Sangsun Kim

Development of a low cost fuel cell inverter system with DSP control

In this paper, the development of a low cost fuel cell inverter system is detailed. The approach consists of a three-terminal push-pull dc-dc converter to boost the fuel cell voltage (48V) to /spl plusmn/200 VDC. A four switch [insulated gate bipolar transistor (IGBT)] inverter is employed to produce 120-V/240-V, 60-Hz ac outputs. High performance, easy manufacturability, lower component count, safety and cost are addressed. Protection and diagnostic features form an important part of the design. Another highlight of the proposed design is the control strategy, which allows the inverter to adapt to the requirements of the load as well as the power source (fuel cell). A unique aspect of the design is the use of the TMS320LF2407 DSP to control the inverter. Two sets of lead-acid batteries are provided on the high voltage dc bus to supply sudden load demands. Efficient and smooth control of the power drawn from the fuel cell and the high voltage battery is achieved by controlling the front end dc-dc converter in current mode. The paper details extensive experimental results of the proposed design on Department of Energy (DoE) National Energy Technology Laboratory (NETL) fuel cell.

Analysis and design of a new voltage sag compensator for critical loads in electrical power distribution systems

In this paper a new voltage sag compensator for powering critical loads in electric distribution systems is discussed. The proposed scheme employs a PWM AC-AC converter (4 IGBTs per-phase) along with an autotransformer. During a disturbance such as voltage sag, the proposed scheme supplies the missing voltage and helps in maintaining rated voltage at the terminals of the critical load. The approach does not employ any energy storage components such as bulk capacitors/inductors and provides fast response at low cost. Under normal conditions the approach works in by-pass mode, delivering utility power directly to the load, this method of control allows the transformer to be rated only for transient conditions, thus reducing its required size. A four-step switching technique to drive AC-AC converter is employed to realize snubber less operation. A design example is presented, simulation results are shown for a three-phase, 230 V, 5 kVA system. Experimental results on a single phase unit are discussed. The proposed approach can be easily integrated into a distribution transformer supplying critical loads.

Control of multiple single-phase PFC modules with a single low-cost DSP

In this paper, a new control scheme is proposed for controlling multiple single-phase power factor correction (PFC) modules with a single low-cost digital signal processor (DSP). The proposed scheme allows for multiple PFC modules of different current ratings to be operated in parallel and controlled via a single DSP. The DSP based control handles simple current sharing and provides size reduction. The paper describes a current sense technique for each PFC module and a closed loop control algorithm for the output voltage and input current control for operating multiple modules. In the example design, the switching frequency was set at 120 kHz and two continuous conduction mode (CCM) PFC stages were operated in parallel and controlled via a single TMS320LF2407 DSP. Experimental results show that the proposed scheme is capable to be used for modern switching power supplies.

A parallel-connected single phase power factor correction approach with improved efficiency

In this paper, a new parallel-connected single phase power factor correction (PFC) topology using two flyback converters is proposed to improve the output voltage regulation with simultaneous input power factor correction and control. This approach offers lower cost and higher efficiency by parallel processing of the total power. Flyback converter-I primarily regulates output voltage with fast dynamic response and processes 55% of the power. Flyback converter-II with ac/dc PFC stage regulates input current shaping and PFC, and processes the remaining 45% of the power. This paper presents a design example and circuit analysis for 200 W power supply. A parallel-connected interleaved structure offers smaller passive components, less losses even in continuous conduction inductor current mode, and reduced volt-ampere rating of dc/dc stage converter. TI-DSP, TMS320LF2407, is used for implementation. Simulation and experimental results show the performance improvement.

A new hybrid active power filter (APF) topology

In this paper, a new hybrid active power filter topology is presented. A higher-voltage, low-switching frequency IGBT inverter and a lower-voltage high-switching frequency MOSFET inverter are used in combination to achieve harmonic current compensation. The function of the IGBT inverter is to support utility fundamental voltage and to compensate for the fundamental reactive power. The MOSFET inverter fulfils the function of harmonic current compensation. To further reduce cost and to simplify control, the IGBT and MOSFET inverters share the same DC-link via a split capacitor bank. With this approach, harmonics can be cancelled over a wide frequency range. Compared to the conventional APF topology, the proposed approach employs lower DC-link voltage and generates less noise. Simulation and experimental results show that the proposed active power filter topology is capable of compensating for the load harmonics.

Three-phase active harmonic rectifier (AHR) to improve utility input current THD in telecommunication power distribution system

Modern telecommunication power supply systems have several parallel connected switch mode rectifiers to provide -48 V DC. Typical switch mode rectifier configuration includes a three phase diode rectifier followed by a DC-DC converter. Such a system draws significant harmonic currents for the utility resulting in poor input power factor and high total harmonic distortion (THD). In this paper, a three phase active harmonic rectifier (AHR) scheme is proposed. In AHR scheme, a diode rectifier module is replaced by 6-IGBT PWM rectifier to supply load harmonics as well as its own active power. Each DC-DC converter module is connected to a shared 48 V dc-link. The AHR module together with parallel connected switch mode rectifiers is controlled to achieve clean input power characteristics. The VA ratings of AHR scheme is compared with an active power filter (APF) approach. The control design is based on the synchronous reference frame approach. Analysis, simulation and experimental results show that AHR offers several advantages such as lower VA rating, better current control response, efficient use of AHR dc-link, small size, and stable dc-link voltage control.

Control of multiple single phase PFC modules with a single low-cost DSP

In this paper, a new control scheme is proposed for controlling multiple single-phase power factor correction (PFC) modules with a single low-cost digital signal processor (DSP). The proposed scheme allows for multiple PFC modules of different current ratings to be operated in parallel and controlled via a single DSP. The DSP based control handles simple current sharing and provides size reduction. The paper describes a current sense technique for each PFC module and a closed loop control algorithm for the output voltage and input current control for operating multiple modules. In the example design, the switching frequency was set at 120 kHz and two continuous conduction mode (CCM) PFC stages were operated in parallel and controlled via a single TMS320LF2407 DSP. Experimental results show that the proposed scheme is capable to be used for modern switching power supplies.

Control strategies for active power filter in three-phase four-wire systems

In this paper, new control strategies for an active power filter (APF) under balanced and unbalanced load conditions in three-phase four-wire power systems are presented. A reference current generator is designed and space vector modulation (SVPWM) is employed to eliminate harmonic currents in each phase and in the neutral line along with compensation to the reactive power. A per-phase harmonic reference generator (PPHRG) is shown to increase the performance. DC bus voltage control is achieved by compensating the per-phase error on a-b-c axis frame. In the proposed approach, zero state vectors are suitably modified during unbalanced load conditions to achieve better performance. Simulation results show that the active power filter is capable of compensating the load harmonics and the reactive power in three-phase four-wire system.

A modular single-phase power-factor-correction scheme with a harmonic filtering function

Power supply systems in telecommunication applications employ several parallel-connected AC-to-DC and DC-to-DC power converters. Such a system offers modularity, redundancy, and is easily scalable to higher power levels. Such parallel-connected systems normally consist of several single-phase power-factor-correction (PFC) stages connected to the same input utility. In this paper, a modular single-phase PFC scheme with an integrated harmonic filtering function is presented. The proposed approach demonstrates that, with suitable modifications to the PFC control, harmonic filtering capability can be added. In other words, the PFC stage can compensate for harmonics generated by other rectifier loads connected to the same AC input terminals. The paper presents an example employing three AC-DC rectifier stages with only one AC-DC rectifier stage with PFC capability. It is shown that one PFC stage with the proposed control can compensate for harmonics generated by the other two uncompensated rectifier stages. Results from a laboratory prototype system demonstrate that the overall system meets the EN 61000-3-2 harmonic limits.

Three phase active harmonic rectifier (AHR) to improve utility input current THD in telecommunication power distribution system

Modern telecommunication power supply systems have several parallel connected switch mode rectifiers to provide -48 V DC. Typical switch mode rectifier configuration includes a three phase diode rectifier followed by a DC-DC converter. Such a system draws significant harmonic currents for the utility resulting in poor input power factor and high total harmonic distortion (THD). In this paper, a three phase active harmonic rectifier (AHR) scheme is proposed. In AHR scheme, a diode rectifier module is replaced by 6-IGBT PWM rectifier to supply load harmonics as well as its own active power. Each DC-DC converter module is connected to a shared 48 V dc-link. The AHR module together with parallel connected switch mode rectifiers is controlled to achieve clean input power characteristics. The VA ratings of AHR scheme is compared with an active power filter (APF) approach. The control design is based on the synchronous reference frame approach. Analysis, simulation and experimental results show that AHR offers several advantages such as lower VA rating, better current control response, efficient use of AHR dc-link, small size, and stable dc-link voltage control.