Periodic Control of Power Electronic Converters
2: School of Engineering, University of Glasgow, Glasgow, Scotland
3: School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore
4: Department of Energy Technology, Aalborg University, Aalborg, Denmark
A key issue for power electronic converters is the ability to tackle periodic signals in electrical power processing to precisely and flexibly convert and regulate electrical power. This book provides complete analysis and synthesis methods for periodic control systems. It covers the control, compensation, and filtering of periodic signals in power electronic power processing and proposes a unified framework for housing periodic control schemes for power converters, providing a general proportional-integral-derivative control solution to periodic signal compensation in extensive engineering applications - a perfect periodic control solution for power electronic conversion. It provides number of demonstrative practical examples of the application of periodic control to: standalone constant-voltage-constant-frequency (CVCF) singlephase Pulse Width Modulation (PWM) inverters; standalone CVCF singlephase High Frequency Link (HFL) inverters; standalone CVCF three-phase PWM inverters; grid-connected single-phase inverters; grid-connected singlephase "Cycloconverter" type HFL rectifiers; grid-connected three-phase PWM inverters; programmable AC power sources; shunt active power filters; and UPS systems. Periodic Control of Power Electronic Converters is of key importance for researchers and engineers in the field of power electronic converter systems and their applications, for control specialists exploring new applications of control theory in power electronics, and for advanced university students in these fields.
Inspec keywords: adaptive control; power convertors; frequency control; harmonics suppression; periodic control
Other keywords: power converter frequency-adaptive periodic control; fundamental periodic control; power harmonics mitigation
Subjects: General electrical engineering topics; Power supply quality and harmonics; Power convertors and power supplies to apparatus; General and management topics; Self-adjusting control systems; Time-varying control systems; Frequency control; Control of other power systems; Optimal control
- Book DOI: 10.1049/PBPO082E
- Chapter DOI: 10.1049/PBPO082E
- ISBN: 9781849199322
- e-ISBN: 9781849199339
- Format: PDF
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Front Matter
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1 Introduction
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Power electronics technology plays a pivotal role in improving the performance, efficiency, reliability, and security of the electrical power systems. It is a key enabling technology not only for the coming smart electrical power systems but also to create a more sustainable society. In this chapter, we will have a look at power, electronics, and control with an insight into the development of the power electronic systems and their control.
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2 Fundamental periodic control
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The internal model principle (IMP) states that perfect asymptotic rejection/tracking of persistent inputs can only be attained by replicating the signal generator in a stable feedback loop [1]. The signal generator is also called “internal model”of the inputs. W. M. Wonham summarized IMP as “Every good regulator must incorporate a model of the outside world.”Based on IMP [1,2], this chapter presents the fundamental periodic controllers for providing zero steady-state error compensation for periodic signals and elaborates their general design methodology. These IMP-based periodic controllers include repetitive control (RC) [3-21], multi-resonant control (MRSC) [22-34], and discrete Fourier transformation (DFT)-based RC [26,35-36]. The general design methodology comprises a standard internal model for periodic signals and the synthesis methods for universal plug-in structure periodic control (PC) systems. The relationship among these three fundamental periodic controllers will also be demonstrated.
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3 Advanced periodic control for power harmonics mitigation
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The rapidly growing amount of power harmonics injected by power electronic converter interfaced loads and distributed generator systems may cause serious power quality problems in the electrical power systems, such as harmonic losses, resonances, device malfunction, and even entire system instability. Power harmonics induced by power electronics converters usually concentrate on some specific frequencies. For instance, single-phase H-bridge converters mainly produce (4k ± 1) (k = 1, 2, . . . )-order power harmonics, while n-pulse (n = 6, 12, ...) converters, such as in high-voltage direct current (HVDC) transmission systems, mainly produce (nk + 1) (k = 1, 2, .. . )-order power harmonics [1-7], and also diode rectifiers loads used in many applications disturb the grid. As discussed in Chapter 2, the IMP-based fundamental periodic controllers fail to optimally compensate power harmonics with high control accuracy, while maintaining fast dynamic response, guaranteeing robustness, and being feasible for implementation. To address these issues, this chapter will explore advanced IMP-based PC technologies [8] for optimal power harmonics compensation. The general design methodology also comprises an internal model for selective power harmonic signals and synthesis methods for plug-in PC systems. These advanced PC schemes not only exploit the periodicity of reference/disturbance, but also account for its harmonic frequency distribution. The relationship between fundamental periodic controllers and advanced ones will be demonstrated.
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4 Periodic control of power converters
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This chapter will present six application examples of the periodic control of power converters, which includes the voltage control for constant-voltage-constant-frequency (CVCF) pulse-width modulation (PWM) inverters, CVCF highfrequency link (HFL) single-phase and three-phase inverters, current control for grid-connected single-phase and three-phase PWM inverters, and HFL rectifier. Experiments have been carried out to verify the effectiveness of various fundamental and advanced periodic control schemes for power converters.
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5 Frequency-adaptive periodic control
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Connecting power converters to the electrical networks has become a crucial issue due to the fast-growing penetration of renewable energy sources and distributed generation systems. In these practical applications, the frequency of the periodic signals of interest is not constant always but slowly time-varying due to the imbalance between the power generation and the load demand. Both fundamental and advanced PC schemes can achieve zero steady-state error tracking of any periodic signal with a known period due to the introduction of high gains at the interested harmonic frequencies by embedding the corresponding internal models. However, frequency variations will lead to mismatch between their embedded nominal internal models and the actual periodic references/ disturbances, and will shift high gains away from the actual frequency of interest. Thus these PC schemes will fail to accurately track the varying-frequency periodic signals. It means that their internal models are sensitive to frequency variations. Moreover, delay-based PC schemes in their digital forms, such as the digital classic repetitive control (RC), discrete Fourier transform (DFT)-based RC, digital selective harmonic control (SHC), and so on, even require that the period of the references/disturbances can be represented as integer multiple of the sample time of the digital control system. This means that the period of the interested periodic signal should be an integer, but the period will not be an exact integer except by chance. A varying frequency often induces fractional-period harmonics. Such mismatches between the given integer period and actual fractional period will lead these PC strategies to yield low gains at the interested harmonic frequencies and thus produce poor tracking accuracy. For example, the grid frequency is usually varying within a certain range (e.g., 49 Hz ~ 51 Hz) due to the generation-load imbalance and/or continuously connecting and disconnecting of large generation units. The PC schemes may fail to force grid-tied converters to feed good quality power into the grid in the presence of a time-varying grid frequency. Therefore, it calls for frequency-adaptive PC solutions that are able to self-tune the corresponding internal model to match the external signal closely and then accurately compensate the varying-frequency voltages and/or currents for good power quality and also stable operation of the grid-connected systems. The performance of the PC systems depends on how precise the match is between the PC signal generator period and the actual signal period. Addressing the above issues, this chapter explores the frequency-adaptive internal model principle (IMP)-based PC strategies to compensate frequency-varying harmonics. A direct frequency-adaptive resonant controller is investigated. A fractional-delay filter-based internal model is introduced to provide a general frequency-adaptive PC solution to the compensation of frequency-varying periodic signals. The frequency sensitivity, design, and implementation methodology of frequency-adaptive PC systems are discussed. Compatible synthesis methods for plug-in frequency-adaptive PC schemes are also presented.
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6 Frequency-adaptive periodic control of power converters
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This chapter will give three application examples of frequency-adaptive periodic control (FAPC) of power converters under frequency variations, which include voltage control for programmable AC power sources, current control for grid-connected photovoltaic (PV) inverters, and current harmonics compensation for shunt active filters.
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7 Continuing developments of periodic control
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This chapter will discuss the most recent developments of the periodic control (PC) technology, such as the PC for multi-period signals and the periodic signal filtering problem. All these developments would extend the PC to more extensive engineering practice and can enable PC to further improve system performance.
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Back Matter
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