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EP-4311061-B1 - BIPOLAR POWER SUPPLY SYSTEM AND CONTROL METHOD

EP4311061B1EP 4311061 B1EP4311061 B1EP 4311061B1EP-4311061-B1

Inventors

  • YU, XINYU
  • XIN, KAI

Dates

Publication Date
20260506
Application Date
20210330

Claims (10)

  1. A bipolar power supply system (200), comprising a voltage conversion unit (120), an inverter unit (240), and a controller, wherein the voltage conversion unit (220) is configured to: receive electric energy provided by a power generation module, and output a direct current to the inverter unit (240) after performing direct current conversion; the inverter unit (240) is configured to: convert the direct current into an alternating current, and output the alternating current to a power grid; the voltage conversion unit (220) comprises a positive voltage conversion apparatus (221) and a negative voltage conversion apparatus (222), the inverter unit (240) comprises a positive inverter (241) and a negative inverter (242), a positive output end of the positive voltage conversion apparatus (221) is connected to a positive input end of the positive inverter (241), a negative output end of the negative voltage conversion apparatus (222) is connected to a negative input end of the negative inverter (242), a negative output end of the positive voltage conversion apparatus (221) and a positive output end of the negative voltage conversion apparatus (222) are connected to a first end of a neutral wire (230), and a negative input end of the positive inverter (241) and a positive input end of the negative inverter (242) are connected to a second end of the neutral wire (230); and the controller is configured to: detect whether a neutral wire (230) current meets a preset current range, wherein the neutral wire (230) current is a current passing through the neutral wire (230); and control, when the neutral wire (230) current does not meet the preset current range, the positive voltage conversion apparatus (221) and the negative voltage conversion apparatus (222) to change output voltages when output power of the positive voltage conversion apparatus (221) and the negative voltage conversion apparatus (222) remains unchanged, until the neutral wire (230) current meets the preset current range, wherein in this manner of adjusting the neutral wire (230) current, the output power of the voltage conversion apparatuses is kept unchanged; wherein the preset current range is [-I t1 , It 2 ], -I t1 represents a first preset current threshold, I t2 represents a second preset current threshold, a direction of the neutral wire (230) current is from the inverter unit (140) to the voltage conversion unit (120), a positive direction of the current range is from the inverter unit (140) to the voltage conversion unit (120), a negative direction of the current range is from the voltage conversion unit (120) to the inverter unit (140), and the controller is specifically configured to: determine that the neutral wire (230) current is greater than I t2 ; and control the positive voltage conversion apparatus (221) and the negative voltage conversion apparatus (222) to increase a voltage difference between the output voltage of the positive voltage conversion apparatus (221) and the output voltage of the negative voltage conversion apparatus (222) when the output power of the positive voltage conversion apparatus (221) and the negative voltage conversion apparatus (222) remains unchanged, until the neutral wire (230) current falls within the preset current range [-I t1 , I t2 ]; or determine that the neutral wire (230) current is less than -I t1 ; and control the positive voltage conversion apparatus (221) and the negative voltage conversion apparatus (222) to decrease a voltage difference between the output voltage of the positive voltage conversion apparatus (221) and the output voltage of the negative voltage conversion apparatus (222) when the output power of the positive voltage conversion apparatus (221) and the negative voltage conversion apparatus (222) remains unchanged, until the neutral wire (230) current falls within the preset current range [-I t1 , I t2 ]; and the controller is further configured to determine whether the output voltage of the positive voltage conversion apparatus (221) is greater than a first preset voltage threshold, wherein the first preset voltage threshold is an adjustable upper limit value of the output voltage of the positive voltage conversion apparatus (221); and the controller is further specifically configured to: when the neutral wire (230) current is greater than I t2 , and the output voltage of the positive voltage conversion apparatus (221) is less than the first preset voltage threshold, control the positive voltage conversion apparatus (221) and the negative voltage conversion apparatus (222) to increase the voltage difference between the output voltage of the positive voltage conversion apparatus (221) and the output voltage of the negative voltage conversion apparatus (222) when the output power of the positive voltage conversion apparatus (221) and the negative voltage conversion apparatus (222) remains unchanged, until the neutral wire (230) current falls within the preset current range [-I t1 , I t2 ]; or when the neutral wire (230) current is greater than I t2 , and the output voltage of the positive voltage conversion apparatus (221) is greater than or equal to the first preset voltage threshold, control the positive voltage conversion apparatus (221) to decrease output power.
  2. The system (100) according to claim 1, wherein the controller comprises a first control unit disposed in the positive voltage conversion apparatus (221) and a second control unit disposed in the negative voltage conversion apparatus (222); the first control unit is specifically configured to: when the neutral wire (230) current is greater than I t2 , control the positive voltage conversion apparatus (221) to increase the output voltage; and the second control unit is specifically configured to: when the neutral wire (230) current is greater than I t2 , control the negative voltage conversion apparatus (222) to decrease the output voltage.
  3. The system (100) according to claim 1, wherein the controller comprises a first control unit disposed in the positive voltage conversion apparatus (221) and a second control unit disposed in the negative voltage conversion apparatus (222); the first control unit is specifically configured to: when the neutral wire (230) current is greater than I t2 , control the positive voltage conversion apparatus (221) to increase the output voltage; and the second control unit is specifically configured to: when the neutral wire (230) current is greater than I t2 , control the output voltage of the negative voltage conversion apparatus (222) to remain unchanged.
  4. The system (100) according to claim 1, wherein the controller comprises a first control unit disposed in the positive voltage conversion apparatus (221) and a second control unit disposed in the negative voltage conversion apparatus (222); the first control unit is specifically configured to: when the neutral wire (230) current is greater than I t2 , control the output voltage of the positive voltage conversion apparatus (221) to remain unchanged; and the second control unit is specifically configured to: when the neutral wire (230) current is greater than I t2 , control the negative voltage conversion apparatus (222) to decrease the output voltage.
  5. The system (100) according to claim 1, wherein the controller comprises a first control unit disposed in the positive voltage conversion apparatus (221) and a second control unit disposed in the negative voltage conversion apparatus (222); the first control unit is specifically configured to: when the neutral wire (230) current is less than -I t1 , control the positive voltage conversion apparatus (221) to decrease the output voltage; and the second control unit is specifically configured to: when the neutral wire (230) current is less than -I t1 , control the negative voltage conversion apparatus (222) to increase the output voltage.
  6. The system (100) according to claim 1, wherein the controller comprises a first control unit disposed in the positive voltage conversion apparatus (221) and a second control unit disposed in the negative voltage conversion apparatus (222); the first control unit is specifically configured to: when the neutral wire (230) current is less than -I t1 , control the positive voltage conversion apparatus (221) to decrease the output voltage; and the second control unit is specifically configured to: when the neutral wire (230) current is less than -I t1 , control the output voltage of the negative voltage conversion apparatus (222) to remain unchanged.
  7. The system (100) according to claim 1, wherein the controller comprises a first control unit disposed in the positive voltage conversion apparatus (221) and a second control unit disposed in the negative voltage conversion apparatus (222); the first control unit is specifically configured to: when the neutral wire (230) current is less than -I t1 , control the output voltage of the positive voltage conversion apparatus (221) to remain unchanged; and the second control unit is specifically configured to: when the neutral wire (230) current is less than -I t1 , control the negative voltage conversion apparatus (222) to increase the output voltage.
  8. The system (100) according to any one of claims 1 and 5 to 7 wherein the controller is further configured to: determine whether the output voltage of the negative voltage conversion apparatus (222) is greater than a second preset voltage threshold, wherein the second preset voltage threshold is an adjustable upper limit value of the output voltage of the negative voltage conversion apparatus (222); and the controller is specifically configured to: when the neutral wire (230) current is less than -I t1 , and the output voltage of the negative voltage conversion apparatus (222) is less than the second preset voltage threshold, control the positive voltage conversion apparatus (221) and the negative voltage conversion apparatus (222) to decrease the voltage difference between the output voltage of the positive voltage conversion apparatus (221) and the output voltage of the negative voltage conversion apparatus (222) when the output power of the positive voltage conversion apparatus (221) and the negative voltage conversion apparatus (222) remains unchanged, until the neutral wire (230) current falls within the preset current range [-I t1 , I t2 ]; or the controller is further configured to: when the neutral wire (230) current is less than -I t1 , and the output voltage of the negative voltage conversion apparatus (222) is greater than or equal to the second preset voltage threshold, control the negative voltage conversion apparatus (222) to decrease output power.
  9. A control method for a bipolar power supply system, wherein the bipolar power supply system comprises a voltage conversion unit, an inverter unit, and a controller; the voltage conversion unit is configured to: receive electric energy provided by a power generation module, and output a direct current to the inverter unit after performing direct current conversion; the inverter unit is configured to: convert the direct current into an alternating current, and output the alternating current to a power grid; the voltage conversion unit comprises a positive voltage conversion apparatus and a negative voltage conversion apparatus, the inverter unit comprises a positive inverter and a negative inverter, a positive output end of the positive voltage conversion apparatus is connected to a positive input end of the positive inverter, a negative output end of the negative voltage conversion apparatus is connected to a negative input end of the negative inverter, a negative output end of the positive voltage conversion apparatus and a positive output end of the negative voltage conversion apparatus are connected to a first end of a neutral wire, and a negative input end of the positive inverter and a positive input end of the negative inverter are connected to a second end of the neutral wire; and the method comprises: detecting, by the controller, whether a neutral wire current meets a preset current range, wherein the neutral wire current is a current passing through the neutral wire; and controlling, by the controller when the neutral wire current does not meet the preset current range, the positive voltage conversion apparatus and the negative voltage conversion apparatus to change output voltages when output power of the positive voltage conversion apparatus and the negative voltage conversion apparatus remains unchanged, until the neutral wire current meets the preset current range, wherein in this manner of adjusting the neutral wire current, the output power of the voltage conversion apparatuses is kept unchanged; wherein the preset current range is [-I t1 , It 2 ], -I t1 represents a first preset current threshold, I t2 represents a second preset current threshold, a direction of the neutral wire current is from the inverter unit to the voltage conversion unit, a positive direction of the current range is from the inverter unit to the voltage conversion unit, and a negative direction of the current range is from the voltage conversion unit to the inverter unit; and the controlling, by the controller when the neutral wire current does not meet the preset current range, the positive voltage conversion apparatus and the negative voltage conversion apparatus to change output voltages when output power of the positive voltage conversion apparatus and the negative voltage conversion apparatus remains unchanged comprises: determining, by the controller, that the neutral wire current is greater than I t2 ; and controlling, by the controller, the positive voltage conversion apparatus and the negative voltage conversion apparatus to increase a voltage difference between the output voltage of the positive voltage conversion apparatus and the output voltage of the negative voltage conversion apparatus when the output power of the positive voltage conversion apparatus and the negative voltage conversion apparatus remains unchanged, until the neutral wire current falls within the preset current range [-I t1 , I t2 ]; or the controlling, by the controller when the neutral wire current does not meet the preset current range, the positive voltage conversion apparatus and the negative voltage conversion apparatus to change output voltages when output power of the positive voltage conversion apparatus and the negative voltage conversion apparatus remains unchanged comprises: determining, by the controller, that the neutral wire current is less than -I t1 ; and controlling, by the controller, the positive voltage conversion apparatus and the negative voltage conversion apparatus to decrease a voltage difference between the output voltage of the positive voltage conversion apparatus and the output voltage of the negative voltage conversion apparatus when the output power of the positive voltage conversion apparatus and the negative voltage conversion apparatus remains unchanged, until the neutral wire current falls within the preset current range [-I t1 , I t2 ]; and determining, by the controller, whether the output voltage of the positive voltage conversion apparatus is greater than a first preset voltage threshold, wherein the first preset voltage threshold is an adjustable upper limit value of the output voltage of the positive voltage conversion apparatus; and the controlling, by the controller, the positive voltage conversion apparatus and the negative voltage conversion apparatus to increase a voltage difference between the output voltage of the positive voltage conversion apparatus and the output voltage of the negative voltage conversion apparatus when the output power remains unchanged comprises: when the neutral wire current is greater than I t2 , and the output voltage of the positive voltage conversion apparatus is less than the first preset voltage threshold, controlling, by the controller, the positive voltage conversion apparatus and the negative voltage conversion apparatus to increase the voltage difference between the output voltage of the positive voltage conversion apparatus and the output voltage of the negative voltage conversion apparatus when the output power remains unchanged, so that the neutral wire current falls within the interval [-I t1 , I t2 ]; or the neutral wire current is greater than I t2 , and the output voltage of the positive voltage conversion apparatus is greater than or equal to the first preset voltage threshold, controlling, by the controller, the positive voltage conversion apparatus to decrease the output power.
  10. The method according to claim 9, wherein the controller comprises a first control unit disposed in the positive voltage conversion apparatus and a second control unit disposed in the negative voltage conversion apparatus, and the controlling, by the controller when detecting that the neutral wire current is greater than I t2 , the positive voltage conversion apparatus and the negative voltage conversion apparatus to increase a voltage difference between the output voltage of the positive voltage conversion apparatus and the output voltage of the negative voltage conversion apparatus when the output power of the positive voltage conversion apparatus and the negative voltage conversion apparatus remains unchanged comprises: when it is detected that the neutral wire current is greater than I t2 , controlling, by the first control unit, the positive voltage conversion apparatus to increase the output voltage; and when it is detected that the neutral wire current is greater than I t2 , controlling, by the second control unit, the negative voltage conversion apparatus to decrease the output voltage.

Description

TECHNICAL FIELD This invention relates to the field of circuit technologies, and more specifically, to a bipolar power supply system and a control method. BACKGROUND In the field of direct current power supply, a system architecture for remote power supply includes a unipolar power supply system and a bipolar power supply system. If the bipolar power supply system is used, a direct current voltage level can be equivalently improved, and a power supply current can be decreased, to decrease a line loss. However, there is a unique neutral wire current problem in the bipolar power supply system. If a neutral wire current is not effectively controlled, the neutral wire current may exceed a cable specification, affecting system reliability. In an existing solution for controlling the neutral wire current, the neutral wire current usually needs to be controlled by adjusting output power of a positive voltage conversion apparatus and output power of a negative voltage conversion apparatus in the bipolar power supply system. However, in some new energy power supply scenarios, for example, in a wind power system and a photovoltaic system, the positive voltage conversion apparatus and the negative voltage conversion apparatus differ in maximum output power. If the output power of the positive voltage conversion apparatus and the output power of the negative voltage conversion apparatus are limited, the power supply system cannot provide maximum output power. Consequently, an energy yield is affected, and an additional economic loss is caused. Therefore, a method for controlling the neutral wire current needs to be urgently provided in the industry, to improve management efficiency of controlling the neutral wire current. CN206099366U discloses and ambipolar photovoltaic power generation system, including two photovoltaic power generation unit, every photovoltaic power generation unit is by photovoltaic module, equipment and the de -to -ac converter of converging is constituteed, the de -to -ac converter interchange output of two units is connected in parallel through transformer vice limit winding equivalence, the direct -current input cisoid is established ties, the series connection node is as the neutral point, two units converge the direct current output cisoid of equipment establishes ties, the series connection node is as another neutral point, the photovoltaic module of two units inserts the corresponding equipment that converges separately, and constitute the cisoid relation of establishing ties through the neutral point of the equipment that converges, ambipolar photovoltaic power generation system's direct current terminal voltage is two unit photovoltaic module voltage sums, every photovoltaic power generation unit only bears the voltage -to -ground of this unit, realized not increasing under the overpressure resistant prerequisite of system device, save the mesh of DC cable investment. Ambipolar photovoltaic power generation system has three kinds of mode of connections, is bipolar both ends neutal point earthing mode, bipolar one end neutal point earthing mode and bipolar metal central line mode respectively. EP3467987A1 discloses a converter scheme which comprises a plurality of poles and a plurality of converters, the plurality of poles including at least one positive pole, at least one negative pole and a neutral pole, the plurality of converters including at least one first converter and at least one second converter, the or each first converter connected to the neutral pole and the or the respective positive pole, the or each first converter operable to control a converter voltage across the neutral pole and the corresponding positive pole, the or each second converter connected to the neutral pole and the or the respective negative pole, the or each second converter operable to control a converter voltage across the neutral pole and the corresponding negative pole, wherein the converter scheme includes a controller programmed to perform a voltage control mode when there is an imbalance between power or current levels of the positive and negative poles and when the neutral pole is at a non-zero potential, the controller programmed to perform the voltage control mode to operate each converter to control the corresponding converter voltage so that a pole-to-ground voltage of the corresponding positive or negative pole is equal to or lower than a voltage rating of the corresponding positive or negative pole. SUMMARY The invention is defined by a bipolar power supply system with the technical features of independent claim 1 and by a control method for a bipolar power supply as per claim 9. Advantageous embodiments are defined in the dependent claims. According to a first aspect, a bipolar power supply system is provided, and includes a voltage conversion unit, an inverter unit, and a controller. The voltage conversion unit is configured to: receive electric energy provided by a power generation module, a