This paper presents design and implementation of power converters to emulate motor regeneration power. A new electric motor emulator (EME) model is proposed to simulate the transient phenomenon of a motor under braking. The motor is a device that converts electrical energy through magnetic energy into mechanical energy, and its response time is much slower than that of electrical power conversion. Therefore, it is possible to adopt power converters to emulate motor operation, which can be used to test a designed motor driver and can recover the driving power back to the AC grid during regular operation. In particular, this paper also presents an approach to emulating the transient behavior of a permanent magnet synchronous motor (PMSM) under braking. Simulated and experimental results are presented to verify the feasibility of the discussed design and implementation.

Soft magnetic powder cores with their high saturation flux density and low core loss are excellent alternatives for filter inductors in inverter-based applications. However, their nonlinear current-dependent inductance characteristics pose a challenge for control of grid-connected inverter with LCL filter. In this paper, the variable inductance conundrum is discussed and a modified direct digital control method based on a variable-structure inductance estimation model that takes into consideration wide nonlinear variation in both inverter- and grid-side inductances is proposed. The proposed method is shown to have better grid-voltage harmonic rejection and improved stability margins. However, investigation of stability which is conventionally based on nominal values of filter inductors cannot predict instabilities over the entire range of inductance variation. Hence, a parametric approach to conventional stability methods with a parameter space defined by variation in actual and estimated inductance is explored in this paper. The effect of line impedance on stability is also investigated with impedance-based stability criterion by considering line inductance as an additional dimension in the parameter space. A pattern in stability margins is observed due to inductance variation, with inductance at its minimum being most vulnerable to instability. Experimental results measured from a 5 kW single-phase grid-connected inverter with various LCL filters have verified the feasibility of the proposed control method. The experimental results also match the analytical results with reasonable accuracy.

The nonlinear dynamics of InAs/GaAs quantum dot lasers emitting exclusively on single lasing states, either ground or excited state, is investigated. While a laser emitting on the ground state is of importance for the development of isolator-free transmitters, lasers emitting on the excited states are essential for chaos-based applications, microwave photonics, and self-pulsating devices.

The optical feedback dynamics of two multimode InAs/GaAs quantum dot lasers emitting exclusively on sole ground or excited lasing states is investigated under the short delay configuration. Although the two lasers are made from the same active medium, their responses to the external perturbation are found not much alike. By varying the feedback parameters, various periodic and chaotic oscillatory states are unveiled. The ground state laser is found to be much more resistant to optical feedback, benefiting from its strong relaxation oscillation damping. In contrast, the excited state laser can easily be driven into very complex dynamics. While the ground state laser is of importance for the development of isolator-free transmitters, the excited one is essential for applications taking advantages of chaos such as chaos lidar, chaos radar, and random number generation.

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 this paper. A resonant frequency band is identified by considering four factors: grid-voltage harmonics, grid strength, filter inductance non-linearity and control stability boundary. The LCL parameters are then derived so that the resonant frequency remains within this identified band for a wide operating range. Division-Summation digital control method is used to elaborate the design method. Experimental results have demonstrated stability and much improved harmonic rejection under wide parameter variations.

This paper presents a three-phase back-to-back transformerless inverter for online uninterruptible power supply applications. The inverter consists of a three-phase three-wire input rectifier stage and a three-phase four-wire output inverter stage with their ground wires tied together. Both of the two stages are with sinusoidal pulse width modulation based division-summation (D-Σ) digital control....

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 for the same power rating. Non-linear model of filter inductor is used to estimate the inductance in each switching cycle. This estimate is used to achieve optimal control and no further proportionality constant parameter tuning is required. However, wide variation in both inverter-side and grid-side inductance needs to be considered with LCL filters. A modified D-Σ digital control method is presented in this paper to address this issue. The compensation term for active damping of resonance is also logically derived. Experimental results measured from a 5 kW single-phase grid-connected inverter have verified the feasibility of the proposed method.

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 switching-current ripples, and their equivalent switching frequency and dynamic response are dominated by the high switching frequency, reducing filter size. With different frequencies and power ratings, the inverters have extra power scheduling and control freedom. Moreover, with hybrid-frequency-inverter systems, it is no need to use high power high frequency switching devices. Features of smaller current ripples, passive filter size and better dynamic performance comparing to single frequency and conventional interleaved inverters are verified by simulation results.

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 scheme to extend the D-Σ digital current tracking control to voltage tracking. Output load is estimated every switching cycle so as voltage tracking error can be converted to current tracking error and compensated with a D-Σ digital controller, achieving fast tracking response and low voltage distortion. In the design and implementation, the inverter filter inductances corresponding to various inductor currents were measured at system startup and stored in a single-chip microcontroller RX62T for scheduling loop gain every switching cycle. Experimental results measured from a 10 kVA inverter have verified the analysis and discussion.

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 voltage fluctuation, grid-voltage distortion and inductance variation due to different current levels. Thus, distortion of input current and filter inductor core size can be reduced significantly. However, circulating current may flow through the common ground between the input power factor corrector (PFC) and the output three-phase four-wire inverter. The derived control law based on SPWM can suppress this circulating current and regulate output voltages tightly. Experimental results measured from a three-phase transformerless UPS have confirmed the analysis and discussion of the proposed control approach.

Similar InAs/GaAs quantum-dot lasers emitting on either the ground or excited state are studied under optical feedback. The feedback-sensitivity and dynamics of the excited-state laser are investigated and compared to that of the ground-state laser.

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 inverter system include active power injection, rectification and active power filtering (APF) (including phase power balancing). This paper presents design and implementation of a three-leg split-capacitor shunt multi-function inverter with division-summation (D-Σ) digital control. The adopted D-Σ digital control can accommodate filter inductance variation, reducing core size significantly, and its control laws can be derived directly to cancel the variation effects of dc-bus voltage, switching period and filter inductance. An average power method is adopted in this paper for determining fundamental currents at the source side. In the design and implementation, the inductances corresponding to various inductor currents were estimated at the startup and stored in the microcontroller for scheduling loop gain cycle by cycle, which can insure system stability. Measured results from a three-phase four-wire inverter have confirmed the analysis and discussion.

Unlike a dc distribution system with a three-phase inverter, the one with a single-phase inverter to regulate the dc-bus voltage will result in high voltage ripple. This paper presents dc-bus voltage regulation for a dc distribution system integrated with a single-phase bidirectional inverter. In a dc distribution system, a bidirectional inverter controls its inductor current to balance power flow and to regulate the dc-bus voltage. To reduce the line current distortion and the influence of dc-bus ripple voltage on regulation control, one line-cycle regulation approach (OLCRA) and quarter line-cycle regulation approach (QLCRA) are proposed. The OLCRA can regulate the dc-bus voltage with low ac current distortion, and the QLCRA can regulate the voltage under a fast load variation and with voltage ripple. Moreover, for enhancing the operational reliability and availability of the dc distribution system, the bidirectional inverter shifts the dc-bus voltage to different levels according to the load conditions. This shift mechanism can also reduce the possibility of entering under or over voltage protection without increasing dc-bus capacitance. In addition, the design of dc-bus capacitance for the system and the online estimation of the capacitance at the system startup and under the aging effect are proposed, which can help regulate the dc-bus voltage tightly in the long-term operation. The stability analysis of the dc-bus voltage regulation under capacitance variation is also addressed. Experimental results measured from a 5-kW system with a single-phase bidirectional inverter have verified the analysis and discussion.

Division-summation (D-Σ) digital control has been successfully applied to the single-phase bidirectional inverter with an LC filter, which can cover wide inductance variation and achieve precise inverter current tracking. However, high frequency ripple current injection to the grid cannot be avoided, and an LCL filter is therefore required. Since there typically exist grid voltage harmonics, the injected grid current will contain harmonic components due to the effect of the LCL-filter capacitor. This paper presents an extended application of the D-Σ digital control associated with a filter-capacitor-current compensation to reduce the injected grid-current harmonics. The control laws of the inverter with the D-Σ digital control and compensation approach are derived in detail, and the reduction of grid-current harmonics is analyzed. With the proposed approaches, the phase margin between the output impedance of the inverter and grid impedance can be higher than 80° from low to high frequencies, and the inverter can achieve high harmonic voltage rejection ratio up to 39th harmonic, which is relatively suitable for weak grid connection. Experimental results measured from a 5-kW single-phase bidirectional inverter have verified the feasible application of the D-Σ digital control and proposed compensation.

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 programming. In this paper, improvement of control-law derivation for D-Σ digital controlled three-phase four-wire inverter is presented. By selecting the zero crossing points of phase voltages as region transitions, the control laws and the related parameter tables for the four modes can be unified to a general form. The three-phase four-wire inverter topology can be also adopted as an uninterruptible power supply (UPS) application and it can supply unbalanced, linear and rectified loads. With the proposed load impendence estimation, the D-Σ digital control laws can be applied for voltage tracking. The switching sequences of the four modes and UPS mode are all unified to the switching pattern of the grid-connection mode. Additionally, a D-Σ transformation matrix is identified to simplify the derivation procedure of the division (D) and summation (Σ), which can obtain the control law directly. Experimental results measured from a 10 kVA inverter have verified the analysis and discussion.

This paper presents design and implementation of a dc/dc converter with division-summation (D-Σ) digital control. With the control, the converter is allowed to have wide inductance variation caused by high current flowing through inductor, and to track current reference precisely for achieving tight output voltage regulation. Moreover, the control can reduce steady-state error as compared with peak current-mode control and achieve faster dynamic response over average current-mode control. This paper also presents a precise current reference calculation to avoid sub-harmonic oscillation of inductor current under discontinuous conduction mode. Experimental results have verified the analysis and discussion.

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, namely, grid connection (power factor (PF) 1 ~ ±0.866), rectification with PF correction, PF leading (0 ~ 0.866), and PF lagging (0 ~ -0.866). Moreover, the switching sequences for the four modes are also different from each other, increasing complexity of firmware programming. In this paper, improvement of the control law derivation and region selection for the D-Σ digital control is presented. By selecting the zero-crossing points of phase voltages as region transitions, the control laws and the related parameter tables for the four modes can be unified to a general form. The switching sequences of the four modes are also unified to the switching pattern of the grid-connection mode. Additionally, a D-Σ transformation matrix is identified to simplify the derivation procedure of the division (D) and summation (Σ), which can obtain the control law directly. Measured results from a 10-kVA 3φ bidirectional inverter have been presented to confirm the improvement.

Division-summation (D-Σ) digital control has been successfully applied to the single-phase bidirectional inverter with an LC filter, which can cover wide inductance variation and achieve precise inverter current tracking. However, high frequency ripple current injection to the grid cannot be avoided, and an LCL filter is therefore required. Since there typically exist grid voltage harmonics, the injected grid current will contain harmonic components due to the effect of the LCL-filter capacitor. This paper presents an extended application of the D-Σ digital control associated with a filter-capacitor-current compensation to reduce the injected grid-current harmonics. The control laws of the inverter with the D-Σ digital control and compensation approach are derived in detail, and the reduction of grid-current harmonics is analyzed. With the proposed approaches, the phase margin between the output impedance of the inverter and grid impedance can be higher than 80° from low to high frequencies, and the inverter can achieve high harmonic voltage rejection ratio up to 39th harmonic, which is relatively suitable for weak grid connection. Experimental results measured from a 5-kW single-phase bidirectional inverter have verified the feasible application of the D-Σ digital control and proposed compensation.

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 of grid connection, rectification with power factor collection, and STATCOM by taking into account wide filter-inductance variation and grid-voltage distortion, reducing core size significantly. The control laws for achieving the desired functions are derived in detail and they are expressed in general forms for readily software programming. In the design and implementation, the inductances corresponding to various inductor currents were measured at the start-up and stored in the microcontroller for scheduling loop gain cycle by cycle. Experimental results from an 8 kVA 3φ inverter have confirmed the analysis and discussion of the proposed control approach.