Bidirectional AC-DC Power Converter Input Voltage Control

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Solution Overview

Problem

The increasing integration of intermittent renewable energy sources in power grids poses challenges for maintaining power balance and stability, as traditional control paradigms assume stable mains voltage, which is no longer valid, leading to potential power instability and the need for a new approach to manage bidirectional power flow.

Innovation Solution

Implementing bidirectional reactive power controllers with input voltage control in ac-dc power converters, allowing for both active and reactive power flow in both directions, and enabling the electric load to stabilize the mains voltage by regulating the input voltage and frequency, thereby acting as a smart load to stabilize the grid.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional output voltage control is used in ac-dc power converters, then the converter can regulate output voltage effectively, but it cannot stabilize the mains voltage when intermittent renewable energy sources cause power grid fluctuations

Engineering Contradiction:

Improvepower grid stabilityVSAvoidadaptability to intermittent renewable energy

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent inverts the traditional control approach by switching from output voltage control to input voltage control. Instead of regulating the output voltage as is conventional, the controller now regulates the input voltage (mains voltage) by adjusting the input current. This inversion enables the power converter to stabilize the mains voltage and provide support to the power grid when intermittent renewable energy sources cause fluctuations, thereby resolving the contradiction between reliability and adaptability.

Inventive Principle:

Principle #13The other way round (Inversion)

2Adaptability or versatility

If reactive power converters are used for electric spring implementation, then mains voltage regulation is achieved, but the power converter cannot handle active power flow bidirectionally

Engineering Contradiction:

Improvevoltage regulation capabilityVSAvoidactive power flow capability

Core Design Contradiction:

Adaptability or versatilityVSUse of energy by moving object

Solution Approach 1:

The patent implements a universal power converter that can handle both active and reactive power flows bidirectionally. The controller is designed to independently control both the active power component (in-phase with mains voltage) and the reactive power component (quadrature with mains voltage). This multi-functionality allows the same power converter to perform voltage regulation (reactive power function) while also enabling active power flow bidirectionally, thus resolving the contradiction between voltage regulation capability and active power flow capability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If scheduled load shedding is implemented for power balance, then power system stability is maintained, but real-time dynamic power balance cannot be achieved

Engineering Contradiction:

Improvepower system stabilityVSAvoidreal-time response speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent implements a feedback control mechanism where the controller continuously monitors the mains voltage and adjusts the input current accordingly to maintain voltage stability. This real-time feedback control enables the power converter to respond dynamically to power grid fluctuations caused by intermittent renewable energy sources, achieving both power system stability and real-time dynamic power balance, thereby resolving the contradiction between reliability and response speed.

Inventive Principle:

Principle #23Feedback

4Productivity

If smart loads with ON/OFF control are used, then real-time power balance is achieved, but consumer convenience is reduced due to appliance shutdown

Engineering Contradiction:

Improvereal-time power balance capabilityVSAvoidconsumer convenience

Core Design Contradiction:

ProductivityVSEase of operation

Solution Approach 1:

The patent introduces the power converter as an intermediary device between the power grid and the electric load. Instead of directly controlling the load to achieve power balance (which would require ON/OFF control and reduce consumer convenience), the converter mediates by regulating the input voltage and managing power flow bidirectionally. This allows real-time power balance to be achieved through voltage regulation and active power flow control without interrupting the normal operation of electric appliances, thus resolving the contradiction between productivity and ease of operation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentEP2856598B1Input ac voltage control bi-directional power converters

Publication Date: 2023.07.19 THE UNIVERSITY OF HONG KONG

Figure 1(a-1)~1(c-2)
Figure 2
Figure 3A~4

AI summary

A family of power converters has input ac voltage regulation instead of output dc voltage regulation. The bi-directional converters control power flows and maintain the input ac voltage at or close to a certain reference value. These bi-directional power converters handle both active and reactive power while maintaining the input ac voltage within a small tolerance. Use of these converters is favorable for future power grid maintenance in that they (i) ensure the load demand follows power generation and (ii) provide distributed stability support for the power grid. The converters can be used in future smart loads that help stabilize the power grid.