S.J. Chiang

Residential photovoltaic energy storage system

This paper introduces a residential photovoltaic (PV) energy storage system, in which the PV power is controlled by a DC-DC power converter and transferred to a small battery energy storage system (BESS). For managing the power, a pattern of daily operation considering the load characteristic of the homeowner, the generation characteristic of the PV power, and the power-leveling demand of the electric utility is prescribed. The system looks up the pattern to select the operation mode, so that powers from the PV array, the batteries and the utility are utilized in a cost-effective manner. As for the control of the system, a novel control technique for the maximum power-point tracking (MPPT) of the PV array is proposed, in which the state-averaged model of the DC-DC power converter, including the dynamic model of the PV array, is derived. Accordingly, a high-performance discrete MPPT controller that tracks the maximum power point with zero-slope regulation and current-mode control is presented. With proposed arrangements on the control of the BESS and the current-to-power scaling factor setting, the DC-DC power converter is capable of combining with the BESS for performing the functions of power conditioning and active power filtering. An experimental 600 W system is implemented, and some simulation and experimental results are provided to demonstrate the effectiveness of the proposed system.

A multimodule parallelable series-connected PWM voltage regulator

This paper presents the analysis and design of a single-phase voltage regulator (VR) and its multinodule parallel control. The VR employs the pulsewidth modulation three-arm rectifier-inverter topology. The inverter side adjusts the load voltage with the series regulating structure aiming to minimize converter capacity and attain higher efficiency. The rectifier side regenerates the load power and executes the active power filter function to achieve unity power factor. Based on such high-performance VR, a resistive droop method combined with the P-V droop and Q-/spl delta/ shift scheme is then proposed to control the current sharing such that multiple VRs can be paralleled directly without any control interconnection. The proposed parallel control technique possesses the features of fast response, precise voltage regulation, equal fundamental and harmonic current sharing, tolerance for parameter mismatch, and so on. Two prototype 1 KVA VRs are implemented, and the effectiveness is demonstrated by some simulation and experimental results.

Parallel control of the UPS inverters with frequency-dependent droop scheme

This paper presents a control approach for paralleling the UPS inverters with no control interconnection. The reference voltage of the inverter is generated to simulate a reactor connected between the inverter and the load at the fundamental frequency. The intention is to control the real and reactive power sharing of the inverters with the Q-V and P-/spl omega/ droop scheme without connection of a true transfer reactor. At the harmonic frequency the reference voltage turns to simulate a resistor, aiming that the load harmonic current can be shared equally and the voltage distortion is low. Two 1 kVA inverters are setup for demonstrating the effectiveness of the proposed approach.

Modeling and controller design of a current-mode controlled converter

In this paper, the reduced-order dynamic modeling and controller design of a push-pull DC-DC converter with current-mode control are presented. First, the small-signal equivalent circuit of the converter and its corresponding transfer function model are found. Then the selection of slope compensation and the model reduction are performed using the concept of dominant energy mode. Based on the reduced converter models, a quantitative design procedure is derived to find the parameters of the closed-loop controller such that the prescribed regulating specifications can be matched. Theoretic bases, the design and implementation of the proposed controller are described in detail. The performance of the converter and the validity of the proposed controller are demonstrated by some simulation and experimental results. >

Parallel operation of shunt active power filters with capacity limitation control

This paper presents a capacity-limitation technique to enlarge the power capacity that can be handled by the shunt active power filters (APFs). The capacity limited includes the reactive power as well as the amplitude of the distortion current supplied by the APFs. Under capacity-limitation control m+1 APFs supply the load reactive power with m APFs supplying their rated power and one APF supplying a fraction of its rated value. Similarly, n+1 APFs supply the load current harmonic with n APFs supplying the distortion current limited in amplitude and one APF supplying a fraction of its limited amplitude. Advantages of the proposed approach include high flexibility for extending system capacity, high reliability due to no control interconnection, reducing power capacity demand of APF, high modularity due to identical APFs, stable reactive power and harmonic current sharing and its performance is insensitive to parameters mismatch of APFs, cost-effective due to modularization, and so on. Three single-phase 1 KVA APFs are designed and implemented. The effectiveness is demonstrated by some experimental results.

Parallel operation of three-phase four-wire active power filters without control interconnection

This paper presents the parallel operation of the three-phase four-wire active power filters (APFs). Functions of the proposed APF include compensation of reactive power, harmonic current, unbalanced power and zero-sequence current of the load. The objective is to achieve unity power factor, balanced line current and zero neutral-line current. Compensation of all components is capacity-limited, cooperating with the cascaded load current sensing scheme, multiple APFs can be paralleled to share the load power without requiring any control interconnection. Besides providing the theoretic bases and detailed design of the APFs, two 6 kVA APFs are implemented. The effectiveness of the proposed methods is validated with some experimental results.

Multimodule parallel series-loaded resonant converters

The design and implementation of a multimodule parallel series-loaded resonant (SLR) converter system is presented. The SLR converter to be paralleled is operated in the n=2 discontinuous mode (DCM). Its dc analysis and dynamic modeling are made. In parallel operation, an average control technique is proposed to compensate the mismatch in current control characteristics of each parallel converter. Good dynamic and static current sharing characteristics are obtained. In addition, to obtain good output voltage regulating control performance, a design procedure is presented to find the parameters of feedback voltage controller according to the prescribed specifications. >

Robust control of current-mode controlled converters

A robust controller for multimodule current-mode push-pull power converters is presented. First, the small-signal equivalent circuit and transfer function model of the converter system are found. Then the slope compensation is selected and model reduction is performed using the concept of dominant energy mode. Based on the reduced converter models, a PI (proportional-integral) controller is quantitatively and systematically designed to the prescribed specifications. A robust controller is proposed and augmented to improve the control performance when parameter variations caused by system configuration change and by operating point shift occur. The performance of the converter and the effectiveness of the proposed controller are demonstrated by simulated and experimental results.<<ETX>>

A three-phase four-wire power conditioner with load-dependent voltage regulation for energy saving

This paper presents a multi-functional three-phase four-wire power conditioner. It can compensate the reactive power, harmonic current, unbalanced power and zero-sequence current of the load with a capacity-limitation manner. It also can regulate multiple load voltages simultaneously based on the prescribed P-V characteristics of distinct loads for energy saving. Detailed design of the controllers providing these multiple functions is presented. A 6 kVA system with the inverter regulating two different load types simultaneously is implemented. The effectiveness of the proposed techniques is confirmed through some experimental results.

H/sub /spl infin// loop-shaping controller designs for the single-phase UPS inverters

This paper proposes the H/sub /spl infin// loop-shaping approach to the design of sinusoidal output voltage tracking controllers for single-phase UPS inverters. By modeling the uncertainty in load as plant output multiplicative perturbation, two H/sub /spl infin// loop-shaping control schemes that use only a capacitor voltage sensor are presented. The first design adopts a single-loop control scheme which has the advantage of simple control structure and easy implementation. But its transient performance and robustness are not satisfactory. The second controller with a dual-loop structure, additionally employing the output of a capacitor current estimator as feedback, provides improved performance over the single-loop scheme and has the feature of low distortion, good regulating performance and insensitivitye to the variation in load. The results are verified through computer simulation and hardware experiment.