FTEEE-1677 Secondary-Side-Regulated Soft-Switching Full-Bridge Three-Port Converter Based on Bridgeless Boost Rectifier and Bidirectional Converter for Multiple Energy Interface – IEEE EEE Project 2016-2017

FTEEE-1677 Secondary-Side-Regulated Soft-Switching Full-Bridge Three-Port Converter Based on Bridgeless Boost Rectifier and Bidirectional Converter for Multiple Energy Interface – IEEE EEE Project 2016-2017

ABSTRACT:

A systematic method for deriving soft-switching three-port converters (TPCs), which can interface multiple energy, is proposed in this paper. Novel full-bridge (FB) TPCs featuring single-stage power conversion, reduced conduction loss and low voltage stress are derived. Two non-isolated bidirectional power ports and one isolated unidirectional load port are provided by integrating an interleaved bidirectional Buck/Boost converter and a bridgeless Boost rectifier via a high frequency transformer. The switching bridges on the primary side are shared, hence the number of active switches is reduced. Primary-side pulse width modulation and secondary-side phase shift control strategy are employed to provide two control freedoms. Voltage and power regulations over two of the three power ports are achieved. Furthermore, the current/voltage ripples on the primary-side power ports are reduced due to the interleaving operation. Zero-voltage-switching and zero-current-switching are realized for the active switches and diodes, respectively. A typical FB-TPC with voltage-doubler rectifier developed by the proposed method is analysed in detail. Operation principles, control strategy and characteristics of the FB-TPC are presented. Experiments have been carried out to demonstrate the feasibility and effectiveness of the proposed topology derivation method.

STORAGE battery capable of long-term energy buffering has been a critical element in renewable power systems due to the intermittent nature of sustainable energy. Renewable energy power systems need to interface several energy sources such as photovoltaic (PV) array, fuel cells with the load along with a battery backup. A three-port converter (TPC) finds applications in such systems, because it has multiple interfacing ports and can accommodate a primary source and a storage and combines their advantages by utilizing a single power stage. In comparison with using multiple traditional two-port converters, the most attractive features of using a TPC are reduced power conversion stages and reduced component count. Hence the efficiency and power density are improved and the cost is reduced. Due to its advantages, the TPC is continuously evolving and new topologies and innovations have been continuously emerging.

The structure of the proposed FB TPC is shown in the diagram. Two bidirectional Buck/Boost converters are employed to interface two bidirectional power ports on the primary-side of the FB TPC. The two switching legs, composed of S1, S2 and S3, S4, of the two bidirectional Buck/Boost converters are driven in the interleaved fashion (with 180° phase shift). From a topological point of view, the two switching-legs also build a voltage-fed full-bridge inverter. A high frequency AC voltage, vP, is generated from the mid-points of the two switching-legs. It has been well-known that, an AC voltage can be converted to a regulated DC voltage efficiently by employing a bridgeless Boost rectifier, because the conduction loss and the number of semiconductor components are reduced.

The FB TPC has two bidirectional power ports and one isolated output port. The two bidirectional ports can be used to interface renewable energy sources, storage elements, regenerative DC loads or voltage buses with bidirectional power flows, whereas, the isolated output port can only be used to interface DC load or voltage bus with an unidirectional power flow. Single-stage power conversion between any two of the three ports is achieved. The voltage and power of Port1 and Port2 on the primary side can be balanced by regulating the duty cycle of the bidirectional Buck/Boost converter, while the output voltage/power of the Port3 on the secondary-side can be controlled by the bridgeless Boost rectifier. Low voltage/current ripples on the primary-side power ports can be ensured because the two bidirectional Buck/Boost converters always operate with an interleaving fashion.

STEPS:

  1. Operational principles of the fb-tpc with Voltage doubler
  2. CCM
  3. Secondary-Side Switches:
  4. Topology Extension Primary-side Inductors and Power Devices
  5. Primary-side Inductors and Power Devices
  6. Report Generation

Operational principles of the fb-tpc with Voltage doubler:

The power control of the primary side power ports is independent of the secondary-side load port. Because the duty cycle of the primary-side switches is only determined by the voltages of the battery and the PV source, and has nothing to do with the phase shift angle φ. The key waveforms of the primary-side interleaved Buck/Boost converter are illustrated, where D is the duty cycle of the switches S1 and S3, and Ts is the switching period. The switches in the same switching-leg are driven complementary, and the phase angle between the two switching-legs is 180° as constant to reduce the current ripple and enhance the circuit reliability. Since the operation of the interleaved bidirectional Buck/Boost converter is very simple, it will not be analysed in detail in this paper. The operation of the proposed converter mainly focuses on the power flow from the primary-side to the load side.

CCM:

The converter operates in the CCM if the primary side switches commute before the secondary side inductor current, iLf, and decreases to zero. The key waveforms of the CCM mode, where vAB and vCD are the voltage differences between the midpoint primary and secondary side bridges, vLf and iLf are the voltage and current of the Boost inductor Lf, φ is the phase shift angle between S1 and S6, and α is defined to be the equivalent phase angle during which the primary side current returns to zero after S1 turns on. Φ ≥ α is satisfied in the

CCM. There are six stages in half of the switching period. The equivalent circuit of each switching stage

Secondary-Side Switches:

According to the operation principles of the converter, the body diodes of the secondary-side switches, S5 and S6, always conduct before applying gating signals no matter which mode the converter works in. That means the drain-source voltages of S5 and S6 have decreased to zero before applying gating signals. Therefore, ZVS can be achieved for the secondary-side switches. Meanwhile, the changing rates of the currents through rectifying diodes D1 and D2 are limited by the inductor Lf. So the currents of D1 and D2 always decrease to zero slowly, which means ZCS is achieved. So the main power losses of the rectifying diodes are conduction losses.

Topology Extension:

An advantage of the proposed TPC derivation method is that the number of the isolated load port can be extended easily to interface multiple loads. This can be realized by using a multi winding transformer and multiple bridgeless Boost rectifiers. The configuration of the proposed multiport converter with multiple isolated output ports. The topology of the bridgeless Boost rectifier can be selected from those according to the requirement of practical application. The topology extension and control principles of the proposed multiport converter are similar to the existing multiport converters based on multi-winding transformer. The output voltage/power of each load port can be regulated by phase shifting the driving signals of the active switches in each bridgeless Boost rectifier with respect to the primary-side switches. Since the output power of each load port is only determined by the phase-shift angle of its own bridgeless Boost rectifier, independent regulation of each load port can be achieved.

Primary-side Inductors and Power Devices:

In order to verify the effectiveness of the FB-TPC under closed-loop control, the power management and control strategies for a PV-battery power system presented are applied to the proposed FB-TPC. The power management of the PV-battery power system is to balance the power between the PV and the battery while maximizing the output power of the PV source. The control block diagram. Four regulators, PV voltage regulator (IVR) for MPPT, battery voltage regulator (BVR) for maximum charging voltage control, battery current regulator (BCR) for maximum charging current control and output voltage regulator (OVR) for load voltage control, are employed to achieve the power management of the system. The detailed analysis and operating principles of the power management system have been presented, and will not be analysed here.

Report Generation:

A systematic method for synthesizing three-port converters (TPCs) from interleaved bidirectional converter and bridgeless Boost rectifiers has been proposed. The bidirectional converter and the bridgeless Boost rectifier are connected by a high-frequency transformer to interface multiple bidirectional sources and isolated output load simultaneously. Single-stage power conversion is realized to improve conversion efficiency of the power system. Voltage and power regulations over two of the three power ports are achieved by using interleaved pulse width modulation on primary-side switching-bridges and phase-shift modulation on secondary-side switches. Furthermore, soft-switching operation of all of the active-switches and diodes has been achieved. The voltage/current ripples are reduced thanks to the excellent performance of the proposed TPC topologies and modulation strategies. The voltage stresses of the devices are reduced because the voltages of devices are naturally clamped by the input and output voltages.

REFERENCE:

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