Green and Efficient Power Distribution Solution for Rail Transit

Zhejiang Rockwell Energy Technology Co., Ltd.

1. Industry Background and Pain Point Analysis

1.1 Industry Background

Urban rail transit is a major energy consumer in cities. The traditional traction power supply system adopts an "AC power supply + onboard rectification" architecture, which suffers from regenerative braking energy waste, large equipment footprint, and high energy consumption. Full DC power supply represents a technological revolution for rail transit power supply.

Flexible DC Power Supply and Distribution System

1.2 Four Major Pain Points of Traditional Rail Transit Power Supply

Pain Point	Manifestation	Physical Root Cause
Regenerative Braking Waste	Braking energy dissipated as heat through resistors	AC architecture cannot directly recover energy
Large Equipment Footprint	Bulky substations + rectifier units	Power frequency transformer + rectifier
Low Energy Efficiency	Losses from multiple conversion stages	AC to DC through multiple stages
High Construction Cost	Numerous equipment pieces and large civil works	Complex architecture

1.3 Core Differences Between Traditional and SST Full DC Power Supply (Physical Essence)

Traditional AC Power Supply

Aspect	Physical Principle	Limitation
Urban Grid → AC Substation	Step-down power supply	Onboard rectification required
Onboard Rectification	AC → DC for traction	Braking energy cannot be fed back

SST Full DC Power Supply

Aspect	Physical Principle	Advantage
SST Substation	AC → DC±35kV	Single-stage conversion
DC Ring Network	Direct DC supply	Regenerative braking energy directly fed back

Physical Essence: The full DC architecture enables regenerative braking energy to be fed back directly to other trains or the grid through the DC ring network. This is the physical foundation for achieving +5% energy efficiency improvement.

2. Solution Overview and Value Proposition

2.1 Solution Definition (BLUF)

The SST Full DC Power Supply Solution replaces traditional AC power supply with a three-level DC architecture of DC±35kV/1500V/750V:

Construction cost -20%
Energy efficiency +5%
Verified through the Guangzhou Metro Line 8 pilot project

On-site Operation Diagram

2.2 Core Value Proposition

Value Dimension	Quantitative Metric	Description
DC Voltage Levels	±35kV/1500V/750V	Three-level DC power supply
Construction Cost	-20%	Eliminates transformers and rectifiers
Energy Efficiency	+5%	Regenerative braking direct feedback
Pilot Project	Guangzhou Metro Line 8	Engineering verification

3. System Architecture Design

3.1 System Topology (Layered Breakdown)

Urban Grid ──► SST Substation (DC±35kV)
                    │
                    ├──► DC Ring Network
                    │      ├──► Onboard DC1500V
                    │      └──► Onboard DC750V
                    │
                    └──► Regenerative Braking Energy Feedback

Topology Layer-by-Layer Explanation

Layer	Composition	Power Flow	Design Rationale
Substation	SST	Urban Grid → DC±35kV	Single-stage conversion
DC Ring Network	±35kV Bus	Substation → Trains	Direct DC supply
Train Power Supply	DC1500V/750V	Ring Network → Onboard	Regenerative feedback

3.2 Regenerative Braking Feedback Principle

When a train brakes, the motor operates as a generator. In traditional solutions, this energy is dissipated as heat through resistors. The SST full DC architecture allows braking energy to be fed directly through the DC ring network to adjacent accelerating trains or back to the grid, significantly improving energy utilization.

4. Core Equipment and Technical Parameters

Parameter	Value	Physical Significance
DC Voltage Levels	±35kV/1500V/750V	Three-level DC power supply
Construction Cost	-20%	Eliminates transformers and rectifiers
Energy Efficiency	+5%	Regenerative braking feedback
Pilot Project	Guangzhou Metro Line 8	Engineering verification

5. Technical Highlights and In-Depth Physical Principle Analysis

5.1 Highlight 1: Full DC Architecture

Physical Principle: Eliminates power frequency transformers and rectification stages. The urban grid power is converted to DC through SST in a single stage.

Quantified Benefit: Construction cost reduced by 20%, fewer equipment pieces.

5.2 Highlight 2: Regenerative Braking Feedback

Physical Principle: The DC ring network allows braking energy to be fed back directly, eliminating resistive heat dissipation losses.

Quantified Benefit: Traction energy consumption reduced, energy efficiency +5%.