Search

Based on the comparisons of several inverter configurations in the aspects of efficiency, response, volume, current distortion, and price, in this article, we present a feasible three-phase four-wire (3Φ4W) grid-connected hybrid-frequency parallel inverter system (HbFPIS) with ripple compensation to achieve low current distortion and fast response. An HbFPIS consists of a low-frequency-high-power inverter (LFHPI) and a high-frequency-low-power inverter (HFLPI) connected in parallel. An LFHPI design results in higher power output with lower frequency (LF) switching devices, such as insulated gate bipolar transistors (IGBTs) being more cost-effective. An HFLPI design can reduce switching loss by lowering the power requirement of high-frequency (HF) switching devices while increasing dynamic response. With the direct digital control and ripple compensation, LF current ripples are attenuated by the HFLPI to a smaller level, remaining mainly HF current ripples and, thus, resulting in smaller filter size and weight. The design of an HbFPIS ensures that the system has high power output with cost-effective devices, fast response, and smaller output filters. Ripple attenuation, current tracking capability, and inverter stability are analyzed in the article. Low current distortion and fast current tracking performance are validated by the 300-kW simulated and the 10-kW experimental results of a 3Φ4W HbFPIS in grid-connected and active power filter modes.

The paper discusses a self tuning control algorithm for a multivariable plant applied to a grammage cross profile control of a paper machine. The plant model represents the steady-state couplings as well as the dynamics behaviour of the system. The control algorithm handles special situations including the case where the numper of measurments is not equal to the numper of actuators and the case where special actuators are locked. The whole identification algorithm with a specical filter and an estimation of the required measurment accuary for a succesful identification of the steady-state couplings will be discussed. The paper shows how to proof the stability of the control system including the cases of locked actuators and identification errors. Finally, the whole conrol system is verified by in house simulations and at a real plant. The obtained control results are discussed.

Finite control set predictive controllers perform a direct digital control of power converters without a modulation stage such as pulsewidth modulation. Opposed to the inherent positive traits such as high flexibility and enhanced bandwidth, an increase in harmonic content is usually reported. The concept of variable sampling time (VST) has been recently introduced as a means to alleviate the harmonic content. The nonuniform sampling approach can be seen as an extra degree of freedom that is conferred to the controller, keeping its model-based feature. This paper goes beyond the state-of-the-art of VST controllers, introducing a new scheme for the computation of the sampling time. The resulting VST controller is experimentally assessed for a two-level five-phase induction motor drive, where steady-state and dynamic performance tests confirm the interest of the proposal.

This paper presents bidirectional grid-connected modular multilevel converters (MMC) with direct digital control and division-summation processes to achieve power-injection and rectification functions. A direct digital control is developed to track current references, regulate dc-bus voltage and cell voltage, and balance the upper and lower dc-bus voltages. It can accommodate wide filter-inductance variation and take care of source voltage harmonics to achieve tight current tracking and low distortion output current. Based on the power-balance principle, the commands of arm currents can be determined directly. In this paper, the MMC configuration is introduced first, and then the control laws for current tracking and voltage regulation are derived in detail. Experimental and simulated results obtained from two 50 kW MMCs operated in power-injection and rectification modes have verified the analysis and discussion.

This is the first journal paper from the ASHRAE research project RP-1747 “Implementation of RP-1547 CO2-based Demand Controlled Ventilation for Multiple Zone HVAC Systems in Direct Digital Control ...

This paper presents a sinusoidal pulsewidth modulation (SPWM) based direct digital control with average-voltage model (AVM) and division–summation process for paralleled three-phase three-wire (3 φ 3W) grid-connected converters to reduce circulating currents. With the direct digital control, plant of each single-phase converter can be derived directly, and a controller is then designed to cover the variation effects of filter inductance and grid voltage. Based on SPWM and AVM over a switching cycle, each 3 φ 3W converter can be decomposed into three single-phase converters and each converter is controlled individually to track its sinusoidal reference current tightly, reducing circulating currents significantly. Equal current sharing is therefore also achieved. The control laws for achieving grid connection are derived in detail. In the design and implementation, the inductances corresponding to various inductor currents are measured offline and stored in the controller for scheduling loop gain cycle by cycle. Experimental and simulated results from a three-converter system confirm the analysis and discussion of the proposed control approaches.

Ripple-based constant on -time and off -time control techniques can achieve fast step-down and step-up transient performance along with an improved light-load efficiency. However, they suffer from varying switching frequency at the steady state and often require a phase-locked loop for frequency regulation. This paper proposes a constant on/off -time hybrid modulation technique in a digitally current-mode controlled synchronous buck converter. The proposed technique considers an event-based sampling mechanism using one sample per switching cycle, which makes it useful for high-frequency implementation. This requires a monoshot timer and a digital voltage controller $G_c(z)$ . The proposed technique can be configured to a constant on -time or off -time modulator with seamless transition because of sharing $G_c(z)$ ; thus, improved step-up/down transient performance can be retained. Furthermore, a discrete-time framework is proposed for fast-scale stability analysis, and the effects of finite sampling and practical parasitics are discussed. Discrete-time small-signal models are derived for the direct digital control design with enhanced stability and performance. A frequency adaptation method is discussed to customize the switching frequency in real time. A buck converter prototype is tested, and the usefulness of the proposed modulation technique is verified experimentally.

Soft magnetic powder cores with their high saturation flux density and low core loss are excellent alternatives for filter inductors in inverter-based applications. However, their nonlinear current-dependent inductance characteristics pose a challenge for control of grid-connected inverter with LCL filter. In this paper, the variable inductance conundrum is discussed and a modified direct digital control method based on a variable-structure inductance estimation model that takes into consideration wide nonlinear variation in both inverter- and grid-side inductances is proposed. The proposed method is shown to have better grid-voltage harmonic rejection and improved stability margins. However, investigation of stability which is conventionally based on nominal values of filter inductors cannot predict instabilities over the entire range of inductance variation. Hence, a parametric approach to conventional stability methods with a parameter space defined by variation in actual and estimated inductance is explored in this paper. The effect of line impedance on stability is also investigated with impedance-based stability criterion by considering line inductance as an additional dimension in the parameter space. A pattern in stability margins is observed due to inductance variation, with inductance at its minimum being most vulnerable to instability. Experimental results measured from a 5 kW single-phase grid-connected inverter with various LCL filters have verified the feasibility of the proposed control method. The experimental results also match the analytical results with reasonable accuracy.

This paper presents a current ripple compensation algorithm for paralleled three-phase three-wire (3P3W) hybrid frequency inverter systems (HbFIS) which are feasible for high power applications when using hybrid low- and high-speed switching devices. An HbFIS consists of two inverters connected in parallel, in which one is a low-frequency-high-power inverter (LFHPI), the other is a high-frequency-low-power inverter (HFLPI). Using direct digital control for HFLPI together with compensating the current ripple caused by LFHPI, the HbFIS can reduce the amplitude of its overall output current ripples. An HbFIS supplied by the shared dc voltage source is studied based on the proposed ripple compensation algorithm. Simulated results have verified the compensation algorithm with reduced THD at its output currents.

This work aimed to create a beam steering system based on a resonant micromirror with a control drive and sense modules implemented with low-voltage electronics and piezoelectric actuation and sensing. Solution's optimization goal was to create scalable architecture with minimal power consumption and reduce an overall MOEMS system size. We applied a direct digital control methodology for resonant piezoelectric elements by designing a level-translating electronics to directly interface actuator and sense elements with MAX1000 FPGA development board. This implementation merged control and measurement loops into VLSI design operating in the FPGA. The system behavior studied with 2D-scanning mirrors featuring an in-house piezoelectric MEMS-platform with AIN patterned actuation and sensing elements by measuring the generated laser reflection and pattern cross-correlating it with electrical signals. The developed MOEMS system provides the means for 2D optical scanning with a 1.8V logic level drive. Characterization results presented, study a mirror reflection pattern correlation with optical signals, and implemented control methods enabled frequency control with feedback in all operating conditions. The mirror feedback loop in the time domain provides reliable phase delay and oscillation period information. The calibrated look-up table post-processing module leverages this information and calculates the mirror's angular position at a given moment in time. The direct digital interface with a resonant piezoelectric mirror can deliver controllable beam steering in a single-supply, low-voltage, and high integration environment. The digital control loop allows for measurement and adjustment on a cycle-to-cycle basis, enabling further algorithm development for advanced functions like cross-sensor compensation, safety, and sensor fusion.

Centralized direct digital control systems have several drawbacks, for example, massive wiring requirements, difficult diagnosis, and difficult fault detection procedures. Most of these drawbacks may impose heavy costs on the maintenance of the control system. These disadvantages have given rise to the development of NCSs. In a network-based control system, sensors, actuators, controllers, human–machine interfaces, and other possible components of the system share their data over a network [1]. In this chapter, adaptive network sliding mode fuzzy logic control system approach is explained. Lyapunov stability analysis is used to analyze the stability of the studied controller.

This chapter provides the user with a basic understanding of the control architecture and technology necessary to implement a building automation system executing direct digital control. The sensor and actuator technology level has traditionally been hardwired, but that is changing too. Traditionally sensors and actuators only used electrical signals rather than networking technology. Industry standard signals like 4 to 20 milliamps that are wired to a controller are most common. The most common implementation of distributed systems is to have both a zone level controller, tailored to simple applications like the variable air volume (VAV) terminal unit, as well as an equipment level, or general purpose, controller for larger pieces of equipment like the VAV air handler. The enterprise supervisor was selected for discussion first under this building automations systems technology section because it is responsible for overall building coordination. In the past, approaches have been taken from custom computer based systems to dedicated personal computers, as well as to develop custom microprocessor-based equipment.

Optimize performance of energy management and building systems at your facility with this state-of-the-art user’s guide.

This chapter provides enough background to appreciate the basis for the rational design and implementation of bioprocess monitoring and control systems. It introduces those characteristics of living organisms germane to monitoring/control and to basic concepts, strategies, and hardware of monitoring/control systems. The emphasis is confined to fermentation processes and to automated, digital control systems employing some type of digital computer. The chapter examines the differences between direct digital control (DDC) and distributed control. One can get a sense of DDC by thinking about supermarket checkout lines. The chapter reviews basic control concepts and control algorithms. The bases of most models used for process control are the fundamental laws of conservation of mass and energy.

This paper presents modified control laws for accommodating magnetizing and demagnetizing inductances in an LC single-phase converter with division-summation (D-Σ) processes to improve current tracking performance. Conventionally, the magnetizing and demagnetizing inductances are considered identical over a switching cycle. Therefore, only is nominal inductance from the manufacturer’s datasheet taken into account in deriving the control laws for current tracking in converters. However, in this work, it has shown that with a switching frequency of 100 kHz, powder core inductor obtains varying inductance. The range of variation between the inductances of magnetization and demagnetization depends nonlinearly on many aspects. However, in this paper a simple model of inductance estimation is proposed. It has shown that with the accommodation of significant inductance difference over a switching cycle, it is possible to improve the tracking performance of the current control system.

Typical variable air volume (VAV) terminals spend the majority of time at their minimum airflow setpoints. These are often higher than the minimum ventilation requirements defined by code, resulting in excess energy use and a risk of over-cooling the spaces. We developed and tested a time-averaged ventilation (TAV) control strategy in an institutional building on the UC Berkeley campus to address this issue. Whenever a zone does not require cooling, TAV alternates the VAV damper between partially open and fully closed so that the average airflow matches a predefined ventilation setpoint. Compared to the existing, base case scenario using single-max VAV logic, this strategy reduced the mean zone airflow fraction from 0.44 to 0.27 during the intervention period. The corresponding reductions in average heating, cooling, and fan power were 41%, 23%, and 15% respectively. In addition to being programmed directly in a native control system, TAV may be applied via sMAP as a low-cost retrofit strategy in any building that has a BACnet network and direct digital control (DDC) to each VAV terminal.

The article presents a solution ensuring the automated process control system (APCS) of underwater oil and gas production to function in a heterogeneous information environment. The authors consider the necessity to apply hazard identification and risk assessment tools to further control of the process hazards. The modules of expert and simulation model design may serve as such tools. Furthermore, the review of APCS control schemes is given, and a comprehensive scheme of APCS block integration and the composition of the unified APCS software package are proposed. The most suitable scheme for controlling the heterogeneous information environment is the scheme of direct digital control. However, it has a distinct disadvantage which appears in case of a computer failure. One way to avoid this situation is to arrange a computer backup or replace one computer with a system of machines (a cluster). The unified cluster uses the XML-format for the data exchange. This allows for cluster functioning in a heterogeneous information environment. A centralised data repository consisting of a database and file storage is used for storing the incoming data #COMESYSO1120.

Direct Digital Controls (DDCs) are components of building automation systems that have a network interface. In this paper we describe how to create a honeypot for such a device. We have replicated the individual services available on the device with extensive logging mechanisms. To do this, we dealt with both protocol-specific as well as operating system-specific properties. We then conduct an experiment in which the honeypots are made publicly accessible on the Internet in order to check whether existing vulnerabilities are already being exploited in the examined devices. While analysing the data we didn’t find any specific attacks for this device. Finally, we suggest possible improvements for future experiments.

The requirements to modeling dynamic processes in automated systems and educational processes in universities are considered. It is shown that taking into account the dynamics and stochastic processes allows creating adequate models of control processes for the systems of a hierarchical level of direct digital control and higher levels. The problem of creating virtual laboratory stands is relevant both for full-time training, as well as for distance learning. The effectiveness of modeling virtual laboratory processes depends significantly on the selection of tools. In view of systemically related limitations, the selection of a mathematical apparatus is justified as a combination of two requirements: to describe the dynamic properties of an object, the convolution equation should be used; to analyze the properties of signals in dynamical systems, one should apply the theory of random processes.

This paper presents direct digital controlled modular multilevel converters (MMCs) with cell-distributed controllers and hot-swap features to facilitate cell-module number extension and achieve fault-tolerance mechanism. Design of the cell-distributed control system is to facilitate an extension of cell-module number, increase MMC reliability, and simplify the complexity of fault-tolerance mechanism. The direct digital control can take into account wide filter-inductance variation and source voltage harmonics, and achieve a seamless hot-swap feature with low distortion on output currents and low interaction with grid voltages. In this paper, the cell-distributed control system is introduced first, and then the fault-tolerance mechanism for either cell-module unplugging or plugging-in is presented in detail. Experimental and simulated results obtained from an MMC operated in power-injection and with a hot-swap feature have verified the analysis and discussion.

In a dc-microgrid, ac is harmonized with dc, and therefore, a multi-function converter is required to transfer power between ac and dc grids. This paper presents design and implementation of converters with multiple functions that include grid-connection (GC) mode, uninterruptible power supply (UPS) mode, and mode transition. Control laws for the GC and UPS modes based on a direct digital control with division-summation (D- $\Sigma$ ) processes are presented in detail. During operation, mode transition between the two modes is discussed. Experimental and simulated results from two 350 kVA multi-function converters with circulating power test are used to verify the analyses, designs and discussions.

This paper presents verification and implementation of two three-phase four-wire $(3\Phi 4\mathrm{W})$ 350 kVA multi-function converters. In the paper, direct digital control laws for achieving multiple functions, including power injection, rectification, active power filtering (APF), and three-phase power balancing, are presented and derived in detail. Because of the limitations of test-equipment and components, this study conducts circulating power test. Experimental and simulated results from two 350 kVA multifunction converters are used to verify the analyses, designs and discussions.

This paper presents the design and implementation of an improved ripple-compensation direct digital controlled three-phase four-wire (3Φ4W) grid-connected hybrid-frequency inverter system (HbFIS). The HbFIS consists of a low-frequency-high-power inverter (LFHPI) and a high-frequency-low-power inverter (HFLPI) in parallel. With the improved ripple-compensation direct digital control, lower frequency current ripples are attenuated to a smaller level without suffering from repetitive ripple estimation and direct ripple tracking. This raises the frequency of output current ripples, resulting in smaller filter size and weight. LFHPI design allows the system to have higher power output with lower-frequency switching devices like IGBTs, which are more cost friendly in industrial applications. HFLPI design can reduce equivalent switching loss and power rating of high frequency switching devices. Both the power and switching frequency design arrangements ensure the system to have higher power output with lower cost devices, higher dynamic performance and smaller output filters. The hybrid frequency LC filter design is based on current ripple cancellation and equivalent grid impedance. The ripple compensation capability and the better performance of HbFIS with the compensation are validated by simulated and experimental results of a 10 kW 3Φ4W grid-connected HbFIS.

In this paper, a decoupled direct digital control with division-summation (D-Σ) process and average common-mode voltage model for LCL three-phase three-wire (3Φ3W) converters is proposed. Based on the average voltage within one switching cycle of the converter operation, direct digital control laws are decoupled by selecting a proper form for their duty ratios. Thus, the decoupled direct digital control laws can be derived and conducted phase by phase without coupling terms in a natural frame, which results in a complete single-phase control even under unbalanced or distorted grid-voltage conditions. Additionally, the control can take into account filter inductance variations with currents. System model and equations are derived to investigate the current tracking capability and stability of the system. Simulated and experimental results of a 5 kW 3Φ3W LCL grid-connected converter have verified the validity of the decoupled control.

This system deals with the design and development of a remote temperature control system along with the real time data logging facility. The system utilizes thermistor to sense the temperature of the ambiance in a process control application and implements a direct digital control method for controlling the temperature. In addition the recorded temperature values are stored with respect to time this in returns helps us to understand the temperature change in the environment and we can implement or take action accordingly. The decision making device is cub bled with other peripherals like LCD, memory, real time clock and keyboard. The system utilizes the RS232 protocol for communication. The system and application code is designed in Keil 5.0 and .NET frame work using C#. This system utilizes an error free communication and a cost efficient system for industrialize the system is so friendly as it utilizes ISP technology to burn the system code that one can easily manipulate it according to the user needs hence it may be considered as the user friendly device for small scale industry.

As programmable logic controllers (PLC) technology, programming languages and communication capabilities have advanced, PLCs offer many control devices to be attached directly to the PLC. For this reason PLC education became an important issue in many interdisciplinary engineering departments of the Universities. In this paper an automation set for the laboratory of PLC is developed which can be operated in various ways by programming a PLC as desired. The designed set also enables the students to understand the operation principle of an elevator. This developed educational laboratory set can be used as a practice for sensors and actuators, control systems and industrial automation courses. The laboratory tool also provides a method to improve learning outcomes, skills and the real-time experiences in engineering education such as electrical, electronics, mechatronics and control engineering.