# Three-Phase Unbalance Analysis Method Based on Three-Phase Motor Current Instantaneous Information
## 3 Simulation Analysis and Experimental Verification
### Simulink Simulation and Result Analysis  
Using Simulink's \"sps_lib\" library, a simulation model is constructed to simulate a three-phase unbalance by adjusting the resistance of a varistor, as shown in Figure 19 (phases A, B, and C, equivalent to phases U, V, and W). The three-phase programmable voltage source has an RMS value of 380 V, a phase of 0\({}^{\circ}\), and a frequency of 60 Hz. The three-phase asynchronous motor (squirrel cage) has an output power of 18.5 kW, an RMS value of 380 V, a frequency of 60 Hz, and pole pairs of 2. The motor stator resistance and inductance are 0.597 \(\Omega\) and 0.001 H, respectively, the rotor resistance and inductance are 0.626 \(\Omega\) and 0.005 H, respectively, and the mutual inductance is 0.035 H. Resistors R1 and R2 are 0.002 \(\Omega\), R3 is 0.001 \(\Omega\), and R4 is 10-k\(\Omega\). Breaker 1 and Breaker 2 have an interconnection resistance of 0.001 \(\Omega\). Breaker 1 is on from 0 s to 2\(\pi\) seconds and 4\(\pi\) seconds to the stop time and off the rest of the time; breaker 2 is on from 2\(\pi\) seconds to 4\(\pi\) seconds and off the rest of the time. A sinusoidal signal of amplitude 1, phase of 0 rad, and frequency of 0.5 rad/s with an instantaneous negative amplitude is set as the value of the variable resistor. The stop time (duration of the simulation) is 16 s.  
Simulation result data, such as stator currents, were recorded and the three-phase current signals between 3 and 15 s are shown in Figure 20. Using the method proposed in this paper to calculate the three-phase current instantaneous information with a sliding window of 0.5 s, the results are shown in Figure 21.  
Figure 19: Simulation of three-phase unbalance by adjusting the resistance of the varistor. Figure 18: When adding switching noise: (**a**) the C.V. of the instantaneous frequency; (**b**) the C.V. of the instantaneous amplitude. For three-phase unbalance cases with continuously varying amplitudes, the proposed method can effectively represent the degree of three-phase unbalance variation. Usually in practical application scenarios, disturbances, such as harmonics, may be involved in the power supply. The 5 th and 8 th harmonics are added to the voltage source, and the harmonics are superimposed on the fundamental signal from a 0.05 s duration to the stop time. The 5 th harmonic is set to a negative sequence with an amplitude of 0.03 of the amplitude of the main positive sequence component (fundamental frequency voltage) and a phase of 0\({}^{\circ}\). The 8 th harmonic is set to a negative sequence with an amplitude of 0.01 of the amplitude of the main positive sequence component (fundamental frequency voltage) and a phase of 0\({}^{\circ}\). The three-phase current signal is shown in Figure 22. As can be seen in Figure 22b, after superimposing the harmonics, it can be seen by comparing Figure 20b that the three-phase current signal is distorted. Figure 21: Results of instantaneous information with a sliding window of 0.5 s: (**a**) instantaneous frequency; (**b**) instantaneous amplitude; (**c**) the C.V. of the instantaneous frequency; (**d**) the C.V. of the instantaneous amplitude. Figure 20: Adjusting the variable resistor, the three-phase unbalance amplitude changes: (**a**) 3–15 s signal; (**b**) 3–3.1 s signal; (**c**) 7–7.1 s signal; (**d**) 9–9.1 s signal. The FFT values and the THD of the 3-4 s signals of phases A, B, and C were calculated separately, and the results are shown in Figure 23 (the fundamental frequency amplitude is 100%). After superimposing the harmonics, the 5 th and 8 th harmonics can be seen in the FFT spectrum, both with a THD of 4.0921%. After superimposing the harmonics, the three-phase current instantaneous information was calculated using the method proposed in this paper with a sliding window of 0.5 s, and the results are shown in Figure 24.  
Figure 23: The FFT results and the THD of the 3 s–4 s current signals of phases A, B, and C: (**a**) A-phase; (**b**) B-phase; (**c**) C-phase.