LOAD AND SOURCE BATTERY SIMULATOR BASED ON Z-SOURCE RECTIFIER
Abstract
This paper proposes a battery simulator (BS) based on a Z-source rectifier (ZSR), with the intention of emulating the discharge or charge characteristic of an actual lithium-polymer battery with high-voltage and large-capacity. The proposed BS is used for power-testing for battery applications. The battery model combined with a Shepherd model and a Thevenin model is adopted to freely change the properties and specifications of the battery and to replicate the dynamic behavior of the battery, which is discreti zed to utilize the digital controller of the BS. The closed-loop voltage controller at the dc-side of the ZSR is designed to emulate the rapid dynamic characteristics of the battery based on small-signal methods, considering the influence of the components of the impedance network. In this paper, battery voltage control algorithm (BVCA) is also utili zed to minimi ze the voltage stress across switches while controlling two dc-side voltages within a wide range of output voltages. Simulation and experimental results are provided to verify the BS of the new feature and the proposed control method.
EXISTING SYSTEM:
As a solution to the above problems, the definition of the batter y simulator (BS), which can replaced with a real battery, is introduced in the previous literature. The BS provides the following advantages .1) Changes of the properties and specifications of the batter y are easily managed. 2) The simulation of the batter y as the load or the source is possible with the use of a one-stage simulator. 3) The development and test of complex real-time systems such as the batter y-connected power converter is available. To realize the battery-terminal voltage with a wide voltage range, the batter y-terminal voltage of the programmable dc supply needs to be extende, a conventional BS was designed with a two-stage system, where the device for the ac-dc power conversion and the dc-dc power converter for the step-down or the step-up were combined in a series. The two-stage s ystem is advantageous, since the dynamic performance of the closed-loop controlled system can be improved, and any disturbance in the grid will not affect the output voltage of the second stage without a proper decoupling method. In the one-stage solution, any disturbance in the grid should be rapidl y compensated in the closed-loop control to guarantee a proper decoupling while in the two-stage solution this disturbance will not affect the output voltage of the second stage without a proper decoupling method. However, the two-stage system that is in a series leads to a relatively low efficiency compared to one-stage system.
PROPOSED SYSTEM:
This paper proposes the BS as the source and load based on the ZSR, which is intended to emulate the discharge or charge characteristic of an actual lithium-polymer batter y. The BS is available for the bi-directional power flow. Based on smallsignal methods, the closed-loop voltage controller for the output voltage of the ZSR is designed to guarantee a fast response with no overshoot as well as system stabilit y considering the influence on the components of an impedance network. A battery voltage control algorithm (BVCA) for the ZSR with grid-connection is applied to minimize the voltage stress across switches while controlling the capacitor voltage and the output voltage of the ZSR over a wide range. For the BS, the battery model needs to reflect the I-V characteristics of the actual battery. The battery model combined with the Shepherd model and the Thevenin model is used. In addition, this paper proposes z-transform-based discretization methods using the superposition principle, since the battery model in the time domain is transformed for application to the digital controller in the z-domain
CONCLUSION
This paper presents a BS including the ZSR with bi- directional power flow for power testing for the power converter related to a batter y. To reflect the I-V characteristics of the actual batter y, a dynamic discharge or charge curve was obtained through the batter y model combined with the Shepherd model and the Thevenin model. The simulated batter y model accounts for SLPB60216216, a Dow Kokam’s model of the actual lithium-polymer battery. Also, this model can be easil y extended to other batteries with diverse properties and specifications. The object of the BS based on the ZSR allows the output voltage of the ZSR to track the charge or discharge curve of the battery derived from the batter y model. Therefore, the performance of the BS depends on the voltage controller for the output voltage of the ZSR. Since the dc-side voltage controller is associated with the Zsource impedance network, the small-signal modeling was analyzed considering the Z-source network. To replicate the rapid dynamic behavior of the battery, the design for the closed-loop voltage controller for the output voltage of the ZSR was performed by using the shoot-through duty cycle-tooutput voltage transfer function based on the above analysis. The proposed BS is responsible for grid-connection and two dc side voltage controls. For this application, the BVCA for the ZSR was utilized to minimize the voltage stress across switches. As a result, the peak value of voltage stress across the switches is 524 V, which is a decrease by 15% compared to the conventional method (i.e., the peak value of voltage stress across the switches = 616V). Simulation and experimental results are presented to verify the proposed BS and control method.
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