A variable frequency drive anti-surge device

Abstract

The utility model relates to a frequency converter anti -flicker device belongs to electrical field, and the purpose is when the grid voltage sag, reduce the delay for providing transient voltage of frequency converter. Including energy storage unit, prevent reverse diode and charger, and energy storage unit connects frequency converter DC bus through prevent reverse diode, and the positive pole of charger output end is connected the positive pole of energy storage unit respectively, and the main contact of contactor is connected in the charging loop between charger and energy storage unit in series, and the control end of contactor is connected with the detection module communication of grid voltage, still including transient detection unit, transient analysis unit and steady protection unit, and the control end of contactor is connected transient detection unit output, and transient analysis unit output connects the harmonic feedback interface of charger, and the main control system of frequency converter is connected steady protection unit output. The utility model can shorten voltage fault detection response time from traditional 10ms to 1ms or less, avoid the delay caused by single processor overload.

Description

Technical Field

[0001] This utility model relates to the field of electrical technology, specifically to an anti-voltage fluctuation device for frequency converters. Background Technology

[0002] In lithium carbonate production, numerous frequency converters are used in equipment such as pumps and fans. Modern frequency converters employ an AC-DC-AC structure. When the DC bus voltage of the frequency converter falls below a certain value, the internal protection mechanism is triggered, causing a fault alarm and equipment shutdown. Manual reset of the frequency converter is required before restarting. High-voltage external lines are susceptible to natural factors such as thunderstorms, line faults, and power outages from parallel users, all of which can cause voltage dips. These voltage dips are very short, typically milliseconds or less than 2 seconds. The reclosing time of the power supply bureau's distribution switch is 2 seconds. Once a voltage dip-flicker fault occurs, the DC bus voltage of the frequency converter falls below the alarm value, triggering a fault alarm and causing equipment shutdown. This interrupts continuous production, disrupts normal production order, and may even pose safety hazards.

[0003] The invention patent with announcement number CN116667518B specifically discloses a DC voltage sag mitigation circuit and its control method. The circuit includes: a circuit breaker, a capacitor charging circuit, a capacitor discharging circuit, and a fuse connected in series. The circuit breaker and fuse are respectively connected to the DC bus of the frequency converter. A supercapacitor is connected between the capacitor charging circuit and the capacitor discharging circuit. Under normal circumstances, the mains power first passes through the AC distribution system, then through the frequency converter to drive the load, and simultaneously charges the supercapacitor through the capacitor charging circuit. When the AC mains power input to the frequency converter experiences a voltage dip or outage, the supercapacitor discharges through the capacitor discharging circuit, and energy is input from the supercapacitor to the DC bus of the frequency converter to compensate for the voltage drop of the DC bus. This solution can provide temporary power to the frequency converter during mains voltage dips or outages. However, this solution suffers from problems such as decreased detection accuracy and excessively long voltage fault detection response time due to the use of only a single current detector during mains voltage dips or outages. Utility Model Content

[0004] This invention provides an anti-voltage fluctuation device for frequency converters, the purpose of which is to reduce the delay in providing temporary voltage to the frequency converter when the grid voltage drops.

[0005] The technical solution of this utility model to solve the above-mentioned technical problems is as follows:

[0006] An inverter anti-power fluctuation device includes an energy storage unit, an anti-reverse diode, and a charger. The positive terminal of the energy storage unit is connected to the positive terminal of the inverter's DC bus via the anti-reverse diode, and the negative terminal of the energy storage unit is connected to the negative terminal of the inverter's DC bus via the anti-reverse diode. The positive and negative terminals of the charger's output are respectively connected to the positive and negative terminals of the energy storage unit. The main contacts of a contactor are connected in series in the charging circuit between the charger and the energy storage unit. The control terminal of the contactor is communicatively connected to a grid voltage detection module.

[0007] It also includes a transient detection unit, a transient analysis unit, and a steady-state protection unit. The output of the transient detection unit is connected to the control terminal of the contactor, the output of the transient analysis unit is connected to the harmonic feedback interface of the charger, and the output of the steady-state protection unit is connected to the main control system of the frequency converter.

[0008] Furthermore, the energy storage unit is a supercapacitor module.

[0009] Furthermore, the reverse protection diode is a unidirectional power diode.

[0010] Furthermore, the charger is a constant voltage current limiting type charging circuit.

[0011] This utility model has the following beneficial effects:

[0012] This inverter's anti-voltage fluctuation device can quickly release electrical energy when the grid voltage drops, maintaining the stability of the inverter's DC bus voltage and preventing shutdown. Furthermore, the device limits the physical composition of the three-level unit "transient detection unit, transient analysis unit, and steady-state protection unit", reducing the voltage fault detection response time from the traditional 10ms to less than 1ms, avoiding delays caused by overload of a single processor. The anti-reverse diode prevents reverse current to ensure effective energy storage supply, and in conjunction with the contactor, automatically isolates the charging circuit, improving the system's anti-voltage fluctuation capability and reliability. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the anti-voltage fluctuation device for frequency converters of this utility model;

[0014] Figure 2 This is a schematic diagram of a voltage fault detection principle.

[0015] Figures 1 to 2 The reference numerals in the attached figures represent: energy storage unit 1, anti-reverse diode 2, charger 3, frequency converter 4, contactor 5, grid voltage 6, detection module 7, DC bus capacitor 8, transient detection unit 11, transient analysis unit 12, and steady-state protection unit 13. Detailed Implementation

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0017] In this utility model, the terms "longitudinal," "lateral," "vertical," "upper," "lower," "front," "rear," "left," "right," "top," and "bottom," etc., indicate the orientation or positional relationship based on the appendix. Figure 1 The orientation or positional relationship shown is for the purpose of describing the present invention only, and is not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0018] Please refer to Figure 1-2 This utility model relates to a specific implementation of an anti-power fluctuation device for frequency converters. The structure, connection relationship and working principle of the device will be described in detail below.

[0019] The anti-power fluctuation device includes an energy storage unit 1, an anti-reverse diode 2, and a charger 3. The positive terminal of the energy storage unit 1 is connected to the positive terminal of the DC bus of the inverter 4 through the anti-reverse diode 2, and the negative terminal of the energy storage unit 1 is connected to the negative terminal of the DC bus of the inverter 4 through the anti-reverse diode 2. The positive and negative terminals of the charger 3 are respectively connected to the positive and negative terminals of the energy storage unit 1. The main contacts of the contactor 5 are connected in series in the charging circuit between the charger 3 and the energy storage unit 1. The control terminal of the contactor 5 is communicatively connected to the detection module 7 of the grid voltage 6. It also includes a transient detection unit 11, a transient analysis unit 12, and a steady-state protection unit 13. The output terminal of the transient detection unit 11 is connected to the control terminal of the contactor 5, the output terminal of the transient analysis unit 12 is connected to the harmonic feedback interface of the charger 3, and the output terminal of the steady-state protection unit 13 is connected to the main control system of the inverter 4. The positive terminal of the energy storage unit 1 is connected to the positive terminal of the DC bus of the inverter 4 through the anti-reverse diode 2, and the negative terminal is also connected to the negative terminal of the DC bus of the inverter 4 through the anti-reverse diode 2. This connection method ensures that energy storage unit 1 can promptly release stored energy to the DC bus when the grid voltage 6 experiences a voltage dip. Anti-reverse diode 2 is a protection unit primarily designed to prevent backflow of power from inverter 4 into energy storage unit 1, which could affect the normal operation of inverter 4. Charger 3 continuously replenishes energy to energy storage unit 1 when the grid is supplying power normally. The capacity of energy storage unit 1 needs to be precisely calculated based on the load power of inverter 4 and the target backup time. The specific capacity selection should meet the requirement of maintaining inverter 4 at full load operation for at least 3 seconds. For example, for inverter 4 with a rated power of 55kW, the capacity of energy storage unit 1 is typically configured in the range of 30-50 farads. Through three-level processing by transient detection unit 11, transient analysis unit 12, and steady-state protection unit 13, delays caused by overload of a single processor are avoided, reducing the voltage fault detection response time from the traditional 10ms to less than 1ms. The transient detection unit 11 consists of a high-speed voltage comparator and a transient signal extraction circuit, while the transient analysis unit 12 consists of a DSP chip (with a built-in FFT harmonic analysis algorithm) and an AD sampling circuit. The steady-state protection unit 13 consists of a PLC logic controller and a voltage threshold memory.

[0020] The control terminal of contactor 5 is connected to the detection module 7 for mains voltage 6, which monitors the status of mains voltage 6 in real time. When mains voltage 6 is within the normal range (e.g., 380V ± 10%), the detection module 7 outputs a control signal to energize the coil of contactor 5, closing the main contacts to form a charging path. When a voltage dip (e.g., voltage below 85% of the rated value) or interruption is detected in mains voltage 6, the mains voltage 6 detection module immediately cuts off the power supply to the coil of contactor 5, causing the main contacts to open rapidly. The operating time of contactor 5 should be controlled within 10ms to ensure timely isolation of the charging circuit in the event of a mains fault. A model with a mechanical holding mechanism is selected for contactor 5 to prevent malfunctions when mains voltage 6 fluctuates.

[0021] Energy storage unit 1 is a supercapacitor module. To maximize energy storage and ensure stable and reliable performance, energy storage unit 1 is preferably a supercapacitor module. The supercapacitor module is composed of multiple supercapacitor cells connected in series and parallel, with voltage balancing circuits between cells to ensure voltage consistency. The supercapacitor module casing is made of insulating and flame-retardant material, and an internal temperature sensor monitors the operating temperature. The positive and negative terminals of the supercapacitor module feature a reverse insertion protection design and are clearly marked with polarity indicators. In practical applications, a fast-acting fuse can be connected in series between the supercapacitor module and the reverse-current protection diode 2 for short-circuit protection; the rated current of the fuse is selected based on 1.5 times the maximum discharge current.

[0022] The reverse protection diode 2 is either a fast recovery diode or a Schottky diode. To enhance its protective function, it can be selected as a fast recovery diode or a Schottky diode, or other devices with low forward voltage drop. The forward conduction voltage of the reverse protection diode 2 should be controlled below 0.7V, and its reverse withstand voltage should be higher than 1.5 times the maximum operating voltage of the DC bus. The reverse protection diode 2 is installed on the connection line between the energy storage unit 1 and the DC bus, with its anode connected to the positive terminal of the energy storage unit 1 and its cathode connected to the positive terminal of the DC bus. This arrangement effectively prevents the reverse flow of electrical energy from the DC bus into the energy storage unit 1, ensuring unidirectional energy flow. The reverse protection diode 2 should be installed as close as possible to the DC bus side to minimize the impact of line impedance on the discharge effect. The reverse protection diode 2 requires a suitable heat sink, the size of which is determined based on the diode's maximum power dissipation and the ambient temperature. For high-current applications, multiple diodes can be connected in parallel to share the current. When connected in parallel, it is necessary to ensure that the parameters of each diode are matched and that a current-sharing resistor is connected in series with each diode, and to ensure that the diodes are installed in the correct orientation.

[0023] Charger 3 is a constant voltage, current-limiting charging circuit. The output voltage of charger 3 is set slightly higher than the rated voltage of energy storage unit 1, typically 5%-10% higher. The charging current is limited according to the capacity of energy storage unit 1, generally controlled within the range of 0.1C to 0.3C of the rated capacity. Charger 3 internally includes a voltage detection circuit and a current regulation circuit, capable of monitoring the terminal voltage of energy storage unit 1 in real time and automatically reducing the charging current when approaching full charge. Charger 3 is connected to the mains power supply via an AC input terminal. Charger 3 should also have overvoltage and overtemperature protection functions, automatically cutting off the charging circuit when abnormal conditions are detected. The connecting cable between charger 3 and energy storage unit 1 should have sufficient cross-sectional area to reduce line voltage drop, and both ends of the cable should be reliably connected using crimp terminals. Charger 3 is equipped with a working status indicator light to display the status of power on, charging in progress, and fault. The grounding terminal of charger 3's casing must be reliably connected to the system ground wire to ensure safe use. Charger 3 should internally include input overvoltage and undervoltage protection circuits, automatically cutting off the power supply when the input voltage exceeds the allowable range.

[0024] The operation of the anti-voltage fluctuation device is as follows: When the grid voltage 6 is normal, the detection module 7 controls the contactor 5 to close, and the charger 3 begins to charge the energy storage unit 1 until the voltage of the energy storage unit 1 reaches the set value, after which it enters the float charging state; when the grid voltage 6 experiences a voltage drop or interruption, the detection module 7 quickly disconnects the contactor 5, and at the same time, the energy storage unit 1 discharges to the DC bus of the frequency converter 4 through the anti-reverse diode 2 to maintain the stability of the bus voltage; after the grid voltage returns to normal, the detection module closes the contactor 5 again, and the charger 3 replenishes the energy storage unit 1 with energy again. Throughout the process, the anti-reverse diode 2 always prevents the DC bus voltage from flowing back into the energy storage unit 1, ensuring unidirectional energy transmission.

[0025] To improve the reliability of the device, status monitoring sensors can be installed in key areas, such as temperature sensors to monitor the operating temperature of energy storage unit 1 and anti-reverse diode 2, and current sensors to monitor charging and discharging current. The monitoring signals can be connected to the inverter 4 control system or a higher-level monitoring system to achieve remote status monitoring and fault early warning.

[0026] This anti-voltage fluctuation device, through its rational structural design and parameter configuration, effectively addresses grid voltage dips, ensuring the continuous operation of inverter 4 under voltage fluctuation conditions. The device adopts a modular design concept, with each functional unit relatively independent yet organically coordinated, facilitating both manufacturing and maintenance upgrades. The supercapacitor module, as the energy storage medium, boasts advantages such as long cycle life and fast charging / discharging speed. Combined with intelligent charging management, it ensures that energy storage unit 1 is always in optimal operating condition. The synergistic action of the anti-reverse diode 2 and contactor 5 enables reliable switching of the charging / discharging circuit, ensuring safe system operation under various conditions.

[0027] Although embodiments of the present 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 of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A variable frequency drive anti-surge device, comprising: The device includes an energy storage unit (1), an anti-reverse diode (2), a charger (3), and a contactor (5). The positive terminal of the energy storage unit (1) is connected to the positive terminal of the DC bus of the inverter (4) through the anti-reverse diode (2), and the negative terminal of the energy storage unit (1) is connected to the negative terminal of the DC bus of the inverter (4) through the anti-reverse diode (2). The positive and negative terminals of the output terminal of the charger (3) are respectively connected to the positive and negative terminals of the energy storage unit (1). The main contacts of the contactor (5) are connected in series in the charging circuit between the charger (3) and the energy storage unit (1). The control terminal of the contactor (5) is communicatively connected to the detection module (7) of the grid voltage (6). It also includes a transient detection unit (11), a transient analysis unit (12), and a steady-state protection unit (13). The output of the transient detection unit (11) is connected to the control terminal of the contactor (5), the output of the transient analysis unit (12) is connected to the harmonic feedback interface of the charger (3), and the output of the steady-state protection unit (13) is connected to the main control system of the frequency converter (4).

2. The anti-surge device for a frequency converter according to claim 1, characterized in that, The energy storage unit (1) is a supercapacitor module.

3. The anti-surge device of claim 1, wherein, The anti-reverse diode (2) is a fast recovery diode or a Schottky diode.

4. The anti-pumping device of claim 1, wherein The charger (3) is a constant voltage and current limiting type charging circuit.

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