a laboratory model of a dual active bridge dc-dc converter for a smart user network
TRANSCRIPT
A laboratory model of a dual active bridge dc-dc converter for a smart
user network
D. Menniti, N. Sorrentino, A. Pinnarelli, M.Motta, A. Burgio and P.Vizza
M.Motta - EEEIC 2015 2
Introducing to the Smart User Network (SUN) What’s the problem? The master converter
The dual acvite bridge (DAB) coverter Basic principles Feedback control scheme
Laboratory model The test system The case for the transient stability study The implemented feedback controller for the DAB
converter Conclusion and future aim
SUMMARY
M.Motta - EEEIC 2015 3
INTRODUCING TO THE SUN
A SUN essentially is a private network connected to the LV network (the grid) by means of a bidirectional AC-DC power electronic interface (PEI). The local network of the SUN is DC-powered; the distributed energy resources (DERs), the energy storage systems (ESSs) and loads are all connected in parallel to the DC bus by means of appropriate power converters.
What’s the problem ? Fixing the voltage of the DC bus (VDC) at a constant reference value (VDCref) is a key factor for the proper operation of the SUN. The master converter takes care of this task.The paper presents a dual active bridge (DAB) converter to charge/discharge the batteries which can be operated as master converter when the SUN operates in islanded mode.
The smart user
network (SUN)
DC poweredLocal network
M.Motta - EEEIC 2015 4
BASIC PRINCIPLES OF A DAB
A DAB is an isolated bidirectional DC/DC converter composed of two full-bridge DC/AC converters and an isolation high frequency (HF) transformer which provides a step-up voltage gain, a galvanic isolation and, furthermore, a leakage inductance which is the main energy transfer element.
High frequency square voltage
Direct voltage Direct voltage
Inductor current
M.Motta - EEEIC 2015 5
A DAB CONVERTER FOR A SUN
The DAB converter which connects the battery ESS to the dc bus is a suitable substitute for operating as master converter. At this purpose a simple, conventional PI controller can be adopted to control the power converter:
The tuning of PI controller coefficients, namely Kc and Ti in (3), was performed by the traditional trial-and-error method. For the considered laboratory test, the authors tuned these coefficients assuming:- 1% steady-state accuracy;- 200 ms settling time to restore the actual Vdc to within the 3% of Vref;- overshoot/undershoot of Vdc to within the 4% of Vref.
M.Motta - EEEIC 2015 6
THE TEST SYSTEMLABORATORY TEST
To confirm the feasibility and the effectiveness of the DAB converter in controlling the dc bus voltage of a smart user network, a 400 W single-phase laboratory model was built; this model was also used to verify the good dynamic response of the DAB converter under transient condition due to a step change in power balancing.
M.Motta - EEEIC 2015 7
THE TEST SYSTEMLABORATORY TEST
VBATT V 48VH1, VH2 V 48, 480Vref V 450Kc V-1 0.0036 Ti s 0.0359R1 220R2 2000L1 uH 10L2 uH 50C1 mF 1.32C2 mF 1.10N - 10
The DAB converter incorporates the inductor L2, the high frequency transformer Tr1 and two identical ac-dc converters, namely H1 and H2.
The ac-dc converters H1 and H2 are two identical IGBT full bridge rectifiers (mod. IRAM136-3063B) with integrated gate drivers.
M.Motta - EEEIC 2015 8
THE DYNAMIC RESPONSELABORATORY TEST
At the beginning of the laboratory test, both switches S1 and S2 are closed. The DAB feedback controller is disabled and the phase shift angle φ is forced to be equal 0 whereas the amplitude of Vb is regulated so to measure a Vdc equal to about 463.20 V.
At time t1, the feedback control is activated and the DAB converter starts to compensate the error between Vdc and Vref.
M.Motta - EEEIC 2015 9
THE DYNAMIC RESPONSELABORATORY TEST
At the beginning of the laboratory test, both switches S1 and S2 are closed. The DAB feedback controller is disabled and the phase shift angle φ is forced to be equal 0 whereas the amplitude of Vb is regulated so to measure a Vdc equal to about 463.20 V.
M.Motta - EEEIC 2015 10
THE DYNAMIC RESPONSELABORATORY TEST
At time t1, the feedback control is activated and the DAB converter starts to compensate for the error between Vdc and Vref.
At time t2, the switch S2 is opened so causing a deep variation in power balancing; now, the DAB converter is the only power source in the laboratory model and it has to provide the whole load demand, including power losses.
M.Motta - EEEIC 2015 11
THE DYNAMIC RESPONSELABORATORY TEST
At time t1, the feedback control is activated and the DAB converter starts to compensate for the error between Vdc and Vref.
The good performance of the DAB converter in re-establishing the dc bus voltage at the reference value after the deep step change in power balancing is evident.
M.Motta - EEEIC 2015 12
CONCLUSION AND FUTURE AIM
In this paper the application of a dual active bridge (DAB) converter in smart user network (SUN) has been presented. The DAB converter has been investigated using a 400W laboratory model of a SUN.
The laboratory results have demonstrated that the DAB converter provides a high level of reliability and resilience against disturbances, safeguarding the SUN even against a sudden disconnection of the SUN itself from the grid. Indeed, when disconnection occurred, the dc bus voltage slightly decreased with respect the reference, converging again to the reference in a short settling time.