# EV Range Extender in a Two-Battery HEECS Chopper-Based Powertrain

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Proposed Chopper-Based Powertrain

#### 2.1. Concept

#### 2.2. HEECS Chopper

_{HEECS}and efficiency η

_{HEECS}are approximately expressed as

_{1}, E

_{2}, d, P

_{1}, P

_{2}, and ηchop represent the voltage of E

_{1}, the voltage of E

_{2}, the duty ratio, the output power of E

_{1}, the output power of E

_{2}, and the efficiency of the chopper, respectively. Thus, the overall efficiency of the HEECS is higher than the efficiency of the chopper [5].

#### 2.3. Freedom of Parameter Optimization

_{1}, E

_{1}+ E

_{2}, and the voltage gradient when the speed increases.

_{1}is kept constant in the low-speed range, and at a certain speed, the DC link voltage can be increased by the buck chopper until reaching E

_{1}+ E

_{2}. Then, over a certain high speed, it becomes constant. The parameters should be optimized in the following respects. (1) The switching loss in the low-speed range should be minimized by the best combination of E

_{1}and speed when the buck chopper begins to work. (2) Depending on the tested driving mode cycle, the total energy savings should be maximized by the selection of the DC link voltage gradient as the speed increases. (3) Motor efficiency can be improved by the best Pulse Width Modulation (PWM) selection for a low ripple current. (4) The buck chopper efficiency also influences the overall efficiency optimization. (5) Other factors not mentioned here can also be varied. It is expected that we need plenty of time to optimize these parameters. Thus, in this paper, we investigate a simple strategy, which is mentioned later in Section 3.2, to empirically optimize the parameters.

## 3. Case Studies

#### 3.1. Test Car Specifications

#### 3.2. Open-Loop Efficiency Map

_{1}+ E

_{2}. On the other hand, for the HEECS chopper-based powertrain, the output voltage was controlled according to the speed.

_{1}+ E

_{2}= 350 V, and the in-wheel motor can rotate at 83 km/h without any additional control. Then, the flux-weakening control begins to work at rotations greater than 83 km/h, and the in-wheel motor can then rotate over that speed. Equation (3) was empirically selected, and the parameters E

_{1}and the gradient that responds to the speed were determined by a trial-and-error approach in the 10–15-mode and JC08-mode driving test cycle.

- Speed v [km/h]: 10, 20, 30, 40, 50, 60, 70, 80;
- Load torque T
_{m}[Nm]: −60, −50, −40, −30, −20, −10, 10, 20, 30, 40, 50, 60.

#### 3.3. Simulated Driving Range

#### 3.3.1. Comparison of Test cycles

#### 3.3.2. Simulation Conditions

_{acc}, the friction force F

_{rol}, and the aerodynamic force F

_{air}, which are calculated by Equations (4)–(6), respectively. Since the vehicle has two front drive wheels, the load torque per in-wheel motor is equal to half of the driving resistance, and the rotation torque is calculated by Equation (7).

_{m}and motor angular velocity ω

_{m}. The required battery output is calculated using the efficiency map at the operating point. The efficiency η

_{total}is linearly interpolated from four measurement points around the operating points. The battery energy consumption in powering W

_{bat_p}and regenerating W

_{bat_r}is calculated by Equations (8) and (9), respectively. The total energy consumption is obtained by Equation (10).

#### 3.3.3. Simulation Results

#### 3.4. Experiments with the Motor Test Bench

#### 3.4.1. Experimental Conditions

_{1}+ E

_{2}. The load torque was given by the load motor connected to the in-wheel motor, and the torque was changed to be equal to Equation (7) every 1 s for all driving conditions. The smooth transient of the mode change from low constant voltage to chopper operation and so on needs “intermittent pulse density control”, which is published in Reference [12].

#### 3.4.2. Experimental Results

_{m}> 60 Nm. The torque range of WLTC mode is very large and often exceeds T

_{m}> 60 Nm, so calculation errors occurred in the application of Equations (8) and (9).

#### 3.5. Discussion

## 4. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 1.**Powertrains for electric vehicles: (

**a**) Non-chopper powertrain; (

**b**) Series-chopper-based powertrain [7].

**Figure 3.**Operation of the two-battery HEECS chopper: (

**a**) Low-speed range; (

**b**) middle-speed range; (

**c**) high-speed range.

**Figure 4.**Efficiency maps of non-chopper powertrain: (

**a**) Total efficiency; (

**b**) inverter efficiency; (

**c**) motor efficiency.

**Figure 5.**Efficiency maps of HEECS chopper-based powertrain: (

**a**) Total efficiency; (

**b**) inverter efficiency; (

**c**) motor efficiency.

Vehicle Weight (M) | 833.8 kg |

Total Inertia (J_{m} + J_{l}) | 0.45 |

Coefficient of Total Visions Friction (D) | 0.065 |

Coefficient of Rolling Friction (μ) | 0.00944 |

Constant Drag (C_{d}) | 0.33 |

Wheel Radius (r) | 0.275 m |

Gravitational Acceleration (g) | 9.8 m/s^{2} |

Frontal Project Area (A) | 1.648 m^{2} |

Atmospheric Density (ρ) | 1.22 kg/m^{3} |

10–15 | JC08 | |
---|---|---|

Duration [s] | 660 | 1204 |

Maximum speed [km/h] | 70 | 81.6 |

Average speed [km/h] | 22.7 | 24.4 |

Driving Distance [m] | 4165 | 8172 |

Low | Middle | High | |
---|---|---|---|

Duration [s] | 589 | 433 | 455 |

Maximum speed [km/h] | 56.5 | 76.6 | 97.4 |

Average speed [km/h] | 25.7 | 44.5 | 60.8 |

Driving Distance [m] | 3095 | 4756 | 7158 |

Energy Consumption per 1 km Traveling [Wh/km] | Reduction Ratio [%] | ||
---|---|---|---|

HEECS | Non-Chopper | ||

10–15 | 25.7 | 27.5 | 6.0 |

JC08 | 26.5 | 28.1 | 5.1 |

WLTC-Low | 21.6 | 24.8 | 10.3 |

WLTC-Mid | 28.4 | 29.8 | 3.8 |

Energy Consumption per 1 km Traveling [Wh/km] | Reduction Ratio [%] | ||
---|---|---|---|

HEECS | Non-Chopper | ||

10–15 | 27.8 | 29.6 | 6.3 |

JC08 | 29.1 | 30.7 | 5.3 |

WLTC-Low | 27.8 | 29.7 | 6.4 |

WLTC-Mid | 32.1 | 32.7 | 1.9 |

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Tamura, A.; Ishibashi, T.; Kawamura, A.
EV Range Extender in a Two-Battery HEECS Chopper-Based Powertrain. *World Electr. Veh. J.* **2019**, *10*, 19.
https://doi.org/10.3390/wevj10020019

**AMA Style**

Tamura A, Ishibashi T, Kawamura A.
EV Range Extender in a Two-Battery HEECS Chopper-Based Powertrain. *World Electric Vehicle Journal*. 2019; 10(2):19.
https://doi.org/10.3390/wevj10020019

**Chicago/Turabian Style**

Tamura, Ayataro, Takayuki Ishibashi, and Atsuo Kawamura.
2019. "EV Range Extender in a Two-Battery HEECS Chopper-Based Powertrain" *World Electric Vehicle Journal* 10, no. 2: 19.
https://doi.org/10.3390/wevj10020019