# Non-Intrusive Load Disaggregation by Linear Classifier Group Considering Multi-Feature Integration
## 2 Appliance Modeling  
### Appliance Behaviour Modelling  
The aim of NILM is to identify the electrical appliances inside the user. The schematic diagram is shown in Figure 1. Self-adaptive establishment of an exclusive appliance model library for different users is important to non-intrusive load identification. The NILM acquires the comprehensive power consumption data at the power supply entrance. The power consumption data of all loads is included in one collected signal, out of which the power consumption information of individual loads should be separated and extracted. Therefore, exploiting distinguishable features to model appliance behavior is a significant work for NILM. Low-frequency signals contain less load information, so most of the existing low-rate NILM studies can only use power indicators to characterize devices. The power values of some electrical appliances are very close, so the accuracy is low when power is the only feature of identification. In fact, the operating features of the load can be extracted from the load data. Through the analysis of the concrete operation process of each appliance, some distinguishing features can be found. The power consumption curves of several typical appliances are shown in Figure 2.  
Figure 2 presents power consumption curves of several typical appliances, which show regular operating features. As presenting a fixed working cycle and interval time in Figure 2, the refrigerator runs in a periodic cycle for 15 min and closes for 51 min. A complete operation cycle of the dishwasher can be divided into three main stages: wash, rinse and dry. The operation cycle is determined by its internal structure. An oven is also an intermittent running load, but the ON/OFF-duration is not fixed. The operation time is between 15 min and 1 h, decided by the users' setting. Observing the curve of washer dry, we can find that the longest time is the first ON time followed by several ON/OFF cycles. The number of ON/OFF cycles is related to laundry loads. In this work, the following eight features are selected, divided into two categories, i.e., intrinsic features and statistical features. Intrinsic features, known as the electrical features, are determined by the appliance itself. Statistical features reflect users' habits of using specific appliances, which can be called non-electrical features [34]. For example, TV is used more in the evening than daytime, and the lamp has similar statistical features. Intrinsic features include the following four criteria:  
* Active power change. This refers to the event caused by the state transition of appliances, and appears as the rising or falling edge. The typical appliances can be divided into three types: single-state, continuous varying and multi-state. The single-state load has a pair of identical rising/falling edges and constant power consumption between them, such as microwave,  
Figure 1: The schematic diagram of non-intrusive load monitoring (NILM). Figure 2: Load profiles of eight typical appliances. A continuous varying load such as refrigerator generally has a pair of different rising/falling edges and the power consumption during operation is continuously changing. Multi-state load has more than one working stage, such as a dishwasher. * On-duration. This refers to the continuous operating time in a periodic cycle, which is mainly applied to the loads with fixed operating periods, such as a refrigerator. As mentioned above, the On-duration of the refrigerator is 15 min. * Off-duration. It stands for the continuous standby time in a periodic cycle. For instance, the Off-duration of refrigerator is 51 min. Figure 3 illustrates the On-duration and Off-duration of refrigerator in a cycle. * On times. This means the number of turning on contained in each operation cycle. The \"On times\" is used for identification of household appliances with a fixed operating process, such as dishwashers. The dishwasher experiences the same process every time in a complete washing process.