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In this paper is presented the simulation of the dispatch of power for a home with controllable loads. The home is supplied from the main power grid and from photovoltaic panels (PV). The power that can be supplied from the main grid is limited. There are considered the cases when the home is supplied with power only from the main power grid, respectively the cases when the home is supplied with power from the PV and main grid. The home has several loads, of which three controllable loads, namely an air conditioning (AC) unit, a washing machine and a fridge. The controllable loads are used to balance the power if the power supplied to the home is not enough.
Abstract - In this paper is presented the simulation of the dispatch of power for a home with controllable loads. The home is supplied from the main power grid and from photovoltaic panels (PV). The power that can be supplied from the main grid is limited. There are considered the cases when the home is supplied with power only from the main power grid, respectively the cases when the home is supplied with power from the PV and main grid. The home has several loads, of which three controllable loads, namely an air conditioning (AC) unit, a washing machine and a fridge. The controllable loads are used to balance the power if the power supplied to the home is not enough.
Keywords: controllable loads; power dispatch; power demand; power grid; photovoltaic panels.
I. INTRODUCTION
The load can be turned on or off when needed for system balance purposes, it is considered as a controllable load.[l]
An example of a controllable load in an electric power system from the operator point of view is the pumping capacities of a pumped hydro storage system or a group of loads whose power supply can be interrupted and/or restricted during peak periods. [1]
A controllable load can also be any load whose power demand can be managed and/or limited, or its operation may be delayed over time.[l]
The researches on controllable loads focused on the following.
An overview of the demand-side resource accomplishments from controllable loads to generalized demand-side resources that included distributed generation and electric energy storage is presented in [2].
Various approaches of the management of controllable loads, respectively the analyzed load characteristics, control strategies and efficacy are presented in [3].
The algorithm for the implementation of a power demand controller was presented in [4]. The controller needed the installed power values and the load factor for the total load and the noncontrollable load.
The control of power system frequency and voltage by controllable loads which were distributed was performed in [5].
The management of microgrid power was presented in [6] considering different cases. The power demand of the microgrid's controllable loafs was either changer or delayed to another time, considering also uncertainties caused by the power supplied from a wind turbine, which were modeled by Monte Carlo simulation method.
The impact and the scheduling of price-responsive and controllable loads was analyzed in [7] for a distribution system.
The optimal operation of a smart grid was studied in [8] so that the inter-connection point power flow fluctuations were minimized. The controllable loads used comprised batteries and heat pumps which helped reduce the maximum power demand and the cost of electric power.
A model for automatic generation control that also had predictive control was analyzed in [9], in order to reduce the imbalance between the power supplied and demand in the power grid.
In [10], the usual residential loads were categorized according to usage, working periods, constraints and possible degree of control. Also, there were performed simulations considering the power demand and the power cost.
A robust optimization model was analyzed in [11] for a smart home. The model considered the controllable loads and photovoltaic system, produced load schedules with different power cost and robust levels.
The rest of the paper is structured as follows. In Section II is presented an overview of the types of loads (loads classification), in Section III is presented the case study and in Section IV are presented the conclusions.
II. OVERVIEW OF THE TYPES OF LOADS
Considering controllability, the loads can be classified in controllable loads and noncontrollable loads.
The noncontrollable loads can't be scheduled and the by power curve is fixed over a period of time. The controllable loads, on the other hand, can be scheduled, turned on or off, therefore the power curve is not fixed over a period of time .[11]
The controllable loads can be divided in: interruptible loads, non-interruptible loads and thermostatically controlled loads.[ll]
An interruptible load is allowed to begin to work, but can be stopped if necessary. The power demand is assumed to be constant, and the duration of the task consists of time steps. A non-interruptible load can't be stopped once it starts working. Thermostatically controlled loads are interruptible but with unique characteristics (for e.g. refrigerators, water heaters or air conditioners). So, the thermostat parameters can be reset without depreciation of the service provided.[10,l 1]
The controllable loads can also be divided in: passive controllable load and active controllable load. The passive controllable loads consist of different residential loads (for e.g. air conditioners, washing machines, fridges). These loads can be turned off or shifted by the load's utilities monitor. So, the power demand in a certain time is lower. This type of load cannot supply power to the grid at any time. The active controllable loads consist of battery storage, Vehicle-to-Grid (V2G), the cogeneration units and, compared with the passive ones, can supply power to the grid. Also, they can be charged from the power grid or discharged to the power grid. [3]
III. CASE STUDY
The case study is performed for a home that has controllable loads considering a day.
The home is supplied from the main power grid and from photovoltaic panels (PV).
The objective is to cover the power demand:
Power supplied from the main power grid [W] >Power demand [W] (1)
Power supplied from the main grid [W] + Power supplied from the PV [W] >Power demand [W] (2)
When the condition from Eq. 1 or Eq. 2 is not meet, then the controllable loads are used.
The power that is supplied from the power grid is limited and is presented in Fig. 1.
The power that is supplied by the PV is presented in Fig. 2.
The simulations will be performed for the cases when:
* the home is supplied with power only from the main power grid;
* the home is supplied with power from the main power grid and PV.
The installed power of the home appliances is presented in Table 1. There are also presented the number of appliances and the work hours.
There are three controllable loads: an air conditioning unit, a washing machine and a fridge.
The power demand of the home is presented in Fig.
The controllable loads will be used to balance the power if the power supplied to the home is not enough.
The simulation is performed with the CitectSCADA software. The simulation interface is presented in Fig. 4.
The simulation results of the power dispatch are presented in Fig. 5 and Fig. 6. In this case the controllable loads are not used.
It can be observed from the simulation that the power demand is not covered, in the case the power is supplied from the main grid, but also from the main grid and PV, between 14 o'clock and 17 o'clock.
The power that is necessary to be supplied to the loads in order to cover the power demand is smaller in the case the PV is considered. It can also be observed that the AC unit is working in this time interval, so it is responsible for the higher power demand.
Also, the washing machine is working at 17 o'clock, so it also responsible for the higher power demand. Also, the fridge is working during the specified interval.
Considering the fact that the AC unit is a controllable load, it can used to lower the power demand, either by turning it off or by changing the thermostat temperature so the power required is lower. The fridge can also be used to lower the power, just as in the case of the AC unit. Regarding the washing machine, it can also be used to lower power demand by turning it off or by postponing the use.
In case of the simulation options, the controllable loads can only be stopped. Considering the required power, only the AC unit is turned off.
The results of the power dispatch for the case in which the AC is turned off are presented in Fig. 7 and 8. In this case the controllable loads are used.
It can be observed from the simulation that the power demand is covered, if the AC unit is turned off in both cases (power supplied from the main grid and from the PV). So, the power supplied is higher than the power demand.
It is observed that the power supplied from the grid, respectively from the grid and from the PV is in several cases higher than the demand, so a battery storage unit can be installed to store the excess power. This power can later be used to cover the demand.
IV. CONCLUSIONS
In this paper were performed simulations of the power dispatch for a home with loads that can be turned off or on, which are known as controllable loads.
The home was supplied either from the main power grid or from the main grid and photovoltaic panels. The power that was supplied from the main grid was limited, so in case the power demand was not covered the controllable loads were used.
The power that was necessary to be supplied to the loads in order to cover the power demand was smaller in the case the PV was considered. It can also be observed that the AC unit was the main responsible for the higher power demand.
In this case, the air conditioning unit was turned off, so the power supplied was higher than the demand.
Also, considering the differences between the power supplied and the power demand during the day, a storage unit can be used. This storage unit can be used to cover the demand.
REFERENCES
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