Aerospace and Electronic Systems Magazine September 2017 - 18

Feature Article:

DOI. No. 10.1109/MAES.2017.160122

Study on a New Power by Wire Thrust Vector Control
System With High Reliability
Kangwu Zhu, Junyong Fu, Cheng Fang, Baoliang Ji, Shanghai Institute of Spaceflight
Control Technology, Shanghai, China

INTRODUCTION
The thrust vector control (TVC) system is used to control the attitude and direction of a launch vehicle by regulating the swinging
angle of the rocket engine. At present, the electro-hydraulic (EH)
TVC systems are most widely used due to their excellent dynamic
and steady-state control performances. The launch vehicles that
use EH TVC systems include the Space Shuttle, Saturn V, Atlas
V, Long March series, Soyuz, Arian V, et al. When output power is
larger than 5 kW, the energy of the EH TVC system usually comes
from the rocket engine, gas generator, or compressed nitrogen. The
EH TVC systems that are powered by battery are usually used in
the third stage or upper stage of launch vehicles, where the output
power of the system is smaller than 5 kW [1].
In last decade, with the rapid development of battery technology, the energy density of the battery has been increased greatly
to satisfy the needs of high power EH TVC systems. And compared with other traditional energy systems, the battery is simpler,
cheaper, easier to maintain, and more reliable. Therefore, for the
next generation launch vehicles under development, the battery
can serve as an attractive option for energy supply in high power
EH TVC system [2], [3]. In order to distinguish the system powered by a battery from the system powered by other methods, these
systems are called power by wire (PBW) systems.
For a PBW system, the high-pressure oil tubes used to provide energy are replaced by wires, and the complicated external
hydraulic energy source can be canceled [4]-[6]. Therefore, the
PBW systems are more compact and reliable.
So far, various PBW systems have been proposed. According
to the basic working principle, the PBW system can be classified
into three types: pump control system, valve control system, and
hybrid system. However, the control performance of a pump control system is weak, the energy efficiency of a valve control system
is very low, and the hybrid PBW system is a complicated system
that is unreliable [7]-[9].

In this article, the characteristics of a typical PBW system will
be analyzed first, and then the concept of an ideal PBW system
will be presented. Based on this, a new PBW TVC system will
be proposed and studied. At last, a quad redundant PBW system
with high reliability is designed to meet the requirement of mancarrying launch vehicles in the future.

NEW PBW TVC SYSTEM STUDY
TYPICAL PBW TVC SYSTEMS STUDY
The working principle of a typical valve control PBW TVC system
is shown in Figure 1. The system is composed of a constant pressure variable displacement pump, constant speed midfrequency
motor, EH nozzle-flapper servo valve, hydraulic actuator, position
transducer, and controller.
In the system, battery, motor, and pump make up the energy
subsystem to produce high pressure hydraulic oil. The hydraulic
accumulator stores the hydraulic oil and releases it when high flow
rate is needed. The servo valve, hydraulic actuator, transducer, and
controller make up the position feedback control subsystem. Because the time constant of the servo valve is very small, the bandwidth of the valve control TVC system can be greater than 10 Hz.
In addition to control performance, the hydraulic efficiency is
another important performance evaluation index. The hydraulic efficiency of a valve control system is

ηh =

pLoad qLoad
× 100%
ps qp

where ηh is the hydraulic efficiency of the system, ps is the output
pressure of the pump, pLoad is the pressure of the load, qLoad is the
flow rate of the load, and qp is the output flow rate of the pump.
The pressure of the load is
pLoad =

Authors' current address: Research and Development Center,
Shanghai Institute of Spaceflight Control Technology, Shanghai, China, E-mail: (zjuzkw@zju.edu.cn).
Manuscript received May 31, 2016, revised November 6, 2016,
and ready for publication December 27, 2016.
Review handled by M. Jah.
0885/8985/17/$26.00 © 2017 IEEE
18

(1)

FL
× 100%
Ap

(2)

where FL is the load on the actuator and Ap is the piston area of the
actuator.
The valve control system is a constant pressure variable displacement system; the output pressure equals to the set value under various working conditions. The pressure control valve and the
actuator of the pump control the angle of the swash plate to change

IEEE A&E SYSTEMS MAGAZINE

SEPTEMBER 2017

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