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This paper presents a division-summation (D-Σ) digital controlled three-phase four-leg voltage source inverter with load impedance estimation for uninterruptible power supply applications. The D-Σ digital control developed for current tracking can accommodate wide filter inductance variation, which has been successfully adopted in grid-tied applications. This paper proposes a load impedance estimation...
This paper presents a grid-connected bi-directional modular multilevel converter (MMC) with division-summation (D-Σ) digital control to achieve power injection and rectification functions. The D-Σ digital control is adopted to track current reference, regulate dc-bus voltage and cell voltage, and balance the upper and lower dc-bus voltages. It can accommodate wide filter inductance variation and take...
This study investigates the cell voltages and arm currents in double-star modular multilevel converters (DSMMCs) based on power balance and current tracking control law. DSMMCs have been widely applied to static synchronous compensators, high-voltage direct-current transmission, back-to-back power transfer systems, wind/solar power generation and battery storage systems. The size of capacitors in...
This study presents design of D-Σ digital controlled hybrid-frequency inverters with LCL filter for grid-connected applications. Hybrid-frequency inverters consist of inverters with different frequencies and power ratings connected in parallel. The lower frequency inverter has higher power rating, while the higher frequency inverter has lower one. The inverters are controlled to cancel out low-frequency...
Resonant frequency of an LCL filter in grid-connected inverters decreases with increase in inductive grid impedance. It is also affected by drop in magnetic permeability of filter inductor with increase in current. This resonant frequency variation affects grid-voltage harmonic rejection and compromises stability. Hence, an improved resonant frequency based LCL filter design method is presented in...
The natural swinging filter inductance due to core's magnetic permeability can affect control stability. Conventional control methods generally adopt larger cores to avoid this issue. Division-Summation (D-Σ) digital control, on the other hand deals with the problem by including this filter inductance variation in the control law. It allows the use of much smaller core than conventional control methods...
This paper presents a three-phase transformerless uninterruptible power supply (UPS) with sinusoidal pulse width modulation (SPWM) based division-summation (D-Σ) digital control. A transformerless UPS controls the power flow between dc link and utility grid, as well as tracks the ac reference voltage. The proposed control law derived with D-Σ digital approach takes into account the effects of dc-link...
There has been a growing demand of using multi-function inverters for grid-connected systems applied to nonconventional energy sources, such as solar, wind and so on. In addition to power quality conditioning, the inverter can also be used for bidirectional active power exchange with a three-phase four-wire grid. Therefore, the inverter acts as a multi-function compensator. The functions of the proposed...
This paper presents a comparative study of three multi-function three-phase inverters, which include three-phase three-wire full-bridge (FB) inverter, three-phase four-wire half-bridge (HB) inverter and neutral-point-clamped (NPC) inverter. Each inverter is controlled by the division-summation (D-Σ) digital control and the control law for each inverter is derived in short. The comparison among these...
This paper presents a division-summation (D-Σ) digital control based three-phase four-wire inverter with capacitor-current compensation. The inverter is adopted to uninterruptible power supply applications and can supply unbalanced, linear and rectified loads. With the proposed capacitor-current compensation scheme, the D-Σ digital control which was originally developed for current tracking can be...
A division-summation (D-Σ) digital control for three-phase inverters to achieve active and reactive power injection has been presented. It can overcome the limitation of abc to dq frame transformation. However, the D-Σ control requires four sets of control laws to cover four quadrant operations: grid connection (PF 1 ∼ ±0.866), rectification with power factor correction, PF leading (0 ∼ 0.866), and...
This paper presents an SPWM-based division-summation (D-Σ) digital control for paralleled three-phase grid-connected inverters. The proposed D-Σ control approach derives the plant, and then obtains the control gains or duty-ratio control laws to cancel the variation effects of dc voltage, switching period and inductance. With the D-Σ digital control, each inverter can track sinusoidal reference current...
This paper presents a division-summation (D-Σ) digital control applied to a three-phase active power filter (APF) with a three-leg inverter. The three-leg inverter shapes the source current sinusoidally by injecting harmonic currents to compensate the load current. The proposed D-Σ digital control approach summarizes the inductor-current variations over one switching cycle to derive control laws directly,...
This paper presents design and implementation of a 20 kVA division-summation (D-Σ) digital controlled three-phase four-wire multi-function inverter system. The inverter can be operated in grid-connected or stand-alone mode to act as a renewable-energy ac power-supply system. In the stand-alone mode, since the D-Σ digital control law includes load impedance estimation, the inverter can track sinusoidal...
ObjectivesThe aims of this study were to examine the expression of androgen receptors (AR) in oral squamous cell carcinoma (OSCC) cells and tumors and to determine the role of AR in regulating OSCC cell growth.
Materials and MethodsFour OSCC cell lines were used for analyzing AR expression and transcriptional activity. The effects of AR knockdown on the growth and tumorigenicity of OSCC cells were...
A division-summation (D-Σ) digital control can track sinusoidal reference current in four operation modes: grid-connection, rectification, PF leading and PF lagging mode. It can overcome the limitation of abc to α-β-γ frame transformation and cover wide filter inductance variation. However, the switching sequences for the four modes are different from each other, increasing complexity of firmware...
To investigate the clinical, enzymological and mitochondrial gene profiles of complex I deficiency in Chinese, clinical and laboratory data of the patients (79 boys, 54 girls) were retrospectively assessed. Activities of mitochondrial respiratory chain complexes in peripheral leucocytes were spectrophotometrically measured. The entire mitochondrial DNA (mtDNA) sequence was analyzed in 62 patients...
This paper presents an SVPWM-based division-summation (D-E) digital control for a three-phase grid-connected inverter with wide inductance variation. The proposed D-E approach summarizes all of the individual inductor-current variations over one switching cycle to derive control laws directly, which can overcome the limitation of d-q transformation. The inverter with this control can achieve the functions...
This paper presents a division-summation (D-Σ) digital control for a three-phase bi-directional photovoltaic inverter with wide inductance variation. The bi-directional inverter fulfilling grid connection and rectification with power factor correction has been implemented in the laboratory. The proposed D-Σ approach summarizes the inductor-current variations over one switching cycle to derive control...
This paper presents an optimal negative current control for four-phase interleaved bi-directional converters to achieve soft-switching features. Four-phase buck/boost converters with bi-directional operation and in discontinuous conduction mode (DCM) are designed and implemented. The optimal negative current is determined and controlled to reduce reactive power loss, while achieves ZVS and ZCS turn-on...
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