Cascade-type frequency converter, open-phase detection method of power unit of cascade-type frequency converter and computer readable storage medium

Abstract

The invention provides a cascaded frequency converter, a phase loss detection method of a cascaded frequency converter power unit and a computer readable storage medium. The cascaded frequency converter comprises a phase-shifting transformer which can be connected with a power grid; each power unit group comprises a plurality of cascaded power units, and each power unit is connected with the phase-shifting transformer; each power unit comprises a control unit, and the control unit is connected with the direct current bus of the power unit and is configured to determine a measured value of the bus voltage; and the main control module is connected with the control unit and is configured to judge whether the power unit is open-phase or not based on the peak-to-peak value of the measured value. According to the cascaded frequency converter and the open-phase detection method, open-phase detection of the power unit can be realized without additionally arranging an open-phase detection circuit, the hardware cost can be reduced, the wiring time can be reduced, the detection convenience can be improved, and the measurement precision, sensitivity and accuracy are considered.

Description

Technical Field

[0001] The present invention generally relates to the technical field of cascade frequency converters, and in particular to a cascade frequency converter, a phase loss detection method for a cascade frequency converter power unit, and a computer-readable storage medium. Background Art

[0002] Cascade variable-frequency drive (VFD) is a power control device that controls the motor by changing the motor output voltage frequency and voltage amplitude. Cascade inverters are widely used in scenarios such as fans, water pumps, belt conveyors, and experimental power supplies. The cascade high-voltage cascade inverter includes multiple power units, each of which includes a three-phase AC input terminal. When the cascade inverter is operating normally, the three-phase AC input of the power unit needs to exist at the same time, otherwise it will cause damage to the phase-shifting transformer, power unit and other components of the cascade inverter. Therefore, it is very important to detect whether the three-phase AC input of the cascade inverter power unit is missing a phase.

[0003] Some traditional solutions realize the phase loss detection of the power unit by setting up an additional phase loss detection circuit, but this method has high hardware cost, many wiring hours and inconvenient detection. Therefore, a new technical solution is urgently needed to solve these technical problems.

[0004] The contents of the background technology section are merely the technologies known to the inventors and do not necessarily represent the prior art in the field. Summary of the invention

[0005] In view of one or more of the problems existing in the prior art, the present invention provides a cascade frequency converter, comprising:

[0006] A phase-shifting transformer, wherein the phase-shifting transformer can be connected to a power grid;

[0007] A plurality of power cell groups, each power cell group comprising a plurality of power cells connected in cascade, each power cell being connected to the phase-shifting transformer; each power cell comprising a control unit connected to a DC bus of its power cell and configured to determine a measured value of a bus voltage; and

[0008] A main control module is connected to the control unit and is configured to determine whether the power unit is missing a phase based on the peak-to-peak value of the measured value.

[0009] Optionally, the control unit is further configured to determine a peak-to-peak value of the measured value based on the measured value of the bus voltage, and send the peak-to-peak value to the main control module.

[0010] Optionally, the control unit is further configured to send the measured value of the bus voltage to the main control module; the main control module is further configured to determine the peak-to-peak value of the measured value based on the measured value of the bus voltage.

[0011] Optionally, the control unit includes a first capacitor, a second capacitor, a first resistor, a first amplifier and a controller, wherein the first end of the first capacitor is connected to the positive DC bus; the first end of the second capacitor is connected to the negative DC bus; the two ends of the first resistor are respectively connected to the second end of the first capacitor and the second end of the second capacitor; the positive and negative input ends of the first amplifier are respectively connected to the two ends of the first resistor, and the output end of the first amplifier is connected to the controller; the controller is connected to the main control module; the first capacitor and the second capacitor are configured to isolate the DC component of the bus voltage; and the first amplifier is configured to amplify the AC component of the bus voltage.

[0012] Optionally, the control unit includes a second resistor, a third resistor, a fourth resistor, a third capacitor, a second amplifier, a third amplifier and a controller, wherein the second resistor is connected to the positive DC bus; the third resistor is connected to the negative DC bus; the positive and negative input terminals of the second amplifier are respectively connected to one end of the second resistor and one end of the third resistor, and the output terminal of the second amplifier is connected to one end of the third capacitor; the other end of the third capacitor is connected to the positive input terminal of the third amplifier and one end of the fourth resistor, and the other end of the fourth resistor is connected to the signal ground, the output terminal of the third amplifier is connected to the controller, and the controller is connected to the main control module; the second resistor and the third resistor are configured to step down the bus voltage; the second amplifier is configured to amplify, reduce or follow the stepped-down bus voltage; the third capacitor is configured to isolate the DC component of the stepped-down bus voltage; the third amplifier is configured to amplify the AC component of the stepped-down bus voltage.

[0013] Optionally, the main control module is configured to compare the peak-to-peak value with a reference value, and when the difference between the peak-to-peak value and the reference value is greater than or equal to a preset error value, it is determined that the power unit is phase-deficient; when the difference between the peak-to-peak value and the reference value is less than the preset error value, it is determined that the power unit is not phase-deficient.

[0014] Optionally, the preset error value includes a fixed value; or the preset error value is dynamically adjustable, and the preset error value is related to the output current or power of the cascade inverter.

[0015] Optionally, there are multiple power units, and the main control module is further configured to determine the average value of the peak-to-peak value of the bus voltage of the multiple power units based on the peak-to-peak value of the bus voltage of the multiple power units; and determine the reference value based on the average value.

[0016] Optionally, the main control module is also configured to: determine the output voltage, output current and power factor of the cascade inverter; determine the theoretical bus voltage peak-to-peak value based on the output voltage, the output current and the power factor; determine the reference value based on the theoretical bus voltage peak-to-peak value.

[0017] Optionally, the main control module is also configured to: obtain the theoretical bus voltage peak-to-peak value of the cascade inverter under different output voltages, different output currents and different power factors based on a simulation method; store the correspondence between the theoretical bus voltage peak-to-peak values ​​under the different output voltages, different output currents and different power factors; determine the actual output voltage, output current and power factor of the cascade inverter; based on the correspondence, query the theoretical bus voltage peak-to-peak value corresponding to the actual output voltage, output current and power factor; determine the reference value based on the queried theoretical bus voltage peak-to-peak value.

[0018] Optionally, the main control module is further configured to: determine the peak-to-peak value of the bus voltage of the power unit under the output voltage, output current and power factor of the cascade inverter under normal conditions; and determine the reference value based on the peak-to-peak value under normal conditions.

[0019] Optionally, the main control module is further configured to: perform neural network training based on the waveform of the bus voltage of the power unit under the output voltage, output current and power factor of the cascade inverter in normal state and phase loss state to obtain a neural network model; input the output voltage, output current and power factor of the cascade inverter during operation into the neural network model; and determine the reference value through the output result of the neural network model.

[0020] Optionally, the main control module is further configured to determine whether the power unit is missing a phase through the neural network model.

[0021] The present invention also provides a method for detecting phase loss of a power unit of a cascade frequency converter performed by the cascade frequency converter as described above, comprising:

[0022] S1: determining a measured value of a bus voltage of the power unit by a control unit; and

[0023] S2: Determine whether the power unit is missing a phase based on the peak-to-peak value of the measured value through the main control module.

[0024] The present invention also provides a computer-readable storage medium, comprising computer-executable instructions stored thereon, wherein the executable instructions implement the above-mentioned phase loss detection method when executed by a processor.

[0025] The cascade frequency converter and the phase loss detection method of the present invention can realize the phase loss detection of the power unit without setting up an additional phase loss detection circuit, which can reduce hardware costs, reduce wiring man-hours, improve detection convenience, and take into account measurement precision, sensitivity and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 A schematic diagram of a cascade frequency converter according to some embodiments of the present invention is shown.

[0028] Figure 2 A partial schematic diagram of a cascade frequency converter according to some embodiments of the present invention is shown.

[0029] Figure 3 A partial schematic diagram of a cascade frequency converter according to some embodiments of the present invention is shown.

[0030] Figure 4 A partial schematic diagram of a cascade frequency converter according to some embodiments of the present invention is shown.

[0031] Figure 5 A partial schematic diagram of a cascade frequency converter according to some embodiments of the present invention is shown.

[0032] Figure 6 A schematic flow chart of a phase loss detection method according to some embodiments of the present invention is shown.

[0033] Figure 7 A schematic flow chart showing sub-steps of step S2 according to some embodiments of the present invention is shown. DETAILED DESCRIPTION

[0034] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0035] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0036] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", and "coupled" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0038] Many different embodiments or examples are provided below to realize different structures of the present invention. In order to simplify the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides various specific processes and examples of materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0039] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0040] The present invention provides a cascade frequency converter and a phase loss detection method, which can be used to detect whether a power unit of the cascade frequency converter is phase-deficient. The cascade frequency converter includes a phase-shifting transformer, a plurality of power unit groups and a main control module. The phase-shifting transformer can be connected to a power grid. Each power unit group includes a plurality of cascaded power units. Each power unit is connected to a phase-shifting transformer. Each power unit includes a control unit, which is connected to a DC bus of its power unit and configured to determine a measured value of a bus voltage. The main control module is connected to the control unit and configured to determine whether a power unit is phase-deficient based on a peak-to-peak value of the measured value of the bus voltage. A detailed description is given below.

[0041] Figure 1 FIG. 1 is a schematic diagram of a cascade frequency converter 100 according to some embodiments of the present invention. Figure 1 As shown, the cascade inverter 100 includes a phase-shifting transformer 10, a power unit group and a main control module 30. The phase-shifting transformer 10 includes a primary coil (not shown), an iron core 101 and a secondary coil 102. The primary coil includes a three-phase coil, which can be connected to a high-voltage power grid (for example, 10kV / 50Hz, etc.). The secondary coil 102 can be connected to the power unit group. Each power unit group includes a plurality of cascaded power units 20 (a purple rectangle represents a power unit, a row of power units constitutes a power unit group, and three rows of power units constitute three power unit groups). Each power unit 20 can be connected to the secondary coil 102. The three power unit groups form the three-phase output terminals U, V, W and the neutral point O of the cascade inverter 100. The three-phase output terminals U, V, W can be connected to the motor M.

[0042] Figure 2 FIG. 1 shows a partial schematic diagram of a cascade frequency converter 100 according to some embodiments of the present invention. Figure 2As shown, the power unit 20 includes a rectifier bridge composed of three-phase AC input terminals R, S, T and diodes D1~D6, and the rectifier bridge can perform AC-DC conversion. The power unit 20 also includes a control unit 222. The control unit 222 is connected to the DC bus (DC+, DC-) of the power unit 20, and is configured to determine the bus voltage measurement value Vm of the power unit 20. The control unit 222 may include a voltage detection circuit or a voltage sensor, etc. The main control module 30 is connected to the control unit 222, and is configured to determine whether the power unit 20 is out of phase based on the peak-to-peak value Vp-p of the measured value Vm. It can be understood that the peak-to-peak value Vp-p of the bus voltage is the difference between the maximum value and the minimum value of the measured value Vm.

[0043] In some embodiments, Figure 2 As shown, the power unit 20 may also include fuses Fuse1, Fuse2, diodes D7-D10, and insulated gate bipolar transistors IGBT1-IGBT4. The control unit 222 may be connected to the control electrodes g1-g4 of IGBT1-IGBT4, and may control the on and off of IGBT1-IGBT4 based on the control command of the main control module 30.

[0044] In some embodiments, the peak-to-peak value Vp-p of the bus voltage may be determined by the control unit 222. Figure 2 As shown, the control unit 222 can determine the peak-to-peak value Vp-p of the measured value Vm based on the measured value Vm of the bus voltage, and send the peak-to-peak value Vp-p to the main control module 30.

[0045] In other embodiments, the peak-to-peak value Vp-p of the bus voltage may be determined by the main control module 30. Figure 2 As shown, the control unit 222 may send the measured value Vm of the bus voltage to the main control module 30. The main control module 30 may determine the peak-to-peak value Vp-p of the measured value Vm based on the measured value Vm of the bus voltage.

[0046] When the cascade frequency converter is in standby mode, the output power of the power unit is 0. Ideally, the three-phase AC voltage input to the power unit 20 at this time can obtain a DC bus voltage (excluding AC components) after the AC-DC conversion of the rectifier bridge. However, in fact, due to the presence of the discharge resistor, measurement circuit, control power supply and other circuits of the power unit itself, the bus voltage on the output side of the rectifier bridge is not completely a DC component, but includes some AC components, which causes slight fluctuations in the bus voltage. It is difficult for traditional bus voltage detection circuits to accurately identify the situation of slight fluctuations in bus voltage, resulting in inaccurate measurement results. The cascade frequency converter of the present invention improves the measurement circuit of the control unit, can isolate the DC component of the bus voltage on the output side of the rectifier bridge, and only measures the AC component of the bus voltage on the output side of the rectifier bridge, so that slight voltage fluctuations can be accurately identified, which helps to improve the measurement accuracy, sensitivity and accuracy of the power unit phase loss in standby mode. The following is a detailed introduction.

[0047] Figure 4 FIG. 2 shows a partial schematic diagram of a cascade frequency converter according to some embodiments of the present invention. Figure 4As shown, the control unit 222 includes a first capacitor C11, a second capacitor C12, a first resistor R11, a first amplifier A1 and a controller 2220. The first end of the first capacitor C11 is connected to the positive DC bus DC+. The first end of the second capacitor C12 is connected to the negative DC bus DC-. The two ends of the first resistor R11 are respectively connected to the second end of the first capacitor C11 and the second end of the second capacitor C12. The positive and negative input ends of the first amplifier A1 are respectively connected to the two ends of the first resistor R11. The output end of the first amplifier A1 is connected to the controller 2220. The controller 2220 is connected to the main control module 30. The first capacitor C11 and the second capacitor C12 can isolate the DC component of the bus voltage. When the cascade inverter is on standby, the first amplifier A1 can amplify the AC component of the bus voltage. The cascade frequency converter of this embodiment isolates the DC component of the bus voltage on the output side of the rectifier bridge through the first capacitor C11 and the second capacitor C12, and the first amplifier A1 only measures the AC component of the bus voltage on the output side of the rectifier bridge, which can sense the slight voltage fluctuation caused by circuit factors such as the discharge resistor of the power unit itself, the power supply of the control circuit, and the sampling resistor, which helps to improve the measurement precision, sensitivity and accuracy. Exemplarily, after the first capacitor C11 and the second capacitor C12 are isolated, an AC component below 0.1V can be obtained. Exemplarily, after amplification by the first amplifier A1, a low-voltage AC component of about 3.3V can be obtained. Optionally, the first resistor R11 is a variable resistor, which can adjust the amplification factor of the entire circuit, improve the measurement sensitivity and dynamic range, and avoid the damage of the first amplifier A1, thereby improving the measurement safety. Optionally, when the first amplifier A1 is configured as a differential amplifier circuit, the first resistor R11 can be omitted. Optionally, when the first amplifier A1 is configured as a single-ended sampling, the second capacitor C12 can be omitted. In practical applications, the circuit structure can be appropriately adjusted according to requirements, which is within the protection scope of the present invention.

[0048] Figure 5 FIG. 2 shows a partial schematic diagram of a cascade frequency converter according to some embodiments of the present invention. Figure 5As shown, the control unit 222 includes a second resistor R12, a third resistor R13, a fourth resistor R14, a third capacitor C13, a second amplifier A2, a third amplifier A3 and a controller 2220. The second resistor R12 is connected to the positive DC bus DC+. The third resistor R13 is connected to the negative DC bus DC-. The positive and negative input terminals of the second amplifier A2 are respectively connected to one end of the second resistor R12 and one end of the third resistor R13. The output terminal of the second amplifier A2 is connected to one end of the third capacitor C13. The other end of the third capacitor C13 is connected to the positive input terminal of the third amplifier A3 and one end of the fourth resistor R14. The other end of the fourth resistor R14 is connected to the signal ground. The output terminal of the third amplifier A3 is connected to the controller 2220. The controller 2220 is connected to the main control module 30. The second resistor R12 and the third resistor R13 can step down the bus voltage on the output side of the rectifier bridge. The second amplifier A2 can amplify, reduce or follow the stepped-down bus voltage. The third capacitor C13 can isolate the DC component of the stepped-down bus voltage. The third amplifier A3 can amplify the AC component of the stepped-down bus voltage. The cascade inverter of this embodiment can step down the high voltage (for example, above 1000V) on the output side of the rectifier bridge through the second resistor R12 and the third resistor R13 and amplify or reduce or follow the second amplifier A2 to obtain a low-voltage bus voltage (for example, about 3.3V). The DC component of the low-voltage bus voltage is isolated by the third capacitor C13. The third amplifier A3 can only amplify the AC component of the low-voltage bus voltage, thereby sensing the slight voltage fluctuation caused by circuit factors such as the discharge resistor of the power unit, the power supply of the control circuit, and the sampling resistor, which helps to improve the measurement precision, sensitivity and accuracy. Optionally, the fourth resistor R14 is a variable resistor, which can adjust the amplification factor, improve the measurement sensitivity and dynamic range, and avoid damage to the third amplifier A3, thereby improving the measurement safety.

[0049] It should be understood that the amplification factor of the second amplifier A2 is much smaller than that of the third amplifier A3. It should be noted that the present invention does not limit the magnitude relationship between the amplification factors of the second amplifier A2 and the third amplifier A3 and the first amplifier A1. In practical applications, they can be set according to requirements.

[0050] Understandably, Figure 4 and Figure 5In an embodiment, the first amplifier A1 or the third amplifier A3 amplifies and outputs the measured value Vma of the AC component of the low-voltage bus voltage to the controller 2220. The controller 2220 can determine the peak-to-peak value Vp-pa of the measured value Vma based on the measured value Vma of the AC component of the low-voltage bus voltage, and send the peak-to-peak value Vp-pa to the main control module 30. Alternatively, the controller 2220 can send the measured value Vma of the AC component of the low-voltage bus voltage to the main control module 30, and the main control module 30 can determine the peak-to-peak value Vp-pa of the measured value Vma based on the measured value Vma. The main control module 30 can determine whether the power unit is out of phase based on the peak-to-peak value Vp-pa.

[0051] When the cascade inverter is actually implemented, when the output power of the power unit is not 0, the bus voltage has a large fluctuation, so there will be a large AC component. At this time, the first amplifier A1 and the third amplifier A3 may be saturated (the output voltage of the amplifier exceeds the power supply voltage or exceeds the input voltage range allowed by the ADC or controller), which may cause the measured bus voltage to be inaccurate. In order to avoid the problem of inaccurate measurement results caused by amplifier saturation, preferably, when the output power of the power unit is 0, the main control module 30 can judge whether the power unit is out of phase based on the peak-to-peak value Vp-pa (AC component). Preferably, when the output power of the power unit is not 0, the main control module 30 can judge whether the power unit is out of phase based on the peak-to-peak value Vp-p (the superposition of the AC component and the DC component). In other words, when the cascade inverter is in standby mode, the main control module can judge whether the power unit is out of phase based on the AC component of the bus voltage. When the cascade inverter is in operation, the main control module can judge whether the power unit is out of phase based on the AC and DC superposition of the bus voltage. It should be noted that when the cascade inverter is in standby or running state, the main control module can determine whether the power unit is missing a phase based on the AC component of the bus voltage, or any one or a combination of the AC and DC superposition, depending on the actual situation.

[0052] In some embodiments, the main control module 30 / control unit 222 / controller 2220 may include control circuits, central processing units (CPU), micro control units (MCU), graphic processing units (GPU), digital signal processors (DSP), other general-purpose processors, application specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), complex programmable logic devices (CPLD) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components and other components or circuits.

[0053] In some embodiments, the control unit 222 or the main control module 30 can calculate the peak-to-peak value Vp-p (or peak-to-peak value Vp-pa) based on the measured value Vm (or measured value Vma) of the bus voltage within a preset time window. Exemplarily, for example, the preset time window can be at least one power frequency cycle (for example, 1 / 50 Hz). However, the present invention is not limited thereto. The preset time window can be appropriately adjusted according to demand, which is within the protection scope of the present invention.

[0054] In some embodiments, the main control module 30 is configured to compare the peak-to-peak value Vp-p (or the peak-to-peak value Vp-pa) with the reference value Vref, and determine whether the power unit is out of phase based on the comparison result. When the difference ΔV between the peak-to-peak value Vp-p (or the peak-to-peak value Vp-pa) and the reference value Vref is greater than or equal to the preset error value E, the main control module 30 determines that the power unit 20 is out of phase. When the difference ΔV between the peak-to-peak value Vp-p (or the peak-to-peak value Vp-pa) and the reference value Vref is less than the preset error value E, the main control module 30 determines that the power unit 20 is not out of phase. In some embodiments, the preset error value E can be a fixed value. Alternatively, the preset error value E can be dynamically adjustable. For example, the preset error value E is related to the output current or power of the cascade inverter 100. The preset error value E can be dynamically adjusted based on the output current or power of the cascade inverter 100. The output current or power of the cascade inverter 100 is larger, and the preset error value E can be appropriately increased. Correspondingly, the output current or power of the cascade inverter 100 is smaller, and the preset error value E can be appropriately adjusted to be smaller. The preset error value E is positively correlated with the output current or power of the cascade inverter 100. The preset error value E is dynamically adjustable, which is beneficial to balance the detection sensitivity and reliability (reducing false alarms). In addition, it should be noted that the reference value compared with the peak-to-peak value Vp-p or Vp-pa can be the same reference value, or the reference value compared with the peak-to-peak value Vp-p is greater than the reference value compared with Vp-pa. In practical applications, it can be set according to needs.

[0055] In some embodiments, there are multiple power units 20 and multiple voltage detection modules 40 . Figure 3 FIG. 1 shows a partial schematic diagram of a cascade frequency converter 100 according to some embodiments of the present invention. Figure 3 As shown, multiple power units 20-1, 20-2...20-N respectively include control units 222-1, 222-2...222-N, where N is a positive integer greater than 1. The control units 222-1, 222-2...222-N are respectively connected to the DC buses of the power units 20-1, 20-2...20-N, and are respectively used to determine the measured values ​​Vm1, Vm2...VmN of the bus voltages of the power units 20-1, 20-2...20-N. Alternatively, they are respectively used to determine the measured values ​​Vma1, Vma2...VmaN of the AC components of the bus voltages of the power units 20-1, 20-2...20-N.

[0056] In some embodiments, the control units 222-1, 222-2, ... 222-N send the measured values ​​Vm1, Vm2, ... VmN to the main control module 30, respectively. The main control module 30 calculates the peak-to-peak values ​​Vp-p1, Vp-p2, ... Vp-pN based on the measured values ​​Vm1, Vm2, ... VmN, respectively. Alternatively, the control units 222-1, 222-2, ... 222-N send the measured values ​​Vma1, Vma2, ... VmaN to the main control module 30, respectively. The main control module 30 calculates the peak-to-peak values ​​Vp-pa1, Vp-pa2, ... Vp-paN, respectively, based on the measured values ​​Vma1, Vma2, ... VmaN, respectively.

[0057] In some embodiments, the control units 222-1, 222-2, ... 222-N respectively calculate the peak-to-peak values ​​Vp-p1, Vp-p2, ... Vp-pN based on the measured values ​​Vm1, Vm2, ... VmN, and send them to the main control module 30. Alternatively, the control units 222-1, 222-2, ... 222-N respectively calculate the peak-to-peak values ​​Vp-pa1, Vp-pa2, ... Vp-paN based on the measured values ​​Vma1, Vma2, ... VmaN, and send them to the main control module 30.

[0058] In some embodiments, the main control module 30 can determine whether the power units 20-1, 20-2...20-N are out of phase based on the peak-to-peak values ​​Vp-p1, Vp-p2...Vp-pN of the bus voltages of the power units 20-1, 20-2...20-N. The main control module 30 can compare the peak-to-peak values ​​Vp-p1, Vp-p2...Vp-pN with the reference value Vref, respectively, and determine whether the power units are out of phase based on the comparison results. For example, when the difference ΔV between the peak-to-peak value Vp-p1 and the reference value Vref is greater than or equal to the preset error value E, the main control module 30 determines that the power unit 20-1 is out of phase. For another example, when the difference ΔV between the peak-to-peak value Vp-p2 and the reference value Vref is less than the preset error value E, the main control module 30 determines that the power unit 20-2 is not out of phase. In this way, the main control module 30 can determine whether the power units 20-1~20-N are out of phase.

[0059] In some embodiments, the main control module 30 may determine whether the power units 20-1, 20-2 ... 20-N are phase-deficient based on the peak-to-peak values ​​Vp-pa1, Vp-pa2 ... Vp-paN of the AC components of the bus voltages of the power units 20-1, 20-2 ... 20-N. The main control module 30 may compare the peak-to-peak values ​​Vp-pa1, Vp-pa2 ... Vp-paN with the reference value Vref, respectively, and determine whether the power unit is phase-deficient based on the comparison result.

[0060] The present invention does not limit the method for determining the reference value Vref. The following describes some methods for determining the reference value Vref by way of example. It should be noted that the following method for determining the reference value does not distinguish between a DC component and an AC component.

[0061] In some embodiments, the main control module 30 may determine the reference value based on a horizontal comparison method. Specifically, the main control module 30 may determine the average value of the peak-to-peak values ​​of the bus voltages of multiple power units based on the peak-to-peak values ​​of the bus voltages of multiple or even all power units; and determine the reference value based on the average value. For example, Figure 3 As shown, the peak-to-peak values ​​of the bus voltages of the power units 20-1 to 20-N are Vp-p1, Vp-p2, ..., Vp-pN, respectively. The main control module 30 can calculate the average value Vp-pave of the peak-to-peak values ​​Vp-p1, Vp-p2, ..., Vp-pN, and determine the reference value Vref based on the average value Vp-pave. For example, the main control module 30 can use the average value Vp-pave as the reference value Vref. For another example, the main control module 30 can use the value after multiplying the average value Vp-pave by a coefficient or the like as the reference value Vref.

[0062] In some embodiments, the main control module 30 can determine the reference value based on a theoretical calculation method. Specifically, the main control module 30 can determine the output voltage, output current and power factor of the cascade inverter 100; based on the output voltage, output current and power factor, determine the theoretical bus voltage peak-to-peak value; based on the theoretical bus voltage peak-to-peak value, determine the reference value Vref. For example, the main control module 30 can use the theoretical bus voltage peak-to-peak value as the reference value Vref. For another example, the main control module 30 can use the value after multiplying the theoretical bus voltage peak-to-peak value by a coefficient or the like as the reference value Vref. Optionally, the reference value Vref is positively correlated with the output current or power, and the larger the output current or power, the higher the reference value Vref.

[0063] In some embodiments, the main control module 30 can determine the reference value based on the simulation method. Specifically, the main control module 30 can obtain the theoretical bus voltage peak-to-peak value of the cascade inverter 100 under different output voltages, different output currents and different power factors based on the simulation method; store the corresponding relationship between the theoretical bus voltage peak-to-peak values ​​under different output voltages, different output currents and different power factors (for example, in the form of a table, curve, etc.); determine the actual output voltage, output current and power factor of the cascade inverter 100; based on the corresponding relationship, query the theoretical bus voltage peak-to-peak value corresponding to the actual output voltage, output current and power factor; determine the reference value Vref based on the queried theoretical bus voltage peak-to-peak value. For example, the main control module 30 can use the queried theoretical bus voltage peak-to-peak value as the reference value Vref. For another example, the main control module 30 can use the value after multiplying the queried theoretical bus voltage peak-to-peak value by a coefficient or the like as the reference value Vref.

[0064] In some embodiments, the main control module 30 can determine the reference value based on the self-learning method. Specifically, the main control module 30 can determine and store (for example, when the product is debugged) the peak-to-peak value of the bus voltage of the power unit under the output voltage, output current and power factor of the cascade inverter 100 in the normal state; based on the peak-to-peak value of the bus voltage of the power unit in the normal state, determine the reference value Vref. For example, the main control module 30 can use the peak-to-peak value of the bus voltage of the power unit in the normal state as the reference value Vref. For another example, the main control module 30 can multiply the peak-to-peak value of the bus voltage of the power unit in the normal state by a coefficient or the like as the reference value Vref. It should be noted that the "normal state" can be the state when the cascade inverter 100 is operating normally, including but not limited to the state of no lack of equality.

[0065] In some embodiments, the main control module 30 may determine the reference value based on an AI learning method (e.g., a neural network training method). Specifically, the main control module 30 may perform neural network training based on the waveform of the bus voltage of the power unit under the output voltage, output current, and power factor of the cascade inverter 100 in a normal state and a phase-loss state to obtain a neural network model; input the output voltage, output current, and power factor of the cascade inverter when it is running into the neural network model; and determine the reference value Vref through the output result of the neural network model.

[0066] In some embodiments, the main control module 30 can determine whether the power unit is missing a phase through a neural network model. For example, the output voltage, output current and power factor of the cascade inverter during operation are input into the neural network model, and the neural network model can determine whether the power unit is missing a phase, and can determine which power unit is missing a phase or normal and output it.

[0067] In some embodiments, the main control module 30 can detect whether the power unit is missing phase by analyzing whether there are harmonics of characteristic orders in the bus voltage. This method is particularly suitable for the main control module 30 with strong computing power.

[0068] In some embodiments, Figure 1 As shown, the number of power units 20 includes multiple. Figure 2 As shown, the power unit 20 includes a bypass switch Thy1 connected to the control unit 222. The control end G of the bypass switch Thy1 is connected to the control unit 222. The bypass switch Thy1 is set at the output end of the power unit 20. The main control module 30 is also configured to send a conduction instruction ON to the control unit 222 of the power unit 20 with the phase missing when it is determined that one or more of the power units 20 are missing a phase. The control unit 222 of the power unit 20 with the phase missing can control its bypass switch Thy1 to be turned on based on the conduction instruction ON to bypass the power unit 20 with the phase missing. In other embodiments, when the main control module 30 detects that one or more of the power units are missing a phase, it can automatically shut down and stop running to avoid causing more serious faults and facilitate timely maintenance by the staff.

[0069] In some embodiments, Figure 1 As shown, the cascade inverter 100 may also include one or more of a human machine interface (HMI), a cascade inverter advisor (DA), and a programmable logic controller (PLC). The HMI, DA, and PLC are connected to the main control module 30, and can communicate with one or more of the main control module 30 and the control unit 222 of the power unit 20 to share data information.

[0070] In some embodiments, the cascade inverter 100 may include a storage module (not shown). The storage module is used to store the operating data of the cascade inverter 100, the phase loss detection result of the power unit 20, the corresponding relationship between the peak-to-peak values ​​of the theoretical bus voltage of the cascade inverter 100 under different output voltages, different output currents and different power factors (for example, stored in a table, curve, etc.), a neural network model and other information. The storage module may include a memory. The memory may include a random access memory (RAM) or a non-volatile memory (non-volatile memory). Further, the memory may include: at least one of a phase-change random access memory (PRAM), a static random access memory (SRAM), a dynamic random access memory (DRAM), a read-only memory (ROM), and an electrically erasable programmable read only memory (EEPROM). Alternatively, the storage module may include a cloud storage. The storage module may be implemented in software and / or hardware.

[0071] In some embodiments, the cascade inverter 100 may include a display module (not shown). The display module may be connected to at least one of the main control module 30 and the control unit 222, and may be used to visualize the measured value of the output bus voltage, the result of the phase loss detection, etc. The display module may include a display screen. The display screen may include at least one of an LCD display screen (liquid-crystal display, LCD), an LED display screen (light emitting diode, LED), and an OLED display screen (organic light emitting diode, OLED).

[0072] The present invention further provides a phase loss detection method 300 executed by the cascade frequency converter 100 as described above, for detecting whether a power unit 20 of the cascade frequency converter 100 has a phase loss. Figure 6 FIG. 3 is a flow chart of a phase failure detection method 300 according to some embodiments of the present invention. Figure 6As shown, the phase loss detection method 300 includes steps S1 to S2. In step S1, the control unit 222 determines the measured value Vm of the bus voltage of the power unit 20. In step S2, the main control module 30 determines whether the power unit 20 is phase-lost based on the peak-to-peak value Vp-p of the measured value Vm.

[0073] Figure 7 FIG. 5 is a flow chart showing the sub-steps of step S2 according to some embodiments of the present invention. Figure 7 As shown, step S2 includes sub-steps S21 to S24. Sub-step S31, compare the peak-to-peak value Vp-p with the reference value Vref. Sub-step S22, determine whether the difference ΔV between the peak-to-peak value Vp-p and the reference value Vref is greater than or equal to the preset error value E. When the difference ΔV between the peak-to-peak value Vp-p and the reference value Vref is greater than or equal to the preset error value E, execute sub-step S23 to determine that the power unit 20 is out of phase. When the difference ΔV between the peak-to-peak value Vp-p and the reference value Vref is less than the preset error value E, execute sub-step S24 to determine that the power unit 20 is not out of phase.

[0074] In some embodiments, the main control module 30 can determine whether the power unit 20 is missing a phase based on the peak-to-peak value Vp-pa of the measured value Vma of the AC component of the bus voltage, which can improve the measurement precision, sensitivity and accuracy. The relevant content is the same or similar to the aforementioned cascade inverter 100 and will not be repeated here.

[0075] The cascade frequency converter and the phase loss detection method of the present invention can realize the phase loss detection of the power unit without setting up an additional phase loss detection circuit, which can reduce hardware costs, reduce wiring man-hours, improve detection convenience, and take into account measurement precision, sensitivity and accuracy.

[0076] The present invention further provides a computer-readable storage medium, wherein the computer-readable storage medium includes computer-executable instructions stored thereon, and when the executable instructions are executed by a processor, the above-mentioned phase loss detection method 300 is implemented.

[0077] In some embodiments, the processor may include components or circuits such as processing circuits, CPUs, MCUs, GPUs, DSPs, other general-purpose processors, ASICs, FPGAs, CPLDs or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0078] The present invention may take the form of a computer program product implemented on one or more storage media containing program code. Computer-usable storage media include permanent and non-permanent, removable and non-removable media, and information storage may be implemented by any method or technology. The information may be computer-readable instructions, data structures, modules of a program, or other data. Examples of computer storage media include, but are not limited to: PRAM, SRAM, DRAM, other types of RAM, ROM, EEPROM, flash memory or other memory technology, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassettes, magnetic tape disk storage or other magnetic storage devices or any other non-transmission medium that can be used to store information that can be accessed by a computing device.

[0079] It should be noted that this specification provides method operation steps such as embodiments or schematic diagrams, but more or fewer operation steps may be included based on conventional or non-creative labor. The order of steps listed in the embodiments is only one way of executing the order of many steps and does not represent the only execution order. When the actual system or device product is executed, it can be executed in the order of the method shown in the embodiment or flowchart or in parallel.

[0080] It should be noted that, although several modules of the cascade frequency converter are mentioned in the above detailed description, such division is not mandatory. In fact, according to an embodiment of the present invention, the features and functions of two or more modules described above can be implemented in one module. Conversely, the features and functions of one module described above can be further divided into multiple modules for embodiment.

[0081] It should be noted that the present invention may only include Figure 1-7 In other words, not all of the features shown need to be implemented simultaneously in the cascade inverter / phase loss detection method of the present invention. Figure 1-5 Each feature can be applied to Figure 6-7 The phase loss detection method.

[0082] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A cascade frequency converter, characterized in that: include: A phase-shifting transformer, wherein the phase-shifting transformer can be connected to a power grid; A plurality of power cell groups, each power cell group comprising a plurality of cascaded power cells, each power cell being connected to the phase-shifting transformer; each power cell comprising a control unit, the control unit being connected to a DC bus of the power cell and configured to determine a measured value of a bus voltage; and A main control module is connected to the control unit and is configured to determine whether the power unit is missing a phase based on the peak-to-peak value of the measured value.

2. The cascade frequency converter according to claim 1, characterized in that: The control unit is further configured to determine a peak-to-peak value of the measured value based on the measured value of the bus voltage, and send the peak-to-peak value to the main control module.

3. The cascade frequency converter according to claim 1, characterized in that: The control unit is further configured to send the measured value of the bus voltage to the main control module; the main control module is further configured to determine the peak-to-peak value of the measured value based on the measured value of the bus voltage.

4. The cascade frequency converter according to claim 1, characterized in that: The control unit includes a first capacitor, a second capacitor, a first resistor, a first amplifier and a controller, wherein the first end of the first capacitor is connected to the positive DC bus; the first end of the second capacitor is connected to the negative DC bus; the two ends of the first resistor are respectively connected to the second end of the first capacitor and the second end of the second capacitor; the positive and negative input ends of the first amplifier are respectively connected to the two ends of the first resistor, and the output end of the first amplifier is connected to the controller; The controller is connected to the main control module; the first capacitor and the second capacitor are configured to isolate the DC component of the bus voltage; and the first amplifier is configured to amplify the AC component of the bus voltage.

5. The cascade frequency converter according to claim 1, characterized in that: The control unit includes a second resistor, a third resistor, a fourth resistor, a third capacitor, a second amplifier, a third amplifier and a controller, wherein the second resistor is connected to a positive DC bus; the third resistor is connected to a negative DC bus; the positive and negative input terminals of the second amplifier are respectively connected to one end of the second resistor and one end of the third resistor, and the output terminal of the second amplifier is connected to one end of the third capacitor; the other end of the third capacitor is connected to the positive input terminal of the third amplifier and one end of the fourth resistor, and the other end of the fourth resistor is connected to a signal ground, the output terminal of the third amplifier is connected to the controller, and the controller is connected to the main control module; the second resistor and the third resistor are configured to step down the bus voltage; the second amplifier is configured to amplify, reduce or follow the stepped-down bus voltage; the third capacitor is configured to isolate the DC component of the stepped-down bus voltage; and the third amplifier is configured to amplify the AC component of the stepped-down bus voltage.

6. The cascade frequency converter according to any one of claims 1 to 5, characterized in that: The main control module is configured to compare the peak-to-peak value with a reference value, and when the difference between the peak-to-peak value and the reference value is greater than or equal to a preset error value, it is determined that the power unit is phase-deficient; when the difference between the peak-to-peak value and the reference value is less than the preset error value, it is determined that the power unit is not phase-deficient.

7. The cascade frequency converter according to claim 6, characterized in that: The preset error value includes a fixed value; or the preset error value is dynamically adjustable, and the preset error value is related to the output current or power of the cascade inverter.

8. The cascade frequency converter according to claim 6, characterized in that: The number of the power units is multiple, and the main control module is further configured to determine the average value of the peak-to-peak value of the bus voltage of the multiple power units based on the peak-to-peak value of the bus voltage of the multiple power units; and determine the reference value based on the average value.

9. The cascade frequency converter according to claim 6, characterized in that: The main control module is also configured to: determine the output voltage, output current and power factor of the cascade inverter; determine the theoretical bus voltage peak-to-peak value based on the output voltage, the output current and the power factor; and determine the reference value based on the theoretical bus voltage peak-to-peak value.

10. The cascade frequency converter according to claim 6, characterized in that: The main control module is also configured to: obtain the theoretical bus voltage peak-to-peak value of the cascade inverter under different output voltages, different output currents and different power factors based on a simulation method; store the corresponding relationship between the theoretical bus voltage peak-to-peak values ​​under different output voltages, different output currents and different power factors; determine the actual output voltage, output current and power factor of the cascade inverter; based on the corresponding relationship, query the theoretical bus voltage peak-to-peak value corresponding to the actual output voltage, output current and power factor; determine the reference value based on the queried theoretical bus voltage peak-to-peak value.

11. The cascade frequency converter according to claim 6, characterized in that: The main control module is also configured to: determine the peak-to-peak value of the bus voltage of the power unit under the output voltage, output current and power factor of the cascade inverter in a normal state; and determine the reference value based on the peak-to-peak value in a normal state.

12. The cascade frequency converter according to claim 6, characterized in that: The main control module is also configured to: perform neural network training based on the waveform of the bus voltage of the power unit under the output voltage, output current and power factor of the cascade inverter in normal state and phase loss state to obtain a neural network model; input the output voltage, output current and power factor of the cascade inverter during operation into the neural network model; and determine the reference value through the output result of the neural network model.

13. The cascade frequency converter according to claim 12, characterized in that: The main control module is also configured to determine whether the power unit is missing a phase through the neural network model.

14. A method for detecting phase loss of a power unit of a cascade frequency converter performed by the cascade frequency converter according to any one of claims 1 to 13, characterized in that: include: S1: Determine a measured value of a bus voltage of the power unit by a control unit; and S2: Determine whether the power unit is missing a phase based on the peak-to-peak value of the measured value through the main control module.

15. A computer-readable storage medium, characterized in that: The invention comprises computer executable instructions stored thereon, and when the executable instructions are executed by a processor, the phase loss detection method according to claim 14 is implemented.

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