Abstract
Flying-capacitor multiplexed modulation technology is suitable for bipolar DC microgrids with higher voltage levels and higher current levels. The module combination and corresponding modulation method can be flexibly selected according to the voltage level and capacity level. This paper proposes a bipolar bidirectional DC/DC converter and its interleaved-complementary modulation strategy that is suitable for bipolar DC microgrids. The converter consists of two flying-capacitor three-level bidirectional DC/DC converters that are interleaved in parallel 90°, and then cascaded with another module to form a symmetrical structure of the upper and lower arms; the complementary modulation of the upper and lower half bridges constitutes an interleaved complementary multilevel bidirectional DC/DC converter. If the bidirectional converter needs to provide a stronger overcurrent capability, more bridge arms can be interleaved in parallel. Once n bridge arms are connected in parallel, the bridge arms should be interleaved 180°/n in parallel. In bipolar DC microgrids, the upper and lower arms should be complementarily modulated, and the input and output are isolated by the inductance. To solve the current difference, caused by the inconsistent parasitic, the voltage-current double closed-loop-control is used, and the dynamic response is faster during bidirectional operation. This paper proposes theoretical analysis and experiments that verify bipolar bidirectional DC/DC converter for high-power energy storage.
Highlights
With the high penetration of intermittent energy, such as solar and wind [1,2,3], a power electronic interface for distributed energy storage is becoming increasingly attractive
The bidirectional DC/DC converter (BDC) has many advantages: (1) the bus capacitor voltage is stabilized by the midpoint potential balance control of the rear inverter circuit; (2) the BDC is easy to combine by the pulse width modulation (PWM) sequence to achieve multiple modulations; (3) it is easy to design the control loop and suppress phase-to-phase circulation; and (4) the BDC has a strong fault tolerance ability, and failure of any one of the arms does not affect the operation of other arms
This paper proposes a bidirectional DC/DC converter (BDC) topology with multiplexed modulation high-voltage and large-capacity characteristics realized in series-parallel operation
Summary
With the high penetration of intermittent energy, such as solar and wind [1,2,3], a power electronic interface for distributed energy storage is becoming increasingly attractive. The BDCs are widely used in DC microgrids, due to their simple structure, easy expansion, and transmission power being independent of transformers [4,5,6,7] It plays a large irreplaceable role in the distributed energy storage of high voltage and high power. This paper proposes a multiplexed modulation technique of the flying capacitor DC/DC converter to meet the high-voltage and high-power requirements. The BDC has many advantages: (1) the bus capacitor voltage is stabilized by the midpoint potential balance control of the rear inverter circuit; (2) the BDC is easy to combine by the PWM sequence to achieve multiple modulations; (3) it is easy to design the control loop and suppress phase-to-phase circulation; and (4) the BDC has a strong fault tolerance ability, and failure of any one of the arms does not affect the operation of other arms.
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