WO2019113771A1

WO2019113771A1 - Reconfigurable electric vehicle charging system

Info

Publication number: WO2019113771A1
Application number: PCT/CN2017/115587
Authority: WO
Inventors: Guoxing FAN; Sheng ZONG; Xiaobo Yang
Original assignee: Abb Schweiz Ag
Priority date: 2017-12-12
Filing date: 2017-12-12
Publication date: 2019-06-20

Abstract

A reconfigurable electric vehicle charging system (1), including: a first power conversion circuit (10) having a first port (100) and a second port (101), being configured to convert a first AC power input into a first DC power output for charging the electric vehicle in a first power flow direction (D1) from the first port (100) to the second port (101); a second power conversion circuit (11) having a third port (110) and a fourth port (111), being configured to selectively operate in either of conversion of a second AC power input into a second DC power output and conversion of a first DC power input into the second DC power output both in a second power flow direction (D2) from the third port (110) to the fourth port (111), wherein the second DC power output is arranged for charging the electric vehicle; and a switching device (12), being configured to select either of the second AC power input and the first DC power input of the second power conversion circuit (11). This allows for a relatively lower power capacity for a power converter thereof, manufacturing cost, power losses and physical size can be reduced.

Description

RECONFIGURABLE ELECTRIC VEHICLE CHARGING SYSTEM

Technical Field

The invention relates to power conversion circuit for charging batteries or for supply loads from batteries, and more particularly to electric vehicle charging system.

Background Art

Recently, the market of electrical vehicles grows fast. Electrical vehicle (EV) becomes popular, resulting in an increasing requirement for the charging capacity of EVs and consequently an enhancement of power capacity of an AC power grid as its power supply. However, changing the power capacity of an AC power grid takes time and is costly. Photovoltaics (PV) is more and more used in an EV charging system, as complementary power source to the AC power grid. With the implant of the PV equipment, the EV charging system becomes a multiple input ports and/or output ports.

An example of a power conversion system with multiple input ports and output ports is described in Patent EP 2511999 A1, which discloses a reconfigurable power conversion system for storing generated power, having DC to DC power converter coupling energy storage device to power source and another power converter. The reconfigurable power conversion system can store the generated power that is in excess of a grid load demand at particular time of day.

However, there would be some disadvantages with an EV charging system according to the solutions as disclosed in the Patent EP 2511999 A1. For example, at night, the PV panels are unable to generate power, and the power for charging the battery of EV all comes from the AC power grid since the output power of PV is zero at night. The power capacity of PV power converter would not be fully used for the whole day. Even worse, if the power demand for the EV charging at night is in excess of the power capacity of the AC power grid power converter, the charging power is limited by the capacity of AC power grid power convert, the charging time is prolonged, some of the EVs have to wait until the others stops charging releasing power capability they have been using.

Brief Summary of the Invention

It is therefore an objective of the invention to provide a reconfigurable electric vehicle charging system, including: a first power conversion circuit having a first port and a second port, being configured to convert a first AC power input into a first DC power output for charging the electric vehicle in a first power flow direction from the first port to the second port; a second power conversion circuit having a third port and a fourth port, being configured to selectively operate in either of conversion of a second AC power input into a second DC power output and conversion of a first DC power input into the second DC power output both in a second power flow direction from the third port to the fourth port, wherein the second DC power output is arranged for charging the electric vehicle; and a switching device, being configured to select either of the second AC power input and the first DC power input of the second power conversion circuit.

By having the reconfigurable electric vehicle charging system, during a period when the first DC power source is out of service, the second power conversion circuit is re-used for conversion of the second AC power into the first DC power output for charging the EV in parallel with the conversion operation of the first power conversion circuit. Consequently, both of the first power conversion circuit and the second power conversion circuit are used for conversion of an AC power into DC power charging the EV. The power capacity of the first power conversion circuit may be selected by referring to a fraction of the work load of the whole system due to the re-use of the power capacity of the second power conversion circuit for AC to DC conversion where the DC power source is out of service, which, otherwise, should be relatively higher since the first power conversion circuit 10 would have to take the full work load. This allows for a relatively lower power capacity for a power converter thereof, manufacturing cost, power losses and physical size can be reduced.

Preferably, the switching device is further configured to select the second AC power input of the second power conversion circuit in response that the first DC power input is out of service. The first power source generating the first AC and the second AC power inputs includes at least one AC power grid, and the second power source generating the first DC power input includes at least one solar cell or energy storage unit.

Preferably, the second power conversion circuit further includes an inductive element at the third port thereof; an allowable peak current or inductance value of the inductive element is selected from that required for the conversion of the second AC power input into the second DC power output and that required for the conversion of the first DC power input into the second DC power output, whichever is higher. The inductive element may step up voltage where the second power conversion circuit operates both in the conversion of the second AC power input into the second DC power output and the conversion of the first DC power input into the second DC power output.

Preferably, the reconfigurable EV charging system may have additional function where the EV battery may be discharged supplying electrical power to the AC power source and/or energy storage unit like battery. To achieve such purpose, the first power conversion circuit is further configured to convert a second DC power input from the electric vehicle into a first AC power output in a third power flow direction from the second port to the first port; the second power conversion circuit is further configured to selectively operate in either of conversion of a third DC power input from the electrical vehicle into a second AC power output and conversion of the third DC power input from the electrical vehicle into a third DC power output both in a fourth power flow direction from the fourth port to the third port; and the switching device is further configured to select either of the first AC power output and the third DC power output of the second power conversion circuit.

For the scenario of discharging EV battery, a first power sink receiving the first AC power output and the second AC power output includes at least one AC power grid, and a second power sink receiving the third DC power output is an energy storage unit.

Preferably, the switching device includes a first switch and a second switch; the first switch is arranged across the first port of the first power conversion circuit and the third port of the second power conversion circuit, the second switch is arranged at the third port of the second power conversion circuit, and the first switch and the second switch are configured to operate in opposite state.

A loop current may occur among the first power conversion circuit and the second power conversion circuit coupled in parallel. In order to suppress the loop current, preferably it provides a first current sensor, being configured to measure a first value of input current of the first power conversion circuit, a second current sensor, being configured to measure a second value of input current of the second power conversion circuit, and a control system, being configured to generate signals for control electrodes of semiconductor devices of the first power conversion circuit and the second power conversion circuit in consideration of the first value and the second value so as to reduce circulating current between the first power conversion circuit and the second power conversion circuit. Preferably, the control system is further configured to control the electrodes of semiconductor devices of the first power conversion circuit and the second power conversion circuit so as to regulate at least one of a first DC voltage at the second port of the first power conversion circuit and a second DC voltage at the fourth port of the second power conversion circuit to a predetermined value.

Brief Description of the Drawings

The subject matter of the invention will be explained in more detail in the following text with reference to preferred exemplary embodiments which are illustrated in the drawings, in which:

Figure 1 illustrates a reconfigurable EV charging system according to an embodiment of present invention; and

Figure 2 illustrates the control system according to an embodiment of present invention addressing the current sharing issue under the scenario of charging the EV battery with the first switch closed and the second switch open.

The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures.

Preferred Embodiments of the Invention

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. Note, the headings are for organizational purposes only and are not meant to be used to limit or interpret the description or claims. Furthermore, note that the word "may" is used throughout this application in a permissive sense (i.e., having the potential to, being able to) , not a mandatory sense (i.e., must) . " The term "include" , and derivations thereof, mean "including, but not limited to" . The term "connected" means "directly or indirectly connected" , and the term "coupled" means "directly or indirectly connected" .

Figure 1 illustrates a reconfigurable EV charging system according to an embodiment of present invention. As shown in figure 1, the reconfigurable EV charging system 1 has a plurality of ports configured to be respectively electrically coupled with an AC power source, a DC power source, and an EV to be charged.

For example, the AC power source may include at least one AC power grid. The skilled person shall understand the an AC power grid is able to feed AC power to the reconfigurable EV charging system which in turn converts the AC power and supplies the converted to a battery of the EV; besides, if the reconfigurable EV charging system 1 is configured to be capable of bi-directional power conversion, the AC power grid may behave as a power sink for receiving the power fed from the reconfigurable EV charging system.

The DC power source may include at least one solar cell. In some examples, at least a portion of the DC source may include other intermittent power sources such as wind or tidal power. However, some possible intermittent power sources, such as wind and tidal power, may need to be converted to DC before use with the reconfigurable EV charging system 1. All of these types of DC power source can intermittently supply power as a result of their changing environmental conditions, such as sunshine, wind speed and tidal force. This provides the possibility for re-use their power converter for other purpose where their environmental conditions do not allow them to generate power, for example at night, low wind speed and low tidal force.

The DC power source may include at least one energy storage unit. The energy storage unit may include any suitable combination of devices or structures capable of storing electrical energy. Nonexclusive illustrative examples of such devices include, without limitation, electrochemical cells or batteries, capacitors, supercapacitors, flywheels, or the like.

The reconfigurable EV charging system 1 includes a first power conversion circuit 10, a second power conversion circuit 11, and a switching device 12. Either of the first power conversion circuit 10 and the second power conversion circuit 11 may be configured to be conduct unidirectional power conversion or bidirectional power conversion. Either or both of the first power conversion circuit 10 and the second power conversion circuit 11 may include at least one switching element or device. The switching element or device may include at least one semiconductor switching device, such as a power transistor, a power MOSFET, an insulated gate bipolar transistor (IGBT) , a gate turn-off thyristor (GTO) , or the like. By changing the on-off duty ratio and frequency of the switching element or device, the first power conversion circuit 10 and/or the second power conversion circuit 11 can control its output voltage and frequency.

The first power conversion circuit 10 has a first port 100 and a second port 101 of the plurality of ports of the reconfigurable EV charging system 1. The first power conversion circuit 10 may be configured to operate as an AC to DC converter, converting a first AC power input into a first DC power output for charging the electric vehicle in a first power flow direction D1 from the first port 100 to the second port 101. The first AC power is fed, for example, from the AC power source may include at least one AC power grid. When coupling the first port 100 of the first power conversion circuit 10 to the AC power source, the first AC power fed from the AC power source may be converted into the first DC power, such as to charge the electrical vehicle from the AC power source, like the AC power grid.

The second power conversion circuit 11 has a third port 110 and a fourth port 111 of the plurality of ports of the reconfigurable EV charging system 1. The second power conversion circuit 11 may be configured to operate in a selected one of at least two modes. For example, the second power conversion circuit 11 may be configured to selectively operate or function as an AC to DC converter, converting a second AC power input into a second DC power output for charging the electric vehicle in a second power flow direction D2 from the third port 110 and the fourth port 111. The second AC power is fed, for example, from the AC power source which may include the at least one AC power grid. The second power conversion circuit 11 may be configured to selectively operate or function as a DC to DC converter, converting a first DC power input into the second DC power output for charging the electric vehicle in the second power flow direction D2 from the third port 110 and the fourth port 111. The first DC power input is fed, for example, from the DC power source which may include the at least one solar cell or other intermittent power sources. For example, the solar cell may be out of service at night, When coupling the third port 110 of the second power conversion circuit 11 to the AC power source, the second AC power fed from the AC power source may be converted into the second DC power, such as to charge the electrical vehicle from the AC power source, like the AC power grid. When coupling the third port 110 of the second power conversion circuit 11 to the DC power source, the first DC power fed from the DC power source may be converted into the second DC power, such as to charge the electrical vehicle from the AC power source, like the AC power grid.

As describe above, the second power conversion circuit 11 would not be fully utilized unless it were to participate in the EV charging where the DC power source was out of service. To this end, a switching device 12 is provided and configured to select either of the second AC power input and the first DC power input of the second power conversion circuit 11. Under the different connection states of the switching device 12, the third port 110 of the second power conversion circuit 11 is coupled to either the AC power source or the DC power source. For example, the switching device 12 may include a first switch 120 and a second switch 121. The first switch 120 is arranged across the first port 100 of the first power conversion circuit 10 and the third port 110 of the second power conversion circuit 11; the second switch 121 is arranged at the third port 110 of the second power conversion circuit 11. In order to select either of the AC power source and the DC power source to provide power to the second power conversion circuit 11, the first switch 120 and the second switch 121 are configured to operate in opposite state.

For example, during the day when the solar cell of the DC power source is allowed to absorb sufficient light to generate electricity, the first switch 120 is open and the second switch 121 is closed. Consequently, the first power conversion circuit 10 is used for conversion of an AC power supplied from the AC power source (the first AC power input) into an DC power output (the first DC power output) for charging the EV, and in parallel the second power conversion circuit 11 is used for conversion of an DC power supplied from the DC power source (the first DC power input) into an DC power output (the second DC power output) for charging the EV. At night when the solar cell of the DC power source is unable to generate the electricity due to insufficient sunshine, the first switch 120 is open and the second switch 121 is closed. Consequently, both of the first power conversion circuit 10 and the second power conversion circuit 11 are used for conversion of an AC power supplied from the AC power source (the first AC power input and the second AC power input) into an DC power output (the first DC power output and the second DC power output) for charging the EV. When designing the reconfigurable EV charging system 1, the power capacity of the first power conversion circuit 10 may be selected by referring to a fraction of the work load of the whole system due to the re-use of the power capacity of the second power conversion circuit 11 for AC to DC conversion where the DC power source is out of service, which, otherwise, should be relatively higher since the first power conversion circuit 10 would have to take the full work load.

By having the reconfigurable EV charging system according to the present invention allowing for a relatively lower power capacity for a power converter thereof, manufacturing cost, power losses and physical size can be reduced. Besides, more converters are fully utilized during the day and night.

Preferably, the second power conversion circuit 11 may further include an inductive element 112 at the third port 110 thereof. The inductive element 112 may step up voltage where the second power conversion circuit 11 operates both in the conversion of the second AC power input into the second DC power output and the conversion of the first DC power input into the second DC power output. Therefore, an allowable peak current or inductance value of the inductive element 112 is selected from that required for the conversion of the second AC power input into the second DC power output and that required for the conversion of the first DC power input into the second DC power output, whichever is higher. For the allowable peak current, based on the ampere circuit law, the equation is as follow:

Here, N is the turns number of the inductor, I is the peak current which flows through the inductor, Bs is the saturate flux density of core, μ0 is the free space permeability, μr is the relative permeability, le is the length of effective magnetic circuit.

Here I should be the higher allowable peak current between two work modes, otherwise, the inductor goes into saturation status in some cases. On the other hand, for the value of inductance, if the lower value of inductance is selected, the ripple current is higher than the allowable value in one work mode, which means the higher temperature rise appears. Further, the temperature of inductor is over the limits. So the higher value of inductance should be selected.

Preferably, the reconfigurable EV charging system 1 may have additional function where the EV battery may be discharged supplying electrical power to the AC power source and/or energy storage unit like battery.

In order to support the additional function, the first power conversion circuit 10 is further configured to convert a second DC power input from the electric vehicle into a first AC power output in a third power flow direction D3 from the second port 101 to the first port 100, the second power conversion circuit 11 is further configured to selectively operate in either of conversion of a third DC power input from the electrical vehicle into a second AC power output and conversion of the third DC power input from the electrical vehicle into a third DC power output both in a fourth power flow direction D4 from the fourth port 111 to the third port 110, and the switching device 12 is further configured to select either of the first AC power output and the third DC power output of the second power conversion circuit. For example, when coupling the first port 100 of the first power conversion circuit 10 to the AC power source, the second DC power fed from the discharging EV battery may be converted into the first AC power which further is supplied to the AC power source (for example, the AC power grid) as of a first power sink. When coupling the third port 110 of the second power conversion circuit 11 to the AC power source (the first switch 120 is closed and the second switch 121 is open) , the third DC power fed from the discharging EV battery may be converted into the second AC power which further is supplied to the AC power source (for example, the AC power grid) as of a first power sink; and when coupling the third port 110 of the second power conversion circuit 11 to the DC power source (the first switch 120 is open and the second switch 121 is closed) , the third DC power fed from the discharging EV battery may be converted into the a third DC power output to charge the energy storage unit as of a second power sink.

Preferably, for the scenario of charging the EV battery with the first switch 120 closed and the second switch 121 open, a loop current may occur among the first power conversion circuit 10 and the second power conversion circuit 11. In order to suppress the loop current, a first current sensor 13, a second current sensor 14 and a control system 15 are provided. The first current sensor 13 is configured to measure a first value of input current of the first power conversion circuit 10, which, for example, may be arranged at the first port 100 of the first power conversion circuit 10. The second current sensor 14 is configured to measure a second value of input current of the second power conversion circuit 11, which, for example, may be arranged at the third port 110 of the second power conversion circuit 11. The control system 15 is configured to generate signals for control electrodes of semiconductor devices Sp1, Sp2, Sp3, Sp4 of the first power conversion circuit 10 and semiconductor devices Sp5, Sp6, Sp7, Sp8 of the second power conversion circuit 11 in consideration of the first value and the second value so as to reduce circulating current between the first power conversion circuit 10 and the second power conversion circuit 11. And preferably, the control system 15 is further configured to control the electrodes of semiconductor devices of the first power conversion circuit 10 and the second power conversion circuit 11 so as to regulate at least one of a first DC bus voltage Vdc1 (the DC voltage of capacitor Cdc1) at the second port 101 of the first power conversion circuit 11 and a second DC voltage Vdc2 (the DC voltage of capacitor Cdc2) at the fourth port 111 of the second power conversion circuit 11 to a predetermined value

Figure 2 illustrates the control system according to an embodiment of present invention addressing the current sharing issue under the scenario of charging the EV battery with the first switch closed and the second switch open. In this mode, the DC bus voltage Vdc1, Vdc2 of the first power conversion circuit 10 and the second power conversion circuit 11 is regulated by the two paralleled power conversion circuits by adjustment their current loop reference. So an external control loop is bus voltage control loop, and an internal control loop is current control loop. In the parallel-run mode, the Iac_ref is the total current reference for both of the two

power conversion circuits

10, 11. Therefore a main current loop can be set up. The feedback of this loop is the sum value of Is1 and Is3. The output of this loop is the signals Gsp1～Gsp4 for control electrodes of semiconductor devices of the first power conversion circuits 10 and the signals Gsp5～Gsp8 for control electrodes of semiconductor devices of the second power conversion circuits 11. Consequently, the DC bus voltage can be regulated by the paralleled

power conversion circuits

10, 11 without current sharing functionality. Additional current control loop is needed to achieve the current sharing. The coefficient of K is the coefficient of current distribution between the two

power conversion circuits

10, 11. So the current reference of the second power conversion circuit 11 Is3_ref is derived from this coefficient and Iac_ref. The feedback of this additional loop is Is3, the output of this loop is the current sharing control signal, ΔGsp5～ ΔGsp8. Adding this signals to Gsp5～Gsp8, so the Gsp5’～Gsp8’can be got. Therefore, the signals to the electrodes of semiconductor devices Sp1, Sp2, Sp3, Sp4 of the first power conversion circuits 10 are Gsp1～Gsp4, and the signals to the electrodes of semiconductor devices Sp5, Sp6, Sp7, Sp8 of the second power conversion circuits 11 are Gsp5’～Gsp8’.

Preferably, a bidirectional DC to DC power conversion circuit 16 having a fifth port and a sixth port is provided for regulating the EV charging DC voltage. The fifth port of the bidirectional DC to DC power conversion circuit 16 is electrically coupled with each of the second port 101 of the first power conversion circuit 10 and the fourth port 111 of the second power conversion circuit 11.

Though the present invention has been described on the basis of some preferred embodiments, those skilled in the art should appreciate that those embodiments should by no way limit the scope of the present invention. Without departing from the spirit and concept of the present invention, any variations and modifications to the embodiments should be within the apprehension of those with ordinary knowledge and skills in the art, and therefore fall in the scope of the present invention which is defined by the accompanied claims.

Claims

A reconfigurable electric vehicle charging system, including:

a first power conversion circuit having a first port and a second port, being configured to convert a first AC power input into a first DC power output for charging the electric vehicle in a first power flow direction from the first port to the second port;

a second power conversion circuit having a third port and a fourth port, being configured to selectively operate in either of conversion of a second AC power input into a second DC power output and conversion of a first DC power input into the second DC power output both in a second power flow direction from the third port to the fourth port, wherein the second DC power output is arranged for charging the electric vehicle; and

a switching device, being configured to select either of the second AC power input and the first DC power input of the second power conversion circuit.
The reconfigurable electric vehicle charging system according to claim 1, wherein:

the switching device is further configured to select the second AC power input of the second power conversion circuit in response that the first DC power input is out of service.
The reconfigurable electric vehicle charging system according to any of the preceding claims, wherein:

a first power source generating the first AC and the second AC power inputs includes at least one AC power grid;

a second power source generating the first DC power input includes at least one solar cell or energy storage unit.
The reconfigurable electric vehicle charging system according to any of the preceding claims, wherein:

the second power conversion circuit further includes an inductive element at the third port thereof;

an allowable peak current or inductance value of the inductive element is selected from that required for the conversion of the second AC power input into the second DC power output and that required for the conversion of the first DC power input into the second DC power output, whichever is higher.
The reconfigurable electric vehicle charging system according to any of the preceding claims, wherein:

the first power conversion circuit is further configured to convert a second DC power input from the electric vehicle into a first AC power output in a third power flow direction from the second port to the first port;

the second power conversion circuit is further configured to selectively operate in either of conversion of a third DC power input from the electrical vehicle into a second AC power output and conversion of the third DC power input from the electrical vehicle into a third DC power output both in a fourth power flow direction from the fourth port to the third port; and

the switching device is further configured to select either of the first AC power output and the third DC power output of the second power conversion circuit.
The reconfigurable electric vehicle charging system according to claim 5, wherein:

a first power sink receiving the first AC power output and the second AC power output includes at least one AC power grid; and

a second power sink receiving the third DC power output is an energy storage unit.
The reconfigurable electric vehicle charging system according to any of the preceding claims, wherein:

the switching device includes a first switch and a second switch;

the first switch is arranged across the first port of the first power conversion circuit and the third port of the second power conversion circuit;

the second switch is arranged at the third port of the second power conversion circuit; and

the first switch and the second switch are configured to operate in opposite state.
The reconfigurable electric vehicle charging system according to any of the preceding claims, further includes:

a first current sensor, being configured to measure a first value of input current of the first power conversion circuit;

a second current sensor, being configured to measure a second value of input current of the second power conversion circuit; and

a control system, being configured to generate signals for control electrodes of semiconductor devices of the first power conversion circuit and the second power conversion circuit in consideration of the first value and the second value so as to reduce circulating current between the first power conversion circuit and the second power conversion circuit.
The reconfigurable electric vehicle charging system according to claim 8, wherein:

the control system is further configured to control the electrodes of semiconductor devices of the first power conversion circuit and the second power conversion circuit so as to regulate at least one of a first DC voltage at the second port of the first power conversion circuit and a second DC voltage at the fourth port of the second power conversion circuit to a predetermined value.
The reconfigurable electric vehicle charging system according to any of the preceding claims, further including:

a bidirectional DC to DC power conversion circuit having a fifth port and a sixth port; wherein:

the fifth port of the bidirectional DC to DC power conversion circuit is electrically coupled with each of the second port of the first power conversion circuit and the fourth port of the second power conversion circuit.