Grid Inverter Reactive Power Support Without Bulk Capacitors
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Solution Overview
Problem
Existing inverter systems for grid-connected photovoltaic inverters require large-capacity electrolytic capacitors for reactive power support, which increases system cost and volume, and lack efficient methods to implement reactive power support without these capacitors.
Innovation Solution
An inverter system with a controller that manages power switches to store and release reactive power using an inductor within a power frequency cycle, eliminating the need for large-capacity electrolytic capacitors by controlling power switches during specific time periods to invert the current and voltage phases, allowing reactive power storage and release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large-capacity electrolytic capacitor is used for reactive power support, then the reactive power support function is achieved, but the system cost and volume increase
Solution Approach 1:
The patent extracts the reactive power support function from the large-capacity electrolytic capacitor and implements it through the inductor by controlling the inverter bridge to invert current and voltage phases. This removes the bulky capacitor while maintaining the essential reactive power compensation capability.
Solution Approach 2:
The patent changes the operating parameters of the inductor by controlling the power switches to operate in specific time periods within the power frequency cycle, enabling the inductor to store and release reactive power. This parameter control approach replaces the passive capacitor with an actively controlled inductive system.
2Reliability
If reactive power is stored twice per power frequency cycle, then the reactive power support is maintained, but the calculation and control complexity increases
Solution Approach 1:
The patent implements periodic action by controlling the inverter bridge to store reactive power only during the first time period of each power frequency cycle, when voltage and current are out of phase. This single periodic storage event per cycle simplifies the control logic compared to handling two storage events, while still achieving effective reactive power support through the inductor.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the cost and volume of the system by storing reactive power only once per cycle, enhancing calculation and control efficiency and enabling reactive power support without large-capacity capacitors.
Implementation Method 1
controlling both the second power switch and the third power switch to be turned on or both the first power switch and the fourth power switch to be turned on within a first time period of each power frequency cycle... so that reactive power is stored in the inductor
Data Source
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AI summary
An inverter system includes an inverter bridge, an inductor and a controller. The inverter bridge includes first, second, third and fourth power switches. The inductor is connected between the inverter bridge and a power grid. The controller is configured to control both the second power switch and the third power switch to be turned on or both the first power switch and the fourth power switch to be turned on within a first time period of each power frequency cycle. The first time period is from a moment when a current of the power grid becomes zero to a moment when a voltage of the power grid becomes zero. The current of the power grid is in inverse phase with the voltage of the power grid in the first time period, so that reactive power is stored in the inductor.