R.M. Nelms

Evaluation of DSP-Based PID and Fuzzy Controllers for DC–DC Converters

In this paper, digital proportional-integral-derivative (PID)-type and fuzzy-type controllers are compared for application to the buck and boost dc-dc converters. Comparison between the two controllers is made with regard to design methodology, implementation issues, and experimentally measured performance. Design of fuzzy controllers is based on heuristic knowledge of converter behavior, and tuning requires some expertise to minimize unproductive trial and error. The design of PID control is based on the frequency response of the dc-dc converter. Implementation of linear controllers on a digital signal processor is straightforward, but realization of fuzzy controllers increases computational burden and memory requirements. For the boost converter, the performance of the fuzzy controller was superior in some respects to that of the PID controllers. The fuzzy controller was able to achieve faster transient response in most tests, had a more stable steady-state response, and was more robust under some operating conditions. In the case of the buck converter, the fuzzy controller and PID controller yielded comparable performances.

A resonant inverter for electronic ballast applications

Electronic ballasts must provide enough open circuit voltage to start the fluorescent lamp and current limiting while the lamp is running. Resonant inverters may be utilized in electronic ballasts because of their load-dependent characteristics. The three basic types of resonant inverters, the series-loaded, parallel-loaded, and the series-parallel-loaded, are compared using fundamental approximation techniques for their applicability in electronic ballasts operating from a low voltage source. A parallel-loaded resonant inverter operating slightly above its resonant frequency is selected because of the high voltage gains possible. Operation above the resonant frequency allows zero-voltage turn on of the semiconductor devices. Zero-voltage turn off can be achieved with the addition of lossless snubber capacitors. Experimental results from a lab prototype are used to verify the design procedure. >

PID controller modifications to improve steady-state performance of digital controllers for buck and boost converters

The sensitivity of the analog-to-digital converter and inherent time delay in a digital controller can degrade the steady-state performance of a DC-DC power converter. Analog PID controllers were designed for prototype buck and boost converters and then implemented on a TI DSP. Three modifications to the digital PID controllers were investigated to improve their steady-state performance. The modifications were a dead zone, an averaging digital filter and two sets of gains. The digital controller monitors the output voltage error to determine if a modification should be employed to calculate the next duty cycle. Experimental results from both prototype converters indicates that a stable and accurate steady-state response can be obtained while maintaining a good transient response.

A capacitor-charging power supply using a series-resonant topology, constant on-time/variable frequency control, and zero-current switching

A power supply specifically designed for capacitor-charging applications that uses a series-resonant circuit topology, a constant on-time/variable frequency control scheme, and zero-current switching techniques has been developed. The performance of this capacitor-charging power supply (CCPS) has been evaluated in the laboratory by charging several values of load capacitance at various repetition rates. The CCPS has charged a 1 mu F capacitor from 0 to 1500 V DC in 750 mu s, exhibiting a charging power of 1500 J/s. This operation has been repeated at a rate of 800 charges per second, which corresponds to an average power output of 900 W. A 10 mu F capacitor has been charged from 0-1500 V DC in 8 ms. These results indicate that this design is feasible for use in capacitor-charging applications. >

Digital controller design for buck and boost converters using root locus techniques

Root locus techniques to design digital controllers for buck and boost converters are discussed in this paper. The small signal models of both converters are first transformed into discrete-time models using the matched pole-zero mapping method. Digital controllers are designed based on the discrete-time model using the root locus method. By selecting the poles, zeros and gain of the digital controllers, the closed-loop poles are placed at desired locations in the z-plane. The digital controllers are then implemented on a TI DSP. The root locus design method is compared with the frequency response design method. Experimental results from the buck converter indicate that the results obtained using the root locus method are comparable to the results obtained using the frequency response method, while results from the boost converter indicate the nonlinear nature of the boost converter small signal model may degrade the performance of the design using the root locus method.

Modeling double-layer capacitor behavior using ladder circuits

The double-layer capacitor (DLC) is a very complex device that is best represented by a distributed parameter system. Many different lumped-parameter equivalent circuits have been proposed for the DLC. An examination into utilizing a ladder circuit to model a DLC is presented. Parameters for different ladder circuits are determined from AC impedance data. Variations in circuit parameters with DC bias and manufacturing have been investigated. The performance of the ladder circuit has been evaluated in slow discharge and pulse load applications.

Adaptive Electricity Scheduling in Microgrids

Microgrid (MG) is a promising component for future smart grid (SG) deployment. The balance of supply and demand of electric energy is one of the most important requirements of MG management. In this paper, we present a novel framework for smart energy management based on the concept of quality-of-service in electricity (QoSE). Specifically, the resident electricity demand is classified into basic usage and quality usage. The basic usage is always guaranteed by the MG, while the quality usage is controlled based on the MG state. The microgrid control center (MGCC) aims to minimize the MG operation cost and maintain the outage probability of quality usage, i.e., QoSE, below a target value, by scheduling electricity among renewable energy resources, energy storage systems, and macrogrid. The problem is formulated as a constrained stochastic programming problem. The Lyapunov optimization technique is then applied to derive an adaptive electricity scheduling algorithm by introducing the QoSE virtual queues and energy storage virtual queues. The proposed algorithm is an online algorithm. We derive several “hard” performance bounds for the proposed algorithm, and evaluate its performance with trace-driven simulations. The simulation results demonstrate the efficacy of the proposed electricity scheduling algorithm.

Simulation and modeling of a DC-DC converter controlled by an 8-bit microcontroller

Traditionally, analog control technologies have been employed to regulate the output voltage of DC-DC converters. The utilization of digital control techniques for this regulation function is currently under consideration. Critical issues in a digital control implementation include analog-to-digital conversion range, resolution and delay, calculation time, and numerical precision. Results from an investigation into the modeling and simulation of DC-DC converters controlled by an 8-bit microcontroller are described in this paper. Many of these critical issues have been modeled using Matlab/sup TM/ and Simulink/sup TM/ from The Mathworks Inc. Simulation results from this model are compared to experimental waveforms obtained from a buck converter controlled by a Microchip PIC16C74 8-bit microcontroller. Experimental results agree well with the simulation model. The buck converter is represented by its state-space averaged model in the simulation.

Designing a parallel-loaded resonant inverter for an electronic ballast using the fundamental approximation

The three basic types of resonant inverters, the series-loaded, parallel-loaded, and the series-parallel-loaded, are compared using fundamental approximation techniques for their applicability in electronic ballasts operating from a low voltage source. A parallel-loaded resonant inverter operating slightly above its resonant frequency is selected because of the high voltage gains possible. Operation above the resonant frequency allows zero-voltage turn on of the semiconductor devices. Zero-voltage turn off can be achieved with the addition of lossless snubber capacitors. Experimental results from a lab prototype are used to verify the design procedure.<<ETX>>

Adaptive electricity scheduling in microgrids

Microgrid (MG) is a promising component for future smart grid (SG) deployment. The balance of supply and demand of electric energy is one of the most important requirements of MG management. In this paper, we present a novel framework for smart energy management based on the concept of quality-of-service in electricity (QoSE). Specifically, the resident electricity demand is classified into basic usage and quality usage. The basic usage is always guaranteed by the MG, while the quality usage is controlled based on the MG state. The microgrid control center (MGCC) aims to minimize the MG operation cost and maintain the outage probability of quality usage, i.e., QoSE, below a target value, by scheduling electricity among renewable energy resources, energy storage systems, and macrogrid. The problem is formulated as a constrained stochastic programming problem. The Lyapunov optimization technique is then applied to derive an adaptive electricity scheduling algorithm by introducing the QoSE virtual queues and energy storage virtual queues. The proposed algorithm is an online algorithm. We derive several “hard” performance bounds for the proposed algorithm, and evaluate its performance with trace-driven simulations. The simulation results demonstrate the efficacy of the proposed electricity scheduling algorithm.