Dynamic DC Link Voltage Regulation for Braking Energy Recovery
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Solution Overview
Problem
Conventional electric motor drive control circuits face challenges in efficiently managing braking energy recovery due to the inability of voltage regulators to dynamically adjust DC link voltage in response to changing motor speeds, leading to increased capacitor size requirements and inefficiencies.
Innovation Solution
A braking energy recovery system that includes a first regulator, an energy storage device, a second regulator, a sensing mechanism, and a controller, which dynamically regulates the DC link voltage based on motor speed and back EMF to maintain a constant energy balance, using a switchmode regulator and energy management signals to optimize energy storage and release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the voltage regulator maintains a fixed DC link voltage level, then the voltage regulation is simple and stable, but the capacitor size must be increased to handle braking energy recovery
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed DC link voltage regulator to a dynamic voltage regulator that adjusts the DC link voltage level in response to motor operating conditions. The regulator dynamically modifies the voltage setpoint based on feedback signals representing motor speed and current, enabling the system to adapt to varying energy storage and release requirements during acceleration and deceleration cycles, thereby reducing capacitor size while maintaining voltage stability.
2Loss of energy
If the DC link voltage is dynamically adjusted based on motor speed and back EMF, then energy recovery efficiency is improved, but the device complexity increases
Solution Approach 1:
The patent implements feedback by incorporating sensors that continuously monitor motor speed and current, and by feeding this information back to the voltage regulator. The regulator uses this feedback to dynamically adjust the DC link voltage setpoint, optimizing energy recovery during braking by ensuring the capacitor voltage matches the motor's back EMF characteristics, thereby improving energy recovery efficiency without requiring complex external control systems.
Solution Approach 2:
The system applies self-service by enabling the voltage regulator to automatically adjust the DC link voltage based on motor operating conditions without external intervention. The regulator monitors motor speed and current signals and autonomously modifies the voltage setpoint to optimize energy recovery, reducing the need for additional complex control circuitry while improving braking energy recovery efficiency.
3Device complexity
If a uni-directional power regulator is used, then the device complexity is reduced, but the ability to reduce DC link voltage during braking is lost
Solution Approach 1:
The patent applies universality by designing a voltage regulator that performs multiple functions: during normal operation it maintains a fixed voltage level, and during braking it dynamically reduces the voltage level to facilitate energy recovery. This multi-functional regulator eliminates the need for separate uni-directional and bi-directional regulators while maintaining structural simplicity, achieving both voltage adjustment capability and reduced device complexity.
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 solution enables compact energy storage and efficient power delivery, reducing the physical size of capacitors and enhancing performance by dynamically adjusting the DC link voltage in response to motor speed, thereby addressing the inefficiencies of conventional systems.
Implementation Method 1
During rotation of the motor 22, each of motor's stator windings generates a voltage known as back Electromotive Force or back EMF
Implementation Method 2
The fixed DC link voltage comprises a constant voltage level, VLINK, and is stored on DC link capacitor 14
Data Source
AI summary
A braking energy recovery system (50) for an electric motor (62) comprises first regulator (52), energy storage device (54), second regulator (56), sensor (60), and controller (58). The first regulator (52) outputs a DC link voltage to the energy storage device (54). The second regulator (56) couples to the energy storage device and outputs a motor drive signal to the electric motor (62). The sensor (60) senses an operating characteristic of the electric motor. The controller (58) outputs to the first regulator an energy management signal (74) that comprises a time variant signal as a function of (i) motor speed and/or (ii) back EMF determined via the sensed characteristic, whereby the first regulator dynamically regulates the DC link voltage to maintain substantially constant an energy balance that comprises a sum of (a) rotational and/or linear kinetic energy of the electric motor and (b) energy stored in the energy storage device.