# Simulation Study of Power Management for a Highly Reliable Distribution System using a Triple Active Bridge Converter in a DC Microgrid

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Modeling of the Power Distribution System with the TAB Converter

#### 2.1. Topology of the TAB Converter

_{sw}represents the switching frequency, and L

_{e1}, L

_{e2}, and L

_{e3}denote the inductances that are connected to the different ports, whereas V

_{1}, V

_{2}, and V

_{3}are the input DC sources connected to the primary, secondary, and tertiary sides, respectively.

#### 2.2. Modeling of the Power Distribution System with the TAB Converter

_{DC}supply input power for each load. During the normal operation of the data center, the input DC source transmits power to the loads from the input sources.

## 3. Power Management for the Proposed Distributed System

#### 3.1. Phase-Shift Control of the TAB Converter

_{1}, u

_{2}, and u

_{3}) in each port on the sides of the transformer under phase-shift control. Considering the phase shift of the full-bridge cell of the primary side as the reference value, the phase-shift angle of the control signals between the primary and secondary sides is described as δ

_{2}[rad], whereas the phase-shift angle of the switch signal between the primary and tertiary sides is described as δ

_{3}[rad].

_{1}, V

_{2}, and V

_{3}, and equal inductances at the three ports L

_{e}

_{1}, L

_{e}

_{2}, and L

_{e}

_{3}, the relationship between the power flow and the phase-shift angle can be expressed by the following simplified equations [26]:

_{2}and δ

_{3}; thus, accurate power flow control is obtained. In the design of the parameters of the TAB converter, when the DC input source and the power flows are selected, the phase shift can be calculated based on the phase shifts δ

_{2}and δ

_{3}, and is in the recommended range of 0–0.5236 [rad] [26]. Normally, the inductance and the power flows of the TAB converter can be controlled only by the phase-shift angle.

#### 3.2. Load Balancing Control

_{S}

_{1}, P

_{S}

_{2}, and P

_{S}

_{3}. After analyzing the power from the load side, P

_{R}

_{1}, P

_{R}

_{2}, and P

_{R}

_{3}, and the balanced power in each line, $\overline{{P}_{\mathrm{rack}}}$, the reference power ${P}_{2}^{*}$ and ${P}_{3}^{*}$ at each port of the TAB converter is selected. From Equation (2), it is obvious that the power transmitted in the TAB converter is controlled by the real-time load power and the input power at each power rack. Therefore, by using the load balancing control, the input power of the DC power distribution system can be balanced, while the TAB converter can transmit power between the power racks by using phase-shift control. We propose a power flow control method, which is shown in Figure 5, and consists of the closed-loop phase-shift control and the load balancing control. When the load power in the terminal of the DC power distribution system is varied during full-load or half-load operation, the load balancing control scheme detects the power demand and gives a command to the TAB converter; thus, the power transmission in the power distribution system is adjusted accordingly, with the help of the TAB converter.

## 4. Power Management Simulation

#### 4.1. Simulation Setup

#### 4.2. Simulation Results

_{S}

_{1}, P

_{S}

_{2}, and P

_{S}

_{3}are under the unbalanced condition, delivering 5 kW, 5 kW, and 20 kW, respectively, to the resistive loads. In the second period, when load balancing control is applied and the TAB converter is used, the power flows P

_{S}

_{1}, P

_{S}

_{2}, and P

_{S}

_{3}are adjusted to the same amplitude of 10 kW, ensuring balanced power in the power distribution system under balanced full-load operation. Meanwhile, each of P

_{S}

_{1}and P

_{S}

_{2}transmits 5 kW of power to P

_{S}

_{3}through the TAB converter.

_{S}

_{1}, P

_{S}

_{2}, and P

_{S}

_{3}are adjusted to an amplitude of 5 kW, while P

_{S}

_{1}and P

_{S}

_{2}transmit 2.5 kW of power to P

_{S}

_{3}through the TAB converter, ensuring the transmission of half-power to P

_{R}

_{3}. The waveforms of the power flow in the racks of P

_{S}

_{1}, P

_{S}

_{2}, and P

_{S}

_{3}are changed from the unbalanced to the balanced amplitude using the power flow control, and the power from the input source can be conserved when the load is decreased from full-load to half-load. Further, from the waveforms of P

_{R1}, P

_{R2}, and P

_{R3}, it is clear that the load power required by the users is guaranteed during full-load and half-load operation.

#### 4.3. Discussion of the TAB Converter and Overall System Losses

## 5. Reliability Assessment of Power Distribution System

#### 5.1. Definition of the Reliability

_{(s)}: system reliability, which describes the probability of a system remaining in operation from time zero to time t.

#### 5.2. Reliability Block Diagram Analysis

_{1}–R

_{n}, and the systems function well only when all of the components function properly. If R

_{(S)}represents the total reliability of a system with n elements connected in series, then the overall reliability of a system connected in series can be easily calculated from the reliability of each component:

## 6. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 2.**Diagram of a DC power distribution system in a data center using the triple active bridge (TAB) converter in a DC microgrid.

**Figure 8.**Simulation results for the proposed power distribution system with the TAB converter and power flow control.

**Figure 9.**Block diagram of connection types: (

**a**) Series and parallel connection; (

**b**) Combined connection.

DC Voltage V_{DC} | Switching Frequency | External Inductance | Transformer Leakage Inductance |
---|---|---|---|

380 V | 15 kHz | 43.47 µH | 1.1 µH |

**Table 2.**Simulation parameters for the 380-V TAB converter used in the DC power distribution system.

Power Flow | Full Load without TAB | Full Load with TAB | Half Load with TAB |
---|---|---|---|

P_{1} | 0 | 5 kW | 2.5 kW |

P_{2} | 0 | 5 kW | 2.5 kW |

P_{3} | 0 | 10 kW | 5 kW |

P_{S}_{1} | 5 kW | 10 kW | 5 kW |

P_{S}_{2} | 5 kW | 10 kW | 5 kW |

P_{S}_{3} | 20 kW | 10 kW | 5 kW |

P_{R}_{1} | 5 kW | 5 kW | 2.5 kW |

P_{R}_{2} | 5 kW | 5 kW | 2.5 kW |

P_{R}_{3} | 20 kW | 20 kW | 10 kW |

Component | MTBF (h) | Reliability (%) (within 5 Years) |
---|---|---|

AC utility supply | 99.9999 | |

AC rectifier | 1,960,032 | 97.790126 |

Inverter | 1,817,016 | 97.618276 |

Lead Acid Battery | 1,173,590.3 | 83.318464 |

Switchgear | 446,426.18 | 90.654689 |

**Table 4.**Reliability comparison between a conventional power distribution system and the proposed power distribution system.

System | Reliability (% in 5 Years) | Downtime (Hours) |
---|---|---|

Conventional DC power distribution system | 88.455% | 1011.342 |

Proposed power distribution system | 97.5258% | 216.73992 |

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**MDPI and ACS Style**

Yu, Y.; Wada, K.
Simulation Study of Power Management for a Highly Reliable Distribution System using a Triple Active Bridge Converter in a DC Microgrid. *Energies* **2018**, *11*, 3178.
https://doi.org/10.3390/en11113178

**AMA Style**

Yu Y, Wada K.
Simulation Study of Power Management for a Highly Reliable Distribution System using a Triple Active Bridge Converter in a DC Microgrid. *Energies*. 2018; 11(11):3178.
https://doi.org/10.3390/en11113178

**Chicago/Turabian Style**

Yu, Yue, and Keiji Wada.
2018. "Simulation Study of Power Management for a Highly Reliable Distribution System using a Triple Active Bridge Converter in a DC Microgrid" *Energies* 11, no. 11: 3178.
https://doi.org/10.3390/en11113178