EPE Association: EPE 1985 - 06 - Lecture Session 1.06: VARIOUS CONVERTER APPLICATIONS

EPE 1985 - 06 - Lecture Session 1.06: VARIOUS CONVERTER APPLICATIONS
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 1985 - Conference > EPE 1985 - 06 - Lecture Session 1.06: VARIOUS CONVERTER APPLICATIONS

   [return to parent folder]

   DC CONVERTER FOR HYDROGENERATORS STATIC EXCITATION IN A WIDE VARIATION RANGE OF THE MAINS PARAMETERS
By V. Mihaescu; M. Lungu; M. Oprisan [View]
[Download]

Abstract: The paper describes both the overall solution of the new d.c. converter meant for hydrogenerators static excitation systems and the specific supply, synchronizing gate control and protection circuits ensuring its operation within wide variation limits of the mains parameters (voltage-frequency) U= (0.2 ... 1.5) Un, f = (0.8 ... 1.6) fn, characteristic in case of failure (shortcircuits in the mains turbine racing in case of load discharge). The operation of the converter under such circumstances permits to maintain a permanent control of the hydrogenerator excitation, under failure conditions and enables the forcing of the excitation at low voltages due to electrical disturbance in the network, in order to maintain a shortcircuit current apt to trigger protection selectively, on the affected branches only, the rest of the consumers remaining energized. Such performances of the converter ensure an increased operating safety for the static excitation system and, implicitly, economic advantages for the user, limiting economic losses. by maintaining some important industrial objectives in operation.

   A FORCED COMMUTATED CYCLOCONVERTER WITH CONTROL OF THE SOURCE AND LOAD CURRENTS
By Gunther Kastner; José Rodriguez [View]
[Download]

Abstract: This paper presents a new power converter, which uses 9 bidirectional switches with turn-off capability to connect directly the three-phase source to the three-phase load. Each bidirectional switch is composed by two power MOSFET transistors working in the switching mode. The converter works with a high switching frequency and for this reason the harmonics in the load and in the source currents can be easily removed by using small filters. A novel strategy based in the special vectors formulation is used to control the load currents. A drastical reduction of the input harmonics is obtained by controlling the reactive component of the input currents. The converter acts as a controlled three-phase current source and the frequency of the fundamental component of the load current can be higher than the source frequency (50 Hz) without affecting the harmonic distortion. The input currents of the converter are practically sinusoidal and they remain in phase with the source voltage independantly of the amplitude and frequency of the output currents. The converter presents no restriction to the direction of the power flow between the source and the load and for this reason it is well suited to be used in the four-quadrant speed control of AC machines. Experimental results were obtained in the field oriented speed control of a three-phase squirrel cage induction motor. The drive exhibits a very good dynamic behaviour.

   STATIC INVERTER CONCEPTS FOR MULTIPHASE MACHINES WITH SQUARE-WAVE CURRENT - FIELD DISTRIBUTIONS
By H. Weh; U. Schröder [View]
[Download]

Abstract: Winding arrangement and wave form of the phase currents are determining factors for the effectivity of the power conversion in electric machinery. Frequency inverters employing new Semiconductor (SC) components such as GTO's and power transistors enable the realization of higher number of phases with independently controlled currents and limited amount of circuit elements. New permanent magnets and new achievements in the architecture of magnetic circuits in general lead to concepts of electrical machines with high magnetic flux densities, reduced armature reaction and high efficiency. Rectangular current shape, (spatial and depending on time) and rectangular field distribution within the pole area yield a higher rate of interaction between field and current, /1,2/. Synchronous motors with permanent magnet excitation as well as reluctance motors are particularly suitable for using multiphase windings. Frequency inverters in multiphase configuration and individually controlled phase currents together with the improved excitation scheme of machines contribute considerably to implement high performance conversion systems /2,3/.

   A REACTIVE CURRENT COMPENSATOR FOR SINGLE-PHASE MODULAR STAND-ALONE PWM-INVERTERS
By H. Kuyken; P. De Visschere; D. Baert; E. De Vleeschauwer [View]
[Download]

Abstract: This paper deals with the problem of delivering reactive power with small single-phase pulse-width modulation (PWM) inverters. Most of the basic converters being used in small inverters do not allow reverse power flow. Hence, problems are encountered when a non-resistive load is applied. During intervals when the inverter output voltage and output current have an opposite sign, energy is transferred back to the inverter. One has to provide an external path to deviate or absorb this energy, otherwise the inverter output voltage would be seriously distorted. Several solutions have already been proposed to meet this problem and most of these techniques will be discussed in this paper. With the solution we propose, inverter operations with non-resistive loads with high efficiency and small distortion are possible. An inverter of 1500 Watt, based on this principle, bas been realised in our laboratory and can handle reactive loads with power factors of 0.6 with negligible power losses.

   SINGLE PHASE PWM INVERTER WITH POWER MOSFET TRANSISTORS FOR SPEED DRIVE OF ELECTRICAL MACHINES
By A. Berthon; Pham Huu Phut [View]
[Download]

Abstract: PWM inverters are very suitable for eliminating lower frequency harmonics which generate vibrations and losses. The use of power MOSFET transistors allows good accuracy for the switching angles and the use of a microprocessor increases control flexibility of the inverter drive. The advantages and drawbacks of power MOSFET transistors have been reviewed. Then a circuit which protects these transistors against overvoltage transients has been devised. This allows to use them up to 2/3 of the transistors drain-source breakdown voltage with their normal current.

EPE 1985 - 06 - Lecture Session 1.06: VARIOUS CONVERTER APPLICATIONS
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 1985 - Conference > EPE 1985 - 06 - Lecture Session 1.06: VARIOUS CONVERTER APPLICATIONS
	[return to parent folder]

	DC CONVERTER FOR HYDROGENERATORS STATIC EXCITATION IN A WIDE VARIATION RANGE OF THE MAINS PARAMETERS By V. Mihaescu; M. Lungu; M. Oprisan	[View] [Download]
Abstract: The paper describes both the overall solution of the new d.c. converter meant for hydrogenerators static excitation systems and the specific supply, synchronizing gate control and protection circuits ensuring its operation within wide variation limits of the mains parameters (voltage-frequency) U= (0.2 ... 1.5) Un, f = (0.8 ... 1.6) fn, characteristic in case of failure (shortcircuits in the mains turbine racing in case of load discharge). The operation of the converter under such circumstances permits to maintain a permanent control of the hydrogenerator excitation, under failure conditions and enables the forcing of the excitation at low voltages due to electrical disturbance in the network, in order to maintain a shortcircuit current apt to trigger protection selectively, on the affected branches only, the rest of the consumers remaining energized. Such performances of the converter ensure an increased operating safety for the static excitation system and, implicitly, economic advantages for the user, limiting economic losses. by maintaining some important industrial objectives in operation.

	A FORCED COMMUTATED CYCLOCONVERTER WITH CONTROL OF THE SOURCE AND LOAD CURRENTS By Gunther Kastner; José Rodriguez	[View] [Download]
Abstract: This paper presents a new power converter, which uses 9 bidirectional switches with turn-off capability to connect directly the three-phase source to the three-phase load. Each bidirectional switch is composed by two power MOSFET transistors working in the switching mode. The converter works with a high switching frequency and for this reason the harmonics in the load and in the source currents can be easily removed by using small filters. A novel strategy based in the special vectors formulation is used to control the load currents. A drastical reduction of the input harmonics is obtained by controlling the reactive component of the input currents. The converter acts as a controlled three-phase current source and the frequency of the fundamental component of the load current can be higher than the source frequency (50 Hz) without affecting the harmonic distortion. The input currents of the converter are practically sinusoidal and they remain in phase with the source voltage independantly of the amplitude and frequency of the output currents. The converter presents no restriction to the direction of the power flow between the source and the load and for this reason it is well suited to be used in the four-quadrant speed control of AC machines. Experimental results were obtained in the field oriented speed control of a three-phase squirrel cage induction motor. The drive exhibits a very good dynamic behaviour.

	STATIC INVERTER CONCEPTS FOR MULTIPHASE MACHINES WITH SQUARE-WAVE CURRENT - FIELD DISTRIBUTIONS By H. Weh; U. Schröder	[View] [Download]
Abstract: Winding arrangement and wave form of the phase currents are determining factors for the effectivity of the power conversion in electric machinery. Frequency inverters employing new Semiconductor (SC) components such as GTO's and power transistors enable the realization of higher number of phases with independently controlled currents and limited amount of circuit elements. New permanent magnets and new achievements in the architecture of magnetic circuits in general lead to concepts of electrical machines with high magnetic flux densities, reduced armature reaction and high efficiency. Rectangular current shape, (spatial and depending on time) and rectangular field distribution within the pole area yield a higher rate of interaction between field and current, /1,2/. Synchronous motors with permanent magnet excitation as well as reluctance motors are particularly suitable for using multiphase windings. Frequency inverters in multiphase configuration and individually controlled phase currents together with the improved excitation scheme of machines contribute considerably to implement high performance conversion systems /2,3/.

	A REACTIVE CURRENT COMPENSATOR FOR SINGLE-PHASE MODULAR STAND-ALONE PWM-INVERTERS By H. Kuyken; P. De Visschere; D. Baert; E. De Vleeschauwer	[View] [Download]
Abstract: This paper deals with the problem of delivering reactive power with small single-phase pulse-width modulation (PWM) inverters. Most of the basic converters being used in small inverters do not allow reverse power flow. Hence, problems are encountered when a non-resistive load is applied. During intervals when the inverter output voltage and output current have an opposite sign, energy is transferred back to the inverter. One has to provide an external path to deviate or absorb this energy, otherwise the inverter output voltage would be seriously distorted. Several solutions have already been proposed to meet this problem and most of these techniques will be discussed in this paper. With the solution we propose, inverter operations with non-resistive loads with high efficiency and small distortion are possible. An inverter of 1500 Watt, based on this principle, bas been realised in our laboratory and can handle reactive loads with power factors of 0.6 with negligible power losses.

	SINGLE PHASE PWM INVERTER WITH POWER MOSFET TRANSISTORS FOR SPEED DRIVE OF ELECTRICAL MACHINES By A. Berthon; Pham Huu Phut	[View] [Download]
Abstract: PWM inverters are very suitable for eliminating lower frequency harmonics which generate vibrations and losses. The use of power MOSFET transistors allows good accuracy for the switching angles and the use of a microprocessor increases control flexibility of the inverter drive. The advantages and drawbacks of power MOSFET transistors have been reviewed. Then a circuit which protects these transistors against overvoltage transients has been devised. This allows to use them up to 2/3 of the transistors drain-source breakdown voltage with their normal current.