Direct AC Power Converter Peak Current Reduction
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Solution Overview
Problem
Existing direct AC power converters experience high peak currents in boost choppers and limited output voltage due to non-continuous operation and charge/discharge cycles, resulting in inefficiencies and increased power losses.
Innovation Solution
A direct AC power converter configuration that includes a DC link, rectifying circuits, a boost chopper with a capacitor, and a switch, where the capacitor is charged during periods of higher discharge duty, allowing for a virtual DC link voltage greater than 1/√2 times the rectified voltage, and the discharge duty is optimized to minimize peak currents and enhance output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the boost chopper operates in non-continuous mode with alternating charge/discharge periods, then the output voltage is limited to 1/√2 times the crest value of input AC voltage, but the device complexity and operation are simplified
Solution Approach 1:
The patent implements continuous conduction mode operation where the boost chopper maintains continuous current flow through the inductor, eliminating the alternating charge/discharge periods. This allows the output voltage to exceed 1/√2 times the input voltage crest value while maintaining stable operation without complex periodic switching control
2Ease of operation
If the boost chopper operates in non-continuous mode, then the control is simpler, but the peak current in the inductor becomes large
Solution Approach 1:
By operating in continuous conduction mode, the inductor current flows continuously without interruption, preventing the large peak currents that occur in non-continuous mode. This maintains simpler control while eliminating the harmful peak current effect
3Ease of operation
If charge and discharge periods are set alternately at each 1/4 cycle, then the operation control is simplified, but the output voltage remains limited and power losses increase
Solution Approach 1:
The continuous conduction mode eliminates the alternating charge/discharge periods, allowing power transfer to occur continuously throughout the AC cycle. This reduces power losses while maintaining operational simplicity through unified control parameters
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 configuration reduces peak currents in the boost chopper and achieves higher output voltages by optimizing charge and discharge duties, leading to improved efficiency and reduced power losses.
Implementation Method 1
a first rectifying circuit (5, 51), having a plurality of input terminals (51a and 51b) into which an AC voltage is input, and a pair of output terminals (51c and 51d) connected to the DC link (7) for output of a rectified voltage (Vrec) of the AC voltage
Implementation Method 2
an inverter (6), converting the voltage applied to the DC link (7) into another AC voltage
Implementation Method 3
The boost chopper (3) has a capacitor (34) at an output stage
Data Source
Figure 1
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Figure 3
AI summary
In a direct power converter employing a boost chopper, a peak current flowing an inductor of the boost chopper is reduced. When a rectifying duty dr, a discharge duty dc, a voltage between both ends Vc of a capacitor (34), and a rectified voltage Vrec of an AC voltage Vin are introduced, a virtual DC link voltage Vdc in an inverter (6) is expressed by dc•Vc+dr•Vrec. The discharge duty dc is a time ratio of continuity of a switch (41). The rectifying duty dr has a value obtained by subtracting the discharge duty dc and a zero voltage duty dz from 1. The zero voltage duty dz is a time ratio for the inverter (6) to adopt a zero voltage vector regardless of a magnitude of a voltage to be output from the inverter (6). The capacitor (34) is charged in the boost chopper (3) at a part of a period during which the virtual DC link voltage Vdc is larger than the rectified voltage Vrec.