# US 12,119,754 B1 · Isolated DC/DC converter topology structure for fuel cell system

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- Number: US 12,119,754 B1
- Document ID: US12119754B1
- Status: Granted
- Kind: B1
- Application number: 18/677,237
- Filed: 2024-05-29
- Granted: 2024-10-15
- Earliest claimed: 2023-06-01
- Assignees: Tongji University
- Applicants: Tongji University
- Inventors: Tiancai Ma; Qilin Liu; Daohai Jiao; Weikang Lin; Kaihang Song
- Web page: https://patentgrep.com/patent/US12119754B1

## CPC

- H02M 3/33584: {Bidirectional converters}
- H02M 1/32: Means for protecting converters other than automatic disconnection
- H02M 1/36: Means for starting or stopping converters
- H02M 3/1582: {Buck-boost converters (H02M3/1584 takes precedence)}
- H02M 3/33573: {Full-bridge at primary side of an isolation transformer}
- Y02E 60/50: Fuel cells
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

Isolated direct DC/DC converter topology structure for fuel cell system includes: Boost converter topology structure and bidirectional full-bridge converter topology structure connected in sequence. Input of the Boost converter topology structure is connected to fuel cell, and output of the Boost converter topology structure is connected to other key components of the fuel cell system and input of the bidirectional full-bridge converter topology structure. Output of the bidirectional full-bridge converter topology structure is connected to power cell. Usage of the Boost converter topology structure and usage of the bidirectional full-bridge converter topology structure change under different operating states of the fuel cell system. Based on insulation performance and high efficiency of the fuel cell system, the usage of the Boost converter topology structure and the usage of the bidirectional full-bridge converter topology structure change. Low efficiency caused by DC/DC converter with single isolated topology structure is effectively overcome.

## Claims

### Claim 1

An isolated direct current/direct current (DC/DC) converter for a fuel cell system, comprising:
a Boost converter topology structure and a bidirectional full-bridge converter topology structure connected in sequence, wherein an input end of the Boost converter topology structure is connected to a fuel cell, and an output end of the Boost converter topology structure is connected to other key components of the fuel cell system and an input end of the bidirectional full-bridge converter topology structure; the other key components comprise:
an air compressor and a hydrogen circulation pump; an output end of the bidirectional full-bridge converter topology structure is connected to a power cell; and usage of the Boost converter topology structure and usage of the bidirectional full-bridge converter topology structure change under different operating states of the fuel cell system;
the Boost converter topology structure comprises: a power switching transistor Q9, an inductor L2, a filter capacitor Cf2, and a diode D9, one end of the inductor L2 is connected to a positive electrode of the fuel cell, an other end of the inductor L2 is respectively connected to a drain of the power switching transistor Q9 and an anode of the diode D9, a cathode of the diode D9 is respectively connected to one end of the filter capacitor Cf2, the input end of the bidirectional full-bridge converter topology structure, and the other key components of the fuel cell system, and an other end of the filter capacitor Cf2 is connected to a source of the power switching transistor Q9, the input end of the bidirectional full-bridge converter topology structure, and a negative electrode of the fuel cell;
the bidirectional full-bridge converter topology structure comprises: a left topology structure, an inductor L1, a transformer, a right topology structure, and a filter capacitor Cf1; an input end of the left topology structure is the input end of the bidirectional full-bridge converter topology structure, and an output end of the right topology structure is the output end of the bidirectional full-bridge converter topology structure;
the input end of the left topology structure is respectively connected to the cathode of the diode D9 and the other end of the filter capacitor Cf2, an output end of the left topology structure is connected to one end of the inductor L1 and an other end of a primary coil of the transformer, and an other end of the inductor L1 is connected to one end of the primary coil of the transformer; a secondary coil of the transformer is connected to an input end of the right topology structure; the filter capacitor Cf1 is parallelly connected to the input end of the right topology structure; and the power cell is parallelly connected to two sides of the filter capacitor Cf1;
the isolated DC/DC converter for the fuel cell system prevents a voltage of a bus from surging quickly:
wherein, when the fuel cell system is integrally started, the fuel cell is not powered on, the power cell is required to supply power to the other key components of the fuel cell system, a pulse width modulation (PWM) duty cycle incremental method is adopted to start the fuel cell system, and a power switching transistor Q5, a power switching transistor Q6, a power switching transistor Q7, and a power switching transistor Q8 on the right topology structure are started preferentially;
during starting, a voltage change rate and a voltage value of voltage Vdc collected by a voltage sensor are monitored; when the voltage change rate of Vdc exceeds a preset threshold, an increase rate of a duty cycle is reduced, and to prevent over-voltage of Vdc, a voltage Vdc limiting protection algorithm is also set, until Vdc reaches a preset voltage; and
after Vac is stabilized and the fuel cell operates normally, the Boost converter topology structure is introduced to the fuel cell, to generate electricity, and a power switching transistor Q1, a power switching transistor Q2, a power switching transistor Q3, and a power switching transistor Q4 in the left topology structure are started while the power switching transistor Q9 is started; and
the isolated DC/DC converter for the fuel cell system sets an energy transfer direction based on an energy flow requirement,
wherein, when the fuel cell system is started, the power cell supplies power to the other key components of the fuel cell system, and energy of the bidirectional full-bridge converter topology structure flows from the right topology structure to the left topology structure; and
after the fuel cell system operates normally, the fuel cell supplies power to the other key components of the fuel cell system, and the energy of the bidirectional full-bridge converter topology structure flows from the left topology structure to the right topology structure.

### Claim 2 (depends on 1)

The isolated DC/DC converter for the fuel cell system according to claim 1, wherein that the usage of the Boost converter topology structure and the usage of the bidirectional full-bridge converter topology structure change under the different operating states of the fuel cell,
wherein, during starting the fuel cell, the fuel cell is not powered on, the power cell supplies power to the other key components of the fuel cell system via the bidirectional full-bridge converter topology structure, and the Boost converter topology structure is not used; and
after the fuel cell is started, the fuel cell supplies power to the other key components of the fuel cell system via the Boost converter topology structure, and supplies power to the power cell via the Boost converter topology structure and the bidirectional full-bridge converter topology structure, and the Boost converter topology structure and the bidirectional full-bridge converter topology structure are used simultaneously.

### Claim 3 (depends on 1)

The isolated DC/DC converter for the fuel cell system according to claim 1, wherein the left topology structure comprises: the power switching transistor Q1, the power switching transistor Q2, the power switching transistor Q3, the power switching transistor Q4, a diode D1, a diode D2, a diode D3, and a diode D4; and
a drain of the power switching transistor Q1 is respectively connected to the cathode of the diode D9, the one end of the filter capacitor Cf2, a cathode of the diode D1, a drain of the power switching transistor Q3, and a cathode of the diode D3; and a source of the power switching transistor Q1 is respectively connected to an anode of the diode D1, the one end of the inductor L1, a drain of the power switching transistor Q2, and the cathode of the diode D2; a source of the power switching transistor Q2 is respectively connected to the other end of the filter capacitor Cf2, an anode of the diode D2, a source of the power switching transistor Q4, and an anode of the diode D4; a source of the power switching transistor Q3 is respectively connected to an anode of the diode D3, a drain of the power switching transistor Q4, a cathode of the diode D4, and the other end of the primary coil of the transformer; and the other end of the inductor L1 is connected to the one end of the primary coil of the transformer.

### Claim 4 (depends on 1)

The isolated DC/DC converter for the fuel cell system according to claim 1, wherein the right topology structure comprises: the power switching transistor Q5, the power switching transistor Q6, the power switching transistor Q7, the power switching transistor Q8, a diode D5, a diode D6, a diode D7, a diode D8, the inductor L1, the filter capacitor Cf1, and the transformer; and
a drain of the power switching transistor Q5 is respectively connected to a cathode of the diode D5, a drain of the power switching transistor Q7, a cathode of the diode D7, one end of the filter capacitor Cf1, and a positive electrode of the power cell; a source of the power switching transistor Q5 is respectively connected to one end of the secondary coil of the transformer, an anode of the diode D5, a drain of the power switching transistor Q6, and a cathode of the diode D6; a source of the power switching transistor Q6 is respectively connected to an anode of the diode D6, a source of the power switching transistor Q8, an anode of the diode D8, the other end of the filter capacitor Cf1, and a negative electrode of the power cell; a source of the power switching transistor Q7 is respectively connected to an anode of the diode D7, a drain of the power switching transistor Q8, a cathode of the diode D8, and the other end of the secondary coil of the transformer; and the other end of the inductor L1 is connected to the one end of the primary coil of the transformer.

### Claim 5 (depends on 4)

The isolated DC/DC converter for the fuel cell system according to claim 4, wherein the voltage sensor is disposed on a side of the filter capacitor Cf2; and a current sensor is disposed on a side of the inductor L2.

### Claim 6 (depends on 5)

The isolated DC/DC structure for the fuel cell system according to claim 5, wherein temperature sensors are disposed at the power switching transistor Q1, the power switching transistor Q2, the power switching transistor Q3, the power switching transistor Q4, the power switching transistor Q5, the power switching transistor Q6, the power switching transistor Q7, the power switching transistor Q8, and the power switching transistor Q9.