Fixed-point Microcontroller Research Articles

A Novel Per Unit (P.U.) Integer Format Applied to the Control of a Grid-Tied Solar PV Inverter

In advanced power electronic applications such as a grid-tied solar photovoltaic (PV) inverter, control algorithms demand high-level computational support, typically provided by an expensive 32-bit digital-signal-processor (DSP) or microcontroller. In cost-sensitive markets, this may prove to be a significant component of the overall cost of the system. Using a low-cost 16-bit microcontroller is, therefore, highly desirable. However, it poses certain challenges such as fewer bits for the mathematical and logical operations, computations in the fixed-point environment, and lower speeds. In this article, a novel per-unit integer system is proposed towards using a low-cost microcontroller for complex computations, which overcomes the above limitations while maintaining the core functionality in a fixed-point environment. An improved hybrid phase locked loop implementation scheme, that uses the p.u. integer system has also been presented, which significantly reduces the execution time for grid-synchronization. To demonstrate the performance of the proposed concepts, control of a grid-tied PV inverter has been implemented on a low-cost fixed-point microcontroller (dsPIC33FJ16GS402) as well as on an advanced DSP microcontroller (TMS320F28069). Timing analysis and experimental results for a 1 kW grid-tied PV system confirm that the performance of the system using a low-cost microcontroller is comparable to that of the advanced microcontroller.

Novel deadbeat power control strategy for grid connected systems

This paper introduces a novel approach for power control of three phase voltage source inverter (VSI) in grid connected distribution generation system. In this approach, the control of active and reactive power is based on deadbeat control strategy. First, the difference between the reference and actual currents are introduced in different approach. Then current to power substitutions are carried out to obtain direct relationship between the required inverter voltage and instantaneous power errors. There is no need for coordinate transformation or PLL, where the required inverter voltage vector calculations carried out in α–β stationary reference frame. The proposed technique introduces two cross coupling components in the control function. Including these two components, the controller can achieve nearly zero steady-state tracking error of the controlled variables. To obtain fixed switching frequency operations, space vector modulation (SVM) is used to synthesize the required inverter voltage vector and to generate the switching pulses for the VSI. The proposed strategy has the simplicity of the direct power control (DPC) technique and doesn’t require any current control loops. The proposed strategy is experimentally implemented using fixed-point microcontroller. Simulation and experimental results are presented to confirm the superiority of the proposed strategy.

Isolated digitally controlled voltage mode forward converter with excellent audio rejection

This paper presents the implementation of feedforward in digital domain to meet the audio susceptibility as per MIL STD 461C for voltage mode digitally controlled DC-DC converters. The feed-forward is accomplished through the estimation of duty ratio based on the input voltage at every switching cycle. The prototype converter developed is having galvanic isolation in the forward and feedback path and is based on single ended forward topology. An optimised discrete controller is provided in the feedback path to achieve desired dynamic performance. The feed forward scheme was implemented along with discrete feedback controller using a 16-bit fixed point microcontroller. The design of optimised discrete compensator and the audio rejection of a converter with such a feedback controller are presented. The simulation model of the converter with proposed digital feed forward/feedback controller using SIMULINK and its results against input disturbances are also presented. Experimental results are presented in this paper to validate the theoretical analysis.

Natural Commutation Technique to Reduce Voltage Surges and Switching Losses in a Cycloconverter-Type High-Frequency Link Inverter

This paper presents an isolated cycloconverter-type high-frequency (HF) link inverter that consists of three arms of bidirectional switches at the transformer secondary. This topology has the advantages of light weight and reduced switch count, when compared to other types of HF link inverters. However, like all HF link inverter topologies, this topology suffers from a high-voltage surge problem and power device switching loss. In order to overcome these problems, the natural commutation method that enables soft-switching operation is applied. To verify the viability of the scheme, a low-power laboratory prototype based on the Siemens 80C167 fixed-point microcontroller is constructed. In addition, the simulation of the inverter is also carried out. The prototype inverter is able to supply output voltage at 120 V’rms, with a total harmonics distortion of less than 1%. The total power conversion efficiency reaches 86% when the output power is over 300 W.

Comparison of iterative and fuzzy logic based Maximum Power Point Tracking (MPPT) algorithms

Voltage – current characteristics of photovoltaic (PV) generators rely on many auxiliary conditions as irradiance, temperature or load profile. Independently on the type of installation (stand-alone, grid connected, hybrid) a solar panel generation system should always be operated at it's maximum electrical power point under defined conditions. Many algorithms have been proposed as maximum power point seeking techniques. A comparison of two methods is described considering an iterative approach and a fuzzy logic controller. Both dynamical properties and tracking accuracy are analyzed based on laboratory experiments and measurements led on an exemplary installation. In addition a misinterpretation avoidance apparatus is proposed for flat-topped power characteristics under partial shading or low irradiance. Power electronic system is described as well as the control system prototype based on a fixed-point microcontroller. Measurement results are presented and conclusions are given.

On the Use of Soft Computing Techniques for Helicopter Control in Environment Protection Mission Scenarios

Abstract This paper presents some results related to fuzzy control from the research on autonomous helicopter control conducted in the framework of the COMETS project. Soft-computing techniques have been applied to improve performance of the Multi-Loop PID model based helicopter controller without increasing significantly the computational requirements. Thus, the resulting control system can be implemented by using a simple on-board fixed point microcontroller. Moreover, fuzzy logic has been also used for testing the helicopter model by inducing nonlinear behaviors (including multiple stable and unstable equilibriums and limit cycles). Experimental results with MARVIN helicopter illustrate the methods (on-line videos are available).

A new pulse-width modulation (PWM) scheme for modular structured multilevel voltage source inverter

This work proposes a new switching scheme for a particular multilevel topology, known as the modular structured multilevel inverter (MSMI). The proposed scheme is based on symmetric regular sampled unipolar PWM, with multiple modulating waveforms and a single carrier. Mathematical equations that define the PWM switching instants are derived. These equations are suitable for digital implementation. An experimental five-level MSMI test-rig is built to implement the proposed algorithm. The derived equations are implemented by a low-cost fixed-point microcontroller. Several tests to quantify the performance of the inverter under the proposed modulation scheme are carried out.

An advanced low-cost sensorless induction motor drive

An advanced solution for low-cost implementation of the sensorless vector control of an induction motor is presented in this paper. The proposed system is based on a new set of variables for the induction motor model. The system works using vectors coordinates in a stationary /spl alpha/-/spl beta/ frame of references. A phase-locked loop was used to control the angle between the flux vector and the stator current vector. The induction motor model variables and the rotor velocity are calculated from simple equations based on the steady state relationships for the active and reactive powers. A current controller for the current-regulated pulsewidth-modulation inverter based on the simplified load model is presented. The proposed current controller is based on the back-electromotive-force calculation. The developed sensorless system was investigated both in simulations and experiments. The overall system was implemented using a simple and cheap fixed-point microcontroller.

Implementation of Fuzzy Systems using Micro Processors/Controllers

This paper presents an algorithm for implementation of fuzzy systems using inexpensive general-purpose hardware. The two major difficulties encountered in implementing fuzzy systems using 8/16 bit micro processors/controllers are: (i) handling floating point arithmetic and (ii) determination of membership values. Existing membership functions (mfs) do not satisfy, simultaneously, ease in optimization and low-end hardware implementation. Mfs, recently proposed by us [1], as negative powers of 2 satisfy these two contradicting requirements. The complete algorithm for hardware implementation of the best offline design solution is described. The worst-case execution time is computed as a function of the number of inputs (m) and the number of rules (c). The performance, applicability and limitations of the proposed algorithm are illustrated using a benchmark example. Optimized fuzzy model is coded and implemented using Intel 8XC196KC 16 bit fixed point microcontroller, and the results obtained are included.