Output compensation method in parallel inverter system

Abstract

The application discloses an output compensation method in a parallel inverter system. The method comprises the following steps: collecting the voltage U and the current I of each inverter output to the load circuit, wherein the voltage U is the voltage between the output end of the inverter and the capacitor C2, and the current I is the current flowing through the inductors L1 and L2; calculating the total power W of the inverter in an AC cycle through the collected voltage U and current I, wherein the total power W is obtained by integrating the instantaneous power; monitoring the total power W according to the output of the bang-bang controller, increasing the compensation value Offset by a compensation step step_up when detecting that W is less than zero; decreasing the compensation value Offset by a compensation step downstep_down when W is greater than or equal to zero; performing amplitude limiting processing on the calculated compensation value Offset[n], wherein the amplitude limiting range is [0, Umax], wherein Umax is the difference between the maximum output voltage and the typical output voltage agreed in advance; and adding the compensation value Offset[n] to the voltage loop control quantity of the inverter.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inverters, and particularly relates to an output compensation method in a parallel inverter system. BACKGROUND

[0002] With the rapid development of power electronics technology, inverters have been widely used in new energy power generation, industrial control and power conversion fields. Parallel inverter systems 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 can cause instability of the system, especially when the output voltages are inconsistent, which can easily cause the bus voltage to abnormally rise, thereby damaging the key devices such as IGBT (Insulated Gate Bipolar Transistor) in the inverter.

[0003] In actual applications, the problem of inconsistent voltage when inverters are connected in parallel is common, especially in the case of load fluctuation, input power variation or control system response delay, the output voltage of a certain inverter may be lower than that of other inverters. This can cause the bus voltage to rise, and in severe cases, it can cause IGBT to burn out, affecting the reliability and safety of the system.

[0004] In order to solve the above problems, some control strategies are proposed in the prior art, which usually adjust the output power, output voltage or frequency of the inverter to achieve voltage balance. However, these methods have certain limitations, such as slow response speed, inaccurate compensation, etc., which are difficult to meet the requirements of modern high-performance power systems. Especially in complex load and frequent fluctuation application scenarios, the existing technology is difficult to achieve fast and stable control of the voltage, and the inverter is still vulnerable to bus voltage fluctuations, thereby increasing the risk of damage to the system.

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

[0006] Therefore, there is an urgent need for a control method that can compensate for the output voltage of the inverter in real time and effectively, through fast response and dynamic adjustment, to achieve stable control of the bus voltage and prevent the inverter from being damaged due to abnormal voltage rise. SUMMARY

[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 solutions provided in the present application are described as follows:

[0009] The first aspect of the present application provides an output compensation method in a parallel inverter system, applied to a circuit system including multiple single-phase inverters running 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 including multiple power switching devices for converting AC power into DC power, and the inverter module including multiple power switching devices for inverting DC power into AC power and outputting 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, wherein the voltage U is the voltage across 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 an 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, and when 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 decreased by a compensation step downstep_down;

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

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

[0019] 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, i.e. 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-derivative (PID) controller, which is configured to calculate a control amount of the output voltage according to an error between a feedback output voltage U and a set value, and dynamically adjust the output of the inverter in combination with a compensation value Offset.

[0021] Optionally, the inverter module comprises a full-bridge inverter circuit, which is composed of four power switching devices, i.e., insulated gate bipolar transistors (IGBTs), each of which is connected between the positive and negative poles of the DC side of the inverter and the load circuit, for realizing conversion of DC power into AC power.

[0022] Optionally, the rectifier module comprises an uncontrolled rectifier bridge circuit, which is composed of six diodes, for rectifying input AC power into DC power and supplying the inverter module.

[0023] Optionally, the output end of the inverter module is connected to the load circuit through an LC filter, which comprises an inductor Lf and a capacitor Cf, for filtering high-frequency harmonic components in the output voltage of the inverter.

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

[0025] Optionally, the parallel inductors L1 and L2 of the load circuit are respectively connected in parallel with a load capacitor C2, for forming a parallel resonant circuit.

[0026] Optionally, each inverter of the parallel inverters further comprises an isolation transformer, which is configured to transmit 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 integration of the instantaneous power, including being calculated by:

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

[0029] The instantaneous power P(t) is integrated with respect to time t, and the calculation formula is:

[0030]

[0031] wherein T is one AC cycle, and P(t) is the instantaneous power.

[0032] Optionally, the amplitude limiting of the compensation value Offset[n] comprises a dynamic amplitude limiting range, which is automatically adjusted according to the running state of the inverter system and the load variation;

[0033] When the system load mutates or the voltage fluctuates greatly, increase the upper limit of the limiting amplitude Umax;

[0034] When the system runs smoothly, decrease the upper limit of the limiting amplitude Umax.

[0035] From the above technical solutions, the present application has the following advantages:

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

[0037] 2. The Bang-Bang controller is used to dynamically adjust the compensation value. When the power W is less than zero, the compensation is increased. When the power W is greater than or equal to zero, the compensation is reduced. This mechanism ensures that the system can quickly respond in the case of load change or instability, and avoids voltage mutation.

[0038] 3. The compensation value Offset[n] is limited in amplitude to prevent overcompensation or undercompensation, and to avoid unnecessary fluctuations of the inverter system. By setting the maximum output voltage Umax, the compensation value is ensured to change within a reasonable range, and the stability of the system is improved.

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

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

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

[0042] In order to more clearly illustrate the technical solutions in the present application, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

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

[0044] Figure 2 Structure diagram of an embodiment of the circuit system of the single-phase inverters in parallel provided in the method of the present application. DETAILED DESCRIPTION

[0045] Referring to Figure 1 , Figure 2 , the present application first provides an embodiment of a method applied to a circuit system comprising a plurality of single-phase inverters in parallel, the circuit system comprising:

[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 comprising two parallel inductors L1 and L2 and a parallel capacitor C2.

[0047] Each inverter comprises a rectifier module and an inverter module, the rectifier module comprising a plurality of power switching devices for converting AC power into DC power, and the inverter module comprising a plurality of power switching devices for inverting the DC power into AC power and outputting to the load circuit.

[0048] Referring to Figure 2 , the present application provides an embodiment of a circuit system comprising a parallel configuration of two inverters, each inverter being connected to a common DC bus VDC through a rectifier module and an inverter module and ultimately outputting to a load circuit.

[0049] The rectifier module of each inverter comprises a rectifier bridge composed of six diodes G1, G2, G3, G4, G5 and G6, for rectifying AC power output by a generator into DC power and supplying 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 composed of four IGBT power switching devices G7, G8, G9 and G10, for converting DC power into AC power. The four IGBTs are respectively connected between the positive and negative poles of the DC bus and the load, and by controlling the switching operation of the IGBTs, the conversion from DC to AC is achieved to generate an AC voltage output suitable for the load requirements.

[0052] The output end 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 resonance circuit. Inductors L1 and L2 help suppress current surges, and capacitor C2 helps 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 respectively output to the same load end through their respective inverter modules and load circuits. By operating in parallel, the power output capability of the entire system can be improved, while also dispersing the load pressure of each inverter and enhancing the reliability of the system.

[0054] In this embodiment, all parallel-operating inverters are preset with the same output voltage, and voltage compensation is performed using the following method, which includes:

[0055] S101, each inverter collects the voltage U and current I output to the load circuit, where the voltage U is the voltage across the inverter output 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 the voltage U and current I from the output end of its AC side.

[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: The current collected is 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 in the load current can be accurately reflected.

[0059] S102, calculate the total power W of the inverter in an AC cycle based on the collected voltage U and current I, where 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 an AC cycle. The instantaneous power is integrated, and 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 the voltage and the current P(t) = U(t) x I(t). To obtain the total power over a cycle, the instantaneous power over one AC cycle T needs to be integrated.

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

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

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

[0067] In this step, the Bang-Bang controller is used to monitor the dynamic changes 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 the power. It adjusts the control amount of the system according to the real-time monitored power value through a fast switching mechanism.

[0069] When the total power W is detected to be less than zero, it indicates that the system is power deficient 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 the total power W is detected to be greater than or equal to zero, it indicates that the system is power sufficient or exceeds the expected value, at which time the compensation value Offset is decreased and the compensation step step_down is decreased.

[0071] S105, limit the calculated compensation value Offset[n] to the range [0, Umax], where Umax is the difference between the maximum output voltage and the typical output voltage agreed upon in advance;

[0072] In order to avoid excessive 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 a reasonable range and prevent the occurrence of system overvoltage or undervoltage. By limiting the compensation value, the system ensures stable operation and prevents extreme situations.

[0073] In this step, the system limits the compensation value Offset[n] to ensure that the compensation adjustment is within a reasonable range, avoiding instability caused by excessive adjustment. The compensation value is limited to the range [0, Umax], where Umax is a pre-set maximum allowed value that limits the maximum amplitude of the compensation.

[0074] The compensation value Offset[n] is the adjustment amount calculated by the system to correct the inverter output voltage based on the power deviation. When the inverter output power does not match the load requirements, the system adjusts this compensation value to correct the output voltage, thereby maintaining system power balance. This compensation value directly affects the inverter's 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 adverse situations may occur:

[0076] If the compensation value is too large, it will cause the system output voltage to be too high, possibly exceeding the safe working voltage range of the load, thereby causing an overvoltage risk. This situation may damage the load equipment or cause electrical faults.

[0077] On the contrary, if the compensation value is too small, it may not effectively correct the output voltage, causing the system to remain in a power imbalance state, and even possibly causing an under-voltage phenomenon, making it impossible for the load to obtain stable power supply.

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

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

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

[0081] The 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, avoiding the risk of overvoltage.

[0082] In formula, the calculation method of Umax is:

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

[0084] Where:

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

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

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

[0088] The main purpose of the clipping process is to prevent excessive adjustment of the compensation value, thereby avoiding extreme situations in the system, including:

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

[0090] The clipping process plays a key role in the output compensation method of parallel inverters. By clipping 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 negative effects caused by excessive compensation adjustment.

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

[0092] Wherein, if the control quantity is the voltage amplitude, the compensation value is directly added; if the control quantity is the real-time value of the voltage, the compensation value is multiplied by the current phase angle θ, i.e. 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 amplitude or real-time value of the voltage.

[0094] If the control quantity is the amplitude of the voltage, 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] The compensation value = Offset x sin(θ), where θ is the phase of the current voltage. This processing method can accurately adjust the waveform of the voltage, 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 demand of the load by accurately adjusting the output voltage of the inverter. The key of this step is how to effectively integrate the compensation value into the voltage control mechanism, which includes two cases: the control quantity is the amplitude of the voltage, 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 demand of the load circuit and maintain the power balance of the system. The voltage loop control quantity can be the amplitude of the voltage (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 amplitude of the voltage, 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 very simply add the compensation value to the original voltage amplitude, increasing or decreasing the peak value of the voltage output.

[0102] This method is simple and has small computational complexity, and is particularly suitable for application scenarios that require stable output voltage amplitude, such as regulated power supplies or constant voltage control systems. In this case, the waveform of the voltage remains unchanged, and the system only needs to adjust its amplitude according to the power demand.

[0103] This method is suitable for occasions that do not require accurate control of the voltage waveform shape, mainly focusing on the overall size of the output voltage.

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

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

[0107] This method is more accurate and can make fine 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, ensuring the accuracy and stability of the voltage output waveform. It is suitable for occasions that require precise control of the voltage waveform shape, especially in applications that require harmonic control or have high requirements for the voltage waveform.

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

[0109] By adjusting the compensation value using the voltage phase angle θ, the compensation can be synchronized with the voltage waveform. For example, when the voltage waveform is at the peak value, the compensation value has the maximum effect; when the voltage waveform is at zero, the compensation value has the minimum effect. In this way, the effect of compensation can better reflect the changes of the actual voltage waveform.

[0110] In the specific calculation process, the frequency of the change of the voltage phase angle depends on the frequency of the AC voltage of the system (for example, 50Hz or 60Hz). Over time, the system continuously monitors the voltage phase angle and calculates and adjusts the compensation value in real time.

[0111] Whether added directly to the voltage amplitude or multiplied by the sine value 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 remains stable when the load demand fluctuates.

[0112] By applying the compensation value Offset[n] to the voltage amplitude or the 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 adds 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 according to the current phase angle of the voltage and dynamically adjusts the output voltage waveform. This compensation mechanism ensures that the voltage output of the system remains 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 the circuit system of multiple single-phase inverters operating in parallel. The various components of the system are described in detail below.

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

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

[0116] The common bus voltage VDC is a stable DC voltage source provided to each parallel-operating inverter. This bus voltage can be sourced from multiple different power forms, such as rectified AC power, solar panels, batteries, etc.

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

[0118] The AC side of each inverter is used to convert the inverted DC power into AC power output, driving external loads. The AC side is connected to a load circuit designed for power regulation and optimization.

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

[0120] The inductors L1 and L2 are configured in parallel in the load circuit. These inductor components help regulate the inverter's current output.

[0121] When the inverter output voltage changes, the inductors smooth the output current by suppressing transient changes in current, reducing current harmonic components in the system, and improving the quality of the output current. Inductor components buffer current changes, reducing the impact on the load and improving the power factor of the system.

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

[0123] The capacitor C2 is connected in parallel in the load circuit to smooth the inverter's output voltage.

[0124] The main role of the capacitor in the load circuit is to absorb transient fluctuations in voltage, reducing the ripple of the output voltage. This helps maintain the stability of the inverter output voltage, especially in cases where the load changes significantly or the voltage fluctuates frequently, and the capacitor C2 can effectively act as a buffer.

[0125] The capacitor can provide a short-term high-current output to support the sudden current demand of the load, ensuring that the system remains stable 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 alternating voltage at the input into a stable direct current voltage, which is provided to the inverter module. Common rectifier devices include diode bridge rectifier circuits, which rectify the positive and negative half-wave alternating current into a unidirectional direct current voltage.

[0128] Power switching devices can efficiently convert and regulate power 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 direct current power into alternating current power again and outputting it to the load circuit.

[0130] Multiple power switching devices (such as IGBT or MOSFET) are also used in the inverter module, which operate at high frequencies to generate the required alternating output voltage.

[0131] The core function of the inverter module is to provide a stable alternating voltage output by converting direct current into alternating current. By adjusting the operating frequency and duty cycle of the switches, the inverter can generate alternating current output of the required frequency and amplitude to meet the needs of different loads.

[0132] The parallel inverter system is characterized by multiple inverters that can operate in parallel to drive one or more loads simultaneously.

[0133] Parallel operating inverters can share load current through load balancing mechanisms, thereby improving system stability and reliability. At the same time, the parallel structure also makes the system more flexible in terms of power demand expansion.

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

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

[0136] In an optional embodiment, the voltage control loop of the inverter uses a proportional-integral-derivative (PID) controller. The PID controller calculates the control amount of the output voltage based on the error between the feedback output voltage U and the set value, and dynamically adjusts 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 (IGBT). The main function of the IGBT device is to control the conversion of direct current to alternating current. Each power switching device is connected between the positive and negative poles of the inverter DC side and the load circuit, and through switching operation, the inverter realizes the conversion of direct current energy to alternating current energy. This full-bridge structure can provide bipolar voltage output for the load, ensuring stable operation of the inverter.

[0138] In an alternative embodiment, the inverter module includes a full-bridge inverter circuit composed of four power switching devices, which are insulated gate bipolar transistors (IGBT). Each power switching device is connected between the positive and negative poles of the inverter DC side and the load circuit, and is used to realize the conversion of direct current energy to alternating current energy.

[0139] In an alternative embodiment, the rectifier module includes a non-controlled rectifier bridge circuit composed of six diodes, which is used to rectify the input alternating current energy into direct current energy and supply 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 (IGBT). The main function of the IGBT device is to control the conversion of direct current to alternating current. Each power switching device is connected between the positive and negative poles of the inverter DC side and the load circuit, and through switching operation, the inverter realizes the conversion of direct current energy to alternating current energy. This full-bridge structure can provide bipolar voltage output for the load, ensuring stable operation of the inverter.

[0141] In this embodiment, the rectifier module of the inverter includes a non-controlled rectifier bridge circuit. The non-controlled rectifier bridge circuit is composed of four diodes, which are used to rectify the input alternating current energy into direct current energy and supply the inverter module with the rectified direct current energy. The advantage of the rectifier bridge circuit is that it is simple in structure and easy to implement, and can effectively convert alternating current power into the required direct current power for the inverter, thereby providing the required direct current input for the inverter process.

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

[0143] In this embodiment, an LC filter is connected between the output of the inverter module and the load circuit. 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 output voltage of the inverter. When the inverter is operating, the output voltage may contain high-frequency components, which can have an adverse effect on the load. The presence of the LC filter can effectively remove these high-frequency noises, thereby providing a more pure AC output for the load.

[0144] In an optional embodiment, a DC capacitor C DC .

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

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

[0147] In an optional embodiment, the parallel inductors L1 and L2 of the load circuit are connected in parallel with the load capacitor C2, respectively, to form a parallel resonance circuit. The main function of the parallel resonance circuit is to adjust the resonance frequency of the load circuit, so that the circuit reaches a resonance state at a specific frequency, thereby reducing the energy loss between the inductor and the capacitor. Through the design of the resonance 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, which 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 further 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 to the needs of the load, thereby optimizing the power supply performance of the inverter. In the event of a system failure, 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 foregoing method embodiments, which will not be repeated here.

[0151] In 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, and actual implementation can have another division manner, for example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the units shown or discussed can be indirect coupling or communication connection through some interface, device or unit, and can be electrical, mechanical or other forms.

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

[0153] In addition, each functional unit in each embodiment of the present application can be integrated in one processing unit, or each unit can be physically present separately, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of a software functional unit.

[0154] The integrated unit, if realized in the form of a software functional unit and sold or used as an independent product, can be stored in a computer readable storage medium. Based on this understanding, the technical solutions of the present application essentially or the part of the prior art that makes a contribution or the whole or part of the technical solutions can be embodied in the form of a software product, which is stored in a storage medium and includes a plurality of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application. The foregoing storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and various program code storage media.

Claims

1. An output compensation method in a parallel inverter system, characterized by, The application is applied to a circuit system comprising multiple single-phase inverters operating in parallel, and the circuit system comprises: 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 comprising two parallel inductors L1 and L2 and a parallel capacitor C2; Each inverter comprises a rectification module and an inversion module, the rectification module comprises multiple power switching devices for converting AC power into DC power, and the inversion module comprises multiple power switching devices for inverting DC power into AC power and outputting to the load circuit; All the inverters operating in parallel are preset with the same output voltage, and the voltage compensation is performed by using the following method, which comprises: Each inverter collects the voltage U and the current I output to the load circuit, wherein the voltage U is the voltage across 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 using 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, and 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 decreased by a compensation step downstep_down; The calculated compensation value Offset[n] is subjected to amplitude limiting processing in the range of [0, Umax], wherein Umax is the difference between the maximum output voltage and the typical output voltage; The compensation value Offset[n] is added to the voltage loop control quantity of the inverter; 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), wherein θ is the current voltage phase.

2. The output compensation method in the parallel inverter system according to claim 1, characterized by, The voltage control loop of the inverter adopts a proportional-integral-derivative (PID) controller, which is used to calculate the control quantity of the output voltage according to the error between the feedback output voltage U and the set value, and dynamically adjusts the output of the inverter in combination with the compensation value Offset.

3. The output compensation method of claim 1, wherein The inversion module comprises a full-bridge inversion circuit composed of four power switching devices, i.e., insulated gate bipolar transistors (IGBTs), each of which is connected between the positive and negative poles of the DC side of the inverter and the load circuit, for realizing the conversion of DC power into AC power.

4. The output compensation method of claim 1, wherein The rectification module comprises an uncontrolled rectification bridge circuit composed of six diodes, for rectifying the input AC power into DC power and supplying the inversion module.

5. The output compensation method of claim 1, wherein The output end of the inversion module is connected to the load circuit through an LC filter comprising an inductor Lf and a capacitor Cf, for filtering out the high-frequency harmonic components in the output voltage of the inverter.

6. The output compensation method of claim 1, wherein The DC side of each inverter is configured with a DC capacitor C DC .

7. The output compensation method of claim 1, wherein The parallel inductors L1 and L2 of the load circuit are respectively connected in parallel with the load capacitor C2, for forming a parallel resonant circuit.

8. The output compensation method of claim 1, wherein Each of the parallel inverters further comprises an isolation transformer for transmitting the AC power output by the inverter to the load circuit and providing electrical isolation between the inverters.

9. The output compensation method of claim 1, wherein, The total power W is obtained by integration of the instantaneous power, which is calculated by: The method for calculating the total power W of the inverter in one AC cycle is: The total power W is obtained by integration of the instantaneous power, which is calculated by: The calculation formula is:

10. The output compensation method according to any one of claims 1 to 9, characterized in that, Where T is one AC cycle, and P(t) is the instantaneous power. The amplitude limiting of the compensation value Offset[n] comprises a dynamic amplitude limiting range, which is automatically adjusted according to the running state of the inverter system and the load change; When the system load is suddenly changed or the voltage is greatly fluctuated, the upper limit Umax of the amplitude limiting is increased; When the system runs smoothly, the upper limit Umax of the amplitude limiting is reduced.

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