Energy Conservation with Semco Infratech Battery Solution
This article looks at A programmable Microcontroller Unit (MCU)-based battery tester as a low-cost and compact configuration. The proposed battery tester is composed of an MCU, a signal-capturing circuit, an HMI (Human-machine Interface), and a programmable sinusoidal load. To validate the dynamic characteristics of the lithium-ion battery in practical applications, a programmable sinusoidal load is implemented and tested. Furthermore, it implements the possibility to recycle the extracted energy from the lithium-ion battery during the diagnostic process. Moreover, the loading current can be preset and programmed by the HMI.
Driven by surging environmental consciousness and the looming energy crisis, electric vehicles (EVs) including electric scooters, cars, and hybrid vehicles, have emerged as a frontrunner in the mobility revolution. Since lithium-ion batteries are the most used power source for EVs, some current research focuses on SOC and SOH for power batteries, which is an important research topic. Yang and colleagues have devised a battery testing apparatus that records battery-related data through capturing and loading circuits. The loading circuit releases battery energy through constant level current (CC) or various other types of currents. The loading circuit characteristics of the above-mentioned method actually differ greatly from the non-periodic and irregular shape of the actual work conditions. It's also important to note that the test process's total power consumption causes thermal problems, necessitating the use of a heat sink and thermal management system.
Thus, in addition to the power waste issue mentioned above, it also results in other issues like being rigid, costly, and complicated. It is actually possible to recycle the electrical energy that is taken out of the power battery during the working condition simulation. In the industry today, two battery test methods are commonly employed. The easiest method, which calls for adding a second backup battery, involves transferring the electrical energy extracted from the tested battery to the designated backup battery. The other method is more effective, but it costs more and requires a much more complicated system. After being extracted from the tested battery, the electrical energy is transformed into an Alternate Current and connected to an inverter to return it to the power grid. To address the aforementioned drawback, the proposed sinusoidal load is applied in this paper. After the test process is complete, the extracted energy from the test battery can be put back into the test battery.
Scheme Description of The Proposed Battery Tester
The circuit architecture of the proposed programmable battery test system is depicted in Fig. 1. It consists of one sinusoidal load, a control core (dsPIC33FJ64GS606), a USB module, an auxiliary power circuit, a signal (voltage and current) capturing circuit, and a DC level offset circuit.
In this study, the sinusoidal load is the key part of the proposed battery tester. The proposed sinusoidal load is used to provide different load current conditions for the tested battery. In actuality, the sinusoidal load has the ability to transmit electrical energy during the negative half-cycle and supply dynamic loading current during the positive half-cycle.
Model Analysis of Sinusoidal Load
The proposed sinusoidal loading circuit is implemented by the class E topology, as depicted in Fig. 2 (a). The original class E topology consists of two inductors (L1 and L2), two capacitors (C1 and C2), and one MOSFET switch (S).
Fig. 2 (a) The original Class E circuit structure. (b) the equivalent circuit of a sinusoidal loading circuit.
The former inductor (L1) of the original class E main circuit is connected with Vs to form a current source. In this study, a tested battery is used as the voltage source Vs. To generate the required bidirectional loading behavior, the modified class E circuit structure is employed. First of all, the input inductor is combined with the other components as shown in Fig. 2 (b). Then, the load resistance (Ro) is removed from class E topology to achieve the said circuit characteristics. Moreover, for simplifying the circuit, L2 and C2 in the specific frequency range are integrated to a capacitive component Ceq,
Afterward, we combine the C1 and Ceq to an equivalent capacitance C=C1+Ceq, and then the resonant frequency is given by
Fig. 3 Circuit topology of the sinusoidal load.
Asymmetrical load current may also arise in certain operating conditions because of the power switch's body diode. As illustrated in Fig. 3, the previous power switch in Fig. 2 (b) is connected in series with another power switch S2 to create a sinusoidal load circuit that improves the aforementioned phenomenon.
In this study, the switching frequency (fs) of the sinusoidal load is set identically with the resonant frequency (fr). Based on the above design, the input inductor current IL is almost symmetric waveform in each half-cycle. The circuit operation in a switching period is divided into three intervals as follows.
Mode I [t0-t1] ：
Suppose both the power switches (S1 and S2) are off, the initial current IL1
(t0)=0 and the voltage of C arrives at the maximum value as VC(t0)= -VC_max. In this mode, the capacitor C begins to resonate with the inductor L, and then the electrical energy is transferred from the capacitor C to the inductor L, as shown in Fig. 4(a). Fig. 4(b) shows the corresponding Laplace transform circuit.
Fig. 4 Mode I. (a) The equivalent circuit. (b) the Laplace transform circuit.
As shown in Fig. 4(b), we can obtain the equation by Kirchhoff’s voltage laws (KVL), as follows:
By the inverse Laplace transformation, we can get the inductor current IL(t) and vC(t) as
When t=t1, the vC(t=t1) resonates to zero voltage, and both the power switches are turned on at this moment to achieve zero voltage switching.
Mode II [t1-t2] ：
At t=t1, the resonant capacitor’s voltage is decreased to zero, that is to said, zero voltage switching is achieved when the power switches (S1 & S2) are both turned on. And then the resonant inductor L is magnetized by the voltage source Vs. Therefore, the IL(t) is rising linearly, and the electrical energy is stored in L.
Fig. 5(a)-(b) depicts the equivalent circuit and the Laplace transform circuit, respectively.
Fig. 5 Mode II. (a) the equivalent circuit. (b) the Laplace transform circuit.
By KVL, and VC(t1)=0, Fig. 6(b) can be obtained as:
And then the inductor current IL1(t) is derived by using the inverse Laplace transformation.
Where IL(t1) can be indicated as：
When t=t2, the power switches are turned off and this mode is ended.
Fig. 6 Mode III. (a) the equivalent circuit. (b) the Laplace transform circuit.
Mode III [t2-t3]：
Fig. 6(a) depicts the equivalent circuit in Mode III, where the equivalent circuit looks exactly the same as the circuit shown in Fig. 4(a). However, the initial current IL(t2) and the initial voltage of VC(t2) are still different from the initial conditions in Mode I. The resonant inductor L resonates with the resonant capacitor C and transfers the electrical energy stored in L to C. Hence, the Laplace transform circuit can be depicted in Fig. 6(b), and the KVL equation is given as
And then the inductor current IL(t) and the voltage drop VC(t) of the resonant capacitor are described as follows by using the inverse Laplace transformation
When t=t3, the power switches are turned on, and this interval is completed.
All the key parameters of the proposed sinusoidal load are listed in Table I. In this study, an 8S1P lithium-ion battery module is used as the test target to verify the theoretical feasibility.
In practical applications of power batteries, the loading current is non-periodical and unpredictable. Therefore, it is not easy to simulate the loading current of the power battery for an online test. However, the sinusoidal waveform inherently has wide-range slew-rate characteristics, which is suitable for demonstrating the related experiments.
A tester for lithium-ion batteries is used without the need for extra grid-tied equipment or backup batteries. The suggested sinusoidal loading technique recycles the extracted energy every cycle and offers a wide range of slew-rate discharging conditions to conform to real-world work scenarios. This process of recycling energy leads to better power conservation and helps the user to save energy. If you are someone looking for a battery testing solution that simultaneously can save power, Semco Infratech is the best solution in the market right now.