for mode-specific components and overall system complexity.
Data Source
AI summary
A two-stage bi-directional AC-DC power converter with a controller has a main control loop and an auxiliary control loop. The main control loop regulates the output of the DC-DC converter stage. The auxiliary control loop receives a converter signal that includes information about ripple induced on the external DC power by the AC-DC converter stage. The converter signal is bandpass filtered to isolate the ripple information and loop compensation is applied to the filtered signal. The compensated signal is bandpass filtered again to generate a ripple control signal. In inverter mode the ripple control signal is subtracted from the main control signal to reduce a loop gain of the main control loop only at the ripple frequency. In rectifier mode, the ripple control signal is added to the main control signal to increase a loop gain of the main control loop only at the ripple frequency.