WSEAS TRANSACTIONS on SYSTEMS

# 2.2 Structure of hybrid system

ISG (Integrated Started Generator) hybrid electric vehicle belongs to parallel hybrid electric vehicle (PHEV). It is also one kind of light hybrid electric vehicle (LHEV) based on ISG technology. ISG system usually takes thin electric machinery with permanent magnetism.

Hybrid Control Unit (HCU) is the control center of vehicle, communicating with control module of flywheel system (FCM), ISG control module (ICM) and engine control module (ECM), harmonizing functions of all the units. In the driving process, the main task of HCU is to solve the problem of torque distribution between ISG and ICE (Internal Combustion

Engine) [6-10]. The hybrid

system takes

four-cylinder

ICE with maximal power of 45Kw and ISG with maximal power of 30Kw as its dynamic system.

A FESS with peak power of 35Kw and rotary inertia of 1.8Kg.m^{2 }is chosen. The maximal rotary speed of flywheel is 18000r/min while the minimal rotary speed is 1350r/min. The Flywheel system is controlled by FCM, which receives commands of charging or discharging from HCU and then gives commands to the motor or generator of FESS. Except for harmonizing functions of all the controllers and determining energy management of vehicle, HCU also needs to deal with various fault signals. The structure of hybrid system is presented by Fig.2.

## Fig.2 Structure of hybrid system with FESS

### ISSN: 1109-2777

Jianhui He, Guoqiang Ao, Jinsheng Guo, Ziqiang Chen, Lin Yang

2.3 Energy characteristics of FESS FESS stores power by mechanical form and the stored energy is the function of flywheel’s

rotary speed (

ω

).

E=

1 2

Jω^{2 }(t) =

lπρω ^{2 }(t)(R^{4 }− r ^{4 })

4

(1)

Where

ρ

is the density of flywheel，

R

/ r is

the outer/inner diameter of flywheel,

l

is the

length of flywheel and

J is the rotary inertia

of flywheel.

Chemical battery uses SOC （ State Of Charge）as its energy storage state. In order to be convenient for control, a parameter is also needed to denote the energy storage state of FESS. As for FESS, the rotary speed ^{ω }varies

between its maximal value ^{ωmax }and minimal

value ^{ωmin }. The current rotary speed can be

measured by sensor to confirm accurately the energy storage state of FESS.

Define

( ) m i n 2 m λ (t ) = a x m i n 2 ω 2 ω ω ω 2 − − t

(2)

If

ω(t) = ω_{min }

, then

λ =0

. If

ω(t) = ω_{max }

,

then

λ =1

. The value of

λ

varies linearly

with ^{ω }^{2 (t) }in zone [0,1] and can be defined as

the parameter that confirms the energy storage state of FESS.

During the process of absorbing or releasing energy, power absorbed or released by FESS in

the period of ^{Δt }can then be expressed by

energy storage state

λ (t )

as follow:

λ(t + Δt)− λ(t) =

ΔE − E_{loss }

m 2 a x ω

m i 2 n − ω

⋅

2 J

(3)

As for the dynamic system of HEV, working

640

Issue 5, Volume 8, May 2009