Conventional Multiloop Control Research Articles

Multiloop Control With Two Duty-Ratio Feedforward Current Loops via Sensing Series-Capacitor Current for Voltage Doubler PFC Converter

In this paper, the voltage doubler PFC converter with two boost inductors and one series-capacitor is studied. Only when both symmetrical duty ratios are larger than 0.5, the conventional multiloop control with one inner current loop and one voltage loop can be directly applied to the voltage doubler PFC converter due to its topology asymmetry. To remove this duty-ratio limit, the multiloop control with two duty-ratio feedforward current loops is proposed where the series-capacitor current is sensed to reconstruct two inductor currents. It follows that the number of sensor in the proposed control is three equal to the number of sensor in the conventional multiloop control. The proposed method is implemented in a Field Programmable Gate Array (FPGA) chip. The provided simulation and experimental results validate the effectiveness.

State Feedback Reshaping Control of Voltage Source Converter

Admittance reshaping is a widely used strategy to address the converters low-frequency stability issues in weak grid, caused by the PLL and its interaction with the dc and ac voltage controls. However, the asymmetric control of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$d$</tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$q$</tex-math></inline-formula> -axis current references and the coupling between the converter ac and dc sides restricts the damping capability of single-input single-output feedbacks. This phenomenon gets even worse in the presence of nearby converters. This article extends the concept of admittance reshaping to multi-input multi-output control. A full state feedback is added to the current reference of the converter to increase the damping of the conventional multiloop control. A systematic offline algorithm is delegated to design the feedback, and a scalar coefficient is employed to activate/deactivate online the reshaping feedback, making the proposed solution user-friendly. The proposed control is analyzed both in time and frequency domains and tested in parallel-operation with other converters, and shows higher damping capability than conventional solutions and good robustness with respect to grid impedance and operating point variations. Experimental tests under ac and dc disturbances are conducted both in lab setup and in hardware-in-the-loop.

Optimization and model-based control of sustainable ethyl-methyl carbonate and diethyl carbonate synthesis through reactive distillation

As excellent solvents of lithum-ion electrolyte, ethyl-methyl carbonate (EMC) and diethyl carbonate (DEC) are synthesized through transesterification of dimethly carbonate (DMC) and ethanol. Process intensification, optimization and the corresponding control scheme of the synthesized process are essential when sustainability is becoming a necessity. In the present work, the intensified flowsheet for EMC and DEC production process was firstly proposed and optimized with conventional reactive distillation (RD) and reactive dividing wall column (RDWC), respectively. Compared with RD process, RDWC could achieve 25.3% and 8.2% total annualized cost reduction for EMC and DEC production process, respectively. And carbon dioxide emission could be decreased by 29.4% and 11.7% by further integrating RD and separation column into RDWC arrangement for DEC and EMC production. Then multi-loop PI control schemes were developed as benchmark and linear model predictive controller was designed to handle the persistent feed disturbance. The superiorities of model-based controllers for the strongly interactive and coupled system are demonstrated by the dynamic response comparisons in terms of settling time, overshoot and integral of squared error (ISE), especially for the controlled variables with poor control performance under conventional multi-loop PI control structure. To summarize, the comprehensive control performance index-ISE with MPC is reduced by 55.9%–99.1%, as compared to those under PI control strategy.

Design and Implementation of Four-Switch Current Sensorless Control for Three-Phase PFC Converter

Four-switch current sensorless control for three-phase four-switch converter with power factor correction (PFC) function is presented in this letter. In comparison with conventional multiloop control methods, the proposed control strategy requires sensing of two line voltages and two capacitor voltages only to achieve PFC function. As there is no sensing current, the proposed sensorless control scheme reduces the cost and complexity of design. The performance of the proposed control is validated by its implementation in digital signal processing (DSP) TMS320F28335, and the result shows that the proposed scheme is able to provide comparable PFC performance without sensing current.

Multi-loop control of UPS inverter with a plug-in odd-harmonic repetitive controller

This paper proposes an improved multi-loop control scheme for the single-phase uninterruptible power supply (UPS) inverter by using a plug-in odd-harmonic repetitive controller to regulate the output voltage. In the suggested control method, the output voltage and the filter capacitor current are used as the outer and inner loop feedback signals, respectively and the instantaneous value of the reference voltage feedforwarded to the output of the controller. Instead of conventional linear (proportional-integral/-resonant) and conventional repetitive controllers, a plug-in odd-harmonic repetitive controller is employed in the outer loop to regulate the output voltage, which occupies less memory space and offers faster tracking performance compared to the conventional one. Also, a simple proportional controller is used in the inner loop for active damping of possible resonances and improving the transient performance. The feedforward of the converter reference voltage enhances the robust performance of the system and simplifies the system modelling and the controller design. A step-by-step design procedure is presented for the proposed controller, which guarantees stability of the system under worst-case scenarios. Simulation and experimental results validate the excellent steady-state and transient performance of the proposed control scheme and provide the exact comparison of the proposed method with the conventional multi-loop control method.

Multiloop Interleaved Control for Three-Level Switch-Mode Rectifier in AC/DC Applications

In this paper, multiloop interleaved control (MIC) is proposed, and it is combined with conventional multiloop control and the interleaved pulsewidth modulation scheme. The average behavior of the interleaved three-level switch-mode rectifier (SMR) behaves similar to the conventional boost-type SMR even though two capacitor voltages are imbalanced. It implies that conventional multiloop control can be applied to the interleaved three-level SMRs to achieve the desired power factor correction function. The proposed MIC is digitally implemented and verified in a field-programmable-gate-array-based system. The provided results show that MIC stably works and the capacitor voltages are eventually balanced during the system operations.

Bidirectional Current Sensorless Control for the Full-Bridge AC/DC Converter With Considering Both Inductor Resistance and Conduction Voltages

The full-bridge converter is often connected between the ac grid and the dc bus. In the conventional multiloop control, the inner current control loop shapes the ac-side current waveform, and the outer voltage control loop regulates the dc-bus voltage. In this paper, the single-loop bidirectional current sensorless control (BCSC) for the full-bridge ac/dc converter with considering both the inductor resistance and conduction voltage is first proposed. The average-value behavior of the full-bridge ac/dc converter is analyzed and it is simplified to an equivalent single-switch model. Based on this developed equivalent model, BCSC is designed and implemented in the FPGA-based system. There is only voltage control loop in the proposed BCSC (i.e., no current control loop), but BCSC is able to regulate the dc-bus voltage and shape the ac-side current. The provided results in both the rectifier operation and the inverter operation demonstrate the effectiveness of the proposed BCSC.

Modeling and Small-Signal Analysis of a Switch-Mode Rectifier With Single-Loop Current Sensorless Control

The conventional multiloop control with one inner current loop and one outer voltage loop is often applied to a single-phase boost-type switch-mode rectifier where the output of the voltage loop is a current amplitude signal. In the duty phase control (DPC) proposed recently, the output of the voltage loop is a phase signal used to generate the switching signals without current loop and sensing current. To improve the clamped current waveform of DPC, a single-loop current sensorless control (SLCSC) with some nominal parameters had also been proposed to compensate for the voltage drops across the switch, diodes, and inductor resistance. In this paper, the effect of the differences between nominal and real circuit parameters on the input current waveforms of SLCSC are addressed in detail. The results are helpful in the design of SLCSC. From the simulated and experimental results, we can find that the output voltage is well regulated by the only voltage loop and the input current harmonics are significantly improved.

Single-Loop Current Sensorless Control for Single-Phase Boost-Type SMR

In this paper, the first single-loop current sensorless control (SLCSC) in continuous current mode (CCM) for single-phase boost-type switching-mode rectifiers (SMRs) is developed and digitally implemented in a DSP-based system. Compared to the conventional multiloop control with one inner current loop and one outer voltage loop, there is only one voltage loop in the proposed SLCSC, where the voltage loop's output is used to shift the nominal duty ratio pattern generated from the sensed input and output voltages. Because of no current loop, the efforts of sampling and tracking inductor current can be saved. It implies that the proposed SLCSC is simple and very adaptable to the implementation with mixed-signal ICs. First, the effects of shifting nominal duty ratio pattern on the input current waveform are analyzed and modeled by considering the inductor resistance and conduction voltages. The result of analysis shows that the pure sinusoidal current can be inherently generated by the nominal duty ratio pattern where the current amplitude is roughly proportional to the controllable phase of nominal duty ratio pattern. Then, a voltage controller is included to regulate the DC output voltage by tuning this controllable phase. Finally, some simulated and experimental results have been given to demonstrate the performance of the proposed SLCSC.

Duty Phase Control for Single-Phase Boost-Type SMR

In this paper, a novel duty phase control (DPC) for single-phase boost-type switching-mode-rectifier (SMR) is developed and digitally implemented in DSP-based system. Compared to the conventional multiloop control structure with inner current loop and outer voltage loop, it is noted that there is only one voltage loop tuning the phase of predefined duty pattern (i.e. duty phase) in the proposed DPC. Due to no current loop, sampling inductor current and tracking current are unnecessary when SMRs are operated to shape the current waveform and regulate the output voltage. It implies that the single-loop DPC is simple and adaptable to the implementation with digital and analog integrated circuits. In this paper, first, the effect of the duty phase on the input current is analyzed and modeled. It shows that the sinusoidal current waveform can be naturally generated by the predefined duty pattern and the current amplitude is roughly proportional to the controllable duty phase. Then, a voltage controller is designed to regulate the dc output voltage by tuning this duty phase. Finally, some simulated and experimental results have been given to illustrate the performances of the proposed DPC.

A Practical Multiloop Controller Design for Temperature Control of a TV Glass Furnace

This brief presents a practical application of the conventional multiloop control method for the temperature control of a television (TV) glass furnace. To control the temperatures of the TV glass furnace, two inputs and three outputs are selected as major process variables. With the process experimental data, a multi-input multi-output model is established as a combination of input-output transfer functions in the form of the first-order-plus-dead-time system. Based on the plant models, a multiloop control, which is a combination of cascade and single loops, is used, and stability and robustness are examined with respect to major uncertain model parameters. Practical implementation in a distributed control system showed satisfactory results of the proposed control algorithm for the 150-ton/day-production furnace.

MODELING AND CONTROL OF A TEMPERATURE-BASED HIGH-PURITY DISTILLATION COLUMN*

Industrial distillation columns typically lack adequate on-line instrumentation required for implementing high performance, model-based control systems which depend on composition measurements. The typical practice is to base product quality control schemes instead on tray temperature measurements since these are usually available on-line. While this strategy has been applied with success on a wide variety of distillation columns, some special considerations may be necessary in dealing with high-purity columns. This paper presents results which address some of the key issues involved with the use of tray temperature measurements as surrogates for composition measurements, and with the development of appropriate input/output models for multi variable control of high-purity columns. For the purpose of illustration, we investigate the performance of several model predictive control schemes based on a linear model, a “high frequency” model, and a nonlinear temperature transformation, along with that of conventional multiloop PID control. Closed-loop control performances are compared for setpoint changes as well as for changes in unmeasurable load disturbances.

Temperature Profile Control of a Rotary Dryer with Multivariable Model Predictive Control

This paper presents a control system for a rotary dryer having to cope with large load disturbances. In order to maintain the product moisture content and degree of oxidation at specified values. it is necessary to control the temperature profile of the material in the dryer. However, instead of controlling the entire temperature profile. the developed system requires only two measurements; One of these is the material temperature at the exit of the dryer. and the other is the temperature at which the drying mechanism changes from constant rate of drying to falling rate of drying, which is termed the critical point. A “soft sensor” was developed which can infer the position of the critical point from the material temperatures measured at three different points along the dryer. The developed 2x2 multivariable model predictive controller (MPC) when integrated with the “soft sensor” showed superior performance when compared to a conventional multi-loop PID control system

Improved process conditioning using internal control loops

Abstract Singular-value analysis is employed in the development of processes displaying good controllability properties. Excess manipulatable variables may be used in the form of internal control loops which enhance the process conditioning, giving improved performance in the primary control loops of a conventional multi-loop control system.