A method for controlling the intermediate dc voltage in a voltage source converter

Abstract

The application provides a kind of voltage source converter intermediate DC voltage control method, it relates to power electronics field, the method includes: real-time detection of the electric quantity parameter of converter, electric quantity parameter includes input voltage, output voltage and output current;According to the electric quantity parameter, the feedforward additional amount of load power and the current reference value of inner loop control is calculated by virtual three-phase method and instantaneous power theory;According to the electric quantity parameter, the real-time current change rate is calculated, and the output current change rate reference value is obtained by load power calculation;The current change rate reference value and real-time current change rate are compared, and according to the comparison result, it is determined that load step occurs.The application switches the feedforward and feedback control strategy dynamically, significantly improves the DC voltage dynamic response speed and steady-state accuracy of voltage source converter when load mutates, realizes the effect of quickly suppressing voltage fluctuation and automatically recovering steady-state control.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a method for controlling the intermediate DC voltage of a voltage source converter. Background Technology

[0002] With the rapid development of power electronics technology, voltage source converters are widely used in modern power systems. AC-DC-AC voltage source converters, due to their good decoupling capability from the AC systems on both sides, are extensively used for connecting different AC power systems. In these applications, the stable control of the intermediate DC voltage of the voltage source converter is crucial. Currently, DC voltage control typically employs a dual-loop control strategy. The outer loop is the voltage loop, generally using PI control, which calculates the converter input current reference value required to maintain voltage stability using the error between the DC reference voltage and the sampled value. The inner loop is the current loop, causing the converter input current to track the reference value. However, the DC capacitor voltage exhibits integral characteristics when power changes, and the outer loop responds slowly to load changes, resulting in poor dynamic characteristics.

[0003] In existing power feedforward control, the active power calculation method is difficult to take into account both steady-state and dynamic characteristics. Furthermore, conventional active power feedforward is difficult to reflect power changes during load step changes and suppress capacitor voltage fluctuations. The feedback control of capacitor voltage is also difficult to respond in a short time, resulting in large DC voltage fluctuations and long adjustment times, which is not conducive to stable power supply under complex load conditions. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for controlling the intermediate DC voltage of a voltage source converter. By dynamically switching between feedforward and feedback control strategies, the dynamic response speed and steady-state accuracy of the DC voltage of the voltage source converter under load changes are significantly improved, and the effect of quickly suppressing voltage fluctuations and automatically restoring steady-state control is achieved.

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

[0006] In a first aspect, a method for controlling the intermediate DC voltage of a voltage source converter, the method comprising:

[0007] Real-time monitoring of the converter's electrical parameters, including input voltage, output voltage, and output current;

[0008] Based on the electrical parameters, the load power and the feedforward additional amount of the current reference value of the inner loop control are calculated using the virtual three-phase method and instantaneous power theory.

[0009] Based on the electrical parameters, the real-time current change rate is calculated, and the reference value of the output current change rate is obtained by calculating the load power.

[0010] The reference value of the current change rate is compared with the real-time current change rate, and the load step is determined based on the comparison results.

[0011] When a load step occurs, the capacitor voltage is collected in real time, the target capacitor voltage and adjustment time are set, and the reference current increment for capacitor energy is calculated.

[0012] The reference current increment is used as the feedback increment to replace the feedforward increment, thereby achieving the switching of feedback control.

[0013] Based on the switching of feedback control, the load power is calculated to determine the steady-state capacitor energy waveform, and the capacitor energy waveform is compared with the current capacitor energy. Based on the comparison result, steady-state judgment and mode recovery are performed to achieve control of the intermediate DC voltage of the voltage source converter.

[0014] Furthermore, based on the electrical parameters, the feedforward amount of the load power and the current reference value of the inner loop control is calculated using the virtual three-phase method and instantaneous power theory, including:

[0015] Based on the basic electrical parameters of the converter operation, a virtual three-phase voltage and current are constructed using a delay method to build a virtual three-phase AC environment;

[0016] Based on instantaneous power theory, the instantaneous active power of phase A in a virtual three-phase AC environment is calculated, and the load active power is obtained by summing the instantaneous power of the three phases and dividing by 3.

[0017] For a three-phase input AC environment, the additional amount of the three-phase feedforward reference current is calculated using a sine function based on the effective value and phase of the input voltage.

[0018] For a single-phase input environment, the additional single-phase feedforward reference current is calculated using a sine function based on the effective value and phase of the input voltage.

[0019] Furthermore, based on the electrical parameters, the real-time current change rate is calculated, and a reference value for the output current change rate is obtained through load power calculation, including:

[0020] Based on the electrical parameters, the rate of change of the output current is calculated differentially, with a differential interval of 100μs.

[0021] The reference value of the output current change rate is calculated as a function of the converter's angular frequency, power, effective voltage value, phase, and time.

[0022] Furthermore, the reference value of the current change rate is compared with the real-time current change rate, and based on the comparison results, a load step is determined, including:

[0023] Set a preset threshold;

[0024] The reference value of the current change rate is compared with the real-time current change rate. When the difference between the two exceeds a preset threshold, a load step is determined to have occurred.

[0025] Furthermore, when a load step occurs, the capacitor voltage is collected in real time, a target capacitor voltage and adjustment time are set, and the reference current increment for capacitor energy is calculated, including:

[0026] When a load step occurs, the DC capacitor voltage is collected in real time. The DC capacitor energy is obtained by calculating half of the product of the DC capacitor capacitance value and the square of the DC capacitor voltage. The target voltage of the DC capacitor is set, and the target energy of the DC capacitor is obtained by calculating half of the product of the DC capacitor capacitance value and the square of the target voltage.

[0027] Set the adjustment time, and divide the difference between the DC capacitor energy and the DC capacitor target energy by the adjustment time to obtain the reference value of the input active power.

[0028] For a three-phase input AC environment, the additional reference current for phases A, B, and C is equal to the coefficient obtained by calculating the active power reference value with the effective value of the rectifier side voltage, multiplied by the sine value of the sum of the angular frequency, time, and phase angle.

[0029] For a single-phase input AC environment, the input voltage is collected in real time, and the square root of two is multiplied by the active power reference value and divided by the input voltage to obtain the reference current additional value.

[0030] Furthermore, the reference current increment is used as the feedback increment to replace the feedforward increment, thereby achieving the switching of feedback control, including:

[0031] The reference current is used as a feedback input to replace the feedforward input, thus switching from feedforward control to feedback control.

[0032] Furthermore, based on the switching of feedback control, the load power is calculated to determine the steady-state capacitor energy waveform, and the capacitor energy waveform is compared with the current capacitor energy. Based on the comparison result, steady-state judgment and mode recovery are performed to achieve control of the intermediate DC voltage of the voltage source converter, including:

[0033] In feedback control mode, the duration of capacitor energy feedback control is timed, and when it exceeds the time required for power feedforward after power step, the capacitor energy feedback control is disabled.

[0034] For a three-phase input AC environment, based on the load power, the steady-state target energy is obtained by adding a sinusoidal fluctuation component related to the angular frequency, phase angle, and load power. At the same time, it can be found that under steady state, the maximum value of the capacitor energy is equal to the steady-state target energy plus the load power divided by twice the angular frequency, and the minimum value of the capacitor energy is equal to the steady-state target energy minus the load power divided by twice the angular frequency.

[0035] For a single-phase input AC environment, based on the load power, the steady-state target energy is increased by adding a sinusoidal fluctuation term related to the inverter's angular frequency, phase angle, and load power, then subtracting a sinusoidal fluctuation term related to the rectifier's angular frequency and phase angle, and finally subtracting a constant term related to the maximum and minimum energy values ​​to obtain the DC steady-state capacitor energy. At the same time, it can be found that under steady-state conditions, the maximum value of the capacitor energy is equal to the steady-state target energy of the DC capacitor plus half the difference between the maximum and minimum values ​​of the DC capacitor energy, and the minimum value of the capacitor energy is equal to the steady-state target energy of the DC capacitor minus half the difference between the maximum and minimum values ​​of the DC capacitor energy.

[0036] When the following conditions are met: the capacitor energy is greater than the maximum value of the capacitor energy, the steady-state capacitor energy takes the maximum value; the capacitor energy is between the minimum and maximum values ​​of the capacitor energy; the steady-state capacitor energy is equal to the current capacitor energy; the capacitor energy is less than the minimum value of the capacitor energy, the steady-state capacitor energy takes the minimum value; the feedback additional quantity is turned off, and the feedback control is exited to restore the feedforward control, thereby realizing the control of the intermediate DC voltage of the voltage source converter.

[0037] Secondly, a voltage source converter intermediate DC voltage control system includes:

[0038] The feedforward control module is used to detect the electrical parameters of the converter in real time, including input voltage, output voltage, and output current. Based on the electrical parameters, the module calculates the load power and the feedforward additional amount of the current reference value of the inner loop control using the virtual three-phase method and instantaneous power theory.

[0039] The load step detection module is used to calculate the real-time current change rate based on the power parameters, and to obtain a reference value for the output current change rate through load power calculation; the reference value for the current change rate is compared with the real-time current change rate, and the load step is determined based on the comparison result.

[0040] The feedback control switching module is used to determine when a load step occurs, to collect the capacitor voltage in real time, set the target capacitor voltage and adjustment time, and calculate the reference current additional amount of capacitor energy; the reference current additional amount is used as the feedback additional amount to replace the feedforward additional amount in order to realize the switching of feedback control.

[0041] The processing module is used to calculate the load power to determine the steady-state capacitor energy waveform based on the switching of feedback control, compare the capacitor energy waveform with the current capacitor energy, and perform steady-state judgment and mode recovery based on the comparison result, so as to realize the control of the intermediate DC voltage of the voltage source converter.

[0042] Thirdly, a computing device includes:

[0043] One or more processors;

[0044] A storage device for storing one or more programs that, when executed by one or more processors, cause the one or more processors to implement the method.

[0045] Fourthly, a computer-readable storage medium storing a program that, when executed by a processor, implements the method.

[0046] The above-described solution of the present invention has at least the following beneficial effects:

[0047] By real-time monitoring of input voltage, output voltage, and output current, the system promptly grasps the operating status, providing an accurate data foundation for subsequent calculations and ensuring rapid response. The virtual three-phase method and instantaneous power theory are used to calculate the feedforward additional amount of the load power and inner-loop control current reference value, achieving pre-adjustment and enhancing system stability and response speed. Load steps are detected by comparing the current change rate reference value with the actual value, and capacitor voltage is collected in real-time upon detection of a step to calculate the required feedback additional amount, achieving a smooth switch from feedforward to feedback control and preventing capacitor overcharging or undercharging. Based on the three-phase or single-phase input environment, an appropriate mathematical model is used to calculate the DC steady-state capacitor energy. When the capacitor energy exceeds the set range, measures are automatically taken to limit it within a safe range. Once the conditions are met, the feedback additional amount is turned off and feedforward control is restored, achieving a smooth transition from emergency to normal operation, ensuring both immediate response capability and long-term stability. Attached Figure Description

[0048] Figure 1 This is a schematic flowchart of an intermediate DC voltage control method for a voltage source converter provided by an embodiment of the present invention.

[0049] Figure 2 This is a schematic diagram of an intermediate DC voltage control system for a voltage source converter provided in an embodiment of the present invention.

[0050] Figure 3 This is a schematic diagram illustrating the specific implementation process of a voltage source converter intermediate DC voltage control method provided by an embodiment of the present invention. Detailed Implementation

[0051] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0052] like Figure 1 As shown, an embodiment of the present invention proposes a method for controlling the intermediate DC voltage of a voltage source converter, the method comprising the following steps:

[0053] Step 11: Real-time detection of the converter's electrical parameters, including input voltage, output voltage, and output current;

[0054] Step 12: Based on the electrical parameters, calculate the load power and the feedforward additional amount of the current reference value of the inner loop control using the virtual three-phase method and instantaneous power theory.

[0055] Step 13: Calculate the real-time current change rate based on the power parameters, and obtain the reference value of the output current change rate through load power calculation;

[0056] Step 14: Compare the reference value of the current change rate with the real-time current change rate, and determine whether a load step has occurred based on the comparison result;

[0057] Step 15: When a load step occurs, collect the capacitor voltage in real time, set the target capacitor voltage and adjustment time, and calculate the reference current additional amount of capacitor energy.

[0058] Step 16: Use the reference current increment as the feedback increment to replace the feedforward increment, so as to achieve the switching of feedback control.

[0059] Step 17: Based on the switching of feedback control, calculate the load power to determine the steady-state capacitor energy waveform, compare the capacitor energy waveform with the current capacitor energy, and perform steady-state judgment and mode recovery based on the comparison results to achieve control of the intermediate DC voltage of the voltage source converter.

[0060] In this embodiment of the invention, load steps are quickly identified by calculating the real-time current change rate, and the system switches to feedback control mode. The input current is directly adjusted according to the capacitor energy demand, shortening the dynamic adjustment time. Feedforward additional quantities are calculated based on the virtual three-phase method and instantaneous power theory to avoid filtering delays and ensure the accuracy of steady-state control. It supports three-phase / single-phase input environments and is applicable to any input / output frequency combination. Universal control is achieved through capacitor energy steady-state waveform analysis. The amplitude limit of the feedback additional quantity can be adapted to the overload capacity of different equipment. By quickly suppressing voltage fluctuations, the stress on key components such as capacitors and power devices is reduced, improving system reliability.

[0061] In a preferred embodiment of the present invention, step 11 above may include:

[0062] The input voltage, output voltage, and output current of the converter are monitored in real time to obtain the basic electrical parameters of the converter operation.

[0063] In this embodiment of the invention, real-time detection of the input voltage, output voltage, and output current of the converter enables a comprehensive and accurate understanding of the converter's operating status, providing strong support for system monitoring and management. By acquiring power parameters in real time, potential problems such as voltage anomalies and current overloads can be detected in a timely manner, thereby quickly triggering a fault warning mechanism to avoid equipment damage or system crashes.

[0064] In this embodiment of the invention, the specific steps include:

[0065] Detect the instantaneous value of the output voltage on the load side of the converter at time t. u T ( t and instantaneous value of output current i T ( t This allows you to obtain the basic electrical parameters for the converter's operation.

[0066] In a preferred embodiment of the present invention, step 12 above may include:

[0067] Step 121: Based on the basic electrical parameters of the converter operation, construct virtual three-phase voltage and current using the delay method to build a virtual three-phase AC environment;

[0068] Step 122: Based on the instantaneous power theory, calculate the instantaneous active power of phase A in the virtual three-phase AC environment, and obtain the load active power by dividing the sum of the three-phase instantaneous power by 3.

[0069] Step 123: For a three-phase input AC environment, calculate the additional amount of the three-phase feedforward reference current using a sine function based on the effective value and phase of the input voltage.

[0070] Step 124: For a single-phase input environment, calculate the additional single-phase feedforward reference current using a sine function based on the effective value and phase of the input voltage.

[0071] In this embodiment of the invention, a virtual three-phase voltage and current are constructed using a time-delay method, enabling the system to simulate a three-phase AC environment under a single-phase input environment. This enhances the compatibility and flexibility to different input environments. Using instantaneous power theory, the instantaneous active power of each phase in the virtual three-phase AC environment is calculated, and the load active power is obtained by summing the three-phase instantaneous power and dividing by 3. This method can more accurately reflect the actual power demand of the load. Based on the effective value and phase of the input voltage, the additional feedforward reference current for both three-phase and single-phase phases is calculated using a sine function. This can more accurately predict the load's changing trend and provide stronger support for feedforward control.

[0072] In this embodiment of the invention, the specific steps include:

[0073] Step 121: Based on the acquired basic electrical parameters of the converter operation, the single-phase voltage or current signal is equivalently delayed by 120 degrees and 240 degrees (relative to the original signal) using a delay method, thereby constructing a virtual three-phase voltage. , , Three-phase current , , To construct a virtual three-phase communication environment, in, This is the voltage of phase A. This is the voltage of phase B. This is the voltage of phase C. This is the current in phase A. Phase B current For phase C current, The fundamental frequency period on the inverter side.

[0074] Power frequency downtake T inv =0.02s, the load side of the converter can be regarded as phase A of a virtual three-phase system.

[0075] Step 122: Calculate the instantaneous active power of phase A and the load active power in the virtual three-phase AC environment using instantaneous power theory. The formula is: in, For the active power of the load, The instantaneous active power of phase A. This is the voltage of phase A. This is the voltage of phase B. This is the voltage of phase C. This is the current in phase A. Phase B current This represents the C-phase current.

[0076] Step 123: For a three-phase input environment, detect the effective value of the A-phase input voltage. phase Calculate the additional amount of the three-phase feedforward reference current. , , Represented as: ,in, , , This is an additional amount for the three-phase feedforward reference current. For the active power of the load, The effective value of the input voltage. For phase, The fundamental angular frequency of the input voltage. For time, the additional amount of the three-phase feedback reference current at this time All are 0.

[0077] Step 124: For a single-phase input environment, detect the effective value of the input voltage. phase Calculate the additional single-phase feedforward reference current. Represented as: ,in, This is an additional amount for the single-phase feedforward reference current. The effective value of the input voltage. For the active power of the load, The fundamental angular frequency of the input voltage. For time, For phase, the additional amount of feedback reference current at this time It is 0.

[0078] In a preferred embodiment of the present invention, step 13 above may include:

[0079] Step 131: Based on the electrical parameters, the rate of change of the output current is obtained by differential calculation, with a differential interval of 100μs.

[0080] Step 132: Calculate the reference value of the output current change rate using functions of the converter's angular frequency, power, effective voltage value, phase, and time.

[0081] In this embodiment of the invention, the current change rate is obtained by differential calculation based on the electrical parameters, which can more accurately monitor the dynamic changes of the current and help to detect load steps in a timely manner; by calculating the reference value of the output current change rate, the control strategy of the converter can be optimized, and the stability and reliability of the system can be improved.

[0082] In this embodiment of the invention, the specific steps include:

[0083] Step 131: Calculate the rate of change based on the output current sampling. , is represented as: in, The rate of change of current, For the difference interval, we take [value]. =100μs, This is the current sample value at the current moment. This is the current sample value from the previous moment.

[0084] Step 132: Obtain the effective value of the output voltage, the phase of the output voltage, and calculate the reference value of the output current change rate, expressed as: ,in This is a reference value for the rate of change of output current. This is the effective value of the output voltage. For the output voltage phase, Active power The fundamental angular frequency of the output voltage. It is a time variable.

[0085] In a preferred embodiment of the present invention, step 14 above may include:

[0086] Step 141: Set a preset threshold;

[0087] Step 142: Compare the reference value of the current change rate with the real-time current change rate. If the difference between the two exceeds a preset threshold, it is determined that a load step has occurred.

[0088] In this embodiment of the invention, by comparing the reference value of the current change rate and the output current change rate in real time, the system can quickly detect the step change of the load and respond in a timely manner to prevent system instability caused by sudden load changes. Setting a preset threshold makes the system more sensitive to the detection of load changes and can detect problems in the early stage of load changes. Setting a preset threshold and automatically comparing the reference value and the output current change rate enables the system to achieve automated control, reduce manual intervention, and improve operating efficiency.

[0089] In this embodiment of the invention, the specific steps include:

[0090] Step 141: Analyze historical current change rate data using statistical methods (such as mean, standard deviation, maximum value, minimum value, etc.), and set preset thresholds based on historical data analysis and system requirements.

[0091] Step 142: A load step is considered to have occurred if the following conditions are met; otherwise, it is considered that no load step has occurred. ,in This is a reference value for the rate of change of current. To output the rate of change of current in real time. A preset threshold is set for power step.

[0092] In a preferred embodiment of the present invention, step 15 may include:

[0093] Step 151: When a load step occurs, the DC capacitor voltage is collected in real time. The DC capacitor energy is obtained by calculating half of the product of the DC capacitor capacitance and the square of the DC capacitor voltage. The target voltage of the DC capacitor is set, and the target energy of the DC capacitor is obtained by calculating half of the product of the DC capacitor capacitance and the square of the target voltage.

[0094] Step 152: Set the adjustment time. Based on the difference between the DC capacitor energy and the DC capacitor target energy, divide the difference by the adjustment time to obtain the reference value of the input active power.

[0095] Step 153: For a three-phase input AC environment, the additional reference current of phases A, B, and C is equal to the coefficient obtained by calculating the active power reference value with the effective value of the rectifier side voltage, multiplied by the sine value of the sum of the angular frequency, time, and phase angle.

[0096] Step 154: For a single-phase input AC environment, the input voltage is collected in real time, and the square root of two is multiplied by the active power reference value and divided by the input voltage to obtain the reference current additional amount.

[0097] In this embodiment of the invention, by acquiring the DC capacitor voltage and calculating the DC capacitor energy in real time, the system can quickly sense the energy changes caused by load jumps. Based on the difference between the DC capacitor energy and the target energy, the system dynamically adjusts the input active power reference value, enabling the system to respond quickly to load changes and maintain energy balance. By calculating the input current reference value and using it as a feedback quantity, the system can adjust the input current in real time to maintain the stability of the DC capacitor energy. By calculating the difference between the DC capacitor energy and the target energy and adjusting the input active power accordingly, the system can more accurately control energy flow. Optimized energy management helps reduce system energy consumption, improve energy efficiency, and thus reduce operating costs. Different input current reference value calculation methods are provided for three-phase and single-phase input AC environments, enabling the system to flexibly adapt to different AC environments. By switching from feedforward control to feedback control, the system can more flexibly respond to load changes and external disturbances. The system can automatically adjust the input active power reference value according to load changes and energy status, and realize the switching of control strategies, improving the system's intelligence level.

[0098] In this embodiment of the invention, the specific steps include:

[0099] Step 151: Based on the determination that a load step occurs, use a voltage sensor to collect the voltage value of the DC capacitor in real time, set the target voltage of the DC capacitor, and calculate the DC capacitor energy and the target DC capacitor energy. ,in, This is the capacitance value of the DC capacitor. For DC capacitor energy, , These are the target voltage and target energy of the DC capacitor, respectively. The rated voltage can be selected.

[0100] Step 152: Set the adjustment time and calculate the reference value of the input active power based on the DC capacitor energy and the target DC capacitor energy. ,in, DC capacitor energy, The target energy of the DC capacitor. The optional adjustment time indicates the desired capacitor voltage at which... The internal value becomes the target value.

[0101] Step 153, for a three-phase input AC environment, the additional feedback reference current for phases A, B, and C. , , Represented as: ,in , , These are the additional feedback reference currents for phases A, B, and C, respectively. , This is the effective value of the rectifier-side voltage. Angular frequency, For time variables, The phase angle is the additional amount of the three-phase feedforward reference current. , , All are 0.

[0102] Step 154: For a single-phase AC input environment, the input voltage is acquired in real time, and the current reference value is calculated. in, This is the current reference value. , To achieve instantaneous synchronization of current and voltage, ensuring unity power factor, and taking into account... It could be 0, therefore it can be The output is limited to The upper and lower limits of the amplitude limit , The feedforward reference current is determined based on the specific overload capacity of the equipment. It is 0.

[0103] In a preferred embodiment of the present invention, step 16 above may include:

[0104] The reference current is used as a feedback input to replace the feedforward input, thus switching from feedforward control to feedback control.

[0105] In this embodiment of the invention, when a load step occurs, the feedback supplement gradually replaces the feedforward supplement, achieving a shock-free transition through dynamic weight adjustment and avoiding current oscillations caused by traditional hard switching. During the transition phase, a hybrid feedforward + feedback mode is briefly employed to ensure control continuity and improve system stability. The feedback supplement is directly generated based on the capacitor voltage deviation, accurately compensating for power imbalance. The feedback supplement is directly calculated based on the capacitor energy demand, providing instantaneous current compensation during load abrupt changes and reducing DC voltage fluctuations. The feedback control, which does not rely on power calculations for harmonic filtering, is more adaptable to nonlinear loads (such as rectifiers).

[0106] In a preferred embodiment of the present invention, step 17 above may include:

[0107] Step 171: In feedback control mode, time the duration of capacitor energy feedback control. When the time required for power feedforward after power step exceeds the time required for power step, enable the power disable judgment of capacitor energy feedback control.

[0108] Step 172: For a three-phase input AC environment, based on the load power, the steady-state target energy is obtained by adding a sinusoidal fluctuation component related to the angular frequency, phase angle, and load power. At the same time, it can be found that under steady state, the maximum value of the capacitor energy is equal to the steady-state target energy plus the load power divided by twice the angular frequency, and the minimum value of the capacitor energy is equal to the steady-state target energy minus the load power divided by twice the angular frequency.

[0109] Step 173: For a single-phase input AC environment, based on the load power, add a sinusoidal fluctuation term related to the inverter's angular frequency, phase angle, and load power to the steady-state target energy, then subtract a sinusoidal fluctuation term related to the rectifier's angular frequency and phase angle, and finally subtract a constant term related to the maximum and minimum energy values ​​to obtain the DC steady-state capacitor energy. At the same time, it can be found that under steady-state conditions, the maximum value of the capacitor energy is equal to the steady-state target energy of the DC capacitor plus half the difference between the maximum and minimum values ​​of the DC capacitor energy, and the minimum value of the capacitor energy is equal to the steady-state target energy of the DC capacitor minus half the difference between the maximum and minimum values ​​of the DC capacitor energy.

[0110] Step 174: When the following conditions are met, if the capacitor energy is greater than the maximum value of the capacitor energy, the steady-state capacitor energy takes the maximum value; if the capacitor energy is between the minimum and maximum values ​​of the capacitor energy, the steady-state capacitor energy is equal to the current capacitor energy; if the capacitor energy is less than the minimum value of the capacitor energy, the steady-state capacitor energy takes the minimum value, the feedback additional quantity is turned off, and the feedback control is exited to restore the feedforward control, thereby realizing the control of the intermediate DC voltage of the voltage source converter.

[0111] In this embodiment of the invention, by controlling the duration of timed capacitor energy feedback and initiating an exit judgment after exceeding a preset threshold, feedback control can be accurately exited, improving control effectiveness. Different steady-state capacitor energy calculation methods are designed for three-phase and single-phase AC input environments, enhancing the adaptability of the control strategy to different power systems. Judgment conditions for capacitor energy and its allowable range are set to prevent excessive energy fluctuations and ensure stable DC capacitor voltage. Accurate calculation of steady-state capacitor energy and its maximum and minimum values ​​based on parameters such as load power helps to understand energy change patterns, rationally control the timing of feedback exit, avoid unnecessary energy loss, and improve the energy conversion and operating efficiency of the voltage source converter.

[0112] In this embodiment of the invention, the specific steps include:

[0113] Step 171: After entering the feedback control mode, the duration of this capacitor energy feedback control is timed and represented as... T u ,when T u > When the capacitor energy feedback control is enabled, the power-off judgment is activated, whereby... To correctly calculate the power feedforward energy after a power step P inv The required time, when using the virtual three-phase method described above, should meet the following requirements. in, The minimum duration threshold for feedback control is determined by the dynamic characteristics of the system and is typically set to 3.4ms (at a power frequency of 50Hz). This is the fundamental frequency period on the inverter output side.

[0114] Step 172: For a three-phase input AC environment, obtain the current load power, input voltage angular frequency, phase angle of each phase, and the preset steady-state target energy. Calculate the steady-state capacitor energy using the following formula: ,in, For steady-state capacitor energy, For steady-state target energy, For load power, Angular frequency, The phase angle, Let time be the variable. Simultaneously, the formulas for the maximum and minimum values ​​of the capacitor energy under steady-state conditions can be obtained as follows: ,in, and These represent the maximum and minimum values ​​of the capacitor energy. For steady-state target energy, For load power, The inverter's angular frequency is calculated, and the maximum value is then set. and minimum value Store them separately in their respective data storage areas.

[0115] Step 173: For a single-phase input AC environment, obtain the current load power, inverter angular frequency, rectifier angular frequency, corresponding phase angles (inverter phase angle, rectifier phase angle), and steady-state target energy. The steady-state capacitor energy formula is: ,in, For steady-state capacitor energy, For steady-state target energy, For load power, The inverter's angular frequency. The rectifier angular frequency, The inverter phase angle, The rectifier phase angle, and To exchange part of the energy The maximum and minimum values ​​can be obtained numerically. Simultaneously, the formulas for the maximum and minimum values ​​of the capacitor energy under steady-state conditions can be obtained as follows: ,in and These represent the maximum and minimum values ​​of the capacitor energy. For steady-state target energy, and For the constant terms related to the maximum and minimum values ​​of the alternating current energy, after the calculation is completed, the maximum value will be... and minimum value Store them separately in their respective data storage areas.

[0116] Step 174, the conditions for judging capacitor energy are as follows, ( > and = )or( ≤ ≤ and = )or( < and = ),in, For capacitor energy, For steady-state capacitor energy, and These are the maximum and minimum values ​​of the capacitor energy. After determining the capacitor energy, if the exit condition is met, the output of the feedback auxiliary quantity is turned off, and the control mode is switched from feedback control back to feedforward control mode, thereby achieving effective control of the intermediate DC voltage of the voltage source converter.

[0117] like Figure 2 As shown, an embodiment of the present invention also provides an intermediate DC voltage control system 20 for a voltage source converter, comprising:

[0118] Feedforward control module 21 is used to detect the electrical parameters of the converter in real time, including input voltage, output voltage and output current; based on the electrical parameters, it calculates the load power and the feedforward additional amount of the current reference value of the inner loop control through the virtual three-phase method and instantaneous power theory;

[0119] The load step determination module 22 is used to calculate the real-time current change rate based on the power parameters, and to obtain the output current change rate reference value through load power calculation; compare the current change rate reference value with the real-time current change rate, and determine whether a load step has occurred based on the comparison result;

[0120] The feedback control switching module 23 is used to determine when a load step occurs, collect the capacitor voltage in real time, set the target capacitor voltage and adjustment time, and calculate the reference current additional amount of capacitor energy; the reference current additional amount is used as the feedback additional amount to replace the feedforward additional amount in order to realize the switching of feedback control.

[0121] The processing module 24 is used to calculate the load power to determine the steady-state capacitor energy waveform based on the switching of feedback control, compare the capacitor energy waveform with the current capacitor energy, and perform steady-state judgment and mode recovery based on the comparison result, so as to realize the control of the intermediate DC voltage of the voltage source converter.

[0122] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the intermediate DC voltage of a voltage source converter, characterized in that, The method includes: Real-time monitoring of the converter's electrical parameters, including input voltage, output voltage, and output current; Based on the electrical parameters, the feedforward additional amount of the load power and the current reference value of the inner loop control is calculated using the virtual three-phase method and instantaneous power theory. This includes: constructing a virtual three-phase voltage and current using a delay method based on the basic electrical parameters of the converter operation, thus building a virtual three-phase AC environment; calculating the instantaneous active power of phase A in the virtual three-phase AC environment using instantaneous power theory, and obtaining the load active power by dividing the sum of the three-phase instantaneous power by 3; for a three-phase input AC environment, calculating the three-phase feedforward reference current additional amount using a sine function based on the effective value and phase of the input voltage; and for a single-phase input environment, calculating the single-phase feedforward reference current additional amount using a sine function based on the effective value and phase of the input voltage. Based on the electrical parameters, the real-time current change rate is calculated, and the reference value of the output current change rate is obtained by calculating the load power. The reference value of the current change rate is compared with the real-time current change rate, and the load step is determined based on the comparison results. When a load step occurs, the capacitor voltage is collected in real time, the target capacitor voltage and adjustment time are set, and the reference current increment for capacitor energy is calculated. The reference current increment is used as the feedback increment to replace the feedforward increment, thereby achieving the switching of feedback control. Based on the switching of feedback control, the load power is calculated to determine the steady-state capacitor energy waveform, and the capacitor energy waveform is compared with the current capacitor energy. Based on the comparison result, steady-state judgment and mode recovery are performed to achieve control of the intermediate DC voltage of the voltage source converter.

2. The intermediate DC voltage control method for a voltage source converter according to claim 1, characterized in that, Based on the electrical parameters, the real-time current change rate is calculated, and a reference value for the output current change rate is obtained by calculating the load power, including: Based on the electrical parameters, the rate of change of the output current is calculated differentially, with a differential interval of 100μs. The reference value of the output current change rate is calculated as a function of the converter's angular frequency, power, effective voltage value, phase, and time.

3. The intermediate DC voltage control method for a voltage source converter according to claim 2, characterized in that, The reference value of the current change rate is compared with the real-time current change rate, and based on the comparison results, a load step is determined, including: Set a preset threshold; The reference value of the current change rate is compared with the real-time current change rate. When the difference between the two exceeds a preset threshold, a load step is determined to have occurred.

4. The intermediate DC voltage control method for a voltage source converter according to claim 3, characterized in that, When a load step change is detected, the capacitor voltage is collected in real time, a target capacitor voltage and adjustment time are set, and the reference current increment for capacitor energy is calculated, including: When a load step occurs, the DC capacitor voltage is collected in real time. The DC capacitor energy is obtained by calculating half of the product of the DC capacitor capacitance value and the square of the DC capacitor voltage. The target voltage of the DC capacitor is set, and the target energy of the DC capacitor is obtained by calculating half of the product of the DC capacitor capacitance value and the square of the target voltage. Set the adjustment time, and divide the difference between the DC capacitor energy and the DC capacitor target energy by the adjustment time to obtain the reference value of the input active power. For a three-phase input AC environment, the additional reference current for phases A, B, and C is equal to the coefficient obtained by calculating the active power reference value with the effective value of the rectifier side voltage, multiplied by the sine value of the sum of the angular frequency, time, and phase angle. For a single-phase input AC environment, the input voltage is collected in real time, and the square root of two is multiplied by the active power reference value and divided by the input voltage to obtain the reference current additional value.

5. The intermediate DC voltage control method for a voltage source converter according to claim 4, characterized in that, The reference current increment is used as the feedback increment to replace the feedforward increment in order to achieve the switching of feedback control, including: The reference current is used as a feedback input to replace the feedforward input, thus switching from feedforward control to feedback control.

6. The intermediate DC voltage control method for a voltage source converter according to claim 5, characterized in that, Based on the switching of feedback control, the load power is calculated to determine the steady-state capacitor energy waveform, and the capacitor energy waveform is compared with the current capacitor energy. Based on the comparison result, steady-state judgment and mode recovery are performed to achieve control of the intermediate DC voltage of the voltage source converter, including: In feedback control mode, the duration of capacitor energy feedback control is timed, and when it exceeds the time required for power feedforward after power step, the capacitor energy feedback control is disabled. For a three-phase input AC environment, based on the load power, the steady-state target energy is obtained by adding a sinusoidal fluctuation component related to the angular frequency, phase angle, and load power. At the same time, it can be found that under steady state, the maximum value of the capacitor energy is equal to the steady-state target energy plus the load power divided by twice the angular frequency, and the minimum value of the capacitor energy is equal to the steady-state target energy minus the load power divided by twice the angular frequency. For a single-phase input AC environment, based on the load power, the steady-state target energy is increased by adding a sinusoidal fluctuation term related to the inverter's angular frequency, phase angle, and load power, then subtracting a sinusoidal fluctuation term related to the rectifier's angular frequency and phase angle, and finally subtracting a constant term related to the maximum and minimum energy values ​​to obtain the DC steady-state capacitor energy. At the same time, it can be found that under steady-state conditions, the maximum value of the capacitor energy is equal to the steady-state target energy of the DC capacitor plus half the difference between the maximum and minimum values ​​of the DC capacitor energy, and the minimum value of the capacitor energy is equal to the steady-state target energy of the DC capacitor minus half the difference between the maximum and minimum values ​​of the DC capacitor energy. When the following conditions are met: the capacitor energy is greater than the maximum value of the capacitor energy, the steady-state capacitor energy takes the maximum value; the capacitor energy is between the minimum and maximum values ​​of the capacitor energy; the steady-state capacitor energy is equal to the current capacitor energy; the capacitor energy is less than the minimum value of the capacitor energy, the steady-state capacitor energy takes the minimum value; the feedback additional quantity is turned off, and the feedback control is exited to restore the feedforward control, thereby realizing the control of the intermediate DC voltage of the voltage source converter.

7. A voltage source converter intermediate DC voltage control system, wherein the system implements the method as described in any one of claims 1 to 6, characterized in that, include: The feedforward control module is used to detect the electrical parameters of the converter in real time, including input voltage, output voltage, and output current. Based on the electrical parameters, the load power and the feedforward additional amount of the current reference value of the inner loop control are calculated using the virtual three-phase method and instantaneous power theory. The load step determination module is used to calculate the real-time current change rate based on the power parameters, and to obtain the reference value of the output current change rate through load power calculation. The reference value of the current change rate is compared with the real-time current change rate, and the load step is determined based on the comparison results. The feedback control switching module is used to determine when a load step occurs, collect the capacitor voltage in real time, set the target capacitor voltage and adjustment time, and calculate the reference current additional amount of capacitor energy. The reference current increment is used as the feedback increment to replace the feedforward increment, thereby achieving the switching of feedback control. The processing module is used to calculate the load power to determine the steady-state capacitor energy waveform based on the switching of feedback control, compare the capacitor energy waveform with the current capacitor energy, and perform steady-state judgment and mode recovery based on the comparison result, so as to realize the control of the intermediate DC voltage of the voltage source converter.

8. A computing device, characterized in that, include: One or more processors; A storage device for storing one or more programs that, when executed by one or more processors, cause the one or more processors to implement the method as described in any one of claims 1 to 6.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a program that, when executed by a processor, implements the method as described in any one of claims 1 to 6.

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