Cascade Control

Abstract: The aim of this paper is the control of an electric traction system. Firstly, the operation of the half-bridge bidirectional DC-DC converter employed for this kind of applications is detailed. Secondly, the control of the system is proposed by using a cascade control scheme. Later, by means of a three-leg three-phase inverter that employs a pulse width modulation strategy, the torque and speed control is achieved for a Surface Permanent Magnet Synchronous Machine (SPMSM). Vector control is also used to achieve this goal. The results exhibit successful responses for both, dynamic and steady state, for operation in motor mode and energy regeneration mode.

Resumen: El propósito del presente artículo consiste en el control de un sistema de tracción eléctrica. En primer lugar, se detalla el modo de funcionamiento del convertidor bidireccional DC-DC tipo medio puente empleado para este tipo de aplicaciones. Segundo, se propone un control del sistema bajo el esquema tipo cascada. Luego, por medio de un inversor trifásico de tres ramales que emplea una estrategia modulación, se realiza el control de torque y velocidad de una Máquina Sincrónica de Imanes Permanentes en Superficie (SPMSM) usando criterios de control vectorial. Los resultados obtenidos muestran respuestas exitosas tanto en régimen dinámico como estacionario en operación modo motor y modo regeneración de energía.

The mobile gantry-crane system is a mechanism used to move loads from one place to another in industrial processes, where the mobilization is carried out in the shortest possible time, without neglecting the stability of the system, especially that of load, which allows determining the behavior's quality. The mathematical modeling corresponding to the system is carried out. The controls considered are PID controls (continuous-discrete and discrete-discrete), root locus and frequency compensator, system override, dead beat and servo system, in order to find the one that presents the best performance in terms of the error and robustness. To verify its good behavior from disturbances and parametric changes, the cascade control technique is used, where priority is given to the stability of the load (pendulum angle). The proposed controllers are implemented in a physical system to make the comparison between the results obtained. Programming is developed using an ARM Cortex-M7 core® microcontroller.

Single zone (SZ) air handling units (AHUs) are widely applied in the conditioned spaces. A SZ AHU typically consists of a chilled water cooling coil, a hot water heating coil, and a supply fan. For a constant volume (CV) SZ AHU or variable air volume (VAV) SZ AHU operating at a minimum airflow, the control valve of either the cooling coil or heating coil is modulated to vary the supply air temperature and consequently control space air temperature. Traditionally, a single control loop is applied to modulate the control valve directly based on the space air temperature. The traditional control is simplistic in nature, however, suffers significant drawbacks. Due to the thermal capacity of both the water in the coils and the air in the conditioned space, the system often becomes unstable due to nonlinear characteristics of the SZ AHU system and leads to hunting of the control valve. On the other hand, cascade control makes the control system more adaptive and robust. A cascade control can be applied to a SZ AHU in order to stabilize the system. The primary controller reads the room air temperature and determines the required supply air temperature for a secondary controller which then controls the heating/cooling coil valve. The purpose of this paper is to demonstrate the stability of the cascade control method in a SZ AHU system. A model of the SZ AHU system with transfer functions is developed for conventional and cascade control methods and root-locus analysis is performed. The results conclude that the cascade control improves the stability of the control valve by reducing the sensitivity to the change in the operating conditions.

... Permissions & Reprints. Adaptive exact linearization control of batch polymerization reactors using a Sigma-Point Kalman Filter. ... Keywords: Batch process operation; Exact I/O-Linearization control; Online parameter estimation; Sigma-Point Kalman Filter. Article Outline. ...

Eventhough the composition control of chemical reactors is an old, widely studied, and still relevant problem in chemical process control, it still presents some aspects that remain unexplored or unresolved. For instance, a unifying approach is needed to systematize the existing ad hoc controller constructions, to rigorously explain their remarkable robustness property, and to explore the possibility of improving their construction and functioning. In this paper, some aspects of these control problems are addressed by resorting to recently developed approaches in constructive non-linear control, yielding a systematic controller construction coupled to a simple tuning scheme that can be executed with standard tuning rules, a closed-loop stability criterion, and an explanation of the closed-loop dynamics behaviour. Specifically, a linear cascade (master/slave) control configuration is proposed, which leads to global internal stability of the controlled system with asymptotic regulation of the output-stream composition about a given desired setpoint. A simulation example is used to illustrate the results. Copyright © 2002 John Wiley & Sons, Ltd.

A new prototype parabolic-trough collector system was erected at the Plataforma Solar de Almerı́a (PSA) (1996–1998) to investigate direct steam generation (DSG) in a solar thermal power plant under real solar conditions. The system has been under evaluation for efficiency, cost, control and other parameters since 1999. The main objective of the control system is to obtain steam at constant temperature and pressure at the solar field outlet, so that changes in inlet water conditions and/or in solar radiation affect the amount of steam, but not its quality or the nominal plant efficiency. This paper presents control schemes designed and tested for two operating modes, “Recirculation”, for which a proportional-integral-derivative (PI/PID) control functions scheme has been implemented, and “Once-through”, requiring more complex control strategies, for which the scheme is based on proportional-integral (PI), feedforward and cascade control. Experimental results of both operation modes are discussed.

Buildings are maintained at slightly positive pressure by air handling units (AHUs) to reduce infiltration of unconditioned outdoor air. The conventional AHUs rely either on direct building pressure control or volume tracking control with a single loop proportional integral (PI) controller to maintain positive building pressure. Even though this type of control structure is simplistic, it is observed that it may lead to hunting of return fan speed, especially with direct building pressure control. For the direct building pressure control, accurate and stable building pressure measurement is challenging due to wind and intermittent pressure changes caused by the opening of doors. On the other hand, the building static pressure is highly sensitive to the differential airflow therefore; the error in airflow measurement makes the volume tracking method unfavorable. In general, cascade control makes the control system more adaptive and robust. In this case, the primary controller reads the building static pressure and determines the differential flow rate setpoint for secondary controller which then controls the return fan speed. The purpose of this paper is to evaluate the performance of the cascade control on the building static pressure in comparison with the two conventional controls by simulation. Performance of the two conventional controls as well as cascade control is simulated. The results conclude that the cascade control improves the stability of the system by reducing the sensitivity to the change in the operating conditions and controller gains.

A parallel control strategy is developed for process applications by “reverse engineering” the functions of the baroreceptor reflex—the biological control system that regulates arterial blood pressure. The specific control architecture and algorithm employed by the reflex are ...

In addition to absorption chillers, today’s gas cooling technology includes gas engine driven heat pump systems (GEHP) in a range of capacities and temperature capacities suitable for most commercial air conditioning and refrigeration applications. Much is expected from GEHPs as a product that would help satisfy the air conditioning system demand from medium and small sized buildings, restrict electric power demand peaks in summer and save energy in general. This article describes a kind of control strategy for a GEHP, a cascade fuzzy control. GEHPs have large and varying time constants and their dynamic modeling cannot be easily achieved. A cascade control strategy is effective for systems that have large time constants and disturbances, and a fuzzy control strategy is fit for a system that lacks an accurate model. This cascade fuzzy control structure brings together the best merits of fuzzy control and cascade control structures. The performance of the cascade fuzzy control is compared to that of a cascade PI (proportional and integral) control strategy, and it is shown by example that the cascade fuzzy control strategy gives a better performance, reduced reaction time and smaller overshoot temperature.

Summary: Experimental investigations in different mixing conditions (impulse and vibromixing) in a Saccharomyces cerevisiae batch cultivation are presented in this paper. The investigation is carried out in a 5 l laboratory bioreactor (working volume 3 l). ...