Shigeta Ueda

A Current Source GTO Inverter with Sinusoidal Inputs and Outputs

With the application of gate turn-off thyristors (GTOs) and PWM control techniques, a current source inverter capable of producing sinusoidal input/output (I/O) voltages and currents has been developed. The sinusoidally modulated current is fed to the GTOs in the rectifier and inverter sections. The overvoltage-absorption capacitors connected to the ac input and output terminals function as a filter and, consequently, the waveforms of the input/output voltages and currents become sinusoidal. Because the PWM control utilizes the high-speed switching characteristics of the GTOs, the dc link current smoothing reactor and the overvoltage absorption capacitors are greatly reduced. The dc link voltage in the rectifier section is controlled to adjust the ac motor current. This is accomplished by using the firing angle shift method in conjunction with the method involving varying the width of the bypass gate pulses, which put the rectifier section into a bypass state. The current source GTO inverter is used to drive an 11-kW induction motor. As a result, excellent acceleration and deceleration characteristics are obtained, which verifies that the new current source inverter is quite suitable for driving an ac motor at variable speeds.

A New Current Source GTO Inverter with Sinusoidal Output Voltage and Current

A new current source inverter with sinusoidal output voltage and current is presented. Gate turn-off thyristors (GTOs) and pulsewidth modulation (PWM) control techniques are used in the current source inverter to produce the sinusoidal output voltage and current. Three capacitors are connected to the ac output terminals to absorb overvoltages which occur when the GTO current is cut off and to provide a filter function for reducing harmonics in the output current. Voltage spikes, which have been a serious problem in the practical application of this inverter, are suppressed by adding gate pulses which force the inverter into a state of shoot-through. Moreover, this inverter permits the capacitance of an ac output terminal capacitor for absorbing overvoltages to be reduced to one-tenth or less of that of a commutating capacitor in a conventional thyristor type current source inverter. A 3.7-kW induction motor is driven by the inverter. The motor efficiency and noise level are measured and compared with those obtained when the motor is driven by a conventional voltage source PWM inverter. An operating efficiency five or six percent higher and noise level 10 dB lower are obtained for the former. Therefore, this current source GTO inverter is very suitable for ac motor variable speed drives.

Magnetic noise reduction technique for an AC motor driven by a PWM inverter

A technique for reducing magnetic noise from an AC motor driven by a pulsewidth modulation (PWM) inverter is proposed. In this technique, the meaningless magnetic noise is converted into selected information. The technique can be adopted independently of the inverter rated output power. The relationship between carrier waveform frequency in PWM control and harmonics contained in the motor current is first clarified by a harmonics analysis. Then a hardware circuit configuration and carrier frequency control software in a microcomputer are introduced. Using a musical melody as the selected information, the effect of this control is experimentally confirmed. It is shown that the desired sound can be obtained from the AC motor, and the motor voltage and motor current waveforms are not affected by such control. >

Minimum harmonics PWM control for a self-commutated SVC

To maintain voltage stability in electric power systems, self-commutated static VAr compensators (self-commutated SVCs) employing high power gate turn-off thyristors (GTOs) have been developed. This paper presents a lower harmonic two-pulse PWM control technique which can decrease the harmonics in output voltage by selecting switching angles. Because of the lower GTO switching frequency, high efficiency power converters can be obtained. The decreased harmonics by the proposed PWM control were confirmed by numerical analysis and experiments using small-scale equipment. The technique has been applied to a 50 MVA self-commutated SVC which has been installed in the Shinshinano substation of Tokyo Electric Power Company, and field testing of this equipment is now in progress.<<ETX>>

Active-gate-control for snubberless IGBTs connected in series

High-voltage IGBT power converters require IGBT series connection. To reduce the converter loss and simplify converter configuration, snubber circuits should be omitted. The authors have developed a technique for snubberless IGBT series connection by means of active-gate-control. Under the developed active-gate-control, the gate-voltage are set to increase with collector-voltage of each IGBT. The increased gate-voltage decreases IGBT impedance and limits the collector-voltage. The collector-voltages of the IGBTs connected in series can be balanced by clamping the collector-voltage of each single IGBT independently. Under the active-gate-control, the collector-voltages are directly converted to gate-voltage references, and the gate is charged before the collector-voltage reaches the clamping voltage. So the active-gate-control is so fast that the surge voltages at the recovery state can be clamped. Under the control the clamping voltage increases with increasing turn-off current and it is saturated at larger currents. By increasing the clamping voltage with increasing turn-off current, the increase of turn-off loss caused by collector-voltage clamping can be limited. Moreover saturating the clamping voltage at further higher currents prevents overvoltage failure.

A large capacity GTO inverter with low-loss snubber circuits

A large capacity inverter using high power gate turn-off (GTO) thyristors which can be used instead of a cycloconverter in AC drives is presented. With the techniques of multiple configuration and GTO series connection, the inverter capacity is increased effectively. High conversion efficiency is obtained by using low-loss snubber circuits using energy recovery units (ERUs) have good performance in PWM operation. High energy recovery efficiency is obtained, especially in leading operation (turn-on operation when free-wheeling diode conducts). These snubber circuits have the superior ability for clamping overvoltage at GTO turn-off.<<ETX>>

Control Strategies of a Hybrid Multilevel Converter for Expanding Adjustable Output Voltage Range

This paper proposes a new arrangement and new control strategies for a hybrid multilevel converter aiming at a high power high efficiency converter system with being free from harmonic distortion of the output. The strategies enable one to expand the adjustable output voltage range up to 100% with keeping very low harmonic distortion of the output voltages. The triangular-carrier based PWM and space-vector based PWM strategies are applied to the voltage control. Effectiveness is verified by simulation and experimental results. The proposed hybrid multilevel converter is applicable to medium voltage networks as a high power grid-interface converter.

A triple redundant controller which adopts the time-sharing fault recovery method and its application to a power converter controller

A novel fault recovery method, in which memory copy from a normal system to a fault detected system is executed in time-sharing fashion, has been implemented in a triple redundant controller. This method reduces data copy bandwidth required for recovery of the fault detected system, and allows non-stop fault recovery with only a little hardware overhead, even when the controller contains multiple processors and operates at a very short operating period. The developed controller contains triplicated processing units, each of which consists of seven 60 MIPS processor boards connected by a 30 MHz 4 byte bus. One processor board contains a bus arbiter, and each of the remaining six processor boards contains three sets of 100 Mbps two-way optical links, which can be utilized for inter-system memory copy as well as for connecting to 10 units. This controller has been applied to a power converter controller, and a 104 microsecond operating period was achieved.

A Hybrid Multi Converter System Having Full Adjustable Output Voltage Range

This paper proposes a new arrangement and new control strategy for a hybrid multi-converter system. It consists of two GTO converters and a neutral-point-clamped IGBT converter connected in series. A bulky and expensive transformer with phase-shifted secondary windings, which the original arrangement required, is not necessary. Phase-difference control between the two GTO converters is proposed and it expands the adjustable output voltage range up to 100%. Phase-difference control however increases harmonic distortion of the output voltage. Third-harmonic injection to a sinusoidal reference is also proposed to reduce the harmonic distortion. Finally, the effectiveness is verified by simulation and experimental results.

PWM control method of multiple inverters for Maglev

A new pulse width modulation (PWM) strategies in a current and speed control circuit for multiple inverters employing large capacity gate turn-off (GTO) thyristors assuming a magnetically levitated transportation system (Maglev) as a load is presented. To realize the strategies, the necessity of the dead-time compensation scheme is also explained. Simulated results and experimental results of small model multiple inverters and a synchronous motor with multi-CPU constructed control circuits are presented.<<ETX>>