The new proposed method is the hybridization between SSDI techniques and active methods developed for modal active
control such as time sharing control and modal observer in order to control several modes of a structure with a good
performance but without operative energy. It is designed in order to minimize the number of control components. The
principal application field is the transportation.
It is based on several modal SSDI controllers which act on the same actuator voltage. They are synchronized on each
extremum of the corresponding modal displacement. Modal displacements are reconstructed thanks to a modal model of
the smart structure from a modal observer. In order to reduce the number of actuators, the time sharing method is adapted
to SSDI techniques: all the modal SSDI are connected to the same piezoelectric actuator, but only one controller is
selected to control the voltage inversion for each step time. In order to select modal SSDI controller having the most
effective action for damping, a computation of modal energies is realized from the estimated modal state. A controller
selector is used to connect the modal SSDI command, whose corresponding mode has the highest modal energy , to
the switch trigger.
An application on a smart clamped free beam including one actuator and two sensors is presented. Three modes are
controlled and the modal responses are observed on five modes. The results show that the control reduces significantly
the vibration of targeted modes. Moreover, the method is not subject to stability problems.
Smart structures controlled by active algorithms proved their high efficiency. But active control requires external
energy and heavy amplifier which strongly limit the applications in the transportation field. An alternative to
active control is given by semi-active control which does not require operative energy but which is less efficient
than active control. The proposed hybrid control associates the active control with semi-active control in order
to benefit from the respective advantages of both methods. This hybrid control is intended to control vibration
modes with the same performances than active control while reducing significantly the operative energy.
An application on the second mode of clamped-free smart beam is presented. The results show that this new
control approach appears to be able to decrease the required external energy and to reduce the power and
consequently the weight of the active control amplifiers while maintaining the same damping performances. This
control can be used, for example, in the transportation field to improve the lifetime of systems which use smart
This paper presents a combination of the SSD (Synchronized Switch Damping) semi-active control and techniques
developed for active control. The principle of modal SSDI is to synchronize the piezoelectric voltage inversion or
switching with the extremum of the targeted mode modal displacement. This modal displacement is estimated even in
the case of complex, broadband or noisy excitation with a modal observer. The switching process control induces a non
linear processing of the piezoelectric voltage which results in a cumulative self generated control voltage in phase with
the mode speed, thus generating an important damping of the targeted mode. This voltage self building is optimal if the
piezoelectric voltage is maximum when the modal displacement of the targeted mode is extremum. But in the case of
complex excitation or when the targeted mode amplitude is lower than higher modes, the performances are altered. The
proposed method consists in implementing a decision algorithm allowing waiting for the next voltage extremum before
to trig the voltage inversion, the whole process being globally synchronized with the targeted modal displacement.
Indeed, the targeted mode amplitude is reduced by using part of the energy of the higher modes which enhances the build
up of the self generated piezoelectric control voltage. Simulations carried out on a clamped free beam are presented.
Results obtained first with a bimodal excitation then in the case of pulse excitation demonstrates a large increase of the
damping on the targeted mode.