Digital Feedback Control System Research Articles

Characteristics of a dc 75 kA power supply in the superconducting magnet test facilities

To investigate properties of superconducting R&D conductors and coils for the Large Helical Device (LHD), a dc 75 kA power supply system which consists of three 25 kA unit banks has been designed and constructed. One unit bank has two double-star-rectifier connections with the inter-phase reactors. The algorithm of the digital feedback control system is installed in each unit bank. In this algorithm, each 6 phase is operated independently on the process of averaging, proportioning and integrating. The experiments of several short samples and one of the R&D coils have been done under the maximum ramp rate of the power supply, 999 A/s per unit. It is confirmed that the measured current stability is less than ±0.75%, and the deviation between a set value and an output value of the load current is less than ±1% under the short circuit test.

Robust digital control of a high-performance engine

The design of a robust digital multivariable feedback control system for the F-100 turbofan jet engine is considered. The control system design problem is posed, and conditions for satisfying performance specifications and stability robustness are stated. The discrete LQG/LTR methodology is used to design a compensator that meets the stated specifications. New results for multi-input LQR loop shaping are derived. To get a reasonably low-order compensator, frequency-weighted reduced-order models are exploited, with the reduction error treated as an uncertainty.

Quantizer effects on steady-state error specifications of digital feedback control systems

Suppose that for a linear, time-invariant, single-input single-output (SISO) plant a digital dynamic controller has been designed so that the corresponding discrete-time linear feedback control system will satisfy certain specified steady-state error criteria (e.g., the output v(kT) will follow the input r(kT) within a certain given error bound). Corresponding to this idealized linear system, the digital implementation of the dynamic controller will result in a nonlinear feedback control system. To what extent the resulting nonlinear digital feedback control system satisfies the steady-state-error criteria of the original idealized linear prototype feedback control system is investigated. Digital controller implementations which use fixed-point arithmetic or floating-point arithmetic are considered. Designs which are well scaled are assumed, i.e., overflow nonlinearities in digital controllers are not addressed. >

インバータ運転を用いた省エネルギー形定圧油圧源 油圧源電動機の状態量からの圧力の算定

Advances in power electronics and microprocessors have provided new opportunities in the application of inverter-motor drive systems. The speed control of AC induction motors can be realized easily by use of an inverter-motor drive at a low cost, high efficiency and wide speed range. From the viewpoint of saving energy, the authors have proposed and developed a new type of variable delivery hydraulic power source with an inverter-motor drive. In this power source, the speed of the fixed displacement pump is controlled by the inverter motor so as to deliver the necessary minimum flow rate for the duty cycles of the servo system.In this system, the system pressure and pump delivery flow rate are estimated indirectly by the state variables of the inverter motor. The principle of the pressure estimation is experimentally confirmed. The programmed control system and digital feedback control system using an estimated system pressure are developed. It is demonstrated that both systems are able to control the hydraulic power source according to the duty cycles of the servo system.

Quantization and overflow effects in digital implementations of linear dynamic controllers

The stability of a class of single-input/single-output (SISO) digital-feedback control systems is investigated. The systems considered contain a linear dynamic plant, a digital controller, and suitable D/A (digital-to-analog) and A/D converters. The design of such systems is usually accomplished by ignoring the nonlinear effects caused by quantization and overflow truncation. Simulations of specific examples establish the quantization in such systems can lead to loss of asymptotic stability of the origin. Obtained results prove that when quantization is taken into account (but overflow is neglected), one only has convergence to some (small) neighborhood about the origin. The results also prove that for initial conditions sufficiently far from the origin, overflow effects can lead to unbounded solutions. In particular, this is the case for observable systems with at least one eigenvalue in the open right-half plane (RHP). The case of systems with no eigenvalues in the open RHP, but with eigenvalues on the j omega -axis, is still unresolved. >

Optimal digital feedback control systems counting computation time of control laws

Since microprocessors are easily obtained, multivariable control theory can be applied to many practical control problems, for example control of robots. However, when the time constant of the plant is short and the dynamic order of the plant is high, the time delay due to the computation time of the control law cannot be neglected. In this paper, the author proposes design methods for linear optimal regulators and linear optimal servosystems in which the delay arising from the computation time of the processors is counted properly. From the theoretical point of view, the results are interesting since all the control laws derived in this paper are obtained using only conventional results of optimal regulator theory.

A new method of optimal digital PID feedback control†

This paper presents a now method of optimal digital PID feedback control for a linear multivariate system by using a, parameter optimization technique. The most difficult points for the design of optimal digital PID feedback control system by the modern control theory are : (1) the control structure of it is specified in advance, (2) unless all the state variables are fed back, the optimal control cannot be obtained by dynamic programming or the maximum principle. However, the optimal digital PID feedback gains are determined by using the parameter optimization technique in this paper. When there are some states which are not fed back in the control system, the optimal feedback gains depend on the initial states. First, the optimal solution is presented in the case where all the initial Btates are known. Next, it is extended to the case where the initial states are random variables and their statistical properties are known,

Digital Compensation for Control and Simulation

This paper describes a technique for improving the performance of digital feedback control systems and operational digital simulators by making use of the computer to perform information programming or data processing. The system stability can be improved and the system error can be reduced by digital programng of the input and error signals together with digital correction computations. This technique of digital compensation is illustrated by an example.