This paper proposes a novel “Direct Space Vector PWM (Direct SVPWM)” strategy based on the direct AC/AC conversion approach for three-phase to three-phase matrix converters. This method allows the sine input and sine output waveforms as a major premise, and gives top priority to the improvement of the output control performance in motor drive applications, for instance, provides maximum riding comfort for an elevator, etc. Output voltage harmonics, switching losses, and common-mode voltage can be reduced across the entire voltage region. In addition, the switching count can be reduced even further by fully utilizing the output current detection value.Direct space vectors are first defined, and the selection method of space vectors is described. Next, the PWM duty calculation technique is explained. Finally, the validity of the proposed method is proven from the comparison with the conventional virtual indirect method based on the experimental and analysis results.
PWM rectifiers which can realize unity power factor and sinusoidal input current have been widely investigated to overcome problems of reactive power and harmonic current in electric power systems. However, in such PWM rectifiers, an LC filter which is necessary for absorption of carrier harmonics and for reduction of commutation spike voltage may cause waveform distortion and transient oscillation of the ac input current. As a solution to these problems, a new control method introducing state feedback control of the LC filter was proposed in our previous paper. To achieve stable operation in this method, the control frequency or carrier frequency of the PWM rectifier must be higher than 5 times the resonant frequency of the LC filter. So, a method to reduce the required carrier frequency is necessary to implement high power PWM rectifiers.In this paper, a parallel connection of two bridge circuits is introduced to reduce the required carrier frequency. A new control method for the parallel connected PWM rectifiers is proposed. The main circuit configuration and inter-bridge current between the two component bridge circuits are investigated. To achieve the reduction of the required carrier frequency without affecting the controllability, a new method of generating PWM pattern is developed. The effectiveness of the proposed control method is confirmed by some experimental results employing a test system.
There is a possibility of the realization of high output power density converters by introducing flying capacitor multilevel topologies. However, as the number of the levels increases, the number of circuit components will exceed the practical limit of the implementation. Thus, from the practical viewpoint, the main circuit and related gate drive circuits including floating gate power supplies should be integrated. In this letter, charge pump circuits, already proposed for conventional 2-level converters, are extended to the floating gate power supplies for the flying capacitor multilevel converters.
A matrix converter (MC) is a three-phase AC-to-AC direct converter without any energy storage requirement. It is expected to be a next generation converter by reason of possibilities of small size and high efficiency. At present, there are some problems to prevent it from being used practically. One of the problems is the distortion in the input current. The control methods proposed so far have not realized the enough reduction of the input current harmonics compared with conventional PWM rectifiers. As a solution to these problems, many approaches have been proposed. In the present paper, an improved PWM method that can achieve both sinusoidal input and output currents simultaneously is considered. In this method, the MC is treated as a controlled voltage source viewed from the load side. On the other hand, it is treated as a controlled current source viewed from the line side. The proposed control method is based on the mathematical expression of the function of the PWM operation of MC. To improve the input current waveform, two line-to-line voltages of the three-phase line are used to control the output current. The output duty ratio of the two line-to-line voltages is utilized to improve the input current waveform without affecting the controllability of the output current. In addition, the compensation of the variations in the line voltage and the output current are introduced. In this way, the proposed method can realize the sinusoidal input and output currents. The effectiveness of the proposed control method is confirmed by some experimental results employing a laboratory prototype.
Abstract High performance power conversion requires high switching frequency power converters. Resonant dc link inverters, which are investigated in this paper, are suitable for this purpose because they cause no switching loss in principle. But in these inverters, loss of the resonant oscillation and occurrence of high peaks in the resonant capacitor voltage are serious problems. In this paper, we investigate a control method for resonant dc link inverters which can overcome these problems. First of all, we summarize the basic control principle of an ideal resonant dc link inverter. Then we present an analyzing method for the practical resonant dc link inverter introducing two equivalent circuits in which the influence of the power losses in the resonant link and in the inverter load is considered. From these equivalent circuits, the problems of existing control methods are clarified. Based on the results of this analysis, we propose an optimum and keep the capacitor voltage at an allowable level. A simple compensation method for the influence of storage time of switching devices, which affects the implementation of the proposed control method, is described. Some experimental results are included to confirm the validity of the analytical results and the effectiveness of the proposed control method.
SUMMARY Multilevel inverters have very attractive features, such as lower harmonics in the output, lower EMI, and reduction of the required voltage rating of power semiconductor devices. Among them, lower harmonics in the output can reduce the volume of the output harmonic filter and additional losses caused by the harmonics. Therefore, multilevel inverters are expected to realize higher power density and higher efficiency. In this paper, as a basis of the quantitative investigation of these features, the harmonics in the PWM output voltage of multilevel inverters are analyzed theoretically. As an application of the theoretical results, the usefulness of the theoretical results is verified by the prediction of the harmonic contents of the load current.
This paper proposes a novel commutation method that improves efficiency of bidirectional isolated AC/DC Dual-Active-Bridge (DAB) converter based on matrix converter (MC). Although some modulation methods have been proposed, characteristics of the converter in low power region have not been discussed. In this region, efficiency of converter decreases because of commutation fault, which increases stress to devices and leads to shorten lifetime of the converter. In this paper, an advanced commutation method to reduce the commutation failure is proposed. The proposed method combines current commutation and voltage commutation implemented by a simple algorithm based on the waveform of modulation signal without information of the current direction. In addition, seamless and safe operation is inherently assured owing to no requirement of change in switching operation mode. The validity of the proposed method is verified by experiment employing a laboratory prototype.
This paper proposes the use of multilevel converters to achieve a high output power density converter. Generally, high output power density converters are achieved by 2-level converters using high switching frequency operation and ultra low loss power devices. However, the higher switching frequency operation will cause several problems such as the increase in switching loss and an electromagnetic interference. Gallium Nitride (GaN) integrated multilevel converters are, for example, effective to solve the problems. Quantitative investigations are carried out for the total volume of multilevel converters, including filtering components, heat sink, dc-link capacitors, and gate-drivers. The investigations show that the multilevel converters will become excellent method to increase output power density of power converters.
Input Series Output Series (ISOS) connected Dual Active Bridge (DAB) converters have advantages in the application of bidirectional power transmission and isolation. However, it is difficult to maintain the voltage balance. In this study, the voltage balancing control method for ISOS-connected DAB converters with no auxiliary circuits is proposed. It is clarified that the voltages in not output side but input side should be controlled in heavy load. When the load is small, the controller generates a deviation on the input side DC voltage according to the stored energy. In a no-load state, a reactive power is intentionally generated in AC side of DAB to discharge the excessive voltage. The simulation and experimental results indicate that the proposed method can balance the DC voltage in bidirectional power transmission and no-load state without any additional devices.
