Nobuyoshi Mutoh

Prediction-data-based maximum-power-point-tracking method for photovoltaic power generation systems

A new maximum-power-point-tracking (MPPT) method for a photovoltaic (PV) power generation system was studied which can efficiently generate PV power even under changing weather conditions. In order to research a method suitable for the actual photovoltaic power system, PV characteristics of the maximum power point were measured for more than six months using a PV curve tracer. The actual maximum power points vary with conditions such as the surface temperature and the quantity of solar radiation. So, relationships between the maximum power point and circuit variables such as open circuit voltage and short circuit current were examined under various conditions appearing in the PV power generation system. It was found through measurements that the relationship between the maximum power and the current that the output power was almost a linear function in the actual solar arrays, regardless of the weather conditions. The MPPT method was proposed based on the obtained findings. It was verified through simulations and experiments that the proposed method enables the solar arrays to quickly generate the maximum power as determined by weather conditions at the time.

A method for MPPT control while searching for parameters corresponding to weather conditions for PV generation systems

A method for a maximum power point tracking (MPPT) control while searching for optimal parameters corresponding to weather conditions is described in this paper. The conventional method has problems that it becomes impossible to acquire the generating power at the maximum power point in low solar radiation (irradiation) states. It was found experimentally that the maximum output power and the optimal current which gives this maximum had a linear relation in low irradiation states. The linearity is maintained in low irradiation states because the surface temperature of solar arrays is seldom changed. On the other hand, as the surface temperature changes in high irradiation states, the linearity collapses. However, assuming that there is no temperature change within several ms, the proportionality (voltage) coefficient between the maximum output and optimal current is searched for using the hill-climbing method. This procedure is done when the irradiation (mean value) is more than half the rated power. Below the mean value, the MPPT control is done based on the inherent linearity regarding solar arrays using the proportionality (voltage) coefficient obtained at the mean irradiation. The proposed MPPT method can enlarge the controllable range of the output power for lower solar radiation in comparison with the conventional method. Effectiveness of the method is verified by experiments.

Stabilizing control method for suppressing oscillations of induction motors driven by PWM inverters

A novel control method that suppresses oscillations generated when an induction motor is driven by PWM (pulse width modulated) inverters is described. The suppression is done by keeping the power direction constant throughout the period of oscillation of the negative current component of the inverter input current. This period is determined only by the frequency of the PWM signals. Because it is not affected by motor parameters, such as the number of poles or motor capacity, the gains of the regulator in the control system do not have to be adjusted, even if this method is applied to various kinds of induction motor drive systems. Experiments have proven that oscillations can be suppressed regardless of the motor type or speed. This stabilizing control is suitable for general-purpose inverters that drive various types of motors. >

New methods to suppress EMI noises in motor drive systems

New methods are studied that can suppress EMI noises, especially the common-mode current produced in motor drive systems. One is a packaging technique that forms power converters using a four-layer printed power circuit board. The other is a method based on the generation mechanism of the common-mode current which was developed from experimental analyses. It is proved by experiments that the former can effectively control the common-mode current, including radiated emissions, and the latter can suppress it without any compensators between the inverter and the motor.

A torque controller suitable for electric vehicles

A torque controller suitable for electric vehicles is studied. The controller ensures that an induction motor generates motor torque efficiently, stably and accurately. The torque control system feeds back an assumed motor torque calculated using the secondary magnetic flux and the torque current detected from current sensors of the primary currents. The motor torque is controlled by using the torque current reference determined from the generated secondary magnetic flux and the magnetizing current reference. The magnetizing current reference is determined on the basis of the torque current reference so that motor torque generation efficiency is always optimal. The magnetizing current regulator is operated according to the magnetizing current reference. This ensures the motor generates the motor torque stably even in transient states. Fundamental performance characteristics, such as response, accuracy and efficiency of the motor torque are verified by simulation and experiments. The torque controller is judged suitable for the drive system of electric vehicles.

Multilayer power printed structures suitable for controlling EMI noises generated in power converters

Electromagnetic interference (EMI) noises generated in power converters are diffused on the surface of conductors. This means influences occur from radiated EMI noises emitted from power transmission lines as well as conducted EMI noises transmitted from them. EMI noises diffusing on the surface of conductors are generally difficult to control using conventional concentrated constant theory. Thus, a new approach based on distributed constant circuit theory is needed in order to control EMI noises. A power converter structure to control EMI noises using multilayer power printed circuit technology is studied in this paper. A structure which can control EMI noises should simultaneously satisfy two conditions, i.e., one to shut down and one to attenuate EMI noises. The structure satisfying these conditions is studied through simulations using the Transmission-Line Modeling Method. The simulations show that the diffusion of EMI noises is controlled by dividing the flow of currents produced by EMI noises into the horizontal and perpendicular directions. That is, the horizontal current flow is controlled inside using the differences in the resistance produced from differences between inner and outer diameter of power transmission lines and the perpendicular current flow can be controlled by properly designing the thickness of the dielectric layer sandwiched between P-and N-power transmission lines with the symmetrical structure. Moreover, it is confirmed by simulations and experiments that the attenuation of EMI noises is affected by the width of the power transmission lines. It is expected that the results obtained in this paper can provide important rules when designing power converters with EMI noise control functions which use the multilayer power printed circuit technology.

A motor driving controller suitable for elevators

An induction motor driving controller which can improve the performance of elevators is studied. The controller has three features. Firstly, it has an energy-saving control by which the induction motor stably generates motor torque at the maximum efficiency, regardless of the number of passengers boarding the car, even if both acceleration from a standstill and deceleration from steady-state are done for any elevator. Secondly, it can suppress vertical vibrations of elevators while performing energy-saving control. Thirdly, it ensures good performance of elevators even when the source voltage is reduced due to an overload on the source sides. The controller is judged suitable for the drive system of elevators on the basis of simulations and experiments.

New methods to control EMI noises generated in motor drive systems

This paper describes methods that control electromagnetic interference noises generated in power converters (pulsewidth-modulation converter and inverter) by using power printed circuit techniques. Two kinds of differential and common-mode noises are generated in motor drive systems. A method is proposed that controls the differential mode noises by symmetrically forming the structure of the positive (P)- and negative (N)-power transmission lines of the power converter using a four-layer printed power circuit technique. Simulations done using the method show that differential mode currents appearing between the terminals of the power converters and the smoothing capacitors can be almost completely eliminated and the common-mode currents are shunted into the artificial ground plane. Another method is also proposed that controls the shunted common-mode currents so as to prevent series resonance phenomena by inserting a damping impedance between the frame of the machine and the ground. Experiments verify that the common-mode currents generated in the motor drive systems can be effectively reduced by the two proposed methods.

High-Response Digital Speed-Control System for Induction Motors

High-speed response is obtained for a vector control system by using new methods of speed control compensation, even when the secondary flux is lowered as a noise reduction measure. Moreover, simple circuits are developed which generate primary current reference signals quickly.

EMI noise controlling methods suitable for electric vehicle drive systems

Methods to control EMI noises, especially common mode currents and radiations which are generated in electric vehicle (EV) drive systems, are studied in this paper. EMI noises, including common mode currents and near magnetic fields were measured using a prototype of the EV drive systems. FFT analyses of the voltage and current appearing in the EV drive systems showed that EMI noise sources are produced by voltage fluctuations occurring at the time of switching operations and the produced noise sources cause common mode currents to flow into the ground when the body frame is connected to the ground. Moreover, the flowing common mode currents induce radiated EMI noises while the generated EMI noises are transmitted between the inverter, batteries and motors; thus the produced radiated EMI noises have an effect on nearby vehicles. A method is proposed that controls common mode currents produced in EV drive systems so as to prevent a series resonance phenomenon from occurring in common current paths formed in EV drive systems. This technique is also effective in controlling radiated EMI noises. Furthermore, in order to control radiated EMI noises, a method is proposed that cancels the surface current flowing in P and N power transmission lines between the inverter and batteries. Effectiveness of these proposed EMI noise controlling methods was verified from simulations and experiments.