DC-Bus Controller Using Mean Value Calculator for Ripple Prevention
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Solution Overview
Problem
Conventional DC-bus voltage and current control methods for voltage and current source inverters are limited by slow transient recovery due to bandwidth constraints caused by double frequency ripple, leading to distorted current delivery to the grid and instability issues, particularly in distributed power generation systems.
Innovation Solution
A DC-bus voltage or current controller using a mean value calculator to prevent ripple from entering the closed-loop system, combined with an adaptive droop controller that operates with reverse proportional gain, allowing for optimized DC-bus voltage or current regulation to minimize power losses across varying load and grid conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional PI-based control methods are used for DC-bus voltage regulation, then simplicity and ease of design are achieved, but the speed of transient recovery is limited due to slow integration
Solution Approach 1:
The patent transforms the control approach by changing the mathematical operation from integration (PI controller) to differentiation (slope calculation). The controller calculates the slope of the DC-bus voltage waveform and compares it with a reference slope, enabling fast transient response without the saturation issues of PI controllers. This parameter change from integral to differential action resolves the contradiction between ease of design and transient recovery speed.
2Speed
If the bandwidth of the control method is increased to improve transient recovery speed, then speed of transient recovery is improved, but the double frequency ripple propagates to the current control loop causing distortion
Solution Approach 1:
The patent introduces a slope calculation mechanism as an intermediary between the DC-bus voltage and the current control loop. By calculating the slope (rate of change) of the voltage rather than using the voltage directly, the controller can respond quickly to transients while the slope comparison inherently filters out the double frequency ripple. This intermediary transformation allows high bandwidth operation without propagating harmful ripple to the current loop.
3Speed
If fast integration is used in PI-based controllers to improve transient response, then speed of transient recovery is improved, but saturation and instability occur due to large DC values being integrated
Solution Approach 1:
The patent replaces the mechanical integration process of PI controllers with a differential approach that calculates the slope of the voltage waveform. Instead of accumulating large DC values through integration, the controller computes the instantaneous rate of change and compares it with a reference slope. This substitution eliminates the saturation problem entirely, as differentiation of a steady DC value yields zero, preventing accumulator overflow and maintaining stability while enabling fast transient response.
Data Source
AI summary
Provided are DC-bus voltage or DC-bus current controller methods and circuits, for a voltage or current source inverter. A mean value calculator provides an output signal comprising the mean value of the DC-bus voltage or current, which is used as a feedback signal in a closed loop of the voltage or current source inverter controller, such that a ripple in the DC-bus voltage or current is substantially prevented from entering the closed-loop. In some embodiments a droop controller, which may be adaptive, is used in the closed loop with reverse proportional gain. The adaptive droop controller may provide a constant or variable DC-bus voltage or current. Embodiments regulate the DC-bus voltage or current to an optimized value such that power losses for load and grid conditions are minimized or reduced, and voltage and current ripple is minimized. Embodiments may be used in voltage and current source inverters connected to the utility power distribution grid, in power generation systems, in distributed generation systems, and renewable energy systems.