This paper presents a 4 kW, 450 kHz voltage-source inverter with a series resonant circuit for induction melting applications, which is characterized by the power control based on pulse density modulation (PDM). The pulse-density-modulated inverter makes an induction melting system simple and compact, thus leading to higher efficiency. A modulation strategy is proposed to realize the induction melting system capable of operation at the frequency and power level of interest. Some interesting experimental results are shown to verify the validity of the concept.
This paper deals with the effect of inner current control loops on the system performance of a position-sensorless interior permanent magnet (IPM) motor drive system. The position estimation method applied to the motor drive system has been proposed by the authors. Some simulation results show that the inner current loops integrated in the control system make it possible to suppress interference between the q-axis voltage and the d-axis current, thus leading to significant improvements in the stability of position control. Furthermore, this paper discusses a simulation method using the so-called "variable-sampling-time discrete-time system" available in MATLAB/Simulink. The simulation method is intended for the position-sensorless IPM motor drive system including a digital-controlled PWM inverter.
No abstract is provided for this article.
This paper presents an intensive discussion on a long-distance high-voltage direct-current (HVDC) transmission system that combines two modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC) with dc power cables. Hereinafter, a single MMCC-DSCC is referred to as a DSCC converter or just as a DSCC for the sake of simplicity. The HVDC transmission system is required to provide low-voltage-ride-through (LVRT) capability to enhance transmission system availability. This paper proposes a new LVRT method without any direct information exchange between the two DSCC converters. The validity of the method is verified, using simulated waveforms from the software package of “PSCAD/EMTDC” and experimental waveforms from a three-phase 200-V, 400-Vdc, 10-kW, 50-Hz downscaled HVDC system with a set of 300-meter-long dc power cables.
SUMMARY This paper discusses power flow analysis and DC capacitor voltage regulation of a modular multilevel cascaded converter (MMCC) based on double‐star chopper cells (DSCC). This analysis reveals the relationship between the circulating current through the DC link and the average power flowing out of or into each chopper cell. The DC component of the circulating current supplies half the active output power to the upper and lower strings of the chopper cells, while in contrast the fundamental frequency component transfers an amount of power between the upper and lower strings. Thus, the MDCC–DSCC can balance the capacitor voltages among the cells by controlling the amplitude of the fundamental frequency component of the circulating current. A new control method based on power flow analysis is employed, and its effectiveness is verified by circuit simulation.
A novel design concept of an interphase reactor in a three-phase twelve-pulse thyristor rectifier is proposed for reducing supply current harmonics. This concept requires only an interphase reactor with a small inductance value, and requires no additional switching devices. As the inductance value is decreased, the supply current approaches a sinusoidal waveform, which is more sinusoidal than that of a 36-pulse thyristor rectifier. The basic principle of the proposed concept is discussed in detail, and confirmed by using digital computer simulation. Experimental results verify the effectiveness and practicability of the proposed design concept of the interphase reactor.
This paper proposes a new harmonic current-free ac/dc power conversion system characterized by the integration of a small-rated series active filter with a large-rated doubleseries diode rectifier.The dc terminals of the active filter are directly connected in parallel with those of the diode rectifier, thereby forming a common dc bus.The active filter enables the diode rectifier to draw three-phase sinusoidal currents from the utility.In addition, it can provide the supplementary value-added function of regulating the common dc-bus voltage to a limited extent of 65%, slightly increasing the rms voltage rating, but not increasing the peak voltage rating.Experimental results obtained from a 5-kW laboratory system verify the practical viability and cost effectiveness of the proposed system. Index Terms-Diode
This paper presents a modular multilevel cascade converter based on double-star chopper-cells (MMCC-DSCC) intended for its applications to a STATic synchronous COMpensator (STATCOM). The DSCC is characterized by cascade connection of multiple bidirectional chopper-cells per leg, thus leading to flexible circuit design, low voltage steps, low voltage harmonics, and low EMI emissions. However, no paper has been published on its application to STATCOMs with experimental verification. This paper designs, constructs, and tests a 200-V 10-kVA STATCOM based on the DSCC with focus on steady-state and transient-state performance as well as startup performance. Experimental results verify that it can start up by itself without using any auxiliary circuit, and that it achieves controlling the same amount of negative-sequence reactive power as the converter capacity.
The guidelines for harmonic mitigation, announced on Oct. 3, 1994, are currently applied on a voluntary basis to control harmonic levels and promote better practices in both power systems and equipment design. In general, individual high-power consumers and low-power end-users are responsible for limiting current distortion produced by power electronics equipment, while electric power companies or utilities are responsible for limiting voltage distortion at the point of common coupling in distribution systems. The purpose of conventional shunt active filters, which have already been installed in the vicinity of one or more harmonic producing loads, is to compensate for harmonic currents caused by the identified loads.This paper deals with control strategy and site selection of a shunt active filter which will be installed on a power distribution system by electric power companies. The major objective of the shunt active filter discussed is to damp, harmonic resonance between many capacitors for power factor improvement and line inductors in the distribution system, rather than to mitigate voltage distortion. This paper also proposes a basic concept of the best point of installation of the shunt active filter. Simulated results are shown to verifly the validity and effectiveness of the concept. The computer simulation developed in this paper is characterized by the use of a model for a virtual distribution system of a residential area.
This paper describes start-up and low-speed operation of an electric motor driven by a modular multilevel cascade inverter based on double-star chopper cells. This paper proposes a square-wave method to suppress the peak circulating current. The theoretical analysis developed in this paper reveals that the peak circulating current when using the square-wave method gets smaller by 50% than that when using the sinusoidal-wave method proposed in the previous work. The experimental results obtained from a 400-V 15-kW downscaled system verify that stable operation is achieved at an ultralow speed of 17 min <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with a load torque of τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> = 40%, as well as "three-phase" dc-current feeding operation. Moreover, the motor can start up from a standstill without producing any overvoltage or overcurrent.
No abstract is provided for this article.
A novel approach to compensate for harmonics in power systems is proposed. The approach differs from conventional passive and active filters in its compensation principle. A practical system configuration to implement the approach is presented. It consists of a small-VA-rating PWM (pulsewidth-modulated) converter and a passive filter. The compensation principle is described, and compensation characteristics are examined theoretically and experimentally. The practicability and validity of the approach are experimentally demonstrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
This paper describes a 6.6-kV adjustable-speed motor drive for pumps and blowers without transformer. The power conversion system consists of a front-end diode rectifier, a five-level diode-clamped pulsewidth modulation (PWM) inverter with a voltage balancing circuit, and a hybrid active filter for harmonic-current mitigation of the diode rectifier. The control of the inverter is characterized by superimposing a third-harmonic zero-sequence voltage on each of the three-phase reference voltages to achieve the so-called overmodulation and reduce the switching stress of insulated gate bipolar transistors (IGBTs). A 200-V 5.5-kW downscale model is designed, constructed, and tested with focus on the five-level PWM inverter and the voltage balancing circuit. Experimental results obtained from the 200-V downscale model verify the viability and effectiveness of the 6.6-kV adjustable-speed motor drive, showing that the four split dc capacitor voltages are well balanced in all the operating conditions and that the switching stress of the IGBTs is reduced at low modulation indexes.
