Power Conversion Apparatus with Active Power Factor Correction
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Solution Overview
Problem
Conventional power conversion apparatuses for three-phase AC to DC conversion face issues such as increased size and cost, circuit loss, and control complexity, particularly due to the need for AC reactors and complex control circuits to improve the power factor.
Innovation Solution
A power conversion apparatus comprising a three-phase rectification circuit, a step-up converter circuit, a smoothing device, voltage and AC current detection circuits, and a control circuit that calculates and generates pulse signals to control the step-up converter, avoiding the need for AC reactors and simplifying the control loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AC reactors are provided between the three-phase AC power supply and the full-wave rectification circuit to improve the supply power factor, then the supply power factor is improved, but the size of circuits and cost increase
Solution Approach 1:
The patent removes the AC reactors from the circuit configuration. Instead of using AC reactors between the power supply and rectification circuit, the invention uses a different approach by controlling the switching devices in the voltage converter circuit to achieve power factor improvement without the bulky reactor components.
Solution Approach 2:
The patent replaces the passive AC reactor-based power factor correction with an active control system using switching devices (IGBTs and diodes) controlled by a control unit. This substitution of mechanical/passive components with electronic control achieves the same function with reduced size and complexity.
2Reliability
If AC reactors are provided between the three-phase AC power supply and the full-wave rectification circuit to improve the supply power factor, then the supply power factor is improved, but circuit loss increases and heat generation occurs
Solution Approach 1:
The patent replaces the passive AC reactor-based power factor correction with an active control system using switching devices (IGBTs and diodes) controlled by a control unit. This substitution of mechanical/passive components with electronic control achieves the same function with reduced size and complexity.
3Reliability
If single-phase rectification circuits and converter circuits are provided for each phase to improve power factor, then the supply power factor is improved, but the size of circuits and cost increase
Solution Approach 1:
The patent merges all three phases into a single integrated voltage converter circuit with common switching devices and control. Instead of having separate rectification and converter circuits for each phase, the invention uses a unified three-phase bridge circuit with shared components, reducing overall circuit size while maintaining power factor improvement.
4Reliability
If step-up converter with double feedback loop is used to improve supply power factor, then the supply power factor is improved, but control responsiveness deteriorates and control circuit becomes complicated
Solution Approach 1:
The patent removes one feedback loop from the control system. Instead of using a double feedback loop that monitors both output voltage and output current, the invention uses a simplified single feedback loop that only monitors output voltage, while the power factor improvement is achieved through the inherent operation of the voltage converter circuit.
Solution Approach 2:
The patent uses feedback control to maintain stable output voltage. The control unit adjusts the switching duty ratio based on the detected output voltage to keep it constant, which simultaneously achieves power factor improvement without requiring complex double feedback loops.
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 effectively improves the input power factor to about 0.95, reducing circuit size, cost, and complexity while maintaining high control responsiveness and stability.
Implementation Method 1
a reactor (31) which stores the output current of the three-phase rectification circuit
Implementation Method 2
a switching device (32) which controls charge and discharge of the current stored in the reactor (31)
Data Source
AI summary
A three-phase rectification circuit rectifies output voltage of a three-phase AC power supply, a step-up converter circuit steps up the output voltage, and a smoothing device smoothes the stepped-up output voltage. A voltage detection circuit detects output voltage VoL of the smoothing device, and an AC current component detection circuit extracts AC component included in output current of the three-phase rectification circuit and outputs a detection signal ViL corresponding to the AC component. A control circuit calculates a deviation ΔVdc1 (=Vs−VoL−ViL) among an output voltage instruction Vs for output voltage of the step-up converter circuit and detection signals VoL and ViL obtained by the detection circuits, and generates a pulse signal for suppressing the deviation ΔVdc1 to zero, thereby performing PWM control for a switching device of the step-up converter circuit.