Real-Time Control Based on a CAN-Bus of Hybrid Electrical Systems

: Power management of a one-converter parallel structure with battery and supercapacitor is 1 addressed in this paper. The controller is implemented on a DSP from Microchip and uses a Controller 2 Area Network (CAN) bus communication for data exchange. However, the low data transmission 3 rate of the CAN bus data impacts the performances of regular power management strategies. This 4 paper details an initial strategy with a charge sustaining mode for an application coupling a battery 5 with supercapacitors, in which low performances have been witnessed due to the high sampling time 6 of the CAN bus data. Therefore, a new strategy is proposed to tackle the sample time issue based on 7 a depleting mode. Simulation and experimental results with a dsPIC33EP512MU810 DSP based on a 8 10 kW hybrid system proves the feasibility of the proposed approach. 9

Submitted to Energies, pages 1 -14 Version September 25, 2020 submitted to Energies 2 of 14 components, i.e. limit the cost and weight of the battery pack, nevertheless with an increase of the total 34 volume [23]. Therefore, SCs are used as an assistant to the main source to deliver power during fast 35 acceleration or braking, and also allows to limit the battery current and temperature by an appropriate 36 assistance of the SCs during high current and high temperature of the battery pack. Moreover, the 37 operation of the battery at high current needs to be avoid in order to impact positively the durability 38 of the battery [20,24]. 39 The implementation of these controllers is generally done with high-performance DSP/µC 40 with internal current/voltage controllers, PWM outputs to control the converters and its own 41 current/voltage sensors. In such configuration, the implementation does not introduce issues. 42 Nowadays, embedded and networked automotive bus communication such as the Controller Area 43 Network (CAN) is widely used for vehicle networks. It is used for the communication between the 44 controllers, the sensors and the actuators [25][26][27][28][29]. The controller can retrieve data from each component 45 (i.e. voltage, current, temperature of the BT and SCs) and the DSP send periodic messages necessary to 46 control the DC/DC converter [30][31][32][33]. It should be pointed out that the sampling frequency of the data 47 on the CAN bus is relatively low compared to a regular implementation on a DSP/µC that use analog 48 inputs and the PWM peripherals [34]. In fact, in the case of a regular implementation, the CPU and the 49 peripherals have a sampling time nearly equal to 100µs for the inner current loops and nearly equal to 50 1ms for the outter voltage loops. Therefore, the performances of the controllers are not degraded by 51 the sampling (see [3] for more information and [35,36] for theoretical details). In practice, the CAN bus 52 data sampling frequency is defined by the manufacturers of top-of-the-shelf equipment and modifying 53 it in a wide range is not always possible, at least in a range defined by the manufacturer. 54 is not always possible, at least in a defined range. It follows that designers need to face such issue 55 by defining an appropriate controller with low data transmission rate [28]. Therefore, this paper aims 56 to detail experimental knowledge about the power management of a hybrid system controlled by a

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The main contribution of this paper is focused on the description of an initial strategy [37] with a 60 charge-sustaining mode. Experimental results show that the proposed controlled [37] failed under high 61 sampling time and quantization of the CAN bus data that deteriorate the closed-loop performances.

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It is the reason why a new rule-based strategy is proposed in this paper to tackle the sample time 63 issue based on a depleting mode. Experimental results based on a 10 kW hybrid power pack coupling 64 battery and supercapacitors prove the feasibility of the proposed approach.

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The paper is organized as follows. In section 2, a 10 kW experimental system is detailed.

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Section 3 details a regular controller for power management of a hybrid electrical system, where the 67 closed-loop controller performance degradations are being emphasised with the CAN bus. Therefore, a 68 sampled-data controller based on a charge depleting mode is described in section 4, where experimental 69 results are presented to show the effectiveness of the proposed controller.  Explorer 16 development board As regular batteries, these data decrease over the time due to the cycling and the batterie temperature

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[38] and this knowledge can be integrated into the controller for a real-time update of the saturation 84 functions. On another side, the SCs can provide 140A during few minutes and thus can assist the 85 battery during over-battery current to limit the battery temperature.  Table 1 gives the electric 92 characteristics of the 10 kW hybrid system.  The three first variables of  Figure 1 represents a parallel power electronic system understudy composed of only one-converter.

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The controller is designed to provide a smooth current transition on the source with the lower current 120 dynamic, namely the battery in this study. Also, the power between the battery and the SCs needs to 121 be appropriately shared to match the power load requirement. The maximal currents of the battery 122 and SCs, the state of charge (SoC) of the SCs, the battery temperature must be taken into account as 123 constraints in the controller design [37]. This regular controller refers to charge-sustaining mode, where a certain level. Consequently, the control structure is based on three nested loops as shown in Figure 1  CAN frame data v bt (109ms, see data in Table 2) has been clearly identified as responsible for this 157 unexpected behaviour.    The state machine block depicted Figure 5 is detailled in Figure 6, where states are:

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• State 0: the battery current (i bt ) doesn't exceed the maximum value [i bt_max_ch − δi bt , i bt_max_dis + 206 δi bt ] and the SCs voltage is also in the bounds [v * sc − δv sc , v * sc + δv sc ], i.e. normal operation of the 207 hybrid system. Therefore, the SCs is set equal to zero.

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• State 1: the battery current (i bt ) is higher than a user-defined threshold i bt_max_dis + δi bt . Therefore, 209 flag flag_control_ibt_max_dis is set to one and controller 1 is activated until the battery current is 210 lower than i bt_max_dis − ∆i bt .

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• State 2: the battery current (i bt ) is higher in absolute value than a user-defined threshold

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It is important to mention that adequate values of the thresholds δi bt and ∆i bt need to be adopted 223 to avoid chattering phenomenon.

Controller 2 238
When flag flag_control_vsc is set to one (states 3 or 4), the SCs voltage is bring back at its nominal 239 value v * sc :

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• Whenever v sc ≥ v * sc + δv sc , controller 2 computes a positive value of the SCs current as follows: so that the SCs is discharged at the maximum value i sc max as long as v sc ≥ v * sc + δv sc and later 241 discharge the SCs by progressively reducing i * sc until reaching i * sc = 0 when v sc = v * sc . This 242 behaviour is highlighted in the Figure 9.

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• Whenever v sc ≤ v * sc − δv sc , controller 2 computes a negative value of the SCs current as follows: so that the SCs is charged at the maximum value −i sc max as long as v sc ≤ v * sc − δv sc and later 244 charge the SCs by progressively reducing i * sc until reaching i * sc = 0 when v sc = v * sc .

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Controller 2 is a static controller based on equations 1 and 2 (see also Fig. 9 for a graphical 246 representation). When the system is in state 3 or 4, the battery provides power to the load and also   Figure 11 shows an experimental result for a load current profile composed of 5s at 95A and 1s 265 at zero current, i.e. for operating points where the battery current is greater than i bt_max_dis (state 1) 266 and operating points where the SCs can be recharge (state 3). As expected, the SCs current provides 267 current to the load for state equal to one. We can notice in Figure 12 that the SCs voltage is regulated at 268 the desired value v * sc equal to 32V and that the SCs current is always initialized at a value different 269 from zero (see comments in section IV.B.2) to improve the convergence of i bt to i bt_max_dis .

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In fact the commutation from controller 2 to controller 1 needs an adequate re-initialization of 271 the integral term of the PI controller and the commutation from controller 1 to controller 2 doesn't 272 introduce difficulty. When controller 1 is engaged, thanks to the initialization flag in Figure 7, the integral term S is initialized at i bt − i bt_max_ch or i bt − i bt_max_dis according to the system state. As 274 noticed just above, this reduce the convergence time of i bt to i bt_max_dis or i bt_max_ch through a fast drop 275 of the battery current as shown in Figure 11.b. 276 We can noticed that the results are acceptable despite the important sampling-time of the data 277 and that the current battery remains to the limit current value i bt_max_dis or i bt_max_ch defined by the 278 designer. We have shown that the PI controller (state 1 and 2) have been engaged so that the SCs assist 279 the battery as long as the SoC of the SCs is not too high or low (see Figure 8). Furthermore, every time 280 that the SCs can be charge or discharge (i.e. the battery current i bt doesn't exceed the allowed value), 281 controller 2 is activated.