# Two-Sided Matching Decision Method of Electricity Sales Package Based on Disappointment Theory
## 2 Construction of Evaluation Index System for Electric Power Customers and Power-Selling Companies
### Electric Power Customers' Evaluation Index of Electricity Sales Package
#### 2.1.2 Power Quality  
The factors that measure power quality mainly include voltage sag, harmonic, and three-phase voltage unbalance. Voltage sag is a common voltage disturbance phenomenon in the distribution system. It is an accidental event. No matter how much the reliability of the power system is improved, voltage sag will still exist. Therefore, the degree of voltage sag and the frequency of voltage sag have become one of important standards to measure the quality of power supply by power supply companies. Voltage sag refers to the sudden event that the effective value of bus voltage drops sharply and rapidly and lasts for a very short time [19]. In the power grid, the duration of this phenomenon is mostly 0.5-1.5 s. The International Institute of Electrical and Electronic Engineers (IEEE) defines voltage sag as the phenomenon that the effective value of the supply voltage rapidly drops to 90-10% of the rated value and then returns to the normal value. Voltage sag is mainly caused by short-circuit faults, transformer excitation, and induction motor startup. Short-circuit faults mainly include three-phase grounding short-circuits, single-phase grounding short-circuits, two-phase interphase short-circuits, and two-phase grounding short-circuits. Voltage sag will lead to unit shutdown, misoperation of production machinery, machine damage, and other consequences, resulting in equipment damage, shutdown, or even scrap, and production line interruption. Its coverage is extremely extensive. So far, the semiconductor industry, petrochemical industry, automobile manufacturing, and chemical fiber industry have suffered huge human and material resources and financial losses caused by voltage sag [20]. Therefore, the smaller the amplitude and frequency of the voltage sag of the electric energy provided by the power-selling company, as well as the corresponding anti-interference core technology for different sensitive loads, the higher the power stability of the electricity sold by the company, and the more popular it will be with the electric power customers. A simple and effective voltage sag detection method was proposed in [21]. By sampling the signal for a period, the voltage amplitude is calculated from formula (1) to determine whether the voltage sag occurs. \[U_{RMS}=\sqrt{\frac{1}{N}\int\limits_{t_{0}}^{t_{0}+T}u_{i}{}^{2}(t)dt} \tag{1}\]  
where \(U_{RMS}\) is the effective value of voltage, \(N\) is the number of sampling points in a period, and \(T\) is the signal period. Harmonic current refers to the current of each sinusoidal component whose frequency is an integral multiple of the frequency of the original periodic current when the non  
Figure 1: The proportion of clean energy consumption to total energy consumption from 2017 to 2021.  
sinusoidal periodic current function is expanded in the Fourier series. With the rapid development of science and technology, a large number of powerful electronic nonlinear devices have emerged, such as computers, monitors, induction cookers, and washing machines [22]. There are also traditional nonlinear devices, such as transformers, rotating electrical machines, and fluorescent lamps [23], which are more and more widely used in low-voltage distribution networks and by ordinary electric power customers. Although the single harmonic impact of these new harmonic sources is small, due to their large number, the cumulative harm can not be ignored, which will cause serious harmonic pollution. The harm of harmonic current is mainly reflected in two aspects: first, harmonic current will cause power loss and increase the burden of users' electricity charges; second, the increase in current will cause the equipment temperature to rise, accelerate the insulation aging, and greatly shorten the service life of the equipment.