Patent Grant
11491883
This Utility Application is a National Stage Application of PCT/US2019/026779 filed on 10 Apr. 2019, which is based on the Provisional Patent Application No. 62/655,708 filed on 10 Apr. 2018.
The present invention is directed to plug-in electric vehicles (PEVs), and in particular, to on-board chargers (OBCs) for PEVs.
In overall concept, the present invention directs itself to a compact on-board charger for efficient bi-directional charging of both low voltage (LV) battery and high voltage (HV) battery on PEVs.
The present invention is also directed to an integrated on-board charger adapted for a three-phase power grid connection that is capable of a bi-directional operation (from the HV and LV batteries to the grid, from the grid site to the HV and LV batteries, as well as between the HV and LV batteries, and for charging the vehicle (propulsion system) from the grid, as well as discharging the vehicle to the grid.
In addition, the present invention is directed to a compact, highly efficient high power three-phase on-board charger (OBC) system with a modular configuration of the On-board Charger integrated with the Auxiliary Power Module (APM) that is capable of a bi-directional power flow between multiple ports of the OBC.
The present invention is further directed to a three-port power electronic system with one input and two outputs which enables a unique power transfer control methodology simultaneous regulated power transfer towards both output ports from the AC power grid.
The present invention is also directed to the combination of different variations of triple-active bridge (TAB)-derived topologies and control routines which are capable of bi-directional operations among three different ports of the charging system in PEVs.
The present invention is further directed to a power management control strategy in OBCs that is capable of managing bi-directional power flow among three ports (input port and two output ports) of the power electronic system in PEVs at different loading conditions.
In addition, the present invention is directed to an optimization strategy for minimization of the reactive and active circulation of power among different ports of the power electronic system in PEVs, to reduce a peak current stress on MOSFET devices included in the OBC, and to ensure soft switching of all MOSFET devices of the triple-active-bridge (TAB)-based topologies.
The present invention also addresses an analytical predictive model to predict the phase difference between currents in the primary and secondary sides of a transformer to enhance synchronous rectification, to minimize losses in the power electronic system of PEVs, and to overcome a requirement for a high bandwidth secondary side current sensor which is achieved by a predictive model-based synchronous rectification control.
In addition, the present invention addresses a three-port power electronic system for PEVs with one input port and two output ports, capable of simultaneously regulating power transfer with sets of integrated transformers towards both output ports while achieving controlled regulation of output voltages.
Furthermore, the present invention is directed to a three-phase input interface flexible for operation with a single-phase input source, and to a control routine to minimize the circulating power using an approach of a combined phase shift and duty ratio control strategy for the triple-active-bridge (TAB)-based topologies.
In addition, the present invention addresses an OBC capable of achieving a simultaneous charging (G2B) of two batteries (HV and LV) from a grid, grid to HV battery (G2H) charging, grid to LV battery (G2L) charging, HV battery to LV battery (H2L) charging, as well as grid to vehicle (G2V) charging, and vehicle to grid (V2G) discharging.
Electric vehicles (EVs) and Plug-In Hybrid Electric Vehicles (PHEVs), commonly referred to herein as Plug-In Electric Vehicles (PEVs), are vehicles propelled by electricity, as opposed to the conventional vehicles which operate on organically based or other liquid/gaseous fuel. The Plug-In Electric Vehicles are composed of an energy storage sub-system (ESS), and an inverter followed by a propulsion machine for electric propulsion called a power train.
There is a trend among industries and researchers to focus on the electrification of transportation, especially in the field of PEVs, due to the environmental issues and the increasing market growth that can be foreseen in the coming decades. According to the report from International Energy Agency, numbers of both electric car stock and electric car sales continually keeps growing.
Electric vehicles (EVs) operate with higher energy conversion efficiency, produce a lower level of exhaust emissions, and lower levels of acoustic noise and vibration, than conventional vehicles. The electricity for electric vehicle operation can be provided either external the vehicle and stored in the ESS, or can be produced on-board with the help of the storage source(s) contained in the ESS.
The battery charger is a device which converts the alternating current (AC) distributed by electric utilities to the direct current (DC) needed to recharge a battery. There are a number of different types of battery chargers based on the way they control the charging rate. Electric vehicle battery chargers may be on-board (residing in the electric vehicle) or off-board (at a fixed location outside the vehicle).
Thus, on-board chargers provide flexibility of battery charging using power outlets. However, on-board chargers contribute to additional weight, volume and cost of the car. Due to their charging power, limitations and slow charging process, it would take between 4-20 hours to fully charge a PEV battery using conventional on-board chargers. Thus, a high power charger which does not need additional bulky on-board or off-board power equipped electronic interfaces, and which would provide faster on-board charging without an additional cost and weight would be highly desirable in the PEVs industry.
Typical on-board chargers include an AC-DC stage for rectification of the AC voltage from the power grid, a Power Factor Correction (PFC), and a DC-DC stage for battery current and voltage regulation.
In the on-board power electronic converter of a PEV, a conventional on-board battery charger operates independent of the propulsion machine and the propulsion inverter. This structural approach is detrimental due to additional or extra components, weight, and cost of the vehicle design. In order to reduce the size, weight and cost of the on-board chargers, different integrated chargers have been designed.
In recent publications, bi-directional on-board charger solutions are sought which not only charge the HV battery from the grid, but also is able to transfer the power from the battery side back to the grid. In addition to the on-board charger, a typical power interface structure for EVs also includes a separate power unit called Auxiliary Power Module (APM) operating to charge the low voltage (LV) battery.
The OBS and APM are two independent battery charger units incorporated in an electric vehicle (EV). The on-board charger (OBC) is the power electronics interface between the power grid and the high voltage (HV) traction battery, and the auxiliary power module (APM) is a separate power unit to charge the low voltage (LV) battery which supply consumer electronics on a vehicle, such as audio, air conditioner, lights, etc.
To reduce charging time and alleviate range anxiety, power ratings of the OBC and battery capacity increase with the help of three-phase power outlets, which are widely used in Europe and Asia. Moreover, many studies have been conducted on bi-directional power flow of OBC, which not only can charge the HV battery from the grid, but also can feed the power from the battery to the grid side.
It would be highly beneficial for PEVs to integrate both units (OBC and APM) together in order to achieve a charger design that would be capable of bi-directional operation with high efficiency, while being smaller in volume, lighter in weight, and less costly compared to those of the existing on-board chargers and auxiliary power modules combined. A compact and highly efficient bi-directional 3-phase charger that would be capable of charging both LV and HV batteries is an attractive solution for the next generation of EVs. Furthermore, this integration will address the pre-conditioning and depleted LV battery issues in EVs, as there have been many reports/concerns regarding depleted LV batteries in EVs, where a car cannot ever be started, and the LV battery is to be replaced.
There have been numerous attempts to the field of PEVs to integrate an Auxiliary Power Module (APM) into a bi-directional on-board charger (OBC) with different configurations.
One design that integrates the auxiliary power module from the grid side, as shown in
Another configuration, depicted in
A current doubler rectifier with current ripple cancellation was proposed in J. S. Glaser, et al., “Current doubler rectifier with current ripple cancellation”, U.S. Pat. No. 7,880,577B1, issued Feb. 1, 2011. The circuit utilizes three coupled inductors on the secondary side in an E-core structure. However, disadvantageously, neither the circuit is integrated with any resonant converter, nor the operational principles of the circuit are made applicable to the resonant converter, which makes it inapplicable for LV charging applications.
A rectifying circuit formed with dual current doublers connected in series/parallel was described in K. A. Wallace, “Dual coupled current doubler rectification circuit,” U.S. Pat. No. 5,933,338 A, Aug. 3, 1999. This circuit needs separate cores for realizing the secondary inductors and makes the converter significantly bulkier. Also, current ripple cancellation cannot be achieved by this topology, which further will require high output capacitance.
Another integrated charger topology shown in
Three-phase on-board chargers have been widely investigated. One integration method of the OBC is to connect an add-on three-phase power electronics interface to the propulsion system, as shown in
To resolve the concern caused by propulsion system integration, some studies have been conducted on multiport integration through a coupled transformer using additional windings. For instance, a three-port dual active full bridge DC/DC converter is proposed in H. Tao, et al., “Transformer-Coupled Multiport ZVS Bidirectional DC-DC Converter with Wide Input Range”, In IEEE Transactions on Power Electronics, vol. 23, no. 2, pp. 771-781, March 2008, for fuel cell and supercapacitor applications, which is shown in
In G. Waltrich, et al., “Multiport Converter for Fast Charging of Electrical Vehicle Battery”, in IEEE Transactions on Industry Applications, vol. 48, no. 6, pp. 2129-2139, November-December 2012, a multiport converter is described with a stationary storage port to reduce the required current from the grid for charging station configuration, as shown in
It would be highly desirable to provide a compact OBC free of the shortcomings of the conventional converters, which would be capable of a highly-efficient bi-directional power transfer between the power grid and HV and LV batteries, between HV and LV batteries, and between the grid and the vehicle.
It is therefore an object of the present invention to provide a compact single-phase and three-phase integrated on-board charger system capable of simultaneous charging of both high voltage (HV) and low voltage (LV) batteries from the power grid and which integrates the functionalities of both the on-board charger (OBC) and the auxiliary power module (APM) to achieve bi-directional operation with high efficiency.
It is another object of the present invention to provide a highly compact, highly efficient bi-directional three-phase on-board charger capable of simultaneous charging both low voltage (LV) and high voltage (I-IV) batteries in the electric vehicles.
It is a further object of the present invention to provide a three-port power electronic system for electric vehicles with one input port and two output ports capable of simultaneous regulated power transfer between the input port and the output ports while maintaining reference voltage levels.
In addition, it is an object of the present invention to provide a unique power flow control methodology for both a single- and three-phase integrated OBC and APM which enables simultaneous charging of HV and LV batteries from the AC grid side in a multi-port on-board charging system for electric vehicles.
It is a further object of the present invention to provide a combination of alternative configurations of triple-active bridge (TAB)-derived topologies and control methods which are capable of bi-directional power flow among the multiple ports of the power electronic system.
Furthermore, it is an object of the present invention to provide a novel control and power management strategy that can manage the bi-directional power flow among three ports at different loading conditions, and an optimization strategy to minimize the reactive and active circulating power among different ports, thus reducing the peak current stress on MOSFET devices.
Further, it is an object of the present invention to ensure soft-switching at the MOSFETs of the triple-active-bridge (TAB)-based topologies of the charging system in EVs applications.
In addition, it is an object of the subject invention to create an analytical model to predict the phase difference between the primary and secondary sides' currents of a charger's transformer to enhance synchronous rectification and to minimize losses, as well as to eliminate the requirement of a high bandwidth secondary side current sensor.
It is still an object of the present invention to provide a charger system for EVs with a three-phase input interface flexible for operation with single-phase input source.
It is also an object of the present invention to provide a control methodology to minimize the circulating power using phase shift and duty ratio combined strategy for the triple-active-bridge (TAB)-based topologies for chargers of PEVs.
In addition, it is an object of the present invention to achieve various functionalities, namely, simultaneous charging (G2B) of HV and LV batteries from a power grid, grid to HV battery (G2H) charging, grid to LV battery (G2L) charging, HV battery to LV battery (H2L) charging, grid to vehicle (G2V) charging, and vehicle to grid (V2G) discharging in the charger in EVs.
In one aspect, the present invention is directed to an on-board charging system for plug-in electric vehicles (PEVs) which includes an on-board charger (OBC) having an input port operatively coupled to an alternative current (AC) power grid, a first output port operatively coupled to a first (HV) battery, and a second output port operatively coupled to a second (LV) battery. The OBC is configured for substantially simultaneous bi-directional power transfer between at least two of the input port, the first output, and the second output ports respectively.
The OBC is further equipped with a power transfer control sub-system integrated in the OBC and operatively coupled to the input and the first and second output ports for bi-directional regulated power transfer therebetween while maintaining reference voltage levels. The control sub-system is configured for a combined phase shift and duty ratio control at the input and the first and second output ports in a resonant-based and a pulse width modulation (PWM)-based modes of operation respectively.
The OBC further includes a transformer sub-system integrated therewith and operatively coupled, by a primary side to the input port, and by secondary and tertiary sides to the first and second output ports, respectively.
A DC/DC converter is integrated in the OBC in operative coupling to the transformer sub-system where the DC/DC converter includes a first converter sub-system operatively coupled between the input port and the primary side of the transformer sub-system, a second converter sub-system operatively coupled between the secondary side of the transformer sub-system and said first output port, and a third converter sub-system operatively coupled between the secondary side of the transformer and the second output port.
The first, second, and third bridge sub-systems, and the transformer sub-system, preferably form a triple active bridge (TAB) converter sub-system.
The OBC is contemplated in numerous embodiments, and may have a configuration selected from a group including a resonant-based configuration and a pulse-width modulation (PWM)-based configuration. Each of the first and second converter sub-systems includes at least two MOSFET devices interconnected to form a half-bridge DC/DC converter circuit, or at least four MOSFET devices interconnected to form a full bridge DC-DC converter circuit. The third converter sub-system includes MOSFET devices interconnected to form a half-bridge DC/DC converter circuit, a full-bridge DC/DC converter circuit, or an active current doubler rectifier circuit.
In the resonance-based configuration, when each of the first and second converter sub-systems includes the half-bridge configuration, the OBC includes a resonant capacitor C1 connected between the first converter sub-system and the primary side of said transformer sub-system, and a resonant capacitor C2 connected between the secondary side of the transformer sub-system and the second converter sub-system.
In the resonance-based configuration, the OBC further includes resonant capacitors C1/2 and C2/2 included in the half-bridge configuration of the first and second converter sub-systems.
In the PWM-based configuration, the DC/DC converter further includes a first shim inductor L1 and a first DC-blocking capacitor C1, each connected between the first converter sub-system and the primary side of the transformer sub-system, a second shim inductor L2, and a second DC-blocking capacitor C2, each connected between the secondary side of the transformer sub-system and the second converter sub-system, and a third inductor L3 interconnected between the secondary side of the transformer sub-system and the third converter sub-system.
The subject on-board charger system, further includes a resonant inductor L1 interconnected between the first converter sub-system and the primary end of the transformer sub-system, and a resonant inductor L2 interconnected between the secondary side of said transformer sub-system and the second converter sub-system with the L1 and L2 enhancing power density of the DC/DC converter.
A switching sub-system controls the power flow during the grid-to-vehicle charging and vehicle-to-grid discharging.
A power interruption device (switch/relay) is connected between the first port and the input converter sub-system between the first converter sub-system and the primary side of the transformer sub-system and at the primary side of the transformer sub-system.
The power transfer control sub-system operates in a mode of operation selected from a group consisting of a simultaneous charging mode of operation, a reactive power flow optimization mode of operation, and a synchronous rectification mode of operation.
In the simultaneous charging mode of operation, the first, second, and third converter sub-systems are configured as full-bridge DC/DC converter circuits, and the power flow towards the first and second output ports and the output voltage levels V1, V2, V3 at the input port, and the first and second output ports, respectively, are controlled by independent control variables including duty rations δ1, δ2, δ3 of the full-bridge DC/DC converter circuits of the first, second and third converter sub-systems and phase angle differences φ1 and φ2, between fundamental voltage waveforms of the first and second and the first and third converter sub-systems, respectively.
The first converter sub-system includes Q1, Q2, Q3, Q4 MOSFET devices, the second converter sub-system includes Q5, Q6, Q7, Q8 MOSFET devices, and the third converter sub-system includes Q9, Q10, Q11, Q12 MOSFET devices.
In the reactive power flow optimization mode of operation, the subject control sub-system generates the variables φ2, φ3, φ3 sets=0, and determines δ to ensure a soft switching condition for the MOSFET devices.
In the synchronous rectifier mode of operation, the control sub-system includes a PWM generator supplying a PWMA control signal to the first converter sub-system, a generalized harmonic computational sub-system computing a phase angle difference value θSR between the gate pulses for the first and second converter sub-systems required for synchronizing with a zero current crossing of a resonant current in the second converter sub-system, a delay computational sub-system coupled to the generalized harmonic computational sub-system receiving the PWMA signal and the phase difference value θSR therefrom, and computing a gate signal PWMB based on the PWMA and θSR,
The delay computational sub-system supplying the gate signal PWMB to the second converter sub-system attains a synchronous rectification in the second and third converter sub-systems.
A synchronous rectification mechanism is incorporated in the MOSFET devices Q5, Q6, Q7, and Q8 of the second converter sub-system during the grid-to-vehicle charging mode of operation, and in the MOSFET devices Q1, Q2, Q3, and Q4 of the first converter sub-system during the vehicle-to-grid discharging mode of operation.
In another aspect, the present invention is directed to a three-phase on-board charger system for plug-in electric vehicles (PEV), which includes a modular on-board charger (OBC) having an input port coupled to a three-phase power grid and a first and second output ports coupled to an on-board high voltage (HV) battery and an on-board low voltage (LV) battery, respectively. The modular on-board charger includes a plurality of electronic modules interconnected in a one-stage configuration, or a two-stage configuration.
In the two-stage configuration, the on-board charger (OBC) includes a first electronic module operatively coupled between the input port and a DC link, where the first electronic module includes a bi-directional three-phase Power Factor Correction (PFC) rectifier sub-system. A second electronic module operatively is coupled to the DC capacitor CDC of the DC link, where the second electronic module includes a plurality of MOSFET devices interconnected in a bridge sub-system. A third electronic module operatively coupled to the bridge sub-system, where the third electronic module includes an integrated transformer sub-system. A fourth electronic module operatively coupled between the integrated transformer sub-system and the first output port, where the fourth electronic module includes a rectifier sub-system for the HB battery coupled to the fourth electronic module. The OBC further includes a fifth electronic module which is operatively coupled between the integrated transformer sub-system and the second output port, where the fifth electronic module includes a rectifier sub-system for the LV battery coupled to the fifth electronic module.
The subject OBC also includes a control sub-system operatively coupled to the electronic modules to implement a combined phase shift-and-duty ratio-based power flow control for charging the HV and LV batteries from the power AC grid, for the HV battery to the LV battery charging, for charging the PEV from the AC power grid, and discharging the PEV to the AC power grid.
In the one-stage configuration, the on-board charger (OBC) includes a sixth electronic module operatively coupled to the input port, where the sixth electronic module including a single-stage AC/DC converter sub-system with the third electronic module operatively coupled to the sixth electronic module.
The fourth and fifth electronic modules are operatively coupled to the integrated transformer sub-system in the third electronic module, with the HV and LV batteries coupled to the first and second output ports, respectively and the control sub-system operatively coupled to the electronic modules.
In the two-stage configuration, the bi-directional three-phase PFC rectifier of the first electronic module may be selected from a group consisting of: a three phase boost PFC rectifier, a three-phase buck PFC rectifier, a three-phase Vienna-type PFC rectifier, a three single-phase buck PFC rectifier, and a modular multi-level converter,
The bridge sub-system in the second electronic module may be selected from a group consisting of: two full bridges connected in parallel, two half bridges connected in parallel, two individual half bridges, two individual full bridges, a three-phase bridge, three full bridges, and three half bridges.
The transformer sub-system in the third electronic module may be selected from a group consisting of: at least two separate transformers, at least two transformer sets with primary windings delta interconnected with capacitors and secondary windings interconnected in series with capacitors, and a single three-phase transformer; and
The rectifier sub-system of each of the fourth and fifth electronic modules, respectively, may be selected, depending on the configuration of the transformer sub-system from a group consisting of: at least two half bridges, at least two full bridges, at least two half bridges connected in parallel, and at least two full bridges connected in parallel.
The DC Link may be selected from a group consisting of: a split DC Link, and a non-split DC Link.
In the one-stage configuration, the AC/DC converter of the sixth electronic module may be selected from a group consisting of: three single-phase AC-DC converters connected in parallel, a Matrix-based three-phase AC-DC Triple Active Bridge (TAB) converter, and a SWISS-based TAB converter with split AC capacitors.
The transformer sub-system in the third electronic module may be selected from a group consisting of: at least two separate transformers, three transformers with primary windings delta-interconnected with capacitors and secondary windings serially connected with capacitors, and a single three-phase transformer.
The rectifier sub-system in the fourth and fifth electronic modules, respectively, may be selected from a group consisting of: at least two half bridges, at least two full bridges, at least two half bridges connected in parallel, and at least two full bridges connected in parallel.
The control sub-system executes a pulse frequency modulation (PFM) or pulse width modulation (PWM).
In one embodiment, where the subject OBC system has a split power flow, the two-stage configuration may include a bi-directional three-phase PFC rectifier in the first electronic module, two triple active full bridge converters connected in parallel in the second electronic module integrated with two transformers and six shim inductors of the third electronic module.
In an alternative implementation, the subject OBC system has a split power flow, and further includes a three-phase boost PFC rectifier in the first electronic module, and two single-phase DC/DC converters in each of the fourth and fifth electronic modules, respectively, where each single-phase DC/DC converter is integrated with a respective transformer sub-system in each split power flow.
In another embodiment, the subject OBC system may include a three-phase boost PFC rectifier in the first electronic module, and an integrated three-phase DC-DC converter in each of the fourth and fifth electronic modules; or a three single-phase H-bridge PFC rectifiers in the first electronic module integrated with triple active bridge (TAB) converters coupled in parallel.
These and other objects and advantages of the present invention will be more apparent when considered in conjunction with the Drawings and the Detailed Description of the Preferred Embodiment(s).
Referring to
The PFC rectifier 16 is included in an alternative current (AC) side 17 of the OBC system 10, while the integrated transformer 14 and the DC/DC converter 12, are included in a direct current (DC) side 19 of the OBC system 10. The AC side 17 and the DC side 19 are interconnected through a DC link 21 having a DC link capacitor CDC.
The transformer sub-system 14 includes, in the implementation shown in
In the topology shown in
Topology wise, the inductors L1, L2 and L3 provide sufficient inductive energy to achieve zero-voltage-switching for MOSFETs Q1-Q4 (in the bridge sub-system 22), Q5-Q8 (in the bridge sub-system 20), and Q9-Q11 (in the bridge sub-system 24), respectively. The inductors L1, L2, and L3 can be achieved by the leakage inductance of the transformer sub-system 14 to further enhance the power density of the DC/DC converter 12.
The capacitors C1 and C2 serve the purpose of blocking the DC component in the current in different operating modes. The DC component of current arises from different mechanisms, such as: (a) asymmetrical pulse width modulation, (b) parasitic imbalance of the devices, and (c) start-up load transients of the DC/DC converter 12.
A unique control methodology is implemented with the topology shown in
There are various topological alternative implementations of the subject system are contemplated which are applicable in simultaneous charging of the HV battery 26 and LV battery 28, as well as the bi-directional power flow in a three-port network system with the subject power transfer control strategy, detailed in further paragraphs.
There are primarily two categories of alternative embodiments of the subject system 10, including: a) Resonant-based topologies, and b) Pulse width modulation (PWM)-based topologies.
Resonant-based topologies are depicted in
In the circuitry shown in
The resonant inductors L1 and L2 can be realized by the leakage inductances from the transformer sub-system 14 to further enhance the power density of the DC/DC converter 12.
The resonant based topological variations are summarized in Table. I. It is noted that not every variation is capable of grid-to-both batteries (G2B) operation, which will be detailed in further paragraphs.
Pulse width modulation based topological alternative implementations are presented in
The capacitors C1 and C2 function as the DC-blocking capacitors, inductances L1, L2 and L3 are shim inductors functioning to provide the inductive energy for the zero-voltage-switching of the MOSFET devices in the charger sub-systems 30, 32, 34, also referred to herein as Block 1, Block, Block 3, respectively. Similarly, the inductors L1, L2 and L3 can be realized by the leakage inductances of the transformer sub-system 14 to further improve the power density of the DC/DC converter 12.
In the circuit configuration shown in
For instance, a triple-active-bridge (TAB) converter, shown as
In the pulse width modulation-based implementation, shown in
The pulse width modulation-based implementations of the subject system 10 contemplated in the subject system 10, are summarized as Table II. Not every alternative embodiment is capable of grid-to-both batteries operation, as will be detailed in further paragraphs.
The alternative topologies contemplated in the subject OBC system 10 also may include back-to-back (B2B) switches/relays 39. As shown in
During the HV-to-LV (H2L) power flow, the back-to-back switch/relay(s) 44 can be turned off to break the electrical connections between the active part (DC/DC converter 12) of the circuit and the primary side circuit (Block 1). It is noted that for both topologies shown in
Power Flow Control Methodology for Single-Phase and Three-Phase Integrated OBC and APM
(a) Simultaneous Charging
The control system 45 implemented in the subject charger system 10 is capable of charging two energy storage sources (HV battery, LV battery) 26, 28 from another source, which may be the power system AC grid 18. In addition, the control system 45 has the flexibility for grid-to-vehicle (G2V), vehicle-to-grid (V2G), and HV-to-LV (H2L) operations. Charging can be performed within a wide range of operating conditions of 85 V-265 V single-phase AC, 100 V-1000 V for HV battery, and 8 V-28 V for LV battery.
The integrated DC/DC conversion stage of the subject converter architecture, as shown in
In the model shown in
The dual-output triple active bridge (TAB) cannot be treated as two independent dual active bridge converters due to the unavoidable power flow between Port-2 and Port-3, shown in
In order to control the power flow towards the two output ports 62, 64, as well as to regulate the output voltage levels, the subject control system 45 uses up to five independent control variables, i.e. three duty ratios (δ1, δ2, δ3) of three full-bridges (primary, secondary and tertiary) incorporated in Blocks 1, 2, 3 shown in
The power transfer expression from port-x to port-y (where, x, y could be 1, 2, 3) is as follows:
In order to minimize the circulating active power for a given set of load power levels P2 and P3, the power transfer between any two ports (out of the three ports P12 P2, P3) is fixed, and thus must be regulated at their reference values as follows:
Three-level bridge voltage waveforms on the primary, secondary and tertiary sides are shown in
Q1:delay=0;Q3:delay=π−2δ1 (Eq. 8)
Q5:delay=φ2+δ2−δ1; Q7:delay=π+φ2−δ2−δ1 (Eq. 9)
Q9:delay=φ3+δ3−δ1; Q11:delay=π+φ3−δ3 (Eq. 10)
The design of conventional control loops as used in dual active bridge converters is not applicable to this problem due to the cross-couplings in power flow among the ports. Therefore, the subject control methodology with a three-loop structure (for controlling three reference variables), shown in
The above mathematically implies that the phase shift angle φ2 can be used as a control variable for the Port-2 output voltage. Similarly, the phase shift angle φ3 can be used as a control variable for the Port-3 output voltage, as both P13 and P23 include φ3 and V3 as common terms.
Furthermore, in order to account for the cross-coupled power flow in the control loop, the third reference variable shall be the active power flow reference P23 flowing between Port-2 and Port-3. The corresponding control variable could be either δ2 or δ3, as φ2 and φ3 are involved in controlling the output voltages.
It is observed that φ3 has an important role in controlling the Port-2 output voltage (equivalently power P2), and so does φ2 in controlling Port-3 power, i.e. P3. Therefore, the control loops generating the phase angle differences cannot be totally decoupled, which is solved by providing cross-loop gains to the output of the voltage controllers. Assuming X1 and X2 to be the voltage controller outputs, sin(φ2) and sin(φ3) can be generated as follows:
sin(φ2)=X1+G2X2 (Eq. 11)
and
sin(φ3)=X2+G1X1 (Eq. 12)
After satisfying the hard constraints on active power transfer, there still remains the freedom in selection of the remaining two control variables, i.e. δ1 and δ3. If no other optimization constraints are applied, these two phase shift angles can be set to zero in order to transfer the maximum power.
(b) Reactive Power Flow Optimization
The subject control system 45 operates to minimize the net circulating reactive power inside the converter 12. As a part of the control variable generation algorithm, peak current stress minimization and reactive power optimization algorithms are incorporated without violating the three independent equality constraints on active power transfer towards two DC outputs. This is beneficial in selecting active semiconductors with less current rating, in minimizing the conduction losses leading to a higher conversion efficiency, as well as easier thermal management.
As evident from the three hard constraints set on the active power transfer among the three ports (presented in previous paragraphs), three control variables are generated from the control loop structure and the remaining two variables have the freedom for optimization constraints. In order to minimize the circulating conduction losses, the main objective of the control approach is to make the net reactive power injected into the network to zero. The three-port network can be modeled as three coupled transmission lines, one of which is depicted in
The reactive power flow from Port-1 to Port-2 and in the reverse direction can be expressed as follows:
As follows from Eqs. 13-14, for an asymmetric network, the sum of two reactive powers is not equal to zero with no interdependence constraint being applied to δ1 and δ2, which essentially means that there will inevitably be a phase difference between any bridge voltage and switch current, which unavoidably increases the peak level of the device current.
In case of a three-port network, there are six different paths for reactive power flow, which must sum to zero and hence, the following condition can be set:
Q12+Q13+Q23+Q21+Q32+Q31=0 (Eq. 15)
Eq. 15 essentially results into a quadratic relation between cos(δ1) and cos(δ3) for a given set of φ2, φ3, δ2 generated from the control loop. Therefore, applying reactive power minimization constraints reduces the degrees of freedom for selection of duty ratios from two to one. If no additional constraints are imposed, δ3 can be set to zero for enabling maximum power transfer and δ1 can be determined.
Furthermore, an additional constraint arises due to ensuring soft-switching at all the MOSFETs, which requires a minimum reactive power to be flowing from the input port. Assuming a minimum phase lag angle θ required between the fundamental of primary bridge voltage and primary winding current at a particular load power to ensure ZVS (Zero-Voltage-Switching), the minimum reactive power from Port-1 is as follows:
Q1=Q12+Q13>Q1,min=P1 tan(θ) (Eq. 16)
where P1 denotes the active power input from port-1.
θ can be calculated from the condition that instantaneous inductive energy during switching has to be greater than the energy stored in MOSFET output capacitors. Therefore, there exist four equality constraints and one inequality constraint (for soft-switching), based on which four control variables can be explicitly determined whereas the fifth variable will have a range of solution. The control system block diagram with constraints on reactive power and soft-switching is shown in
(c) Synchronous Rectification Operation
An efficient bi-directional power flow can be achieved by incorporating synchronous rectification in the secondary MOSFETs (Q5-Q8, shown in
In case of any resonant based variations presented in the previous paragraphs, the secondary side of the converter requires rectification to convert the high frequency AC output of the transformer to DC. Conventionally, diodes are used on the secondary side, which can automatically detect the phase of current by switching at zero crossing of current. The use of diodes as secondary rectification devices leads to higher conduction loss due to on-state voltage drop of the diode and also hinders the bidirectional operation capability of circuit. In order to enable bidirectional power transfer capability and improve efficiency, diodes are replaced by switches, depicted in
In order to regulate the output voltage and control the power flow, primary side control using pulse frequency modulation (PFM) is conducted and the required phase angle difference between primary and secondary gate pulses is calculated using the proposed generalized harmonics modeling approach. The equivalent circuit of an isolated resonant DC/DC converter is present at
Since the input to the AC equivalent model (shown in
where k is the order of the harmonics
Furthermore, the phase difference between primary and secondary current is expressed as:
Therefore, the net current expression flowing on the secondary side is given as the sum of all odd harmonics current:
The secondary side 68 gate pulses (i.e. synchronous rectification) can be generated by detecting the zero crossing (online/offline) of the formulated resonant current for a given set of load resistance and switching frequency. The order of harmonics up to which this sum needs to be carried out possesses a trade-off between accuracy and computational complexity. The generalized harmonic model and the overall control block diagram are demonstrated in
The implementation of the synchronous rectification control is not only restricted to digital domain, but also can be performed using analog solutions, as shown in
Three-Phase Integrated OBC Capable of Simultaneous Charging Both HV and LV Batteries from the Grid.
Various topologies are contemplated herein which constitute the subject on-board charging system 10 that are capable of realizing simultaneous charging by means of alternative triple active bridge and transformer configurations, including a single-stage configuration 100 and a two-stage configuration system 102 of the subject system 10, which can be controlled through pulse frequency modulation (PFM) or pulse width modulation (PWM).
The modular two-stage configurations 102 are presented by a block diagram depicted in
The two-stage charger system 102, as shown in
The operation of each block 2, 3, 4, 5 is influenced by the preceeding stage. Different combinations of the modular stages 104, 106, 108, 110, 112 (presented in Table III) result in numerous alternative topologies. For instance, the integrated transformers in Block 3 may be parallel connected, delta or star connected, or have a three-phase structure, with alternative bridge configurations (a half-bridge or a full-bridge) as well.
The single-stage system 100 is depicted as a modular diagram shown in
One of the topologies of the two-stage charger 102 is presented in
By using the parallel structure (converters 122 and transformers 124), the maximum achievable power transfer capability is increased with reduced conduction losses and voltage/current stress on the circuitry components. The modular design of the three-phase high-power integrated OBC 102 shown in
By means of electromagnetic integration of the transformers 124 and by splitting the power flow in parallel paths, the subject system 102 can be used for simultaneous charging of the HV and LV batteries at high-power ratings.
There are numerous alternative embodiments contemplated in the subject OBC system 102.
Architecture I (Three-Phase PFC+Single-Phase DC/DC Converter)
This architecture embodiment, shown in
The Topology shown in
Alternative to the Topology shown in
An alternative embodiment of the subject two-stage system 102 is depicted in
Architecture II (Three-Phase PFC+Three-Phase DC/DC Converter)
In this architecture, alternative topologies are contemplated which are focused on the DC/DC stage. Instead of using multiple single-phase converters connected in parallel, a three-phase integrated topology is suggested for two output ports, which can be categorized as a resonance-based and a PWM-based, shown in
The topology shown in
The topology, shown in
Architecture III (Three Single-Phase PFC+Single-Phase DC/DC Converter)
In this architecture, single-phase converters are implemented in a modular configuration, as shown in
Architecture IV (Single-Stage System)
In the architecture of the single-stage charger configuration 100 of the subject system 10, shown in
The topology of the configuration 100, shown in
The configuration 100 using a matrix-based three-phase AC/DC TAB converter 180 is shown in
Architecture V (MMC-Based System)
In this architecture, the PFC rectifier stage is replaced with the MMC system 186, which brings modularity and fault tolerance capability.
The MMC-based integrated onboard charger 186 can be interfaced with the propulsion system of an EV, as shown in
Power Flow Control
A conventional control strategy for a Triple Active Bridge (TAB)-based converter may be supported by the phase shift modulation (PSM) concept, which brings convenience for circuit modelling and control loop design. However, due to the nature of multi-directional power flow, this PSM-based control strategy suffers from high circulating power in the tank, especially when the converter operates at high power rating, which results in high conduction loss and demanding hardware design.
To overcome the high current circulation issue, a combined phase shift—and—duty ratio power flow control strategy is proposed in the subject system.
The subject control methodology is capable of simultaneous charging of both HV and LV batteries from the power system AC grid. Moreover, it can achieve the functionalities, including grid to HV battery (G2H) charging, grid to LV battery (G2L) charging, HV battery to LV battery (H2L) charging, and vehicle to grid (V2G) discharging.
The subject control system 200 which has a three-loop structure is shown in
The topology of a TAB-based converter used in the subject OBC system 100, 102 is equivalent to the delta configuration, as shown in
where L1, L2 and L3 are the primary, secondary and tertiary power inductors, respectively.
As shown in
f(δ1,δ2,δ3,φ1,φ2,φ3)=Min{|P12|+|P23|+|P31|} (Eq. 24)
A quick solution can be obtained by reducing one freedom of control variable:
φ1=0, φ2=φ3 (Eq. 25)
There are some restrictions on the reactive power control. Because of the three-port structure, reactive power flows between ports P1, P2, P3 are not inherently equal, which needs the boundary condition of δ control variable. φ1 is set as 0 to obtain maximum power flow capability. By using φ2=φ3, no circulating active power flows between port-2 and port-3. δ3 is utilized for the LV battery side voltage regulation. The control diagram for the subject control system 200 is expressed in
It is important to note that the subject power flow control strategy is applicable both to the three-phase integrated charging system, and the single-phase, as well as to the subject OBC system using any number of phases and power levels.
The state-of-charge (SoC) map, shown in
A detailed SoC plot based on the subject control methodology in the time domain is illustrated in
Although this invention has been described in connection with specific forms and embodiments thereof, it will be appreciated that various modifications other than those discussed above may be resorted to without departing from the spirit or scope of the invention as defined in the appended claims. For example, functionally equivalent elements may be substituted for those specifically shown and described, certain features may be used independently of other features, and in certain cases, particular locations of elements, steps, or processes may be reversed or interposed, all without departing from the spirit or scope of the invention as defined in the appended claims.
This invention was made with Government support under IIP 1602012 awarded by the National Science Foundation. The Government has certain rights in the invention.
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| Number | Date | Country | |
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| 20210155100 A1 | May 2021 | US |
| Number | Date | Country | |
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| 62655708 | Apr 2018 | US |
