Real Time Analysis of Microprocessor Control System

The article is dedicated to optimizing the digital current control loop of a thyristor converter-driven electric drive, essential for ensuring stable, precise, and reliable operation of electric drives in automated and industrial systems. The primary goal of this research is to develop and enhance the digital current regulator (DCR), which enables the drive system to achieve desired performance, including rapid and stable response to current changes without excessive overshoot or oscillations. Optimization of the current loop improves energy efficiency, enhances dynamic properties, and increases resistance to external disturbances, all of which are critical for modern electric drive systems. The introduction discusses key aspects of digital current loop optimization, specifically dynamic characteristics such as time delays, sampling rate, and bandwidth, which significantly impact the efficiency of digital controllers. Special attention is given to the tuning of proportional-integral (PI) controller parameters, allowing quick and stable response to current changes. The developed model allows preliminary simulation of the current loop’s performance, providing an opportunity to test different configurations before actual implementation. To improve the accuracy and stability of the system, filtering methods are proposed to reduce the impact of high-frequency noise, ensuring the system’s precision and robustness against external interference. Optimization criteria are introduced, including minimizing the integral square error (ISE) and reducing energy consumption, which significantly decreases system losses and increases the energy efficiency of electric drives. In developing the optimized control loop, the following assumptions are considered: 1) the thyristor converter (TC) operates in continuous current mode, 2) the current loop dynamics are studied within a narrow range of TC phase angle changes, and 3) a discrete dynamic TC model is used with averaging of electromotive force (EMF) over the conduction interval. Optimizing the digital current loop addresses several critical tasks, including enhancing control accuracy, reducing overshoot and oscillations, and improving the system’s dynamic response, allowing for reduced delays and a faster reaction to load changes. The optimization results of the digital current regulator (DCR) show reduced energy consumption and significant improvements in control accuracy. The high-speed performance of the digital current loop enables fast transient processes within a single sampling interval of the thyristor converter, which is crucial for systems requiring rapid regulation. Additionally, the digital control loop provides flexibility in control, as it allows for system adjustments to different operating conditions through a software-based approach. The study’s final results demonstrate the potential of digital current loops in modern electric drives. With advances in microprocessor technology, digital regulators enable more complex control algorithms, including adaptive and predictive strategies, which further enhance system efficiency. These approaches are especially relevant for industrial electric drives that require high precision and response speed, making digital current loops a promising solution for contemporary automated control systems.

This paper addresses modeling and control issues related to practical high-frequency digital PWM control of constant-frequency boost, buck-boost and flyback converters. Discrete-time models, including the effects of A/D sampling and delays in the digital control loop, are derived for two cases: output voltage A/D sampling during transistor off time in combination with trailing-edge (TE) DPWM, and A/D sampling during transistor on time in combination with leading-edge (LE) DPWM. We show that off-time sampling with TE-DPWM, which is a common approach in digital controller realizations, can result in desirable minimum-phase responses, thus simplifying compensator design in wide bandwidth closed-loop voltage regulators based on boost or flyback converters. The results are verified by simulation and experimental results on a boost converter prototype.

The empirically developed force control in cases of the robotic polishing and the rehabilitation robots serve as a motivation for the study of the peculiar dynamic behaviour of digital force control. The effect of the sampling times of the digital controllers are studied analytically, and the corresponding stability charts are presented for different gain and mechanical parameters describing also the different sampling frequencies at the force sensors and in the digital control loop. The types of bifurcations are also identified at the stability limits. As one of the practical conclusions, the negative role of differential gain is explained in digital force control.Key wordsforce controlled robotsdifferential gaindelayed oscillator

In order to make BEPC-II to run at a higher energy, the Institute of High Energy Physics undertook an upgrading project. One of the important factors limiting the energy boost is the power and performance of the dipole magnet power supplies; therefore, these four magnet power supplies are developed for the BEPC-II upgrading. The power supplies adopt topologies of thyristor rectifiers to realize a high-power output. In the control unit of each power supply, a digital current closed loop is adopted, and the key components in the feedback loop are thermostatically controlled. In order to improve the performances of the power supplies, analog voltage regulators are added to the inner control loops. These four power supplies have been tested and have already been officially used in BEPC-II, and their powers have reached the requirements of the upgrading. The test results of the current stability are described and shown in this paper, which testifies that the stabilities meet the design parameters. A digital control is applied to each SCR rectifier control. The performances of the power supplies are improved by the combination of digital current control loops and the analog voltage control loops, which makes the performances of the dipole magnet power supplies meet the requirements of the upgrading project.

Application of Digital Control Techniques for Satellite Medium Power DC-DC ConvertersThe objective of this paper is to present a work concerning a digital control loop system for satellite medium power DC-DC converters that is done in Space Research Centre. The whole control process of a described power converter is based on a high speed digital signal processing. The paper presents a development of a FPGA digital controller for voltage and current mode stabilization that was implemented using VHDL. The described controllers are based on a classical digital PID controller. The converter used for testing is a 200 kHz, 750W buck converter with 50V/15A output. A high resolution digital PWM approach is presented. Additionally a simple and effective solution of filtering of an analog-to-digital converter output is presented.

Abstract. Switched-mode power supplies (SMPS) convert an input DC-voltage into a higher or lower output voltage. In automotive, analog control is mostly used in order to keep the required output voltages constant and resistant to disturbances. The design of robust analog control for SMPS faces parameter variations of integrated and external passive components. Using digital control, parameter variations can be eliminated and the required area for the integrated circuit can be reduced at the same time. Digital control design bears challenges like the prevention of limit cycle oscillations and controller-wind-up. This paper reviews how to prevent these effects. Digital control loops introduce new sources for dead times in the control loop, for example the latency of the analog-to-digital-converter (ADC). Dead times have negative influence on the stability of the control loop, because they lead to phase delays. Consequently, low latency is one of the key requirements for analog-to-digital-converters in digitally controlled SMPS. Exploiting the example of a 500 kHz-buck converter with a crossover frequency of 70 kHz, this paper shows that the 5 µs-latency of a ΔΣ-analog-to-digital-converter leads to a reduction in phase margin of 126°. The latency is less critical for boost converters because of their inherent lower crossover frequencies. Finally, the paper shows a comparison between analog and digital control of SMPS with regard to chip area and test costs.

A digital control loop scheme for a high speed PLL is suggested to detect amplitude errors at the output of the oscillator. Reliability specifications of the PLL are likely to be violated in case of excessive output swing in the oscillators. In addition, low amplitude swings will have negative influences on the phase noise of LC oscillators. As a result, the performance and reliability of the PLL will be reduced. The design includes a novel amplitude error detector. The amplitude error detector generates a digital word to show the situation of the amplitude error. The structure is implemented in 65nm CMOS technology. The power consumption of one amplitude error detector from 1V power supply is 0.76mW.

A digital pulsewidth control loop (PWCL) with a fixed-delay rising edge and digital stability control is proposed for multiphase clock applications. In the duty-cycle tracking mode, the linear range of the input duty cycle was measured to be 28%-70%, with a maximum linearity deviation of 0.5%. In the duty-cycle correction mode, the correction range of the input duty cycle was measured to be 25%-75%, with the output duty cycle within 50 plusmn 0.4%. The chip was fabricated by using a 0.25-mum CMOS process with a 2.5-V supply. The chip area and the power consumption were 200 mumtimes250 mum and 18 mW at an input clock frequency of 1.0 GHz, respectively

A high precision temperature control system capable of maintaining the temperature of superconducting quantum interference devices (SQUIDs) constant to within 1.0 μK root-mean square over a narrow frequency band was designed and built for use with the superconducting readout system of the Gravity Probe B experiment. The system utilizes an analog ac temperature bridge with a digital proportional-integral control loop which incorporates a peaking filter. A disturbance attenuation factor of 86 or greater over the required frequency band was demonstrated in system tests with the cryogenic hardware, allowing the SQUID system to achieve the required stability. The control system was robust against variations in the thermal characteristics of the cryogenic hardware.

DC-DC converters are extensively used for switched mode power supplies. Hence, this chapter presents a design, modelling and hardware implementation of a digitally controlled system and its application to DC-DC buck converter being interfaced with Texas Instruments DSP TMS320F2812 controller for voltage control mode. ADC, compensator and digital PWM are the main building blocks that appears in digital controller design. Conventionally, analog controller is popular to get the desired output voltage in DC-DC converters, whereas, digital controllers offer high speed arithmetic and high resolution. Analog PI controller design approach is reviewed and the digital PI controller design is being implemented in this chapter. Digital control has been applied using standard frequency responses with design by emulation approach. Modulation delay in digital control is very critical while designing for fast control loops. Therefore, this chapter also introduces discrete time modelling of synchronous buck converter from practical standpoint considering feedback loop delays. Whereas, this chapter illustrates PI digital controller design methodology, hardware implementation and experimental verification. Experimental results have been taken from a closed loop 18W buck converter. The transient and steady state performance of the converter using PI controller are also presented with appropriate simulation and hardware results.

34th Annual Frequency Control Symposium

This paper presents effect of LC with clamping diodes dv/dt filter on current-controlled PMSM drives in case where 3-phase inverter output currents are measured and used in the digital control loop. In particular, this case can be reported in some cases. Firstly, power devices are equipped with integrated pilot current sensors. Secondly, PCB technology based Rogowski coils are installed in inverter leg with analog circuit to feed a signal to microcontroller. Thirdly, hall type current sensors are packaged in inverter output terminal through a bus bar. In those cases, it is inevitable to measure inverter currents because it is hard to move the location of current sensor. In this manner, the effect of filter resonance should be considered properly to control the motor current accurately because the measured inverter output current includes both motor and filter resonant current. If the resonant current of the filter is not compensated properly, it causes the DC offset of motor current which bring about the torque ripples. In order to compensate the offset, inserting a two stage Discrete Fourier Transform (DFT) is used and the calculated offset is subtracted from the sampled current. Judging by simulation and experimental results, it is confirmed that the compensation method eliminates the offset of the motor current effectively, and thereby reducing the torque ripple as well.

Stability of discrete linear feedback systems with pulse-width-modulation power dispatch An adaptation of the circle criterion to pulse-width-modulation type nonlinearities in a digital control loop is presented. Formulae are derived for both gain and the mode of oscillations of the system response. Standard examples are taken, including that of a plant with a pole at the origin.

Traditional haptic rendering creates virtual springs using DC motors with current amplifiers and encoder-based position feedback. It is well known that the stiffness of virtual environments is limited by quantization, discretization, and amplifier bandwidth effects. In this paper we propose a novel control architecture that, rather than canceling motor electrical dynamics, uses them to achieve better performances. First we recognize that the inductance L provides a natural sensor-less stiff behavior at high frequencies. Second, electrical resistance R serves as the basis of a wave transform that, performed through an analog circuit, allows to build a more stable interface with virtual environments, achieving robustness to servo delays and discretization. Encoder feedback and digital control loop are required only to provide parametric robustness at low frequencies. A prototype 1-DOF system has been implemented and confirms the promise of this novel paradigm

We used a digital feedback control loop system to produce reproducible fixed volume transmission holograms of high diffraction efficiency. Different strategies were investigated to obtain holograms of good quality and the highest refractive index modulation depth. Using this control system, we were able to record holograms with stationary fringes. Additionally to using the stationary fringe recording, a double recording-fixing schedule resulted in being the most appropriate one to produce reproducible holograms of better characteristics. This strategy is discussed and compared with other already established ones.