IEEE TRANSACTION ON POWER ELECTRONICS, 2017
ABSTRACT: Power Quality (PQ) improvement in distribution level is an increasing concern in modern electrical power systems. One of the main problems in LV networks is related to load voltage stabilization close to the nominal value. Usually this problem is solved by Smart Distribution Transformers, Hybrid Transformers and Solid-state Transformers, but also Dynamic Voltage Conditioner (DVC) can be an innovative and a cost effective solution. The paper introduces a new control method of a single-phase DVC system able to compensate these long duration voltage drifts. For these events, it is mandatory to avoid active power exchanges so, the controller is designed to work with non-active power only. Operation limits for quadrature voltage injection control is formulated and reference voltage update procedure is proposed to guarantee its continuous operating. DVC performance for main voltage and load variation is examined. Proposed solution is validated with simulation study and experimental laboratory tests. Some simulation and experimental results are illustrated to show the prototype device’s performance.
- Power Quality
- Power conditioning
- Power electronics
- Dynamic Voltage Conditioner DVC
- Dynamic Voltage Restorer DVR
- LV Distribution System
- Smart Grid
Fig. 1. DVC reference voltage generation block diagram.
EXPECTED SIMULATION RESULTS:
Fig. 2. Simulation – DVC operation limit update procedure under voltage – limits due to : Case 2.b) – (a) grid and minimum grid voltage, (b) PCC and PCC reference voltage, (c) load power factor.
Fig. 3. Experimental – DVC response to load variation, adding and removing the load – (a),(d) PCC voltage, (b),(e) DVC injected voltage, (c),(f) load current.
A new device concept, which goes beyond typical DVR functionalities, is presented. The proposed device is named DVC (Dynamic Voltage Conditioner), it is an active voltage conditioner able to cover both short- and fast-events, as a typical DVR, and long-events (in the grid voltage range from 0.9-1.1 p.u.). So it can perfectly satisfy modern power system DSO requirements. In particular the paper presents only the control strategy that can be adapted during steady state condition (long-events) for a single-phase DVC. Indeed, the steady state condition is not reported in literature and the single phase configuration seems to be the best economic solution for smart grid LV distribution system. The device controller, here introduced for first time, has been designed to operate with non-active power during steady state condition. So, to guarantee DVC continuous working, the paper describes a control method to generate DVC reference voltage considering its limits. Moreover, single-phase design can decrease device initial cost and it is also more compatible with LV distribution and mostly single-phase domestic loads.
Designed control method is verified by MATLAB based simulation and laboratory experimental test bed. Results show that, the device has good performance and it can improve PQ level of the installed distribution Smart Grid network effectively (mainly in the grid voltage range from 0.9-1.1 p.u.). This is essential for nowadays modern network because the proposed DVC can give flexibility to the system operator in order to move all problematic single-phase loads on a specific phase (where the DVC is installed).
Even if the paper analyzed a single-phase system, all the theoretical analysis on device limits can be extended for three phase system and it will be addressed in future works. It should be noted that, this solution since it injects the compensation voltage in quadrature to line current, creates phase shifting on installed phase voltage so, it can impose voltage unbalance issues to the supplied three-phase loads. Therefore this device can be used effectively in LV distribution network with single phase loads only.
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