Series dynamic compensation type frequency converter high and low voltage ride through device and control method thereof

Abstract

The invention relates to a coal feeder frequency converter high and low voltage ride-through power supply system, and discloses a series dynamic compensation type frequency converter high and low voltage ride-through device and a control method thereof, and the device comprises a series isolation type topological structure which is connected between a frequency converter DC bus and a rectification circuit; the double-excitation type converter is composed of a first switching tube (Q1), a second switching tube (Q2) and a high-frequency transformer, the first switching tube and the second switching tube work in a complementary mode, and bidirectional pulses are applied to the primary side of the high-frequency transformer. According to the series connection dynamic compensation type frequency converter high and low voltage ride-through device, through an innovative series connection isolation type dynamic compensation topology and hardware-software hybrid control strategy, the technical problems that an existing parallel connection type frequency converter voltage ride-through device is single in function, high in energy consumption, large in impact and poor in compatibility are fundamentally solved; and bidirectional treatment of voltage sag and sag of the frequency converter power supply system is realized.

Description

Technical Field

[0001] This invention relates to a high and low voltage ride-through power supply system for a coal feeder frequency converter, specifically a series dynamic compensation type frequency converter high and low voltage ride-through device and its control method. Background Technology

[0002] When a thermal power plant experiences a short-term voltage drop in the power grid and the power plant's electricity supply due to lightning strikes, electrical equipment short circuits, or grounding, it will cause low voltage in the power supply and control power supply of the frequency converter. These low voltage lockout protections of the frequency converter will activate, and the auxiliary machines (motors) equipped with the frequency converter will stop running, resulting in boiler shutdown and machine shutdown accidents. This will cause local power grid instability and have a significant impact on the power grid.

[0003] In recent years, power generation companies and design units have increasingly favored the use of frequency converter technology in the design of auxiliary equipment for many thermal power plants. However, most frequency converters have poor low-voltage ride-through capability, or even no low-voltage ride-through capability at all. It can be said that the lack of low-voltage ride-through capability in auxiliary equipment for thermal power plants is a widespread problem throughout the country. A large number of low-voltage motors in auxiliary equipment for thermal power generation and petrochemical enterprises are driven by frequency converters. When the power grid of these enterprises experiences a "power fluctuation," the lack of low-voltage ride-through capability in the frequency converter triggers its low-voltage protection function, causing the frequency converter to lock out its output, thereby causing the low-voltage motor to stop operating.

[0004] When the grid voltage suddenly rises, the excessively high voltage on the bus will cause equipment alarms and shutdowns. High voltage will reduce the service life of the frequency converter and even cause insulation degradation, which can directly lead to equipment damage in severe cases. Conventional frequency converter low voltage ride-through power supply devices usually adopt a parallel power supply method with the DC bus. When the grid experiences a low voltage fluctuation, the low voltage ride-through device starts to work and provides a stable DC power supply to the frequency converter's DC bus. At this time, the frequency converter's power supply comes entirely from the low voltage ride-through device. However, when the grid experiences a high voltage fluctuation, because the low voltage ride-through device is connected in parallel with the frequency converter's DC bus, it cannot effectively control the high voltage fluctuation.

[0005] Therefore, we propose a series dynamic compensation type high and low voltage ride-through device for frequency converters to solve the problems mentioned above. Summary of the Invention

[0006] The purpose of this invention is to provide a high and low voltage ride-through device for a series dynamic compensation type frequency converter, so as to solve the problems mentioned in the background art, such as the inability to manage high voltage ride-through and fixed voltage output, high power consumption of low voltage ride-through devices, full load upon startup, and large inrush current.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a high- and low-voltage ride-through device for a series dynamic compensation type frequency converter, comprising:

[0008] A series-isolated topology is used to connect the inverter's DC bus to the rectifier circuit.

[0009] The dual-ended converter consists of a first switch (Q1), a second switch (Q2), and a high-frequency transformer. The first and second switches operate in a complementary manner, and a bidirectional pulse is applied to the primary side of the high-frequency transformer.

[0010] The step-up / step-down circuit includes a BUCK step-down circuit consisting of a third switching transistor (Q3) and a filter inductor (L2);

[0011] The differential voltage sampling circuit uses three-stage differential voltage detection to detect the voltage difference between the actual DC bus voltage and the reference voltage in real time and output an analog signal.

[0012] The hybrid control unit receives the analog signal output by the differential voltage sampling circuit and generates a PWM control signal based on a hybrid modulation method of hardware differential voltage detection and software PID calculation.

[0013] Energy storage units, using supercapacitors or batteries, are used to provide energy support when the grid voltage is interrupted;

[0014] The dual-excited converter works in conjunction with the buck-boost circuit. When the DC bus voltage is lower than the first threshold, the dual-excited converter outputs a compensation voltage to boost the voltage. When the DC bus voltage is higher than the second threshold, the buck-boost circuit performs voltage reduction regulation to achieve bidirectional dynamic voltage compensation.

[0015] Preferably, the dual-excited converter includes:

[0016] The first absorption capacitor (CX1) and the second absorption capacitor (CX2) are connected in parallel between the drain and source of the first switch (Q1) and the second switch (Q2), respectively, to absorb the turn-off peak voltage.

[0017] The first freewheeling diode (DX1) and the second freewheeling diode (DX2) are respectively connected to the two ends of the primary winding of the high-frequency transformer and are used for freewheeling after the switching transistor is turned off.

[0018] The full-bridge uncontrolled rectifier circuit is connected to the secondary side of the high-frequency transformer, and the output terminal is equipped with a filter circuit and anti-reverse diodes (DF3, DF4).

[0019] Preferably, the third switch (Q3) of the buck-boost circuit is normally on under normal operating conditions, and only operates in PWM mode under high voltage ride-through mode to achieve bus voltage buck regulation.

[0020] Preferably, the differential voltage sampling circuit includes:

[0021] The first-stage voltage divider circuit is used to convert the 0-800V DC bus voltage into a 0-4V first analog signal (ADC_U1).

[0022] The voltage reference circuit outputs a second analog signal (ADC_U2) representing the rated bus voltage, where 2.5V corresponds to a target voltage of 500V;

[0023] The differential detection circuit calculates the difference between the first analog signal and the second analog signal and outputs a third analog signal (ADC_U3). The third analog signal is directly input to the hybrid control unit for PID calculation.

[0024] Preferably, the start-up threshold of the hybrid control unit is 0.25V, corresponding to a bus voltage deviation of 50V; when the amplitude of the third analog signal (ADC_U3) exceeds the start-up threshold, the hybrid control unit immediately starts PWM output and adjusts the PID response speed according to the amplitude ratio of the third analog signal.

[0025] Preferably, the energy storage unit is connected to the input side of the dual-excited converter, supports AC and DC dual power input, and does not need to share the same AC bus power supply as the frequency converter.

[0026] Preferably, the compensation voltage is dynamically and automatically adjusted within the range of 0-300V based on the depth of voltage drop or rise in the mains voltage.

[0027] Preferably, the high and low voltage ride-through control method includes the following steps:

[0028] The differential voltage sampling circuit detects the voltage difference between the actual DC bus voltage and the reference voltage of the frequency converter in real time and outputs an analog signal. When the voltage difference exceeds a preset start-up threshold, the hybrid control unit starts PWM modulation and generates a control signal based on the hardware voltage difference detection result and the software PID algorithm. The operating mode is selected according to the bus voltage status: if the bus voltage is lower than the rated range, the dual-excited converter is controlled to output a compensation voltage for series boost compensation; if the bus voltage is higher than the rated range, the BUCK step-down circuit is controlled to perform step-down regulation. When the voltage difference falls back to the normal range, the PWM output is immediately turned off and the device returns to standby mode.

[0029] Preferably, during the low voltage ride-through process, the first switch (Q1) and the second switch (Q2) of the dual-excited converter are turned on complementaryly at a frequency of 60KHz, and the amplitude of the output compensation voltage is dynamically adjusted in real time according to the voltage drop depth to maintain the bus voltage stable within the range of 500V±30V.

[0030] Preferably, during high voltage ride-through, the third switch (Q3) operates in PWM mode to reduce the bus voltage from a sudden rise of over 700V to within the range of 500V±30V, while the dual-excited converter remains in standby mode, achieving bidirectional coordinated control between the two.

[0031] Compared with the prior art, the beneficial effects of the present invention are: the series dynamic compensation type inverter high and low voltage ride-through device, through the innovative series isolation type dynamic compensation topology and hardware-software hybrid control strategy, fundamentally solves the technical problems of existing parallel inverter voltage ride-through devices, such as single function, high energy consumption, large impact and poor compatibility, and realizes bidirectional management of voltage sag and swell in the inverter power supply system.

[0032] 1. Achieving bidirectional high and low voltage ride-through, overcoming the functional limitations of parallel topologies: This invention adopts a series isolation topology, using a dual-excited converter and a BUCK step-down circuit to work together. When the 380VAC voltage drops, a positive compensation voltage is output to boost the voltage; when the voltage surges, the step-down circuit is activated to reduce the bus voltage. Compared with existing parallel schemes that only support low voltage, this invention is the first to simultaneously manage grid voltage dips and surges in a single device. The compensation voltage is dynamically adjusted in real time within the range of 0-300V according to the dip depth, enabling the frequency converter drive system to have complete voltage disturbance rejection capability.

[0033] 2. Reduce power consumption and increase power density, optimize energy efficiency: The compensation voltage is dynamically adjusted in real time according to the voltage drop depth of the grid, and only outputs the required power when the bus voltage deviates. For the typical working condition of 50% AC grid voltage drop depth, the series compensation type only needs to provide 50% power output. Compared with the traditional parallel fixed voltage support method, the dynamic voltage compensation requires less output power and is more efficient.

[0034] 3. Hardware differential pressure detection and software PID hybrid modulation result in faster response speed: The differential voltage sampling circuit directly converts the voltage difference between the target voltage and the actual voltage into an analog signal. This signal serves as both a start-up trigger and a PID feedback quantity. Hardware detection replaces the traditional software sampling-calculation-modulation process. The higher the analog amplitude, the faster the PID response speed. There is no need for the MCU to perform software differential calculation, which significantly improves the dynamic compensation response speed of the device.

[0035] 4. Isolated topology and dual power input design, with strong system compatibility: The series isolation structure means that it does not need to share the same bus power supply as the frequency converter, supports simultaneous AC and DC dual power input, avoids interference with the original frequency converter control system, can be directly installed in the existing system without modifying the existing power distribution circuit, and has strong engineering implementation convenience.

[0036] 5. Two-way coordinated control of boost and buck circuits for higher operational reliability: The dual-excited boost circuit and the BUCK buck circuit can compensate for each other and work simultaneously. When the compensation voltage overshoots, the two-way circuits automatically coordinate to adjust. The control logic further improves the reliability and stability of the system, avoiding the risk of single-circuit regulation lag or instability. Attached Figure Description

[0037] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0038] Figure 1 Internal topology diagram of the frequency converter

[0039] Figure 2 This is a schematic diagram of the high and low voltage ride-through device for the frequency converter of the present invention.

[0040] Figure 3 This is a circuit diagram of the bus voltage isolation sampling circuit of the present invention;

[0041] Figure 4 This is a diagram of the sampling isolation power supply for the present invention;

[0042] Figure 5 This is a circuit diagram of the voltage reference circuit of the present invention;

[0043] Figure 6 This is a circuit diagram for the differential sampling of the target value in this invention. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Please see Figures 1-6 The present invention provides the following technical solution: a series dynamic compensation type inverter high and low voltage ride-through device, comprising: a series isolation type topology connected between the inverter DC bus and the rectifier circuit;

[0046] The dual-ended converter consists of a first switch (Q1), a second switch (Q2), and a high-frequency transformer. The first and second switches operate in a complementary manner, and a bidirectional pulse is applied to the primary side of the high-frequency transformer.

[0047] The step-up / step-down circuit includes a BUCK step-down circuit composed of a third switching transistor (Q3) and a filter inductor (L2); the differential voltage sampling circuit adopts three-stage differential voltage detection to detect the voltage difference between the actual DC bus voltage and the reference voltage in real time and output an analog signal.

[0048] The hybrid control unit receives the analog signal output by the differential voltage sampling circuit and generates a PWM control signal based on a hybrid modulation method of hardware differential voltage detection and software PID calculation; the energy storage unit uses a supercapacitor or battery to provide energy support when the grid voltage is interrupted.

[0049] The dual-excited converter works in conjunction with the buck-boost circuit. When the DC bus voltage is lower than the first threshold, the dual-excited converter outputs a compensation voltage to boost the voltage. When the DC bus voltage is higher than the second threshold, the buck-boost circuit performs voltage reduction regulation to achieve bidirectional dynamic voltage compensation.

[0050] like Figure 1 As shown, the series dynamic compensation inverter high / low voltage ride-through device of the present invention is connected in series between the three-phase uncontrolled rectifier bridge and the DC bus support capacitor C2, forming a series isolation topology. The specific electrical connection relationship is as follows:

[0051] The three-phase AC input power (380VAC±20%) is connected to the three-phase uncontrolled rectifier bridge inside the frequency converter. The positive DC output of the rectifier bridge is connected in series to the input terminal S1 of this device. The output terminal S1* of this device is connected to the positive terminal of the DC bus support capacitor C2. The negative DC output of the rectifier bridge is directly connected to the negative terminal of capacitor C2. The third switching transistor Q3 is an IGBT module. Its collector is connected to the positive output of the rectifier bridge, and its emitter is connected to the filter inductor L2. The cathode of the freewheeling diode D7 is connected to the emitter of Q3, and its anode is connected to the negative terminal of capacitor C2, realizing unidirectional conduction and isolation. The energy storage unit uses a supercapacitor module, which is connected to the two ends of the input filter capacitor C1 of the dual-excited converter through the DC contactor KM1. The supercapacitor module is equipped with an independent charging management unit, supporting redundant AC and DC dual power supply. The AC input is taken from the 380VAC of the plant's safety section, and the DC input is taken from the DC 220V DC power supply.

[0052] like Figure 2As shown, the dual-excited converter adopts an isolated dual-terminal excitation topology. The first switch Q1 and the second switch Q2 are N-channel MOSFETs. The gate drive signal is provided by a dedicated driver chip UCC21520. The two PWM signals (PWM1 and PWM2) have a fixed frequency of 60kHz, and the duty cycle D is limited to the range of 0-45%, ensuring complementary conduction of the two transistors and allowing a 200ns dead time. The high-frequency transformer core uses EE-type ferrite. The primary winding uses 2×0.1mm×100 strand Litz wire wound with 20 turns, and the secondary winding uses 0.1mm×60 strand Litz wire wound with 40 turns, resulting in a turns ratio of 2:1. The absorption capacitors CX1 and CX2 are 1nF / 1000VCBB21 film capacitors, connected in parallel to the drain and source of Q1 and Q2 to absorb turn-off peak voltages. The freewheeling diodes DX1 and DX2 are UF4007 ultrafast recovery diodes, providing a freewheeling path for the leakage inductance energy. The secondary-side rectification uses a full-bridge uncontrolled rectification. Diodes DF1-DF4 are MBR20200CT Schottky diodes. The rectified filter inductor L3 is 200μH, and the filter capacitor C3 is a 470μF / 250V high-frequency low-resistance electrolytic capacitor. Anti-reverse diodes DF3 and DF4 are connected in series in the output circuit to prevent reverse voltage from flowing back into the bus. The third switch Q3 of the buck-boost circuit is normally on under normal operating conditions, and only operates in PWM mode in high-voltage ride-through mode to reduce the bus voltage from a sudden rise of over 700V to a range of 500V±30V.

[0053] like Figures 3 to 6 As shown, the differential voltage sampling circuit adopts a three-stage precision detection architecture. The first-stage voltage divider circuit uses a precision resistor network (R1-R5) to form an attenuation network with a voltage division ratio of 1:196, converting the 0-800V bus voltage into a first analog signal ADC_U1 of 0-4.08V, which is then fed into the OPA197 operational amplifier's follower buffer. The second-stage voltage reference circuit uses a high-precision reference chip REF5025, outputting a 2.5V reference voltage ADC_U2, corresponding to a 500V target voltage. After being followed by the operational amplifier, the output impedance is less than 1Ω. The third-stage differential detection circuit uses an instrumentation amplifier INA827 with a gain G=5, calculating the difference between ADC_U1 and ADC_U2 and outputting a third analog signal ADC_U3. When the bus voltage is 500V, ADC_U3=0.25V (start-up threshold); when the voltage drops to 300V, ADC_U3=1V. A clamping diode is set at the output terminal to limit ADC_U3 to the 0-5V range, protecting the MCU's ADC input port. This circuit enables "hardware to replace software in performing difference calculations", which significantly improves the response speed of the device's dynamic compensation.

[0054] The hybrid control unit is based on an STM32F103C8T6 microcontroller. The ADC_U3 is connected to the MCU's PA0 pin, configured with 12-bit resolution and a 1MHz sampling rate, using DMA mode for continuous acquisition without CPU intervention. PWM1 and PWM2 are outputs complementaryly from timer TIM1, and PWM3 is output from timer TIM2. The dead time of 200ns is configured via the TIM1_BDTR register. The control algorithm employs a hybrid modulation of hardware fast startup and software PID: when ADC_U3 > 0.25V, the MCU comparator immediately triggers an interrupt to start PID calculation, with a response time of less than 500ns; the software part uses an incremental PID algorithm, with parameters Kp=0.8, Ki=0.05, and Kd=0.01 determined by the Ziegler-Nichols tuning method. The PID calculation result is directly mapped to the PWM duty cycle D=min(ΔUk×0.1,0.45). The protection logic includes: when ADC_U3>4.5V, a hardware fault is determined and PWM is immediately blocked; when the current of Q1 and Q2 is detected by the sampling resistor and exceeds 80A, the DESAT protection of the driver chip will turn off the switching transistor within 200ns.

[0055] Taking a grid voltage drop to 60% of the rated voltage (228VAC) as an example, the device's operation process is as follows: At t=0ms, the grid voltage is normal, the bus voltage is 530V, ADC_U3=0.15V (<0.25V), and the device's standby power consumption is less than 5W; At t=5ms, a phase A ground fault occurs, the voltage drops to 228VAC, the bus voltage is 300V, and ADC_U3=1V (>0.25V); At t=5.5ms, ADC_U3 exceeds the threshold, triggering an interrupt, the MCU starts PID calculation, TIM1 outputs PWM1 and PWM2, initially... With a duty cycle D=0.2, the dual-excited converter outputs a compensation voltage U2=200V, which stabilizes at 200V±5V after closed-loop regulation. During t=5.5ms-200ms, the device continuously outputs the compensation voltage, and the bus voltage Utotal=U1+U2=500V±20V. The frequency converter maintains normal operation, and the motor speed fluctuation is less than 2%. At t=200ms, the grid fault is cleared and the voltage is restored. The bus voltage rises back to 530V, ADC_U3 drops to 0.15V, and the MCU immediately clears the PWM duty cycle to zero. The device returns to standby mode within 1ms. The high-voltage ride-through process is similar. When the grid voltage suddenly rises to 456VAC, ADC_U3=-1V triggers the buck mode. The MCU starts TIM2 to adjust the duty cycle of Q3 to stabilize the bus voltage at 500V.

[0056] Under the same operating conditions of a 380VAC system, a 50% deep voltage drop, and a load power of 10kW, the present invention compares with the conventional parallel scheme as follows: The present invention provides a series compensation output of 200V / 20A=4kW, with a device loss of 200W (efficiency 95%), a 32A circuit breaker capacity with no additional impact, a starting inrush current less than 1.5 times the rated current, and a supercapacitor configuration of 16 strings at a cost of approximately 2000 yuan; the conventional parallel scheme provides an output of 500V / 20A=10kW, with a loss of 500W (efficiency 95%), requires a 63A circuit breaker capacity increase, a starting inrush current 5-8 times the rated current, and a supercapacitor configuration of 48 strings at a cost of approximately 6000 yuan. Test results show that the present invention reduces output power by 60%, reduces losses by 300W, reduces device size by 40%, reduces overall cost by 35%, and has high compatibility with the circuit breaker at the upper level.

[0057] In a large-scale coal feeder group control system for thermal power plants, the output of this device can be connected in parallel to support multiple frequency converters. The system configuration is as follows: one 12kW through-feed device simultaneously supports three 3.3kW frequency converters. The output of the device is connected to the DC bus of each frequency converter through a 15A fast fuse. Current sharing control detects the current of the 5mΩ sampling resistor in each branch, and the MCU allocates the duty cycle according to the total current to achieve a current sharing accuracy of less than 5%. Redundancy design ensures that if any branch fails, the fast fuse will blow without affecting the operation of other branches, significantly improving system reliability.

[0058] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high / low voltage ride-through device for a series dynamic compensation type frequency converter, characterized in that, include: A series-isolated topology is used to connect the inverter's DC bus to the rectifier circuit. The dual-ended converter consists of a first switch (Q1), a second switch (Q2), and a high-frequency transformer. The first and second switches operate in a complementary manner, and a bidirectional pulse is applied to the primary side of the high-frequency transformer. The step-up / step-down circuit includes a BUCK step-down circuit consisting of a third switching transistor (Q3) and a filter inductor (L2); The differential voltage sampling circuit uses three-stage differential voltage detection to detect the voltage difference between the actual DC bus voltage and the reference voltage in real time and output an analog signal. The hybrid control unit receives the analog signal output by the differential voltage sampling circuit and generates a PWM control signal based on a hybrid modulation method of hardware differential voltage detection and software PID calculation. Energy storage units, using supercapacitors or batteries, are used to provide energy support when the grid voltage is interrupted; The dual-excited converter works in conjunction with the buck-boost circuit. When the DC bus voltage is lower than the first threshold, the dual-excited converter outputs a compensation voltage to boost the voltage. When the DC bus voltage is higher than the second threshold, the buck-boost circuit performs voltage reduction regulation to achieve bidirectional dynamic voltage compensation.

2. The high and low voltage ride-through device for a series dynamic compensation type frequency converter according to claim 1, characterized in that: The dual-excited converter includes: The first absorption capacitor (CX1) and the second absorption capacitor (CX2) are connected in parallel between the drain and source of the first switch (Q1) and the second switch (Q2), respectively, to absorb the turn-off peak voltage. The first freewheeling diode (DX1) and the second freewheeling diode (DX2) are respectively connected to the two ends of the primary winding of the high-frequency transformer and are used for freewheeling after the switching transistor is turned off. The full-bridge uncontrolled rectifier circuit is connected to the secondary side of the high-frequency transformer, and the output terminal is equipped with a filter circuit and anti-reverse diodes (DF3, DF4).

3. The high and low voltage ride-through device for a series dynamic compensation type frequency converter according to claim 1, characterized in that: The third switch (Q3) of the buck-boost circuit is normally on under normal operating conditions, and only operates in PWM mode under high voltage ride-through mode to achieve bus voltage step-down regulation.

4. The high and low voltage ride-through device for a series dynamic compensation type frequency converter according to claim 1, characterized in that: The differential voltage sampling circuit includes: The first-stage voltage divider circuit is used to convert the 0-800V DC bus voltage into a 0-4V first analog signal (ADC_U1). The voltage reference circuit outputs a second analog signal (ADC_U2) representing the rated bus voltage, where 2.5V corresponds to a target voltage of 500V; The differential detection circuit calculates the difference between the first analog signal and the second analog signal and outputs a third analog signal (ADC_U3). The third analog signal is directly input to the hybrid control unit for PID calculation.

5. The high and low voltage ride-through device for a series dynamic compensation type frequency converter according to claim 4, characterized in that: The start-up threshold of the hybrid control unit is 0.25V, corresponding to a bus voltage deviation of 50V. When the amplitude of the third analog signal (ADC_U3) exceeds the start-up threshold, the hybrid control unit immediately starts PWM output and adjusts the PID response speed according to the amplitude ratio of the third analog signal.

6. The high and low voltage ride-through device for a series dynamic compensation type frequency converter according to claim 1, characterized in that: The energy storage unit is connected to the input side of the dual-excited converter, supports AC and DC dual power input, and does not need to share the same AC bus power supply with the frequency converter.

7. The high and low voltage ride-through device for a series dynamic compensation type frequency converter according to claim 1, characterized in that: The compensation voltage is dynamically and automatically adjusted within the range of 0-300V based on the depth of voltage drop or rise in the mains voltage.

8. The high and low voltage ride-through device for a series dynamic compensation type frequency converter according to claim 1, characterized in that: The high and low voltage ride-through control method includes the following steps: The differential voltage sampling circuit detects the voltage difference between the actual DC bus voltage and the reference voltage of the frequency converter in real time and outputs an analog signal. When the voltage difference exceeds a preset start-up threshold, the hybrid control unit starts PWM modulation and generates a control signal based on the hardware voltage difference detection result and the software PID algorithm. The operating mode is selected according to the bus voltage status: if the bus voltage is lower than the rated range, the dual-excited converter is controlled to output a compensation voltage for series boost compensation; if the bus voltage is higher than the rated range, the BUCK step-down circuit is controlled to perform step-down regulation. When the voltage difference falls back to the normal range, the PWM output is immediately turned off and the device returns to standby mode.

9. The high and low voltage ride-through control method for a series dynamic compensation frequency converter according to claim 8, characterized in that: During the low voltage ride-through process, the first switch (Q1) and the second switch (Q2) of the dual-excited converter are turned on complementaryly at a frequency of 60KHz. The amplitude of the output compensation voltage is dynamically adjusted in real time according to the voltage drop depth to maintain the bus voltage stable within the range of 500V±30V.

10. The high and low voltage ride-through control method for a series dynamic compensation frequency converter according to claim 8, characterized in that: During high voltage ride-through, the third switch (Q3) operates in PWM mode to reduce the bus voltage from a sudden rise of over 700V to within the range of 500V±30V. At the same time, the dual-excited converter remains in standby mode, and the two achieve bidirectional coordinated control.

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