Nonlinear Decentralized Position Control of Electrohydraulic Actuators in Road Simulation

In this paper, a nonlinear position tracking controller is derived based on feedback linearization to globally linearize the nonlinear dynamics of an electrohydraulic actuator with nonlinear state feedback. A detailed computer model is developed for a four-post road simulation system with a transit bus as the test vehicle. Using this model, comparisons are conducted between the proposed nonlinear decentralized controller and a traditional linear decentralized controller. Previously introduced interaction measures suitable for time domain analysis of nonlinear systems confirm that, for the test vehicle considered, load plate position loop interactions are quickly eliminated by either the linear or nonlinear decentralized position controllers. The performance of the road simulator as gauged by a position tracking error metric for a typical rough road profile is improved by over 60% across all actuators and response matching of sprung mass vertical acceleration PSD is likewise improved by over 50% when using the nonlinear decentralized controller. H o w e v e r , c o n v e n t i o n a l P I D ( + Δ p ) c o n t r o l l o o p s a c t i n g o n e l e c t r o h y d r a u l i c h a r d w a r e h a v e p r a c t i c a l d i f f i c u l t i e s s u c h a s s t a b i l i t y m a r g i n s , a c t u a t o r a n d t e s t f i x t u r e b a n d w i d t h l i m i t a t i o n s a n d i n e v i t a b l e n o n l i n e a r i t i e s i n t h e e l e c t r o h y d r a u l i c s y s t e m . F u r t h e r m o r e , w h e n c o n s i d e r i n g a l l f o u r a c t u a t o r s a n d t h e t e s t v e h i c l e , t h e w h o l e s y s t e m i s a d y n a m i c a l l y c o u p l e d n o n l i n e a r s y s t e m . T h e s e a l l h a v e a n e g a t i v e b e a r i n g o n t h e e f f o r t t o m a t c h t h e d r i v e s i g n a l s ( xd( t ) ) w i t h t h e a c t u a l p i s t o n p o s i t i o n i n a r e p e a t a b l e m a n n e r u s i n g o n l y P I D ( + Δ p ) c o n t r o l l o o p s . T h e t e s t i n g c o m m u n i t y e m p l o y i n g e l e c t r o h y d r a u l i c a c t u a t o r s h a s f o u n d i t n e c e s s a r y t o u s e t h e P I D c o n t r o l l e r a s a n ' i n n e r ' c o n t r o l l o o p a n d i n c l u d e ' o u t e r ' c o m p e n s a t i o n l o o p s t o i m p r o v e c o n t r o l a c c u r a c y , s t a b i l i t y a n d r e p e a t a b i l i t y ( 1 , 2 ) A s u m m a r y o f t h e ' o u t e r ' - l o o p c o m p e n s a t i o n t e c h n i q u e s , w h i c h g e n e r a l l y i n v o l v e i t e r a t i v e ( m a i n l y o f f - l i n e ) c o m p u t a t i o n o f d r i v e s i g n a l s xd( t ) t h a t a t t e m p t t o m a t c h f i e l d m e a s u r e d r e s p o n s e s w i t h o n - s i m u l a t o r r e s p o n s e s , i s g i v e n i n ( 1 - 4 ) . T h e s e a p p r o a c h e s g e n e r a l l y a p p l y t h e i t e r a t i o n s w i t h M u l t i p l e I n p u t M u l t i p l e O u t p u t ( M I M O ) s e t u p s t o s y s t e m a t i c a l l y a d d r e s s t h e i s s u e o f n o n l i n e a r i t y a n d l o a d c r o s s - c o u p l i n g . T h e ' i n n e r ' - l o o p i s g e n e r a l l y l e f t t o t h e d e c e n t r a l i z e d P I D ( + Δ p ) l o o p s .