In recent years, the demand of an isolated AC/DC converter for the grid connection has increased. The authors have proposed an isolated AC/DC converter using a soft-switching technique and the control. This paper presents the parameter design of a soft-switching circuit for the isolated AC/DC converter. The effectiveness is verified by experiments.
A novel zero current soft-switching (ZCS) pulse width modulation (PWM)-controlled bidirectional DC-DC converter (BDC) with non-inverting polarity for the multi-mode voltage regulations is proposed in this paper. The multi-mode voltage regulations, i.e. buck, boost and buck-boost can be attained in the bidirectional power flows, thus energy utilization of DC voltage sources such as a battery can be improved significantly in renewable and sustainable electric power supplies. In addition, all the power devices can commutate by ZCS with the aid of single-auxiliary switch-based edge-resonant cells, thereby the switching power losses can be minimized. The effectiveness of the proposed BDC and its steady-state characteristics including the voltage conversion ratio and actual efficiency are verified experimentaly with a 500W-50kHz prototype.
Applying wireless power transfer (WPT) to transportation applications is one of the best solutions to overcome the drawbacks of electric vehicles (EVs) caused by their energy storage systems. Although dynamic charging of EVs can extend their driving distance, control techniques need to be developed to maintain maximum transmitting efficiency and to ensure a stable supply of energy, because a dynamic WPT system has to deal with parameter variations such as distance change, load change, and so on. Since a control strategy based on signal communication between the primary side and secondary side reduces the reliability of the system, this paper proposes a primary-side efficiency control method based on the change in primary current, resulting from the power control with half active rectifier on the secondary side. The reference value of the primary voltage for maximizing the transmitting efficiency is calculated based on the primary-side information. Simulations and experiments demonstrated that the proposed method could achieve not only maximum transmitting efficiency but also the desired load power.
This paper investigates a switching operation when a current-source gate drive circuit is used for large gate capacitance. The current-source gate drive circuit consists of a voltage source, an input inductor, and switching devices such as an H-bridge inverter. The power consumption of this circuit is reduced in comparison with that of a conventional voltage source gate drive circuit because the energy of the capacitor between a gate and a source is not consumed in gate resistance, which is not required for the current source gate drive circuit. The switching operation of the proposed current source gate drive circuit in the high-frequency inverter is evaluated experimentally. In addition, the power consumption is measured when the switching frequency is changed from 100kHz to 1MHz. As a result, it is confirmed that the power consumption of the current-source gate drive circuit is reduced by 62% compared with that of the voltage source gate drive circuit at 1MHz.
An isolated modular boost converter is proposed as one of the solutions to efficiently deliver power from low voltage renewable energy sources such as photovoltaic cells to a high voltage battery. The converter consists of multiple boost modules, each of which comprises a phase shifted full bridge converter, a transformer and a diode rectifier. Both high boost ratio and high efficiency are achieved by connecting the output of the boost modules in series. The fundamental characteristics of the converter are demonstrated. In addition, parallel boost modules operation with imbalanced output power is proposed for further efficiency improvement. It is experimentally confirmed that the proposed power unbalancing scheme between two parallel boost modules improves the efficiency over wide operating ranges without any drawbacks.
This paper proposes a new current control method for permanent-magnet synchronous motors with double independent three-phase windings (DIW-PMSMs). This method employs two role-sharing current controllers, namely “fast-mode current controller” and “slow-mode current canceller”, both of which are realized in the dq synchronous reference frame. The fast-mode current controller is a kind of feedback controllers; however it is designed through the use of the leakage inductance rather than the inductance of DIW-PMSMs. On the other hand, the slow-mode current canceller is designed through the use of the mutual inductance of double independent three-phase windings. The effectiveness and usefulness of the proposed method are verified though tough simulations in which the test motor has small leakage coefficients (i.e. large coupling coefficients), the motor parameters and current commands associated with each winding are widely different, and the motor speed is very high.
In the last decade, a number of offshore wind projects have been implemented or planned to meet the CO2 emission targets and nuclear fission policy, especially in Europe. Some projects adopt high-voltage DC (HVDC) transmission with a long-distance submarine cable laid from offshore to onshore. The HVDC transmission system has the advantages of high efficiency and low cost, when compared with AC systems. On the other hand, a medium-voltage (MV) collector grid uses AC 33kV instead of DC so that the efficiency and cost will be poor in case of high-power turbines because the higher power rating of turbines causes higher current in the collector grid and requires greater separation between the turbines. Presently, the MW rating of the latest wind turbines exceeds 8.0MW, and the MW rating has been increasing as the years go by. Thus, the MVDC collector grid will be installed, and an HVDC/DC converter is required to step up the MVDC to HVDC.
This paper introduces a circuit topology and control scheme of a high-power HVDC/DC converter to convert MVDC to HVDC.
This paper proposes an isolated DC/AC converter that has a small inductor and capacitor. In the proposed converter, an active power decoupling circuit is applied to a synchronous rectifier, which can compensate for the double-line frequency ripple of single-phase AC grid using a small capacitor. In addition, the proposed converter can achieve zero current switching using pulse density modulation (PDM). From the experimental result, the second-order harmonics of the input voltage is reduced to 2% in comparison to the DC components. In addition, the inverter output current THD of 2.2% is achieved.