*6.1. Experimental Setup*

A re-configurable test bed was set up for both synchronous buck and H-bridge topologies as shown in Figure 12. The topologies are shown in Figures 3 and 4. The switch, *SH* was used to configure the options between synchronous buck and H-bridge topologies. *SH* connected or disconnected the *Q*3*Q*<sup>4</sup> leg of H-bridge. The switches *S*<sup>1</sup> and *S*<sup>2</sup> were to connect and disconnect the input source, *Vin* and input resistor, *Rin*. The value of *Vin*, *Cin*, *Rin*, *L*, and *C* were selected based on the discussion of III.A and Table 2. These MOSFETs were controlled by 100 kHz PWM signal generated by the Simulink based Opal-RT controller. The Opal-RT controller gets voltage and current as feedback through Op-Amp based offset clipping and scaling interface circuits. The proposed controller was implemented with a sample time of 20 μS using Opal-RT (OP4510).

**Figure 12.** The re-configurable testbed of AC current injector for synchronous buck and H-bridge topologies.

#### *6.2. Waveforms and Analysis*

The steady state battery voltage and current for different modes of operation using the synchronous buck converter are shown in Figure 13. The DC current of the battery for different modes were +10 A, 0 A, and −10 A. The same operation was verified using the H-bridge converter also. The amplitude of the AC injection current was 5 A and the frequency was 100 Hz. The battery voltage was 13.5 V as DC average. The battery had a very small internal impedance (maximum 15 mΩ). Therefore, small battery voltage ripple due to AC injection was not visible by DC coupling in an oscilloscope. The battery voltage ripple is shown in Figure 14 using AC coupling. In this case the battery was operated in mode 1 for 100 Hz. The AC current peak was changed from 2 A to 5 A to observe the transient response and the effect of AC current to battery voltage. The controller was successfully able to regulate the current.

**Figure 13.** Voltage and current of the battery in steady state for: (**a**) mode 1, (**b**) mode 2, and (**c**) mode 3.

**Figure 14.** Transient response: magnitude change (from 2 A AC peak to 5 A) of battery current in mode 1 at 100 Hz.

The AC part of the battery current was changed from 0 to 2 kHz for all three modes of operation using both synchronous buck and H-bridge converters. The battery voltage and current for 10 Hz, 100 Hz and 1 kHz for mode 1 using the synchronous buck converter is shown in Figure 15. The dynamic response for mode change using the proposed controller is shown in Figure 16. In these cases, both *S*<sup>1</sup> and *S*<sup>2</sup> were turned on. The proposed versatile controller was validated by successfully testing the additional conditions listed in Table 4.

**Figure 15.** Voltage and current of the battery in steady state in mode 1 for: (**a**) 10 Hz, (**b**) 100 Hz, and (**c**) 1000 Hz.

**Figure 16.** Dynamic response: mode change (for 100 Hz 5A AC peak) of battery current: (**a**) mode 1 to 2, (**b**) mode 2 to 1, (**c**) mode 2 to 3, (**d**) mode 3 to 2, (**e**) mode 1 to 3, and (**f**) mode 3 to 1.


**Table 4.** The test conditions for controller validation.
