A novel idea to realize the distributed maximum power point tracking (DMPPT) control of a photovoltaic system interfaced with an AC grid is proposed. The proposed system is based on the idea of string-connected dc-dc module integrated converters (MICs) that was researched by Walker, Erickson, and others. However, those studies focused on working together with a voltage source inverter (VSI) in a constant DC voltage mode. In addition, all commercial products from companies such as Solar Edge, Solar Magic, and Tigo Energy are working together with a VSI in a constant DC voltage mode. In contrast to past works, the proposed system uses controlled string current with a current source inverter (CSI) to link MICs. As a result, the circuit topology and control scheme of the MICs have been greatly simplified. The authors hope that the proposed system is especially suited for SiC-based CSI applications in the near future. This paper first reviews the conventional control schemes. Then a new MIC-based DMPPT technique is proposed. A simulation study using PSIM is conducted to prove the validity and usefulness of the proposed system. Finally, the successful experimental operation of peak power tracking was confirmed by using two cascaded MICs.
This paper proposes a novel filtering method to reduce the stochastic disturbance in modal space. Recently, macro-micro manipulation has been applied in medical fields, especially for cell manipulation. In conventional approaches, a scaling bilateral control with haptic feedback is one of the key technologies for micro manipulation. However, the quality of haptic information deteriorates because of the influence of stochastic disturbance such as quantization noise caused by the interference between the macro-space and micro-space. To solve this problem, a modal filter that compensates for interference terms in each space is proposed. By dealing with the random variable as a mass fluctuation, the interference term of the stochastic disturbance on the master system can be clarified. Using the proposed method, it is possible to reduce the variance of the random variable and extract the expectation value. The validity of the proposed method is confirmed by simulation and experimental results.
This paper proposes a novel time-delay compensation based on the feedback of an elastic force from a wave system. In the previous research, the authors derived wave representation of a time-delay system and showed that there is equivalence between a resonant system, which is expressed by the wave equation, and a time-delay system: both systems consist of a position-input system and a wave-transmission system. Considering the above equivalence, we can infer that the cause of vibrations in the time-delay system is the robustness of the position-input system against the wave-transmission system, as in the case of the resonant system. To reduce the robustness, the feedback of an equivalent elastic force, which is derived from the wave representation, is introduced according to the concept of a resonant ratio control, which is one of vibration control method on a two-mass resonant system. Because the feedback of the elastic force can reduce the equivalent mass of the position-input system, the vibrations due to the time delay are suppressed. The disturbance-suppression performance of the proposed method is superior to that of a Smith predictor and a communication disturbance observer because the proposed method can maintain the feedback characteristic. The validity of the proposed method is confirmed by simulation and experimental results.
This paper discusses the influence of the magnetic properties of the stator core on cogging torque in 8-pole 12-slot surface-mounted permanent-magnet synchronous motors from the perspective of magnetic energy. In the finite element analyses of magnetic fields with modeled stator BH curves, cogging torque decreases drastically when the shape of magnets is changed from an arc to a semi-cylindrical structure. The influence of the stator BH curve on cogging torque is dominant in the low-cogging-torque motor with semi-cylindrical magnets. This is because magnetic energies in the gap and the magnets cancel each other and the magnetic energy in the stator core is dominant in the low-cogging-torque motor. Low maximum permeability and low magnetizing force in a high-B region are preferable for stator magnetic properties to reduce cogging torque. This is explained by the behavior of harmonics in the stator magnetic energy variation. The influences of steel grade, compressive stress, and punching in the stator core on cogging torque analyses are consistent with the results for the modeled BH curves. Low grade electrical steel sheets, high compressive stress, and magnetic annealing are effective to reduce cogging torque in the described motor design.
This paper presents the analysis and PCB design of a class D inverter for wireless power transfer systems operating at 13.56MHz. The effects of parasitic inductance on the switching performance of MOSFETs, transfer efficiency of WPT systems, and power loss are analyzed. At high frequencies, the print circuit board (PCB) design is very critical because it control the parasitic elements on the circuit. This study proposes an improved PCB design that can provide a 23.4% decrease in parasitic inductance over the conventional PCB design.
Recently, contactless electric power distribution has become a very attractive method for providing electric power to mobile equipment such as mobile phones or electric vehicles. Inductive power transfer (IPT) with inductive coupling is currently the most popular way to realize contactless electric power distribution. Another way is capacitive power transfer (CPT) with capacitive coupling. In the past, several studies on CPT have effecively used series LC resonance to enhance the transfer power. However, LC resonance is sensitive to parameter changes, which may be caused by the contact conditions of the capacitive coupling. The authors propose a new power converter suitable for a CPT system that uses a novel improved one-pulse switching active capacitor (I-OPSAC) to enhance power transfer. The proposed system improves the power transfer efficiency without LC resonance and is robust to parameter change. One of the major advantages of I-OPSAC is stable operation without any feedback loops including DC capacitor voltage control. The other major advantage is the easy-to-realize series connection. The paper reports the control scheme and detailed operational characteristics of a cascaded I-OPSAC (C-I-OPSAC), in addition to the simulation and experimental results. The results verified that a C-I-OPSAC enhances transfer power while maintaining stable operation without a feedback loop.
In the design of the induction motor, the equivalent circuit is used to predict its performance. The equivalent circuit consists of the magnetizing reactance and iron loss resistance, primary and secondary resistance and primary and secondary leakage reactance. The secondary leakage reactance of the closed slot rotor is not easy to calculate, because the closed slot rotor has a thin magnetic steel sheet bridge, through which the leakage flux passes. The inductance of the bridge changes depending on the B-H characteristics of the magnetic steel sheet. In this paper, a new equivalent B-H characteristics method is developed to calculate the bridge inductance of the closed slot. First, the bridge inductance of the closed slot is examined with experiments, flux by FEM and magnetic energy and magnetic coenergy by FEM. Then, magnetic energy and magnetic coenergy by FEM yields the bridge inductance of the closed slot for a wide slip range characteristics. From the bridge inductance and bar currents, the magnetomotive force and flux density are calculated for the equivalent B-H characteristics. This equivalent B-H characteristics method is able to respond to the inductance of the closed slot bridge from the unsaturated (small ampere-turn) zone of the magnetic steel sheet to the saturated (large ampere-turn) zone accurately. This yields the proper value of the bridge inductance, for which the conventional equations give a value of infinity.
Sliding-mode control for power converters is gaining significant research interest for achieving a fast transient response to a step load change in a wide operating range. However, power converters also require better dynamic load regulation against load current fluctuations slower than the step change. This paper addresses this issue by deriving a novel control method for synchronous buck converters using Lagrangian dynamics. Simulation results verified improvement in dynamic load regulation against slow sinusoidal load current fluctuations.
This paper proposes a new approach to achieve online identification of the q-axis inductance of the interior permanent magnet synchronous motor (IPMSM) based on the relationship between the mismatch of Lq and the d-axis feedback current. The value of the d-axis feedback current depends on the mismatch of Lq, and the consecutive samplings of the d-axis feedback current make it possible to calculate the true value of Lq. The proposed identification technique has been examined through some experimental tests. The test results demonstrate the fast convergence of the identified Lq to the true one with a small error.
This paper presents a novel load regulation technique for parallel-connected POLs which reads for power supply on chip (power-SoC). In power-SoCs, many POLs are implemented on the same chip. In this case, the conventional loop control (feedback control) may have problems such as oscillation. The proposed strategy regulates the output voltage by changing the number of working POLs under fixed duty ratio. The parallely connected POL system is implemented using MATLAB/Simulink, and the operating characteristics are confirmed. In addition, the proposed control strategy is also verified experimentally.
This paper proposes a remarkably efficient modeling method of stray magnetic couplings in an Electromagnetic Compatibility (EMC) filter that focuses on the dominant magnetic field in a power electronic device. The proposed modeling method was applied for simulating the filter performance of an EMC filter for a Silicon Carbide (SiC) solar inverter, and its effectiveness was verified through a comparison of the measurement and simulation results. With the proposed modeling method, the influence of the stray magnetic couplings on the filter performance can be predicted well. Further, the results matched those of the measurement and simulation with a conventional modeling method. Accordingly, the number of stray magnetic couplings required for accurate prediction can be dramatically reduced from 325 to just one.
In AC/DC converters for on-board chargers, the DC-link capacitor on the output side in a power factor correction (PFC) converter uses aluminum electrolytic capacitors in order to obtain a large capacitance for a low voltage ripple and small size. On the other hand, it is desirable to use a film capacitor instead of the aluminum electrolytic capacitors in order to obtain a long lifetime for the DC-link capacitor. However, the DC-link capacitance must be reduced as compared with the aluminum electrolytic capacitors in order to avoid increasing the size of the DC-link capacitor. This paper presents a control strategy for the AC/DC converter with a reduced DC-link capacitance. This strategy is based on the instantaneous power balance of a PFC converter and a DC/DC converter, and it controls the AC-side input current without being affected by the large ripple voltage of twice the utility line frequency owing to the reduced capacitance. The simulation and experimental results are presented to validate the proposed strategy, and it is confirmed that it is possible to reduce the DC-link capacitance to one-fifth when compared with the conventional AC/DC converter, without additional circuits.
A new network communication system for a power electronics controller that transmits the feedback signal from the sensors using an FPGA-based hardware controller was proposed. Based on the RocketI/O network controller, a customized Rocket I/O protocol was implemented to achieve high-speed feedback communication between two FPGA controllers. One-megahertz variable sampling quasi-multirate deadbeat control was applied for the PWM inverter control. The 1-MHz sampled data were transmitted using the Rocket I/O protocol and proper operation of the feedback control was experimentally verified. To compensate for the network delay of the feedback signal, a communication disturbance observer was combined with the network feedback system. The advantage of the proposed method was verified.
The ability to individually extract different types of disturbances present in AC line currents or voltages is desirable for reference signal calculation algorithms employed in power conditioners, in order to optimize the operation and design of power converters. This paper proposes a novel algorithm based on the dot product of three-dimensional space vectors in the abc coordinate system, for real-time calculation of the instantaneous positive-, negative- and zero-sequence components for individual harmonics. Certain applications are presented, including individually compensating the fundamental reactive power, selected current harmonics and current unbalances. This method is computationally simple and requires no coordinate transformation. The proposed algorithm is validated by simulation and experiments.
High voltage high power semiconductor devices are being used for grid integration of renewable energy sources. 1200V/100A SiC-MOSFETs, 1700V SiC-MOSFETs, 1700V SiC-Schottky diodes, 10kV SiC-MOSFETs, and 10kV JBS diodes have proved to be useful for high-voltage applications. High-voltage SiC devices enable high-switching frequency operation thus reducing the size of the parasitic element. This paper focuses on an alternative approach to the 0.9MW PV power plant currently being constructed in Brazil. The objective of the use of high power SiC devices for integration of the PV power plant into 13.8kV grid is to provide higher efficiency and reduced size and volume.