Solid-State Relay Inrush Current Control for Multi-Load Charging

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Solution Overview

Problem

Current technologies fail to efficiently manage the high inrush current when multiple switching DC chargers are connected simultaneously to an alternating electrical network, leading to premature wear and tear of connection and wiring elements, and potential false tripping of protective switches, especially in scenarios like classrooms with many devices charging at once.

Innovation Solution

An electronic device utilizing solid-state relays (SSR) with zero-crossing connection capabilities, along with a transient filter and a control unit, to manage the inrush current by delaying the activation of SSRs and dividing the loads into groups to maintain current within safe limits, ensuring electrical security and extending the lifespan of connection components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If multiple switching DC chargers are connected simultaneously to the alternating electrical network, then the productivity of charging multiple devices is improved, but the inrush current exceeds the nominal current value causing harmful effects

Engineering Contradiction:

Improvesimultaneous charging capabilityVSAvoidinrush current

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent divides the group of simultaneously connected chargers into multiple subgroups using solid-state relays. Each subgroup is connected to the network through its own SSR, which independently controls the connection timing. This segmentation allows the total inrush current to be distributed across multiple controlled connection events rather than occurring all at once, thus maintaining high productivity while reducing peak current stress on the network and protective devices.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The control unit activates solid-state relays in a predetermined sequence with time delays between activations. Before all chargers are connected, the first SSRs are activated with a preliminary action, allowing their inrush current to subside before subsequent SSRs are activated. This preliminary activation strategy ensures that the sum of inrush currents from all chargers does not exceed the nominal current value, preventing false tripping while enabling simultaneous charging of all devices.

Inventive Principle:

Principle #10Preliminary action

2Object-generated harmful factors

If the inrush current is limited by sequential connection of loads, then the harmful current peaks are reduced, but the connection time and loss of time increase

Engineering Contradiction:

Improvecurrent peakVSAvoidconnection time

Core Design Contradiction:

Object-generated harmful factorsVSLoss of time

Solution Approach 1:

The patent implements periodic activation of solid-state relays with optimized time intervals. The control unit activates SSRs in cycles, with each activation occurring after a predetermined time delay that allows the inrush current from previously activated chargers to stabilize. This periodic action pattern ensures current peaks are limited while minimizing the total connection time, as multiple chargers are still connected in parallel rather than one by one, and the delays are optimized to be as short as possible while still preventing current exceedance.

Inventive Principle:

Principle #19Periodic action

3Reliability

If a thermo-magnetic switch protects the installation with high trip current, then the reliability of protection is improved, but the device complexity and ease of operation worsen due to false tripping

Engineering Contradiction:

Improveprotection reliabilityVSAvoidfalse tripping prevention

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent introduces solid-state relays as intermediary devices between the chargers and the thermo-magnetic switch. These SSRs act as mediators that control the connection timing of each charger subgroup, ensuring that the sum of inrush currents does not trigger the protective switch. This intermediary control layer maintains the reliability of the thermo-magnetic protection while preventing false tripping, as the SSRs manage the inrush current distribution before it reaches the protective device, eliminating the need for complex switch configurations or user interventions.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 limits peak current, prevents premature switch tripping, and ensures stable network current, allowing for safe and efficient simultaneous connection of multiple loads, thereby reducing wear and tear on electrical components and maintaining electrical security.

Implementation Method 1

SSRs with zero-crossing connection capabilities

Methodology Applied

Scientific EffectZero-crossing detection:

Implementation Method 2

transient filter

Methodology Applied

Scientific EffectTransient filtering:

Data Source

PatentUS9509140B2Electronic device for the connection of two or more loads to the alternating electrical network and the executed connection procedure

Publication Date: 2016.11.29 EXO

AI summary

Electronic device for the connection of two or more loads to the alternating electrical network and the executed connection procedure, allowing for the supply of such loads keeping under control inrush current value, as well as supplying the nominal current value during steady state. The device and its procedure comprise a clear solution especially designed for simultaneous charge of significant amount of electronic devices, whose charge is carried out by switching-type DC chargers. This situation is feasible for both single-phase networks of 110 VAC or 220 VAC nominal.