DAB - Dual Active Bridge Converter¶

Overview¶

The Dual Active Bridge (DAB) is a bidirectional isolated DC-DC converter using two active full-bridges connected through a high-frequency transformer. It's widely used in energy storage systems, EV chargers, and solid-state transformers.

Difficulty: Advanced

Estimated Time: 45-60 minutes

Status: Placeholder

Learning Objectives¶

Understand DAB topology and operating principles
Implement phase-shift modulation
Analyze ZVS conditions
Design for bidirectional power flow

Topology¶

    Primary Bridge               Secondary Bridge
         ┌───┐         1:n           ┌───┐
  Vdc1 ──┤S1 ├──┬──────●═══●──────┬──┤S5 ├── Vdc2
         └───┘  │      ║   ║      │  └───┘
                │      ║   ║      │
         ┌───┐  │  Lk  ║   ║      │  ┌───┐
         │S2 ├──┴──────╫───╫──────┴──┤S6 │
         └───┘         ║   ║         └───┘
                       ║   ║
         ┌───┐         ║   ║         ┌───┐
         │S3 ├──┬──────╫───╫──────┬──┤S7 │
         └───┘  │      ║   ║      │  └───┘
                │      ║   ║      │
         ┌───┐  │      ●═══●      │  ┌───┐
  GND ───┤S4 ├──┴─────────────────┴──┤S8 ├── GND
         └───┘                       └───┘

Key Components: - Two full-bridge converters (H-bridges) - High-frequency transformer (n:1) - Series inductance Lk (leakage or external)

Operating Principle¶

Phase-Shift Modulation¶

Power transfer controlled by phase shift φ between bridges:

Primary Bridge:  ┌───┐   ┌───┐   ┌───┐
                 │   │   │   │   │   │
              ───┘   └───┘   └───┘   └───
                 ←──────→
                    φ (phase shift)
Secondary Bridge:    ┌───┐   ┌───┐   ┌───┐
                     │   │   │   │   │   │
                 ────┘   └───┘   └───┘   └

Power Transfer Equation¶

P = (n × Vdc1 × Vdc2 × φ × (π - |φ|)) / (2 × π² × fs × Lk)

Where: - φ = phase shift (radians, -π/2 to π/2) - fs = switching frequency - Lk = series inductance - n = turns ratio

Voltage Gain¶

At φ = π/2 (maximum power):

Vdc2/Vdc1 = n (voltage matching condition)

Key Parameters¶

Parameter	Symbol	Typical Value	Unit
DC Voltage 1	Vdc1	400	V
DC Voltage 2	Vdc2	48-400	V
Power	P	1-50	kW
Switching Frequency	fs	50-200	kHz
Series Inductance	Lk	10-100	μH
Turns Ratio	n	1:1 to 10:1	-

ZVS (Zero Voltage Switching)¶

ZVS Condition¶

For ZVS turn-on, the device must have current flowing through its body diode:

ZVS achieved when: I_Lk(t_switch) > I_min

Where: I_min = (2 × Coss × Vdc) / t_dead

ZVS Region¶

Power
  │          ╱╲
  │         ╱  ╲  ZVS region
  │        ╱    ╲
  │       ╱      ╲
  │──────╱────────╲────────
  │     ╱ Hard     ╲
  │    ╱  switching ╲
  └────────────────────────► φ (phase shift)
      -π/2    0    π/2

Modulation Strategies¶

Single Phase Shift (SPS)¶

Both bridges operate at 50% duty cycle
Only phase shift varies
Simple control
Limited ZVS range

Extended Phase Shift (EPS)¶

Primary bridge: variable duty cycle D1
Secondary bridge: 50% duty cycle + phase shift
Extended ZVS range

Triple Phase Shift (TPS)¶

Both bridges: variable duty cycles D1, D2
Phase shift φ between bridges
Widest ZVS range
Most complex control

Design Procedure¶

Step 1: Determine Power and Voltages¶

Given: Vdc1 = 400V, Vdc2 = 48V, P = 3.3kW

Step 2: Select Turns Ratio¶

For voltage matching:

n = Vdc1 / Vdc2 = 400/48 ≈ 8:1

Step 3: Calculate Inductance¶

For desired phase shift at rated power (e.g., φ = 30° = π/6):

Lk = (n × Vdc1 × Vdc2 × φ × (π - φ)) / (2 × π² × fs × P)

Step 4: Verify ZVS¶

Check that ZVS is maintained over operating range.

Control Architecture¶

                ┌─────────────────────────────────┐
Vdc2_ref ──────►│                                 │
                │   Voltage     Current    Phase  │
                │   Controller → Controller → Shift │──► PWM
Vdc2_meas ─────►│     (PI)        (PI)    Modulator│
                │                                 │
Idc2_meas ─────►│                                 │
                └─────────────────────────────────┘

Bidirectional Operation¶

Mode	Phase Shift	Power Flow
Forward	φ > 0	Vdc1 → Vdc2
Reverse	φ < 0	Vdc2 → Vdc1
Zero	φ = 0	No power transfer

Exercises¶

Exercise 1: Basic DAB¶

Build DAB with Vdc1 = 400V, Vdc2 = 48V, n = 8:1
Apply φ = 30° phase shift
Measure power transfer

Exercise 2: Phase Shift Sweep¶

Sweep φ from -60° to +60°
Plot P vs φ
Verify theoretical curve

Exercise 3: ZVS Analysis¶

Add output capacitance to switches
Observe switch waveforms
Identify ZVS/hard-switching transitions

Exercise 4: Bidirectional Operation¶

Implement voltage control loop
Apply step change in Vdc2_ref
Observe automatic direction change

Applications¶

Application	Power	Voltage Range
EV OBC	3-22 kW	400V ↔ 48-450V
Energy Storage	10-100 kW	400V ↔ 200-400V
Solid-State Transformer	1-10 MW	MV ↔ LV
DC Microgrid	5-50 kW	380V ↔ 48V

LLC Resonant - Unidirectional alternative
Full Bridge - Single active bridge
Onboard Charger - Application

References¶

De Doncker, R.W. "A Three-Phase Soft-Switched High-Power-Density DC/DC Converter"
Zhao, B. "Overview of Dual-Active-Bridge Isolated Bidirectional DC-DC Converter"
Krismer, F. "Accurate Power Loss Model Derivation of a DAB Converter"

Circuit Files¶

Status: Placeholder - dab_basic.ipes - Basic DAB with SPS - dab_zvs.ipes - With ZVS analysis - dab_bidirectional.ipes - Closed-loop bidirectional

Example Version: 1.0 (Placeholder) Last updated: 2026-02 GeckoCIRCUITS v1.0