Zero Steady-state Error Research Articles

Power Control of Cellular Radio Systems Via Robust Smith Prediction Filter

In this paper, a robust Smith prediction filter is proposed for power control design of direct-sequence code-division multiple-access cellular mobile radio systems. Due to the type-I (integrator) structure in the close loop, we first show that zero steady-state tracking error of the averaged received signal-to-noise plus interference ratio (SINR) with respect to a constant target SINR can be ensured. Next, with the Smith predictor to compensate round trip delay, a fixed-order robust H/sub /spl infin// loop filter is developed by using the genetic algorithm to minimize the worst-case variance of the received SINR from the minimax perspective. Using the proposed robust control approach, the statistics of the fading and interference are not needed in the design procedure. To confirm the performance of the proposed method, several simulation results are given in comparison with other methods.

Stationary-frame generalized integrators for current control of active power filters with zero steady-state error for current harmonics of concern under unbalanced and distorted operating conditions

The paper proposes the concepts of integrators for sinusoidal signals. A proportional-integral (PI) current controller using stationary-frame generalized integrators is applied for current control of active power filters. Zero steady-state error for the concerned current harmonics is realized, with reduced computation, under unbalanced utility or load conditions. Designing of the PI constants, digital realization of the generalized integrators, as well as compensation of the computation delay are studied. Extensive test results from a 10-kW prototype are demonstrated.

The chromogranins and the counter-regulatory hormones: do they make homeostatic sense?

1. The chromogranins are ubiquitous proteins which are co-stored and co-secreted with many peptide hormones. All appear to be powerful inhibitors of endocrine secretions. This poses a problem. 2. When endocrine glands are involved in the efferent limbs of homeostatic loops, they are message transmitters. The self-inhibition caused by the co-secretion of a chromogranin will, on the face of it, erase the message. 3. Pairs of counter-regulatory homeostatic hormones also present a problem. 4. If both members of the pair have clearly defined set points, as suggested by their 'time integral' (or 'growth with time') responsiveness to deviations from set point, then, if the two set points are not exactly the same, one or other member will always register an error, leading, eventually, to an overwhelmingly large and unnecessary response. 5. Our model eliminates both paradoxes, and emphasizes the importance of counter-regulation and the co-secretion of chromogranins in 'zero steady-state error' (ZSSE) homeostasis. 6. If hormone A is secreted into the blood in progressively increasing amounts when [Q], the plasma concentration of substance Q, is low, and in decreasing amounts when [Q] is high; and hormone B responds in the opposite manner, then there will be a [Q], designated [Q]p, at which the secretory rate increase, or decrease, of the two hormones is exactly the same. 7. If, in addition, the secretion of both hormones is stimulated by low plasma chromogranin levels, [Cg], but inhibited by high [Cg] then there will be a different [Q]p for every chromogranin concentration in the blood. 8. At one of these points (at a unique [Q] and [Cg]) the concentration of neither hormone will increase or decrease. This is the equilibrium point to which, according to our model, the system always returns regardless of disturbances within physiological limits. 9. This is robust ZSSE control.

Repetitive and periodic controller design

Compensators can be designed to give zero steady-state error in tracking arbitrary periodic or repetitive reference signals. The previously presented technique for design of the compensator has a limited convergence rate for the decay of tracking errors and a limited region of stability. Several alternative design approaches are presented which yield improvements in high-frequency convergence rate while some designs also improve stability. The design approaches are in two classes, designs based on adding periodic correction to an existing controller and total designs for transient and periodic performance. The approaches include FIR and IIR filter design by pole placement and linear quadratic control design.

Tracking periodic inputs using sampled compensators

There are many control system applications where there is a requirement to track a reference signal which is periodic. Examples of this type of application include scanning systems such as those for optical surveillance or radar tracking, and industrial automation systems where robots repetitively follow set trajectories. The conventional integral compensator gives zero error at steady state by providing an infinite gain in the forward path of a control compensator. A compensator based on a digital comb filter can be used to provide infinite gain at a set of harmonically related frequencies. In this way it is possible to provide a digital comb compensator which gives zero steady-state error to a periodic input. The poles of the compensator are determined by the tracking requirement; the zeros must be designed so that the phase shift in the plant will not cause closed-loop instability. An example is given where the shaft angle of a small motor is controlled to track a periodic reference input.

Optimal Control of a Pilot Heat-Exchanger

The first part of the paper gives a practical method for the synthesis of industrial control systems. The application of optimal control theory to industrial control problems is severely restricted by two considerations : It does not give true zero steady-state errors in the presence of step or ramp disturbances (or reference inputs) and the disturbances (or reference inputs) must be known a priori to apply the theory. These two drawbacks are successively considered : the first one is eliminated by the choice of a quadratic criteria which includes the plant'state vector and appropriate time integrals of the output. Optimizing this criteria yielis a regulator structure which includes additionnal open loop integrators, reorganizing this structure to get a classical unitary over-all feedback system leads to a practical control system where the added integrators appeared in front of the plant resulting thus in zero steady state errors control system. For this practical regulator, a predictive optimal command minimizing the transient errors is then applied. This predictive command is computed via the use of a Lyapunov matrix. It is shown that the predictive command depends linearly on the plant'state vector and on the reference input coefficients. The synthesis method is analytical and does not need the usual approximations required when treating this kind of problem via optimal tracking on a non-infinite time interval.The second part of the paper gives a description of the pilot heat-exchanger mathematical model. The pilot plant is counter-flow heat exchanger. The heat exchange process is described by a set of four non-linear partial differential equations where the variations of heat-transfer coefficients with respect to flow-rates and temperatures are considered. After linearization around a steady-state operating point a tedious analytical treatment gives a transfer matrix of transcendental Laplace transforms. The complexity of these transcendental functions being of little pratical use, from these expressions a program, based on parametric identification, computes the parameters of rationnal transfer functions approximating the transcendental model. The resulting transfer functions relate the cold outlet temperature to the hot-fluid flow-rate and to the disturbing cold-fluid flow-rate. The simplified model is made of first and second order transfer functions of the types given below : F1(s)=K1+TsandF2(s)=K(1+T3s)(1+T1s)(1+T2s)The third part of the paper displays experimental results of the pilot plant's control system. The control algorithm is computed via the use of the simplified transfer function, then programmed on a small process computer linked to the pilot heat-exchanger .

Zero steady-state error operation of feedback systems with a time-varying nonlinear element

Zero steady-state error operation of feedback systems with a time-varying nonlinear element