Small-capacity low-voltage active filtering device

Abstract

The utility model discloses a small-capacity low-voltage active filtering device, which is suitable for being dispersedly installed on a low-voltage user side, a main circuit unit adopts a modular design and is connected in parallel on a bus between an alternating current power supply and a nonlinear load, a control mode of one main controller and multiple pairs is adopted, and a main controller is a control core of the whole parallel device. The auxiliary controller only needs to execute a command of the main controller without additional analysis and calculation, so that the plurality of main circuit units which are connected in parallel can be unified and coordinated, the main controller can realize closed-loop control according to a real-time detection result of the current detection unit, compensation current output by each main circuit unit is continuously corrected, and the compensation efficiency is improved. The harmonic or reactive current in the load current on the bus is offset, so that the current waveform of the power supply side is approximate to sine wave, the influence of the harmonic and the reactive current on other equipment and a relay protection device in a power grid is eliminated, the output consistency is good, the application is flexible, and the compensation effect is stable.

Description

Technical Field

[0001] The utility model relates to the technical field of low-voltage power distribution, in particular to an active filter, in particular to a small-capacity low-voltage active filter device. Background Art

[0002] The use of active power filters (APF) is currently the main means of harmonic control. Active power filters are a new type of power electronic device used to dynamically suppress harmonics and compensate for reactive power. They can compensate for harmonics that vary in size and frequency, as well as varying reactive power. They are usually compensated centrally at the grid outlet, with high procurement and installation costs. This affects the enthusiasm of small users with distributed loads for user-side harmonic control and energy-saving transformation, and has a negative impact on the quality of the low-voltage power grid.

[0003] In view of the characteristics of small users with dispersed loads, the power unit compensation capacity of the low-voltage active filter is generally around 30A. It adopts a modular design and can flexibly configure different numbers of modules for different low-voltage power supply equipment. When the current to be compensated by the system exceeds the rated compensation capacity of a single module, it is usually chosen to run multiple modules in parallel.

[0004] There are multiple modules connected in parallel. Figure 1 As shown, N APFs are connected to the busbar between the AC power supply and the linear load respectively, and the secondary measurement circuit of the current transformer is connected to each APF in series. Each APF outputs 1 / N harmonic compensation current according to the measured load current harmonics, so that the total output current reaches the required compensation current. In this parallel mode, its control method is similar to that of a single unit operation. Each APF operates independently, but if an APF fails and exits operation, the other APFs will still output compensation current in a 1 / N manner, resulting in the inability to compensate harmonic current normally. In addition, this parallel mode can usually only use the compensation current calculated by measuring the load current harmonics, but in many cases in the actual distribution system, the total grid-side current can only be measured by the current transformer of the distribution cabinet. Since the output current of each parallel APF affects the grid-side current at the same time, it is difficult to obtain an accurate compensation current, which greatly limits the application of this parallel mode. Utility Model Content

[0005] In order to solve the technical problems existing in the background technology, the utility model proposes a small-capacity low-voltage active filtering device, which adopts a one-master-multiple-slave parallel architecture, can realize closed-loop control according to real-time detection results, and has good output consistency.

[0006] The purpose of the utility model can be achieved through the following technical solutions:

[0007] A small-capacity low-voltage active filter device, comprising:

[0008] The main circuit unit is connected in parallel to the bus between the AC power source and the non-linear load to generate a compensation current to offset the harmonics or reactive current in the load current on the bus;

[0009] A current detection unit, connected to the busbar to detect the harmonics or reactive current of the load current in real time;

[0010] The main controller is connected to the current detection unit and the main circuit unit to control the main circuit unit to generate a compensation current with the same magnitude and opposite polarity as the harmonic or reactive current in the load current according to the harmonic or reactive current of the load current.

[0011] Furthermore, the main circuit units are arranged in multiple numbers and connected in parallel with each other, and the main controller calculates the total reference current that needs to be compensated based on the harmonics or reactive current of the load current and decomposes the total reference current into multiple compensation current signals corresponding to each main circuit unit to control each main circuit unit to generate corresponding compensation current.

[0012] Furthermore, it also includes multiple sub-controllers that are connected to the main controller through optical fibers for communication. The main controller controls a main circuit unit, and the multiple sub-controllers respectively control other main circuit units. The main controller collects the operating status uploaded by each sub-controller at a regular interval in real time and sends the compensation current signal corresponding to each main circuit unit to each sub-controller. The sub-controller controls the main circuit unit connected to it to generate corresponding compensation current according to the compensation current signal sent by the main controller.

[0013] Furthermore, the main controller or the sub-controller outputs a PWM pulse signal according to the compensation current signal corresponding to each main circuit unit to control each main circuit unit to generate the compensation current.

[0014] Furthermore, the main circuit unit comprises:

[0015] An inverter is connected to a bus between an AC power source and a nonlinear load to generate a compensation current to offset harmonics or reactive current in a load current on the bus;

[0016] The intelligent power module is connected to the main controller or the sub-controller, and controls the on and off of the power switch device on the inverter through the PWM pulse signal sent by the main controller or the sub-controller, so that the inverter generates a compensation current with the same magnitude and opposite polarity as the harmonic or reactive current in the load current on the bus;

[0017] The output filter is connected between the inverter and the bus to filter out the high-order harmonics generated by the switching of power switching devices in the compensation current generated by the inverter.

[0018] Furthermore, the inverter is composed of a three-phase bridge inverter circuit.

[0019] Furthermore, the output filter adopts an LCRLL type output filter.

[0020] Furthermore, the main controller and the sub-controller both adopt DSP chips and CPLD chips.

[0021] Furthermore, the current detection unit includes an AC current transformer and a current signal detection and conditioning circuit. The AC current transformer is connected to the busbar, and the current signal detection and conditioning circuit is connected to the main controller to transform and amplify the current signal detected by the AC current transformer and send it to the main controller.

[0022] The beneficial effects of the utility model are as follows: the utility model discloses a small-capacity low-voltage active filtering device, which is suitable for decentralized installation on the low-voltage user side. The main circuit unit adopts a modular design and is connected in parallel on the bus between the AC power supply and the nonlinear load. A one-master-multiple-sub controller is adopted. The main controller is the control core of the entire parallel device. The sub-controller only needs to execute the command of the main controller without additional analysis and calculation, so that multiple main circuit units connected in parallel can be coordinated in a unified manner. The main controller can realize closed-loop control according to the real-time detection result of the current detection unit, continuously correct the compensation current output by each main circuit unit, offset the harmonics or reactive current in the load current on the bus, so that the current waveform on the power supply side is approximately a sine wave, and the influence of harmonics and reactive current on other equipment and relay protection devices in the power grid is eliminated. The output consistency is good, the application is flexible, and the compensation effect is stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of using multiple APFs in parallel.

[0024] Figure 2 It is a system schematic diagram of the utility model.

[0025] Figure 3 It is a system schematic diagram of the main circuit module of the utility model.

[0026] Figure 4 The single-phase equivalent circuit diagram of the output filter of the utility model is shown in FIG.

[0027] Figure 5 The utility model is a circuit diagram of a current signal detection and conditioning circuit. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0029] like Figure 2 As shown, the utility model provides a small-capacity low-voltage active filtering device, including: a main circuit unit, a current detection unit, a main controller and a sub-controller.

[0030] The main circuit unit is provided with N (N≧1) and is connected in parallel on the bus between the AC power source and the nonlinear load to generate a compensation current to offset the harmonics or reactive current in the load current on the bus.

[0031] The current detection unit is connected to the bus to detect the harmonics or reactive current of the load current in real time.

[0032] A main controller is connected to a current detection unit and a main circuit unit to calculate a total reference current that needs to be compensated according to the harmonics or reactive current of the load current, and decompose the total reference current into N compensation current signals corresponding to the N main circuit units, and control the main circuit units to generate corresponding compensation currents, wherein each compensation current signal is 1 / N of the total reference current.

[0033] There are N-1 sub-controllers, which are respectively connected to the remaining N-1 main circuit units and communicate with the main controller through optical fiber to control the main circuit units connected thereto to generate corresponding compensation currents according to the compensation current signals calculated by the main controller.

[0034] Specifically, the main controller receives in real time the harmonics or reactive current of the load current detected by the current detection unit, as well as the operating status (including voltage data, current data, fault status, etc.) uploaded by each sub-controller at a regular interval. The main controller summarizes and analyzes this information, first calculates the total reference current that needs to be compensated, and then, based on the number of main circuit units, decomposes the total reference current into N compensation current signals corresponding to the N main circuit units. Each compensation current signal is 1 / N of the total reference current. The compensation current signal is sent down to N-1 sub-controllers in real time through optical fiber. After receiving the compensation current signal sent down by the main controller, each sub-controller, together with the main controller, controls the N main circuit units to generate corresponding compensation currents, thereby finally realizing the harmonic compensation function of the entire parallel device.

[0035] Specifically, the main controller collects the harmonics in the load current and performs FFT transformation. According to the set compensation order, the harmonic components of the corresponding order are processed, that is, if the harmonic is not compensated, the harmonic component is cleared, and then the remaining harmonic components are inversely transformed to obtain the compensated harmonic components; in addition, in order to compensate for the reactive current in the load current, the main controller symmetrically decomposes the fundamental component of the FFT transformation to obtain the reactive current of the load current, and then couples it with the compensated harmonic component to obtain the total reference current that needs to be compensated.

[0036] The main controller is the control core of the entire parallel device. The sub-controller only needs to execute the commands of the main controller without performing additional analysis and calculation, so that the N main circuit units connected in parallel can be coordinated in a unified manner. The main controller can realize closed-loop control according to the real-time detection results of the current detection unit, that is, real-time sampling of the current that needs to be compensated in the load current on the bus, and constantly correcting the compensation current output by each main circuit unit. When a main circuit unit exits operation due to a fault, the main controller receives the fault status uploaded by the sub-controller connected to the main circuit unit. The main controller immediately decomposes the total reference current into N-1 compensation current signals corresponding to the N-1 main circuit units, and controls the remaining N-1 main circuit units to generate corresponding compensation currents. At this time, each compensation current signal is 1 / N-1 of the total reference current, thereby ensuring that the compensation current can always offset the harmonics or reactive current in the load current on the bus.

[0037] Both the main controller and the sub-controller use DSP chips and CPLD chips. The function of the DSP chip is to complete A / D conversion, command signal calculation, feedback signal processing, and PWM pulse signal generation. The current detection unit sends the electrical signal to the ADC module of the DSP chip for A / D conversion. The DSP chip processes and calculates the collected electrical signal, and obtains the command current signal, which is sent to the full comparison unit of the EV module of the DSP chip. By setting the value of the corresponding register, a PWM pulse signal output is generated to control each main circuit unit to generate compensation current. The CPLD chip provides PWM output control, hardware interlocking, and dead zone control functions. The CPLD chip latches the fault signal. When the main circuit unit fails (DC voltage overvoltage, output compensation current overcurrent, short circuit, overheating), the CPLD immediately blocks the PWM pulse signal output to ensure the safe operation of the device. The CPLD chip provides a hardware interlocking function to ensure that the two IGBTs on the same bridge will not be turned on at the same time to prevent the IGBT module bridge arm from being short-circuited due to sudden power failure or power-on. Avoid short-circuit faults caused by bridge arm direct conduction to meet the reliability requirements of the device. The dead time control function of the CPLD chip ensures that one IGBT on the same bridge arm can be turned on only after it is reliably turned off.

[0038] like Figure 3 As shown, the main circuit unit specifically includes:

[0039] The inverter is composed of a three-phase bridge inverter circuit and is connected to the bus between the AC power source and the non-linear load to generate a compensation current to offset the harmonics or reactive current in the load current on the bus;

[0040] An intelligent power module is connected to the main controller or the sub-controller, and controls the on-off time of the power switch device on the inverter according to the PWM pulse signal sent by the main controller or the sub-controller, so that the inverter generates a compensation current with the same magnitude and opposite polarity as the harmonic or reactive current in the load current on the bus;

[0041] The output filter is connected between the inverter and the bus to filter out the high-order harmonics generated by the switching of power switching devices in the compensation current generated by the inverter.

[0042] Since the inverter uses PWM technology, its output current contains not only currents used to compensate for harmonics and reactive power, but also higher harmonics generated by the on-off of power switching devices. The high-frequency electromagnetic induction generated by such higher harmonics has a significant impact on control, communication equipment, and precision instruments, and will also bring additional losses to power transmission and distribution equipment (such as transmission lines, transformers, etc.). These additional higher harmonics enter the bus and are shunted by the power grid and loads, generating harmonic components in the public electrical environment and at the user's receiving end, causing serious pollution to both the power supply and the user. The output filter uses an LCRLL output filter, which can filter out the higher harmonics generated by the on-off of power switching devices in the compensation current generated by the inverter. Its single-phase equivalent circuit diagram is shown below: Figure 4 As shown in the figure, the LCRLL output filter has a series inductor L on the inverter side. 01 To ensure the compensation capability of harmonics and reactive current, a series inductor L is designed on the grid side. O2 Improve the filtering effect of high-order harmonic current.

[0043] The current detection unit includes an AC current transformer and a current signal detection and conditioning circuit. The AC current transformer is connected to the busbar, and the current signal detection and conditioning circuit is connected to the main controller to transform and amplify the current signal detected by the AC current transformer and send it to the main controller.

[0044] The current signal is detected by using an AC current transformer model TA1321-3K, whose input rated current is 20A, output rated current is 10mA, and sampling frequency can reach 20kHz. The circuit diagram of the current signal detection and conditioning circuit is shown in Figure 5 As shown, the detected AC current signal is converted into an AC voltage of ±1.5V through a resistor, and then increased to 0-3V through an amplifier so as to be sent to the ADC module of the DSP chip.

[0045] The above contents are merely examples and explanations of the structure of the utility model. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the utility model or exceed the scope defined in the claims, they should all fall within the protection scope of the utility model.

Claims

1. A small-capacity low-voltage active filter device, characterized in that: include: The main circuit unit is connected in parallel to the bus between the AC power source and the non-linear load to generate a compensation current to offset the harmonics or reactive current in the load current on the bus; A current detection unit, connected to the busbar to detect the harmonics or reactive current of the load current in real time; The main controller is connected to the current detection unit and the main circuit unit to control the main circuit unit to generate a compensation current with the same magnitude and opposite polarity as the harmonic or reactive current in the load current according to the harmonic or reactive current of the load current.

2. A small-capacity low-voltage active filter device according to claim 1, characterized in that: The main circuit units are arranged in multiple numbers and connected in parallel with each other. The main controller calculates the total reference current that needs to be compensated based on the harmonics or reactive current of the load current and decomposes the total reference current into multiple compensation current signals corresponding to each main circuit unit to control each main circuit unit to generate a corresponding compensation current.

3. A small-capacity low-voltage active filter device according to claim 2, characterized in that: It also includes multiple sub-controllers that are connected to the main controller through optical fibers. The main controller controls a main circuit unit, and the multiple sub-controllers respectively control other main circuit units. The main controller collects the operating status uploaded by each sub-controller at a regular interval in real time and sends the compensation current signal corresponding to each main circuit unit to each sub-controller. The sub-controller controls the main circuit unit connected to it to generate corresponding compensation current according to the compensation current signal sent by the main controller.

4. A small-capacity low-voltage active filter device according to claim 3, characterized in that: The main controller or the sub-controller outputs a PWM pulse signal according to the compensation current signal corresponding to each main circuit unit to control each main circuit unit to generate a compensation current.

5. A small-capacity low-voltage active filter device according to claim 4, characterized in that: The main circuit unit comprises: An inverter is connected to a bus between an AC power source and a nonlinear load to generate a compensation current to offset harmonics or reactive current in a load current on the bus; The intelligent power module is connected to the main controller or the sub-controller, and controls the on and off of the power switch device on the inverter through the PWM pulse signal sent by the main controller or the sub-controller, so that the inverter generates a compensation current with the same magnitude and opposite polarity as the harmonic or reactive current in the load current on the bus; The output filter is connected between the inverter and the bus to filter out the high-order harmonics generated by the switching of power switching devices in the compensation current generated by the inverter.

6. A small-capacity low-voltage active filter device according to claim 5, characterized in that: The inverter is composed of a three-phase bridge inverter circuit.

7. A small-capacity low-voltage active filter device according to claim 5, characterized in that: The output filter adopts an LCRLL type output filter.

8. A small-capacity low-voltage active filter device according to claim 1, characterized in that: The main controller and the sub-controller both adopt DSP chip and CPLD chip.

9. A small-capacity low-voltage active filter device according to claim 1, characterized in that: The current detection unit includes an AC current transformer and a current signal detection and conditioning circuit. The AC current transformer is connected to the busbar, and the current signal detection and conditioning circuit is connected to the main controller to transform and amplify the current signal detected by the AC current transformer and send it to the main controller.

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