## 5 Simulations and Experimental Results  
In this study a 6 SIP lithium battery module serves as a test target to verify the theoretical feasibility. In actuality, the practical loading current of the power battery is neither periodic nor predictable. Hence, it is not easy to simulate the load current of the power battery for an online test. Due to the inherent wide-range slew-rate characteristics of a sinusoidal current waveform, it is suitable to use this waveform to demonstrate the related experimentations. Figure 11 shows the simulated and measured load current waveforms of the AC electronic load under C rate = 0.2 C. All the simulations and experimental results reveal that sinusoidal current waveforms are as previously predicted. When the C rate is changed to 1 C, the simulations and measurement results are demonstrated in Figure 12. It is obvious that the simulations and measurement results are quite consistent. Figure 11: Measured and simulated waveforms of the proposed sinusoidal load under C rate = 0.2 C: (**a**) simulated waveforms; (**b**) measured waveforms. In practical work situations the battery module voltage will decrease with load consumption. To maintain the preset load current amplitude, variable frequency control is used to modulate the current amplitude of the sinusoidal load. Figure 13 demonstrates that the load current amplitude of the proposed sinusoidal load is still maintained at the preset value, even if the battery module voltage is lower. Finally, from integrating the area of the load current waveforms, the energy recycling rate can be calculated. In fact, it is clear that the areas of the positive and negative semi-cycles are different, i.e., the energy drawn from the battery during the test procedure cannot be recycled completely. In addition, although the proposed system has the function of energy recycling when the AC electronic load operates in each operation mode under different operating conditions, the current will cause power consumption when passing through each component, and this consumption cannot be recycled. In general, the Coulomb integral method can be adopted to calculate the SOC by measuring the battery current and integrating it in time. The proposed high-frequency AC electronic load provides a sinusoidal load current, and therefore, the SOC in the positive and negative half cycles can be calculated by the Coulomb integral method to estimate the energy recycling rate. In fact, during the test procedure, the load current will result in some power loss within the battery internal resistances,  
Figure 12: Measured and simulated waveforms of the proposed sinusoidal load under C rate = 1 C: (a) simulated waveforms; (b) measured waveforms. resonant components, and loop impedances; the energy therefore cannot be recycled completely during the battery module test. In order to accurately calculate the energy recycling rate, we first use the current probe and oscilloscope to capture the actual current waveform of the battery module. Secondly, all the acquired data is transferred to an Excel format file and the areas of the positive semi-cycle and the negative semi-cycle are calculated by using an Excel function. Ideally, energy can be completely recovered; in fact, each component on the electronic load will have some power loss, and the recycling rate will not be the same under different test conditions. In Figure 14a, when the C rate is set as 0.2C, the integration value of the positive semi-cycle \(Q_{1}\) is 442.5 ucoulombs and the integration value of the negative semi-cycle \(Q_{2}\) is 380.1 ucoulombs; i.e., the energy recycling rate is \(\eta\) = 85.9%. However, if the C rate is increased to 1C, the integration value of the positive semi-cycle \(Q_{1}\) is 1210.5 ucoulombs, and the integration value of the negative semi-cycle \(Q_{2}\) is 925.4 ucoulombs; hence, the energy recycling rate is reduced to \(\eta\) = 76.5%, as shown in Figure 14b. It is apparent that most of the unrecyclable energy is consumed on circuit components and results in power losses.