Chin-Hsiung Chang

DC-bus voltage control for three-phase bi-directional inverter in DC microgrid applications

This paper presents dc-bus voltage control for a three-phase bi-directional inverter in dc-microgrid applications. The bi-directional inverter can fulfill both grid connection and rectification modes with power factor correction. The proposed control includes two approaches, one line-cycle regulation approach (OLCRA) and one-sixth line-cycle regulation approach (OSLCRA), which take into account dc-bus capacitance and regulate dc-bus voltage to track a linear relationship between dc-bus voltage and inverter inductor current. With the OLCRA, the inverter can tune the dc-bus voltage to the desired voltage accurately every line cycle, which can reduce the frequency of operation mode change and current distortion. The OSLCRA adjusts current command every one-sixth line cycle to adapt to abrupt dc-bus voltage variation. The two approaches together can prevent dc-bus voltage from dramatic change and improve the availability of the dc-microgrid without increasing dc-bus capacitance. Determination of dc-bus capacitance is also presented in this paper. Experimental results measured from a 10 kVA three-phase bidirectional inverter have verified the feasibility of the discussed control approaches.

Iterative learning control with filter-capacitor current compensation for a three-phase four-wire inverter

This paper presents an iterative learning control with filter-capacitor current compensation for a three-phase four-wire inverter, which is adopted to uninterruptible power supply (UPS) applications. It can supply unbalanced, linear and rectified loads. With the proposed iterative learning control, the steady-state error can be reduced significantly cycle by cycle, and it is allowed to have wide inductance variation, reducing core size significantly. Additionally, the compensation for the filter-capacitor current is also considered in the control, which can help to shape output voltage waveform more accurately. In the design and implementation, the inverter inductances corresponding to various inductor currents are measured off-line and tabulated into a single-chip microcontroller for tuning loop gain every switching cycle, ensuring system stability. Experimental results measured from a 10 kVA inverter have verified the analysis and discussion.

Filter-capacitor current compensation for D-Σ digital controlled single-phase bi-directional inverter with LCL filter to reduce grid-current distortion

This paper presents filter-capacitor current compensation for Division-Summation (D-Σ) digital controlled singlephase bi-directional inverter with LCL filter to reduce grid-current distortion. The single-phase bi-directional inverter allows wide filter-inductance variation and it can operate in grid-connection mode and rectification mode with power factor correction. With the D-Σ digital control, the inverter can cover wide inductance variation and can track sinusoidal inductor current reference precisely. However since there typically exist harmonic voltages, the injected grid current will contain harmonic components. With estimated filter-capacitor current compensation, the grid-current distortion can be improved significantly. Experimental results from a 5 kW single-phase bi-directional inverter have verified the feasibility of the proposed compensation approach.

Power compensation based on digital predictive current controlled three-phase bi-directional inverter with wide inductance variation

This paper presents power compensation based on digital predictive current controlled three-phase bi-directional inverter with wide inductance variation. The three-phase bidirectional inverter can fulfill both real power and reactive power compensation for ac grid. With the proposed control, the inverter can track sinusoidal reference currents precisely with unity power factor or power factors -0.5 ~ +0.5, and it is allowed to have wide inductance variation, reducing core size significantly. In the design and implementation, the inductances corresponding to various inductor currents are measured and tabulated into a single-chip microcontroller for tuning loop gain cycle by cycle, ensuring system stability. Moreover, a one-phase shift detection method for anti-islanding operation based on the proposed control is also presented. Measured results from a 10 kVA 3ø bi-directional inverter have confirmed the feasibility of the discussed control approach and detection method.

Ripple-free, single-stage electronic ballasts with dither-booster power factor corrector

A general approach to synthesizing single-stage inverters (SSIs) with power factor correction is first presented and an application example of electronic ballast with dither boost is then addressed in the paper. The proposed method is based on the concept of dither-effect from which eligible power factor corrector (PFC) cells can be generated. Existing inverters associated with proper PFC cells to form SSIs can fulfil power factor correction and its original function. In particular, many families of SSIs are developed, which have not been discussed in literature. To further reduce the system cost and size, a coupling inductor is employed to achieve ripple-free input current. A typical application of an electronic ballast with the proposed ripple-free PFC is analyzed. Simulation and measured results from the system with four GE TBX 26 W compact fluorescent lamps have demonstrated the feasibility of the proposed approach to single-stage electronic ballast applications.