Single DC Link Research Articles

A Dual Two-Level Inverter Scheme With Common Mode Voltage Elimination for an Induction Motor Drive

Pulse-width modulated (PWM) inverters are known to generate common mode voltages which cause motor bearing currents in the induction motor drives. They also result in leakage currents which act as sources of conducted electromagnetic interference in the drive system. The common mode voltage generated by a conventional three-level inverter can be eliminated by switching only the voltage space vectors which do not produce the common mode voltage. This paper presents a PWM switching strategy to eliminate common mode voltage using the open-end winding configuration for the induction motor. The switching strategy presented in this paper, does not generate any alternating common mode voltages in the drive system and hence the electrostatic coupling of the common mode voltage, which results in the bearing currents and the leakage currents, is avoided. The proposed scheme is devoid of neutral point voltage fluctuations and does not require neutral point clamping diodes, when compared to the common mode elimination scheme based on the conventional three-level inverter topology. Also, the present scheme uses a single dc-link with half the voltage compared to the conventional three-level inverter based scheme.

Commutation Torque Ripple Reduction in Brushless DC Motor Drives Using a Single DC Current Sensor

This paper presents a comprehensive study on reducing commutation torque ripples generated in brushless DC motor drives with only a single DC-link current sensor provided. In such drives, commutation torque ripple suppression techniques that are practically effective in low speed as well as high speed regions are scarcely found. The commutation compensation technique proposed here is based on a strategy that the current slopes of the incoming and the outgoing phases during the commutation interval can be equalized by a proper duty-ratio control. Being directly linked with deadbeat current control scheme, the proposed control method accomplishes suppression of the spikes and dips superimposed on the current and torque responses during the commutation intervals of the inverter. Effectiveness of the proposed control method is verified through simulations and experiments.

Feasible enhancement of a three‐phase soft‐switching inverter with an auxiliary resonant DC link snubber

AbstractThe purpose of this paper is to improve power conversion efficiency of a three‐phase voltage source type soft‐switching inverter with a single auxiliary resonant DC link (ARDCL) snubber. First, the operating principle of an ARDCL snubber discussed here is described. Second, this paper proposes an effective pulse pattern generation method of the zero voltage space vector of the three‐phase soft‐switching inverter using IGBTs or power modules that can reduce power losses in the ARDCL snubber treated here. In particular, a zero voltage holding interval in the DC rail busline of this three‐phase soft‐switching inverter is to be regulated according to the generation method of the zero voltage space vector. Third, the maximum modulation depth Mmax under the condition of correction of the instantaneous voltage space vector can be improved by using a new zero voltage space vector generation method. Finally, the feasible experimental results of this inverter are obtained confirming the operating characteristics such as power conversion actual efficiency, as well as conventional efficiency THD and RMS value of the balanced three‐phase output voltage for an experimentally built three‐phase voltage source type soft‐switching pulse modulated inverter using the latest IGBT modules and evaluated from the standpoint of practical applications in industry UPS and new energy systems. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(1): 89–99, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10234

Feasible Enhancement of Three-Phase Soft-Switching Inverter with An Auxiliary Resonant DC Link Snubber

The purpose of this paper is to improve power conversion efficiency of three-phase voltage-source type soft-switching inverter with a single auxiliary resonant DC link (ARDCL) snubber. In the first place, the operating principle of an ARDCL snubber discussed here is described. In the second place, this paper proposes an effective generation scheme of zero voltage space vector of three-phase soft-switching inverter using IGBTs that can reduce power losses in the ARDCL snubber treated here. In particular, a zero voltage holding interval in the DC busline of this soft switching inverter is to be regulated due to, the generation scheme of zero voltage space vector. In the third place, the maximum modulation depth Mmax under the condition of compensation of space voltage space vector can be improved by using a new zero voltage space vector generation scheme. Finally, the feasible experimental results to confirm the operating characteristics such as power conversion efficiency, THD and RMS value of output voltage for three-phase voltage-source type soft-switching inverter using IGBTs is concretely implemented and evaluated from a practical point of view.

Auxiliary resonant DC link snubber assisted voltage-source soft switching inverter with space zero voltage vector generation method

The aim of the work is to improve the power conversion efficiency of a voltage-source three-phase inverter with a single active auxiliary resonant DC link snubber circuit (ARDCL). The operating principle and salient features of the ARDCL snubber circuit are described. An effective space voltage vector generation method is of proposed zero voltage vector of a three-phase soft-switching inverter, which can reduce power losses in the ARDCL snubber circuit. The zero voltage holding interval in the DC bus-line of the three-phase inverter is controlled due to the generation method of the zero voltage vector. The feasible experimental results confirm the relationship between the inverter power conversion efficiency and the proposed zero voltage vector generation method is concretely implemented and evaluated from a practical point of view.

Sensorless induction motor drive with a single DC-link current sensor and instantaneous active and reactive power feedback

This paper proposes a novel torque and speed control structure for low-cost induction motor variable-speed drives with a single DC-link current sensor. The controller is based on reconstruction of the active and instantaneous reactive power from the DC-link current without the use of a shaft sensor. An effective way of achieving tracking of set values of motor torque and flux is to base the estimation on the instantaneous active (P) and reactive power (Q). The paper proposes a way for extracting instantaneous P and Q information from the DC-link current and the pulsewidth modulation pattern. Torque and flux controllers suitable for general purpose and traction applications are proposed. The paper presents analytical considerations, straightforward design guidelines, and experimental results obtained from a traction system with a battery-fed three-phase inverter and a 7.5 kW traction motor.

A novel three-phase, current-fed ZCS-PWM converter incorporating a single resonant DC link soft commutation snubber

This paper presents a novel prototype three-phase current-fed PWM converter with a switched-capacitor-type resonant DC link commutation circuit operating with a new optimum PWM pattern strategy, designed with consideration for a low-pass filter. This converter can operate based on the principle of zero current soft-switching commutation. First, the steady-state operating principle of this converter with a new resonant DC link snubber circuit is described in relation to an equivalent operating circuit, together with the practical design procedure of the switched-capacitor-type resonant DC link circuit. Second, the three-phase current-fed PWM converter with the switched-capacitor-type resonant DC link circuit is discussed from a theoretical viewpoint based on a design example. An actively delayed time correction method to compensate distorted currents due to a relatively long resonant commutation time is newly implemented in the open-loop control scheme so as to obtain a new optimum PWM pattern. Finally, an experimental setup of this converter is demonstrated in a laboratory to confirm the zero current soft-switching commutation of this converter. Comparative evaluations between current-fed hard-switching PWM and soft-switching PWM converters are implemented from the viewpoint of PWM converter characteristics. © 2000 Scripta Technica, Electr Eng Jpn, 132(3): 57–67, 2000

Novel technique for maintaining balanced internal DC link voltages in diode clamped five-level inverters

The paper considers the problem of providing four regulated DC sources for use in a diode clamped five-level inverter. The preferred approach is to provide a single DC link supply and subdivide this into five levels using four series connected capacitor banks which have equally balanced voltages. The paper first considers the use of modified output switching strategies to redistribute energy through the DC link capacitors and maintain correct voltage balance, but concludes that this technique is restricted to outputs with a low modulation. The paper then presents a new technique whereby the voltage across each of these capacitors is maintained constant using a switching circuit: the balancer circuit. The design and control of the balancer circuit is described and its operation is validated on an 11 kW prototype vector controlled induction motor drive. Full four-quadrant operation is demonstrated. This arrangement eliminates the need for complex isolated supply arrangements typically found in multilevel drives. The balancer circuit takes the form of a fourth output leg with the addition of two inductors. This circuit is certainly viable for medium voltage drive applications.

An universal active power line conditioner

The power circuit of a general active power line conditioner (APLC) is based on series and shunt power converters that share a single DC link. In the present paper, a generic control concept for these series and shunt converters is proposed. It is based on the instantaneous real and imaginary power theory. In fact, the resulting equipment deals with the custom power and FACTS concepts. This equipment incorporates not only the compensation functions at the fundamental frequency like a unified power flow controller (UPFC), but also provides active harmonic mitigation capabilities. For these reasons, the compensator proposed here is called the universal active power line conditioner (UPLC). Simulation and experimental results are presented to confirm that the new approach has better performance than those obtained by controllers based on traditional concepts of active and reactive power.

Three phase bridge current controller with singlesensor

Control of phase currents in a three-phase voltage source inverter bridge is important for electric drives and unity power factor converters. To reduce equipment costs and overcome unequal sensor errors, the use of a single DC link current sensor is important. A new technique is described which uses redundant bridge switching states to allow current control with a DC link current sensor.