Direct AC Power Converter Capacitor Charging Dynamics
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Solution Overview
Problem
Conventional direct AC power converters require a larger power capacity for the boost chopper due to unnecessary charging and discharging of capacitors, limiting the voltage output to 1/√2 times the crest value of the input AC voltage.
Innovation Solution
A direct AC power converter configuration that includes a DC link, a first rectifying circuit, a boost chopper with a capacitor, and a switch, where the capacitor is charged during periods with a discharge duty greater than 0, allowing the virtual DC link voltage to exceed 1/√2 times the crest value of the AC voltage, and the discharge duty is minimized to reduce current flow in the boost chopper.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the capacitor is charged and discharged alternately in each 1/4 of a cycle of input AC voltage, then the pulsation of instantaneous power is reduced, but the output voltage remains limited to 1/√2 times the crest value of the input AC voltage and the power capacity of the boost chopper increases
Solution Approach 1:
The patent applies dynamics by making the charging and discharging periods of the capacitor flexible rather than fixed. The controller dynamically adjusts the charging period (when the switch is on) and discharging period (when the switch is off) based on the instantaneous power pulsation requirements, allowing the capacitor to be charged during periods when the rectifying circuit can supply power and discharged when the inverter requires power, thereby optimizing the power capacity utilization of the boost chopper
Solution Approach 2:
The patent changes the operating parameters of the boost chopper by allowing the virtual DC link voltage to exceed 1/√2 times the crest value of the input AC voltage. This is achieved by adjusting the duty cycle of the switch and controlling the capacitor charge/discharge timing, which modifies the voltage transformation ratio and allows higher output voltage while reducing the required power capacity of the boost chopper
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 increases the average voltage output from the inverter beyond 1/√2 times the AC voltage crest value, reducing the required power capacity for the boost chopper and minimizing current flow, thus enhancing efficiency and reducing power losses.
Implementation Method 1
a first rectifying circuit (5, 51) having a plurality of input terminals (51a, 51b) that receive an input of an AC voltage (Vin) and a pair of output terminals (51c, 51d) connected to the DC link (7)
Implementation Method 2
an inverter (6) that converts a voltage applied to the DC link (7) into another multi-phase AC voltage
Implementation Method 3
The boost chopper has a capacitor (34) at its output stage
Data Source
Figure 1
Figure 2
Figure 3
AI summary
In a direct power converter including a boost chopper, an average value or an effective value of a current flowing in 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 at which a switch (41) is conductive. 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 at which the inverter (6) adopts a zero voltage vector irrespective of the magnitude of a voltage output from the inverter (6). In a boost chopper (3), the capacitor (34) is charged during a part of a period during which the virtual DC link voltage (Vdc) is greater than the rectified voltage (Vrec).