HVDC Module Discharge Control for Blocked-State Voltage Balancing
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Solution Overview
Problem
In high voltage direct current (HVDC) transmission networks, the conversion of alternating current (AC) to direct current (DC) and vice versa leads to unstable voltage distribution between modules when they are in a blocked state, potentially causing cascaded failures due to unbalanced voltage drift over time.
Innovation Solution
An electrical assembly with modules containing switching elements and energy storage devices, where a controller modulates the switching of discharge resistors to emulate a resistive load profile, ensuring voltage balancing by adjusting resistance based on voltage thresholds and physical locations, thereby stabilizing voltage distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If modules are left in blocked state with passive voltage distribution, then device complexity is reduced, but voltage stability deteriorates leading to drift and cascaded failures
Solution Approach 1:
Each module uses its own discharge resistor and controller to autonomously regulate its voltage by emulating resistive load characteristics. The module self-adjusts its discharge current based on its own voltage level relative to neighboring modules, eliminating the need for complex centralized voltage balancing control while ensuring stable voltage distribution throughout the HVDC transmission system.
2Reliability
If discharge resistors are continuously switched to balance voltage, then voltage distribution stability is improved, but energy loss increases
Solution Approach 1:
The discharge switching elements are controlled to switch discharge resistors periodically rather than continuously. The controller monitors voltage levels and activates discharge resistors only when voltage imbalance is detected, allowing the system to maintain stable voltage distribution while minimizing unnecessary energy dissipation through resistive loading.
3Reliability
If emulated resistive load profile is applied with positive slope, then voltage balancing is achieved, but control precision requirements increase
Solution Approach 1:
The system changes the effective resistance parameter dynamically by switching discharge resistors in and out based on voltage levels. Instead of requiring precise continuous control, the system uses discrete switching of resistive elements to create an emulated load profile with positive slope, where the equivalent resistance increases as voltage increases, naturally achieving voltage balancing through passive element characteristics rather than active control precision.
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 prevents voltage drift and ensures stable voltage distribution between modules, reducing the risk of cascaded failures and optimizing power consumption by emulating a resistive load profile that offsets negative impedance characteristics and environmental unbalancing effects.
Implementation Method 1
each discharge circuit including a discharge switching element and a discharge resistor
Data Source
AI summary
An electrical assembly includes a number of modules, each module including at least one module switching element and at least one energy storage device, each module switching element and each energy storage device in each module arranged to be combinable to provide a voltage source, each module including a discharge circuit with a discharge switching element and a discharge resistor, each discharge switching element switchable to switch the corresponding discharge resistor into and out of the corresponding module, wherein the electrical assembly includes a controller configured to control the discharge switching elements to modulate the switching of each discharge resistor into and out of the corresponding module in a voltage balancing mode when the modules are in a blocked state so that each module emulates a resistive load profile to balance a distribution of voltages between the modules, wherein the resistive load profile includes at least one positive resistive slope.