Table of contents monday, September 9, 1: 30pm-4: 00pm modular Multi-Level Converters, hvdc, and dc grids I 3
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- Bu səhifədəki naviqasiya:
- Poster Session: Control, Modelling and Optimization of Power Converters
- Poster Session: Electrical Machines
| P2515 Circulating Current Control for Carrier-Based Discontinuous Modulation in Inverters with Parallel Legs [#513]
Andre Nicolini, Antonio Ricciotti, Fernanda Carnielutti and Humberto Pinheiro, Federal University of Santa Maria, Brazil; Federal University of Rondonia, Brazil This paper presents a discrete time controller for the circulating current of three-phase voltage fed converters with two magnetically coupled legs that uses carried-based discontinuous modulation. The discontinuous modulation produces multilevel equivalent PWM line-to-line output voltages with reduced harmonic distortion and equally distributes the commutations between the switches. A state machine is used to reduce the number of commutations. Using this state machine a non-linear controller is proposed to keep the circulating current close to zero. Moreover, it is important to mention that the implementation of the proposed modulation and controller are straightforward, requiring neither a complex hardware nor a high development effort. Furthermore, simulation and experimental results are presented to demonstrate the good performance of the proposed method. P2516 A Phase-Shift PWM-Controlled ZVS Boost Full-Bridge AC-AC Converter for High-Frequency Induction Heating Applications [#65]
This paper presents a new single-stage utility frequency ac (UFAC)-high frequency ac (HFAC) resonant power converter for high frequency induction heating(IH) applications. The newly-proposed ac-ac converter features a boost converter and full-bridge HF resonant inverter integrated circuit (Boost-Full-Bridge, BFB) with a source voltage sensorless control scheme. The experimental results of a 3.0,kW-40kHz prototype are demonstrated on zero voltage soft switching(ZVS) operations and steady-state characteristics based on the phase shift pulse-width-modulation (PS-PWM) power regulation, then the validity of the proposed ac-ac converter is revealed from a practical point of view. P2517 Control Approach for a Class of Modular Multilevel Converter Topologies [#951]
This paper presents a generalised control that can be applied to a class of modular multilevel converter topologies. The approach splits up into current control based on the state-space representation and branch energy balancing. For the branch energy balancing, an optimisation process leading to minimal additional current stress is presented. After describing the control approach independently from any specific topology, it is applied exemplarily to the Modular Multilevel Matrix Converter. A comparison with a previously published branch energy balancing for the Modular Multilevel Matrix Converter is conducted, and the control approach is verified by simulation and experimental results. Poster Session: Control, Modelling and Optimization of Power Converters Tuesday, September 20, 11:00AM-12:30PM, Room: Exhibit Hall, Chair: Pericle Zanchetta, Luca Solero P2701 Digital Autotuning Controller for Point-of-Load Converter Based on Non-Intrusive Start-up Transient Observer [#718] M. Ali, K. H. Loo and Y. M. Lai, The Hong Kong Polytechnic University, Hong Kong A new method for online estimation of power-stage parameters and autotuning of feedback controller for point-of-load (POL) converter is presented in this paper. The autotuning controller presented has been specifically developed to handle wide variations of the resonant frequency of LC output filter and the equivalent series resistance (ESR) zero of output capacitor. The resonant frequency of LC output filter and the time constant of output capacitor's ESR zero are estimated by examining the start-up transient response of converter and online measurement of steady-state output voltage ripple, respectively, hence the proposed method is non-intrusive and does not affect converter's normal operation. Based on these results, digital compensator is automatically tuned based on some user defined phase margin and crossover frequency to provide the desired transient response and output voltage regulation over wide variations of power-stage parameters. Simulation and experimental results from a 12 V-to-1.5 V, 22.5 W, 500 kHz digitally controlled POL buck converter are provided to verify the effectiveness of the proposed method. P2702 Control of D-STATCOM During Unbalanced Grid Faults Based on DC Voltage Oscillation and Peak Current Limitations [#764]
The safe operation of grid connected power converters during abnormal condition is a key issue in order to guarantee its operation and to avoid undesired trips. In this paper different control methods for the operation of a D-STATCOM are evaluated, where the reference currents are determined in such a way that none of the phase currents goes over the limits, as well as the DC voltage fluctuations remain in safe operation limit. Therefore, the contribution of this paper lays on the combination of the DC voltage oscillations and the current limit control. As it is shown in the following, three different control strategies are evaluated. The amplitude of the oscillations which are superimposed on the DC voltage as well as peak amplitude of the phase currents are calculated for each, considering a generic imbalance in the network. The effectiveness of the presented control strategies are verified by simulating a D-STATCOM tied to an industrial distribution network. Moreover a scaled scenario has been reproduced experimentally which shows that the results cope well with the analytical equations and the simulation results.. P2703 Staircase Modulation of Modular Multilevel Converters with Minimal Total Harmonic Distortion and Maximal Number of Output Voltage Levels [#831]
This paper proposes a generalized staircase modulation method for modular multilevel converters (MMCs). Compared to high-frequency modulations, the staircase modulation has a lower switching frequency and losses, and lower dV-dt stresses for power electronics devices. By using Karush-Kuhn-Tucker (KKT) conditions, this paper proposes a method with rigorous proof to calculate the switching angles that is computationally efficient and achieves global minimal total harmonic distortion (THD) of phase voltages within the entire modulation index range. This method produces the maximal number of voltage levels (i.e., 2n+1, where n is the number of submodules in each arm) to further reduce the THD. Capacitor voltage balancing control is incorporated in the staircase modulation scheme. Simulation results validate the analysis. P2704 FPGA Implementation of Model Predictive Direct Current Control [#933]
An FPGA implementation of Model Predictive Direct Current Control (MPDCC) is reported in this paper. A central scheduler enumerates switching sequences and assigns these to several explorer units, which predict the system response and compute their associated cost. The proposed FPGA design is scalable, modular and requires little hardware resources. A five-level active neutral point clamped inverter with a medium-voltage induction machine is considered. The MPDCC scheme controls the machine's stator currents, the neutral point potential and the inverter's phase capacitor voltages at a low switching frequency. P2705 Active Damping of LC Resonance for Paralleled Indirect Matrix Converter Based on Cascaded Control [#952]
The indirect matrix converters (IMC) offer the advantages of high reliability and compactness in structure due to no large energy storage components in virtual DC side, and thus have a promising application in the future. However, the LC resonance caused by input filter is one reason keeps it from being utilized in industry. Different from pervious solutions of LC resonance damping for single IMC, this paper proposes an active damping strategy for the paralleled IMC with both interleaved operation and cascaded control of input LC filter. The key is to apply the closed-loop control of grid currents to generate the references for capacitor voltages, which are tracked by the inner capacitor voltage loop. By designing the control parameters properly, this method can not only suppress the LC resonance effectively but also offer accurate control of grid currents. In order to further mitigate resonance, the interleaved operation is applied to reduce specific order harmonic around resonant frequency of LC filter. No additional cost will be required for the proposed interleaved and cascaded control strategy. Furthermore, the feed-forward terms of voltage drop on filter inductor and capacitor currents are added to the control, in such a way that the decoupling effects between the d-axis and q-axis are removed and the dynamic response becomes better. Both simulation and experiments are given to verify the correctness and feasibility of the proposed strategy. P2706 Virtual Circuit Design of Grid-Connected Half-Bridge Converters with Higher-Order Filters [#1077]
This paper presents a structured design method for half-bridge converters with higher-order lossless output filters, focusing on the popular LCL filters. The method builds on the theory of terminated ladder networks and on a control algorithm actively emulating the ladder network termination. Given a desired transfer function, a normalized ladder network is accordingly synthesized and scaled to meet the physical requirements. The component sizing and the active damping of filter resonances are simultaneously tackled. The associated digital-control architecture for LCL filters is explained. A Kalman observer is employed to deal with the inherent sample delay. An LCL filter is designed based on the proposed method and is experimentally validated with the half-bridge converters operating as active front end. The grid reactive currents are stepped and the results show properly damped responses. The system has good disturbance rejection and is passive according to the simulated input admittance. The robustness of the system is also demonstrated by numerical sensitivity analysis. These excellent characteristics can facilitate the design of the upper-layer or incorporated outer-loop controller, and can enhance the performance of the complete system. P2707 Commutation Technique for High Frequency Link Inverter without Operational Limitations and Dead Time [#1639]
An improved commutation technique for the ac-ac output converter circuit of a pulse width modulated high frequency link (HF-link) inverter is proposed in this paper. The high frequency link inverter converts a DC input voltage into line frequency AC output voltage using a high-frequency transformer for voltage step-up and galvanic isolation, without an intermediate rectification and dc bus. In this topology, there is a direct ac-ac converter which processes the HF-link square-wave voltage into the desired sinusoidal ac output voltage. To do this requires a commutation method to prevent shoot-through when output current changes direction or commutates from one switch to the next. Conventionally, dead time is used but this adds distortion to the output waveform. Previously a commutation technique without dead time was introduced but it required a number of assumptions on the inverter load impedance and link voltage characteristics that made it useful for a stand-alone R-L load but not practical for grid connection. The commutation method in this paper does not require dead time and does not impose any limitation on the output inductance and link voltage magnitude and frequency. Simulations were performed using MATLAB and Plexim, experimental verification used the dSpace1007 HIL platform. P2708 Research on the Current Control method of N-paralleled Converter System for the High-Power Inductor Tester [#875]
This paper develops the N-paralleled converters with LCL filter system model and expands the virtual resistor control method for harmonic current control. Power electronic converter can be controlled as a current source. For some application the current source can be used to test the inductor characteristic, such as temperature rise, noise or vibration. While in some cases, several converters are connected in parallel to increase the output current amplitude. The N-paralleled converters with LCL output filter system presents complex resonances feature. And the output current of the system becomes out of control. This paper develops the closed-loop model of N-paralleled converters with the LCL filter system and reveals the output current amplification by analyzing the resonance feature of the system at first. Then the virtual resistor based current control method is expanded in the harmonic current control. For the application of N-paralleled converters with an LCL filter system to test the inductor characteristic, the amplitude of output harmonic current need be considered carefully. With the optimal virtual resistor value the output harmonic current can also be controlled well. Simulation and experimental results prove the validation of the system model and optimization for damping resistor value. P2709 Modeling and Bifurcation Analysis of Converters with Power Semiconductor Filter [#976]
An input filtering technique, named as Power Semiconductor Filter (PSF), has been previously proposed. Such solid-state filter can eliminate or reduce the use of bulky passive filters, so as to increase the power density of the entire converter. This paper will investigate into the bifurcation phenomena with the PSF using a peak-voltage modulator to regulate the voltage across the SPD. Detailed sampled-data modeling and stability analysis will be given. To tackle the occurrence of bifurcation, a compensation ramp introduced into the peak-voltage modulator will be proposed. The behaviors with and without the compensation ramp in the modulator will be demonstrated on a 48W, 40-140V / 24V buck converter. By studying the eigenvalue locus on the z-plane, the models can predict the onset of limit cycles and illustrate how the compensation ramp can make the locations of the eigenvalues lie within unit cycle. P2710 Suppression of Circulating Current in Paralleled Inverters with Isolated DC-link [#167]
In this paper, it is described how the circulating current flows between inverters which have isolated DC-link such as Cascaded H Bridge (CHB) topology, when they operating in parallel. In this case, Zero Sequence Circulating Current (ZSCC) flowing through shared DC-link cannot flow between inverters in parallel. However, circulating current is provoked by asynchronous switching instant of devices and difference of DC-link voltages of parallel inverters. The circulating current should be suppressed by sharing inductor which is inserted between inverters. Generally, all of the inverters should synthesize the same output voltage reference for load current control, to minimize the size of this sharing reactor. However, this conventional method cannot guarantee to diminish circulating current in the transient state and even in the steady state. In this paper, to reduce circulating current, after deriving circulating current model, circulating current control method is devised based on the model. This proposed algorithm is applied to Active Front End 5Level-CHB inverter system for medium voltage drive. Simulation and experimental results are provided to verify the effectiveness of the proposed control scheme. P2711 Small-Signal Model for the ISOP DC-DC Converters in the 5-Level T-Rectifier [#375]
A small-signal model for the Input-Series Output-Parallel (ISOP) DC-DC converters is developed in this paper. The proposed model is obtained applying the State-Space Averaging technique. The ISOP DC-DC converter consists of multiple DC-DC modules connected in series at the input and in parallel at the output. In this paper, the ISOP DC-DC converters are used in combination with the 5-level unidirectional T-Rectifier for electric generating units in More Electric Aircraft systems. The small-signal model for the ISOP DC-DC converters has been verified through the direct comparison with the converter full digital-switching model, realized in the Matlab/Simulink environment. Simulation results exhibit a good agreement between small-signal model and switching model. P2712 DC Bus Splitting Voltage Feedforward Injection Method for Virtually-Grounded Three-Phase Inverter [#526]
The virtually-grounded grid-connected voltage-source three-phase inverter has b been proven to be more effective in alleviating the common-mode noise than the one without the virtual ground and in extending the utilization of DC bus voltage, as compared to the four-wire configuration. However, similar to the four-wire configuration, such virtually-grounded configuration would have DC bus unbalance, which would cause modulation saturation and output current distortion. Typically, two splitting capacitor voltages are measured and compared to produce a common-mode DC bias voltage to the output voltage of the inverter and thereby eliminate such effect. To reduce the number of sensors, a DC voltage feedforward injection method, which utilizes the intra-cycle average value of the duty cycles of the gate signals, is proposed to mitigate possible modulation saturation and output current distortion under the unbalanced condition of DC splitting voltage. A 3kW prototype has been built and evaluated to investigate the effectiveness of the proposed method. P2713 High Performance SiC Power Block for Industry Applications [#546]
SiC power devices have been optimized in performance over the past decade. However, wide industry adoption of SiC technology still faces challenges from system design perspective. This paper demonstrates an integrated air-cooled three phase SiC power block for industrial applications comprising high performance gate driver, low parasitic layout, optimized thermal management, as well as a flexible control platform. Experimental results are provided to demonstrate the superior performance of the design. P2714 Switching Angles Generation for Selective Harmonic Elimination by Using Artificial Neural Networks and Quasi-Newton Algorithm [#632]
A hybrid method based on artificial neural networks (ANNs) and Quasi-Newton algorithm is proposed to generate the switching angles for selective harmonic elimination (SHE), which makes a compromise among the memory consumption, executing efficiency and the solution precision. Unlike the other ANNs based methods which use ANNs to directly give the final switching angles, this hybrid method just uses ANNs to give the initial values, which lowers the precision requirement on training the ANNs, so, the number of the neurons can be reduced and less on-chip memories are required. Then, the Quasi-Newton algorithm is used to solve the exact switching angles from the initial values given by the ANNs, which guarantees the solving efficiency and the solution precision. The case of 11-level staircase modulated converter is studied by using the single-layer back-propagation (BP) neural networks. The trained neural networks have only 9 neurons in the hidden layer and the output initial values can meet the convergent requirement of the Quasi-Newton algorithm in the full range of modulation index. The total executing time is about 70ms on a STM32F407 microcontroller, as the executed code is automatically generated by MATLAB, the executing time could be further reduced if the code is manual optimized. Experiment results are also shown to verify the correctness of the switching angles generated by the proposed hybrid method. P2715 Minimum RMS Current Operation of the Dual-Active Half-Bridge Converter using Three Degree of Freedom Control [#1262]
This paper discusses how triple duty-ratio control can be used to operate the Dual Active Half-bridge converter with the least possible transformer RMS current. Following introduction of all possible modes of operation, results from a numerical optimization-based approach are used to identify the best mode. Using information gleaned from careful observation of simulation results corresponding to the minimum current trajectory in this mode, key insights regarding circuit conditions to be satisfied for optimal operation are obtained. This information is used to propose the framework of a 3D modulation strategy, which operates with minimum RMS current and is also found to ensure ZVS of all devices. Thus the proposed modulation scheme offers significant efficiency advantages over simple phase-shift (1D) control or 2D asymmetric control, particularly at light loads and in applications with widely varying voltage-ratios. Poster Session: Electrical Machines Tuesday, September 20, 11:00AM-12:30PM, Room: Exhibit Hall, Chair: Bruno Lequesne, Mohammad Islam P2901 Comparison of Torque Characteristics in Permanent Magnet Synchronous Machine with Conventional and Herringbone Rotor Step Skewing Techniques [#1050] Weizhong Fei, Patrick Chi Kwong Luk and Wenyi Liang, Cranfield University, United Kingdom Torque characteristics, such as torque ripple and average torque, are of particular importance and primary concern during the design stage of permanent magnet synchronous machines for many high-performance applications. Thus, various design techniques have been developed and implemented to improve the torque characteristics in permanent magnet synchronous machines. The impacts of rotor step skewing techniques including both conventional and herringbone styles on the torque characteristics in permanent magnet synchronous machine are comprehensively investigated and compared by analytical approach, synthesized two-dimensional and three-dimensional finite element analysis in this paper. The results have shown that both the conventional and herringbone rotor step skewing techniques can significantly reduce the torque ripple with a slight compromise on the average torque output. Despite the herringbone rotor step skewing technique is less effective than the conventional one on cogging torque reduction from three-dimensional finite element analysis, it actually can result in higher average torque with smaller torque pulsations in the proposed permanent magnet synchronous machine with load conditions. Finally, experiments on the prototype machines under open-circuit conditions are carried out to validate the estimated results and findings.
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