2. Integrated On-Board Charger (iOBC) Topologies
The iOBCs can be classified into isolated and non-isolated, as illustrates in
Figure 3. Most non-isolated iOBCs use AC line as an input, using the motor winding. Each leg of the traction inverter is connected to each phase of motor winding. Thus, the inverter can be used as an active front-end (AFE) rectifier during charging. The non-isolated iOBC can also be built using a three phase and multiphase machine. Single three phase motor based iOBCs have been investigated in
[11][12][13]. In these works, two operations (charging and traction) have been tested.
Figure 3. OBC integrated PE converter system topology classification.
These topologies use a contactor switch as shown in
Figure 4 to connect the grid supply to the neutral point of the machine winding
[14]. The stator winding can be utilized as a grid side filter. The motor uses symbols R and L
f as stator resistance and inductance, respectively. The main drawback of this topology is the current stress on the one leg, which is three times higher than on the other converter legs. Another single-phase charging solution with two IMs and two sets of dedicated converters is described in
[15] (see
Figure 5). The power from the battery is transferred to both motors, hence the driving torque is shared by them. An improved interleaving switching based integrated charger based on a two-motor drive was introduced in
[16]. Two slow recovery diodes, D
1 and D
2, are added to alleviate the CM noise. As each diode provides a low-frequency path for the input current, the system ground is connected to the input terminal. Additional boost inductors, L
1 and L
2, are utilized for the purpose of compensating for the small CM inductance. This technique effectively improves the efficiency and current waveforms concurrently. Four motor iOBCs are also suitable for single phase supply, described in
[17][18]. For the mode to take place it is necessary to disconnect the positive terminal of the battery from the dc-bus and to connect it to two isolated neutral points of two machines, as shown in
Figure 6.
Figure 4. Single motor drive integrated on-board charger proposed by Gupta et al.
[14] in 2020 (iOBC1).
Figure 5. Dual motor drive integrated on-board charger proposed by Woo et al.
[15] in 2015 (iOBC2).
Figure 6. Four motor drive integrated on−board charger proposed by Subotic et al.
[17] in 2014 (iOBC3).
A single-phase traction inverter integrated OBC is proposed in
[19] (see
Figure 7). For the charging mode from a single-phase grid, the traction inverter is configured as full bridge rectifier and inverter boost converter, using switches’ S
1 to S
5 configuration to connect the battery. This topology has a very simple structure and control, V2G features and small size.
Figure 7. Induction motor drive integrated on−board charger with motor winding reconfiguration proposed by Khan et al.
[19] in 2012 (iOBC4).
A PMSM drive integrated charging system has been introduced in
[20] for electric motorcycle application. A rectifier and line filter used as an extra component in this system is depicted in
Figure 8. A four-phase synchronous reluctance motor (SRM) winding is utilized in the iOBC system described in
[21], as shown in
Figure 9. This topology used one bridge of the inverter as a buck-boost converter and the other two bridges as a rectifier. The V2G and G2V functionalities of SRM drive iOBC have been explained in
[22]. At first, two converter phases are utilized as a rectifier, with machine windings being employed as input filters. Then, when the grid voltage is rectified, the third phase acts as a dc-dc buck-boost converter to adjust the voltage to a value required by the battery. The fourth phase is not used during the charging process. To reduce switching losses, switch S
4 is set permanently. There is no separate DC-DC converter for charging the battery in this topology, which gives simple reconstruction flexibility. Thus, the cost and size of the charger system decrease.
Figure 8. PMSM drive integrated on−board charger with neutral point access proposed by Tuan et al.
[20] in 2021 (iOBC5).
Figure 9. SRM drive integrated on−board charger proposed by Khayam Huseini et al.
[21] in 2015. (iOBC6). The charging mode configuration is highlighted in red.
A cost effective 3-ph on-board charging system with interfaced converter is depicted in
[23] and shown in
Figure 10. The specific role of the interfaced converter in this topology is to configure the system during operating mode. Due to its simplicity, it allows high-power charging with comparatively less size and weight. An additional three-phase interface converter is used to avoid hardware reconfiguration. A fast three-phase charging system based on a split phase machine has been described in
[24][25][26][27][28] and is shown in
Figure 11. The mid-point of three phase winding is connected to the grid through an EMI filter and a H-bridge front-end converter with a battery connected to the machine. The main disadvantages of this topology are stator leakage inductance due to employed distributed winding, and complexity in control. An integrated on-board charger with open-end stator winding (OEW) configurations of three-phase IM is described in
[29][30].
Figure 10. Three Phase integrated on−board charger with interface converter proposed by Shi et al.
[23] in 2018. (iOBC7).
Figure 11. Three Phase Split-Phase Motor integrated on−board charger proposed by Hagbin et al
[27] in 2014 (iOBC8).
The stator winding reconfiguration of these topologies can be carried out by using a switch as shown in
Figure 12. Recently, Hyundai published a patent for a multi-charging system which is used in the Hyundai IONIQ 5 model, based on a OEW machine
[31]. Another similar approach with asymmetrical hybrid multilevel converter as described in
[32]. The OEW machine was also utilized to implement a dual drive integrated charger in
[33][34].
Figure 12. Integrated On−Board Charger based on Open-End Winding Machine proposed by Brull et al.
[29] in 2016 (iOBC9).
Recently, segmented winding based three phase induction machines have caught researcher’s attention. This type of multi-winding machine is derived from the traditional three-phase machine, using the same number of stator slots and rotor poles. Various segmented three-phase machines have been reported in the literature, including the three-phase six-winding machine as shown in
Figure 13 reported in
[35][36], and the three-phase nine-winding machine depicted in
Figure 14 and described in
[37][38]. Multiphase machines have more than three phases; typically five, six and nine. They are categorized in two types as symmetrical and asymmetrical machines based on the spatial angle of two consecutive machine phases. They can have one or multiple isolated neutral points. The nine phase machines have higher torque and lower copper loss then six phase machines. The nine phase machine based iOBC topologies are investigated in
[39][40].
Figure 13. Integrated On−Board Charger based on 3-Phase 6-Segmented Winding Machine proposed by Han et al.
[36] in 2018. (iOBC10).
Figure 14. Integrated On−Board Charger based on 3-Phase 9-Segmented Winding Machine proposed by Raherimihaja et al.
[37] in 2018 (iOBC11).
Since these topologies have a higher phase inverter as shown in
Figure 15, a significant drawback of these converters is the relatively higher number of semiconductor switches and the complexity of the corresponding driving circuit. An impressive solution was introduced in
[41] to reduce the number of switches.
Figure 15. Integrated On−Board Charger based on Nine Phase Winding Machine proposed by Abdel-Khalik et al.
[38] in 2017 (iOBC12).
The nine-switch converter was utilized with six phase machines as shown in Figure 16, where the stator coils act as filter during charging. The advantages of this topology are zero torque production during charging, the power factor is unity at the grid side and no phase transposition is needed. Additionally, only three additional switches are needed for changing the mode. The most challenging drawback is the utilization of low dc-link capacitance.
Figure 16. Integrated On−Board Charger based on Nine Phase Six Phase Winding Machine proposed by Diab et al.
[41] in 2016. (iOBC13).
A five-phase machine approach (non-isolated method) as shown in
Figure 17 is described in
[42][43][44]. An efficiency analysis of the various integrated charger topologies shows that a nine-phase charger corresponds to the highest efficiency (reaching 86% during the charging mode). During charging, the efficiency varies from 79% to 86% based on the applied topology, while the efficiencies are slightly higher, between 81% and 89%, during the V2G mode. On the other hand, the isolated iOBCs can be implemented in two methods. One method can provide galvanic isolation by an additional transformer placed on the low-frequency AC side, as in
[45]. Otherwise, the electrical isolation can be performed by reconfiguring the connections of the electrical machine to make it act as a transformer, which is proposed in
[46][47], with six-phase and a nine-phase machines, respectively. In
[48], a six-phase machine is used as transformer as shown in
Figure 17 and provides galvanic isolation in both three- and single-phase input operation, with the peculiarity of achieving torque-free charging in single-phase configuration.
Figure 17. Integrated On−Board Charger based on Five Phase Winding Machine proposed by Sabotic et al.
[42] in 2016 (iOBC14).
Figure 18. Isolated Integrated On−Board Charger based on Six Phase Machine Reconfiguration proposed by Pascetto et al.
[48] in 2020 (iOBC15).
To sum up, researchers have seen the different aspects of the previously mentioned topologies, showing technical features such as V2G, torque ripple issues, and torque generation during charging. Thus, all topologies are compared according to the average torque production during the charging process, hardware reconfiguration between the propulsion and the charging modes, V2G feature, torque ripple issues, and the charging power as a ration of the traction power.