Half-Bridge DC Link Capacitor Discharge With dV/dt Current Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In high-voltage traction networks of electric or hybrid vehicles, existing methods for actively discharging DC link capacitors face challenges with large currents and heat dissipation, requiring a reliable and efficient solution to prevent transistor damage and ensure safe energy conversion.
Innovation Solution
A half-bridge circuit with high-side and low-side transistors, a voltage divider, and a differentiator/comparator system, controlled by a driver module and control unit, allows for proportional current determination and regulation, enabling safe and efficient discharge of DC link capacitors by managing heat dissipation and current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a resistive load is used to actively discharge the DC link capacitor, then the energy stored in the capacitor is converted into heat, but the currents become very large and the heat dissipation becomes problematic
Solution Approach 1:
The patent introduces a half-bridge circuit as an intermediary between the DC link capacitor and the resistive load. This circuit includes transistors that act as controlled switches, mediating the discharge process by regulating current flow through the resistive load, thereby controlling heat generation and dissipation rather than allowing uncontrolled direct discharge.
Solution Approach 2:
The patent changes the operating parameters of the discharge system by using pulse-width modulation (PWM) control of the transistors in the half-bridge circuit. This allows the system to vary the duty cycle and frequency of current flow through the resistive load, thereby controlling the average power dissipation and heat generation while maintaining effective capacitor discharge.
2Ease of operation
If transistors are used in the half-bridge circuit to control discharge current, then current regulation is achieved, but the transistors cannot be operated in permanent short circuit as they could be destroyed
Solution Approach 1:
The patent employs feedback control through a differentiator circuit that monitors the voltage across the DC link capacitor and generates a control signal proportional to the rate of voltage change (dV/dt). This feedback signal is used to control the transistor switching, automatically adjusting the discharge current to prevent excessive currents that could damage the transistors while maintaining effective discharge.
Solution Approach 2:
The patent uses periodic pulse-width modulation (PWM) switching of the transistors instead of continuous operation. The transistors are switched on and off in controlled pulses, allowing them to dissipate heat between pulses and avoiding permanent short circuit conditions that would destroy the devices while still achieving effective capacitor discharge over time.
3Measurement precision
If direct current measurement is used to control discharge, then current monitoring is achieved, but the system becomes more complex
Solution Approach 1:
The patent replaces direct electrical current measurement with a mathematical substitution approach. Instead of measuring current directly with current sensors, the system measures the voltage across the capacitor and its rate of change (dV/dt) using a differentiator circuit, then uses this information to control the discharge current. This substitutes a complex current measurement system with a simpler voltage-based control system.
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 solution effectively manages high currents, prevents transistor damage, and ensures efficient heat dissipation, providing a robust, self-regulating, and fast discharge mechanism for DC link capacitors, suitable for high-voltage systems.
Implementation Method 1
Via the differentiator, the discharge current of the DC link capacitor is now determined without direct current measurement, since said discharge current is proportional to the change in voltage at the DC link capacitor over time
Implementation Method 2
Due to the high currents in normal operation, the transistors of the half-bridge circuit are very well thermally coupled to dissipate the heat loss
Implementation Method 3
One way of actively discharging is to connect a resistive load that converts the energy stored in the DC link capacitor into heat
Data Source
AI summary
An apparatus for actively discharging at least one DC link capacitor, comprising at least one half-bridge circuit having a high-side transistor and a low-side transistor, wherein the half-bridge circuit is arranged in parallel with the DC link capacitor, wherein a voltage divider comprising at least two resistors is arranged in parallel with the DC link capacitor, wherein a tap of the voltage divider is connected to at least one differentiator, wherein at least one driver module for generating gate driver signals is assigned to the half-bridge circuit, and at least one control unit, wherein the control unit is designed in such a way that, in an active discharge mode, at least one transistor of the half-bridge circuit is controlled as a function of an output signal of the differentiator, as well as to an associated method.