Direct current coupling power system and control method thereof

Abstract

A DC-coupled power system receives an AC voltage from an AC power source, and includes an AC-DC converter, a battery module, a DC-coupled charger, and a control unit. The AC-DC converter is used for converting an AC voltage into a first DC voltage and providing the first DC voltage and power supply power to a DC bus. The battery module is directly connected with the DC bus. The DC coupling charger receives the first DC voltage and provides load power to supply power to a load. The control unit is used for judging the electric quantity of the battery module and comparing the load power with the contract power capacity so as to set the AC-DC converter in one of a plurality of modes.

Description

Technical Field

[0001] The present invention relates to a DC-coupled power system and a control method thereof, and more particularly to a DC-coupled power system with a charge-discharge battery module and a control method thereof. Background Art

[0002] In the prior art, a DC-coupled power system needs to convert alternating current from an AC power source into direct current through an AC-DC converter, and then further convert the direct current through a plurality of DC-DC converters to provide it to a battery module for energy storage and a DC-coupled charger for charging an electric vehicle.

[0003] As is well known, the setting of DC-DC converters in a DC-coupled power system will increase the operating power of the system, the line layout required for the operating system and the coordination control logic between multiple DC-DC converters will also become complicated, the system cost and the equipment installation space requirements will increase, and energy losses will occur when the DC-DC converters perform power conversion. The above problems are all important issues that those skilled in the art need to address when improving DC-coupled power systems. Summary of the Invention

[0004] The present disclosure provides a DC-coupled power system. The DC-coupled power system receives an AC voltage from an AC power source, and includes an AC-DC converter, a battery module, a DC-coupled charger, and a control unit. The AC-DC converter is used to convert the AC voltage into a first DC voltage and provide the first DC voltage and the power supply to a DC bus. The battery module is directly connected to the DC bus. The DC-coupled charger is coupled to the DC bus, receives the first DC voltage, and provides a load power to supply power to a load. The control unit is coupled to the AC-DC converter, the battery module, and the DC-coupled charger, and is used to determine the power level of the battery module, compare the load power and the contract power capacity, and set the AC-DC converter in one of a constant voltage mode, a constant power mode, and a constant voltage-constant power mode.

[0005] The present disclosure provides a control method for a DC-coupled power system. The method includes: receiving an AC voltage from an AC power source; converting the AC voltage into a first DC voltage through an AC-DC converter, and providing the first DC voltage and the power supply to a DC bus; receiving the first DC voltage from the DC bus through a DC-coupled charger, and providing a load power to supply power to a load; and determining the power level of the battery module through a control unit, comparing the load power and the contract power capacity, and setting the AC-DC converter in one of a constant voltage mode, a constant power mode, and a constant voltage-constant power mode.

[0006] In summary, since the DC-coupled power system of the present invention does not have an additional DC-DC converter, the DC-coupled power system of the present invention has many beneficial technical effects such as saving the operating power and the lines required for operation, simplifying the system control logic, avoiding the energy loss rate during power conversion by the DC-DC converter, and saving the system cost and the space occupied by the equipment. Description of the Drawings

[0007] Figure 1 Schematic diagram of a DC-coupled power system according to an embodiment of the present disclosure document.

[0008] Figure 2 For Figure 1 Schematic diagram of the voltage-power curve of the battery module of the embodiment.

[0009] Figure 3 For Figure 1 Flowchart of the control method of the DC-coupled power system of the embodiment.

[0010] Figure 4 For Figure 1 Timing diagram of the DC-coupled power system of the embodiment.

[0011] Figure 5 Schematic diagram of a DC-coupled power system according to another embodiment of the present disclosure document.

[0012] Figure 6 Schematic diagram of a DC-coupled power system according to another embodiment of the present disclosure document.

[0013] Figure 7 Schematic diagram of a DC-coupled power system according to another embodiment of the present disclosure document.

[0014] Figure 8 For Figure 1 Flowchart of the control method of the DC-coupled power system of the embodiment.

[0015] Figure 9 Schematic diagram of a DC-coupled power system according to a prior art of the present disclosure document.

[0016] Description of the Reference Numerals:

[0017] 100, 500, 600, 700, 900: DC-coupled power system

[0018] ADC1, ADC5, ADC6, ADC7, ADC9: AC-DC converter

[0019] BAT1, BAT5, BAT6, BAT7, BAT9: Battery module

[0020] DCC1, DCC5_1, DCC5_2, DCC5_3, DCC6, DCC7, DCC9: DC Coupled Chargers

[0021] CU1, CU5, CU6, CU7, CU9: Control Units

[0022] PS: AC Power Supply

[0023] VAC1, VAC5, VAC6, VAC7: AC Voltages

[0024] CDC: Contract Power Capacity

[0025] DCB1, DCB5, DCB6_1, DCB6_2, DCB7, DCB9: DC Buses

[0026] VDC1, VDC5, VDC6: DC Voltages

[0027] P_supply: Supply Power

[0028] P_load1, P_load51, P_load52, P_load53: Load Powers

[0029] EV1, EV5_1, EV5_2, EV5_3, EV6, EV7, EV9: Electric Vehicles

[0030] CV: Constant Voltage Mode

[0031] CP: Constant Power Mode

[0032] CVP: Constant Voltage - Constant Power Mode

[0033] T0, T1, T2, T3, T4: Time Points

[0034] LV_FC, LV_COF: Voltage Levels

[0035] 300, 800: Control Methods

[0036] S310, S320, S330, S340, S350, S360, S810, S820, S830, S840, S850: Steps I_supply: Supply Current

[0037] PE6: Positive Electrode

[0038] NE6: Negative Electrode

[0039] SPG7: Solar Power Generation System

[0040] WPG7: Wind Power Generation System

[0041] P_sol: Solar Power

[0042] P_win: Wind power

[0043] MPPT1, MPPT2: Maximum power point tracking units

[0044] AAC1, AAC2: DC - DC converters Detailed implementation manners

[0045] The embodiments of the present disclosure document will be described below in conjunction with the relevant drawings. In the drawings, the same reference numerals represent the same or similar elements or method flows.

[0046] Please refer to Figure 1 , Figure 1 , which is a schematic diagram of a DC - coupled power system 100 according to an embodiment of the present disclosure document. In the Figure 1 embodiment, the DC - coupled power system 100 includes an AC - DC converter ADC1, a battery module BAT1, a DC - coupled charger DCC1, and a control unit CU1.

[0047] As Figure 1 shown, the AC power supply PS can be a power supply device of an existing power grid (such as the mains power). The AC power supply PS can provide an AC voltage VAC1 to the AC - DC converter ADC1 of the DC - coupled power system 100.

[0048] In some cases, the power supply power of the AC power supply PS may be limited by the contract power capacity CDC. The contract power capacity CDC is a preset power value, which can be agreed upon in a contract between the operator of the power grid and the owner of the DC - coupled power system 100 of the present disclosure. When the input power required by the DC - coupled power system 100 exceeds the contract power capacity CDC, the owner of the DC - coupled power system 100 may have to pay an additional fee according to the contract.

[0049] The AC - DC converter ADC1 can receive the AC voltage VAC1. The AC - DC converter ADC1 can convert the AC voltage VAC1 into a DC voltage VDC1 and provide the DC voltage VDC1 and the power supply power P_supply to the DC bus (DCbus) DCB1.

[0050] The battery module BAT1 is directly connected to the DC bus DCB1. It is worth mentioning that there is no DC - DC converter in the battery module BAT1. Since the battery module BAT1 is directly connected to the DC bus DCB1, the battery module BAT1 directly receives the DC voltage VDC1 from the AC - DC converter ADC1 and adjusts the voltage level of the DC voltage VDC1 to charge or discharge the battery module BAT1.

[0051] In addition, no DC-DC converter is provided between the battery module BAT1 and the DC bus DCB1, nor is there a DC-DC converter between the battery module BAT1 and the AC-DC converter ADC1.

[0052] The DC-coupled charger DCC1 is coupled to the DC bus DCB1. The DC-coupled charger DCC1 can receive the DC voltage VDC1 and provide the load power P_load1 to charge the electric vehicle EV1.

[0053] The load power P_load1 can be changed according to actual requirements. For example, when the DC-coupled charger DCC1 is connected to the electric vehicle EV1 and multiple electric vehicles (not shown in Figure 1 ) or when the electric vehicle EV1 needs fast charging and the power demand increases, the load power P_load1 can be increased. When the multiple electric vehicles are fully charged and disconnected, the load power P_load1 will decrease.

[0054] The control unit CU1 is coupled to the AC-DC converter ADC1, the battery module BAT1, and the DC-coupled charger DCC1. The control unit CU1 can be used to determine the power level of the battery module BAT1, and compare the load power P_load1 and the contract power capacity CDC to set whether the AC-DC converter ADC1 should operate in the constant voltage (CV) mode, the constant power (CP) mode, or the constant voltage-constant power (CVP) mode.

[0055] In the constant voltage mode CV, the control unit CU1 can control the AC-DC converter ADC1 to maintain the voltage level of the DC voltage VDC1 on the DC bus DCB1 at the voltage level LV_FC. In the constant power mode CP, the control unit CU1 can control the AC-DC converter ADC1 to make the supply power P_supply equal to the contract power capacity CDC. In the constant voltage-constant power mode CVP, the control unit CU1 can control the AC-DC converter ADC1 to maintain the voltage level of the DC voltage VDC1 on the DC bus DCB1 at the voltage level LV_COF. As for how to determine whether the AC-DC converter ADC1 should operate in the constant voltage mode CV, the constant power mode CP, or the constant voltage-constant power mode CVP, the determination method can be seen in the control method 300 below Figure 3 of the control method 300.

[0056] In summary, since the DC-coupled power system 100 does not have an additional DC-DC converter, the DC-coupled power system 100 has many beneficial technical effects such as saving operating power and the lines required for operation, simplifying the system control logic, avoiding the energy loss rate during power conversion by the DC-DC converter, and saving system costs and the space occupied by equipment.

[0057] Please refer to Figure 2 , Figure 2 For Figure 1 the voltage-electricity schematic diagram of the battery module BAT1 in the embodiment. Figure 2 The Y-axis represents the voltage level of the battery module BAT1, and the X-axis represents the percentage of the electricity amount of the battery module BAT1. The percentage of the electricity amount can represent the electricity amount stored in the battery module BAT1 or the state of charge (SOC). In other embodiments, the scale value of the X-axis can be defined by the depth of discharge (DOD) of the battery module BAT1. For example, the scale value of the X-axis is from Figure 2 the left side to the right side of

[0058] In this embodiment, the battery module BAT1 may include lithium iron phosphate (LFP) batteries. The voltage level of the battery module BAT1 changes with the change of the electricity amount. When the battery module BAT1 discharges and discharges a large amount of electricity, the electricity amount in the battery module BAT1 will decrease, and the voltage level of the battery module BAT1 will drop; conversely, when the battery module BAT1 discharges less electricity, the electricity amount in the battery module BAT1 will be more, and the voltage level of the battery module BAT1 will be higher.

[0059] It should be noted that from Figure 2 the voltage-power curve of

[0060] LV_FC ≥ VDC1 ≥ LV_COF Equation <1>

[0061] Corresponding to Equation (1), the voltage level of the battery module BAT1 and the operating voltage range of the DC voltage VDC1 can be limited between the voltage level LV_FC and the voltage level LV_COF.

[0062] Please also refer to Figure 1 、 Figure 3 , Figure 3 is Figure 1 a flowchart of the control method 300 for the DC-coupled power system 100 of the embodiment. Specifically, the control method 300 detects the power level of the battery module BAT1 and the load power P_load1 through Figure 1 the control unit CU1, and determines the power supply P_supply output by the AC-DC converter ADC1 and the DC voltage VDC1 on the DC bus DCB1.

[0063] In step S310, the control unit CU1 can determine whether the load power P_load1 is less than the contract power capacity CDC. When the load power P_load1 is less than the contract power capacity CDC, step S320 is executed; when the load power P_load1 is greater than or equal to the contract power capacity CDC, step S330 is executed.

[0064] In step S320, the control unit CU1 can determine whether the power level of the battery module BAT1 is less than the full charge threshold (i.e., whether the power level of the battery module BAT1 has not reached Figure 2 the percentage of the power level corresponding to the voltage level LV_FC). When the power level of the battery module BAT1 reaches the full charge threshold, step S340 is executed; when the power level of the battery module BAT1 is less than the full charge threshold, step S350 is executed.

[0065] In step S330, the control unit CU1 can determine whether the power level of the battery module BAT1 is greater than the discharge threshold (i.e., whether the power level of the battery module BAT1 has reached Figure 2 the percentage of the power level corresponding to the voltage level LV_COF). When the power level of the battery module BAT1 is greater than the discharge threshold, step S350 is executed; when the power level of the battery module BAT1 reaches the discharge threshold, step S360 is executed.

[0066] In step S340, the control unit CU1 can make the AC-DC converter ADC1 operate in the constant voltage mode CV. In the constant voltage mode CV, the DC voltage VDC1 is equal to the voltage level LV_FC. The power supply P_supply can be equal to the load power P_load1 and vary with the load power P_load1. Since the power level of the battery module BAT1 reaches the full charge threshold, it means that the battery module BAT1 has completed charging, so the battery module BAT1 neither charges nor discharges.

[0067] In step S350, the control unit CU1 can operate the AC-DC converter ADC1 in the constant power mode CP. In the constant power mode CP, the supply power P_supply is fixed and can be set to be less than or equal to the contract power capacity CDC to avoid over-contract fines. Due to the limitation of the supply power P_supply, the AC-DC converter ADC1 can adjust the voltage level of the DC voltage VDC1 according to the magnitude of the load current, and thus the battery module BAT1 will naturally charge or discharge due to the change in the voltage level of the DC voltage VDC1.

[0068] In the constant power mode CP, if the load power P_load1 is less than the contract power capacity CDC and the charge level of the battery module BAT1 is less than the full charge threshold, the supply power P_supply can simultaneously provide the load power P_load1 required by the electric vehicle EV1 and the charging power required by the battery module BAT1. Since the AC-DC converter ADC1 operates in the constant power mode CP and its supply power P_supply is limited, when P_load1 decreases or the battery module BAT1 is gradually fully charged, causing the overall load current to gradually decrease, the voltage level of the DC voltage VDC1 will also gradually increase. The charging power required by the battery module BAT1 can be the difference between the contract power capacity CDC and the load power P_load1.

[0069] In the constant power mode CP, if the load power P_load1 is greater than or equal to the contract power capacity CDC and the charge level of the battery module BAT1 is greater than the discharge threshold, the AC-DC converter ADC1 will reduce the voltage level of the DC voltage VDC1 due to the increase in the load current (so as to achieve constant power output), thus causing the battery module BAT1 to naturally discharge to the DC bus DCB1. The load power P_load1 required by the electric vehicle EV1 can be equal to the sum of the discharge power of the battery module BAT1 and the contract power capacity CDC.

[0070] In step S360, the control unit CU1 can operate the AC-DC converter ADC1 in the constant voltage-constant power mode CVP. In the constant voltage-constant power mode CVP, the DC voltage VDC1 is maintained at the voltage level LV_COF, so that the battery module BAT1 cannot discharge externally. The supply power P_supply of the AC-DC converter ADC1 is the contract power capacity CDC, that is, the DC bus DCB1 can only provide the contract power capacity CDC less than the load power P_load1 to the DC coupled charger DCC1. In this case, the DC coupled charger DCC1 can enter the reduced load mode, and the DC coupled charger DCC1 will charge the electric vehicle EV1 at a lower charging speed.

[0071] It is worth mentioning that as the load power P_load1 and the power level of the battery module BAT1 change, the control unit CU1 can dynamically adjust the operating mode of the AC-DC converter ADC1.

[0072] Please also refer to Figure 1 , Figure 3 and Figure 4 , Figure 4 which is Figure 1 the timing diagram of the DC-coupled power system 100 of the embodiment. According to Figure 4 the embodiment of Figure 3 the control method 300, the operation of the AC-DC converter ADC1 switching between different modes can be clearly understood.

[0073] Between time point T0 and time point T1, the load power P_load1 is less than the contract power capacity CDC, and the AC-DC converter ADC1 operates in the constant voltage mode CV. During this period, the DC voltage VDC1 is equal to the voltage level LV_FC. The supply power P_supply is equal to the load power P_load1, and the supply current I_supply of the AC-DC converter ADC1 rises with the supply power P_supply and the load power P_load1. The power level of the battery module BAT1 is equal to the full charge threshold, and the battery module BAT1 neither charges nor discharges.

[0074] Between time point T1 and time point T2, the load power P_load1 is greater than the contract power capacity CDC, and the AC-DC converter ADC1 operates in the constant power mode CP. During this period, the supply power P_supply is fixed at the contract power capacity CDC, and the supply current I_supply of the AC-DC converter ADC1 rises with the load power P_load1. Since the supply power P_supply is fixed while the supply current I_supply rises, the DC voltage VDC1 decreases over time. Affected by the decrease in the DC voltage VDC1, the battery module BAT1 will naturally continue to discharge to the DC bus DCB1.

[0075] Between time point T2 and time point T3, the load power P_load1 is greater than the contract power capacity CDC, and the power level of the battery module BAT1 reaches the discharge threshold. The AC-DC converter ADC1 operates in the constant voltage-constant power mode CVP. During this period, the supply power P_supply is equal to the contract power capacity CDC, the DC voltage VDC1 is equal to the voltage level LV_COF, the supply current I_supply of the AC-DC converter ADC1 does not change, and the battery module BAT1 stops discharging.

[0076] Between time point T3 and time point T4, the load power P_load1 is less than the contract power capacity CDC, and the charge level of the battery module BAT1 has not reached the full charge threshold. The AC-DC converter ADC1 operates in the constant power mode CP. During this period, the supply power P_supply is equal to the contract power capacity CDC, and the supply current I_supply decreases as the load power P_load1 decreases. Since the supply power P_supply is fixed while the supply current I_supply decreases, the DC voltage VDC1 increases over time. Affected by the increase in the DC voltage VDC1, the battery module BAT1 naturally continues to charge.

[0077] After time point T4, the load power P_load1 is less than the contract power capacity CDC, the charge level of the battery module BAT1 reaches the full charge threshold, and the AC-DC converter ADC1 operates in the constant voltage mode CV. During this period, the DC voltage VDC1 is equal to the voltage level LV_FC, the supply power P_supply is equal to the load power P_load1, and the supply current I_supply of the AC-DC converter ADC1 decreases together with the supply power P_supply and the load power P_load1.

[0078] Please refer to Figure 5 , Figure 5 FIG. 500 is a schematic diagram of a DC-coupled power system 500 according to another embodiment of the present disclosure. In the Figure 1 embodiment, the DC-coupled power system 100 includes a single DC-coupled charger DCC1 and is connected to a single electric vehicle EV1. In practical applications, the DC-coupled power system is not limited to including only one DC-coupled charger. The DC-coupled power system 500 includes an AC-DC converter ADC5, a battery module BAT5, and a plurality of DC-coupled chargers (e.g., DC-coupled chargers DCC5_1, DCC5_2, DCC5_3).

[0079] The AC-DC converter ADC5 can convert the AC voltage VAC5 into a DC voltage VDC5 and provide the DC voltage VDC5 and the supply power P_supply to the DC bus DCB5. The battery module BAT5 is directly connected to the DC bus DCB5.

[0080] Each of the DC-coupled chargers is coupled to the DC bus DCB5, receives the DC voltage VDC1, and provides load powers P_load51, P_load52, P_load53 to charge the electric vehicles EV5_1, EV5_2, EV5_3 respectively.

[0081] In this embodiment, the control unit CU5 can control the AC-DC converter ADC5 to operate in different modes according to the power supply P_supply provided by the AC-DC converter ADC5 and along with the change of the total load power. The total load power in this embodiment is the sum of the load powers P_load51, P_load52, and P_load53.

[0082] Please refer to Figure 6 , Figure 6 which is a schematic diagram of a DC-coupled power system 600 according to another embodiment of the present disclosure document.

[0083] In this embodiment, the AC voltage VAC6 can be a three-phase AC voltage from the AC power supply PS. The AC-DC converter ADC6 can receive the AC voltage VAC6, convert the AC voltage VAC6 into a DC voltage VDC6, and provide the DC voltage VDC1 and the power supply P_supply to the DC buses DCB6_1 and DCB6_2. The DC bus DCB6_1 can be used to provide a positive voltage, and the DC bus DCB6_2 can be used to provide a negative voltage, and the two can form a loop.

[0084] The control unit CU6 is coupled to the AC-DC converter ADC6 and the battery module BAT6. The positive electrode PE6 and the negative electrode NE6 of the battery module BAT6 are directly connected to the DC buses DCB6_1 and DCB6_2. The DC-coupled charger DCC6 has two electrodes at its input, and these two electrodes can also be connected to the DC buses DCB6_1 and DCB6_2. The DC-coupled charger DCC6 can charge the electric vehicle EV6.

[0085] Please refer to Figure 7 , Figure 7 which is a schematic diagram of a DC-coupled power system 700 according to another embodiment of the present disclosure document. The configuration of the DC-coupled power system 700 can correspond to Figure 1 the DC-coupled power system 100. The difference between the two is that Figure 7 the embodiment of

[0086] further integrates the solar power generation system SPG7 and the wind power generation system WPG7 into the DC-coupled power system 700. Figure 1 , Figure 7 The AC-DC converter ADC7 in

[0087] In this embodiment, the solar panel of the solar power generation system SPG7 can be coupled to the DC bus DCB7 through the maximum power point tracking unit MPPT1 and provide solar power P_sol. The wind turbine of the wind power generation system WPG7 is coupled to the DC bus DCB7 through the maximum power point tracking unit MPPT2 and provides wind power P_win. Both the maximum power point tracking units MPPT1 and MPPT2 have the function of a DC-DC converter.

[0088] Please refer to Figures 1 and 8 at the same time. Figure 8 for Figure 1 Flow chart of a control method 800 of a DC coupled power system 100 according to an embodiment. The control method 800 is a time-based control method for saving electricity costs generated by the DC coupled power system 100.

[0089] Power companies usually adopt the Time-of-Use (TOU) model to charge electricity. The TOU model means that the power company divides a day into different time periods (for example, peak time, normal time and off-peak time), and the electricity charges for different time periods are different. Generally speaking, the electricity price is the highest during the peak time period, and the electricity price is the lowest during the off-peak time period. Figure 8 In the control method 800 , the battery module BAT1 may be used to store electricity at the lowest electricity price during off-peak hours, and the electricity stored in the battery module BAT1 may be preferentially used during peak hours.

[0090] In step S810, the DC coupled power system 100 may determine whether the current time is a peak time period of electricity charges. If the current time is a peak time period, step S820 is executed; if the current time is an off-peak time period, step S850 is executed.

[0091] In step S820, the control unit CU1 may determine whether the power of the battery module BAT1 has reached the full charge threshold (i.e., whether the battery module BAT1 has completed charging). If the power of the battery module BAT1 has reached the full charge threshold, step S830 is executed; if the power of the battery module BAT1 has not reached the full charge threshold, step S840 is executed.

[0092] In step S830, the control unit CU1 adjusts the DC voltage VDC1 to a voltage level LV_FC less than the full charge threshold, so that the battery module BAT1 discharges to the DC bus DCB1. This can reduce the power consumption from the AC power source PS during peak hours, thereby saving electricity costs during peak hours.

[0093] In step S840, the control unit CU1 sets the DC voltage VDC1 to a fixed voltage, causing the battery module BAT1 neither to discharge nor to charge, that is, not to charge the battery during peak periods. The fixed voltage can be the voltage level of the DC voltage VDC1 at the moment when it enters step S840.

[0094] In step S850, the control unit CU1 controls the AC-DC converter ADC1 to operate in the constant power mode CP and preferentially charges the battery module BAT1, that is, charges the battery during non-peak periods. It is worth mentioning that during the charging process of the battery module BAT1, the DC voltage VDC1 will gradually rise to the voltage level LV_FC, causing the battery module BAT1 to charge according to the change in the voltage level of the DC voltage VDC1 during off-peak periods.

[0095] In summary, through Figure 8 control method 800, the electricity cost of the DC-coupled power system 100 can be further optimized.

[0096] Please also refer to Figure 1 、 Figure 9 , Figure 9 FIG. is a schematic diagram of a DC-coupled power system 900 according to a prior art of the present disclosure document. The DC-coupled power system 900 is Figure 1 a prior art of the DC-coupled power system 100 of

[0097] The AC-DC converter ADC9 can be coupled to the AC power supply PS and the DC bus DCB9. The battery module BAT9 is coupled to the DC bus DCB1 through the DC-DC converter AAC1. The DC-coupled charger DCC9 is coupled to the DC bus DCB9 through the DC-DC converter AAC2. The control unit CU9 is coupled to the AC-DC converter ADC1, the battery module BAT1, the DC-coupled charger DCC9, and the DC-DC converters AAC1 and AAC2.

[0098] In the DC-coupled power system 900, when the battery module BAT9 is charging or discharging, it is necessary to let the control unit CU9 control the DC-DC converter AAC1, and the DC-DC converter AAC1 is used to transfer energy. When the DC-coupled charger DCC9 charges the electric vehicle EV9, it also needs to obtain energy from the DC bus DCB9 through the DC-DC converter AAC2.

[0099] On the contrary Figure 1, the battery module BAT1 of the direct current (DC) coupled power system 100 is directly connected to the DC bus DCB1, and the battery module BAT1 is charged or discharged by adjusting the voltage level of the DC voltage VDC1 without using a DC-DC converter. In addition, no DC-DC converter is provided between the DC coupled charger DCC1 and the DC bus DCB1 of the DC coupled power system 100. Instead, the DC bus DCB1 directly supplies power, enabling the DC coupled charger DCC1 to provide the load power P_load1 to charge the electric vehicle EV1.

[0100] Compared with the prior art, the DC coupled power system of the present invention has many advantageous technical effects, such as saving the operating power of the DC-DC converter and the lines required for operation, simplifying the system control logic, avoiding the energy loss rate during power conversion by the DC-DC converter, and saving the system cost and the space occupied by the equipment.

[0101] In the specification and claims, certain terms are used to refer to specific elements. However, those skilled in the art should understand that the same element may be referred to by different names. The specification and claims do not use the difference in names as a way to distinguish elements, but rather use the difference in the functions of the elements as the basis for distinction. The term "comprising" mentioned in the specification and claims is an open-ended term and should be interpreted as "comprising but not limited to".

[0102] In addition, unless specifically specified in the specification, any singular term also includes the plural meaning.

[0103] The above are only the preferred embodiments of this disclosure document. Without departing from the scope or concept of this disclosure document, various modifications and equivalent changes can be made to this disclosure document. In summary, all modifications and equivalent changes made to this disclosure document within the scope of the claims are covered by this disclosure document.

Claims

1. A DC coupled power system, receiving an AC voltage from an AC power source, comprising: an AC-DC converter, used for converting the AC voltage into a first DC voltage, and providing the first DC voltage and a power supply to a DC bus; a battery module, directly connected to the DC bus; a DC coupled charger, coupled to the DC bus, receiving the first DC voltage and providing a load power to supply power to a load; and A control unit is coupled to the AC-DC converter, the battery module and the DC coupled charger, and is used to determine the charge level of the battery module and compare the load power with a contract power capacity to set the AC-DC converter to one of a certain voltage mode, a certain power mode and a certain voltage-constant power mode.

2. The DC coupled power system of claim 1, wherein: The constant voltage mode is to maintain the voltage level of the first DC voltage at a first voltage level. The constant power mode is to make the power supply constant and less than or equal to the contract power capacity, and The constant voltage-constant power mode maintains the voltage level of the first DC voltage at a second voltage level, and keeps the power supply power constant and less than or equal to the contracted power capacity.

3. The DC-coupled power system as claimed in claim 2, wherein when the load power is less than the contracted power capacity and the power level of the battery module is a full charge threshold, the control unit enables the AC-DC converter to operate in the constant voltage mode.

4. A DC-coupled power system as described in claim 2, wherein when the load power is less than the contracted power capacity and the power of the battery module is less than a full charge threshold, or when the load power is greater than or equal to the contracted power capacity and the power of the battery module is greater than a discharge threshold, the control unit enables the AC-DC converter to operate in the constant power mode.

5. The DC-coupled power system as claimed in claim 2, wherein when the load power is greater than the contracted power capacity and the power level of the battery module is a discharge threshold, the control unit enables the AC-DC converter to operate in the constant voltage-constant power mode.

6. The DC coupled power system of claim 1, wherein the DC bus further comprises: a first power line, coupled to the AC-DC converter, the battery module and the DC coupling charger, for providing a high potential; and A second power line is coupled to the AC-DC converter, the battery module and the DC coupling charger to provide a low potential.

7. The DC coupled power system of claim 1, further comprising: a solar power generation system coupled to the DC bus to provide solar power; and A wind power generation system is coupled to the DC bus to provide wind power.

8. The DC-coupled power system as claimed in claim 1, further comprising a plurality of DC-coupled chargers, each of the DC-coupled chargers being coupled to the DC bus and receiving the first DC voltage to charge a corresponding plurality of loads.

9. A control method for a DC coupled power system, comprising: Receiving an AC voltage from an AC power source; Converting the AC voltage into a first DC voltage through an AC-DC converter, and providing the first DC voltage and a power supply to a DC bus; Receiving the first DC voltage from the DC bus through a DC-coupled charger and providing a load power to supply power to a load; and A control unit is used to determine the power level of a battery module and compare the load power with a contract power capacity to set the AC-DC converter to one of a certain voltage mode, a certain power mode, and a certain voltage-constant power mode.

10. The control method according to claim 9, wherein: The constant voltage mode is to maintain the voltage level of the first DC voltage at a first voltage level. The constant power mode is to make the power supply constant and less than or equal to the contract power capacity, and The constant voltage-constant power mode makes the power supply constant and less than or equal to the contracted power capacity, and makes the voltage level of the first DC voltage maintain at a second voltage level.

11. The control method as claimed in claim 10, wherein when the load power is less than the contracted power capacity and the power of the battery module is at a full charge threshold, the AC-DC converter is operated in the constant voltage mode.

12. The control method as described in claim 10, wherein when the load power is less than the contract power capacity and the power of the battery module is less than a full charge threshold, or when the load power is greater than or equal to the contract power capacity and the power of the battery module is greater than a discharge threshold, the AC-DC converter is operated in the constant power mode.

13. The control method as claimed in claim 10, wherein when the load power is greater than the contracted power capacity and the power level of the battery module is a discharge threshold, the control unit enables the AC-DC converter to operate in the constant voltage-constant power mode.

14. The control method as claimed in claim 9, wherein the DC bus further comprises a first power line and a second power line, and the control method further comprises: Providing a high potential through the first power line; and A low potential is provided through the second power line.

15. The control method according to claim 9, further comprising: Providing solar power to the DC bus through a solar power generation system; and A wind power generation system is used to provide wind power to the DC bus.

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