Laszlo Mathe

On the Perturb-and-Observe and Incremental Conductance MPPT Methods for PV Systems

This paper presents a detailed analysis of the two most well-known hill-climbing maximum power point tracking (MPPT) algorithms: the perturb-and-observe (P&O) and incremental conductance (INC). The purpose of the analysis is to clarify some common misconceptions in the literature regarding these two trackers, therefore helping the selection process for a suitable MPPT for both researchers and industry. The two methods are thoroughly analyzed both from a mathematical and practical implementation point of view. Their mathematical analysis reveals that there is no difference between the two. This has been confirmed by experimental tests according to the EN 50530 standard, resulting in a deviation between their efficiencies of 0.13% in dynamic and as low as 0.02% under static conditions. The results show that despite the common opinion in the literature, the P&O and INC are equivalent.

Review of modular power converters solutions for smart transformer in distribution system

While the use of power electronics based Smart Transformer (ST) is becoming a reality in traction applications, and it has been considered as an interesting option for interfacing different transmission systems, the possibility to use it in distribution systems is still considered futuristic. Replacing primary distribution transformers with ST can lead to more flexible handling of the distribution feeders, while replacing secondary distribution transformers can allow decoupling of distribution network. This paper reviews different power converter solutions for the ST focusing on modularity, control and communication needs, to meet high reliability requirements. Five topologies for the ST are considered and compared.

Motor Integrated Permanent Magnet Gear in a Battery Electrical Vehicle

This paper presents the physical construction and test results of two new demonstrators of a Motor Integrated Permanent Magnet Gear (MIPMG), which is a second version of an already tested demonstrator. The demonstrators will be used as traction units for a Battery Electrical Vehicle (BEV) and the background for the specifications are elaborated. Simulated as well as measured results of rotational losses of the first and second version are compared. The efficiency of the new design is investigated and compared to the drivetrain of the Tesla Roadster and two direct drive axial flux motors in a few operating points, the MIPMG v.2 seems superior when used as traction unit in urban traffic.

Spread Spectrum Modulation by Using Asymmetric-Carrier Random PWM

This paper presents a new fixed-carrier-frequency random pulsewidth modulation method, where a new type of carrier wave is proposed for modulation. Based on simulations and experimental measurements, it is shown that the spread effect of the discrete components from the motor current spectra and acoustic spectra is very effective and is independent from the modulation index. The flat motor current spectrum generates an acoustical noise close to the white noise, which improves the acoustical performance of the drive. The new carrier wave is easy to implement digitally, without employing any external circuits. The modulation method can be used in both open- and closed-loop motor control applications.

Analysis of communication based distributed control of MMC for HVDC

Modular Multilevel Converter (MMC) has gained a lot of interest in industry in the recent years due to its modular design and easy adaption for applications that require different power and voltage level. However, the control and operation of a real MMC consisting of large number of sub modules for high power and high voltage application is a very challenging task. For the reason that distributed control architecture could maintain the modularity of the MMC, this control architecture will be investigated and a distributed control system dedicated for MMC will be proposed in this paper. The suitable communication technologies, modulation and control techniques for the proposed distributed control system are discussed and compared. Based on the frequency domain modeling and analysis of the distributed control system, the controllers of the different control loops are designed by analytical methods and Matlab tools. Finally, sensitiveness of the distributed control system to modulation effect (phase-shifted PWM), communication delay, individual carrier frequency and sampling frequency is studied through simulations that are made in Matlab Simulink and PLECS.

DC-link compensation method for slim DC-link drives fed by soft grid

Slim DC-link PWM (AC) drives for low-performance applications are emerging on the market. Such drives equipped with a small DC-link capacitance exhibit instability tendencies, if installed on a soft line, giving a degraded performance. The total harmonic distortion (THD) and the partially weighted harmonic distortion (PWHD) of the line current are degraded, if resonance between the line impedance and the DC-link capacitance occurs. Likewise, the motor performance is affected negatively giving extra torque ripple, vibration and acoustic-noise emission. This paper proposes a novel DC-link compensation method, which ensures the stability of the slim DC-link on a soft grid. The proposed compensation method may be used for open- and closed-loop control schemes, requiring a small overhead in the digital implementation.

Synchronization of the distributed PWM carrier waves for modular multilevel converters

The half-bridge modular multilevel converter has proven itself to be a suitable solution for HVDC application. In order to achieve high modularity and fault tolerance, distributed control strategy is one possible solution and is discussed in this paper. When distributed control strategy is used, there is a central controller and a local controller in each sub-module (SM). A problem appears when implementing the modulation using this type of control strategy; this is the lack of synchronization between the internal clocks of the different submodules controllers of the MMC. This will cause a drift between the PWM outputs of each sub-module increasing the total harmonic distortion of the output voltage. This paper presents a solution to synchronize the PWM outputs of the MMC submodules using EtherCAT communication protocol focusing on phase shifted PWM modulation technique.

Performance comparison of phase shifted PWM and sorting method for modular multilevel converters

Modular Multilevel Converters (MMC) are the solution of preference in HVDC applications due to modularity, scalability, low losses and low filtering requirement. Carrier-based (PWM) and carrier-less (nearest level control) modulation can be applied. By using advanced sorting methods focusing on keeping the capacitor voltage ripple under some limit, unnecessary switching events are eliminated leading to reduced switching losses. This paper presents a comparison between the steady-state performances in terms of output voltage THD and equivalent switching frequency of the Phase Shifted Carrier PWM and NLC plus sorting methods.

Control of a Modular Multilevel Converter With Reduced Internal Data Exchange

Modular multilevel converters (MMC) are penetrating due to their superior performances. Due to the modular structure of the converter, communication platform has to be established between the submodules (SMs) and a central controller unit (CCU). When the communication platform is designed for such an application, several key parameters have to be considered such as high-speed data transfer with low propagation delay, data integrity, and ability for accurate synchronization. In order to minimize the data flow in the MMC, a hierarchical control is proposed where a CCU calculates an identical reference for all the SMs, while the modulation and capacitor voltage balancing is performed in the controller from the SM. Thus, at each sampling instance, only four bytes references are sent by the central controller to the controllers from the SM, while one or two bytes are received from SMs. Furthermore, the control algorithm is validated through experiments.

Implementation of PLL and FLL trackers for signals with high harmonic content and low sampling frequency

The accurate tracking of phase, frequency, and amplitude of different frequency components from a measured signal is an essential requirement for many digitally controlled equipment. The accurate and robust tracking of a frequency component from a complex signal was successfully applied for example in: grid connected inverters, sensorless motor control for rotor position estimation, grid voltage monitoring for ac-dc converters etc. Usually, the design of such trackers is done in continuous time domain. The discretization introduces errors which change the performance, especially when the input signal is rich in harmonics and the sampling frequency is close to the tracked frequency component. In this paper different discretization methods and implementation issues, such as Tustin, Backward-Forward Euler, are discussed and compared. A special case is analyzed, when the input signal is reach in harmonics and the sampling frequency is only 10 times larger than the tracked frequency component.