PWM Rectifier Capacitance Calculation Unit
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Solution Overview
Problem
Existing PWM rectifiers face challenges in accurately measuring the capacitance of smoothing capacitors, leading to potential misjudgment of capacitor lifespan and increased ripple current and DC voltage fluctuations, especially when the peak AC voltage and charging resistor values contain errors.
Innovation Solution
A PWM rectifier system that includes a capacitance calculation unit to determine the capacitance of the smoothing capacitor based on DC voltage measurements at the start and end of the initial boost period and integrated power, allowing for accurate capacitance measurement without relying on peak AC voltage or charging resistor values, and includes additional units for warning and stopping operations when capacitance falls below a threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitance measurement relies on peak AC voltage and charging resistor values, then the measurement method is simple, but measurement precision deteriorates due to errors in these parameters
Solution Approach 1:
The patent replaces the conventional measurement method that relies on physical component parameters (peak AC voltage and charging resistor values) with an electrical measurement approach using detected current and time. By substituting the measurement basis from physical component specifications to electrical signals, the system achieves higher precision without requiring additional hardware components.
Solution Approach 2:
The patent introduces an intermediary measurement approach by using the relationship between detected current, time, and voltage to calculate capacitance. Instead of directly measuring capacitance through physical parameters, the system uses electrical measurements (current detection and time measurement) as intermediaries to derive capacitance value, thereby improving accuracy.
2Duration of action of stationary object
If smoothing capacitor capacitance decreases, then the rectifier can continue operating, but ripple current and DC voltage fluctuations increase
Solution Approach 1:
The patent implements a feedback mechanism by continuously monitoring capacitance values and comparing them against predetermined thresholds. When capacitance decreases below the threshold, the system generates warnings or stops operation, creating a closed-loop control system that maintains DC voltage stability and prevents unreliable operation.
3Ease of manufacture
If diode rectification method is used, then device cost is reduced, but power line harmonics and reactive power increase
Solution Approach 1:
The patent changes the operating parameters of the rectifier by implementing PWM control with variable switching duty cycles. By dynamically adjusting the switching parameters rather than using fixed diode rectification, the system achieves unity power factor and reduced harmonics while maintaining cost-effectiveness through controlled switching operations.
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
Enables accurate capacitance measurement of smoothing capacitors, preventing premature or unnecessary replacement and reducing ripple current and DC voltage fluctuations, while maintaining a low-cost and space-efficient design.
Implementation Method 1
a smoothing capacitor 5 incorporated into a DC link
Implementation Method 2
PWM rectifier that converts AC power to DC power by controlling a switching element using a PWM signal (pulse width modulation signal)
Data Source
AI summary
A PWM rectifier includes a main circuit unit carrying out AC-DC power conversion by PWM-control, a PWM control unit PWM-controlling the main circuit unit, a DC voltage detection unit detecting a DC voltage across a smoothing capacitor connected to the DC-side of the main circuit unit, a DC voltage storage unit storing respective DC voltages at the start and end times of an initial boost period during which the smoothing capacitor having been charged to an AC voltage peak value is further charged to a higher voltage, an input power calculation unit calculating input power flowing in from the AC-side based on an AC voltage and current, an integral power calculation unit calculating integral power from the input power over the initial boost period, and a capacitance calculation unit calculating the capacitance of the smoothing capacitor based on the respective DC voltages and the integral power.