Підвищення точності формування вихідної напруги перетворювача зі змінними параметрами навантаження

У статті на основі теорії інваріантності розглянуто прийоми підвищення точності роботи системи з перетворювачем за умови зміни параметрів навантаження. На основі запропонованої функціональної схеми двоканального керування наведено формули, які дозволяють визначати структурні зв’язки та внутрішні впливи на параметри складових системи керування для зменшення впливу збурень, що з’являються як за рахунок зміни параметрів навантаження, так і за рахунок зміни значення напруги живлення. Реалізація наведених пропозицій дає більш точне формування вихідної напруги. Наведена функціональна схема забезпечує реалізацію регулювання та стабілізацію амплітуди. За рахунок зміни періоду роботи генератора пилкоподібної напруги, що визначається частотою генератора, керованого напругою, і залежить від вихідної частоти інвертору, яка змінюється в залежності від параметрів навантаження під час роботи перетворювача, точність стабілізації амплітуди вихідної напруги підвищується.In the article on the basis of the theory of invariance the increase of accuracy of work of system with the converter for nuclear magnetic logging under condition of change of parameters of loading is considered. Based on the proposed functional scheme of two-channel control, formulas are given to determine the structural relationships and internal influences on the parameters of the control system components to reduce the impact of disturbances that occur both by changing load parameters and by changing the supply voltage. To maintain the required value of the carrier voltage amplitude, it is necessary to increase the reference voltage or decrease the amplitude of the sawtooth voltage, which is equivalent to increasing the gain of the feedback circuit. In this case, if you increase the gain of the feedback circuit, you must ensure that the stability of the system is maintained. The implementation of these proposals gives a more accurate formation of the bypass probing signal. The given functional scheme provides realization of regulation and stabilization of amplitude. The paper considers various options for reducing the effect of power supply perturbation on the output parameters of the converter. By changing the period of operation of the sawtooth voltage generator, which is determined by the frequency of the voltage-controlled generator and depends on the output frequency of the inverter, which varies depending on the parameters and properties of the rock during logging, the accuracy of stabilizing the amplitude of the probe signal increases. In the proposed two-channel control system, the first channel provides regulation and stabilization of the amplitude of the output voltage in accordance with the reference voltage. The second channel provides a change in the frequency of the sawtooth voltage generator by determining the period of the voltage-controlled generator from the phase detector, which determines the deviation of the real frequency from the frequency of the reference generator. The application of the above techniques allows to build circuit implementations of the system with transducers for nuclear magnetic logging, which meet the requirements for the accuracy of the formation of the bypass probing signal.В статье на основе теории инвариантности рассмотрены приемы повышения точности работы системы с преобразователем при изменении параметров нагрузки. На основе предложенной функциональной схемы двухканального управления приведены формулы, позволяющие определять структурные связи и внутренние воздействия на параметры составляющих системы управления для уменьшения воздействия возмущений, возникающих как за счет изменения параметров нагрузки, так и за счет изменения значения напряжения питания. Реализация приведенных предложений дает более точное формирование выходного напряжения. Приведенная функциональная схема обеспечивает реализацию регулирования и стабилизации амплитуды. За счет изменения периода работы генератора пилообразного напряжения, которое определяется частотой генератора, управляемого напряжением, и зависит от выходной частоты инвертора, изменяющейся в зависимости от параметров нагрузки во время работы преобразователя, точность стабилизации амплитуды выходного напряжения повышается

IMPROVEMENTS IN INVERTER MODELING AND CONTROL

In this dissertation, the generalized averaging method models for inverters, reactive power control methods for photovoltaic inverters, and a noise immunity improvement for hybrid position observers for brushless dc motor drives are studied. Models of inverters and other converters based on averaging have been widely used in numerous simulation applications. Generalized averaging can be applied to model both average and switching behavior of converters while retaining the faster run times associated with average-value models. Herein, generalized average models for single- and three-phase pulse width modulation inverters are proposed. The modulation signal for the proposed model could be either a sinusoidal waveform without high order harmonics or a sinusoidal waveform with third-harmonic injection. And this generalized average models also can apply for modeling three-phase pulse width modulation inverters with varying modulation signal frequency in the reference frame. These models are based on a quasi-Fourier series representation of the switching functions that includes fundamental and switching frequency components as well as sideband components of the switching frequency. The proposed models are demonstrated both in simulation and experimentally and are found to accurately portray both the fundamental and the switching behavior of the inverter. In particular, the use of sideband components allows accurate representation of the variation in switching ripple magnitude that occurs in the steady state. The generalized average models are found to have simulation run times that are significantly faster than those associated with detailed models. Therefore, the proposed generalized average models are suitable for simulation applications in which both accuracy (including the switching behavior) and fast run times are required (e.g., long simulation times, systems with multiple converters, and repeated simulations). Variations in the output power of intermittent renewable sources can cause significant fluctuations of distribution system voltage magnitudes. Reactive power control methods that employ the reactive power capability of photovoltaic three-phase inverters to mitigate these fluctuations are proposed. These control methods cause the three-phase inverters to substitute reactive output power for real output power when fluctuations in the solar power are experienced, allowing the fluctuations to be controlled. Performance metrics for assessing the ability of these controllers to perform this mitigation are defined. The controllers are examined using the IEEE 123-bus feeder distribution system, and it is found that the controllers can effectively mitigate voltage magnitude fluctuations and that the appropriate choice of controller depends on the performance metrics of interest. Finally, a noise immunity improvement for hybrid position observers for brushless dc motor drives is proposed. A finite state machine is used to detect Hall-effect sensor transitions to determine if these transitions are true transitions or the result of momentary glitches. This filter causes a delay in the detection of the Hall-effect sensors that is compensated in the proposed observer. The proposed observer is compared in simulations with the original hybrid position observer under both non-noisy and noisy conditions for both constant and variable speed operation, and it has good performance even under high noise and variable speed conditions

Formation of the Spectral Composition of the Output Voltage of Converters for Nuclear Magnetic Resonance

In this paper, we consider the construction of an asynchronous control system for semiconductor converters for nuclear magnetic resonance. The relevance of research in this direction, main problems that arise during the construction of these systems are shown. Derived the mathematical model of the inverter, on the basis of which a control system with asynchronous pulse-width modulation is constructed. Proposed an equivalent converter circuit with a constant structure, constant parameters, and an equivalent EMF generator. Established correspondence between the equivalent circuit of the converter and its mathematical model in the form of differential equations. On the basis of mathematical equations, a structural diagram of the converter with a control system was developed and the principle of operation of the device was described according to it. To develop an algorithm for the control system, the dependence of the frequency change relative to the resonant frequency on the phase shift between the current through the filter and the voltage on the antenna circuit is determined. For which the model was built in Simulink and the corresponding simulation was carried out. Numerical dependences of reference signal frequency change and phase shift were obtained. The increase in efficiency of device for nuclear magnetic resonance is considered due to the use of multilevel inverters with tuning the frequency of operation to the frequency of the resonant circuit. Simulation of a three-level diode-clamped inverter showed that when the capacitance of the resonant circuit changes and, therefore, the resonant frequency of the circuit, the input current increases. The work obtained specific numerical dependencies. Time diagrams of voltages and currents on the main elements of the converter are given, which illustrate the implementation asynchronous pulse-width modulation in the control system. After working out the automatic frequency control algorithm, the increase in current consumption can be leveled off. The simulation results also show that it is possible to reduce the amplitude of the third harmonic. The disadvantages of the proposed system include the fact that the frequency of the converter is adjusted at each subsequent period of its operation. At the same time, the parameters of the filter can change again, which leads us to believe that adjusting the frequency will never give a 100% result, but will only allow to get as close as possible to the set parameters of the sounding signal. The work also indicates that it is possible to improve the spectral composition of the probing voltage generated by the converter by using more levels of a diode-clamped multi-level inverter. However, increasing the number of levels reduces the action speed of the system and complicates the control system itself. Therefore, the need to maintain a balance between the number of levels of the inverter and the complexity of the system is indicated

STABILITY IMPROVEMENTS FOR GENERALIZED AVERAGE-VALUE MODEL OF DC-DC CONVERTERS

Power electronics have a significant role in modern electrical devices, for instance, hybrid electric vehicles. Power electronics are the technology in between the source and the load circuits and can convert the power from dc to ac or from dc to ac. There are also many types of dc-dc converters, like such as boost and buck converters, which exhibit switching ripple behavior. A boost converter increases the output voltage (with respect to the input voltage) and reduces the output current. A buck converter decreases the output voltage and increases the output current. Many models are used to predict the behavior of the boost and buck converters. The detailed (DET), state-space averaged (SSA), and generalized averaging method (GAM) models are capable of predicting the average behavior of dc-dc converters. For DET and GAM models, the rippling behavior can also be predicted. These models differ in terms of required run time, existence of constant equilibrium points, and accuracy. The DET model has a long run time and does not have constant equilibrium, but it is very accurate. The SSA technique is a mathematical and time-invariant model that capable of describing the behavior of a dc-dc boost converters. It can derive the small signal ac equations of a switching converter and is used to illustrate the average behavior of any linear or nonlinear system in converters. The SSA does not take extensive runtime simulation and has constant equilibrium points, and can be applied to continuous, discrete and sample data systems. The GAM model can predict the average and ripple behavior in power electronic systems and has constant equilibrium and fast run time. However, it has a numerical stability issue. The integrator stabilized multifrequency averaging (ISMFA) model is employed to solve the stability issue in the GAM model, but it is a complicated dynamic method and has restrictions in its process. In the present study, a simplified but stable GAM model is introduced to predict the average and ripple behavior of boost dc-dc converters and to overcome the limitations of other methods. In this work, the stabilized GAM model has been used for a dc-dc boost converters. The stability of the proposed model is analyzed. The performance of the improved GAM model is compared with the DET, SSA, and GAM models. The results show that the stabilized GAM model is stable with the additional poles created by the GAM assignable by parameter choice. The new GAM model predicts the same results as the existing GAM method without the underlying stability concerns. The stabilized GAM model exhibits constant ii equilibrium point and requires significantly lower run times than the DET model, but it is also able to predict the ripple performance of the converter. The stabilized GAM model does not take a long run time, is less complicated, has fewer restrictions, has constant equilibrium and internal stability, and has more straightforward implementation than other models, like the ISMFA model. It represents a suitable alternative to DET models when high accuracy simulations are desired without long simulation run times

Dynamic modeling, simulation and data logging of a hybrid power system for a remote house in Qinghai Province in China

Hybrid power systems include both renewable and traditional energy. In China, some rural areas not connected to the grid are more suitable for isolated hybrid power systems than grid extension, because of lack of roads and infrastructures. Government’s policies have largely boosted the development of renewable energy, making the hybrid power system more affordable for those areas. In this research, the system is firstly sized for optimum net present cost using HOMER according to given weather data and generated hourly load data. Then, the transient stability of the designed system is checked through the dynamic modeling and simulation in Simulink based on each component’s dynamic equations and control system. Designed control systems, which keep the stable operation of the designed system, include a supervisory controller, MPPT (Maximum Power Point Tracker), inverter controller and so on. Due to nonlinear and time variant load, the controller of the DC voltage regulator is designed based on a robust control method. A data logger with web transfer is then designed to monitor an isolated PV system. Sensor data are collected by Arduino boards and transferred to Thingspeak web server by the python program on PC. The collected data is downloaded and analyzed on MATLAB to analyze the system operation. Therefore, this thesis presents system sizing, dynamic modeling and its simulation results, a data logging system with data visualization on a web server and lab test results