Unfolding Inverter Power Factor Control via Bidirectional Current
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Solution Overview
Problem
Power converting apparatuses with unfolding inverters face limitations in controlling reactive power and power factor, especially when grid voltage is unstable, which affects the stable output of AC power.
Innovation Solution
The apparatus includes a converter, an inverter, an output current detector, an output voltage detector, and a controller that controls bidirectional currents based on the difference between grid voltage and output current, allowing for the conversion of DC power to AC power and enabling control of reactive power and power factor by managing the phase difference between grid voltage and output current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an unfolding inverter is used for power conversion, then device complexity is reduced, but control capability over reactive power and power factor deteriorates
Solution Approach 1:
The patent applies dynamics by making the converter operate bidirectionally with dynamic current control. The converter switches between charging and discharging modes based on real-time power factor requirements, enabling the unfolding inverter to control reactive power dynamically without adding complex circuit structures. The controller adjusts current direction and magnitude adaptively to maintain desired power factor.
Solution Approach 2:
The patent implements self-service by using the converter's inherent bidirectional capability to simultaneously perform power conversion and power factor correction. The system uses its own internal components (converter and controller) to regulate reactive power without requiring external correction circuits, making the simple unfolding inverter structure provide advanced control functionality.
2Ease of operation
If control is performed only at zero-crossing point in unfolding inverter, then ease of operation is improved, but stability of AC power output deteriorates under unstable grid voltage
Solution Approach 1:
The patent applies feedback by implementing closed-loop control that continuously monitors output current and voltage. The controller uses real-time feedback signals to adjust switching element timing and duration, enabling stable AC power output even when grid voltage fluctuates. The feedback mechanism allows the system to deviate from simple zero-crossing control while maintaining operational simplicity.
Solution Approach 2:
The patent implements preliminary action by pre-calculating optimal switching timings and durations based on expected grid conditions. The controller prepares control signals in advance considering power factor requirements and grid voltage characteristics, allowing the system to maintain stability proactively rather than merely reacting at zero-crossing points.
3Adaptability or versatility
If additional circuits are added to enable reactive power control, then adaptability is improved, but manufacturing cost increases
Solution Approach 1:
The patent applies universality by designing the converter to perform multiple functions: DC-AC power conversion, bidirectional current control, and power factor correction. The existing converter components are utilized for both primary power conversion and reactive power management, eliminating the need for separate correction circuits and reducing manufacturing costs while maintaining adaptability.
Solution Approach 2:
The patent implements merging by combining the power conversion function and power factor correction function into a single integrated control system. The controller simultaneously manages switching elements for both purposes, and the converter structure serves dual roles, reducing component count and simplifying manufacturing while achieving comprehensive control capability.
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 solution allows for stable AC power output connected to the grid, with enhanced control over reactive power and power factor, reducing manufacturing costs by eliminating the need for additional circuits and enabling bidirectional operation of the converter.
Implementation Method 1
a converter configured to convert a level of input DC power
Implementation Method 2
an inverter configured to convert a half sine wave voltage from the converter into an AC voltage
Implementation Method 3
control to store energy in a capacitor unit in a first period in which a current is output from the converter; and output the energy from the capacitor in a second period subsequent to the first period
Data Source
AI summary
Disclosed are a power converting apparatus and a photovoltaic module including the same. The photovoltaic module includes: a converter configured to convert a level of DC power; an inverter configured to convert a half sine wave voltage from the converter into an AC voltage; and a controller configured to control the converter and the inverter based on an output current and an output voltage of the inverter, wherein a plurality of switching elements in the inverter is respectively turned on once in each cycle, and wherein the controller is configured to, based on a difference between a grid voltage and an output current of the inverter, control a bidirectional current to flow to the converter. Accordingly, the power converting apparatus including the unfolding inverter is able to control a power factor.