3.1. Scheduling Model for Multi-Microgrid Systems
Gas Turbine (GT) Model [
17]:
where:
is the amount of natural gas consumed by microgrid I for GT operation in period
t;
and
are the electric and thermal outputs of microgrid I from GT operation in period
t;
and
are the efficiencies of GT in converting to electric and thermal energy for microgrid I in period
t;
is the heating value of natural gas;
and
are the maximum electric and thermal outputs of GT for microgrid I in period
t.
Ground Source Heat Pump (HP) Model [
17]:
where:
is the thermal output of microgrid I from HP operation in period
t;
is the electric to the thermal conversion efficiency of HP for microgrid I in period
t;
is the electric power consumed by microgrid I for HP operation in period
t;
is the maximum electric power for HP operation for microgrid I in period
t.
Electric Cooler (EC) Model [
17]:
where:
is the cooling output of microgrid I from EC operation in period
t;
is the electric to cooling conversion efficiency of EC for microgrid I in period
t;
is the electric power consumed by microgrid I for EC operation in period
t;
is the maximum electric power for EC operation for microgrid I in period
t.
Absorption Cooler (AC) Model [
17]:
where:
is the cooling output of microgrid I from AC operation in period
t;
is the thermal to cooling conversion efficiency of AC for microgrid I in period
t;
is the thermal power consumed by microgrid I for AC operation in period
t;
is the maximum thermal power for AC operation for microgrid I in period
t.
Energy Storage Device Model [
17]:
Energy storage devices include Thermal Storage (TS) and Electric Storage (ES). Since the models for thermal and electric energy storage devices are similar, we will illustrate the model using the example of an electric energy storage device.
Storing excess electric energy in the electric storage device and releasing electric energy when the generated energy is insufficient to meet the electric load is modeled as follows:
where:
represents the current capacity value of microgrid
i’s electric storage device in period
t;
and
are the efficiencies of the electric storage device for charging and discharging in period
t;
and
are the charging and discharging powers of microgrid
i’s electric storage device in period
t;
and
are the minimum and maximum states of the charge ratios of microgrid
i’s electric storage device;
represents the total capacity of microgrid
i’s electric storage device;
and
represent the initial and final stored electric energy in microgrid
i’s electric storage device for a day, as electric storage devices operate in a cyclical manner over a day;
and
are auxiliary binary variables representing the charging and discharging states of microgrid
i’s electric storage device in period
t, and these states are mutually exclusive;
and
are the maximum charging and discharging powers of microgrid
i’s electric storage device in period
t.
The user-side load of a microgrid includes the electrical load, thermal load, and cooling load. The electrical load can be divided into two categories: fixed load and transferable load. Users participate in demand response within the microgrid by adjusting their transferable load.
Fixed Load: These loads are considered crucial as they cannot be transferred. They cannot participate in any demand response programs and need to be serviced by the microgrid.
Transferable Load: These loads are controllable and can be shifted from one time interval to another but cannot be reduced. They can only participate in price-based demand response programs.
The price-based demand response plan for electric loads involves transferring transferable loads out of the microgrid during periods of high grid electricity prices and moving these loads back to the microgrid during periods of lower grid electricity prices. The sum of the transferred transferable loads at each moment should be equal to the sum of the received transferable loads at each moment. This approach aims to reduce users’ electricity costs and alleviate energy supply pressure during peak demand periods. A price-based demand response indirectly influences thermal and cooling loads through various energy conversion devices, as illustrated in
Figure 1.
The model is described as follows:
where:
is the initial electric load demand of microgrid I in period
t;
is the electric load demand of microgrid I after load demand response in period
t;
represents the electric load transferred into microgrid
i at time
t;
represents the electric load transferred out of microgrid
i at time
t;
and
are auxiliary binary variables representing the transfer-in and transfer-out states of electric loads in microgrid
i during time interval
t, and the states of transferring in and out are mutually exclusive;
is the coefficient representing the proportion of transferred-in electric load in microgrid
i within the initial load at time
t;
is the coefficient representing the proportion of the transferred-out electric load in microgrid
i within the initial load at time
t; in this paper,
and
are both set to 15%;
represents the cost reduction of the price-based demand response for electric loads in microgrid
i;
represents the electricity purchase price from the main grid for microgrid
i at time
t.