摘要:

A model describing the transient turnoff behaviour of a fast-recovery power diode is derived and implemented into a simulation program for analysis of electrical networks. The modelling is based on the physical processes in the low-doped middle region of the semiconductor device, using the charge control approach and approximating the excess charge distribution by sinusoidal curves. The transient behaviour of the model is verified by experimental measurements in a chopper circuit with a MOSFET as the switching element.

DOI:10.1049/ip-b.1992.0009

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Measurements of anode current redistribution at turn-off are used to demonstrate the effect of different snubber circuit and gate drive conditions on the behaviour of a 56 mm, 1400 A, 2500 V GTO thyristor. The discussion offers a comprehensive explanation for the differences in device behaviour observed as both the turn-off gain and snubber capacitance are altered. Levels of redistribution are shown to be affected by the choice of snubber capacitance and level of snubber circuit stray inductance. Another important result shows that a low turn-off gain reduces the level of redistribution and thus allows the use of smaller snubber capacitors. Finally, it is concluded that even with continuing advances in devices manufacture, a close-coupled anode circuit design and high-performance gate drive are necessary for applications requiring a reduced snubber capacitance.

DOI:10.1049/ip-b.1992.0010

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Four half-bridge zero voltage switched (ZVS) convertor topologies are compared for offline applications in the 100–200 W range at a full-load switching frequency of 1 MHz. First, the quasi-resonant convertor (QRC) and the parallel-loaded resonant convertor (PRC) are studied. A review of the theory of circuit operation is followed by design procedures and experimental results which indicate that neither circuit provides satisfactory performance. Hence the multiresonant convertor (MRC) and series parallel-loaded resonant convertor (SPRC), which are derived from the previous topologies, are considered. Again, theoretical operation is reviewed, design procedures evolved and experimental results presented and discussed. The possibilities for increasing switching frequency are investigated for each topology and technological bottlenecks are identified. Both circuits are shown to be suitable for these applications, the MRC providing higher efficiency at the cost of wider control frequency range and poorer repeatability.

DOI:10.1049/ip-b.1992.0011

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Soft commutation (zero voltage switching or zero current switching (ZVS or ZCS)) allows high frequency operation of power static convertors, reduction of losses and parasitic interferences. The popular PWM inverter cannot naturally benefit from the soft commutation, but only slight changes are to be made to perform ZVS with a PWM inverter (equipped with its filter). A theoretical approach deals with power convertors using soft commutation and the resulting switching limits; it shows that only little restriction in the operating area is induced by these switching conditions. Experimental results on a MOSFET inverter and an IGBT inverter validate this analysis.

DOI:10.1049/ip-b.1992.0012

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Many techniques have been proposed for generating PWM waveforms for controlling AC motor drives. This paper demonstrates the practicality of generating real-time, software-based PWM waveforms using low-cost microprocessors. It uses a space vector methodology and extends the concept of a computationally efficient trapezoidal modulation strategy to more desirable sinusoidal schemes. Within the algorithm, the apportioning of null (zero) voltage vector times (during which all three output phases are equal) is identified as a degree of freedom which can be used to optimise the resultant PWM waveform. The optimisation criterion chosen here was that of minimum motor harmonic losses. The traditional space vector modulation technique, which divides the null voltage vector times equally between the two possible null states, is shown to surpass both the triangulation and the bus-clamping generation strategies when evaluated in terms of both this criterion and other practical factors.

DOI:10.1049/ip-b.1992.0013

出版商:IEE    

年代:1992

数据来源: IET

摘要:

Novel research results on control of forced-commutated cycloconvertors (FCCs)with matrix topology are summarised. The space-vector-modulation (SVM) technique for control of the 3-phase/3-phase matrix convertor is presented. The SVM technique provides FCC output voltages of any frequency, from zero to a maximum value constrained by the switching frequency, and any amplitude, up to √(3)/2 of the input voltage amplitude, without low-frequency harmonics. Time-domain-simulation results and spectral analysis of the output voltages and input currents are shown. The space-vector modulator is digitally implemented in a microprocessor system with reduced real-time computation. The switching times are precalculated offline and the results are stored in EPROMs. A multistepped switching procedure for safe control of the matrix-convertor switches is also presented. The safe-control algorithm is implemented with a sequential circuit by using a PROM lookup table. The FCC space-vector modulator is experimentally verified.

DOI:10.1049/ip-b.1992.0014

出版商:IEE    

年代:1992

数据来源: IET

摘要:

This paper deals with a doubly fed asynchronous machine (DFAM) supplied by a current-controlled cycloconvertor (CCC) at the rotor, and AC mains at the stator. A microprocessor is used to achieve control of the system by magnitude, frequency or phase shift of the output currents of the cycloconvertor. It also ensures the bank selection process. The mathematical model of the DFAM presented is based on a vectorial representation. Steady-state analysis of the CCC-fed DFAM has been carried out in the synchronous reference frame, and expressions of various output variables are developed. Performances of the drive are determined analytically. After theoretical analysis, the effect of the control parameters is investigated. Experimental results obtained show a good correlation with analytical predictions. Moreover, the range of variations of load angle must be limited to be within a certain value to verify stability conditions, and currents must not exceed the upper limits that the machine can carry.

DOI:10.1049/ip-b.1992.0015

出版商:IEE    

年代:1992

数据来源: IET

摘要:

The development of industrial excimer-and CO2TEA pulse lasers with average optical powers in the kilowatt range, requires pulsing circuits delivering average power levels of tens of kilowatt. Excitation pulses with voltage rise times in the order of 100 ns and peak voltages of more than 40 kV are required for efficient operation of the laser. To meet these requirements, primary switching must be carried out at tens of kA, at voltage levels in excess of 40 kV, and at repetition rates of several kHz. These requirements place extreme demands on the active switching elements employed in the pulser for primary pulse conversion. Traditionally, thyratrons have been used as switching elements. However, under these operating conditions, their lifetimes are drastically limited, making them not a commercially viable choice. Endeavours to overcome these limitations have led to the development of an all solid-state driven pulser. This pulser makes use of a modular, thyristor switched, pulse power supply unit for primary pulse conversion. Pulses of 40 μs duration are supplied to a four-stage series magnetic pulse compressor to transform the pulses down to 150 ns for efficient laser excitation.

DOI:10.1049/ip-b.1992.0016

出版商:IEE    

年代:1992

数据来源: IET

摘要:

ASDEX Upgrade is a diverter-type tokamak commissioned in the spring of 1991 at IPP, Garching. The highly elongated plasma (elongation factor = 1.6) requires a sophisticated plasma stabilisation system for both horizontal and vertical position control. A system of passive and active coils serves as a means of stabilising the plasma. The two active coils are powered by two 4-quadrant thyristor convertors at a power level of about 30 MVA. A digital computer study has shown that a 4-quadrant, phase-controlled thyristor convertor can stabilise the plasma position of ASDEX Upgrade. In this study, an exact model of the power supply system was used. A thyristor breaking system prevents the active coils from being overcharged by currents induced in the active coils in the event of a fast plasma disruption, where the plasma current of 2 MA decays within several milliseconds. A pyrobreaker serves as a back-up solution if the thyristor protection system fails. This supply and protection system was installed in 1989 and was tested with a dummy load until May 1990. These tests have shown satisfactory results. The final acceptance test with the original load were done in the spring of 1991.

DOI:10.1049/ip-b.1992.0017

出版商:IEE    

年代:1992

数据来源: IET