Brake Chopper Control via PWM Staggering for DC Link Voltage Regulation
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Solution Overview
Problem
Conventional brake chopper control methods often result in fixed braking powers, leading to unnecessarily high braking power and inefficient voltage regulation in DC voltage intermediate circuits of frequency converters.
Innovation Solution
The method involves controlling braking power by staggering the control operations of parallel brake resistors using pulse width modulation, adjusting the on-periods of switches based on the intermediate circuit voltage to match momentary braking needs, and utilizing modulators for precise power management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional tolerance band control is used with parallel brake resistors, then braking power can be increased, but the braking power becomes fixed and may be unnecessarily high for momentary needs
Solution Approach 1:
The patent applies dynamics by transitioning from fixed braking power to variable braking power through pulse width modulation. The control unit dynamically adjusts the duty cycle of switching signals sent to parallel brake resistors, enabling the braking power to vary continuously based on momentary voltage levels and braking needs, thus resolving the contradiction between having sufficient braking power and adapting to varying requirements
Solution Approach 2:
The patent changes the parameter of braking power from fixed to variable by modulating the duty cycle of the switching signals. By varying the duty cycle parameter, the effective braking power is adjusted in real-time according to the intermediate circuit voltage level, allowing the system to provide high braking power when needed while consuming minimal power during normal operation
2Power
If multiple brake resistors are connected in parallel with simultaneous control, then braking power is increased, but current ripple and interference increase
Solution Approach 1:
The patent applies periodic action by using pulse width modulation with switching signals that periodically activate and deactivate the parallel brake resistors. The control unit generates periodic switching signals with varying duty cycles, creating a controlled periodic action that maintains high braking power while reducing current ripple through the intermediate circuit capacitor
Solution Approach 2:
The patent uses dynamic control of the switching signals to adjust the duty cycle in real-time. This dynamic adjustment allows the system to optimize the switching patterns of parallel brake resistors, maintaining effective braking power while minimizing harmful current ripple and interference through coordinated switching actions
3Reliability
If high braking power is applied continuously, then voltage regulation is improved, but strain on capacitors and energy loss increase
Solution Approach 1:
The patent applies feedback by continuously monitoring the intermediate circuit voltage level and using this information to adjust the duty cycle of switching signals. The control unit receives feedback from voltage sensors and dynamically modifies the braking power accordingly, ensuring reliable voltage regulation while minimizing energy loss by applying braking power only when and as much as needed
Solution Approach 2:
The patent uses dynamic adjustment of braking power based on real-time voltage conditions. By continuously adapting the duty cycle parameter in response to voltage levels, the system maintains reliable voltage regulation without continuously applying high braking power, thereby reducing energy loss and strain on capacitors
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 allows for dynamic adjustment of braking power, reducing intermediate circuit currents, minimizing ripple and interference, and ensuring even loading of switch components, thereby optimizing power removal and reducing strain on capacitors.
Implementation Method 1
a brake chopper (64) for removing power from the intermediate circuit (60)
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A method for controlling brake resistors and a brake chopper, the number of brake resistors (73, 75, 77) being two or more and the brake resistors being connected in series with switches (72, 74, 76) to be controlled, the series connection being connected between a positive and a negative rail (Udc+, Udc-) of a DC voltage intermediate circuit, the method comprising the step of determining a magnitude for a voltage (Udc) of the DC intermediate circuit; and determining a first voltage limit (Ulim1) and a second voltage limit (Ulim2). The method further comprises the steps of switching brake resistors to the intermediate circuit in a periodically alternating manner, each switch being switched during a switching period and the on-period of each switch in a switching period being responsive to the magnitude of the voltage in the DC voltage intermediate circuit when the voltage is above the first predetermined limit and below the second predetermined limit.