Series-Connected Limiter Cells for DC Voltage Overvoltage Protection
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Solution Overview
Problem
Existing DC voltage networks face challenges in effectively limiting overvoltages resulting from switching operations, as current solutions like varistors and RC networks are either expensive, bulky, or unsuitable for frequent energy absorption, and brake choppers require expensive controllable switching elements for high voltages.
Innovation Solution
The apparatus comprises multiple limiter cells connected in series, each with a controllable switching element, discharge resistor, and capacitor, allowing voltage to be dropped across all cells, with switching elements operated based on capacitor voltage to manage overvoltages, enabling the use of less expensive components and independent voltage regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If varistors are used to limit overvoltages, then high discharge currents can be absorbed, but they age quickly under frequent energy absorption
Solution Approach 1:
The protection function is segmented between the brake chopper (controllable switching element with resistor) that handles frequent overvoltages, and the varistor that provides backup protection. This division allows each component to operate in its optimal range, extending overall system reliability.
Solution Approach 2:
The brake chopper acts as an intermediary that absorbs frequent overvoltage events before they reach the varistor, protecting the varistor from frequent activation and extending its service life while maintaining overvoltage protection capability.
2Reliability
If RC networks are used for overvoltage limitation, then overvoltages can be absorbed, but the capacitor is expensive, large, and heavy
Solution Approach 1:
The overvoltage protection function is segmented into multiple limiter cells connected in series, each handling a portion of the total voltage. This allows the use of smaller capacitors in each cell rather than one large capacitor, reducing overall size and weight while maintaining protection capability.
Solution Approach 2:
The solution transitions from a single large capacitor handling the full voltage to multiple smaller capacitors distributed across series-connected cells, effectively moving from a one-dimensional (single component) to a multi-dimensional (distributed system) approach, reducing weight and size.
3Reliability
If brake choppers are used for high voltages above 1000 V, then overvoltages can be limited, but expensive controllable switching elements are required
Solution Approach 1:
The high voltage protection function is segmented into multiple limiter cells connected in series, each operating at a lower voltage level. This allows the use of less expensive switching elements rated for lower voltages rather than requiring expensive high-voltage switching elements, while maintaining overall high-voltage protection capability.
Solution Approach 2:
The solution moves from using expensive high-voltage switching elements in a single cell to using multiple less expensive low-voltage switching elements distributed across series-connected cells, effectively trading component count for reduced per-component cost and improved manufacturability.
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 effectively limits overvoltages in DC voltage networks by using modular, series-connected limiter cells with capacitors to buffer voltage changes, allowing for precise control and reducing the risk of component damage, even at high voltages above 1000 V, without the need for expensive switching elements.
Implementation Method 1
each of which comprises an arrangement of a controllable switching element (11-1, . . . , 11-n), a discharge resistor (12-1, . . . , 12-n) and a capacitor (13-1, . .. , 13-n), across all of which the voltage (Uges) applied between the first supply potential level (2) and the second supply potential level (3) is dropped
Implementation Method 2
The resistor 12 is switched into the intermediate circuit in pulsed mode by means of the controllable switching element 11, so that the voltage on the DC-link capacitor 4 is gradually reduced again
Data Source
AI summary
Various embodiments include an apparatus for limiting voltage for a DC voltage network, wherein overvoltages resulting from switching operations occur between a first supply potential level and a second supply potential level of the DC voltage network. The apparatus comprises at least two limiter cells connected in series between the first supply potential level and the second supply potential level. Each limiter cell comprises a controllable switching element, a discharge resistor, and a capacitor, across all of which a voltage applied between the first supply potential level and the second supply potential level is dropped. During operation of the apparatus, based at least in part on the voltage dropped across the respective capacitor of a particular limiter cell, the controllable switching element of the limiter cell is switched on or off.