Adjustable DC Bus Voltage Converter Circuit
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Solution Overview
Problem
In electric motor drive systems, the regeneration of power by loads can raise the DC bus voltage to near its limit, leading to excess power being dissipated as heat through shunt resistors, reducing efficiency and requiring additional cooling, as these systems typically have a fixed upper DC bus voltage limit and lack a mechanism to effectively manage this excess power.
Innovation Solution
A method and system that dynamically adjust the lower voltage threshold of a switch connecting a shunt resistor across the DC bus based on its duty cycle, allowing for adaptive dissipation of power and storage of excess energy in capacitors, thereby reducing the reliance on shunt resistors and maintaining efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shunt resistors are used to dissipate excess power when DC bus voltage reaches the upper limit, then the DC bus voltage can be maintained within acceptable ranges, but system efficiency is substantially reduced and components are subjected to high temperatures requiring additional cooling
Solution Approach 1:
The patent applies dynamics by making the DC bus voltage limit adjustable rather than fixed. The upper voltage limit is dynamically changed based on the duty cycle of the switch - when the duty cycle indicates excessive power dissipation, the upper voltage limit is raised to allow more energy storage capacity, reducing the frequency and amount of power that must be dissipated through shunt resistors. This resolves the contradiction by adapting the voltage constraint to system conditions.
Solution Approach 2:
The patent changes the parameter of DC bus voltage limit from a fixed value to a variable parameter that adjusts based on duty cycle. By monitoring the duty cycle and dynamically modifying the upper voltage threshold, the system optimizes the balance between maintaining voltage stability and minimizing energy loss through resistive dissipation.
2Reliability
If shunt resistors dissipate excess power through heat conversion, then regenerated power from inertial loads can be managed, but additional cabinet cooling is required due to high temperatures
Solution Approach 1:
The dynamic adjustment of the upper DC bus voltage limit based on duty cycle reduces the amount of power that must be dissipated as heat. When the duty cycle indicates high power dissipation conditions, the system raises the voltage threshold, allowing more energy to be stored in the DC bus capacitance rather than being converted to heat, thereby reducing component temperatures and cooling requirements.
3Device complexity
If a fixed upper DC bus voltage limit is used, then system design is simplified, but excess regenerated power must be dissipated through shunt resistors reducing overall system efficiency
Solution Approach 1:
The patent implements feedback by monitoring the duty cycle of the switch and using this information to dynamically adjust the upper DC bus voltage limit. This closed-loop control allows the system to respond to actual operating conditions, increasing energy efficiency by reducing unnecessary power dissipation while adding only moderate control complexity.
Solution Approach 2:
The upper voltage limit parameter is transformed from a fixed design constant to a dynamically adjustable parameter based on real-time duty cycle measurements. This parameter change enables the system to optimize energy efficiency by adapting the voltage threshold to match actual power dissipation conditions.
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 approach enhances the efficiency and reliability of motor drive systems by minimizing power dissipation as heat, reducing component temperatures, and storing excess energy that would otherwise be lost, leading to improved operational efficiency and reduced costs.
Implementation Method 1
a switch that connects a resistive circuit across the DC bus, the switch being closed when the DC bus voltage reaches an upper voltage value and opened when the DC bus voltage reaches a lower voltage value
Implementation Method 2
this excess power regenerated by the electric motor may be absorbed and subsequently dissipated through shunt resistors that can be electrically coupled across the DC bus. Because these resistors simply convert the power to heat
Data Source
AI summary
A method for controlling voltage of a DC bus in a converter circuit is provided. The method includes monitoring a duty cycle of a switch that connects a resistive circuit across the DC bus, the switch being closed when the DC bus voltage reaches an upper voltage value and opened when the DC bus voltage reaches a lower voltage value and altering the lower voltage value based upon the duty cycle of the switch.