CN110061625B - Four-port converter with bipolar output and control method thereof - Google Patents

Abstract

The invention discloses a four-port converter with bipolar output. The input port includes a DC power source V _in1 and a DC power source V _in2 with charging and discharging functions, and the output port includes a load R ₁ and a load R ₂ . By controlling the switching tube, the converter can operate in dual-input and dual-output mode or single-input and three-output mode. In dual-input dual-output mode, V _in1 and V _in2 provide energy to load R ₁ and load R ₂ at the same time; in single-input three-output mode, V _in1 provides energy to load R ₁ and load R ₂ , and V _in2 absorbs excess energy. . The invention has the following beneficial effects: simple structure, low cost, high power density and high system efficiency. It can output a symmetrical and common-ground bipolar voltage, and can also connect loads of three voltage levels. It has a wide range of applications and high reliability. The voltage relationship between the input and output ports of the converter is flexible and can be either boosted or stepped down.

Description

Four-port converter with bipolar output and control method thereof

Technical field

The invention relates to the field of power electronics technology, in particular to a four-port converter with bipolar output and a control method thereof.

Background technique

In recent years, with the intensification of environmental pollution and energy crisis, the use of new energy sources such as solar energy, hydrogen energy, and wind energy for power generation has become a hot research topic. New energy power generation systems are divided into two modes of operation: grid-connected operation and independent operation according to whether they are connected to the power grid. Independently operated new energy power generation systems are widely used in remote mountainous areas, islands, industrial parks, etc. because of their simple structure and high power supply quality. In addition to power supply in areas without power grid, independently operated new energy power generation systems are also widely used in the power supply of new energy vehicles and independent LED lighting systems. However, since the output characteristics of new energy power generation systems are often closely related to environmental factors, the output characteristics of new energy power generation systems under different environmental conditions are random and volatile. Therefore, independent operation of new energy power generation systems must be equipped with energy storage The unit is used to store and regulate electrical energy to meet the requirements of electrical loads for power supply continuity and stability.

Traditional new energy power generation systems use multiple independent converters for power conversion. The system structure is complex, low efficiency, high cost, and cannot achieve centralized control. In order to further improve the efficiency of the system and reduce the system cost, researchers have used multi-port converters The converter is used in new energy power generation systems. However, existing multi-port converters often only include one load end and can only provide a DC bus of one voltage level, which cannot meet the requirements of multiple loads with different voltage levels being connected to the system at the same time. . Therefore, some scholars have proposed new energy power generation systems with bipolar output, which can output symmetrical positive and negative voltages at the same time. Bipolar new energy power generation systems have the following advantages over unipolar new energy power generation systems: 1) When one of the outputs fails to work normally, the other output can still work normally, making the system more reliable; 2) Flow through The current of the ground wire is very small, and when the two loads are the same, the current flowing through the ground wire is 0; 3) When the load power is equal, the power transmitted on a single bus in the bipolar new energy power generation system is unipolar. Half of the new energy power generation system; 4) It can provide output of three voltage levels and has a wider range of applications. The traditional way to achieve bipolar voltage output is to use an isolated forward converter or flyback converter. By sharing a transformer core and winding the transformer with multiple output windings, bipolar output is achieved. This method The disadvantages are complex transformer design, large system size and low efficiency. Therefore, it is necessary to propose a bipolar new energy power generation system based on a non-isolated multi-port converter to overcome the problems of large size, high cost, and low efficiency existing in the existing technology.

Contents of the invention

In view of the shortcomings of the existing technology, the present invention proposes a four-port converter with bipolar output. The converter can output symmetrical and common-ground bipolar voltages at the same time, and one converter can be used to realize that two power sources and multiple loads can be connected to the system at the same time, and can realize the communication between the source and the load through corresponding control. Energy management.

The technical solutions to achieve the purpose of the present invention are as follows:

A four-port converter with bipolar output, including a DC power source V _in1 and a DC power source V _in2 with charging and discharging functions; the positive electrode of V _in1 is connected to the input end of the inductor L ₁ , and the output end of L ₁ is connected to _{The drain of the switch tube S 1 and the positive electrode of the intermediate energy storage capacitor C x , the negative electrode of C} The negative pole of _in1 , the source of S ₁ , the output terminal of L ₂ and the output terminal of R ₁ are all connected to the reference ground; it also includes the input filter capacitor C _in1 connected in parallel to both ends of V _in1 and the output filter capacitor connected in parallel to both ends of R ₁ C ₁ ; the anode of V _in2 is connected to the cathode of diode D ₃ , the anode of D ₃ is connected to the source of switch S ₃ , the drain of S ₃ is connected to the anode of intermediate energy storage capacitor C _y , and the cathode of C _y is connected To the anode of diode D ₄ and the input end of inductor L ₃ , the output end of inductor L ₃ is connected to the input end of load R ₂ ; the cathode of V _in2 , the cathode of D ₄ and the output end of R ₂ are all connected to the reference ground; It also includes an input filter capacitor C _in2 connected in parallel to both ends of V _in2 and an output filter capacitor C ₂ connected in parallel to both ends of R ₂ ; it also includes a diode D ₁ and a switch tube S ₂ , the anode of D ₁ is connected to the input end of L ₁ , D The cathode of ₁ is connected to the source of _S2 , and the drain of _S2 is connected to the cathode of _D3 ; the drain of _S1 is also connected to the drain of _S3 .

Further, a load R ₃ is also included, and both ends of R ₃ are connected to the input ends of R ₁ and R ₂ respectively.

The control method of the above four-port converter is to always turn off the switch S ₃ to make the converter operate in the dual-input and dual-output mode; or to always turn off the switch S ₂ to make the converter operate in the single-input three-output mode.

Compared with the prior art, the beneficial effects of the present invention are:

1. Simple structure, low cost, high power density and high system efficiency.

2. It can output symmetrical and common-ground bipolar voltage, and can also connect loads of three voltage levels. It has a wide range of applications and high reliability.

3. The voltage relationship between the input and output ports of the converter is flexible and can both boost and step down.

Description of the drawings

Figure 1 is a schematic diagram of a four-port converter with bipolar output of the present invention.

Figure 2 is the equivalent circuit diagram of dual-input dual-output mode.

Figure 3(a) and Figure 3(b) are the two main operating waveforms in dual-input and dual-output mode respectively.

Figure 4 is the equivalent circuit diagram of the single-input three-output mode.

Figure 5 is the main operating waveform in single input three output mode.

Figure 6 is a schematic diagram of a control method for a four-port converter with bipolar output.

Figure 7(a) and Figure 7(b) are two steady-state waveforms in dual-input and dual-output mode respectively.

Figure 8 is the steady-state waveform in single-input three-output mode.

Figure 9 is the transient response waveform of load jump in dual-input and dual-output mode.

Figure 10 is the transient response waveform of load jump in single input three output mode.

Figure 11 is the simulation waveform of switching between dual-input dual-output mode and single-input three-output mode.

Detailed ways

The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

A four-port converter with bipolar output, which can be connected to a first power source V _in1 , a second power source V _in2 and a load at the same time, and can output a symmetrical and common ground bipolar voltage, circuit Few devices, high power density, and wide range of applications.

Figure 1 shows the circuit schematic diagram of a four-port converter with bipolar output, including a first power source V _in1 , a second power source V _in2 , a positive output port _Vo1 , and a negative output port _Vo2 , the first input filter capacitor C _in1 , the second input filter capacitor C _in2 , the first intermediate energy storage capacitor C _x , the second intermediate energy storage capacitor C _y , the first output filter capacitor C ₁ , the second output filter capacitor C ₂ , the first inductor L ₁ , the second inductor L ₂ , the third inductor L ₃ , the first switch S ₁ , the second switch S ₂ , the third switch S ₃ , the first diode D ₁ , the second Diode D ₂ , third diode D ₃ , fourth diode D ₄ , first load R ₁ , second load R ₂ . In addition, the third load R ₃ can also be added according to actual needs.

Among them, the first power source V _in1 uses a photovoltaic unit as an input, the second power source V _in2 uses an energy storage unit as an input, and the first load R ₁ , the second load R ₂ and the third load R ₃ all use pure resistors.

The anode of the first power source V _in1 is connected to one end of the first inductor L ₁ and the cathode of the first diode D ₁ , the cathode is connected to the reference ground, and the other end of the first inductor L ₁ is connected to the first switch S _{1 The} drain is _connected to the positive electrode of _the first _intermediate energy storage capacitor C The anode of the diode D ₂ is connected, the other end of the second inductor L ₂ is connected to the reference ground, the cathode of the second diode D ₂ serves as the anode of the positive output port V _o1 of the converter, and is connected to the load R ₁ Positive connection.

The cathode of the second power source V _in2 is connected to the reference ground, the anode is connected to the drain of the second switch S ₂ and the cathode of the third diode D ₃ , and the source of the second switch S ₂ is connected to the first diode. The anode of the tube D ₁ is connected, the anode of the third diode D ₃ is connected to the source of the third switching tube S ₃ , the drain of the third switching tube S ₃ is connected to the drain of the first switching tube S ₁ and the second The anode of the intermediate energy storage capacitor C _y is connected, the cathode of the second intermediate energy storage capacitor C _y is connected to the anode of the fourth diode D ₄ and one end of the third inductor L ₃ respectively, and the cathode of the fourth diode D ₄ Connected to the reference ground, the other end of the third inductor L ₃ serves as the positive pole of the positive output port V _o2 of the converter and is connected to the positive pole of the load R ₂ .

If a third load R ₃ is set in the system, both ends of the load R ₃ are connected to the positive poles of the load R ₁ and the load R ₂ respectively.

The first input filter capacitor C _in1 and the second input filter capacitor C _in2 are connected in parallel to both ends of the photovoltaic input port and the energy storage unit input port respectively; the first output filter capacitor C ₁ and the second output filter capacitor C ₂ are connected in parallel to Both ends of the positive output port and the negative output port.

In the system, the first power source V _in1 can be various power sources that can provide DC output, and the second power source V _in2 can be various energy storage devices with charging and discharging functions.

In specific applications, in order to achieve strict symmetrical bipolar output, it is necessary to ensure that the first inductor L ₁ , the second inductor L ₂ , and the third inductor L ₃ all work in the inductor current continuous conduction mode (Continuous Conduction Mode, CCM). Therefore, L ₁ , L ₂ , and L ₃ should all have larger inductance values.

In order to achieve strict symmetrical bipolar output, it is also necessary to ensure that the voltages of the first intermediate energy storage capacitor C _x and the second intermediate energy storage capacitor C _y are basically constant. Therefore, C _x and C _y should both have larger capacitance values. .

In the dual-input dual-output mode, the third switch _S3 is always turned off, and the first power source V _in1 and the second power source V _in2 provide energy to the load unit at the same time. In one switching cycle, the system includes four switching states, They are: State 1 (S ₁ and S ₂ are both on); State 2 (S ₁ is on, S ₂ is off); State 3 (S ₁ is off, S ₂ is on); State 4 (S 1 and S ₂ are on) S ₂ are both turned off), if the conduction duty cycle d ₁ of S ₁ is greater than the conduction duty cycle d ₂ of S ₂ , then state 1, state 2, and state 4 appear sequentially within a switching cycle. If S ₁ The conduction duty cycle d ₁ of S is less than the conduction duty cycle d ₂ of S ₂ , then state 1, state 3, and state 4 appear sequentially within a switching cycle.

In the single-input three-output mode, the second switch _S2 is always turned off. Only the first power source V _in1 provides energy to the load, and the second power source V _in2 absorbs excess energy. Within a switching cycle, the system includes three types of The switching states are: State 1 (S ₁ is on, S ₃ is off); State 2 (S ₁ is off, S ₃ is on); State 3 (S ₁ and S ₃ are both off).

Figure 2 shows the equivalent circuit of a four-port converter with bipolar output in dual-input dual-output mode. In the dual-input dual-output mode, the photovoltaic unit V _in1 and the energy storage unit V _in2 provide energy to the load at the same time, and the switch tube S ₃ is always turned off.

Figure 3 shows the main operating waveforms of a four-port converter with bipolar output in dual-input and dual-output mode, where d ₁ is the conduction duty cycle of switch S ₁ and d ₂ is the duty cycle of switch S ₂ On-duty cycle, i _L is the current flowing through the inductor L ₁ , v _L is the voltage across the inductor L ₁ , V _cx is the voltage across the first intermediate energy storage capacitor C _x , V _cy is the first intermediate energy storage The voltage across the capacitor C _y . In the dual-input dual-output mode, the converter may have two working states, namely d ₁ >d ₂ and d ₁ <d ₂ , as shown in Figure 3(a) and Figure 3(b).

In the dual-input dual-output mode, according to the volt-second balance relationship of the first inductor L ₁ , the second inductor L ₂ , and the third inductor L ₃ , whether d ₁ >d ₂ or d ₁ <d ₂ , the positive polarity output The terminal voltage V _o1 and the negative polarity output terminal voltage V _o2 are respectively:

It can be seen from the above equation that in the dual-input dual-output mode, the positive output voltage V _o1 and the negative output voltage V _o2 have the same amplitude and opposite voltage polarity, and when the switch S ₁ is turned on When the duty cycle d ₁ changes between 0 and 1, the positive polarity terminal voltage V _o1 can change between 0 and positive zero group maximum, and the negative polarity terminal voltage V _o2 can change between 0 and negative zero group maximum. Therefore, the converter of the present invention can realize both boosting and bucking in the dual-input and dual-output mode.

Figure 4 shows the equivalent circuit of a four-port converter with bipolar output in single-input three-output mode. In the single-input three-output mode, only the photovoltaic unit provides energy to the load, the energy storage unit absorbs the excess energy generated by the photovoltaic unit, and the switch tube _S2 is always turned off.

Figure 5 shows the main operating waveforms of a four-port converter with bipolar output in single-input three-output mode, where d ₁ is the conduction duty cycle of switch tube S ₁ and d ₃ is the duty cycle of switch tube S ₃ On-duty cycle, i _L is the current flowing through the inductor L ₁ , v _L is the voltage across the inductor L ₁ , V _cx is the voltage across the first intermediate energy storage capacitor C _x , V _cy is the first intermediate energy storage The voltage across the capacitor C _y .

In the single-input three-output mode, according to the volt-second balance relationship of the first inductor L ₁ , the second inductor L ₂ , and the third inductor L ₃ , the voltages at the positive and negative output terminals can be obtained as:

It can be seen from the above formula that in the single-input three-output mode, the voltages at the positive output terminal and the negative output terminal have the same amplitude and opposite voltage polarity, and when the switch tube S ₁ and the switch tube S ₃ are turned on When the sum of duty cycles d ₁ + d ₃ changes between 0 and 1, the positive polarity terminal voltage V _o1 can change between 0 and positive zero group, and the negative polarity terminal voltage V _o2 can range from 0 to negative zero group. Big changes. Therefore, the converter of the present invention can realize both boosting and bucking in the single-input three-output mode.

Figure 6 shows a control circuit of a four-port converter with bipolar output. The control circuit includes a first power source controller, a second power source controller, an output voltage controller, a mode selection circuit and a pulse modulation circuit. In this example, the first power source controller implements Maximum Power Point Tracking (MPPT) control, and performs MPPT operation by sampling the voltage V _in1 and current I _in1 at the input end of the photovoltaic unit to obtain the control signal v _e1 , thus Achieve the maximum power output of the photovoltaic; the second power source controller controls the voltage and current of the energy storage unit, by sampling the voltage V _in2 and charge and discharge current I _in2 at both ends of the energy storage unit, and compares it with the preset threshold, thereby Enable the energy storage unit to achieve overcharge protection and over-discharge protection; the output voltage controller samples the two output voltages V _o1 and V _o2 , then calculates V _ox =0.5*V _o1 -0.5*V _o2 , and compares V _ox with the reference The voltage V _{o_ref} is compared to control the output voltage to be constant; the mode selection circuit determines the operating mode of the system according to the output v _oe of the output voltage controller. If v _oe <0, the system operates in the dual output mode. If v _oe >0, the system operates in the dual-input mode; the pulse modulation circuit compares the output of the mode selection circuit with the sawtooth wave to generate a pulse signal to control the on and off of the switching tubes S ₁ , S ₂ and S ₃ . It should be noted that the above control circuit is not the only control circuit of the present invention.

Use PSIM simulation software to conduct time domain simulation analysis of the system. The simulation parameters of the system are set as: C _in1 = C _in2 = C ₁ = C ₂ 470μF, C _x = C _y = 1000 μF, L ₁ = L ₂ = L ₃ = 330 μH , the positive polarity output port voltage V _o1 =24V, the negative polarity output port voltage V _o2 =-24V, the energy storage unit voltage V _in2 =30V, the switching frequency is f _s =100kHz, the system simulation results are shown in Figure 7 to Figure 11 .

Figure 7 is the steady-state waveform of the switch drive signal, the current i _L of the inductor L ₁ and the voltage v _L across the inductor of a four-port converter with bipolar output in the dual-input dual-output mode, where Figure 7(a) It is the steady-state waveform of d ₁ >d _2. Figure 7(b) is the steady-state waveform of d ₁ <d _2. It can be seen from the figure that the simulation results are consistent with the theoretical analysis.

Figure 8 is the steady-state waveform of the switch drive signal, the current i _L of the inductor L ₁ and the voltage v _L across the inductor in the single-input three-output mode of a four-port converter with bipolar output. It can be seen from the figure , the simulation results are consistent with the theoretical analysis.

Figure 9 is the transient response waveform of a four-port converter with bipolar output in dual-input and dual-output mode when the load jumps. At this time, the maximum output power of photovoltaic is 75W. At the initial moment, the photovoltaic module outputs at maximum power, and the load The power consumption is 100W, and the power provided by the energy storage unit is 25W. At 0.1s, the load power increases from 100W to 150W. The power provided by the energy storage unit suddenly changes to 75W. At 0.15s, the load power decreases from 150W to 100W. The system operation is consistent with the initial state. It can be seen from the figure that when the load changes, both the positive and negative output voltages remain constant.

Figure 10 is the transient response waveform of a four-port converter with bipolar output in single-input three-output mode when the load jumps. At this time, the maximum output power of photovoltaic is 125W. At the initial moment, the photovoltaic module outputs at maximum power, and the load The power consumption is 100W, and the power absorbed by the energy storage unit is 25W. At 0.1s, the load power decreases from 100W to 50W. The power absorbed by the energy storage unit suddenly changes to 75W. At 0.15s, the load power increases from 50W to 100W. The system The operating conditions are consistent with the initial state. It can be seen from the figure that when the load changes, both the positive and negative output voltages remain constant.

Figure 11 is the simulation waveform of a four-port converter with bipolar output switching between single-input three-output mode and dual-input dual-output mode. At the initial moment, the photovoltaic output is at a maximum power of 125W, and the load power consumption is 100W. The power absorbed by the energy unit is 25W. The system works in single input and three output mode. The maximum output power of photovoltaic suddenly changes from 125W to 50W in 0.1s. The output power of photovoltaic is greater than the power required by the load. In order to ensure the normal operation of the system, the system runs The mode is switched to the dual-input dual-output mode, and the power provided by the energy storage unit is 50W. At 0.15s, the maximum output power of the photovoltaic suddenly changes from 50W to 125W, and the system operation is consistent with the initial state.

According to the above theoretical analysis and simulation, it can be seen that the four-port converter with bipolar output proposed by the present invention has the advantages of simple structure, low cost, high power density, and high system efficiency. It can output symmetrical and common ground The bipolar voltage can connect loads of at least three voltage levels. It has a wide range of applications, high reliability, and few switching devices. It can realize centralized control, making the design of the control circuit simpler. The input and output ports of the converter The voltage relationship between them is flexible and can both boost and step down. Therefore, the converter proposed by the present invention has obvious advantages compared with the existing technology.

Claims (3)

1. Four-port converter with bipolar output, characterized by comprising a DC power source V _in1 And a DC power source V with charging and discharging functions _in2 ；

V _in1 Is connected to the anode of the inductor L ₁ Input terminal L of (1) ₁ Is connected to the switch tube S ₁ Drain electrode of (C) and intermediate storage capacitor C _x Positive electrode of C _x Is connected to the negative electrode of the inductor L ₂ And diode D ₂ Anode of D ₂ Is connected to a load R ₁ Is provided; v (V) _in1 Is a negative electrode of S ₁ Source, L of (2) ₂ Output of (2) and R ₁ The outputs of which are all connected to a reference ground; and also comprises a third connecting part connected in parallel to V _in1 Input filter capacitor C at two ends _in1 And is connected in parallel to R ₁ Output filter capacitor C at two ends ₁ ；

V _in2 Is connected to diode D ₃ Cathode of D ₃ Is connected to the switch tube S ₃ Source of S ₃ Is connected to the intermediate energy storage capacitor C _y Positive electrode of C _y Is connected to diode D ₄ Anode and inductance L of (2) ₃ Input terminal of (2), inductance L ₃ Is connected to the load R ₂ Is provided; v (V) _in2 Negative electrode of D ₄ And R ₂ The outputs of which are all connected to a reference ground; and also comprises a third connecting part connected in parallel to V _in2 Input filter capacitor C at two ends _in2 And is connected in parallel to R ₂ Output filter capacitor C at two ends ₂ ；

Also comprises a diode D ₁ And a switch tube S ₂ ，D ₁ Is connected to L ₁ Input terminal D of (2) ₁ Is connected to S ₂ Source of S ₂ Is connected to D ₃ A cathode of (a);

S ₁ the drain of (2) is also connected to S ₃ Is formed on the drain electrode of the transistor.

2. The four-port converter of claim 1 further comprising a load R ₃ ，R ₃ Are respectively connected to R at both ends ₁ And R is ₂ Is provided.

3. A control method of a four-port converter according to claim 1 or 2, characterized in that the switching tube S is always turned off ₃ The converter is operated in a dual-input dual-output mode; alternatively, the switching tube S is always turned off ₂ The inverter is operated in a single-input three-output mode.