A flying capacitor voltage equalization interconnection circuit

Abstract

The application discloses a flying capacitor voltage equalization interconnection circuit, comprising a conversion module and an equalization module, the conversion module is a two-phase or more than two-phase N-level flying capacitor conversion circuit, and the N-level flying capacitor conversion circuit comprises a plurality of conversion bridge arms, each conversion bridge arm comprises N-2 flying capacitors, the equalization module comprises a plurality of diode rectifier bridge arms, and the plurality of diode rectifier bridge arms are connected in parallel to both ends of each flying capacitor; the diode rectifier bridge arm is composed of two diodes connected in series; the diode rectifier bridge arms connected in parallel to each flying capacitor of each conversion bridge arm and the diode rectifier bridge arms connected in parallel to one flying capacitor of the next switching bridge arm form an interconnection group, the midpoints of the two diode rectifier bridge arms in the interconnection group are connected to each other through wires, and the sum of the levels of the flying capacitors corresponding to the two diode rectifier bridge arms is N-1; when N is an odd number, the midpoints of the diode rectifier bridge arms connected in parallel to the middle-level flying capacitors of all the conversion bridge arms are connected together.

Description

Technical Field

[0001] This invention relates to the field of power conversion technology, and in particular to a flying capacitor voltage equalization interconnection circuit. Background Technology

[0002] The flying capacitor multilevel converter topology has significant advantages such as simple circuit, few components, low loss, and frequency multiplication output, and therefore has received increasing attention in the field of high-efficiency and high-power-density power conversion. The N-level flying capacitor converter bridge arm consists of (2N-2) switches and (N-2) flying capacitors connected in series. The two ends of the bridge arm are connected to the positive and negative terminals of the DC port. The N-1 switches from the midpoint of the bridge arm to the DC positive terminal are Q1 to Qn-1, forming the upper bridge arm. The N-1 switches from the midpoint of the bridge arm to the DC negative terminal are Q1b to Qn-1b, forming the lower bridge arm. The N-2 flying capacitors are connected from the outside of the Q1 to Qn-2 switches relative to the midpoint of the bridge arm to the outside of the Q1b to Qn-2b switches. According to the target voltage level, they form the first-stage flying capacitor, the second-stage flying capacitor, and so on up to the n-2-stage flying capacitor. Their voltages are 1 / (N-1), 2 / (N-1), and so on up to (N-2) / (N-1) of the bridge arm DC voltage, respectively. During the operation of the switch bridge arm, the operating voltage of each switch is only 1 / (N-1) of the DC voltage of the bridge arm. Through the combination of the on and off states of (2N-2) switches, N different voltage levels relative to the positive or negative DC port are generated at the midpoint of the bridge arm.

[0003] For flying capacitor multilevel converters, capacitor voltage equalization, i.e., the approximation of the actual voltage to the target voltage, is a key technical point and the foundation for reducing voltage stress on switching devices and improving the output current waveform. However, in power conversion systems, input / output voltage or DC bus voltage variations are frequent, some of which are characterized by large amplitude and rapid speed. This poses a challenge to the flying capacitor multilevel converter's ability to track the target voltage, especially when the load current is small. The regulation capability of the flying capacitor voltage is weak, leading to voltage imbalance and increased switching stress, which can even damage the switching devices in severe cases. This problem has seriously hindered the widespread application of flying capacitor multilevel converters. Summary of the Invention

[0004] The purpose of this invention is to provide a flying capacitor voltage equalization interconnection circuit, which has the advantage of enabling each flying capacitor to quickly adjust to the target voltage, especially when the DC bus voltage rises rapidly, ensuring that the flying capacitor voltage follows quickly.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0006] A flying capacitor voltage equalization interconnection circuit includes: a conversion module and an equalization module. The conversion module is a two-phase or more N-level flying capacitor conversion circuit, and the N-level flying capacitor conversion circuit includes multiple conversion bridge arms. Each conversion bridge arm includes N-2 flying capacitors with progressively increasing operating voltages. The equalization module includes multiple diode rectifier bridge arms, and the multiple diode rectifier bridge arms are respectively connected in parallel across each flying capacitor. Each diode rectifier bridge arm is composed of two diodes connected in series.

[0007] Each of the flying capacitors of each of the aforementioned conversion bridge arms forms an interconnection group with the diode rectifier bridge arm connected in parallel with the flying capacitor of one of the stages of another switching bridge arm. The midpoints of the two diode rectifier bridge arms in each interconnection group are connected to each other by a wire, and the sum of the stages of the flying capacitors corresponding to the two diode rectifier bridge arms is N-1.

[0008] When N is odd, the midpoints of the diode rectifier bridge arms connected in parallel with the intermediate stage flying capacitors of all the transformer bridge arms are connected together.

[0009] Further configuration: When the switching frequencies of multiple conversion bridge arms are consistent, there is a phase difference between adjacent conversion bridge arms.

[0010] Further setting: The phase difference is specifically 180 degrees.

[0011] Further setting: The phase difference is specifically 360 / m degrees, where m is the number of transform arms.

[0012] Further configuration: A low-value resistor is provided on the wire between the two diode rectifier bridge arms within the interconnect group.

[0013] Further configuration: The midpoints of the diode rectifier bridge arms connected in parallel with the intermediate stage flying capacitor are connected together and then connected to the midpoint of the DC bus through a low-value resistor.

[0014] In summary, this invention offers the following advantages: By connecting the flying capacitors in series and then to the DC bus within each switching cycle through the interconnection circuit, each flying capacitor can quickly adjust to the target voltage, especially ensuring rapid voltage follow-up when the DC bus voltage rises rapidly. For two or more bridge arms of asynchronous switches, the speed at which the flying capacitor voltage tracks changes in DC voltage is influenced by the phase shift angle between the bridge arms, exhibiting strong balancing capability even with significant phase differences. Placing a low-value resistor between two diode rectifier bridge arms in the same interconnection group can suppress current spikes during switching, thus improving EMI. Connecting the midpoints of the diode rectifier bridge arms corresponding to the intermediate stage capacitors in parallel and then to the midpoint of the DC bus through a low-value resistor helps accelerate the approach of the flying capacitor voltage to the target value. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a four-level flying capacitor converter;

[0016] Figure 2 This is a schematic diagram of a five-level flying capacitor converter;

[0017] Figure 3 This is a schematic diagram illustrating the effect of the flying capacitor voltage on the DC voltage surge when the present invention is not used;

[0018] Figure 4 This is a schematic diagram illustrating the effect of the flying capacitor voltage on the DC voltage surge after adopting this invention;

[0019] Figure 5 This is a schematic diagram of a three-level flying capacitor converter that uses low-value resistors. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the accompanying drawings.

[0021] Example 1:

[0022] A flying capacitor voltage equalization interconnection circuit includes: a conversion module and an equalization module. The conversion module is a two-phase or more N-level flying capacitor conversion circuit, and the N-level flying capacitor conversion circuit includes multiple conversion bridge arms. Each conversion bridge arm includes N-2 flying capacitors with progressively increasing operating voltages. The equalization module includes multiple diode rectifier bridge arms, and the multiple diode rectifier bridge arms are respectively connected in parallel across each flying capacitor. Each diode rectifier bridge arm is composed of two diodes connected in series.

[0023] Each of the flying capacitors in each of the aforementioned switching bridge arms forms an interconnection group with the diode rectifier bridge arm connected in parallel with the flying capacitor in one of the stages of another switching bridge arm. The midpoints of the two diode rectifier bridge arms in each interconnection group are connected to each other by wires, and the sum of the stages of the flying capacitors corresponding to the two diode rectifier bridge arms is N-1. That is, the midpoint of the diode rectifier bridge arm connected in parallel with the highest stage of the flying capacitor in each switching bridge arm is connected to the midpoint of the diode rectifier bridge arm connected in parallel with the lowest stage of the flying capacitor in the next switching bridge arm by wires, and the midpoint of the diode rectifier bridge arm connected in parallel with the next stage of the flying capacitor is connected to the midpoint of the diode rectifier bridge arm connected in parallel with the second-to-last stage of the flying capacitor in the next switching bridge arm by interconnecting wires, and so on until the midpoints of the diode bridge arms connected in parallel with the flying capacitors of all stages are interconnected.

[0024] like Figure 1As shown, in a four-level flying capacitor converter, the midpoint of the diode bridge arm connected in parallel with the highest-level flying capacitor in each switching bridge arm is connected via an interconnecting line to the midpoint of the diode bridge arm connected in parallel with the lowest-level flying capacitor in the next switching bridge arm. Specifically, the midpoint of diode rectifier bridge arm M2 in switching bridge arm P4# is connected to the midpoint of diode rectifier bridge arm M1 in switching bridge arm P1#; the midpoint of diode rectifier bridge arm M2 in switching bridge arm P1# is connected to the midpoint of diode rectifier bridge arm M1 in switching bridge arm P2#; the midpoint of diode rectifier bridge arm M2 in switching bridge arm P2# is connected to the midpoint of diode rectifier bridge arm M1 in switching bridge arm P3#; and the midpoint of diode rectifier bridge arm M2 in switching bridge arm P3# is connected to the midpoint of diode rectifier bridge arm M1 in switching bridge arm P4#. The principle of fast tracking of flying capacitor voltage equalization: There is a time interval between the two phase arms of the asynchronous switch so that Q1 of one arm and Q4 of the other arm can be turned on at the same time. This allows the flying capacitors of the two arms to be connected in series between the positive and negative terminals of the DC bus of the system through auxiliary diodes and interconnects. As a result, when the DC voltage of the system rises rapidly, the voltage of the flying capacitor also increases synchronously and rapidly.

[0025] When N is odd, the midpoints of the diode rectifier bridge arms connected in parallel with the intermediate-stage flying capacitors of all switching bridge arms are connected together. For switching bridge arms with an odd number of flying capacitor stages, such as 3-level, 5-level, or 7-level switching bridge arms, there is an intermediate-stage flying capacitor whose voltage is half the parallel DC bus voltage of the switching bridge arms. The midpoints of the diode rectifier bridge arms connected in parallel with the intermediate capacitors of all switching bridge arms are connected together. For example... Figure 2 As shown, in a five-level flying capacitor converter, the midpoint of the diode bridge arm connected in parallel with the highest-level flying capacitor in each switching bridge arm is connected via an interconnecting line to the midpoint of the diode bridge arm connected in parallel with the lowest-level flying capacitor in the next switching bridge arm. The midpoint of the diode bridge arm connected in parallel with the next-highest-level flying capacitor is connected via an interconnecting line to the midpoint of the diode bridge arm connected in parallel with the second-to-last-level flying capacitor in the next switching bridge arm. That is, the target voltage of the intermediate-level flying capacitors in the five-level flying capacitor converter is half the DC bus voltage of the switching bridge arm. The midpoints of the balancing diode bridge arms of all intermediate-level flying capacitors in the switching bridge arms are connected together. Specifically, the midpoints of the diode rectifier bridge arms M2 of switching bridge arms P1#, P2#, and P3# are interconnected.

[0026] In a three-phase interleaved parallel flying capacitor three-level DC-DC converter, without diode rectifier bridge arms and their midpoint interconnection circuits, the response speed of the flying capacitor voltage to a DC voltage surge is as follows: Figure 3 As shown, the response speed is very slow, exceeding 100ms, resulting in Q1 and Q4 switches experiencing voltages far higher than half the DC bus voltage during this 100ms period. Figure 4It can be seen that, after adopting the diode rectifier bridge arm and its midpoint interconnection circuit of the present invention, the response of the flying capacitor voltage to the DC voltage surge can be shortened to less than 80µs.

[0027] Example 2:

[0028] like Figure 5 As shown, a low-value resistor is placed on the conductor between two diode rectifier bridge arms within the same interconnect group. The midpoints of the diode rectifier bridge arms connected in parallel with the intermediate stage flying capacitor are connected together and then connected to the midpoint of the DC bus through the low-value resistor. By using a common resistor, i.e., a low-value resistor, to connect the midpoint of the DC bus to the midpoints of all the diode bridge arms, a voltage reference point can be provided for the voltage balance of the flying capacitor, reducing voltage balance deviation.

[0029] The embodiments described above do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the above embodiments should be included within the scope of protection of this technical solution.

Claims

1. A flying capacitor voltage equalization interconnection circuit, characterized in that, include: The system includes a conversion module and an equalization module. The conversion module is a two-phase or more N-level flying capacitor conversion circuit, and the N-level flying capacitor conversion circuit includes multiple conversion bridge arms. Each conversion bridge arm contains N-2 flying capacitors with progressively increasing operating voltages. The equalization module includes multiple diode rectifier bridge arms, and the multiple diode rectifier bridge arms are connected in parallel across each flying capacitor. Each diode rectifier bridge arm is composed of two diodes connected in series. Each of the flying capacitors of each of the aforementioned conversion bridge arms forms an interconnection group with the diode rectifier bridge arm connected in parallel with the flying capacitor of one of the stages of another switching bridge arm. The midpoints of the two diode rectifier bridge arms in each interconnection group are connected to each other by a wire, and the sum of the stages of the flying capacitors corresponding to the two diode rectifier bridge arms is N-1. When N is odd, the midpoints of the diode rectifier bridge arms connected in parallel with the intermediate stage flying capacitors of all the transformer bridge arms are connected together.

2. The flying capacitor voltage equalization interconnection circuit according to claim 1, characterized in that, When the switching frequencies of multiple switching bridge arms are the same, there is a phase difference between adjacent switching bridge arms.

3. The flying capacitor voltage equalization interconnection circuit according to claim 2, characterized in that, The phase difference is specifically 180 degrees.

4. The flying capacitor voltage equalization interconnection circuit according to claim 2, characterized in that, The phase difference is specifically 360 / m degrees, where m is the number of transform arms.

5. The flying capacitor voltage equalization interconnection circuit according to claim 1, characterized in that, A low-value resistor is provided on the wire between the two diode rectifier bridge arms in the interconnect group.

6. The flying capacitor voltage equalization interconnection circuit according to claim 1, characterized in that, The midpoints of the diode rectifier bridge arms connected in parallel with the intermediate stage flying capacitor are then connected together and connected to the midpoint of the DC bus through a low-value resistor.

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