A method and device for stabilizing DC side voltage of inverter

Abstract

The present invention discloses a DC side voltage stabilization method for an inverter, wherein the d-axis and q-axis of the inverter voltage control loop are provided with voltage feedforward links respectively, and the voltage feedforward link includes a filter with an adjustable center frequency and a dynamic gain coefficient, and the filter ranges of the filters on the d-axis and the q-axis are different; the voltage feedforward link uses the oscillation frequency component of the inverter input voltage as an introduction signal, and obtains the corresponding voltage feedforward signal according to the disturbance component output by the inverter input voltage through the filter and the dynamic gain coefficient, and superimposes the voltage feedforward signal on the modulation wave to reshape the input impedance of the inverter. The present invention also provides a DC side voltage stabilization device. The method provided by the present invention introduces voltage feedforward links for the d-axis and q-axis of the voltage control loop respectively, and constructs a voltage feedforward for reshaping the inverter input impedance according to the voltage change at the inverter input end, thereby ensuring the stability of the DC side voltage.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current power supply systems, and in particular to a method and device for stabilizing direct current side voltage of an inverter. Background Art

[0002] In recent years, DC power supply systems have been widely used in smart buildings, ships, power supply centers and other fields. As the power level of DC power supply systems continues to increase, its stability issues have also received increasing attention. In practical applications, due to the increasing load and increased volatility introduced on the DC bus, the superposition of inverters and DC converters often makes the DC bus voltage unable to remain stable or even oscillates significantly, which seriously threatens the stable operation of the DC power supply system. To address this problem, for low-power DC power supply systems, there are some methods that sacrifice dynamic performance to ensure stability, such as modifying controller parameters, etc. There are also methods that achieve stability by introducing external devices, but additional costs are introduced and power density and efficiency are reduced. In addition, there are also methods that introduce external controllers: using various filters to feed forward the input voltage, but there is a contradiction between DC side stability and output power quality, and the effect is poor in high-power occasions.

[0003] Patent document CN114421496A discloses a method for suppressing low-frequency oscillation of a DC distribution network based on a bidirectional power converter, including obtaining the operating parameters of the DC distribution network; judging whether the system is stable; constructing a low-frequency oscillation suppression module and adjusting the module parameters; obtaining the DC side output current of the bidirectional power converter and inputting it into the adjusted low-frequency oscillation suppression module to obtain the original compensation current of the DC distribution, and obtaining the compensation current of the DC distribution network after limiting; superimposing the compensation current of the DC distribution network to the current inner loop of the bidirectional power converter to complete the low-frequency oscillation suppression of the DC distribution network based on the bidirectional power converter. This method achieves the stabilization of the DC voltage of the DC distribution network without adding external hardware circuits and changing the steady-state operation characteristics of the DC distribution network, and reduces the risk of oscillation instability in the DC distribution network. This method uses a combination of a first-order low-pass and a first-order high-pass to feed forward the output current on the d-axis for AC side instability.

[0004] Patent document CN111953251A discloses a method for stabilizing the DC side voltage of a traction converter, including: obtaining a DC side capacitor voltage from a traction converter; filtering the DC side capacitor voltage to obtain a DC component of the DC side capacitor voltage; calculating the oscillating component of the DC side capacitor voltage, and calculating the influence of the oscillating component on the voltage; in torque control, calculating the influence of the torque component voltage output by the current loop decoupling part on the DC side voltage; feeding forward the DC side capacitor voltage oscillating component and the output torque component voltage to the torque control command to implement feedforward regulation and obtain a corrected torque command. This method is only applicable to traction converters.

[0005] As the demand for electricity increases, the types of loads connected to a power supply system also increase, resulting in oscillations in the circuits of the power supply system, thus affecting the stable operation of the power supply system. At present, the common solution is to add an additional controller to the system for regulation, but the addition of equipment can be regarded as connecting another load to the circuit, which will affect the power density and efficiency of the power supply; there is also a method of introducing a feedforward signal to compensate for the current to offset the oscillation phenomenon in the current circuit, but this direct introduction of the feedforward signal is only suitable for low-power power supply systems, while in high-power power supply systems there is a contradiction between system stability and output power quality. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a DC side voltage stabilization method for an inverter, which can achieve DC side voltage stabilization without introducing an additional controller to control the inverter.

[0007] A method for stabilizing the DC side voltage of an inverter, wherein the d-axis and q-axis of the inverter voltage control loop are respectively provided with a voltage feedforward link, wherein the voltage feedforward link comprises a filter with an adjustable center frequency and a dynamic gain coefficient, and the filtering ranges of the filters on the d-axis and the q-axis are different; the voltage feedforward link uses an oscillation frequency component of the inverter input voltage as an introduction signal, performs scaling adjustment based on the disturbance component output by the inverter input voltage through the filter in combination with the dynamic gain coefficient to obtain a corresponding voltage feedforward signal, and superimposes the voltage feedforward signal on the modulation wave to reshape the input impedance of the inverter.

[0008] The present invention sets voltage feedforward links for the d-axis and q-axis of the voltage control loop respectively, extracts the disturbance component in the current input voltage through a filter, processes the disturbance component in combination with a dynamic gain coefficient to obtain a corresponding voltage feedforward signal, and superimposes the voltage feedforward signal on the modulation wave to reshape the input impedance of the inverter.

[0009] Specifically, the filter includes a bandpass filter arranged on the d-axis of the voltage control loop and a high-pass filter arranged on the q-axis of the voltage control loop;

[0010] The center frequency of the bandpass filter is consistent with the oscillation frequency component;

[0011] The center frequency of the high-pass filter is 1 / 10 to 1 / 5 of the vibration frequency component.

[0012] Specifically, the bandpass filter is a second-order filter, and its expression is as follows:

[0013]

[0014] In the formula, G f (s) represents the bandpass filter expression, ω d represents the center frequency of the bandpass filter, ξ represents the damping coefficient, and s represents the complex frequency.

[0015] Specifically, the high-pass filter is a second-order filter, and its expression is as follows:

[0016]

[0017] In the formula, G f1 (s) represents the high-pass filter expression, ω g represents the center frequency of the high-pass filter, ξ represents the damping coefficient, and s represents the complex frequency.

[0018] Preferably, the scaling adjustment size of the dynamic gain coefficient is jointly determined based on the input voltage level, the converter power level and the output side power quality. Since an increase in the gain coefficient is beneficial to improving the stability of the DC side but will deteriorate the output power quality, it is necessary to consider the input voltage level, the converter power level and the output side power quality at the same time to constrain the adjustment size, thereby achieving stability on the DC side without affecting the output power quality.

[0019] Specifically, the scaling adjustment size of the dynamic gain coefficient is set with an upper limit value, and the upper limit value is the largest dynamic gain coefficient selected when the output current THD value after scaling adjustment satisfies less than 5%.

[0020] Specifically, the DC side voltage stabilization method has the following specific process:

[0021] Step 1: Collect the input voltage of the inverter and analyze it through fast Fourier transform:

[0022] If there is oscillation in the input voltage, the oscillation frequency component in the input voltage is extracted;

[0023] If there is no vibration in the input voltage, the subsequent steps of adjustment are not performed;

[0024] Step 2: extract the oscillation frequency component according to step 1, separate the input voltage with oscillation through a filter, and obtain the corresponding disturbance component;

[0025] Step 3: Scaling and adjusting the disturbance component obtained in step 2 through a dynamic gain coefficient to obtain a corresponding voltage feedforward signal;

[0026] Step 4: Superimpose the voltage feedforward signal obtained in step 3 on the corresponding dq axis, combine it with the modulation wave output by the voltage control link, and reshape the input impedance of the inverter.

[0027] The present invention also provides a DC side voltage stabilization device, comprising a computer memory, a computer processor, and a computer program stored in the computer memory and executable on the computer processor, wherein the computer memory executes the above-mentioned DC side voltage stabilization method for an inverter; when the computer processor executes the computer program, the following steps are implemented: collecting the current input voltage of the inverter, adjusting the voltage control loop through the DC side voltage stabilization method, and completing the reshaping of the input impedance of the inverter.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The present invention simultaneously introduces different voltage feedforwards into the dq axes of the voltage control loop, thereby resolving the contradiction between system stability and output power quality when a single feedforward link is added in a high-power scenario, thereby achieving DC side voltage stability.

[0030] (2) By setting the upper limit of the amplification factor of the dynamic gain coefficient, the requirements of system stability and output power quality can be met at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of the structure of a DC power supply system provided in this embodiment;

[0032] Figure 2 A schematic diagram of a flow chart of a method for stabilizing the DC side voltage of an inverter provided by the present invention;

[0033] Figure 3 A schematic diagram of introducing a feedforward signal for the DC side voltage stabilization device provided in this embodiment. DETAILED DESCRIPTION

[0034] like Figure 1 As shown, a DC power supply system provided in this embodiment is shown. The system includes a DC bus for providing a power supply voltage, and multiple inverters and converters with EMI filters are connected in parallel on both sides of the bus, as well as a DC load at the terminal, wherein the dq axes of the inverter voltage control loop are respectively provided with a voltage feedforward link, and the voltage feedforward link includes a bandpass filter arranged on the d axis of the voltage control loop, a high-pass filter arranged on the q axis of the voltage control loop, and a dynamic gain coefficient for adjusting the amplification.

[0035] The voltage feedforward link uses the oscillation frequency component of the inverter input voltage as the introduction signal, and obtains the corresponding voltage feedforward signal by scaling and adjusting the disturbance component of the inverter input voltage output through the filter combined with the dynamic gain coefficient. Finally, the voltage feedforward superimposed signal is added to the modulation wave to reshape the input impedance of the inverter.

[0036] like Figure 2As shown, based on the above voltage feedforward link, a DC side voltage stabilization method for an inverter includes:

[0037] Step 1: Collect the input voltage of the inverter and analyze it through fast Fourier transform:

[0038] If there is oscillation in the input voltage, the oscillation frequency component in the input voltage is extracted;

[0039] If there is no vibration in the input voltage, the subsequent steps of adjustment are not performed;

[0040] Step 2: When the input voltage oscillates, it is separated by a bandpass filter and a high-pass filter respectively:

[0041] The bandpass filter is a second-order filter, and its expression is as follows:

[0042]

[0043] In the formula, G f (s) represents the bandpass filter expression, ω d represents the center frequency of the bandpass filter, which is equal to the oscillation frequency component, ξ represents the damping coefficient, s represents the complex frequency, and in this embodiment, ω d In line with the oscillation frequency component, ξ is selected as 0.707;

[0044] The high-pass filter is a second-order filter, and its expression is as follows:

[0045]

[0046] In the formula, G f1 (s) represents the high-pass filter expression, ω g represents the center frequency of the high-pass filter, ξ represents the damping coefficient, s represents the complex frequency, and in this embodiment, ω g Select 1 / 10 to 1 / 5 of the oscillation frequency component, and ξ is 0.707.

[0047] Step 3: Scale the disturbance component obtained in step 2 using the dynamic gain coefficient:

[0048] Among them, the scaling adjustment size of the dynamic gain coefficient is jointly determined based on the input voltage level, the converter power level and the output side power quality. Increasing the dynamic gain coefficient is beneficial to improving the stability of the DC side, but it will deteriorate the output power quality. Therefore, when adjusting the amplification factor, the principle of small to large should be followed, and the parameters should be adjusted while ensuring the output power quality. Specifically, the output current THD value can be obtained by sampling the output current signal, and the maximum current THD value that satisfies the THD value <5% is selected as the upper limit constraint. This is used as a constraint to determine whether the amplification factor selection at this time is reasonable. The initial value of the amplification factor is generally selected as 1.

[0049] If the output power quality does not meet the standard, it means that the amplification factor is too large at this time, and the amplification factor should be reduced by a step size of 0.5. If the bus voltage oscillation does not change, the amplification factor should be increased by a step size of 3. If the bus voltage shows a convergence trend and the output power quality meets the standard, the amplification factor should be kept unchanged;

[0050] If the bus voltage eventually becomes stable and the voltage ripple is within plus or minus 0.5V, the group of parameters is deemed valid and the adjustment is exited.

[0051] Step 4: Introduce the voltage feedforward generated by the bandpass filter to the d-axis, and introduce the voltage feedforward generated by the high-pass filter to the q-axis, and reshape the input impedance of the inverter through different voltage feedforwards.

[0052] In addition, for a power grid with a single-phase inverter structure, a virtual dq axis can be constructed to introduce an equivalent feedforward link.

[0053] This embodiment also provides a DC side voltage stabilization device, including a computer memory, a computer processor, and a computer program stored in the computer memory and executable on the computer processor, wherein the computer memory executes the above-mentioned DC side voltage stabilization method for the inverter.

[0054] like Figure 3 As shown, for the d-axis, the bridge arm input voltage v in First, the corresponding disturbance component is obtained through a second-order bandpass filter, and then the disturbance component is scaled using the dynamic gain coefficient K. The obtained d-axis input voltage feedforward signal is then superimposed on the d-axis voltage loop output;

[0055] For the q axis, the bridge arm input voltage v in First, the corresponding disturbance component is obtained through a second-order high-pass filter, and then the disturbance component is scaled using the dynamic gain coefficient K. The obtained q-axis input voltage feedforward signal is then superimposed on the q-axis voltage loop output.

Claims

1. A method for stabilizing the DC side voltage of an inverter, characterized in that: The d-axis and q-axis of the inverter voltage control loop are respectively provided with a voltage feedforward link, and the voltage feedforward link includes a filter with an adjustable center frequency and a dynamic gain coefficient, and the filtering ranges of the filters on the d-axis and the q-axis are different; the voltage feedforward link uses the oscillation frequency component of the inverter input voltage as an introduction signal, and performs scaling adjustment based on the disturbance component output by the inverter input voltage through the filter in combination with the dynamic gain coefficient to obtain a corresponding voltage feedforward signal, and superimposes the voltage feedforward signal on the modulation wave to reshape the input impedance of the inverter; The filter arranged on the d-axis is a bandpass filter, and the center frequency of the bandpass filter is consistent with the oscillation frequency component; The filter arranged on the q-axis is a high-pass filter, and the center frequency of the high-pass filter is 1 / 10 to 1 / 5 of the vibration frequency component; The bandpass filter is a second-order filter, and its expression is as follows: In the formula, G f (s) represents the bandpass filter expression, ω d represents the center frequency of the bandpass filter, ξ represents the damping coefficient, and s represents the complex frequency; The high-pass filter is a second-order filter, and its expression is as follows: In the formula, G f1 (s) represents the high-pass filter expression, ω g represents the center frequency of the high-pass filter, ξ represents the damping coefficient, and s represents the complex frequency.

2. The method for stabilizing the DC side voltage of an inverter according to claim 1, characterized in that: The scaling adjustment size of the dynamic gain coefficient is determined based on the input voltage level, the converter power level and the output side power quality.

3. The DC side voltage stabilization method for an inverter according to claim 2, characterized in that: The scaling adjustment size of the dynamic gain coefficient is set with an upper limit value, and the upper limit value is the largest dynamic gain coefficient selected when the output current THD value after scaling adjustment satisfies less than 5%.

4. The method for stabilizing the DC side voltage of an inverter according to claim 1, characterized in that: The DC side voltage stabilization method has the following specific process: Step 1: Collect the input voltage of the inverter and analyze it through fast Fourier transform: If there is oscillation in the input voltage, the oscillation frequency component in the input voltage is extracted; If there is no vibration in the input voltage, the subsequent steps of adjustment are not performed; Step 2: extract the oscillation frequency component according to step 1, separate the input voltage with oscillation through a filter, and obtain the corresponding disturbance component; Step 3: Scaling and adjusting the disturbance component obtained in step 2 through a dynamic gain coefficient to obtain a corresponding voltage feedforward signal; Step 4: Superimpose the voltage feedforward signal obtained in step 3 on the corresponding dq axis, combine it with the modulation wave output by the voltage control link, and reshape the input impedance of the inverter.

5. A DC side voltage stabilization device, comprising a computer memory, a computer processor, and a computer program stored in the computer memory and executable on the computer processor, characterized in that: The computer memory executes the DC side voltage stabilization method for the inverter as described in any one of claims 1-4; the computer processor implements the following steps when executing the computer program: collecting the current input voltage of the inverter, adjusting the voltage control loop through the DC side voltage stabilization method, and completing the reshaping of the input impedance of the inverter.

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