This paper discusses the presence of steady-state limit cycles in digitally controlled pulse-width modulation (PWM) converters, and suggests conditions on the control law and the quantization resolution for their elimination. It then introduces single-phase and multi-phase controlled digital dither as a means of increasing the effective resolution of digital PWM (DPWM) modules, allowing for the use of low resolution DPWM units in high regulation accuracy applications. Bounds on the number of bits of dither that can be used in a particular converter are derived. Finally, experimental results confirming the theoretical analysis are presented.

/pdf/quantization-resolution-and-limit-cycling-in-digitally-3i5f297hc0.pdf

Quantization resolution and limit cycling in digitally controlled PWM converters

This paper describes a complete digital PWM controller IC for high-frequency switching converters. Novel architecture and configurations of the key building blocks are A/D converter, compensator, and digital pulse-width modulator, are introduced to meet the requirements of tight output voltage regulation, high-speed dynamic response, and programmability without external passive components. The implementation techniques are experimentally verified on a prototype chip that takes less than 1 mm/sup 2/ of silicon area in a standard 0.5 /spl mu/ digital complementary metal oxide semiconductor (CMOS) process and operates at the switching frequency of 1 MHz.

/pdf/high-frequency-digital-pwm-controller-ic-for-dc-dc-2vpkurwra9.pdf

High-frequency digital PWM controller IC for DC-DC converters

This paper demonstrates a DC-DC converter application in which a multi-bit digital sigma-delta modulator pre-processes the duty-cycle value before application to the DPWM, increasing the effective resolution of the DPWM dramatically. In this method, the DPWM duty-cycle command is pre-processed by a multi-bit digital sigma-delta modulator, so that the DPWM quantization noise is shaped in frequency. As a result, the total quantization noise at the output of the DC-DC converter is reduced, and the effective resolution of the DPWM in the control loop is increased dramatically. A prototype converter was seen to perform with an effective DPWM resolution of at least 11 bits, with an actual DPWM resolution of less than 6 bits

High Resolution DPWM in a DC-DC Converter Application Using Digital Sigma-Delta Techniques

The conditions for limit-cycle oscillations in digitally controlled resonant converters are explored theoretically and are tested by simulation and experiment. The analytical analysis reveals that in a manner similar to digital pulsewidth modulation (PWM) control, limit cycles occur in such systems when the LSB of the control changes the output by a value that is larger than the analog-to-digital converter (ADC) resolution. However, in resonant converters, unlike the case of PWM, limit-cycle oscillations depend on the steady-state control input, since both the power stage gain and the resolution of the digitally generated drive frequency are not constant over the operating frequency range. Consequently, at high gains (close to resonance), the required frequency resolution may not be supported by the digital core. A time-domain behavioral simulation model, developed, and experimentally verified, allows the steady-state behavior of digitally controlled resonant converters to be analyzed, including the phenomenon of limit cycles as well as the closed-loop response. A cycle-by-cycle Powersim (PSIM) simulation model of a digitally controlled resonant converter, developed in this study, includes a digital core realization using C code block. This simulation model enables the exploration of the system in fine details. The proposed method of static analysis and dynamic modeling is experimentally verified on a series-resonant parallel-loaded converter operated in closed-current loop. The digital control algorithm was implemented on a TMS320F2808 DSP core. Very good agreement is found between the analytical derivations, simulations, and experimental results.

/pdf/digital-control-of-resonant-converters-resolution-effects-on-4dhuethukh.pdf

Digital Control of Resonant Converters: Resolution Effects on Limit Cycles

To integrate renewable energy into microgrids with a favorable inertia property, a virtual inertia control application is needed. Considering the inertia emulation capabilities, insufficient emulation of inertia power due to the lower and short-term power of storage systems could significantly cause system instability and failure. To enhance such capability, this paper applies a virtual inertia control topology to the superconducting magnetic energy storage (SMES) technology. The SMES-based virtual inertia control system is implemented in a microgrid with renewables to emulate sufficient inertia power and maintain good system frequency stability. The efficacy and control performance of the proposed control method are compared with those of the traditional virtual inertia control system. Simulation results show that the shortage of system inertia due to renewable penetration is properly compensated by the proposed control method, improving system frequency stability and maintaining the robustness of system operations.

https://www.mdpi.com/1996-1073/12/20/3902/pdf

Applying Virtual Inertia Control Topology to SMES System for Frequency Stability Improvement of Low-Inertia Microgrids Driven by High Renewables

One problem with microprocessor-based high-frequency PWM power converters is resolution limitation caused by the hardware timer. In this paper, a novel PWM technique-double PWM-is proposed. DPWM combines the advantages of low frequency modulating and high frequency switching in power conversion, and effectively increases the resolution in digital control. Theoretical analysis and features are verified on a boost-buck converter with an improved control scheme.

A novel PWM technique in digital control and its application to an improved DC/DC converter

A superconducting magnetic energy storage (SMES) unit consisting of a voltage source converter (VSC) and a chopper is used to damp the oscillation of a synchronous generator. The state feedforward decoupling method based on synchronous frame is used to improve the dynamic response of the VSC. The work modes of the chopper are discussed, and a small signal model of the chopper is established for the regulator design. Simulations and experimental results demonstrate the dynamic performance of the SMES unit.

http://ieeexplore.ieee.org/iel5/7692/21037/00975388.pdf

The power conversion system performance of a superconducting magnetic energy storage unit

CVCF inverters are usually applied in critical situations, whose quality of output waveform is one of the most important aspects in evaluating its performance. This paper analyses the feasibility of the three-phase inverters' output waveform control scheme based on internal model theory in rotating frame. One scheme is present which is the combination of instantaneous feedback control internal model restraining fundamental component disturbance and repetitive control internal model restraining harmonic component disturbance and asymmetrical disturbance. The experiments verify the scheme can work well. Fast response, highly accurate steady output and less distorted waveform is gained.

The control technique of three-phase voltage-source inverter output waveform based on internal model theory

A prototype, double-DSPs controlled power conditioning system (PCS) for super-conducting magnetic energy storage (SMES), is used for experimental study in dynamic simulation test of power system The function of SMES is to improve the dynamic performance of a single-machine infinite bus for power system The experimental results show that the transfer of SMES energy is done almost immediately depending on the system requirement, and SMES is able to restore system stability for short circuit The control algorithms for the SMES are simple and implementation has required very a little hardware

Enhancement of generator transient stability using superconducting magnetic energy storage (SMES) in dynamic simulation test of power system

This paper introduces a double-DSPs controlled power conditioning system (PCS) for superconducting magnetic energy storage (SMES), which is used for experimental study in dynamic simulation tests of power system. Considering of realization, voltage source converter (VSC) with a chopper is adopted in the experimental sample. The VSC in the PCS is a four-quadrant AC/DC converter and chopper is a two-quadrant DC/DC converter, they can perform the functions of charge to or discharge from the coil. In this paper, a kind of configuration of PCS and synchronous frame based control method for SMES has been presented for seeking a better control algorithm in improving stability and damping low-frequency-osciliation. The experimental results are verified to agree well with analysis.

Xuejuan Kong

Papers

A novel PWM technique in digital control and its application to an improved DC/DC converter

The power conversion system performance of a superconducting magnetic energy storage unit

The control technique of three-phase voltage-source inverter output waveform based on internal model theory

Enhancement of generator transient stability using superconducting magnetic energy storage (SMES) in dynamic simulation test of power system

Theoretical analysis and experimental results on super-conducting magnetic energy storage (SMES) in dynamic simulation test of power system