Output compensation method in parallel inverter system

Abstract

The invention discloses an output compensation method in a parallel inverter system. The method comprises the steps that each inverter collects voltage U and current I output by the inverter to a load circuit, the voltage U is the voltage between the output end of the inverter and the two ends of a capacitor C2, and the current I is the current flowing through an inductor L1 and an inductor L2; the total power W of the inverter in an alternating current period is calculated through the collected voltage U and current I, and the total power W is obtained through integration of instantaneous power; the total power W is monitored according to the output of the bang-bang controller, and when it is detected that W is smaller than zero, a compensation step is added to the compensation value Offset; when W is greater than or equal to zero, the compensation value Offset is reduced by one compensation step down; the calculated compensation value Offset [n] is subjected to amplitude limiting processing, the amplitude limiting range is [0, Umax], and Umax is the difference value between the maximum output voltage and the typical output voltage which are agreed in advance; and increasing the compensation value Offset [n] to the voltage loop control quantity of the inverter.

Description

Technical Field

[0001] The present application relates to the field of inverter technology, and in particular to an output compensation method in a parallel inverter system. Background Art

[0002] With the rapid development of power electronics technology, inverters have been widely used in the fields of renewable energy generation, industrial control and power conversion. The parallel inverter system can achieve greater power output and higher system flexibility by operating multiple inverters in parallel. However, when operating in parallel, the output difference between different inverters may cause system instability, especially when the output voltage is inconsistent, which can easily cause abnormal increase in bus voltage and damage key components in the inverter, such as IGBT (insulated gate bipolar transistor).

[0003] In practical applications, the problem of voltage inconsistency when inverters are connected in parallel is quite common, especially when there are load fluctuations, input power changes or the control system does not respond in time, the output voltage of one inverter may be lower than that of other inverters. This will cause its bus voltage to rise, and in severe cases, it may cause the IGBT to burn out, affecting the reliability and safety of the system.

[0004] In order to deal with the above problems, some control strategies have been proposed in the prior art, which usually achieve the purpose of voltage balance by adjusting the output power, output voltage or frequency of the inverter. However, these methods have certain limitations, such as slow response speed and inaccurate compensation, which are difficult to meet the requirements of modern high-performance power systems. Especially in application scenarios with complex loads and frequent fluctuations, it is difficult for the prior art to achieve fast and stable control of voltage, and the inverter is still susceptible to bus voltage fluctuations, thereby increasing the risk of system damage.

[0005] In addition, the existing parallel inverter control system has a certain delay in voltage detection and output regulation, especially when multiple inverters are connected in parallel. Since the output voltage acts on the load together, it is difficult to accurately detect the actual output voltage of each inverter, resulting in the PI controller being unable to adjust the inverter output in real time, further aggravating the problem of bus voltage rise.

[0006] Based on this, there is an urgent need for a control method that can compensate the inverter output voltage in real time and effectively, achieve stable control of the bus voltage through rapid response and dynamic adjustment, and prevent the inverter from being damaged due to abnormal voltage increase. Summary of the invention

[0007] In order to solve the above technical problems, the present application provides an output compensation method in a parallel inverter system.

[0008] The technical solution provided in this application is described below:

[0009] In a first aspect, the present application provides an output compensation method in a parallel inverter system, which is applied to a circuit system including a plurality of single-phase inverters operating in parallel, the circuit system comprising:

[0010] The DC side of each inverter is connected to a common bus voltage VDC, and the AC side of each inverter is connected to a load circuit, which includes two parallel inductors L1 and L2 and a parallel capacitor C2;

[0011] Each inverter includes a rectifier module and an inverter module. The rectifier module includes a plurality of power switching devices for converting AC power into DC power. The inverter module includes a plurality of power switching devices for inverting DC power into AC power and outputting it to the load circuit.

[0012] All inverters running in parallel are preset with the same output voltage and the following method is used for voltage compensation, the method comprising:

[0013] Each inverter collects the voltage U and current I output to the load circuit, where the voltage U is the voltage between the inverter output terminal and the capacitor C2, and the current I is the current flowing through the inductors L1 and L2;

[0014] The total power W of the inverter in one AC cycle is calculated by the collected voltage U and current I, and the total power W is obtained by integrating the instantaneous power;

[0015] According to the output of the bang-bang controller, the total power W is monitored. When it is detected that W is less than zero, the compensation value Offset is increased by a compensation step step_up;

[0016] When W is greater than or equal to zero, the compensation value Offset is reduced by a compensation step downstep_down;

[0017] The calculated compensation value Offset[n] is limited in the range of [0,Umax], where Umax is the difference between the pre-agreed maximum output voltage and the typical output voltage;

[0018] Add the compensation value Offset[n] to the voltage loop control quantity of the inverter;

[0019] Among them, if the control quantity is the voltage amplitude, the compensation value is directly added; if the control quantity is the real-time voltage value, the compensation value is multiplied by the current phase angle θ, that is, the compensation value is Offset*sin(θ), where θ is the current voltage phase.

[0020] Optionally, the voltage control loop of the inverter adopts a proportional integral differential PID controller, and the PID controller is used to calculate the control amount of the output voltage according to the error between the fed-back output voltage U and the set value, and dynamically adjust the inverter output in combination with the compensation value Offset.

[0021] Optionally, the inverter module includes a full-bridge inverter circuit, which is composed of four power switching devices, and the four power switching devices are insulated gate bipolar transistors IGBTs. Each power switching device is respectively connected between the positive and negative poles of the DC side of the inverter and the load circuit, and is used to realize the conversion of DC power into AC power.

[0022] Optionally, the rectifier module includes an uncontrolled rectifier bridge circuit, which is composed of six diodes and is used to rectify the input AC power into DC power and supply it to the inverter module.

[0023] Optionally, the output end of the inverter module is connected to the load circuit via an LC filter, and the LC filter includes an inductor Lf and a capacitor Cf, and is used to filter out high-frequency harmonic components in the inverter output voltage.

[0024] Optionally, the DC side of each inverter is configured with a DC capacitor CDC.

[0025] Optionally, the parallel inductance L1 and the inductance L2 of the load circuit are respectively connected in parallel with the load capacitance C2 to form a parallel resonant circuit.

[0026] Optionally, each inverter of the parallel inverters further includes an isolation transformer, which is used to transmit the AC power output by the inverter to the load circuit and provide electrical isolation between the inverters.

[0027] Optionally, the total power W is obtained by integrating the instantaneous power, including obtaining by calculation in the following manner:

[0028] The method for calculating the total power W of the inverter in one AC cycle is:

[0029] Integrate the instantaneous power P(t) within the cycle over time t, and the calculation formula is:

[0030]

[0031] Where T is an AC cycle and P(t) is the instantaneous power.

[0032] Optionally, the limiting of the compensation value Offset[n] includes a dynamic limiting range, and the dynamic limiting range is automatically adjusted according to the operating state of the inverter system and the load change;

[0033] When the system load suddenly changes or the voltage fluctuates greatly, increase the upper limit Umax;

[0034] When the system runs smoothly, reduce the upper limit Umax.

[0035] It can be seen from the above technical solutions that this application has the following advantages:

[0036] 1. By collecting voltage and current and calculating instantaneous power, this method can monitor the output status of the system in real time, adjust the compensation value in time, avoid voltage fluctuations, ensure the stability of the output voltage, and thus improve the power quality.

[0037] 2. Use the Bang-Bang controller to dynamically adjust the compensation value, increase the compensation when the power W is less than zero, and reduce the compensation when the power WWW is greater than or equal to zero. This mechanism ensures that the system can respond quickly to load changes or instability and avoid voltage mutations.

[0038] 3. Limit the compensation value Offset[n] to prevent over-compensation or under-compensation and avoid unnecessary fluctuations in the inverter system. By setting the maximum output voltage Umax, ensure that the compensation value changes within a reasonable range and improve the stability of the system.

[0039] 4. When the control quantity is the real-time value of voltage, the compensation value is related to the voltage phase angle θ. By calculating the product of the compensation value and the current voltage phase, the voltage output can be adjusted more accurately, further improving the accuracy of voltage control.

[0040] 5. This method is particularly suitable for multiple single-phase inverter systems running in parallel. By presetting the same output voltage and compensation algorithm, it ensures the coordination and consistency between multiple inverters and reduces the voltage deviation and resonance risk in the parallel system.

[0041] 6. By utilizing the fast-response Bang-Bang control algorithm and real-time power monitoring, this method can effectively suppress the impact of load fluctuations or input instability on the system voltage, enhance the dynamic response performance of the system, and ensure that the system remains stable in operation under complex power environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0043] Figure 1A schematic flow chart of an embodiment of an output compensation method in a parallel inverter system provided in the present application;

[0044] Figure 2 The present invention is a schematic structural diagram of an embodiment of a circuit system of multiple single-phase inverters running in parallel used in the method of the present application. DETAILED DESCRIPTION

[0045] See also Figure 1 , Figure 2 The present application first provides an embodiment of a method, which is applied to a circuit system including a plurality of single-phase inverters running in parallel, wherein the circuit system includes:

[0046] The DC side of each inverter is connected to a common bus voltage VDC, and the AC side of each inverter is connected to a load circuit, which includes two parallel inductors L1 and L2 and a parallel capacitor C2;

[0047] Each inverter includes a rectifier module and an inverter module. The rectifier module contains multiple power switching devices for converting AC power into DC power; the inverter module contains multiple power switching devices for inverting DC power into AC power and outputting it to the load circuit.

[0048] See also Figure 2 The present application provides an embodiment of a circuit system, in which two inverters are configured in parallel, each inverter is connected to a common DC bus VDC through a rectifier module and an inverter module, and finally outputs to a load circuit.

[0049] The rectifier module of each inverter consists of six diodes G1, G2, G3, G4, G5, and G6 to form a rectifier bridge, which is used to rectify the AC power output by the generator into DC power and supply it to the inverter module. The rectified DC voltage is filtered by a DC capacitor C1 to smooth the rectified voltage and reduce fluctuations.

[0050] The rectified DC power is delivered to the inverter module through the common DC bus VDC. The DC bus connects the DC side of each inverter together to achieve power distribution for parallel operation.

[0051] The inverter module adopts a full-bridge inverter circuit, which is composed of four IGBT power switch devices G7, G8, G9 and G10, and is used to convert DC power into AC power. The four IGBTs are respectively connected between the positive and negative poles of the DC bus and the load. By controlling the switching operation of the IGBT, the conversion from DC to AC is realized, and an AC voltage output suitable for the load demand is generated.

[0052] The output of each inverter is connected to a load circuit, which includes two parallel inductors L1 and L2, and a parallel capacitor C2. These components are used to filter the voltage output by the inverter to remove high-frequency harmonic components and adjust the frequency characteristics of the output voltage through a parallel resonant circuit. Inductors L1 and L2 help to suppress sudden changes in current, while capacitor C2 helps to stabilize the output voltage.

[0053] In this embodiment, the DC sides of the two inverters are connected together through a common bus, while the AC sides are output to the same load end through their respective inverter modules and load circuits. By operating in parallel, the power output capacity of the entire system can be improved, and the load pressure of each inverter can also be dispersed, thereby enhancing the reliability of the system.

[0054] In this embodiment, all inverters operating in parallel are preset with the same output voltage, and the following method is used for voltage compensation, the method comprising:

[0055] S101, each inverter collects the voltage U and current I output to the load circuit, where the voltage U is the voltage between the inverter output terminal and the capacitor C2, and the current I is the current flowing through the inductors L1 and L2;

[0056] In this step, each inverter collects voltage U and current I from its AC side output terminal.

[0057] Voltage U: The voltage collected is the voltage across the inverter output and the parallel capacitor C2 in the load circuit. This voltage reflects the actual voltage value between the inverter and the load and is a key parameter in the system voltage loop control.

[0058] Current I: Collects the current flowing through the parallel inductors L1 and L2. These inductors are connected in parallel in the load circuit to regulate the flow of AC current. By collecting the current flowing through the inductors, the dynamic changes of the load current can be accurately reflected.

[0059] S102, calculating the total power W of the inverter in one AC cycle through the collected voltage U and current I, wherein the total power W is obtained by integrating the instantaneous power;

[0060] After collecting the voltage U and current I, the system needs to calculate the total power W of the inverter in one AC cycle. Integrate the instantaneous power. In one embodiment, the calculation formula can be as follows:

[0061]

[0062] Where T is an AC cycle and P(t) is the instantaneous power.

[0063] In this embodiment, the power at each instant is the product of voltage and current P(t)=U(t)×I(t). In order to obtain the total power in the entire cycle, the instantaneous power in one AC cycle T needs to be integrated.

[0064] The power balance of the inverter system can be determined by the total power W. If there is a power imbalance in the system, it will be compensated through subsequent steps.

[0065] S103, monitoring the total power W according to the output of the bang-bang controller, and when it is detected that W is less than zero, increasing the compensation value Offset by a compensation step step_up;

[0066] S104, when W is greater than or equal to zero, the compensation value Offset is reduced by a compensation step downstep_down;

[0067] In this step, a Bang-Bang controller is used to monitor the dynamic change of the power W.

[0068] The Bang-Bang controller is a two-state controller that determines whether to compensate based on the positive and negative values ​​of power. It uses a fast switching mechanism to adjust the control amount of the system according to the real-time monitored power value.

[0069] When it is detected that the total power W is less than zero, it indicates that the system power is insufficient and the compensation value needs to be increased. At this time, the controller increases the compensation value Offset by a compensation step upstep_up.

[0070] When it is detected that the total power WWW is greater than or equal to zero, it means that the system power is sufficient or exceeds expectations. At this time, the compensation value Offset is reduced and the compensation step step_down is reduced.

[0071] S105, limiting the calculated compensation value Offset[n], where the limiting range is [0, Umax], where Umax is the difference between the pre-agreed maximum output voltage and the typical output voltage;

[0072] In order to avoid over-adjustment of the compensation value, the system needs to limit the compensation value Offset[n]. The maximum range of the compensation value is limited to 0 to Umax, where Umax is the difference between the maximum output voltage and the typical output voltage. This can prevent the compensation value from exceeding the reasonable range and avoid causing overvoltage or undervoltage in the system. By limiting the compensation value, the system can be ensured to operate stably and extreme situations can be prevented.

[0073] In this step, the system limits the compensation value Offset[n] to ensure that the compensation adjustment is within a reasonable range to avoid system instability due to over-adjustment. The compensation value limit range is set to [0, Umax], where Umax is a pre-set maximum allowable value used to limit the maximum amplitude of the compensation.

[0074] The compensation value Offset[n] is the adjustment value calculated by the system based on the power deviation to correct the inverter output voltage. When the inverter output power does not match the load requirement, the system adjusts the output voltage by adjusting this compensation value to maintain the system power balance. This compensation value directly affects the inverter voltage output, so its changes must be controlled to avoid excessive adjustment or frequent fluctuations.

[0075] If the compensation value Offset[n] is not limited, two unfavorable situations may occur:

[0076] If the compensation value is too large, the system output voltage will be too high, which may exceed the safe operating voltage range of the load, thus causing overvoltage risk. This may damage the load equipment or cause electrical failure.

[0077] On the contrary, if the compensation value is too small, the output voltage may not be corrected effectively, causing the system to be in a power imbalance state continuously, and may even cause undervoltage, making it impossible for the load to obtain a stable power supply.

[0078] In order to avoid these two situations, the compensation value needs to be limited to ensure that its change is within a reasonable range, thereby ensuring that the system can operate safely and stably under any working conditions.

[0079] The compensation value limit range is set to [0, Umax], where Umax is a pre-agreed parameter used to define the upper limit of the compensation value. The specific definition is as follows:

[0080] The lower limit of 0 means that when the system does not need any compensation, the compensation value is zero. At this time, the inverter will operate according to the initially set output voltage without additional adjustment.

[0081] Upper limit of the compensation value. Umax is defined as the difference between the maximum output voltage and the typical output voltage. By setting this upper limit, it can be ensured that even in extreme cases (such as sudden changes in system load or voltage fluctuations), the compensation value will not be too large to avoid overvoltage problems.

[0082] Formulaically, Umax is calculated as:

[0083] Umax=U_{text{max}}-U_{text{nominal}}

[0084] in:

[0085] U_{text{max}} is the maximum allowable output voltage in the system design;

[0086] U_{text{nominal}}) is the typical operating voltage of the system.

[0087] Through this setting, the change of compensation value is always kept within a reasonable range.

[0088] The main purpose of limiting is to prevent the compensation value from being over-adjusted, thereby avoiding extreme conditions in the system, including:

[0089] The ultimate goal of the limiting process is to ensure the overall stability of the system during the compensation adjustment process. By controlling the compensation value within a reasonable range, the system can operate smoothly under various load changes and voltage fluctuations, maintaining a dynamic balance between the inverter output and the load demand. At the same time, the limiting process prevents system instability caused by extreme changes in the compensation value, thereby ensuring the reliability and safety of the system.

[0090] Limiting plays a key role in the output compensation method of parallel inverters. By limiting the compensation value Offset[n], the system can flexibly adjust the output voltage without causing overvoltage or undervoltage problems, ensuring the stability and safety of the inverter system. This mechanism can adapt to various complex working conditions and prevent the negative impact caused by excessive compensation adjustment.

[0091] S106, adding the compensation value Offset[n] to the voltage loop control value of the inverter;

[0092] Among them, if the control quantity is the voltage amplitude, the compensation value is directly added; if the control quantity is the real-time voltage value, the compensation value is multiplied by the current phase angle θ, that is, the compensation value is Offset*sin(θ), where θ is the current voltage phase.

[0093] The calculated compensation value Offset[n] needs to be applied to the voltage loop control quantity of the inverter to adjust the actual output voltage. The voltage loop control quantity is the core parameter of the inverter control voltage, which can be the voltage amplitude or real-time value.

[0094] If the controlled quantity is the voltage amplitude, the compensation value is directly added to the voltage amplitude, which is simple and effective.

[0095] If the control quantity is the real-time value of the voltage, the compensation value needs to be combined with the voltage phase angle θ. At this time, the compensation value is multiplied by the sine value of the current phase angle, and the formula is:

[0096] Compensation value = Offset × sin (θ), where θ is the phase of the current voltage. This processing method can accurately adjust the voltage waveform, making the compensation more accurate.

[0097] In step S106, the system needs to apply the calculated compensation value Offset[n] to the voltage loop control quantity of the inverter, so as to meet the load demand by accurately adjusting the output voltage of the inverter. The key to this step is how to effectively integrate the compensation value into the voltage control mechanism, which includes two specific situations: the control quantity is the voltage amplitude, or the control quantity is the real-time value of the voltage.

[0098] The voltage loop control quantity is an important parameter for the inverter to control its output voltage. By controlling this quantity, the inverter can adjust the output voltage in real time to match the needs of the load circuit and maintain the power balance of the system. The voltage loop control quantity can be the voltage amplitude (i.e. the maximum value of the voltage waveform) or the real-time value of the voltage (i.e. the instantaneous voltage value at any time). These two control methods have different application scenarios, and the specific processing methods are as follows.

[0099] The voltage loop control quantity is the voltage amplitude:

[0100] If the voltage loop control quantity is the voltage amplitude, it means that the inverter adjusts the output by controlling the maximum value of the voltage waveform. At this time, the system directly adds the compensation value Offset[n] to the voltage amplitude.

[0101] In this way, the system can simply add the compensation value to the original voltage amplitude to increase or decrease the peak value of the voltage output.

[0102] This method is simple and requires little computation, and is particularly suitable for applications that require a stable output voltage amplitude, such as a regulated power supply or a constant voltage control system. In this case, the voltage waveform remains unchanged, and the system only needs to adjust its amplitude according to the power demand.

[0103] It is suitable for situations where the voltage waveform shape does not need to be precisely controlled, and the main focus is on the overall size of the output voltage.

[0104] The voltage loop control quantity is the real-time voltage value:

[0105] If the voltage loop control quantity is the real-time value of the voltage, it means that the system needs to control not only the voltage amplitude, but also the shape and phase of the voltage waveform. In this case, the compensation value Offset[n] needs to be combined with the voltage phase angle and corrected according to the sine function of the voltage waveform.

[0106] In this way, the system calculates the instantaneous compensation value according to the current phase of the voltage and superimposes it on the current real-time value of the voltage.

[0107] This method is more accurate and can make detailed adjustments according to the dynamic changes of the voltage waveform. By associating the compensation value with the phase angle of the voltage, the system can correct each instantaneous value of the voltage waveform to ensure the accuracy and stability of the voltage output waveform. It is suitable for occasions where the shape of the voltage waveform needs to be precisely controlled, especially in applications with harmonic control or high requirements for the voltage waveform.

[0108] Voltage phase angle θ is an important characteristic of the voltage waveform, which describes the phase position of the voltage waveform in the AC cycle. For an AC voltage waveform, it is a sine wave or a cosine wave, and its phase angle θ changes continuously over time and cycles between 0 and 2π.

[0109] By adjusting the compensation value using the voltage phase angle θ, it is possible to ensure that the compensation is synchronized with the voltage waveform. For example, when the voltage waveform is at its peak, the compensation value has the greatest effect; and when the voltage waveform is at its zero point, the compensation value has the least effect. In this way, the compensation effect can better reflect the changes in the actual voltage waveform.

[0110] In the specific calculation process, the frequency of the phase angle change of the voltage waveform depends on the system's AC voltage frequency (for example, 50 Hz or 60 Hz). As time goes by, the system will continue to monitor the voltage phase angle and calculate and adjust the compensation value in real time.

[0111] Whether it is added directly to the voltage amplitude or multiplied by the sine of the voltage phase angle, the final calculated compensation value will be added to the voltage loop control quantity. The compensated voltage loop control quantity will guide the inverter to adjust its output voltage accordingly, ensuring that the output voltage can remain stable when the load demand fluctuates.

[0112] By applying the compensation value Offset[n] to the voltage amplitude or voltage real-time value, the system can flexibly adjust the output voltage of the inverter. In the case of voltage amplitude control, the system simply and directly superimposes the compensation value to adjust the maximum value of the output voltage; in the case of voltage real-time value control, the system accurately calculates the instantaneous compensation value based on the current phase angle of the voltage and dynamically adjusts the output voltage waveform. This compensation mechanism ensures that the system's voltage output can remain stable under various load changes and operating conditions, thereby improving the reliability and accuracy of the inverter.

[0113] The method of the present application is applied to a circuit system of multiple single-phase inverters running in parallel, and each component of the system is described in detail below.

[0114] Each inverter consists of a DC side, an AC side, and a load circuit. The inverter is responsible for converting electrical energy from AC to DC and back to AC through its internal rectifier module and inverter module, and outputs it to the load in a stable waveform. The specific structure of the inverter is as follows:

[0115] The DC side of each inverter is connected to a common DC bus, called VDC.

[0116] The common bus voltage VDC is a stable DC voltage source, which is provided to each inverter running in parallel. The bus voltage can come from multiple different power sources, such as rectified AC power, solar panels, batteries, etc.

[0117] With this configuration, all inverters running in parallel share the same DC input power supply, ensuring that each inverter operates at the same base voltage, enhancing the consistency and stability of the system.

[0118] The AC side of each inverter is used to convert the inverted DC power into AC power output to drive the external load. The AC side is connected to the load circuit, which is designed to regulate and optimize the electric energy.

[0119] The load circuit mainly includes two key components: parallel inductance and capacitance. Two parallel inductors L1 and L2, and a parallel capacitor C2 are connected in the load circuit.

[0120] Inductors L1 and L2 are connected in parallel in the load circuit. The function of these inductors is to help regulate the current output of the inverter.

[0121] When the inverter output voltage changes, the inductor smoothes the output current by suppressing the instantaneous change of the current, reducing the current harmonic components in the system and improving the output current quality. The inductor component reduces the impact on the load and improves the power factor of the system by buffering the change of current.

[0122] Using two inductors in parallel can effectively increase the selection space and adjustment range of inductance, allowing the system to adapt to different load requirements and flexibly respond to load changes.

[0123] Capacitor C2 is connected in parallel in the load circuit to smooth the output voltage of the inverter.

[0124] The main function of the capacitor in the load circuit is to absorb instantaneous fluctuations in voltage and reduce the ripple of the output voltage. This helps to maintain the stability of the inverter output voltage, especially when the load changes greatly or the voltage fluctuates frequently, the capacitor C2 can effectively play a buffering role.

[0125] Capacitors can provide short-term high current output to support sudden current demands of the load, ensuring that the system can maintain smooth operation when the load changes.

[0126] The rectifier module of each inverter mainly includes multiple power switching devices (such as diodes, IGBTs, MOSFETs, etc.), which are used to convert the input AC power into DC power.

[0127] The core function of the rectifier module is to convert the AC voltage at the input end into a stable DC voltage and provide it to the inverter module. Common rectifier devices include diode bridge rectifier circuits, which rectify the positive and negative half-wave AC power into a unidirectional DC voltage.

[0128] Power switching devices can efficiently convert and regulate electrical energy through high-speed switching operations, ensuring that the inverter can adapt to different voltage inputs and load changes.

[0129] The inverter module is responsible for converting the rectified DC power into AC power again and outputting it to the load circuit.

[0130] The inverter module also uses multiple power switching devices (such as IGBTs or MOSFETs) that switch at a high frequency to generate the required AC output voltage.

[0131] The core function of the inverter module is to provide a stable AC voltage output by converting DC power into AC power. The inverter can generate AC power output of the required frequency and amplitude to meet the needs of different loads by adjusting the operating frequency and duty cycle of the switch.

[0132] The parallel inverter system is characterized in that a plurality of inverters can be operated in parallel at the same time to jointly drive one or more loads.

[0133] Inverters running in parallel can share load current through load balancing mechanism, thus improving the stability and reliability of the system. At the same time, the parallel structure also allows the system to be expanded according to power requirements, making it more flexible.

[0134] Through precise control of the rectifier module and the inverter module, the inverter can maintain the stability of the output voltage in a complex electrical environment and ensure smooth output of the current.

[0135] This circuit system is a highly integrated inverter system. Through the connection of the DC side with the common bus voltage VDC, the input voltage of each inverter is ensured to be consistent. Through the connection of the AC side with the load circuit, the inverter can flexibly adjust the load current and voltage to ensure that the system has high stability and reliability during operation. The inductance and capacitance in the load circuit can further enhance the power quality of the system, enabling it to cope with complex load changes and provide smooth and stable power output.

[0136] In an optional embodiment, the voltage control loop of the inverter adopts a proportional integral differential PID controller, which is used to calculate the control amount of the output voltage based on the error between the fed-back output voltage U and the set value, and dynamically adjust the inverter output in combination with the compensation value Offset.

[0137] In this embodiment, the inverter module adopts a full-bridge inverter circuit. The full-bridge inverter circuit is composed of four power switching devices, and the power switching devices used are insulated gate bipolar transistors (IGBTs). The main function of the IGBT device is to control the conversion of direct current to alternating current. Each power switching device is respectively connected between the positive and negative poles of the DC side of the inverter and the load circuit. Through the switch operation, the inverter realizes the conversion of direct current power to alternating current power. This full-bridge structure can provide a bipolar voltage output for the load, ensuring the stable operation of the inverter.

[0138] In an optional embodiment, the inverter module includes a full-bridge inverter circuit, which is composed of four power switching devices. The four power switching devices are insulated gate bipolar transistors IGBTs. Each power switching device is respectively connected between the positive and negative poles of the DC side of the inverter and the load circuit to realize the conversion of DC power into AC power.

[0139] In an optional embodiment, the rectifier module includes an uncontrolled rectifier bridge circuit, which is composed of six diodes and is used to rectify the input AC power into DC power and supply it to the inverter module.

[0140] In this embodiment, the inverter module adopts a full-bridge inverter circuit. The full-bridge inverter circuit is composed of four power switching devices, and the power switching devices used are insulated gate bipolar transistors (IGBTs). The main function of the IGBT device is to control the conversion of direct current to alternating current. Each power switching device is respectively connected between the positive and negative poles of the DC side of the inverter and the load circuit. Through the switch operation, the inverter realizes the conversion of direct current power to alternating current power. This full-bridge structure can provide a bipolar voltage output for the load, ensuring the stable operation of the inverter.

[0141] In this embodiment, the rectifier module of the inverter includes an uncontrolled rectifier bridge circuit. The uncontrolled rectifier bridge circuit is composed of four diodes, which are used to rectify the input AC power into DC power and supply the rectified DC power to the inverter module. The rectifier bridge circuit has the advantages of simple structure and easy implementation, and can effectively convert the AC power into the DC power required by the inverter, thereby providing the required DC input for the inverter process.

[0142] In an optional embodiment, the output end of the inverter module is connected to the load circuit via an LC filter. The LC filter includes an inductor Lf and a capacitor Cf, and is used to filter out high-frequency harmonic components in the inverter output voltage.

[0143] In this embodiment, the output end of the inverter module is connected to the load circuit through an LC filter. The LC filter is composed of an inductor L_f and a capacitor C_f, and its main function is to filter out high-frequency harmonic components in the inverter output voltage. When the inverter is inverting, the output voltage may contain high-frequency components, and these high-frequency harmonics may have an adverse effect on the load. The presence of the LC filter can effectively remove these high-frequency noises, thereby providing a purer AC output for the load.

[0144] In an optional embodiment, the DC side of each inverter is configured with a DC capacitor C DC .

[0145] In an optional embodiment, a DC capacitor C is configured on the DC side of each inverter. DC The DC capacitor is used to smooth the DC power and reduce the voltage fluctuation at the input of the inverter. Since the rectified DC power may have ripples and instantaneous fluctuations, the DC capacitor can stabilize the voltage and ensure the input voltage of the inverter module is stable, thereby improving the output quality of the inverter.

[0146] In an optional embodiment, the parallel inductance L1 and the inductance L2 of the load circuit are respectively connected in parallel with the load capacitance C2 to form a parallel resonant circuit.

[0147] In an optional embodiment, the parallel inductors L1 and L2 in the load circuit are respectively connected in parallel with the load capacitor C2 to form a parallel resonant circuit. The main function of the parallel resonant circuit is to adjust the resonant frequency of the load circuit so that the circuit reaches a resonant state at a specific frequency, thereby reducing the energy loss between the inductor and the capacitor. Through the design of the resonant circuit, the power factor of the circuit can be improved and the energy transmission efficiency can be optimized.

[0148] In an optional embodiment, each inverter of the parallel inverters further includes an isolation transformer, wherein the isolation transformer is used to transmit the AC power output by the inverter to the load circuit and provide electrical isolation between the inverters.

[0149] In this optional embodiment, each parallel inverter also includes an isolation transformer. The isolation transformer is used to transmit the AC power output by the inverter to the load circuit and provide electrical isolation between different inverters. Electrical isolation can improve the safety of the system and avoid direct electrical interference between different inverters. The isolation transformer can adjust the amplitude of the output voltage to adapt it to the requirements of the load, thereby optimizing the power supply performance of the inverter. When a system failure occurs, the isolation transformer can provide protection for other circuits to prevent the failure from spreading to the entire circuit system.

[0150] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0151] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0152] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0153] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0154] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, read-only memory), random access memory (RAM, random access memory), disk or optical disk and other media that can store program code.

Claims

1. An output compensation method in a parallel inverter system, characterized in that: Applicable to a circuit system including a plurality of single-phase inverters operating in parallel, the circuit system comprising: The DC side of each inverter is connected to a common bus voltage VDC, and the AC side of each inverter is connected to a load circuit, which includes two parallel inductors L1 and L2 and a parallel capacitor C2; Each inverter includes a rectifier module and an inverter module. The rectifier module includes a plurality of power switching devices for converting AC power into DC power. The inverter module includes a plurality of power switching devices for inverting DC power into AC power and outputting it to the load circuit. All inverters running in parallel are preset with the same output voltage and the following method is used for voltage compensation, the method comprising: Each inverter collects the voltage U and current I output to the load circuit, where the voltage U is the voltage between the inverter output terminal and the capacitor C2, and the current I is the current flowing through the inductors L1 and L2; The total power W of the inverter in one AC cycle is calculated by the collected voltage U and current I, and the total power W is obtained by integrating the instantaneous power; According to the output of the bang-bang controller, the total power W is monitored. When it is detected that W is less than zero, the compensation value Offset is increased by a compensation step step_up; When W is greater than or equal to zero, the compensation value Offset is reduced by a compensation step downstep_down; The calculated compensation value Offset[n] is limited in the range of [0,Umax], where Umax is the difference between the pre-agreed maximum output voltage and the typical output voltage; Add the compensation value Offset[n] to the voltage loop control quantity of the inverter; Among them, if the control quantity is the voltage amplitude, the compensation value is directly added; if the control quantity is the real-time voltage value, the compensation value is multiplied by the current phase angle θ, that is, the compensation value is Offset*sin(θ), where θ is the current voltage phase.

2. The output compensation method in a parallel inverter system according to claim 1, characterized in that: The voltage control loop of the inverter adopts a proportional-integral-differential PID controller, which is used to calculate the control amount of the output voltage according to the error between the fed-back output voltage U and the set value, and dynamically adjust the inverter output in combination with the compensation value Offset.

3. The output compensation method according to claim 1, characterized in that: The inverter module includes a full-bridge inverter circuit, which is composed of four power switching devices. The four power switching devices are insulated gate bipolar transistors IGBTs. Each power switching device is respectively connected between the positive and negative poles of the DC side of the inverter and the load circuit to realize the conversion of DC power into AC power.

4. The output compensation method according to claim 1, characterized in that: The rectifier module includes an uncontrolled rectifier bridge circuit, which is composed of six diodes and is used to rectify the input AC power into DC power and supply it to the inverter module.

5. The output compensation method according to claim 1, characterized in that: The output end of the inverter module is connected to the load circuit via an LC filter. The LC filter includes an inductor Lf and a capacitor Cf, and is used to filter out high-frequency harmonic components in the inverter output voltage.

6. The output compensation method according to claim 1, characterized in that: The DC side of each inverter is equipped with a DC capacitor C DC .

7. The output compensation method according to claim 1, characterized in that: The parallel inductance L1 and the inductance L2 of the load circuit are respectively connected in parallel with the load capacitance C2 to form a parallel resonant circuit.

8. The output compensation method according to claim 1, characterized in that: Each inverter of the parallel inverters further includes an isolation transformer, which is used to transmit the AC power output by the inverter to the load circuit and provide electrical isolation between the inverters.

9. The output compensation method according to claim 1, characterized in that: The total power W is obtained by integrating the instantaneous power, including calculating in the following manner: The method for calculating the total power W of the inverter in one AC cycle is: Integrate the instantaneous power P(t) within the cycle over time t, and the calculation formula is: Where T is an AC cycle and P(t) is the instantaneous power.

10. The output compensation method according to any one of claims 1 to 9, characterized in that: The limiting of the compensation value Offset[n] includes a dynamic limiting range, and the dynamic limiting range is automatically adjusted according to the operating state of the inverter system and the load change; When the system load suddenly changes or the voltage fluctuates greatly, increase the upper limit Umax; When the system runs smoothly, reduce the upper limit Umax.

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