Frequency converter with variable frequency and constant current output

Abstract

The invention relates to the technical field of current output, and discloses a variable-frequency constant-current output frequency converter, which comprises an input module for suppressing surge; the rectification module is connected with the direct current filtering energy storage module; the inverter module is connected with the direct-current filtering energy storage module, and the current detection module is used for sampling output current in real time by using a closed-loop Hall sensor and providing a redundant channel through a precise sampling resistor; and the control module is internally provided with an anti-saturation unit, and when PID output reaches an amplitude limiting value, integral accumulation is limited. According to the method, an anti-saturation unit and a frequency current decoupling strategy are embedded in software, when the impedance of an electroplating and electrolytic bath changes instantaneously, overshoot of PID is immediately reduced, integral saturation is restrained, it is guaranteed that the current amplitude is constant all the time in the frequency switching or load step process, and the defects that PID simulation is fast in response, poor in interference resistance and large in process fluctuation are fundamentally overcome.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of current output, in particular to a frequency converter with variable frequency constant current output. BACKGROUND

[0002] With the rapid development of power electronics technology, frequency converters have been widely used in motor speed regulation, energy-saving control, industrial heating, electroplating, electrolysis, welding and battery formation and detection, etc. The traditional frequency converter usually adopts a "frequency-voltage" coordinated control strategy to achieve the regulation of motor speed or output power by changing the output frequency and voltage amplitude.

[0003] According to the search, the patent with the Chinese patent number CN107482925B discloses a variable frequency constant current source output circuit, relating to the technical field of power electronics. The variable frequency constant current source output circuit comprises a rectification filter unit, a photocoupling isolation inverter unit, an output filter unit, a current feedback regulation unit and an inverter control unit connected in sequence, and the inverter control unit is connected with the photocoupling isolation inverter unit. The present application only adopts an analog signal output circuit, which reduces the requirement for the working speed of the control chip. At the same time, for the current feedback regulation unit, a series of processes such as digital sampling, analog-digital conversion and digital PID logical operation are not needed, but an analog PID circuit is directly used for constant current control. The present application simplifies the structure of the hardware circuit, especially the air-core inductor coil in the output filter unit, effectively reducing the manufacturing cost and the size of the device.

[0004] According to the search, the patent with the Chinese patent number CN104485197A discloses a frequency-adjustable constant magnetic field demagnetizer, which is composed of an alternating current power supply, a circuit breaker protector, a transformer, a rectifier bridge, a switching element, a demagnetizing coil, a control transformer, a control power supply, a compensation system, a CPU board, a feedback module, a protection system and a sensor. Two IGBT modules are used as switching elements, and the CPU board provides two high and low level power supplies for the two switching elements, which are alternately turned on. The switching element is turned on in turn and the frequency can be adjusted. The present application can replace the traditional demagnetizer on the market, has strong applicability, and can adjust the magnetic field size of the demagnetizing coil according to different materials to meet the needs of the scene.

[0005] In the above-mentioned patent, although the analog PID is used to realize constant current control, the response is fast, but the adaptability to load sudden change, such as resistance sudden change in the process of electroplating and electrolysis, is insufficient, which leads to instantaneous fluctuation of current and affects the process stability. Although the demagnetizer realizes constant magnetic field through closed-loop control, it does not explicitly mention the dynamic response ability to load impedance sudden change. Based on this, the present application designs a frequency converter with variable frequency constant current output to solve the above-mentioned problems. SUMMARY

[0006] The purpose of this invention is to provide a frequency converter with variable frequency constant current output, which solves the problem of lack of dynamic response capability in the prior art.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A frequency converter with variable frequency and constant current output, comprising: The input module is compatible with AC220V and AC380V, and integrates an EMI filter and a 25kA gas discharge tube for surge suppression. The rectifier module, connected to the input module, uses four 1200V / 50A fast recovery diodes to form a full-bridge rectifier, with each diode connected in parallel to an RC snubber network of R=10Ω and C=0.1µF to reduce turn-off spikes; A DC filter energy storage module is connected to the rectifier module. The total capacity of the electrolytic capacitor is configured to be ≥2µF / W, and a 2.2µF / 1200V film capacitor and a common mode inductor ≥5mH are connected in parallel. The inverter module is connected to the DC filter energy storage module, and adopts a three-phase full-bridge 1200V / 100AIGBT with a switching frequency of 20kHz to achieve an output of 0.1Hz-400Hz. The current detection module uses a closed-loop Hall sensor to sample the output current I in real time. a The range is 0-150A, the linearity is ≤0.5%, and redundant channels are provided through a 0.1Ω precision sampling resistor; The control module, based on a 32-bit ARM Cortex-M7 MCU with a main frequency of 300MHz and a sampling period of 100µs, executes incremental PID control. ; Where K_p=0.8, Ki=0.05, K_d=0.01, and ΔD(k) is the PID output increment of the kth sampling; where ΔI=I_ref-I a， I_ref is the reference current, I a This is the actual sampling current; ΔI(k) is the difference between the actual current and the target current in the kth sampling, and ΔI(k-1) is the difference between the actual current and the target current in the (k-1)th sampling, ensuring that the current recovery time is ≤20ms when the load jumps by 50%. The frequency adjustment module sets the output frequency via RS-485 digital commands, with a resolution of 0.1Hz and a base frequency of 5-200Hz. The control module has a built-in anti-saturation unit that limits integral accumulation when the PID output reaches the limit value, and adopts a frequency-current decoupling strategy to maintain a constant current amplitude when the frequency switches.

[0008] Preferably, the rectifier module can be replaced with a half-bridge rectifier circuit, using two 1600V / 30AIGBTs, and soft recovery diodes are connected in reverse parallel to reduce reverse recovery losses.

[0009] Preferably, the DC filter energy storage module further includes: Surge absorber, varistor 20D471, response ≤25ns; Pre-charge circuit: A 10Ω / 50W resistor is connected in parallel with the relay to limit the power-on inrush current to ≤5A.

[0010] As shown in the above technical solution, the AC mains power first passes through the input module, which is compatible with both 220V and 380V voltage levels. The integrated EMI filter and 25kA gas discharge tube jointly suppress surges caused by lightning strikes or switching operations. Subsequently, a full-bridge rectifier circuit composed of four 1200V / 50A fast recovery diodes converts the AC power into pulsating DC; the parallel RC snubber network of each diode effectively reduces turn-off spikes. The pulsating DC then enters the DC filtering and energy storage stage, where electrolytic capacitors, film capacitors, and common-mode inductors form a π-type low-pass filter, resulting in a stable DC bus with output ripple below 1%. The pre-charge circuit limits the power-on inrush current to within 5A.

[0011] The stabilized DC power is then fed into a three-phase full-bridge 1200V / 100AIGBT inverter with a switching frequency of 20kHz, capable of outputting AC voltage at any set frequency within the range of 0.1Hz-400Hz. The inverter supports an adjustable V / f curve slope of 0.1-10 and employs an adaptive carrier ratio of 15-100 to ensure a balance between high torque at low frequencies and low noise at high frequencies.

[0012] The output current is detected in real time by a closed-loop Hall sensor. A 32-bit ARM Cortex-M7 MCU executes incremental PID control with a 100µs cycle. Through an anti-saturation unit and a frequency-current decoupling strategy, the current can be restored to within ±1% of the set value within 20ms under a 50% load step condition. Users can set the output frequency with a resolution of 0.1Hz via RS-485 commands, or select 8 preset frequencies via external terminal combinations to achieve flexible field control.

[0013] Preferably, the inverter module supports an adjustable V / f curve slope of 0.1-10; and an adaptive carrier ratio of 15-100, which automatically adjusts with the output frequency.

[0014] Preferably, the current detection module comprises: Temperature compensation ensures a drift of ≤0.1% / ℃ within the range of -40℃ to +85℃; Digital filtering has a bandwidth ≥ 100kHz; Open circuit / short circuit fault diagnosis involves triggering protection within 1ms after an abnormality is detected.

[0015] Preferably, the control module further includes: A phase-locked loop synchronization unit is used to synchronize the output frequency with an external reference during grid-connected or parallel operation. The soft-start unit has a startup current that increases at a rate of 10%I_ref / 100ms. The dead time t_d is fixed at 1.5µs and supports real-time compensation.

[0016] Preferably, the frequency adjustment module supports: Multi-speed preset, 8 frequency bands can be selected via external terminal combination; Modbus-RTU remotely reads and writes frequency, current, and fault information; The carrier frequency can be switched between 20kHz and 50kHz.

[0017] The fan control unit automatically adjusts the duty cycle based on the heatsink temperature T. Maximum 100%; D_fan is the fan PWM duty cycle, and T is the heatsink temperature; LED status indicators: green for operation, red for fault, and yellow for communication.

[0018] Preferably, it also includes a fault diagnosis and protection module for detecting the following conditions: Overcurrent, threshold 1.5I_ref, action time ≤5ms; Overvoltage, threshold 1.2U_dc_nom; Undervoltage, threshold 0.8U_dc_nom; Overheating, radiator temperature 85°C; Output phase loss, detection period 20ms; Upon detecting any fault, immediately disable the PWM and upload the fault code to the host computer.

[0019] Preferably, it also includes a data recording unit, which cyclically stores the most recent 1000 operation records, each record containing a timestamp, I... a Fault codes, sampling interval adjustable from 1 to 60 seconds, EEPROM retention for ≥10 years after power failure, and support for USB offline export.

[0020] As can be seen from the above technical solutions, the current detection module adds full-temperature compensation, a digital filtering bandwidth of over 100kHz, and open / short circuit fault diagnosis functions, and can trigger hardware protection within 1ms, forming a "double insurance" with the software PID loop. The control module adds a phase-locked loop synchronization unit, enabling the equipment to maintain phase and frequency consistency with the external reference when operating in grid-connected or parallel mode; the soft-start unit gradually increases the starting current with a gradual ramp rate of 10%I_ref / 100ms to avoid impacting the power grid and load; a fixed 1.5µs dead time and support for real-time compensation prevent bridge arm shoot-through.

[0021] The heatsink temperature is monitored in real time by the NTC. The fan PWM duty cycle is automatically adjusted according to the formula Duty=min{(T-45) / 40,100%}, with a maximum of 100%, which saves energy and reduces noise. The system continuously monitors for faults such as overcurrent, overvoltage, undervoltage, overheating, and output phase loss. Once triggered, the PWM is immediately blocked and the fault code is uploaded to the host computer via RS-485.

[0022] The data recording unit cyclically stores the most recent 1000 operation records. Each record includes a timestamp, current value, frequency value, and fault code. The sampling interval is adjustable from 1 to 60 seconds. The EEPROM retains data for more than 10 years after power failure and supports offline export via USB, providing complete data support for process quality traceability and equipment health management.

[0023] As can be seen from the above technical solutions, the current detection module adds full-temperature compensation, a digital filtering bandwidth of over 100kHz, and open / short circuit fault diagnosis functions, and can trigger hardware protection within 1ms, forming a "double insurance" with the software PID loop. The control module adds a phase-locked loop synchronization unit, enabling the equipment to maintain phase and frequency consistency with the external reference when operating in grid-connected or parallel mode; the soft-start unit gradually increases the starting current with a gradual ramp rate of 10%I_ref / 100ms to avoid impacting the power grid and load; a fixed 1.5µs dead time and support for real-time compensation prevent bridge arm shoot-through.

[0024] The heatsink temperature is monitored in real time by NTC, and the fan PWM duty cycle is automatically adjusted according to the formula Duty=min{(T-45) / 40,100%}, with a maximum of 100%, which is both energy-saving and noise-reducing.

[0025] The system continuously monitors for faults such as overcurrent, overvoltage, undervoltage, overheating, and output phase loss. Once triggered, it immediately blocks the PWM and uploads the fault code to the host computer via RS-485. The data logging unit cyclically stores the most recent 1000 operation records. Each record includes a timestamp, current value, frequency value, and fault code. The sampling interval is configurable from 1 to 60 seconds. The EEPROM retains data for over 10 years after power failure and supports offline export via USB, providing complete data support for process quality traceability and equipment health management.

[0026] Compared with the prior art, the beneficial effects achieved by the present invention are: 1. This invention embeds an anti-saturation unit and a frequency-current decoupling strategy in the software. When the impedance of the electroplating or electrolytic cell changes instantaneously, the PID immediately reduces overshoot and suppresses integral saturation, ensuring that the current amplitude remains constant during frequency switching or load step transitions. This fundamentally solves the defects of analog PID, which has fast response but poor anti-interference and large process fluctuations.

[0027] 2. This invention introduces a closed-loop Hall sensor in the current detection stage, with dual-channel redundancy for precision sampling resistors. Combined with full-temperature-range temperature compensation, digital filtering, and fault diagnosis hardware protection, a millisecond-level closed loop is formed. Regardless of how the load impedance changes abruptly, the system can capture the current change in real time and immediately adjust the PWM duty cycle to achieve true constant current in the magnetic field, thus making up for the shortcomings of traditional magnetic field closed loops in responding to impedance step changes.

[0028] 3. In this invention, each diode of the rectifier bridge is connected in parallel with an absorption network, and a half-bridge IGBT + soft recovery diode topology can be selected. This not only suppresses turn-off spikes but also reduces reverse recovery losses, reduces component stress, and improves system reliability and lifespan. The input end integrates a gas discharge tube, EMI filter, pre-charge circuit, and varistor. Multiple surge absorption and current limiting designs ensure power-on impact protection and protect the front-end power grid and bus capacitors. Attached Figure Description

[0029] Figure 1 This is a system architecture diagram of the present invention; Figure 2 This is a flowchart of the fault protection logic of the present invention; Figure 3 This is a block diagram of the heat dissipation control system of the present invention; Figure 4 This is a schematic diagram of the topology of the present invention; Figure 5 This is the control flowchart of the present invention. Detailed Implementation

[0030] 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.

[0031] Example 1: Please refer to Figures 1-5 In this embodiment of the invention, a frequency converter with variable frequency constant current output is characterized by comprising: The input module is compatible with AC220V and AC380V, and integrates an EMI filter and a 25kA gas discharge tube for surge suppression. The rectifier module, connected to the input module, uses four 1200V / 50A fast recovery diodes to form a full-bridge rectifier, with each diode connected in parallel to an RC snubber network of R=10Ω and C=0.1µF to reduce turn-off spikes; The DC filter energy storage module is connected to the rectifier module. The total capacity of the electrolytic capacitor is configured to be ≥2µF / W, and a 2.2µF / 1200V film capacitor and a common mode inductor ≥5mH are connected in parallel. The inverter module, connected to the DC filter energy storage module, adopts a three-phase full-bridge 1200V / 100AIGBT, with a switching frequency of 20kHz, to achieve an output of 0.1Hz-400Hz; The current detection module uses a closed-loop Hall sensor to sample the output current I in real time. a The range is 0-150A, the linearity is ≤0.5%, and redundant channels are provided through a 0.1Ω precision sampling resistor; The control module, based on a 32-bit ARM Cortex-M7 MCU with a main frequency of 300MHz and a sampling period of 100µs, executes incremental PID control. ; Where K_p=0.8, Ki=0.05, K_d=0.01, and ΔD(k) is the PID output increment of the kth sampling; where ΔI=I_ref-I a， I_ref is the reference current, I a This is the actual sampling current; ΔI(k) is the difference between the actual current and the target current in the kth sampling, and ΔI(k-1) is the difference between the actual current and the target current in the (k-1)th sampling, ensuring that the current recovery time is ≤20ms when the load jumps by 50%. The frequency adjustment module sets the output frequency via RS-485 digital commands, with a resolution of 0.1Hz and a base frequency of 5-200Hz. The control module has a built-in anti-saturation unit that limits integral accumulation when the PID output reaches the limit value, and adopts a frequency-current decoupling strategy to maintain a constant current amplitude when the frequency switches.

[0032] The rectifier module can be replaced with a half-bridge rectifier circuit, using two 1600V / 30AIGBTs, and soft recovery diodes are connected in reverse parallel to reduce reverse recovery losses.

[0033] The DC filter energy storage module also includes: Surge absorber, varistor 20D471, response ≤25ns; Pre-charge circuit: A 10Ω / 50W resistor is connected in parallel with the relay to limit the power-on inrush current to ≤5A.

[0034] The inverter module supports an adjustable V / f curve slope of 0.1-10; and an adaptive carrier ratio of 15-100, which automatically adjusts with the output frequency.

[0035] The working principle of this invention is as follows: AC mains power (AC220V or AC380V) is first connected to the input terminal of the frequency converter. The input stage integrates an EMI filter and a gas discharge tube with a current capacity of 25kA, which can effectively suppress surge spikes caused by lightning strikes or switching operations. Subsequently, four 1200V / 50A fast recovery diodes form a full-bridge rectifier circuit to convert AC power into pulsating DC power; each diode is connected in parallel with a 10Ω / 0.1µF RC snubber network to absorb voltage spikes at the moment of device turn-off, reducing reverse recovery stress.

[0036] Pulsating DC enters the DC filtering and energy storage stage: Electrolytic capacitors are configured with a capacity of ≥2µF / W, and then a 2.2µF / 1200V film capacitor and a ≥5mH common-mode inductor are connected in parallel to form a π-type low-pass filter, resulting in a stable DC bus with an output ripple of <1%. To avoid the large current surge at power-on, the system uses a pre-charge circuit with a 10Ω / 50W resistor connected in parallel with a relay to limit the surge current to within 5A; once the bus voltage reaches the set threshold, the relay engages, bypassing the resistor to complete the soft power-on.

[0037] A stable DC bus feeds into a three-phase full-bridge 1200V / 100AIGBT inverter with a switching frequency of 20kHz. It can output AC voltage Ua at any set frequency within the range of 0.1Hz-400Hz. The inverter supports an adjustable V / f curve slope of 0.1-10 and employs an adaptive carrier ratio of 15-100, automatically adjusting according to the output frequency. This allows it to provide high torque in the low-frequency range while maintaining low-noise operation in the high-frequency range.

[0038] Output current I a Real-time detection is achieved using a closed-loop Hall sensor (range 0-150A, linearity ≤0.5%), with hardware redundancy provided by a 0.1Ω precision sampling resistor. A 32-bit ARM Cortex-M7 MCU samples at 100µs intervals, and the deviation ΔI = I_ref - I is calculated. a Execute incremental PID: Δu(k)=0.8·ΔI+0.05·ΣΔI+0.01·dΔI / dt; The control module incorporates an anti-saturation unit that freezes the integral when the PID output reaches its limit. Simultaneously, a frequency-current decoupling strategy is employed to maintain a constant current amplitude during frequency switching. The system can recover current within 20ms under a 50% load step condition, with a steady-state error ≤±1%, ensuring the output current I...a It remains stable within the set value If ±1%.

[0039] Users can set the target frequency via RS-485 digital commands (resolution 0.1Hz, base frequency 5-200Hz) or by combining 8 external terminals. The Modbus-RTU protocol supports remote reading and writing of frequency, current, and fault information, enabling centralized monitoring by a host computer.

[0040] Example 2: Please refer to Figures 1-5 In this embodiment of the invention, the current detection module includes: Temperature compensation ensures a drift of ≤0.1% / ℃ within the range of -40℃ to +85℃; Digital filtering has a bandwidth ≥ 100kHz; Open circuit / short circuit fault diagnosis involves triggering protection within 1ms after an abnormality is detected.

[0041] The control module also includes: A phase-locked loop synchronization unit is used to synchronize the output frequency with an external reference during grid-connected or parallel operation. The soft-start unit has a startup current that increases at a rate of 10%I_ref / 100ms. The dead time t_d is fixed at 1.5µs and supports real-time compensation.

[0042] The frequency adjustment module supports: Multi-speed preset, 8 frequency bands can be selected via external terminal combination; Modbus-RTU remotely reads and writes frequency, current, and fault information; The carrier frequency can be switched between 20kHz and 50kHz.

[0043] The fan control unit automatically adjusts the duty cycle based on the heatsink temperature T. Maximum 100%; D_fan is the fan PWM duty cycle, and T is the heatsink temperature; LED status indicators: green for operation, red for fault, and yellow for communication.

[0044] It also includes a fault diagnosis and protection module, used to detect the following conditions: Overcurrent, threshold 1.5I_ref, action time ≤5ms; Overvoltage, threshold 1.2U_dc_nom; Undervoltage, threshold 0.8U_dc_nom; Overheating, radiator temperature 85°C; Output phase loss, detection period 20ms; Upon detecting any fault, immediately disable the PWM and upload the fault code to the host computer.

[0045] It also includes a data recording unit that cyclically stores the most recent 1000 running records. Each record contains a timestamp, Ia, f, and fault code. The sampling interval is configurable from 1 to 60 seconds. The EEPROM retains data for ≥10 years after power failure and supports offline export via USB.

[0046] The working principle of this invention is as follows: the current detection module has a drift of ≤0.1% / ℃ in the entire temperature range of -40℃ to +85℃, and a digital filter bandwidth of ≥100kHz to ensure sampling accuracy; when an open circuit or short circuit abnormality is detected in the Hall sensor, the hardware protection circuit blocks the PWM within 1ms, forming a "double insurance" with the software PID loop of Embodiment 1.

[0047] The phase-locked loop synchronization unit tracks the phase and frequency of the external power grid or parallel generating units in real time, enabling shock-free grid connection or parallel capacity expansion; the soft-start unit gradually increases the starting current at a slope of 10%I_ref / 100ms to avoid surge impact on the power grid and load. The dead time is fixed at 1.5µs and supports real-time compensation to prevent bridge arm shoot-through.

[0048] The heatsink temperature T is monitored in real time by the NTC, and the fan PWM duty cycle is calculated using the formula: Duty = min{(T-45) / 40, 100%}; Automatic adjustment, up to 100%, saving energy and reducing noise. The panel LED displays the system status intuitively in three colors: green (operation), red (fault), and yellow (communication), facilitating on-site operation and maintenance.

[0049] The system continuously monitors for faults such as overcurrent (1.5I_ref, ≤5ms), overvoltage (1.2U_dc_nom), undervoltage (0.8U_dc_nom), overheating (heatsink 85℃), and output phase loss (20ms cycle). Once triggered, it immediately blocks the PWM and uploads the fault code to the host computer via RS-485. The data logging unit cyclically stores the most recent 1000 operation records (timestamp, I...). a (f, fault codes), sampling interval can be set from 1 to 60 seconds, EEPROM retains data for ≥10 years after power failure, and supports USB offline export, providing complete data support for process quality traceability and equipment health management.

[0050] Example 3: Please refer to Figures 1-5 This embodiment discloses a specific implementation of a complete operating process of a variable frequency constant current output inverter. All parameters are measured values ​​and can be directly used for industrial prototype replication.

[0051] The AC mains voltage is set to AC380V, 50Hz. The EMI filter has a common-mode insertion loss ≥60dB@150kHz and a differential-mode insertion loss ≥55dB@150kHz. The gas discharge tube has a DC breakdown voltage of 470V, a current carrying capacity of 25kA, and a recovery time of 8 / 20µs. The rectifier bridge consists of four 1200V / 50A fast recovery diodes with a reverse recovery time trr=35ns. Each diode is connected in parallel with a 10Ω, 0.1µC FRC absorption network, and the measured turn-off peak voltage drops from 520V to 380V.

[0052] The total capacitance of the electrolytic capacitors is 5400µF, corresponding to a capacitance of 1.8µF / W for a 3kW load. Two 2.2µF / 1200V film capacitors are connected in parallel. The common-mode inductor is 5mH. The rated DC bus voltage is 540V, and the peak-to-peak ripple voltage is 2.8V. The pre-charge resistor is 10Ω / 50W. The relay pull-in time is 150ms, and the peak inrush current is 4.2A.

[0053] The three-phase full-bridge IGBT module is model 1200V / 100A, with a switching frequency of 20kHz. In this embodiment, the output frequency is set to 60Hz, and the V / f curve slope is set to 2.0. The adaptive carrier ratio is adjusted to 60, and the fundamental effective value of the output voltage is 230V.

[0054] The Hall sensor has a range of 0-150A, a sensitivity of 40mV / A, and a linearity of 0.4%. The sampling resistor is 0.1Ω, and the temperature drift is 25ppm / ℃. The MCU is an STM32H743 with a main frequency of 300MHz and a PID sampling period of 100µs. The set current I_ref = 50A, proportional coefficient Kp = 0.8, integral coefficient Ki = 0.05, and derivative coefficient Kd = 0.01. When the load suddenly increases from 25A to 75A, the current recovers to 50A ± 1% in 18ms, with an overshoot of 0.7A.

[0055] The RS-485 baud rate is 115200bps. Writing 0x0258 to register 0x0001 sets the output frequency to 60.0Hz. It uses Modbus CRC16 verification and has a response time of 3.2ms.

[0056] The Hall sensor has a temperature drift coefficient of -0.08% / ℃ and a digital filter bandwidth of 120kHz. The hardware comparator threshold is ±2.5A, and PWM is blocked 1ms after triggering. The heatsink temperature detection NTC is 10kΩ, the fan PWM duty cycle is 100% at 85°C, and the measured fan speed is 3200rpm.

[0057] The EEPROM has a capacity of 32kB and records 1000 entries cyclically. Recording format: 4-byte timestamp, 2-byte current value, 2-byte frequency value, and 1-byte fault code. Sampling interval is 5 seconds, and power-off retention is >10 years. USB export rate is 12Mbit / s, and it takes 1.4 seconds to export 1000 entries.

[0058] With an input of AC380V, an output of 60Hz and 50A, and a load power factor of 0.85, the measured overall efficiency is 96.1%, the input power is 15.62kW, the output power is 15.01kW, and the loss is 610W, which meets the requirements for high-efficiency industrial applications.

[0059] Working Principle: The input module is compatible with both AC220V and AC380V dual voltage inputs, and features a built-in EMI filter and a 25kA gas discharge tube to effectively suppress grid surge interference. Electrical energy is converted to DC by the rectifier module. The standard solution uses four 1200V / 50A fast recovery diodes to form a full-bridge rectifier, each connected in parallel with an RC snubber network to reduce turn-off spikes. An alternative solution uses two 1600V / 30A IGBTs to construct a half-bridge rectifier, with a soft recovery diode connected in reverse parallel to reduce losses. The DC filter energy storage module is configured with electrolytic capacitors of specific capacity, connected in parallel with film capacitors and a common-mode inductor to form a stable low-ripple bus. The surge absorber and pre-charge circuit work together to limit the power-on inrush current within a safe threshold.

[0060] DC bus energy is fed into a three-phase full-bridge IGBT inverter module, achieving a wide-range AC output from 0.1Hz to 400Hz through high-frequency switching technology. The current sensing module employs a dual-channel redundant design using a closed-loop Hall sensor and a precision sampling resistor to monitor the output current in real time, ensuring high-precision feedback. The control module, based on a high-performance processor, executes an incremental PID control algorithm. A built-in anti-saturation unit freezes integral accumulation during amplitude limiting, and combined with a frequency-current decoupling strategy, maintains a constant current amplitude during frequency switching. The system quickly recovers stable current under load step disturbances.

[0061] The frequency adjustment module sets the output frequency via digital commands, supports multi-speed presets and remote communication, and achieves adjustable output from a base frequency of 5Hz to 200Hz. The fault diagnosis module monitors abnormal states such as overcurrent, overvoltage, undervoltage, overheating, and output phase loss in real time, triggering a fast protection mechanism to block the PWM signal. The fan system automatically adjusts its speed based on the heatsink temperature, and LED status indicators provide intuitive operational feedback.

[0062] The data logging unit cyclically stores system operating parameters, supporting long-term power-down retention and offline export functions for easy process traceability. The phase-locked loop (PLL) unit ensures frequency synchronization during grid connection or multi-machine parallel operation, and the soft-start function gradually increases current to avoid surge impact. The dead time is fixed and compensated in real time to prevent bridge arm shoot-through risk. Through adjustable V / f curve slope and adaptive carrier ratio technology, the system optimizes output waveform quality and electromagnetic compatibility across a wide frequency range.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A frequency converter with variable frequency and constant current output, characterized in that, include: The input module is compatible with both AC and AC dual voltage inputs and integrates an EMI filter and a gas discharge tube for surge suppression. The rectifier module, connected to the input module, uses multiple fast recovery diodes to form a full-bridge rectifier, with each diode connected in parallel with an RC snubber network to reduce turn-off spikes; A DC filter energy storage module is connected to the rectifier module. Electrolytic capacitors, film capacitors and common-mode inductors together form a T-type low-pass filter for outputting a low-ripple DC bus. The inverter module, connected to the DC filter energy storage module, uses a three-phase full-bridge IGBT to output frequency-adjustable AC voltage over a wide range. The current detection module uses a closed-loop Hall sensor to sample the output current I in real time. a It is used to sample the output current in real time and provide redundant detection channels; The control module is used to perform closed-loop constant current control based on the sampled current and to execute incremental PID control. ； Where K_p=0.8, Ki=0.05, K_d=0.01, and ΔD(k) is the PID output increment of the kth sampling; where ΔI=I_ref-I a， I_ref is the reference current, I a This is the actual sampled current; ΔI(k) is the difference between the actual current and the target current in the kth sampling, and ΔI(k-1) is the difference between the actual current and the target current in the (k-1)th sampling. The frequency adjustment module is used to set and adjust the output frequency; The control module has a built-in anti-saturation unit that limits integral accumulation when the PID output reaches the limit value, and adopts a frequency-current decoupling strategy to maintain a constant current amplitude when the frequency switches.

2. The frequency converter with variable frequency constant current output according to claim 1, characterized in that: The rectifier module can be replaced with a half-bridge rectifier circuit, and soft recovery diodes can be connected in reverse parallel to reduce reverse recovery losses.

3. The frequency converter with variable frequency constant current output according to claim 1, characterized in that: The DC filter energy storage module also includes a surge absorber and a pre-charge circuit. The surge absorber is used to absorb bus surges, and the pre-charge circuit is used to limit the power-on inrush current.

4. The frequency converter with variable frequency constant current output according to claim 1, characterized in that: The inverter module supports continuously adjustable frequency to provide a perfect sine wave in the low-frequency band and maintain low noise in the high-frequency band; it has an adaptive carrier ratio adjustment function that automatically changes with the output frequency to balance harmonic suppression and switching losses; it has a built-in dead time real-time compensation circuit to eliminate output voltage distortion caused by the delay difference between the upper and lower bridge arms; and it is equipped with an output phase loss detection circuit to continuously monitor the integrity of the three phases and immediately trigger protection when a phase is lost.

5. A frequency converter with variable frequency constant current output according to claim 1, characterized in that: The current detection module adopts a dual-channel redundant design of closed-loop Hall sensor and precision sampling resistor, and has a temperature compensation function to maintain sampling accuracy across the entire temperature range; the current detection module has a built-in broadband digital filter to suppress high-frequency interference. It is equipped with an open circuit / short circuit fault diagnosis circuit. When an abnormality is detected, the hardware protection is triggered immediately and forms a double insurance with the software PID.

6. A frequency converter with variable frequency constant current output according to claim 1, characterized in that: The control module is equipped with a phase-locked loop synchronization unit, which is used to maintain phase and frequency consistency with an external reference when the machine is connected to the grid or in parallel with multiple machines. It is equipped with a soft starter unit, and the starting current gradually increases according to a set frequency to avoid impacting the power grid and load. It has a fixed and real-time compensated dead time to prevent bridge arm straight-through; It supports online parameter updates for remote debugging and maintenance.

7. A frequency converter with variable frequency constant current output according to claim 1, characterized in that: The frequency adjustment module supports multiple speed presets and can achieve rapid switching through external terminal combinations; Built-in Modbus-RTU communication interface for remote reading and writing of frequency, current and fault information; It supports multiple carrier frequency switching to balance electromagnetic compatibility and efficiency requirements; The fan control unit automatically adjusts the duty cycle based on the heatsink temperature T. Maximum 100%; D_fan is the fan PWM duty cycle, and T is the heatsink temperature; The LED status indicator unit visually displays the operating, fault, and communication status using different colors and flashing patterns.

8. A frequency converter with variable frequency constant current output according to claim 1, characterized in that: It also includes a fault diagnosis and protection module for continuous monitoring of overcurrent, overvoltage, undervoltage, overheating and output phase loss faults; The fault diagnosis and protection module has multi-level fault threshold settings, which can flexibly adjust the protection sensitivity according to the load characteristics; after detecting a fault, it immediately blocks the PWM and uploads the fault code to the host computer through the communication interface, and records the key operating parameters before and after the fault.

9. A frequency converter with variable frequency constant current output according to claim 1, characterized in that: It also includes a data recording unit that cyclically stores operation records. Each record contains a timestamp, current value, frequency value, and fault code. The sampling interval of the data recording unit is settable to meet the recording accuracy requirements of different operating conditions. The data recording unit also has a power-off retention function to ensure that data is not lost after long-term shutdown.

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