Clock Variation Impact on Digital Control System Performance

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.

With the development of digital signal processing technologies, control and monitoring of power electronics conversion systems have been evolving to become fully digital. As the basic element in the design and analysis phases of digital controllers or filters, a number of unit delays (z−1) have been employed, e.g., in a cascaded structure. Practically, the number of unit delays is designed as an integer, which is related to the sampling frequency as well as the ac signal fundamental frequency (e.g., 50 Hz). More common, the sampling frequency is fixed during operation for simplicity and design. Hence, any disturbance in the ac signal will violate this design rule and it can become a major challenge for digital controllers. To deal with the above issue, this paper first exploits a virtual unit delay (z v -1) to emulate the variable sampling behavior in practical digital signal processors with a fixed sampling rate. This exploitation is demonstrated on a T/4 Delay Phase Locked Loop (PLL) system for a single-phase grid-connected inverter. The T/4 Delay PLL requires to cascade 50 unit delays when implemented (for a 50-Hz system with 10 kHz sampling frequency). Furthermore, digital frequency adaptive comb filters are adopted to enhance the performance of the T/4 Delay PLL when the grid suffers from harmonics. Experimental results have confirmed the effectiveness of the digital filters for advanced control systems.

High Energy Photon Source-Test Facility (HEPS-TF) is a pre-research project for the construction of high energy synchrotron radiation source in the 12th five-year plan period. The purpose is to research the key technology and develop the key equipment of high energy synchrotron radiation source. Superconducting 3W1 magnet is the first self-developed superconducting wiggler magnet in China, and it is also one of the key research topics of HEPS. The author has completed a new digital closed-loop control algorithm for the superconducting 3W1 magnet with large load time constant and the nonlinear characteristics of inductance increasing with current, namely three-branch structure algorithm. In the face of the rapid development of high energy accelerator technology, the application of intelligent technology has become an inevitable development trend in the field of accelerator magnet power supply technology. Although the digital control of accelerator magnet power supply has been widely used, it is the first time to apply the new closed-loop control algorithm to realize fast adjustment and precision tracking in accelerator superconducting magnet power supply in China. According to the nonlinear characteristics of inductance and output current of superconducting magnet, a new digital closed-loop control algorithm for the load of superconducting magnet power supply with large time constant is proposed. This algorithm is quite different from the traditional algorithm and can attain the independent tracking and adjustment of the control target. Finally, by testing the ripple, error and stability of superconducting 3W1 magnet power supply, the correctness, practicability and reliability of power supply system as well as the digital control algorithm are verified. The results provide a new idea for the control of accelerator magnet power supply.

In order to study the control theory, students need to learn about basic theories that are sometimes difficult to understand. Only in-class lecturing is not enough, and hand-on practices are very important, in which theory and practice can be integrated to create knowledge and skills simultaneously. Although there are many learning tools available for practicing with sample exercises, they are not enough for students to understand properly especially in the subject that are abstraction and requires imagination. This paper presents a didactic tool for a study of leveling control system which maintains the surface level using multiple sensors including IMUs and ultrasonic sensors, and multiple models including digital filters, coordination, digital automatic control, and kinematic model. The data obtained from the IMU are used to calculate the tilt angle using the complementary filter method, and from the ultrasonic sensors are used to find the distance between the platform and ground using low-pass filter. The difference tilt from both roll and pitch angles and the distance are used to control the tilt angle and the correct distance using the PID controller. This system can be used to study IMU sensor functions, digital signal processing and digital controller as well, and will enable students to understand and use the sensor system to easily create automatic control systems in the future.

A visual CAD platform for designing the positioning system of optical disk drives is described in this paper. The platform consists of the opto-mechanical assembly (OMA) and its simulator of an optical disk drive, a servo control board (SCB) with a high performance digital signal processor (DSP), and a personal computer (PC). The OMA and SCB form the complete digital positioning control system of an optical disk drive. The OMA simulator and SCB provide a real-time simulation environment under which a digital controller (i.e., the DSP program) is run. On a PC with the CAD software packages, the controller can be conveniently designed and loaded into SCB. Furthermore, the behavior of the disk drive and the status, parameters and structure of the controller are visualized on the PC's display without interrupting the controller. The visualization can be implemented on three levels: post-processing, tracking, and even steering.

The use of multiple digital signal processors (DSPs) to implement a real-time digital controller is described. Specially, the multi-DSP implementation of a multi-input single-output digital controller with small sampling period and throughput time is considered. The optimal scheduling problem to achieve the minimum sampling period when the number of available DSPs is fixed is formulated. A scheduling algorithm based on a branch-and-bound approach for the optimization problem is then proposed. The multi-DSP system has also been realized experimentally. The proposed algorithm has been implemented and tested by a breadboard experiment using three DSPs. >

1 - Introduction

A DSP based digital control platform for a rectifier-inverter system built in the laboratory is presented and described in this paper. The digital platform offers the opportunity to test different control algorithms, of which the discrete PI control, a state feedback based dead beat control algorithm and digital hysteresis controllers have been the focus. An optimum digital control algorithm needs to be selected which can fully utilize the advantages of the digital platform. Stability analyses of the digital controllers and implementation issues have been highlighted

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.

Recently, optimal control on Buck converter for powering the latest computer central processor units (CPUs) has attracted more and more attention. In this paper, a novel digital control algorithm is presented to achieve the time-optimal response for dc-dc Buck converters without relying on any knowledge of converter design parameters such as output inductance, capacitance and even ESR value. This algorithm is based on the parabolic curve fitting analysis for deriving the algorithm formulas under the step load transients. Furthermore, this algorithm can be extended to adaptive voltage positioning (AVP) applications with simple modifications for a low ESR designed Buck converter. Also, it delivers a practical and cost-effective interface to AVP schemes due to the parameter-independent and current-sensorless detecting mechanism. Finally, simulations and experimental results of a 12 V-1.5 V Buck converter prototype are provided to validate the proposed schemes using digital signal processor (DSP) implementation.

In this paper, an efficient power electronic circuit simulation approach is discussed for a digitally controlled three phase active PFC converter system. The control circuit simulation software used in this simulation technique is also applied to the digital signal processor (DSP) based control implementation of a a practical power factor correction (PFC) power conversion circuit with a digital control scheme. This circuit simulation technique is based on a circuit equation modeled by substituting control input dependent time-varying resistors in place of all the power switches incorporated in the bridge arms of the three phase active PFC converter circuit and system treated here, one state-vector equation described by state-variables for inductors and capacitors, together with an algebraic computation method to transform the matrix of the circuit equation into matrix of the state vector equation. In addition, this paper proves the effectiveness of a voltage-fed three phase PFC converter with a digital control PWM strategy and its performance evaluations on the basis of computer-aided simulation results together with experimental result.

This paper describes the medium voltage high power DVR (dynamic voltage restorer) with the new voltage disturbance detection method and the real-time digital voltage control. The new voltage disturbance detector was implemented by using the delta rule of the neural network control. Through the proposed method, we can instantaneously obtain the peak value of each phase voltage even under the single phase input voltage conditions. Compared to the conventional synchronous reference frame method, the proposed one shows the minimum time delay to determine the instance of the voltage sag or voltage swell event. Also real-time digital voltage control technique was adopted, where the inverter output filter capacitance voltage, the filter reactor current and the load current are sampled to calculate the inverter PWM command for the next sampling interval. By using digital control, the disturbance voltage can be compensated to the reference voltage level within two sampling intervals. The proposed disturbance detector and the voltage compensator were applied to the medium voltage high power DVR (22.9 kV/4 MVA) that was developed for the application of semiconductor manufacture plant. The performances of the proposed DVR control were verified through computer simulation and experimental results. Finally, conclusions are given.

A digital adaptive current controller for implementation on a three-phase voltage source inverter is proposed for a demonstration 40 kVA dynamic power filter (DPF). The digital dynamic compensator controller is based on a TMS320E15 digital signal processor (DSP), which will be implemented in a hybrid power compensator of +or-100 kVA power rating. The hybrid power compensator consists of a three-phase thyristor controlled reactive (TCR) source, combined with the three-phase 40 kVA voltage-fed system. The characteristics of the digital current controller for the DPF are introduced and described. Simulation results of this digital control technique on a single-phase DPF are shown and compared with practical results obtained from a low-power (+or-300 VA) single-phase DPF. >

This paper presents the implementation and experimental details of a real-time digital simulator designed for representing a Distribution Static Compensator (D-STATCOM) interfaced with a digital controller. Real-time simulation using conventional fixed time-step integration algorithms can lead to erroneous results due to the lack of synchronism between the simulator time-step and the discrete switching signals coming from the digital controller. The real-time simulation algorithm implemented in this paper overcomes the drawbacks of a fixed time-step algorithm. The real-time algorithm relies on precise registration of timing of the incoming discrete firing pulses and a subsequent correction procedure to calculate the system state. This approach has been implemented on a hybrid digital processing platform comprising of a Digital Signal Processor (DSP) and a Field Programmable Gate Array (FPGA). The platform represents both the power electronic system and the digital control system. Experimental results, for a 5 kV A D-STATCOM system, in verification of the real-time simulator results are also provided.

An integrated digital controller design for dc-dc converter is proposed in this paper. The proposal presents a multiple- band dual-stage (MBDS) delay line A/D converter (ADC) for wide dynamic range of operation with reduced ripple, chip area, and power consumption. This proposal also introduces a novel folding logic for digital error calculation and dual-mode error control PID for improving transient response. A complete closed-loop experimental prototype is demonstrated on a field-programmable-gate- array-based setup. The feasibility and functionality of the proposed digital controller is verified with a closed-loop synchronous buck converter prototype that switches at 1 MHz and regulates over a wide output voltage range of 1.6-3.3 V. The proposed MBDS delay line ADC is fabricated with discrete logic gates and flip-flops. The integrated digital controller is also implemented using standard cell-based design methodology in 0.5-mum CMOS technology. The design reduces 33 % on-chip area compared to an equivalent of 64 tap delay line ADC. The complete digital controller chip takes less than 0.7 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of silicon area and consumes an average current of 92 muA at 1-MHz switching frequency. The voltage-mode digital loop achieves tracking time of less than 10 mus for 1-V step change of the reference voltage and settling time of 20 mus. Post layout simulation and experimental results are demonstrated.