PWM Rectifier for Motor Drive Power Peak Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing motor drive systems face challenges in reducing power supply capacity on the AC power supply side due to electric power peaks during motor acceleration and deceleration, leading to increased installation and operation costs.
Innovation Solution
A PWM rectifier system connected to an electric storage device, which includes a main circuit unit for PWM-controlled switching operations, a DC voltage loop control unit, a current command restriction unit, and a DC voltage command calculation unit that adjusts the DC voltage command based on saturation states and operation modes to optimize energy storage and reuse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power supply capacity is designed to handle electric power peaks during motor acceleration and deceleration, then the motor drive system can operate reliably during quick accelerations and decelerations, but the power supply capacity becomes much larger than needed for average power, increasing installation and operation costs
Solution Approach 1:
The patent introduces a PWM rectifier as an intermediary device between the AC power supply and the motor drive system. This rectifier converts AC power to DC power and enables bidirectional power flow, allowing regenerative energy from motor deceleration to be stored in the DC link capacitor and reused during acceleration, thereby reducing the required power supply capacity while maintaining system reliability
Solution Approach 2:
The patent changes the operating parameters of the power conversion system by implementing PWM control with adjustable duty cycles. By dynamically adjusting the PWM duty cycle, the system can control the amount of power conversion in both rectification and regenerative operations, enabling flexible energy management between the AC power supply, DC link, and motor, thus reducing peak power requirements
2Power
If a PWM rectifier with bidirectional power conversion is introduced to reduce power supply capacity, then regenerative power can be stored and reused, but the device complexity increases
Solution Approach 1:
The PWM rectifier is designed to perform multiple functions: it acts as a rectifier converting AC to DC during motor acceleration, and as a regenerative converter storing energy during motor deceleration. This multi-functionality eliminates the need for separate rectifier and regenerative braking systems, reducing overall device complexity while achieving power supply capacity reduction
Solution Approach 2:
The patent merges the rectifier circuit and regenerative braking circuit into a single unified PWM-controlled power conversion system. By combining these functions into one device with bidirectional power capability, the system reduces component count and complexity compared to having separate circuits for rectification and regenerative energy recovery
3Loss of energy
If DC voltage command is adjusted dynamically to optimize energy storage during saturation states, then power conversion efficiency is improved, but the control system complexity increases
Solution Approach 1:
The patent implements a feedback control mechanism that monitors the DC voltage at the DC link and compares it with a reference value. When the DC voltage exceeds the reference (saturation state), the system automatically adjusts the PWM duty cycle to reduce power conversion, preventing energy loss. This closed-loop feedback control optimizes power conversion efficiency while maintaining manageable control complexity through simple voltage comparison and duty cycle adjustment
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
The system effectively suppresses electric power peaks by storing regenerative energy during deceleration and reusing it during acceleration, reducing the power supply capacity and avoiding the need for trial-and-error DC voltage command settings for each motor operation pattern.
Implementation Method 1
an electric storage device which is connected in parallel with a DC side of the PWM rectifier and can store DC power
Implementation Method 2
a PWM rectifier which converts AC power into DC power and performs a bidirectional power conversion between the DC power and AC power
Data Source
AI summary
A PWM rectifier includes a main circuit unit which performs a power conversion on the basis of a PWM control signal, a DC voltage loop control unit which generates a current command, a current command restriction unit which sets, when an absolute value of the current command exceeds a limit value, the limit value as a final current command, and otherwise sets the current command as the final current command, a DC voltage loop saturation determination unit which determines a saturation state when the final current command is set to the limit value and otherwise determines as a non-saturation state, a DC voltage command calculation unit which changes the DC voltage command into a value obtained by adding an offset to a minimum or maximum value of the DC voltage value, and a PWM control signal generation unit which generates the PWM control signal from the final current command.