CN218888142U - Direct-current active filter for improving electric energy quality of direct-current micro-grid - Google Patents

Abstract

The utility model discloses a DC active filter for improving the power quality of a DC micro-grid, which overcomes the relatively large volume and comparative loss of the passive filter device for suppressing the ripple of the DC micro-grid in the prior art. high, and the passive filter can only compensate for a specific number of ripples, including a DC boost circuit, the input of the DC boost circuit is connected to a DC power module, and the output of the DC boost circuit is connected to a DC load , the DC load is connected to a DC power supply to form a closed loop, the DC boost circuit is also connected to a PWM control circuit, the PWM control circuit is connected to a power factor correction circuit, and the power factor correction circuit is connected to a DC power supply module. The structure is simple and the cost is low. It can filter out the ripple of each frequency in the DC microgrid, improve the power quality of the DC microgrid, and also has a good compensation effect, and can dynamically and continuously compensate the reactive power of the system.

Description

A DC active filter for improving the power quality of DC microgrid

technical field

The utility model relates to the technical field of active filters, in particular to a DC active filter for improving the power quality of a DC microgrid.

Background technique

In recent years, the rapid economic development, people's demand for electric energy and the gradual increase in environmental protection awareness have led to the emergence of distributed power applications. However, due to the access of distributed power sources, on the one hand, it will not only increase the difficulty of controlling the entire system, but also make the cost of the entire operating system higher. Another aspect is that the access to new energy generation will cause the output power to be unbalanced, which will lead to a decrease in the power quality of the entire system. It is easy to cause problems such as voltage flicker and voltage fluctuation. At the same time, because the distributed power supply is connected to the grid through the inverter, some power electronic components required will generate harmonics. affect the normal operation of the entire system.

Microgrid solves the problem of large-scale application of distributed power generation. At present, microgrids mainly exist in the form of AC microgrids, but the influence of amplitude, phase, and frequency must be considered in the entire system of AC microgrids, but there is no influence caused by frequency and phase in DC microgrids. Compared with the AC microgrid, the DC microgrid has many advantages, such as a relatively simple structure, easy to control, and easy to maintain. However, there are a large number of converters and nonlinear load elements in the independent photovoltaic DC microgrid, which will generate a large amount of ripple. These factors have seriously affected the power quality of the DC microgrid.

Passive filtering device is currently the main means to suppress DC micro-grid ripple. Installing it near the ripple source can not only suppress the ripple current, but also compensate the reactive power of the system. The cost of passive filter is low, it has strong reliability, and the maintenance of equipment is also quite convenient. However, the passive filter has a large volume and relatively high loss, and the passive filter can only compensate for a specific order of ripple.

Contents of the invention

The purpose of the utility model is to overcome the problems in the prior art that the passive filter device for suppressing the ripple of the DC micro-grid has a large volume and relatively high loss, and the passive filter can only compensate for a specific number of ripples, and provides A DC active filter for improving the power quality of a DC microgrid, which has a simple structure and low cost, can filter out the ripples of each frequency in the DC microgrid, improve the power quality of the DC microgrid, and has a relatively low cost. With good compensation effect, it can dynamically and continuously compensate reactive power of the system.

In order to achieve the above object, the utility model adopts the following technical solutions:

A DC active filter for improving the power quality of a DC microgrid, comprising a DC boost circuit, the input end of the DC boost circuit is connected to a DC power module, and the output end of the DC boost circuit is connected to a DC load, The DC load is connected to a DC power supply to form a closed loop, and the DC boost circuit is also connected to a PWM control circuit, the PWM control circuit is connected to a power factor correction circuit, and the power factor correction circuit is connected to a DC power supply module.

The utility model adopts a DC boost circuit, which does not need to detect the load current, and does not need to separate the ripple current in the load current, so the high-precision multiplier is omitted, and the control circuit is simple; at the same time, it can control the DC voltage when the ripple current is small. The ripple in the microgrid is filtered out. It can filter out the ripple of each frequency in the DC micro-grid, improve the power quality of the DC micro-grid, and also has a good compensation effect, and can dynamically and continuously compensate the reactive power of the system.

Preferably, the DC power supply module includes an AC power supply and a bridge rectifier circuit connected to the AC power supply, the negative pole of the bridge rectifier circuit is connected to the input terminal of the DC booster circuit, and the positive pole of the bridge rectifier circuit is connected to the DC booster circuit. The output terminal of the voltage circuit is connected.

Through the rectifier bridge, the AC voltage input by the AC power supply is converted into a DC voltage and output to the DC boost circuit.

Preferably, the bridge rectifier circuit includes two diode groups connected in parallel, the diode group includes a first diode and a second diode, and the anode of the first diode is connected to the output end of the DC step-up circuit , the cathode of the first diode is respectively connected to the anode of the second diode and the AC power supply, and the cathode of the second diode is connected to the input end of the DC boost circuit.

In each working cycle of the rectifier bridge, only two diodes work at the same time, and through the unidirectional conduction function of the diodes, the AC power is converted into a unidirectional DC pulsating voltage.

Preferably, the DC boost circuit includes an inductor, the inductor is connected with a power switch tube and a freewheeling diode, the power switch tube is connected with a DC power supply module, and the freewheeling diode is connected with a DC load.

During the charging process, the power switch tube is turned on, and the inductor starts to store energy at this time; during the discharge process, the power switch tube Q is turned off, and the inductor starts to discharge. The state of the power switch tube is controlled by the PWM control circuit. The PWM control circuit outputs a PWM control signal. After the PWM control signal is compared with the carrier signal, the output pulse signal is used to drive the power switch tube to be turned on or off.

Preferably, the DC boost circuit further includes a DC side capacitor, and the DC side capacitor is connected in parallel with the freewheeling diode.

During the charging process, the power switch tube is turned on, and the inductor starts to store energy, and the capacitor supplies power to the load; during the discharge process, the power switch tube is turned off, and the inductor supplies power to the capacitor, so that the output voltage of the DC boost circuit is high. Input voltage to the DC boost circuit.

Preferably, the average input current of the DC step-up circuit is greater than or equal to 1/2 of the variation of the input current.

The current variation of the inductor is equal to the product of the input voltage, the duty cycle of the power switch tube and the duty cycle time of the power switch tube divided by the quotient of the inductance value, so that the value range of the inductor can be obtained, so as to boost the DC voltage The inductance of the circuit is further defined.

When this condition is met, the DC boost circuit can always be in a continuous working state, so that the DC active filter can always work, filter out the ripple in the DC microgrid, improve the power quality of the DC microgrid, and ensure the operation of the DC microgrid stability.

Preferably, the capacity of the power switch tube is the sum of the peak line current and half of the peak-to-peak high-frequency ripple current, and the voltage rating of the power switch tube is greater than or equal to the output voltage of the DC boost circuit.

The capacity value of the power switch tube is the sum of the peak line current and half of the peak-peak high-frequency ripple current, that is, the maximum peak current in the inductor current, and the voltage rating of the power switch tube is at least equal to the output voltage. The power switch tube may be a MOS tube.

Preferably, the current of the DC side capacitor is the sum of the effective value of the switching frequency ripple current and the second harmonic of the line current.

The selection of the DC side capacitor is related to factors such as the ripple current of the switching frequency, the secondary ripple current, the DC output voltage, the output ripple voltage and the holding time. The total current flowing through the capacitor is the sum of the rms value of the switching frequency ripple current and the second harmonic of the line current.

Therefore, the utility model has the following beneficial effects: the use of the DC boost circuit does not need to detect the load current, and does not need to separate the ripple current in the load current, so the high-precision multiplier is omitted, and the control circuit is simple; When the ripple current is small, the ripple in the DC microgrid is filtered. It can filter out the ripple of each frequency in the DC micro-grid, improve the power quality of the DC micro-grid, and also has a good compensation effect, and can dynamically and continuously compensate the reactive power of the system.

Description of drawings

Fig. 1 is a schematic diagram of the system architecture of the DC active filter of the present invention.

Fig. 2 is a schematic circuit diagram of the DC active filter of the present invention.

In the figure: 1. DC boost circuit; 2. DC power supply module; 3. DC load; 4. PWM control circuit; 5. Power factor correction circuit.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the utility model is described in further detail:

Embodiment one:

This embodiment is a DC active filter for improving the power quality of a DC microgrid, as shown in Figure 1, including a DC boost circuit 1, a DC power module 2, a DC load 3, a PWM control circuit 4, and a power factor In the correction circuit 5, the output terminals of the DC power supply module are respectively connected to the power factor correction circuit and the DC boost circuit, the DC boost circuit is connected to the DC load, and the PWM control circuit, and the PWM control circuit is connected to the power factor correction circuit.

The utility model adopts a DC boost circuit, which does not need to detect the load current, and does not need to separate the ripple current in the load current, so the high-precision multiplier is omitted, and the control circuit is simple; at the same time, it can control the DC voltage when the ripple current is small. The ripple in the microgrid is filtered out. It can filter out the ripple of each frequency in the DC micro-grid, improve the power quality of the DC micro-grid, and also has a good compensation effect, and can dynamically and continuously compensate the reactive power of the system.

The specific circuit structure of the DC active filter in this embodiment is shown in Figure 2:

The DC power supply module includes an AC power supply and a bridge rectifier circuit connected to the AC power supply. The bridge rectifier circuit includes a diode D2, a diode D3, a diode D4, and a diode D5. The cathode of the diode D4 is respectively connected to the AC power supply and the anode of the diode D3. The positive pole of D4 is connected to the output terminal of the DC boost circuit, the negative pole of the diode D3 is connected to the input terminal of the DC boost circuit; the negative pole of the diode D5 is respectively connected to the AC power supply and the positive pole of the diode D2, and the positive pole of the diode D5 is connected to the DC boost circuit. The output terminal of the circuit is connected, and the cathode of the diode D2 is connected with the input terminal of the DC boost circuit.

Through the rectifier bridge, the AC voltage input by the AC power supply is converted into a DC voltage and output to the DC boost circuit. In each working cycle of the rectifier bridge, only two diodes work at the same time, and through the unidirectional conduction function of the diodes, the AC power is converted into a unidirectional DC pulsating voltage.

The DC boost circuit includes an inductor L1, a freewheeling diode D1, a power switch tube, and a DC side capacitor C1. In this embodiment, the power switch tube uses a MOS tube Q1. One end of the inductor L1 is connected to the DC power module, and the other end of the inductor L1 is connected to the MOS tube. The drain of Q1 is connected, the drain of MOS transistor Q1 is connected to the positive pole of freewheeling diode D1, the negative pole of freewheeling diode D1 is connected to one end of capacitor C1 and one end of DC load respectively, the other end of capacitor C1 and the other end of DC load are connected to the source of MOS transistor Q1 The gate of the MOS transistor Q1 is connected to the output terminal of the PWM control circuit, the input terminal of the PWM control circuit is connected to the power factor correction circuit, and the power factor correction circuit is also connected to the DC power supply module and the DC boost circuit.

During the charging process, the power switch tube is turned on, and the inductor starts to store energy at this time, and the DC side capacitor supplies power to the load; during the discharge process, the power switch tube Q is turned off, the inductor supplies power to the DC side capacitor, and the inductor starts to discharge . The state of the power switch tube is controlled by the PWM control circuit. The PWM control circuit outputs a PWM control signal. After the PWM control signal is compared with the carrier signal, the output pulse signal is used to drive the power switch tube to be turned on or off.

In order to ensure that the DC boost circuit can always be in a continuous working state, so that the DC active filter can work all the time, filter out the ripple in the DC microgrid, improve the power quality of the DC microgrid, and ensure the operation stability of the DC microgrid. In this embodiment, the following conditions also need to be met:

The average input current I _L of the DC boost circuit is greater than or equal to one-half of the input current variation △ I _L :

The current variation of the inductor is equal to the product of the input voltage, the duty cycle of the power switch tube and the duty cycle time of the power switch tube divided by the quotient of the inductance value, so that the value range of the inductor can be obtained, so as to boost the DC voltage The inductance of the circuit is further defined.

Embodiment two:

Based on the first embodiment, this embodiment further defines the power switch tube, DC side capacitor and inductor in the DC boost circuit:

1. Power switch tube

The capacity value of the power switch tube is the sum of the peak line current and half of the peak-peak high-frequency ripple current, that is, the maximum peak current in the inductor current, and the voltage rating of the power switch tube is at least equal to the output voltage of the DC boost circuit Voltage.

2. DC side capacitance

The selection of capacitors is related to factors such as switching frequency ripple current, secondary ripple current, DC output voltage, output ripple voltage and hold time. The total current flowing through the capacitor is the sum of the rms value of the switching frequency ripple current and the second harmonic of the line current.

3. Inductance

In the DC step-up single circuit in this embodiment, the average output power is equal to the input average power within one half-wave output by the PWM control circuit, and the current is required to be continuous at any moment, so it can be obtained:

In the formula, L represents the inductance value, R represents the DC load resistance, T _s represents the working time of the power switch tube, U _m represents the input voltage of the DC boost circuit, and U _d represents the output voltage of the DC boost circuit.

The above-described embodiment is only a preferred solution of the utility model, and does not limit the utility model in any form. There are other variations and improvements without exceeding the technical solution described in the claims. type.

Claims (8)

1. A DC active filter for improving DC micro-grid power quality, characterized in that it comprises a DC boost circuit, the input of the DC boost circuit is connected with a DC power module, and the output of the DC boost circuit The terminal is connected with a DC load, and the DC load is connected with a DC power supply to form a closed loop, and the DC boost circuit is also connected with a PWM control circuit, and the PWM control circuit is connected with a power factor correction circuit, and the power factor correction circuit and DC power module connection. 2. A kind of DC active filter for improving DC micro-grid power quality according to claim 1, characterized in that, the DC power supply module includes an AC power supply and a bridge rectifier circuit connected to the AC power supply, so The negative pole of the bridge rectifier circuit is connected to the input terminal of the DC boost circuit, and the positive pole of the bridge rectifier circuit is connected to the output terminal of the DC boost circuit. 3. A DC active filter for improving the power quality of a DC microgrid according to claim 2, wherein the bridge rectifier circuit includes two parallel diode groups, and the diode group includes the first A diode and a second diode, the anode of the first diode is connected to the output end of the DC booster circuit, the cathode of the first diode is respectively connected to the anode of the second diode and the AC power supply, and the second and second diodes The cathode of the pole tube is connected with the input terminal of the DC boost circuit. 4. A kind of DC active filter for improving the power quality of DC microgrid according to claim 1, characterized in that, the DC boost circuit includes an inductor, and the inductor is connected with a power switch tube and a freewheeling A diode, the power switch tube is connected to the DC power supply module, and the freewheeling diode is connected to the DC load. 5. A kind of DC active filter for improving the power quality of DC micro-grid according to claim 4, characterized in that, the DC boost circuit also includes a DC side capacitor, and the DC side capacitor and freewheeling diodes in parallel. 6. A kind of DC active filter for improving the power quality of DC microgrid according to claim 4 or 5, characterized in that, the average input current of the DC boost circuit is greater than or equal to two times of the input current variation one-third. 7. A kind of DC active filter for improving DC microgrid power quality according to claim 5, characterized in that, the capacity of the power switch tube is the current of the peak line and half of the peak-to-peak high frequency The sum of the ripple current, the voltage rating of the power switch tube is greater than or equal to the output voltage of the DC boost circuit. 8. A kind of DC active filter for improving the power quality of DC microgrid according to claim 5 or 7, characterized in that, the current of the DC side capacitor is the effective value of the switching frequency ripple current and the line The sum of the second harmonics of the current.

Images