# Impact Analysis of Survivability-Oriented Demand Response on Islanded Operation of Networked Microgrids with High Penetration of Renewables

^{*}

## Abstract

**:**

## 1. Introduction

- In contrast to the existing literature, where DR is triggered by market price signals, DR is triggered by renewable power and load amount in this study. To the best of the author’s knowledge, this is the first study on local-resource triggered DR programs. The major advantages of the local-resource triggered DR program are as follows:
- ♦
- The proposed model doesn’t require any prior information of event occurrence and clearance times. Instead, the proposed model can be activated after detecting the event and can be deactivated after event clearance.
- ♦
- The proposed model maintains the linear tractability of the model and can be implemented using commercial optimization software tools like CPLEX, which guarantee the global optimality of the solution.
- ♦
- Each microgrid can adjust its local demand profile, thus eliminating the need for additional external DR Manager. Surplus or deficit in individual microgrids can be adjusted by sharing power among other microgrids of the network.

- The uncertainties in load and renewable output power are realized via a robust optimization method and the worst-case scenario is considered. In addition, three different scenarios (independent operation, interconnected operation without DR, and the proposed method) are realized and their performance is evaluated.
- Sensitivity analysis of renewable penetration level, amount of shiftable loads, and load absorption level in each microgrid is carried out to evaluate the performance of the proposed method under different conditions.

## 2. Microgrid Network and Survivability-Oriented Demand Response

#### 2.1. Network Configuration

#### 2.2. Demand Response for Survivability Enhancement

**Input Data**: The first step is to read the input data of each microgrid. Input data is comprised of loads (AC, DC, and decomposition of each), renewables output power, component parameters, and penalty costs for load shedding and renewable curtailment. This information is transferred to the next step, where DR operation is carried out.**DR Operation**: The DR operation phase is further decomposed into three steps. In the first step, the ratio of critical and non-critical loads along with fixed and shiftable load ratios are analyzed. Then, the amount of renewable power is analyzed against the amount of load present in each microgrid, which was determined in the previous step. The load shifting is decided to maximize the utilization of renewables and minimize the load shedding amount. This will result in reshaping of the original load profiles. The reshaped load profiles of each microgrid are transferred to the next step, where the optimal operation of the microgrid network is carried out.**Optimal Operation**: In this step, the new load profiles from the previous step are utilized and the available resources are scheduled to minimize the load shedding amount. Load shedding of the whole network for the entire scheduling horizon is carried out in this step. In the islanded mode, service reliability is a major concern. Therefore, the relationship between penalties of load shedding and generation cost of CDGs, defined in the first step, plays an important role to assure the precedence of service reliability over operation cost in the emergency period.

## 3. Problem Formulation

#### 3.1. Deterministic Model

#### 3.1.1. Objective Function

#### 3.1.2. Load Balancing Constraints

#### 3.1.3. Constraints for Controllable Generators

#### 3.1.4. Energy Trading Constraints

#### 3.1.5. Battery Constraints

#### 3.1.6. Demand Response Constraints

#### 3.2. Uncertainty Modeling

#### 3.2.1. Uncertain Variables and Uncertainty Bounds

#### 3.2.2. Worst-Case Identification and Problem Transformation

#### 3.2.3. Tractable Robust Load Balancing

#### 3.3. Final Tractable Robust Counterpart

## 4. Numerical Simulations

#### 4.1. Input Data

#### 4.2. Impact of Interconnection and Demand Response on Survivability

#### 4.2.1. Case 1: Independent Operation

#### 4.2.2. Case 2: Interconnected Operation

#### 4.2.3. Case 3: Interconnected with DR Operation

#### 4.2.4. Performance Comparison

#### 4.3. Discussion and Analysis

#### 4.3.1. Shiftable Load Ratio

#### 4.3.2. Renewable Penetration Level

#### 4.3.3. Load Absorption Level

## 5. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## Nomenclature

Identifiers and Binary Variables | |

$t$ | Index of time, running from 1 to T. |

$m,n$ | Index of microgrids, running from 1 to M and 1 to N, respectively. |

$\mathrm{g}$ | Index of dispatchable generators, running from 1 to G. |

$X$ | Microgrid side identifier, A for AC side and D for DC side microgrid. |

${s}_{m,g}^{X}\left(t\right)$ | Commitment status identifier of dispatchable generator g of X side MG m at t. |

$s{u}_{m,g}^{X}\left(t\right),s{d}_{m,g}^{X}\left(t\right)$ | Start-up and shut-down identifiers of dispatchable generator g of X side MG m at t. |

${c}_{m}\left(t\right)$, ${d}_{m}\left(t\right)$ | Identifier for charging and discharging of BESS in MG m at t. |

${v}_{m}^{X}{}_{}\left(t,{t}^{\prime}\right)$ | Identifier for load shifting allowance in X side MG m from t’ to t. |

Variables and Constants | |

$PU{C}_{m,g}^{XDG}\left({p}_{m,g}^{XDG}\left(t\right)\right)$ | Generation cost of dispatchable unit g of X side MG m at t. |

${p}_{m,g}^{XDG}\left(t\right)$ | Amount of power generated by dispatchable unit g of X side MG m at t. |

$SU{C}_{m,g}^{XDG}\left(t\right)$ | Start-up cost of dispatchable unit g of X side MG m at t. |

$SD{C}_{m,g}^{XDG}\left(t\right)$ | Shut-down cost of dispatchable unit g of X side MG m at t. |

${C}^{CP}$, ${C}^{NP}$ | Penalty for shedding critical and non-critical loads in X side MG m at t. |

${p}_{m}^{XCS}\left(t\right)$, ${p}_{m}^{XNS}\left(t\right)$ | Amount of critical and non-critical load shed in X side MG m at t. |

${C}^{RP},{p}_{m}^{XRS}\left(t\right)$ | Penalty and amount of renewable power curtailed in X side MG m at t. |

${p}_{m}^{XCL}\left(t\right),{p}_{m}^{XNL}\left(t\right)$ | Amount of critical and non-critical load in X side MG m at t. |

${p}_{m}^{X\_AdjL}\left(t\right)$ | Amount of adjusted load in X side MG m at t. |

${p}_{m}^{XSHF}\left(t,{t}^{\prime}\right)$ | Amount of load shifted from t’ to t in X side microgrid m. |

${p}_{m}^{XBC}\left(t\right)$, ${p}_{m}^{XBD}\left(t\right)$ | Amount of electrical energy charged/discharged to/from BESS of X side MG m at t. |

${p}_{m}^{SE}\left(t\right)$, ${p}_{m}^{RE}\left(t\right)$ | Amount of power sent by/received from MG m at t. |

${p}_{m}^{XRG}\left(t\right)$ | Forecasted power of RDG unit of X side MG m at t. |

${P}_{m}^{CAP},{P}_{\left(m,n\right)}^{CAP}$ | Capacity of line connecting mth MG with utility grid and nth MG, respectively. |

${p}_{\left(m,n\right)}^{RE}$(t) | Amount of power received by mth MG from nth MG at t. |

${p}_{\left(m,n\right)}^{SE}$(t) | Amount of power sent by mth MG to nth MG at t. |

${p}_{m}^{TAC}\left(t\right)$, ${p}_{m}^{TDC}\left(t\right)$ | Amount of power sent from AC to DC and DC to AC microgrid in MG m at t. |

${P}_{ILC}^{CAP}$,${\eta}_{m}^{ILC}$ | Capacity and efficiency of ILC connecting AC and DC microgrid in MG m at t. |

${P}_{m}^{XBESS},{p}_{m}^{XSOC}\left(t\right)$ | Capacity and SOC of BEES in X side MG m at t. |

${\eta}_{m}^{XC},{\eta}_{m}^{XD}$ | Charging and discharging loss of BESS in X side MG m. |

${P}_{m}^{XINIT}$ | Initial amount of energy in BESS in X side MG m. |

$T{O}^{Xmax}\left(t\right)$,$F{R}^{Xmax}\left(t\right)$ | Maximum load allowed to shift to and allowed to shift from t in X side MG m. |

${p}_{m}^{XNetL}\left(t\right)$,${p}_{m}^{X\_SL}\left(t\right)$ | Amount of net critical load and shiftable load in X side MG m at t. |

${\widehat{p}}_{m}^{XLOAD}\left(t\right)$,$\u2206{p}_{m}^{XLOAD}\left(t\right)$ | Bounded load and associated uncertainty bound in X side MG m at t. |

${\widehat{p}}_{m}^{XRG}\left(t\right),\u2206{p}_{m}^{XRG}\left(t\right)$ | Bounded RDG output power and associated uncertainty bound in X side MG m at t. |

${\underset{\_}{p}}_{m}^{XLOAD}\left(t\right)$, ${\overline{p}}_{m}^{XLOAD}\left(t\right)$ | Upper and lower bounds of load in X side MG m at t. |

${\underset{\_}{p}}_{m}^{XRG}\left(t\right)$, ${\overline{p}}_{m}^{XRG}\left(t\right)$ | Upper and lower bounds of RDG output power in X side MG m at t. |

${\underset{\_}{z}}_{m}^{XLOAD}\left(t\right),{\overline{z}}_{m}^{XLOAD}\left(t\right)$ | Scaled deviations for load of X side MG m at t. |

${\underset{\_}{z}}_{m}^{XRG}\left(t\right),{\overline{z}}_{m}^{XRG}\left(t\right)$ | Scaled deviations for WT power output of X side MG m at t. |

${\u0413}_{m}^{X}\left(t\right)$, ${\mathsf{\zeta}}_{m}^{X}\left(t\right)$ | Budget of uncertainty and uncertainty adjustment factor of X side MG m at t. |

${\lambda}_{m}^{Xl\pm}\left(t\right)$, ${\lambda}_{m}^{Xr\pm}\left(t\right)$ | Dual variables for load and RDG unit of X side MG m at t. |

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**Figure 4.**Worst-case load and renewable profiles of microgrid 3: (

**a**) Load profile; (

**b**) Renewable power profile.

**Figure 8.**Operation results in independent operation case: (

**a**) Energy transfer; (

**b**) state-of-charge (SOC) of batteries.

**Figure 10.**Operation results in interconnected operation case: (

**a**) Energy transfer; (

**b**) Non-critical load shed.

**Figure 11.**Operation results in interconnected operation case: (

**a**) SOC; (

**b**) Energy exchange among microgrids (MGs).

**Figure 12.**Operation results in demand response (DR) integrated operation case: (

**a**) CDG power; (

**b**) Energy transfer.

**Figure 13.**Operation results in DR integrated operation case: (

**a**) Non-critical load shed; (

**b**) Energy exchanged.

**Figure 16.**Performance comparison of the test cases: (

**a**) Critical load shed; (

**b**) Non-critical load shed; (

**c**) Renewable power curtailed; (

**d**) Reduction in operation cost.

**Figure 17.**Operation results with different shiftable load ratios: (

**a**) Operation cost; (

**b**) Non-critical load shed.

**Figure 18.**Operation results with different shiftable load ratios: (

**a**) Energy transfer; (

**b**) CDG Power; (

**c**) Renewable power curtailed.

**Figure 20.**Operation results with different renewable power levels: (

**a**) Operation cost; (

**b**) Non-critical load shed.

**Figure 21.**Operation results with different renewable power levels: (

**a**) Energy transfer; (

**b**) CDG Power; (

**c**) Renewable power curtailed.

**Figure 23.**Operation results with different load absorption levels: (

**a**) Operation cost; (

**b**) Non-critical load shed.

**Figure 24.**Operation results with different load absorption levels: (

**a**) Energy transfer; (

**b**) CDG Power; (

**c**) Renewable power curtailed.

Parameter | Unit | Microgrid 1 | Microgrid 2 | Microgrid 3 | |||
---|---|---|---|---|---|---|---|

AC CDG | DC CDG | AC CDG | DC CDG | AC CDG | DC CDG | ||

Maximum | kW | 55 | 50 | 55 | 50 | 50 | 40 |

Minimum | kW | 0 | 0 | 0 | 0 | 0 | 0 |

Generation Cost | KRW/kWh | 100 | 106 | 116 | 103 | 104 | 108 |

Parameter | Unit | Microgrid 1 | Microgrid 2 | Microgrid 3 | ||||
---|---|---|---|---|---|---|---|---|

AC Side | DC Side | AC Side | DC Side | AC Side | DC Side | |||

BESS | Capacity | kWh | - | 50 | 50 | - | 50 | 50 |

Efficiency | % | - | 98 | 97 | - | 97 | 98 | |

Converter | Efficiency | % | - | 98 | 98 | - | 98 | 98 |

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## Share and Cite

**MDPI and ACS Style**

Park, S.-H.; Hussain, A.; Kim, H.-M.
Impact Analysis of Survivability-Oriented Demand Response on Islanded Operation of Networked Microgrids with High Penetration of Renewables. *Energies* **2019**, *12*, 452.
https://doi.org/10.3390/en12030452

**AMA Style**

Park S-H, Hussain A, Kim H-M.
Impact Analysis of Survivability-Oriented Demand Response on Islanded Operation of Networked Microgrids with High Penetration of Renewables. *Energies*. 2019; 12(3):452.
https://doi.org/10.3390/en12030452

**Chicago/Turabian Style**

Park, Sung-Ho, Akhtar Hussain, and Hak-Man Kim.
2019. "Impact Analysis of Survivability-Oriented Demand Response on Islanded Operation of Networked Microgrids with High Penetration of Renewables" *Energies* 12, no. 3: 452.
https://doi.org/10.3390/en12030452