Topology and control method of power device multiplexing type full-bridge modular multilevel converter

Abstract

The topology and control method of a power device multiplexing type full-bridge modular multilevel converter are disclosed. The converter consists of three phases and six bridge arms. Each phase consists of upper and lower bridge arms. Each bridge arm is composed of a bridge arm inductor and N structurally identical sub-modules connected in series. Each sub-module consists of a first power switch S1, a second power switch S2, a third power switch S3, a fourth power switch S4, a common capacitor C, and a decoupling capacitor C. dp and decoupling inductor L dp The circuit consists of four power switching devices, each with its own reverse diode; four power switching devices and a common capacitor C form a full-bridge circuit; and the third power switching device S3, the fourth power switching device S4, the common capacitor C, and the decoupling capacitor C... dp and decoupling inductor L dp This forms an active filter decoupling circuit.

Description

Technical fields:

[0001] This invention relates to the field of power electronic multilevel converters. Background technology:

[0002] Increasing the voltage level of power transmission is crucial for improving the efficiency of long-distance power transmission. Traditional two-level converters are no longer suitable for long-distance high-voltage transmission. In recent years, modular multilevel converters have gained widespread application because they can be easily expanded to higher voltage levels and rated power without increasing control complexity or uneven loss distribution, and they do not require the addition of transformers. Modular multilevel converters have attracted widespread attention and have been applied in the field of flexible DC transmission due to their high modularity, strong scalability, easy modification of voltage and power, high output waveform quality, and low switching frequency and voltage stress of power switching devices.

[0003] During the operation of a modular multilevel converter, the submodule capacitors need to withstand power fluctuations of the fundamental and second harmonics. As a result, the capacitor voltage will fluctuate, and the amplitude of the voltage fluctuation is inversely proportional to the frequency of the AC output current. When the frequency is low, the fluctuation amplitude is very large, which places high demands on capacitor performance, increases costs, and large voltage fluctuations may damage switching devices. Therefore, it is necessary to take measures to reduce the voltage ripple of the submodule capacitors. Summary of the Invention:

[0004] The technical problem to be solved by this invention is to reduce capacitor voltage ripple in traditional submodules, and to provide a full-bridge modular multilevel converter topology with an additional active filter decoupling circuit and a control strategy based on this topology, thereby achieving the effects of reducing ripple, protecting power switching devices, and reducing costs.

[0005] To solve the above-mentioned technical problems, the specific technical solution adopted by the present invention is as follows:

[0006] A topology for a power device multiplexing type full-bridge modular multilevel converter is provided. The converter consists of three phases and six bridge arms. Each phase consists of upper and lower bridge arms. Each bridge arm consists of one bridge arm inductor and N structurally identical sub-modules connected in series. The sub-modules are characterized by comprising a first power switch S1, a second power switch S2, a third power switch S3, a fourth power switch S4, a common capacitor C, and a decoupling capacitor C. dp and decoupling inductor L dp The power switching devices are all equipped with a reverse diode.

[0007] In the submodule, the first power switch S1 and the second power switch S2 are connected in series as the first series bridge arm, and the third power switch S3 and the fourth power switch S4 are connected in series as the second series bridge arm. The first series bridge arm, the second series bridge arm, and the common capacitor C are connected in parallel. The input terminal of the submodule is located between the first power switch S1 and the second power switch S2, and the output terminal of the submodule is located between the third power switch S3 and the fourth power switch S4. The outer terminal of the fourth power switch S4 in the second series bridge arm is connected to the decoupling inductor L. dp and decoupling capacitor C dp Series decoupling capacitor C dp Connected to the output of the submodule, the four power switching devices and the common capacitor C form a full-bridge circuit; the third power switching device S3, the fourth power switching device S4, the common capacitor C, and the decoupling capacitor C dp and decoupling inductor L dp This forms an active filter decoupling circuit.

[0008] This invention also provides a control method for a power device multiplexing type full-bridge modular multilevel converter. The method is characterized in that the control signal for the four power switching devices is composed of two PWM waves. The first PWM wave causes the submodule to operate in two states: a first operating state where the first power switching device S1 and the third power switching device S3 are on, and the second power switching device S2 and the fourth power switching device S4 are off; and a second operating state where the first power switching device S1 and the fourth power switching device S4 are on, and the second power switching device S2 and the third power switching device S3 are off. The second PWM wave operates only in the first operating state. Under the control of the modulation signal, it switches from the first operating state where the first power switching device S1 and the third power switching device S3 are on, and the second power switching device S2 and the fourth power switching device S4 are off, to the third operating state where the first power switching device S1 and the third power switching device S3 are off, and the second power switching device S2 and the fourth power switching device S4 are on, and then switches back to the first operating state, repeating this cycle. The first PWM wave is obtained by comparing the output voltage value of the modular multilevel converter with the first triangular carrier wave; the second PWM wave is obtained by the decoupling capacitor C in the active filter decoupling circuit. dp The voltage value was compared with the second triangular carrier frequency, and it was found that the second triangular carrier frequency was higher than the first triangular carrier frequency.

[0009] The present invention also provides a method for suppressing the voltage ripple of the submodule capacitors in the power device multiplexed full-bridge modular multilevel converter, wherein the control method includes the following steps:

[0010] Step 1: When the submodule is in the second working state (S1 and S4 are on, S2 and S3 are off), the DC power supply supplies power to the common capacitor C to charge it.

[0011] Step 2: When the submodule is in its first operating state (S1 and S3 are on, S2 and S4 are off), the DC power supply stops supplying power to the common capacitor C. When the voltage of the common capacitor C is greater than the reference voltage of the submodule, the power in the common capacitor C is transferred to the decoupling capacitor C in the active filter decoupling circuit. dp and decoupling inductor L dp Transfer.

[0012] Step 3: When the submodule switches to the third operating state (S1 and S3 are off, S2 and S4 are on), the common capacitor C no longer supplies power to the decoupling capacitor C. dp and decoupling inductor L dp Power transfer, decoupling inductor L dp The decoupling capacitor C is connected to the parallel diode of the fourth power switching device S4. dp Transmitting its own stored power, decoupling capacitor C dp Then decoupling inductor L dp Transfer power.

[0013] Step 4: When the common capacitor C requires energy from the active filter decoupling circuit, the submodule switches to the first operating state (S1 and S3 are on, S2 and S4 are off), and the decoupling capacitor C... dp and decoupling inductor L dp The stored power is transferred to the common capacitor C.

[0014] The topology of the power device multiplexing type full-bridge modular multilevel converter proposed in this invention is achieved by adding a decoupling capacitor C in the active filter decoupling circuit. dp The voltage is compared with the second triangular carrier wave to obtain the modulation signal. The modulation signal is used to control the power switching device to achieve the decoupling of the decoupling capacitor C in the active filter decoupling circuit. dp Voltage control transfers energy from the common capacitor C, reducing its voltage ripple. Lowering ripple reduces the cost and size of the submodule's capacitor section, improves the safety of switching devices, and makes them less susceptible to damage from capacitor ripple. Attached Figure Description

[0015] Figure 1 This is the main circuit topology diagram of the power device multiplexing type full-bridge modular multilevel converter provided in the embodiment of the present invention.

[0016] Figure 2 This is a submodule structure topology diagram of the power device multiplexing type full-bridge modular multilevel converter provided in the embodiment of the present invention.

[0017] Figure 3 This is a flowchart of the control strategy for a power device multiplexing type full-bridge modular multilevel converter provided in an embodiment of the present invention.

[0018] The implementation method of the present invention will be described in detail below with reference to the embodiments and accompanying drawings: Example

[0019] This embodiment provides a power device multiplexing type full-bridge modular multilevel converter. The converter consists of three phases and six bridge arms. Each phase consists of upper and lower bridge arms. Each bridge arm is composed of a bridge arm inductor and N structurally identical sub-modules connected in series. The sub-modules consist of a first power switch device S1, a second power switch device S2, a third power switch device S3, a fourth power switch device S4, a common capacitor C, and a decoupling capacitor C. dp and decoupling inductor L dp The power switching devices are all equipped with a reverse diode.

[0020] In the submodule, the first power switch S1 and the second power switch S2 are connected in series as the first series bridge arm, and the third power switch S3 and the fourth power switch S4 are connected in series as the second series bridge arm. The first series bridge arm, the second series bridge arm, and the common capacitor C are connected in parallel. The input terminal of the submodule is located between the first power switch S1 and the second power switch S2, and the output terminal of the submodule is located between the third power switch S3 and the fourth power switch S4. The outer terminal of the fourth power switch S4 in the second series bridge arm is connected to the decoupling inductor L. dp and decoupling capacitor C dp Series decoupling capacitor C dp Connected to the output of the submodule, the four power switching devices and the common capacitor C form a full-bridge circuit; the third power switching device S3, the fourth power switching device S4, the common capacitor C, and the decoupling capacitor C dp and decoupling inductor L dp This forms an active filter decoupling circuit.

[0021] The main circuit topology of the power device multiplexed full-bridge modular multilevel converter is as follows: Figure 1 As shown, the submodule topology diagram is as follows: Figure 2 As shown.

[0022] The control strategy for the power device multiplexing type full-bridge modular multilevel converter is as follows:

[0023] The control signals for the four power switching devices are composed of two PWM waves. The first PWM wave (PWM wave 1) causes the submodule to operate in two states: the first state is that the first power switching device S1 and the third power switching device S3 are on, while the second power switching device S2 and the fourth power switching device S4 are off; the second state is that the first power switching device S1 and the fourth power switching device S4 are on, while the second power switching device S2 and the third power switching device S3 are off. The second PWM wave (PWM wave 2) only operates in the first state. Under the control of the modulation signal, it switches from the first state (first power switching device S1 and the third power switching device S3 are on, second power switching device S2 and the fourth power switching device S4 are off) to the third state (first power switching device S1 and the third power switching device S3 are off, second power switching device S2 and the fourth power switching device S4 are on), and then switches back to the first state, repeating this cycle. The first PWM wave is obtained by comparing the output voltage value of the modular multilevel converter with the first triangular carrier wave; the second PWM wave is obtained by the decoupling capacitor C in the active filter decoupling circuit. dp The voltage value is compared with the second triangular carrier frequency, which is higher than the first triangular carrier frequency. The flowchart of the control strategy is as follows: Figure 3 As shown.

[0024] The submodule capacitor voltage ripple suppression method for the power device multiplexed full-bridge modular multilevel converter includes the following steps:

[0025] Step 1: When the submodule is in the second working state (S1 and S4 are on, S2 and S3 are off), the DC power supply supplies power to the common capacitor C to charge it.

[0026] Step 2: When the submodule is in its first operating state (S1 and S3 are on, S2 and S4 are off), the DC power supply stops supplying power to the common capacitor C. When the voltage of the common capacitor C is greater than the reference voltage of the submodule, the power in the common capacitor C is transferred to the decoupling capacitor C in the active filter decoupling circuit. dp and decoupling inductor L dp Transfer.

[0027] Step 3: When the submodule switches to the third operating state (S1 and S3 are off, S2 and S4 are on), the common capacitor C no longer supplies power to the decoupling capacitor C. dp and decoupling inductor L dp Power transfer, decoupling inductor L dp The decoupling capacitor C is connected to the parallel diode of the fourth power switching device S4. dp Transmitting its own stored power, decoupling capacitor C dp Then decoupling inductor L dp Transfer power.

[0028] Step 4: When the common capacitor C requires energy from the active filter decoupling circuit, the submodule switches to the first operating state (S1 and S3 are on, S2 and S4 are off), and the decoupling capacitor C... dp and decoupling inductor L dp The stored power is transferred to the common capacitor C.

Claims

1. A power device multiplexing type full-bridge modular multilevel converter, wherein the converter consists of three phases and six bridge arms, each phase consists of upper and lower bridge arms, and each bridge arm consists of one bridge arm inductor and N structurally identical sub-modules connected in series, characterized in that, The submodule consists of a first power switch S1, a second power switch S2, a third power switch S3, a fourth power switch S4, a common capacitor C, and a decoupling capacitor C. dp and decoupling inductor L dp The power switching devices are all equipped with a reverse diode. In the submodule, the first power switch S1 and the second power switch S2 are connected in series as the first series bridge arm, and the third power switch S3 and the fourth power switch S4 are connected in series as the second series bridge arm. The first series bridge arm, the second series bridge arm, and the common capacitor C are connected in parallel. The input terminal of the submodule is located between the first power switch S1 and the second power switch S2, and the output terminal of the submodule is located between the third power switch S3 and the fourth power switch S4. Between the drain and source of the fourth power switching device S4 in the second series bridge arm and the decoupling inductor L dp and decoupling capacitor C dp Series followed by parallel connection, decoupling capacitor C dp Connected to the output of the submodule, the four power switching devices and the common capacitor C form a full-bridge circuit; the third power switching device S3 and the fourth power switching device S4 Common capacitor C, decoupling capacitor C dp and decoupling inductor L dp This constitutes an active filter decoupling circuit; The control method for the power device multiplexing type full-bridge modular multilevel converter is as follows: the control signal for the four power switching devices is composed of two PWM waves. The first PWM wave causes the submodule to operate in two states: the first operating state is that the first power switching device S1 and the third power switching device S3 are turned on, and the second power switching device S2 and the fourth power switching device S4 are turned off; the second operating state is that the first power switching device S1 and the fourth power switching device S4 are turned on, and the second power switching device S2 and the third power switching device S3 are turned off; the second... The PWM wave operates only in the first operating state. Under the control of the modulation signal, it switches from the first operating state where the first power switch S1 and the third power switch S3 are turned on and the second power switch S2 and the fourth power switch S4 are turned off to the third operating state where the first power switch S1 and the third power switch S3 are turned off and the second power switch S2 and the fourth power switch S4 are turned on, and then switches back to the first operating state, and so on. The first PWM wave is obtained by comparing the output voltage value of the modular multilevel converter with the first triangular carrier wave. The second PWM wave passes through the decoupling capacitor C in the active filter decoupling circuit. dp The voltage value was compared with the second triangular carrier frequency, and it was found that the second triangular carrier frequency was higher than the first triangular carrier frequency.

2. The method for suppressing submodule capacitor voltage ripple in a power device multiplexing type full-bridge modular multilevel converter as described in claim 1, characterized in that: The suppression method includes the following steps: Step 1: When the submodule is in the second working state, the DC power supply supplies power to charge the common capacitor C; Step 2: When the submodule is in its first operating state, the DC power supply stops supplying power to the common capacitor C. When the voltage of the common capacitor C is greater than the reference voltage of the submodule, the power in the common capacitor C is transferred to the decoupling capacitor C in the active filter decoupling circuit. dp and decoupling inductor L dp Transfer; Step 3: When the submodule switches to the third working state, the common capacitor C no longer supplies power to the decoupling capacitor C. dp and decoupling inductor L dp Power transfer, decoupling inductor L dp The decoupling capacitor C is connected to the parallel diode of the fourth power switching device S4. dp Transmitting its own stored power, decoupling capacitor C dp Then decoupling inductor L dp Power transfer; Step 4: When the common capacitor C requires energy from the active filter decoupling circuit, the submodule switches to the first operating state, and the decoupling capacitor C... dp and decoupling inductor L dp The stored power is transferred to the common capacitor C.

Images