Power supply system and line resistance detection method

Abstract

The application provides a power supply system and a line resistance detection method, and belongs to the technical field of power electronics. In the power supply system provided by the application, the controller can detect the line resistance of the DC cable according to the voltage difference between the DC end of the inverter circuit and the output end of the DC conversion circuit and the current of the DC cable. Since the voltage difference is the voltage difference between the DC end of the inverter circuit and the output end of the DC conversion circuit at the same time, and the current of the DC cable is also the current at the same time, the line resistance of the DC cable can be accurately detected based on the ratio of the voltage difference and the current. Accordingly, the controller can accurately indicate that the line resistance is abnormal when the ratio is greater than the first threshold value, so that the operation and maintenance personnel can detect and repair the abnormality in time, thereby ensuring that the power supply system can operate safely and stably.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a method for detecting the resistance of a power supply system and its lines. Background Technology

[0002] Power supply systems such as photovoltaic (PV) power generation systems typically include DC-DC converters and inverters (INVs). The input of the DC-DC converter is connected to a DC power source (such as PV modules), and its output is connected to the DC terminal of the inverter via a DC cable. The AC terminal of the inverter is used to connect to the power grid or a load. The DC-DC converter performs voltage transformation (e.g., boost conversion) on the DC power output from the DC power source before outputting it via the DC cable. The inverter converts the direct current (DC) on the DC cable into alternating current (AC) before outputting it.

[0003] Abnormal resistance in DC cables will cause the power supply system to malfunction. Therefore, there is an urgent need for a solution that can accurately detect whether the resistance of DC cables is abnormal. Summary of the Invention

[0004] This application provides a method for detecting the resistance of a power supply system and its lines, which can accurately detect abnormal states of the line resistance of DC cables between DC converter circuits and inverter circuits.

[0005] Firstly, a power supply system is provided, comprising a DC-DC converter circuit, an inverter circuit, and a controller. The input terminal of the DC-DC converter circuit is connected to a DC power source, and the output terminal of the DC-DC converter circuit is connected to the DC terminal of the inverter circuit via a DC cable. The AC terminal of the inverter circuit is connected to the power grid or a load. The DC-DC converter circuit converts the DC power supplied by the DC power source and outputs it to the DC cable. The inverter circuit converts the DC power from the DC cable to AC power. The controller indicates an abnormal line resistance in the DC cable when the ratio of the voltage difference between the voltage at the DC terminal of the inverter circuit and the voltage at the output terminal of the DC-DC converter circuit at a first moment to the current in the DC cable at a first moment exceeds a first threshold.

[0006] In the solution provided in this application, the controller can detect the line resistance of the DC cable based on the voltage difference between the DC terminal of the inverter circuit and the output terminal of the DC-DC converter circuit, as well as the current in the DC cable. Since this voltage difference represents the voltage difference between the DC terminal of the inverter circuit and the output terminal of the DC-DC converter circuit at the same moment, and the current in the DC cable is also the current at the same moment, it ensures accurate detection of the DC cable line resistance based on the ratio of this voltage difference to the current. Accordingly, when this ratio exceeds a first threshold, the controller can accurately indicate an abnormal line resistance, enabling maintenance personnel to promptly detect and repair the anomaly, thereby ensuring the safe and stable operation of the power supply system.

[0007] In one possible implementation, the controller is also used to shut down the DC-DC converter circuit and the inverter circuit when the line resistance of the DC cable is abnormal.

[0008] A switch is connected in series between the output of the DC-DC converter circuit and the DC terminal of the inverter circuit. If this switch is open, the controller will detect that the line resistance of the DC cable is greater than a first threshold. At this time, the controller will shut down the DC-DC converter circuit and the inverter circuit, which can effectively improve the safety of maintenance personnel when closing the switch again.

[0009] In one possible implementation, the controller is further configured to control the difference between the voltage at the DC terminal of the inverter circuit and the voltage at the output terminal of the DC-DC converter circuit to be greater than or equal to the product of the ratio and a preset coefficient when the ratio is less than or equal to a first threshold.

[0010] When the ratio is less than or equal to the first threshold, it indicates that the line resistance of the DC cable is normal. At this time, the difference between the voltage at the DC terminal of the control inverter circuit and the voltage at the output terminal of the DC-DC converter circuit is greater than or equal to the product of the ratio and the preset coefficient, which ensures that the DC-DC converter circuit reliably outputs power to the DC cable.

[0011] In one possible implementation, the controller is also configured to control the voltage at the output of the DC-DC converter circuit when the ratio is less than or equal to a first threshold. satisfy: .in, is the reference voltage of the DC cable, k is the droop coefficient, and the droop coefficient k is negatively correlated with the ratio, and I is the output current of the DC-DC converter circuit.

[0012] In the solution provided in this application, the droop coefficient is determined by the line resistance of the DC cable, and the voltage at the output terminal of the DC-DC converter circuit is controlled based on the droop coefficient. This enables precise adjustment of the voltage at the output terminal of the DC-DC converter circuit, thereby effectively improving the uniformity of power distribution among multiple DC-DC converter circuits in the power supply system.

[0013] In one possible implementation, the controller is further configured to control the voltage of the DC cable to vary sinusoidally at a preset frequency during the detection period, and to indicate an abnormal line impedance of the DC cable when the ratio of the difference between the first voltage phasor and the second voltage phasor to the current phasor of the DC cable during the detection period is greater than a second threshold. Here, the first voltage phasor is the voltage phasor of the DC terminal of the inverter circuit during the detection period, and the second voltage phasor is the voltage phasor of the output terminal of the DC-DC converter circuit during the detection period.

[0014] The solution provided in this application can also inject a sine wave of a preset frequency into the DC cable, thereby achieving accurate detection and anomaly indication of the DC cable's line impedance. The line impedance includes line resistance and line inductance.

[0015] Secondly, another power supply system is provided, comprising a DC-DC converter circuit, an inverter circuit, and a controller. The input terminal of the DC-DC converter circuit is connected to a DC power source, and its output terminal is connected to the DC terminal of the inverter circuit via a DC cable. The AC terminal of the inverter circuit is connected to the power grid or a load. The DC-DC converter circuit converts the DC power supplied by the DC power source and outputs it to the DC cable. The inverter circuit converts the DC power from the DC cable to AC power. The controller indicates an abnormal line resistance in the DC cable when the ratio of the voltage difference (first voltage difference minus second voltage difference) to the current difference (first current minus second current) exceeds a threshold value. The first voltage difference is the difference between the voltage at the DC terminal of the inverter circuit at a first moment and the voltage at the output terminal of the DC-DC converter circuit at a first moment; the second voltage difference is the difference between the voltage at the DC terminal of the inverter circuit at a second moment and the voltage at the output terminal of the DC-DC converter circuit at a second moment; the first current is the current in the DC cable at a first moment, and the second current is the current in the DC cable at a second moment.

[0016] When sampling the voltage at the output of the DC-DC converter circuit, the voltage at the DC terminal of the inverter circuit, and the current, sampling bias exists, which affects the accuracy of the calculated line resistance. The solution provided in this application calculates the line resistance by the ratio of the voltage difference to the current difference, which can effectively eliminate the interference of sampling bias, improve the accuracy of the calculated line resistance, and thus effectively improve the accuracy and reliability of indicating abnormal line resistance.

[0017] In one possible implementation, the controller is also used to control the voltage of the DC cable to be different at the first and second moments. For example, the controller can control the voltage at the output of the DC-DC converter circuit to be different at the first and second moments, or control the voltage at the DC end of the inverter circuit to be different at the first and second moments, thereby achieving voltage disturbance of the DC cable.

[0018] By perturbing the voltage of the DC cable, it is possible to ensure that there is a significant difference between the sampling data before and after the perturbation. This ensures that the interference of sampling bias can be effectively eliminated by subtracting the sampling data before and after the perturbation, thereby improving the accuracy of the calculated line resistance.

[0019] Thirdly, a method for detecting line resistance is provided, applied to a power supply system including a DC-DC converter circuit and an inverter circuit. The input terminal of the DC-DC converter circuit is connected to a DC power supply, and the output terminal of the DC-DC converter circuit is connected to the DC terminal of the inverter circuit via a DC cable. The AC terminal of the inverter circuit is connected to the power grid or a load. The method includes: when the ratio of the voltage difference between the voltage at the DC terminal of the inverter circuit and the voltage at the output terminal of the DC-DC converter circuit at a first moment to the current in the DC cable at a first moment is greater than a first threshold, it indicates that the line resistance of the DC cable is abnormal.

[0020] In one possible implementation, the method further includes: shutting down the DC-DC converter circuit and the inverter circuit when the line resistance of the DC cable is abnormal.

[0021] In one possible implementation, the method further includes: when the ratio is less than or equal to a first threshold, controlling the difference between the voltage at the DC terminal of the inverter circuit and the voltage at the output terminal of the DC-DC converter circuit to be greater than or equal to the product of the ratio and a preset coefficient.

[0022] In one possible implementation, the controller is also configured to control the voltage at the output of the DC-DC converter circuit when the ratio is less than or equal to a first threshold. satisfy: .in, is the reference voltage of the DC cable, k is the droop coefficient, and the droop coefficient k is negatively correlated with the ratio, and I is the output current of the DC-DC converter circuit.

[0023] In one possible implementation, the controller is further configured to control the voltage of the DC cable to vary sinusoidally at a preset frequency during the detection period, and to indicate an abnormal line impedance of the DC cable when the ratio of the difference between the first voltage phasor and the second voltage phasor to the current phasor of the DC cable during the detection period is greater than a second threshold. Here, the first voltage phasor is the voltage phasor of the DC terminal of the inverter circuit during the detection period, and the second voltage phasor is the voltage phasor of the output terminal of the DC-DC converter circuit during the detection period.

[0024] Fourthly, another method for detecting line resistance is provided, applied to a power supply system including a DC-DC converter circuit and an inverter circuit. The input terminal of the DC-DC converter circuit is connected to a DC power supply, and the output terminal of the DC-DC converter circuit is connected to the DC terminal of the inverter circuit via a DC cable. The AC terminal of the inverter circuit is connected to the power grid or a load. The method includes: when the ratio of the voltage difference obtained by subtracting a second voltage difference from a first voltage difference to the current difference obtained by subtracting a second current from a first current is greater than a threshold, it indicates an abnormal line resistance of the DC cable. The first voltage difference is the difference between the voltage at the DC terminal of the inverter circuit at a first moment and the voltage at the output terminal of the DC-DC converter circuit at a first moment; the second voltage difference is the difference between the voltage at the DC terminal of the inverter circuit at a second moment and the voltage at the output terminal of the DC-DC converter circuit at a second moment; the first current is the current in the DC cable at the first moment, and the second current is the current in the DC cable at the second moment.

[0025] In one possible implementation, before indicating an abnormality in the line resistance of the DC cable, the method further includes controlling the voltage of the DC cable to be different at a first moment and a second moment.

[0026] The line resistance detection methods and the technical effects of various implementation methods provided in the third and fourth aspects above can be referred to the relevant descriptions of the power supply system and various implementation methods provided in the first and second aspects above, and will not be repeated here.

[0027] In summary, this application provides a power supply system and a method for detecting line resistance. In this power supply system, the controller can detect the line resistance of the DC cable based on the voltage difference between the DC terminal of the inverter circuit and the output terminal of the DC-DC converter circuit, as well as the current in the DC cable. Since this voltage difference is the voltage difference between the DC terminal of the inverter circuit and the output terminal of the DC-DC converter circuit at the same moment, and the current in the DC cable is also the current at the same moment, it can ensure accurate detection of the DC cable line resistance based on the ratio of this voltage difference to the current. Accordingly, the controller can accurately indicate an abnormal line resistance when this ratio is greater than a first threshold, so that maintenance personnel can promptly detect and repair the abnormality, thereby ensuring the safe and stable operation of the power supply system. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a power supply system provided in an embodiment of this application; Figure 2 This is a schematic diagram of the structure of a photovoltaic system provided in an embodiment of this application; Figure 3 This is a schematic diagram of the structure of a photovoltaic-storage DC coupling system provided in an embodiment of this application; Figure 4This is a schematic diagram illustrating a method for filtering out the DC component in sampled data, as provided in an embodiment of this application. Figure 5 This is a flowchart of a line impedance detection method provided in an embodiment of this application; Figure 6 This is a flowchart of another line impedance detection method provided in the embodiments of this application. Detailed Implementation

[0029] The following describes in detail, with reference to the accompanying drawings, the power supply system and the method for detecting line resistance provided in the embodiments of this application.

[0030] With the rapid development of new energy power generation technology, pure new energy power generation, due to its volatility and uncertainty, can no longer meet the continuous power supply requirements of users. At the same time, large-scale integration of new energy sources inevitably leads to difficulties in grid regulation, thus requiring complementary energy sources. Adding energy storage systems to the new energy power generation side can effectively solve these problems. Energy storage systems can store excess energy generated by new energy power generation and release it during periods of insufficient power generation or peak demand, thereby stabilizing power generation and reducing the impact on the grid. Based on this, the application scenarios of photovoltaic energy storage (PV-Storage) coupling are increasing. PV-Storage coupling systems typically adopt a DC-coupled architecture. In this architecture, multiple DC converters are coupled to the DC terminal of the inverter through a DC bus, and the distance between the DC converters and the inverter is relatively large. The line impedance between the DC converters and the inverter has a significant impact on the power distribution of multiple DC converters and the rationality of the steady-state operating point of the DC bus voltage. Furthermore, abnormal line impedance can also affect the normal operation of the power supply system. Therefore, how to accurately detect the line impedance (such as line resistance) between the DC converters and the inverter and determine whether the line impedance is abnormal is a technical problem that urgently needs to be solved.

[0031] This application provides a power supply system, which can be a photovoltaic power generation system, an energy storage system, or a photovoltaic-energy storage DC-DC coupled system. For example... Figure 1 As shown, the power supply system includes a DC-DC converter circuit 10, an inverter circuit 20, and a controller 30. The input terminal of the DC-DC converter circuit 10 is connected to a DC power source, and its output terminal is connected to the DC terminal of the inverter circuit 20 via a DC cable. The AC terminal of the inverter circuit 20 is connected to the power grid or a load. The DC-DC converter circuit 10 converts the DC power supplied by the DC power source and outputs it to the DC cable. The inverter circuit 20 converts the DC power from the DC cable into AC power.

[0032] refer to Figure 1The power supply system provided in this application embodiment can be a photovoltaic power generation system. Accordingly, the input terminal of the DC-DC converter 10 is used to connect to a photovoltaic (PV) module, and the DC-DC converter 10 is used to convert the DC power provided by the photovoltaic module into voltage and then output it. For example, the DC-DC converter 10 can be a boost (BST) circuit, which can boost the DC power provided by the photovoltaic module and then output it.

[0033] Or, refer to Figure 2 The power supply system provided in this application embodiment can be a photovoltaic power generation system with multiple units connected in parallel. The photovoltaic power generation system with multiple units connected in parallel includes multiple DC-DC converter circuits 10. The input terminal of each DC-DC converter circuit 10 is used to connect to the photovoltaic module, and the output terminals of the multiple DC-DC converter circuits 10 are connected in parallel to the DC terminal of the inverter circuit 20 through DC cables.

[0034] Or, refer to Figure 3 The power supply system provided in this application embodiment can be a photovoltaic-storage DC-DC coupling system, which includes multiple DC-DC converter circuits 10. The input terminals of some DC-DC converter circuits 10 are used to connect to photovoltaic modules, and the input terminals of some DC-DC converter circuits 10 are used to connect to the energy storage system. The output terminals of the multiple DC-DC converter circuits 10 are connected in parallel to the DC terminal of the inverter circuit 20 via DC cables. The DC-DC converter circuit 10 connected to the photovoltaic modules is used to perform voltage conversion (e.g., boost) on the DC power supplied by the photovoltaic modules before outputting it. The DC-DC converter circuit 10 connected to the energy storage battery is used to perform voltage conversion on the DC power supplied by the energy storage battery before outputting it, and is also used to perform voltage conversion on the DC power supplied by the DC cables to charge the energy storage battery. That is, the DC-DC converter circuit 10 connected to the energy storage battery can achieve bidirectional voltage conversion; this DC-DC converter circuit 10 is also called a DC / DC converter.

[0035] refer to Figure 2 and Figure 3 As can be seen, in scenarios where multiple DC-DC converter circuits 10 are connected in parallel, i.e., in a multi-machine parallel system, the output terminal of each DC-DC converter circuit 10 can be connected to the DC bus (BUS) via a DC cable. The DC bus is connected to the DC terminal of the inverter circuit 20. The connection point between the DC cable and the DC bus can also be called the DC coupling point.

[0036] In this embodiment, the controller 30 is configured to indicate an abnormal line resistance of the DC cable when the ratio of the voltage difference between the voltage at the DC terminal of the inverter circuit 20 and the voltage at the output terminal of the DC-DC converter circuit 10 at a first moment, and the current of the DC cable at a first moment, is greater than a first threshold. The current of the DC cable at the first moment can be either the current at the output terminal of the DC-DC converter circuit 10 or the current at the DC terminal of the inverter circuit 20 at the first moment.

[0037] Since the voltage difference mentioned above is the voltage difference between the two ends of the DC cable, the ratio of this voltage difference to the current can characterize the line resistance of the DC cable, that is, the line resistance R satisfies: Formula (1); in, This represents the voltage at the DC terminal of inverter circuit 20 at the first moment. The voltage at the input terminal of the DC-DC converter circuit 10 at the first moment is... Let be the voltage difference at the first moment, and this voltage difference can be an absolute value. This represents the current in the DC cable at the first moment.

[0038] When the line resistance R is greater than a first threshold, the controller 30 can determine and indicate that the line resistance of the DC cable is abnormal. For example, the controller 30 can issue an alarm signal to indicate that the line resistance of the DC cable is abnormal. The first threshold is greater than the upper limit of the fluctuation range of the line resistance when the DC cable is normal; for example, the first threshold can be tens or hundreds of ohms.

[0039] In the solution provided in this application embodiment, the controller 30 can detect the line resistance of the DC cable based on the voltage difference between the DC terminal of the inverter circuit 20 and the output terminal of the DC-DC converter circuit 10, and the current of the DC cable. Since the voltage difference is the voltage difference between the DC terminal of the inverter circuit 20 and the output terminal of the DC-DC converter circuit 10 at the same moment, and the current of the DC cable is also the current at the same moment, it can ensure that the line resistance of the DC cable is accurately detected based on the ratio of the voltage difference to the current. Accordingly, the controller 30 can accurately indicate an abnormal line resistance when the ratio is greater than a first threshold, so that maintenance personnel can detect and repair the abnormality in a timely manner, thereby ensuring the safe and stable operation of the power supply system.

[0040] This application also provides another power supply system, the structure of which is the same as the above embodiment, and will not be described again here. Furthermore, the controller 30 in this power supply system is used to indicate an abnormal line resistance of the DC cable when the ratio of the voltage difference obtained by subtracting the second voltage difference from the first voltage difference to the current difference obtained by subtracting the second current from the first current is greater than a threshold. This threshold can be equal to the aforementioned first threshold.

[0041] Wherein, the first voltage difference is the difference between the voltage at the DC terminal of the inverter circuit 20 at the first moment and the voltage at the output terminal of the DC-DC converter circuit 10 at the first moment. The second voltage difference is the difference between the voltage at the DC terminal of the inverter circuit 20 at the second moment and the voltage at the output terminal of the DC-DC converter circuit 10 at the second moment. The first current is the current in the DC cable at the first moment, and the second current is the current in the DC cable at the second moment.

[0042] In this embodiment, the ratio of the voltage difference to the current difference can characterize the line resistance of the DC cable, that is, the line resistance R of the DC cable satisfies: Formula (2); in, The first voltage difference mentioned above, This is the second voltage difference mentioned above. For the first current mentioned above, The second current is mentioned above. Both the first voltage difference and the second voltage difference can be absolute values, and the voltage difference between the first voltage difference and the second voltage difference, as well as the current difference between the first current and the second current, can also be absolute values.

[0043] It is understandable that sampling bias exists when sampling the voltage at the output of DC-DC converter circuit 10, the voltage at the DC terminal of inverter circuit 20, and the current of DC cable. This sampling bias will affect the accuracy of the calculated line resistance. By calculating the line resistance R using the above formula (2), the interference of sampling bias can be effectively eliminated, the accuracy of the calculated line resistance R can be improved, and thus the accuracy and reliability of indicating abnormal line resistance can be effectively improved.

[0044] For example, suppose the current sampling bias of inverter circuit 20 is... The voltage sampling bias of inverter circuit 20 is The voltage sampling bias of the DC-DC converter circuit 10 is The actual voltage and current at the DC terminal of inverter circuit 20 at the first moment are respectively... 1 and 1r, the actual voltage and current at the second time point are respectively 2 and 2r. The actual voltage at the output terminal of the DC-DC converter circuit 10 at the first moment is b1, the actual voltage at the second moment is b2. Accordingly, the electrical equations for voltage, current, and resistance at the first sampling moment can be expressed as: Formula (3); The electrical equations for voltage, current, and resistance at the second sampling time can be expressed as: Formula (4); Subtracting the electrical equations shown in formula (3) and formula (4) above, we can obtain: Formula (5); In formula (2) and All are the voltage differences of the sampled voltages, i.e. , In formula (2) and All of these are sampled currents, i.e. , Simplifying formula (2) yields formula (5). From formulas (3) to (5), it can be seen that by subtracting the electrical equations at two sampling times, sampling bias (such as...) can be effectively eliminated. , and The influence of this factor ensures that the calculated line resistance R is highly accurate.

[0045] In one possible implementation, the controller 30 is also used to control the voltage of the DC cable to be different at the first and second moments. For example, the controller 30 can control the voltage at the output terminal of the DC-DC converter circuit 10 to be different at the first and second moments; that is, the controller 30 can perturb (also called voltage scrambling) the voltage at the output terminal of the DC-DC converter circuit 10, thereby perturbing the voltage of the DC cable. Alternatively, the controller 30 can control the voltage at the DC terminal of the inverter circuit 20 to be different at the first and second moments; that is, the controller 30 can scramble the DC terminal of the inverter circuit 20, thereby perturbing the voltage of the DC cable.

[0046] By perturbing the voltage of the DC cable at least once, it can be ensured that there is a significant difference between the sampled data before and after the perturbation. This ensures that the interference of sampling bias can be effectively eliminated by subtracting the sampled data before and after the perturbation, thereby improving the accuracy of the calculated line resistance.

[0047] As a first possible implementation, in the two power supply systems provided in this application embodiment, the DC-DC converter circuit 10, the inverter circuit 20, and the controller 30 can be housed in the same device, such as in a photovoltaic inverter circuit or an energy storage converter. Furthermore, the controller 30 can sample (e.g., in real-time) the voltage and current at the output terminal of the DC-DC converter circuit 10 and the DC terminal of the inverter circuit 20, and record the sampled voltage and current, as well as the corresponding sampling time. This sampling time can be, for example, a sampling timestamp. When it is necessary to detect the line resistance of the DC cable, the controller 30 can calculate the line resistance of the DC cable based on the voltage difference and current at the same sampling time, such as the voltage difference and current at the first sampling time. For example, the controller 30 can detect the line resistance of the DC cable during power supply system startup.

[0048] As a second possible implementation, in the two power supply systems provided in this application embodiment, the DC-DC converter circuit 10 and the inverter circuit 20 can be two independent devices, and the distance between the two devices is relatively far. For example, the DC-DC converter circuit 10 can be an independent DC-DC converter, and the inverter circuit 20 can be an independent inverter. In this implementation, the controller 30 can be located in the same device as the DC-DC converter circuit 10, or it can be located in the same device as the inverter circuit 20, or the controller 30 can be a device independent of the DC-DC converter circuit 10 and the inverter circuit 20.

[0049] For example, in this implementation, one of the DC-DC converter circuit 10 and the inverter circuit 20 is the master (also called the main device), and the other is the slave (also called the slave device). The controller 30 can be located in the same device as the master. Both the master and the slave can sample (e.g., sample in real time) the voltage and current at their respective DC cable ports and record the sampled voltage and current, as well as the corresponding sampling time. This sampling time can be, for example, a sampling timestamp. When it is necessary to detect the line resistance of the DC cable between the DC-DC converter circuit 10 and the inverter circuit 20, the master can send a query command to the slave. The slave can then send its detected and recorded sampling data (including voltage and sampling time) to the master based on the query command. The master can then calculate the line resistance of the DC cable based on the voltage difference and current at the same sampling time, such as the voltage difference and current at the first sampling time. For example, the master can detect the line resistance of the DC cable when the power supply system is started up.

[0050] In this implementation, the slave device can send multiple sets of sampling data to the master device. Each set of sampling data includes the voltage at the slave device's DC cable port and the sampling time of the voltage. Alternatively, each set of sampling data may also include the current at the slave device's DC cable port. The master device can receive the multiple sets of sampling data reported by the slave device and calculate the line resistance of the DC cable based on the sampling data reported by the slave device and the sampling data recorded by the master device itself. Furthermore, the sampling time in the sampling data recorded by the master device and the sampling time in the sampling data recorded by the slave device both include the aforementioned first time.

[0051] For example, for ease of distinction, in this embodiment, the sampling data recorded by the host is referred to as the first sampling data, and the sampling time in the first sampling data is referred to as the first sampling time; the sampling data recorded by the slave is referred to as the second sampling data, and the sampling time in the second sampling data is referred to as the second sampling time. After receiving multiple sets of second sampling data from the slave, the host can compare the first sampling time in the multiple sets of first sampling data recorded by itself with the second sampling time in the multiple sets of second sampling data, and determine the set of first target sampling data and the set of second target sampling data whose first sampling time and second sampling time are closest. That is, the time difference between the first sampling time in the first target sampling data and the second sampling time in the second target sampling data is less than or equal to the time difference between the first sampling time and the second sampling time in any other two sets of sampling data. Then, the host can calculate the voltage difference based on the voltage in the first target sampling data and the voltage in the second target sampling data, and calculate the line resistance of the DC cable based on the voltage difference and the current in the first target sampling data or the second target sampling data.

[0052] Based on the above example, it can be seen that the first sampling time in the first target sampling data and the second sampling time in the second target sampling data are the aforementioned first time. This first sampling time and the second sampling time can be equal or may have a certain deviation. That is, the first time recorded by the host and the first time recorded by the slave can be equal or may have a certain deviation.

[0053] In this embodiment, the master and slave devices have a high-precision time synchronization function, with synchronization accuracy down to the microsecond (µs) or millisecond (ms) level. Correspondingly, the deviation between the first sampling time in the first target sampling data and the second sampling time in the second target sampling data can be on the µs or ms level. This ensures that the deviation between the sampling times in the first and second target sampling data is small, thereby ensuring high accuracy in the calculated line resistance.

[0054] In this embodiment of the application, a communication connection is established between the host and the slave device, enabling them to transmit data based on this communication connection. For example, as... Figures 1 to 3 As shown, assuming the inverter circuit 20 is the main unit and the controller 30 and inverter circuit 20 are located in one device, a communication connection is established between the controller 30 and the DC-DC converter circuit 10. This communication connection can be, for example, RS-485, power line communication (PLC), Ethernet, or a wireless communication connection. This embodiment does not limit the communication method or time synchronization method between devices, as long as the required time accuracy for calculation is met.

[0055] In one possible implementation, the controller 30 in the power supply system can also record and / or display the line resistance of the DC cable. For example, the controller 30 can display the line resistance of the DC cable on its display interface. Alternatively, the controller 30 can send the line resistance to the system controller or network management system, which will then display it on its monitoring interface.

[0056] In one possible implementation, the controller 30 is also used to shut down the DC-DC converter circuit 10 and the inverter circuit 20 when the line resistance of the DC cable is abnormal. Figures 1 to 3 As shown, the power supply system also includes a switch K connected in series between the output terminal of the DC-DC converter circuit 10 and the DC terminal of the inverter circuit 20. The aforementioned first threshold can be greater than the upper limit of the fluctuation range of the line resistance of the DC cable when the switch K is closed.

[0057] Accordingly, when the controller 30 detects that the line resistance of the DC cable is greater than the first threshold, it can determine that switch K is open and promptly control the DC-DC converter circuit 10 and the inverter circuit 20 to shut down. This ensures that when maintenance personnel close switch K again, the voltage at the output of the DC-DC converter circuit 10 and the DC terminal of the inverter circuit 20 are both 0, thus avoiding safety issues.

[0058] In this embodiment, if the power supply system includes multiple DC-DC converter circuits 10, the host can be an inverter circuit 20, or it can be one of the DC-DC converter circuits 10. Furthermore, the host can calculate the line resistance of the DC cable between each DC-DC converter circuit 10 and the inverter circuit 20. The host can also control any DC-DC converter circuit 10 to shut down when it detects that the line resistance of the DC cable between any DC-DC converter circuit 10 and the inverter circuit 20 is greater than a resistance threshold. Alternatively, the host can control both the inverter circuit 20 and the multiple DC-DC converter circuits 10 to shut down when it detects that the line resistance of the DC cable between any DC-DC converter circuit 10 and the inverter circuit 20 is greater than a resistance threshold, to ensure safety.

[0059] In one possible implementation, after the controller 30 detects the line resistance of the DC cable, if the line resistance is normal (i.e., the ratio is less than or equal to a first threshold), the controller 30 further performs droop control on each DC-DC converter circuit 10 in the multi-machine parallel system based on the line resistance to ensure a more uniform power distribution among the DC-DC converter circuits 10. For example, the controller 30 can control the voltage at the output terminal of the DC-DC converter circuit 10. satisfy: Formula (6); in, The reference voltage for the DC cable can be set according to the operating conditions of the power supply system. k is the droop coefficient, also known as the droop impedance, and the droop coefficient k is negatively correlated with the above ratio (i.e., the line resistance of the DC cable). I is the current at the output terminal of the DC-DC converter circuit 10. In the above formula (6), the current I can also be replaced by the power at the output terminal of the DC-DC converter circuit 10.

[0060] It is understandable that if the lengths of the DC cables connected to different DC-DC converters 10 are different, then the cable resistances of the DC cables connected to different DC-DC converters 10 will be different, and the voltage drops across the DC cables will be different. In this embodiment, after detecting the line resistance between each DC-DC converter 10 and the inverter circuit 20, the controller 30 can also determine the droop coefficient corresponding to the DC-DC converter 10 based on the line resistance. Since the droop coefficient is negatively correlated with the line resistance, it can ensure that the equivalent droop coefficients of each DC-DC converter 10 in a multi-machine parallel system are relatively close. The equivalent droop coefficient can be equal to the sum of the droop coefficient and the line resistance. Accordingly, controlling the voltage at the output terminal of the DC-DC converter 10 based on the droop coefficient can effectively ensure that the power distribution of multiple DC-DC converters 10 in the power supply system is relatively uniform.

[0061] In one possible implementation, after the controller 30 detects the line resistance of the DC cable, if the line resistance is normal (i.e., the ratio is less than or equal to a first threshold), the controller 30 further formulates a corresponding control strategy for the DC cable voltage based on the line resistance. This control strategy ensures DC cable voltage matching between the DC-DC converter circuit 10 and the inverter circuit 20 to avoid situations where the power output of the DC-DC converter circuit 10 is uncontrollable or fails to output power.

[0062] In this embodiment, the controller 30 can be used to control the voltage difference between the DC terminal of the inverter circuit 20 and the output voltage of the DC-DC converter circuit 10 to be greater than or equal to the product of the aforementioned ratio and a preset coefficient. Here, the difference refers to an absolute value.

[0063] Since the larger the ratio, the greater the line resistance of the DC cable and the greater the voltage drop of the DC cable, the greater the difference between the voltage at the output terminal of the DC converter circuit 10 and the DC terminal voltage of the inverter circuit 20, which can ensure that the DC converter circuit 10 reliably outputs power to the DC cable.

[0064] For example, after detecting the line resistance of the DC cable, the controller 30 can control the voltage at the DC terminal of the inverter circuit 20 to be the reference voltage of the DC cable (such as the DC bus). Furthermore, the controller 30 can multiply the line resistance by a preset coefficient to obtain the voltage difference. Then, the controller 30 can control the voltage at the output of the DC-DC converter circuit 10 to be the sum of the reference voltage and the voltage difference. Alternatively, in a multi-machine parallel system, the controller 30 can adjust the reference voltage in the above formula (6) according to the line resistance of the DC cable of each DC-DC converter circuit 10. And the adjusted reference voltage Positively correlated with line resistance, for example, the adjusted reference voltage. It equals the sum of the initial value and the voltage difference, where the voltage difference is the product of the line resistance and the preset coefficient. Therefore, for different DC-DC converter circuits 10, the reference voltage in the above formula (6) is... The values ​​can be different, and the greater the line resistance of the DC cable connected to the DC converter circuit 10, the greater the reference voltage in the above formula (6). The larger.

[0065] In one possible implementation, the controller 30 is further configured to control the voltage of the DC cable to vary sinusoidally at a preset frequency during the detection period. For example, the controller 30 can control the voltage at the output of the DC-DC converter circuit 10 to vary sinusoidally at a preset frequency during the detection period, thereby injecting a sinusoidal AC signal of the preset frequency into the DC cable. Alternatively, the controller 30 can control the voltage at the DC terminal of the inverter circuit 20 to vary sinusoidally at a preset frequency during the detection period, thereby injecting a sinusoidal AC signal of the preset frequency into the DC cable. Furthermore, the controller 30 is also configured to indicate an abnormal line impedance of the DC cable when the ratio of the difference between the first voltage phasor and the second voltage phasor to the current phasor of the DC cable during the detection period is greater than a second threshold. Here, the first voltage phasor is the voltage phasor at the DC terminal of the inverter circuit 20 during the detection period, and the second voltage phasor is the voltage phasor at the output of the DC-DC converter circuit 10 during the detection period. The second threshold is greater than or equal to the upper limit of the fluctuation range of the line impedance of the DC cable when it is normal.

[0066] It is understandable that the ratio of the difference between the first voltage phasor and the second voltage phasor to the current phasor can characterize the line impedance Z of the DC cable, which satisfies the following:

[0067] in, For the first voltage phasor mentioned above, and These are the first voltage phasors. The effective value and phase. This refers to the second voltage phasor mentioned above. and These are the second voltage phasors. The effective value and phase. For the above current phasors, and These are the current phasors. The effective value and phase. Let be the angular frequency of the sine wave, and angular frequency satisfy: After the host calculates the line impedance Z according to the above formula (7), the real part of the line impedance Z is the line resistance R, and the imaginary part of the line impedance Z is the line inductance L.

[0068] In one possible implementation, the controller 30 is also used to control the DC-DC converter circuit 10 and the inverter circuit 20 to shut down when the line impedance Z is abnormal.

[0069] In one possible implementation, the controller 30 is also used to record and / or display the line impedance Z. For example, the controller 30 may display the line resistance R and the line inductance L, respectively.

[0070] In one possible implementation, the line inductance L of the DC cable can be expressed as: Formula (8); in, To detect the difference between the effective value of the DC terminal voltage of the inverter circuit 20 and the effective value of the output voltage of the DC-DC converter circuit 10 during the detection period, This represents the effective value of the current in the DC cable during the detection period. To detect the phase difference between the voltage and current of a DC cable during a specific time period, This is the preset frequency.

[0071] In this embodiment, the controller 30 controls the voltage of the DC cable to change according to a sinusoidal wave at a preset frequency during the detection period. Based on the voltage, current, phase and sampling time sampled and received during the detection period, the controller 30 can accurately calculate the line inductance (also known as equivalent inductance) of the DC cable.

[0072] In this embodiment, the detection period is greater than or equal to the sine wave period. Both the host and slave devices can detect and record sampling data at their respective DC cable ports during this detection period. This sampling data includes voltage, current, and sampling time within one sine wave period. The slave device can directly send this sampling data to the host, which then calculates the effective value and phase of the voltage at the slave device's DC cable port based on the sampling data. Alternatively, the slave device can directly calculate the effective value and phase of its own DC cable port based on the sampling data and send the calculated effective value and phase, along with the sampling time, to the host. The host can also calculate the effective value and phase of its own DC cable port based on its recorded sampling data, and then calculate the line inductance L according to the above formula (8). The current I3 in the above formula (8) can be the effective value of the current at the host's DC cable port or the effective value of the current at the slave device's DC cable port.

[0073] In one possible implementation, in order to eliminate the effect of sampling bias, such as Figure 4 As shown, when the host or slave device calculates the effective value of voltage / current based on the sampled data, it can first filter out the DC component in the sampled data and then calculate the effective value of voltage / current. The DC component can be the average value of the sampled data over a sinusoidal period.

[0074] In one possible implementation, the controller 30 can also formulate a corresponding control strategy based on the line inductance L to avoid resonance. For example, the controller 30 is also used to control the difference between the switching frequency of the switching transistor in the DC-DC converter circuit 10 and the resonant frequency of the DC cable to be greater than a first frequency threshold, and to control the difference between the switching frequency of the switching transistor in the inverter circuit 20 and the resonant frequency to be greater than a second frequency threshold. Resonant frequency satisfy:

[0075] Where L is the line inductance and C is the equivalent capacitance of the DC cable. In this embodiment, after the controller 30 detects the line inductance L of the DC cable, it can adjust the switching frequency of the DC-DC converter circuit 10 and the inverter circuit 20 according to the line inductance L to ensure that the switching frequency is consistent with the resonant frequency of the DC cable. The difference is greater than a certain threshold, thus effectively avoiding resonance.

[0076] For example, the switching frequency of the switching transistor in the DC-DC converter circuit 10 and the switching frequency of the switching transistor in the inverter circuit 20 are both greater than the aforementioned resonant frequency. Furthermore, the first frequency threshold can be greater than or equal to 1 / 3 of the switching frequency of the switching transistor in the DC-DC converter circuit 10, and the second frequency threshold can be greater than or equal to 1 / 3 of the switching frequency of the switching transistor in the inverter circuit 20.

[0077] refer to Figures 1 to 3 It can be seen that the line impedance of the DC cable between the DC converter circuit 10 and the inverter circuit 20 includes the line resistance R and the line inductance L. The line resistance R is also called the equivalent resistance, and the line inductance L is also called the equivalent inductance. If the DC cable is long, its line impedance is large, which will affect the operational stability of the power supply system. In this embodiment, since the DC converter circuit 10 or the inverter circuit 20 can accurately detect the line impedance of the DC cable, the power supply system can formulate corresponding control strategies (such as droop control strategy, bus voltage control strategy, and resonance control strategy) based on this line impedance to improve the stability and reliability of the power supply system.

[0078] In one possible implementation, the detection processes for line resistance and line impedance (such as line inductance) can be performed separately, meaning the host computer can detect the line resistance and line impedance (such as line inductance) of the DC cable separately.

[0079] In another possible implementation, the detection process of line resistance and line impedance (such as line inductance) can be performed simultaneously, that is, the host can simultaneously detect the line resistance and line impedance (such as line inductance) of the DC cable.

[0080] For example, the first moment mentioned above can be a sampling moment within the detection period, and the second moment mentioned above can be another sampling moment within the same detection period. Accordingly, the host computer can synchronously calculate the line resistance and line inductance of the DC cable based on the sampling data within that detection period.

[0081] In this embodiment, depending on the operating conditions of the power supply system, the voltage of the DC cable can be controlled by different circuits in the DC-DC converter circuit 10 and the inverter circuit 20. For example, under power-limited conditions, the DC-DC converter circuit 10 can control the voltage of the DC cable; under unlimited power conditions, the inverter circuit 20 can control the voltage of the DC cable.

[0082] In summary, this application provides a power supply system in which the controller can detect the line resistance of a DC cable based on the voltage difference between the DC terminal of the inverter circuit and the output terminal of the DC-DC converter circuit, as well as the current in the DC cable. Since the voltage difference is the voltage difference between the DC terminal of the inverter circuit and the output terminal of the DC-DC converter circuit at the same moment, and the current in the DC cable is also the current at the same moment, the line resistance of the DC cable can be accurately detected based on the ratio of the voltage difference to the current. Accordingly, when the ratio is greater than a threshold, the controller can accurately indicate an abnormal line resistance, allowing maintenance personnel to detect and repair the abnormality in a timely manner, thereby ensuring the safe and stable operation of the power supply system. Furthermore, the controller can also rationally design the steady-state operating point of the DC cable voltage based on the line resistance, and / or evenly distribute the power of each DC-DC converter circuit in a multi-machine parallel system, thereby effectively improving the stability and reliability of the power supply system operation.

[0083] This application embodiment also provides a method for detecting line resistance. This method can be applied to the power supply system described above, which includes a DC-DC converter circuit 10 and an inverter circuit 20. The input terminal of the DC-DC converter circuit 10 is connected to a DC power source, and the output terminal of the DC-DC converter circuit 10 is connected to the DC terminal of the inverter circuit 20 via a DC cable. The AC terminal of the inverter circuit 20 is connected to the power grid or a load. This method can be executed by a controller 30 in the power supply system, and the method includes: when the ratio of the voltage difference between the voltage at the DC terminal of the inverter circuit and the voltage at the output terminal of the DC-DC converter circuit at a first moment to the current in the DC cable at a first moment is greater than a first threshold, indicating an abnormal line resistance in the DC cable.

[0084] In one possible implementation, the method further includes: shutting down the DC-DC converter circuit and the inverter circuit when the line resistance of the DC cable is abnormal.

[0085] In one possible implementation, the method further includes: when the ratio is less than or equal to a first threshold, controlling the difference between the voltage at the DC terminal of the inverter circuit and the voltage at the output terminal of the DC-DC converter circuit to be greater than or equal to the product of the ratio and a preset coefficient.

[0086] In one possible implementation, the method further includes: controlling the voltage at the output terminal of the DC-DC converter circuit when the ratio is less than or equal to a first threshold. satisfy: .in, is the reference voltage of the DC cable, k is the droop coefficient, and the droop coefficient k is negatively correlated with the ratio, and I is the output current of the DC-DC converter circuit.

[0087] In one possible implementation, the method further includes: controlling the voltage of the DC cable to vary sinusoidally at a preset frequency during the detection period, and using this control to indicate an abnormal line impedance of the DC cable when the ratio of the difference between the first voltage phasor and the second voltage phasor to the current phasor of the DC cable during the detection period is greater than a second threshold. Wherein, the first voltage phasor is the voltage phasor of the DC terminal of the inverter circuit during the detection period, and the second voltage phasor is the voltage phasor of the output terminal of the DC-DC converter circuit during the detection period.

[0088] This application embodiment also provides another method for detecting line resistance, which can be applied to the power supply system described in the above embodiment. The power supply system includes a DC-DC converter circuit 10 and an inverter circuit 20. The input terminal of the DC-DC converter circuit 10 is connected to a DC power supply, and the output terminal of the DC-DC converter circuit 10 is connected to the DC terminal of the inverter circuit 20 via a DC cable. The AC terminal of the inverter circuit 20 is connected to the power grid or a load. This method can be executed by a controller 30 in the power supply system, and the method includes: indicating an abnormal line resistance of the DC cable when the ratio of the voltage difference obtained by subtracting a second voltage difference from a first voltage difference to the current difference obtained by subtracting a second current from a first current is greater than a threshold value.

[0089] Wherein, the first voltage difference is the difference between the voltage at the DC terminal of the inverter circuit at the first moment and the voltage at the output terminal of the DC-DC converter circuit at the first moment; the second voltage difference is the difference between the voltage at the DC terminal of the inverter circuit at the second moment and the voltage at the output terminal of the DC-DC converter circuit at the second moment; the first current is the current of the DC cable at the first moment; and the second current is the current of the DC cable at the second moment.

[0090] In one possible implementation, the method further includes controlling the voltage of the DC cable to be different at a first moment and a second moment.

[0091] The following section provides an illustrative description of the process for detecting the line impedance (such as line resistance) of DC cables. Figure 5 As shown, the impedance detection process for this line includes: Step 101: The host controls the voltage of the DC cable to the first voltage and notifies the slave to perform impedance identification.

[0092] For example, assuming the main unit is inverter circuit 20 and controller 30 is located in the main unit, controller 30 can control the voltage at the DC terminal of inverter circuit 20 to a first voltage, that is, control the voltage of the DC bus to a first voltage. Furthermore, the main unit can send commands to the slave unit to instruct it to perform impedance identification.

[0093] Step 102: The slave device records the voltage and current at the output terminal and records the corresponding timestamps.

[0094] Assuming the slave device is DC-DC converter circuit 10, after receiving the instruction from inverter circuit 20, DC-DC converter circuit 10 can detect and record the voltage and current at the output terminal of DC-DC converter circuit 10, and record the corresponding timestamp.

[0095] Step 103: The host records the voltage and current at the input terminal and records the corresponding timestamps.

[0096] In the scenario where the host is the inverter circuit 20, the input terminal refers to the DC terminal of the inverter circuit 20.

[0097] Step 104: The slave device sends the voltage and current information with timestamps to the master device.

[0098] Step 105: The master unit calculates the line impedance based on the slave unit's voltage, its own voltage at the corresponding moment, and the current.

[0099] In this embodiment, steps 102 and 103 can be executed after step 101. Alternatively, steps 102 and 103 can be executed before step 101. For example, both the master and slave devices can detect and record voltage and current in real time, and record the corresponding timestamps. When the master device determines that impedance identification is required, it can issue a command to the slave device, which can then directly report its recorded voltage, current, and corresponding timestamps to the master device. Alternatively, the slave device can report its recorded voltage, current, and corresponding timestamps to the master device in real time (or periodically). When the master device determines that impedance identification is required, it can directly calculate the line impedance based on the received data and the data it detects and records, without issuing a command to the slave device.

[0100] Figure 6 This is a flowchart of another method for detecting line impedance provided in an embodiment of this application. For example... Figure 6 As shown, the impedance detection process for this line includes: Step 201: The host controls the voltage of the DC cable to the first voltage and notifies the slave to perform impedance identification.

[0101] Step 202: The slave device records the voltage and current at the output terminal and records the corresponding timestamp.

[0102] Step 203: The host records the voltage and current at the input terminal and records the corresponding timestamps.

[0103] Step 204: Adjust the voltage of the DC cable of the host to the second voltage.

[0104] In this embodiment of the application, in order to improve the accuracy of impedance detection, the host can also adjust the voltage of the DC cable, that is, disturb the voltage of the DC cable.

[0105] Step 205: The slave device records the voltage and current at the output terminal and records the corresponding timestamp.

[0106] Step 206: The host records the voltage and current at the input terminal and records the corresponding timestamp.

[0107] In steps 205 and 206 above, the host and slave devices can detect the voltage and current at their respective DC cable ports after the voltage of the DC cable changes, and record the corresponding timestamps.

[0108] Step 207: The slave device sends the voltage and current information with timestamps to the master device.

[0109] Step 208: The master unit calculates the line impedance based on the slave unit's voltage, its own voltage at the corresponding moment, and the current.

[0110] In one possible implementation, after step 202 and before step 204, the slave device can first send its recorded timestamped voltage and current information to the master device. After step 204, the master device can again notify the slave device to perform impedance identification. Accordingly, the slave device can again detect and record the voltage and current at the output terminal, as well as the corresponding timestamp, and send the newly recorded timestamped voltage and current information to the master device. The master device can then accurately calculate the line impedance based on the two received data sets and the data recorded by the master device before and after voltage adjustment.

[0111] The line resistance detection methods provided in this application have essentially the same implementation methods and technical effects as the power supply systems provided in the foregoing embodiments. Therefore, for the sake of brevity, the implementation methods and technical effects of the line resistance detection methods will not be described again here.

[0112] In the embodiments of this application, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The term "at least one" refers to one or more, and "multiple" refers to two or more.

[0113] In the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0114] The above description is merely an optional implementation of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A power supply system, characterized in that, The power supply system includes a DC-DC converter circuit, an inverter circuit, and a controller; The input terminal of the DC-DC converter circuit is used to connect to a DC power supply, the output terminal of the DC-DC converter circuit is connected to the DC terminal of the inverter circuit via a DC cable, and the AC terminal of the inverter circuit is used to connect to the power grid or a load. The DC-DC converter circuit is used to convert the DC power supplied by the DC power source into voltage and output it to the DC cable. The inverter circuit is used to convert the direct current of the DC cable into alternating current. The controller is configured to indicate an abnormal line resistance of the DC cable when the ratio of the voltage difference between the voltage at the DC terminal of the inverter circuit and the voltage at the output terminal of the DC converter circuit at the first moment, obtained by subtracting the voltage at the output terminal of the DC converter circuit at the first moment, to the current of the DC cable at the first moment is greater than a first threshold.

2. The power supply system according to claim 1, characterized in that, The controller is also used to shut down the DC-DC converter circuit and the inverter circuit when the line resistance of the DC cable is abnormal.

3. The power supply system according to claim 1 or 2, characterized in that, The controller is further configured to, when the ratio is less than or equal to the first threshold, control the difference between the voltage at the DC terminal of the inverter circuit and the voltage at the output terminal of the DC-DC converter circuit to be greater than or equal to the product of the ratio and a preset coefficient.

4. The power supply system according to any one of claims 1 to 3, characterized in that, The controller is further configured to control the voltage at the output terminal of the DC-DC converter circuit when the ratio is less than or equal to the first threshold. satisfy: ; in, The reference voltage of the DC cable is given, k is the droop coefficient, and the droop coefficient k is negatively correlated with the ratio, and I is the current at the output terminal of the DC-DC converter circuit.

5. The power supply system according to any one of claims 1 to 4, characterized in that, The controller is also used to control the voltage of the DC cable to change in a sinusoidal pattern at a preset frequency during the detection period, and to indicate that the line impedance of the DC cable is abnormal when the ratio of the difference between the first voltage phasor and the second voltage phasor to the current phasor of the DC cable during the detection period is greater than a second threshold. Wherein, the first voltage phasor is the voltage phasor of the DC terminal of the inverter circuit during the detection period, and the second voltage phasor is the voltage phasor of the output terminal of the DC-DC converter circuit during the detection period.

6. A power supply system, characterized in that, The power supply system includes a DC-DC converter circuit, an inverter circuit, and a controller; The input terminal of the DC-DC converter circuit is used to connect to a DC power supply, the output terminal of the DC-DC converter circuit is connected to the DC terminal of the inverter circuit via a DC cable, and the AC terminal of the inverter circuit is used to connect to the power grid or a load. The DC-DC converter circuit is used to convert the DC power supplied by the DC power source into voltage and output it to the DC cable. The inverter circuit is used to convert the direct current of the DC cable into alternating current. The controller is configured to indicate an abnormal line resistance of the DC cable when the ratio of the voltage difference obtained by subtracting the second voltage difference from the first voltage difference to the current difference obtained by subtracting the second current from the first current is greater than a threshold. Wherein, the first voltage difference is the difference between the voltage at the DC terminal of the inverter circuit at the first moment and the voltage at the output terminal of the DC-DC converter circuit at the first moment; the second voltage difference is the difference between the voltage at the DC terminal of the inverter circuit at the second moment and the voltage at the output terminal of the DC-DC converter circuit at the second moment; the first current is the current of the DC cable at the first moment; and the second current is the current of the DC cable at the second moment.

7. The power supply system according to claim 6, characterized in that, The controller is also used to control the voltage of the DC cable to be different at the first time and the second time.

8. A method for detecting line resistance, characterized in that, The method is applied to a power supply system, which includes a DC-DC converter circuit and an inverter circuit. The input terminal of the DC-DC converter circuit is connected to a DC power source, and the output terminal of the DC-DC converter circuit is connected to the DC terminal of the inverter circuit via a DC cable. The AC terminal of the inverter circuit is connected to the power grid or a load. When the ratio of the voltage difference between the DC terminal voltage of the inverter circuit and the output voltage of the DC converter circuit at the first moment to the current of the DC cable at the first moment is greater than a first threshold, it indicates that the line resistance of the DC cable is abnormal.

9. The method according to claim 8, characterized in that, The method further includes: when the line resistance of the DC cable is abnormal, controlling the DC conversion circuit and the inverter circuit to shut down.

10. The method according to claim 8 or 9, characterized in that, The method further includes: when the ratio is less than or equal to the first threshold, controlling the difference between the voltage at the DC terminal of the inverter circuit and the voltage at the output terminal of the DC-DC converter circuit to be greater than or equal to the product of the ratio and a preset coefficient.

11. A method for detecting line resistance, characterized in that, The method is applied to a power supply system, which includes a DC-DC converter circuit and an inverter circuit. The input terminal of the DC-DC converter circuit is connected to a DC power source, and the output terminal of the DC-DC converter circuit is connected to the DC terminal of the inverter circuit via a DC cable. The AC terminal of the inverter circuit is connected to the power grid or a load. When the ratio of the voltage difference obtained by subtracting the second voltage difference from the first voltage difference to the current difference obtained by subtracting the second current from the first current is greater than a threshold, it indicates that the line resistance of the DC cable is abnormal. Wherein, the first voltage difference is the difference between the voltage at the DC terminal of the inverter circuit at the first moment and the voltage at the output terminal of the DC-DC converter circuit at the first moment; the second voltage difference is the difference between the voltage at the DC terminal of the inverter circuit at the second moment and the voltage at the output terminal of the DC-DC converter circuit at the second moment; the first current is the current of the DC cable at the first moment; and the second current is the current of the DC cable at the second moment.

12. The method according to claim 11, characterized in that, Before indicating an abnormal line resistance in the DC cable, the method further includes controlling the voltage of the DC cable to be different at the first and second moments.

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