Diode-clamped Circuit Research Articles

Analysis of a Three-Level Bidirectional ZVS Resonant Converter

A bidirectional three-level soft switching circuit topology is proposed and implemented for medium voltage applications such as 750 V dc light rail transit, high power converters, or dc microgrid systems. The studied converter is constructed with a three-level diode-clamp circuit topology with the advantage of low voltage rating on the high-voltage side and a full-bridge circuit topology with the advantage of a low current rating on the low-voltage side. Under the forward power flow operation, the three-level converter is operated to regulate load voltage. Under the reverse power flow operation, the full-bridge circuit is operated to control high-side voltage. The proposed LLC resonant circuit is adopted to achieve bidirectional power operation and zero-voltage switching (ZVS). The achievability of the studied bidirectional ZVS converter is established from the experiments.

Three-phase five level diode clamped inverter for AC load interfacing in DC Microgrid

In this paper, diode clamped type three-phase five-level inverter is used for AC load interfacing in DC microgrid. Multilevel inverters generate staircase voltage waveform with a series of power semiconductor switches from several layer voltage DC sources. Therefore, the output voltage waveforms in multilevel inverters can be generated at low switching frequency with high efficiency and low distortion. In two-level inverter, various pulse width modulation (PWM) strategies with high switching frequency is required to obtain a output voltage or a current waveform with a small amount of harmonic content. In existing DC microgrid, three-phase conventional two-level Sine-PWM inverter is used and so, total harmonic distortion (THD) is high. To reduce the THD and the size of AC filter and to get the quality output, diode clamped type three-phase five-level inverter is applied in this research. Level shift multi carrier Sine-PWM method is used for the diode clamped circuit topology. The output waveforms of conventional two-level inverter and diode clamped five-level inverter are measured and compared the each output waveform qualities such as voltage THD, current THD and AC filter size. The performance of five level diode clamped inverter is illustrated by PSIM software and experimental results are carried out with prototype.

Phase-Shift PWM Converter with Wide Voltage Operation Capability

A soft switching three-level pulse-width modulation (PWM) converter is presented for industrial electronics with wide voltage range operation, such as solar power or fuel cell applications. Phase shift PWM scheme is used on the input-side to accomplish the zero voltage turn-on on power switches and improve the converter efficiency. Three-level diode-clamp circuit topology is adopted in the presented circuit to lessen the voltage ratings on active devices for high voltage applications. Three sub-circuits with the different turns-ratio of transformers can be selected in the presented converter in order to achieve 10:1 (Vin,max = 10Vin,min) wide input voltage operation when compared to the conventional multilevel converter. The proposed circuit is a single-stage converter instead of two-stage converter to realize wide voltage operation. Therefore, the presented converter has less component counts. Finally, the design procedure and experiments with a 300W laboratory circuit are presented and discussed to confirm the circuit analysis and converter performance.

Improved Transformerless Grid-Tied PV Inverter Effectively Operating at Twice the Switching Frequency With Constant CMV and Reactive Power Capability

In this article, an improved single-phase transformerless inverter is presented, which obviates the leakage current issue to a great extent. The proposed solution uses the dc-bypass (H6 type) topology with a diode clamp circuit, operated by a modified unipolar pulse-width modulation (PWM) scheme. An advantage of reduced switching losses comes with the use of the modified unipolar PWM, which produces effective double switching frequency at the inverter output. Due to the PWM strategy and diode clamp circuit, the common-mode voltage (CMV) of the inverter is constant throughout the operation. Consequently, the ground leakage current is negligible even in the presence of high parasitic capacitance of photovoltaic (PV) panels. Further, the other desirable features of the grid-tied inverters, such as reactive power injection for grid stability and low-voltage ride through (LVRT) are not compromised with the proposed scheme. A combination of high efficiency, constant CMV (and hence, negligible leakage current) and reactive power feeding capability with low component count stand the proposed system out among the existing transformerless grid-tied systems. The design and working principle of the proposed system are discussed and analyzed in detail. Simulation and experiment results are included to validate the proposed solution and its merits.

A diode-clamped cascaded H-bridge STATCOM for voltage balancing of individual capacitors

This paper firstly proposes a novel topology for static synchronous compensator (STATCOM) based on diode-clamped cascaded H-bridge (DCCH) circuit. The proposed topology guarantees the voltages across each capacitor in the same phase are clamped and equal to each other through the diode-clamped circuits. The balancing process through the diode-clamped circuits is bidirectional and it is realized by diode-clamped circuits only. The amount of calculation is thus reduced and the complexity of algorithm is also lowered. The parameter of clamping inductor has a great impact on voltage balancing effect. So, this paper further proposes the parameter selection principle of inductor in diode-clamped circuit. Compared with traditional software individual voltage balancing strategy, the balancing speed of the proposed topology is improved dramatically and the balancing effect is also strengthened. Simulation and experimental results verify the parameter selection method of clamping inductor and validate the effectiveness of proposed topology in Var generation and voltage balancing of individual capacitors.

A DC-Link Voltage Self-Balance Method for a Diode-Clamped Modular Multilevel Converter With Minimum Number of Voltage Sensors

Voltage balance issue of dc-link capacitors is very important for applications of a cascade multilevel converter or a modular multilevel converter. In this paper, a novel diode-clamped modular multilevel converter (DCM <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> C) topology is proposed and a power feedback control method is developed. With the developed control strategy, the proposed diode-clamped circuit becomes a controllable closed loop which enables the capacitor voltages to be clamped by low power rating clamping diodes. The proposed topology and control strategy has quicker response and requires much fewer voltage sensors than the normally used traditional method; therefore, the system performance improvement and cost reduction are expected. Based on the proposed DCM <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> C, a novel <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> +1-level cascade multilevel topology is proposed for a cascade active power filter (CS-APF). The simulation and experimental results from the CS-APF have demonstrated and verified the effectiveness of the proposed novel topology and control method.

Implementation of a single-phase three-leg AC∕AC converter with neutral-point diode-clamped scheme

A single-phase AC/AC converter with neutral-point diode-clamped scheme is proposed. A three-leg configuration, which has a common leg between the AC/DC and DC/AC converters, is adopted to reduce the number of switching devices compared with the conventional three-level AC/AC system. The common leg is operated in both rectifier and inverter modes. The rectifier is controlled to have a constant DC-link voltage and unity input power factor. The AC side of the rectifier has a three-level PWM waveform to reduce the voltage harmonics compared with that of a two-level scheme. The hysteresis current control scheme is used in the inner control loop to track the line current command. A proportional-integral (PI) control is adopted in the outer control loop to maintain the constant DC-link voltage. In the inverter side, a sinusoidal output voltage is generated to provide a stable and clean source voltage to the critical load. The fixed-frequency current controller is adopted to generate the properly PWM waveform. The output voltage is independent of the mains voltage to provide a stable AC power source. The neutral-point diode-clamped circuit configuration is used to reduce the voltage stress of power devices. The system mode1 and control algorithm are described and analysed. Simulations and experimental results based on a laboratory prototype were performed to verify the effectiveness of the proposed control strategies.

Multi-level convertors: a real solution to medium/high-voltage drives?

Multi-level convertors are now being seen as a viable alternative to conventional two-level systems for medium to high-voltage applications (AC variable speed drives). The advantages such convertors provide are discussed and the three common topologies for multi-level inverters are reviewed: isolated H-bridge circuit, flying capacitor circuit, and diode clamped circuit.