전기버스 급속충전기의 PI-IP 혼합 제어기를 이용한 AC/DC 컨버터 DC-Link 전압 제어에 관한 연구 = A Study on AC/DC Converter DC-Link Voltage Control Using PI-IP Hybrid Controller of EV Bus Fast Charger
A Study on AC/DC Converter DC-Link
Voltage Control Using PI-IP Hybrid
Controller of EV Bus Fast Charger BY Gyu-Nam Yang
Department of Electrical Engineering
Graduate School, Chonnam National University
(Supervised by Professor Sung-Jun Park)
(Abstract)
The supply of electric vehicles (xEVs) in the transport sector is increasing in
response to the global demand for reducing carbon dioxide emissions. However,
due to the gradual slow dissemination, the emission is rather difficult, increasing
every year. The reasons for this include a relatively high price compared to an
internal combustion engine vehicle, limiting the driving range on a single charge,
and insufficient charging station. In such a situation where the spread is slow, the
method of preferentially eco-friendly public transportation, which has a higher
usage rate than passenger cars, is being accepted.
In particular, EV buses, which account for a large portion of public
transportation, are rapidly spreading. Accordingly, there is a growing demand
for the introduction of a large-capacity fast charger that can charge a battery
of several hundred kW within 30 minutes. In general, the structure of a fast
charger consists of an AC/DC converter and a 2-stage of an isolated DC/DC
converter. AC/DC converter converts system 3-phase AC power to DC power
and improves power factor. The isolated DC/DC converter uses the rectified
DC output to control the voltage and current required by the EV bus battery
to directly charge the battery.
AC/DC converters have several topologies. Among them, the fast charger for
charging is a 3-level converter, and the Vienna Rectifier has many advantages.
However, the Vienna Rectifier is a unidirectional converter and it is difficult
to control during no-load or light-load operation. In particular, there is a
disadvantage in that it is unstable during initial operation and when the battery
is fully charged. Several methods have been proposed to solve this problem.
Burst mode control [1,2], which is a representative method, has a problem in
that it adversely affects the performance of the secondary-side converter and
the battery being charged due to the large DC-Link voltage ripple. As another
method, a control method with a hysteresis loop was reviewed [3], However,
the problem of induced high inrush current is not effectively improved.[4]
Therefore, in this paper, hardware configuration and voltage control
method for stable control of Vienna Rectifier are presented. Vienna Rectifier
is a unidirectional converter characteristic, but there is instability of control
under light load conditions. Accordingly, we propose a hardware configuration that
can reduce losses by using it as a system power source instead of a conventional
dummy resistor. In addition, the existing PI controller has a large transient
state due to its quick response when a sudden load change occurs, and the
recovery of the steady state may be delayed in the Vienna Rectifier. To
solve this problem, In order to secure reliability in the entire load section,
we propose a voltage control method that determines the setting parameters
of the PI-IP hybrid controller using the load current. The proposed method
proved the validity of the hardware configuration and control algorithm of
Vienna Rectifier presented through PSIM simulations and experiments.
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