Method and system for suppressing subsynchronous oscillation of grid / following new energy hybrid connected system

Abstract

The application discloses a network construction / following network type new energy hybrid connection system subsynchronous oscillation suppression method and system, and remolds the impedance of the hybrid connection system by adding a damping compensation controller in the voltage control link of the network construction type new energy grid-connected inverter to weaken the negative damping characteristic. The method can effectively improve the operation stability of the network construction / following network type new energy hybrid connection system and suppress the system subsynchronous oscillation caused by wide range change of the grid strength. The application can be used for solving the subsynchronous oscillation problem caused by grid connection of new energy power generation equipment.

Description

Technical Field

[0001] The present invention relates to the field of grid-connected inverter control, and in particular to a method and system for suppressing subsynchronous oscillations in a grid-connected / grid-following type new energy hybrid parallel system. Background Art

[0002] In actual engineering, inverters that use a phase-locked loop (PLL) to synchronize the converter with the grid are called grid-following inverters; inverters that simulate or partially simulate the external characteristics of synchronous generator sets and independently establish reference voltages and phase angles are called grid-forming inverters. Existing research has shown that the introduction of grid-forming inverters for renewable energy grid-connected systems can improve the stability of renewable energy grid-connected systems dominated by grid-following inverters under weak grid conditions. However, as the penetration rate of renewable energy power generation increases, its inherent intermittent and fluctuating characteristics will cause the grid strength of power systems with a high proportion of renewable energy to vary over a wide range, which can easily lead to oscillation risks in renewable energy grid-connected systems.

[0003] Current research has largely focused on adding oscillation suppression equipment, but this increases investment costs and the difficulty of installation and site selection, making it difficult to implement in engineering practice. Grid-connected inverters for renewable energy grid-connected systems and those for grid-following systems share the same hardware circuit topology. Therefore, simply converting some inverters in the renewable energy grid-connected system that originally operated with grid-following control to grid-connected control is sufficient. This approach eliminates the need for additional oscillation suppression equipment, reducing investment costs and eliminating the tedious tasks of installation and site selection.

[0004] Grid-connected inverters are prone to subsynchronous oscillations under strong power grids. Adding them to a new energy grid-connected system dominated by grid-following inverters will weaken the system's symmetrical frequency components, and the oscillation components in the supersynchronous frequency band will be weakened. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method and system for suppressing subsynchronous oscillations of a grid-building / grid-following type new energy hybrid parallel system in response to the shortcomings of the existing technology, so as to effectively suppress system oscillations and improve the operating stability of the grid-building / grid-following type new energy hybrid parallel system when the power grid strength changes over a wide range.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: a method for suppressing subsynchronous oscillations of a grid-building / grid-following type new energy hybrid parallel system, wherein the grid-building / grid-following type new energy hybrid parallel system includes a parallel-connected grid-following type new energy grid-connected inverter and a grid-building type new energy grid-connected inverter; the method comprises the following steps:

[0007] S1. Obtain the three-phase voltage u output by the grid-connected new energy inverter aM 、u bM 、u cMAnd the output three-phase current i aM 、i bM 、i cM , the DC side voltage u of the grid-connected new energy inverter dcL , output three-phase voltage u aL 、u bL 、u cL And the output three-phase current i aL 、i bL 、i cL ;

[0008] S2, active power P of grid-connected new energy inverter M and its reference value P M * Calculate the reference angular frequency ω of the active control loop output M ; The voltage amplitude U at PCC point M and its rated value U M * , reactive power Q M and its reference value Q M * Calculate the voltage reference value E output by the reactive control loop M ;

[0009] S3, using the reference angle θ output by the active control loop M To u aM 、u bM 、u cM and i aM 、i bM 、i cM Perform Park transformation respectively to obtain the d-axis component u of the output voltage of the grid-connected new energy inverter dM and the q-axis component u qM , and the d-axis component of the output current i dM and the q-axis component i qM ; By the voltage reference value E M , output voltage d-axis component u dM and the q-axis component u qM , get the d-axis component i of the output current reference value of the grid-connected new energy inverter dM * and q-axis component and i qM * ;

[0010] S4, the d-axis component i of the output current of the grid-connected new energy inverter dM and the q-axis component i qM andi dM Reference value i dM * and i qM Reference value iqM * , get the d-axis component and q-axis component d dM and d qM of the grid-connected type new energy grid-connected inverter duty cycle from the DC side capacitor voltage reference value u dc * and the measured value u dc , get the reference value i dL * of the d-axis component of the grid-connected type new energy grid-connected inverter output current;

[0011] S5, get the phase-locked angle θ pll by phase-locked loop, and use the phase-locked angle θ pll to respectively perform Park transformation on u aL , u bL , u cL and i aL , i bL , i cL , get the d-axis component u dL and q-axis component u qL of the output voltage, the d-axis component i dL and q-axis component i qL of the output current; use the output reference angle θ M to perform inverse Park transformation on d dM and d qM , get three-phase duty cycle signals d aM , d bM , d cM , used for controlling the turn-on and turn-off of the switch tube of the grid-connected type new energy grid-connected inverter;

[0012] get the d-axis and q-axis voltage u dL and u qL and the reference value u dL * , u qL * , the d-axis and q-axis current i dL and i qL and the reference value i dL * , i qL * of the grid-connected type new energy grid-connected inverter from the DC side capacitor voltage reference value u dc , get the d-axis component d dL and q-axis component d qL of the grid-connected type new energy grid-connected inverter duty cycle; use the phase-locked frequency to perform inverse Park transformation on d dL , d qL , get three-phase duty cycle signals d aL , d bL , d cL, used to control the opening and closing of the switching tube of the grid-connected new energy grid-connected inverter.

[0013] By adding a damping compensation controller to the voltage control link of the grid-forming inverter, this invention reshapes the impedance of the grid-forming / grid-following hybrid parallel system and weakens the negative damping characteristics of the system impedance. As a result, the interaction between the grid-forming / grid-following hybrid parallel system and the grid impedance is weakened, subsynchronous oscillations are suppressed, and the system's operational stability is improved over a wide range of grid strength variations.

[0014] In step S2, the reference angular frequency ω M And the voltage reference value E output by the reactive power control loop M The calculation formula is:

[0015]

[0016] Where ω0 is the fundamental angular frequency, D p is the active damping coefficient, J is the virtual inertia, D q is the reactive damping coefficient, and K is the reactive inertia coefficient.

[0017] In step S3, the d-axis component i of the output current reference value of the grid-connected new energy inverter is dM * and q-axis component and i qM * The calculation formula is:

[0018]

[0019] Among them, k pu_M and k iu_M are the proportional coefficient and integral coefficient of the voltage PI controller of the grid-connected new energy inverter, C fM is the filter capacitance value of the grid-connected new energy inverter, F f (s) is the transfer function of the damping compensation controller, and ω0 is the fundamental angular frequency.

[0020] Damping compensation controller F f The transfer function expression of (s) is: where k a 、k b is the damping compensation coefficient, ω a 、ω b is the damping compensation angular frequency, and k a >k b ,ω b >ω a .

[0021] In step S4, the d-axis component and q-axis component d of the duty cycle of the grid-connected new energy inverter are dM and d qM The calculation formula is:

[0022]

[0023] Among them, k pi_M and k ii_M are the proportional coefficient and integral coefficient of the current PI controller of the grid-connected new energy inverter, L fM is the filter inductance value of the grid-connected new energy inverter, V dcM is the DC side voltage value of the grid-connected new energy inverter, and ω0 is the fundamental angular frequency.

[0024] In step S4, the reference value i of the d-axis component of the output current of the grid-connected new energy inverter is dL * The calculation formula is: Among them, k pu_L and k iu_L They are respectively the proportional coefficient and integral coefficient of the DC voltage PI controller of the grid-following new energy grid-connected inverter.

[0025] The d-axis component of the duty cycle of the grid-connected new energy inverter dL and the q-axis component d qL The calculation formula is: Among them, k pi_L and k ii_L are the proportional coefficient and integral coefficient of the current PI controller of the grid-following new energy grid-connected inverter; L fL is the filter inductance value, V dcL is the DC side voltage value.

[0026] As an inventive concept, the present invention also provides a subsynchronous oscillation suppression system for a grid-building / grid-following type new energy hybrid parallel system, including a grid-following type new energy grid-connected inverter and a grid-building type new energy grid-connected inverter; the grid-following type new energy grid-connected inverter and the grid-building type new energy grid-connected inverter are both connected to a processor; the processor is configured or programmed to execute the steps of the above-mentioned method of the present invention.

[0027] Compared with the prior art, the present invention has the following beneficial effects: the present invention provides an improved damping compensation control method to suppress system oscillations caused by wide-range variations in grid strength, and the control method is simple and economical. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1(a) to Figure 1(c) This is a diagram of the main circuit topology and control structure after the damping compensation control method is adopted in an embodiment of the present invention;

[0029] Figure 2 This is a flowchart of the steps of the damping compensation control method adopted in an embodiment of the present invention;

[0030] Figure 3 This is a d-axis voltage waveform diagram of the common coupling point (PCC point) before and after the damping compensation control method is adopted in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0032] like Figure 1(a) to Figure 1(c) As shown, an embodiment of the present invention provides a grid-building / grid-following new energy hybrid parallel system and a damping compensation control method, which is achieved by adding a damping compensation controller in the voltage control link of the grid-building new energy grid-connected inverter. Figure 1 (a) is a circuit topology diagram of a grid-building / grid-following new energy hybrid parallel system. New energy power generation equipment represented by photovoltaics obtains DC voltage through a DC-DC converter, and then outputs a three-phase AC voltage through a grid-following / grid-building type controlled inverter bridge. The main circuit uses an LC filter, and is finally connected in parallel at the PCC point, and then connected to the grid through a 0.4kV / 10kV transformer. Where i L is the output current of the grid-connected new energy inverter, L fL and R fL They are the filter inductance and parasitic resistance of the grid-connected new energy inverter, C fL and R cL are the filter capacitor and damping resistor of the grid-connected new energy inverter; i M is the output current of the grid-connected new energy inverter, L fM and R fM are the filter inductance and parasitic resistance of the grid-connected new energy inverter, C fM and R cM are the filter capacitor and damping resistor of the grid-connected new energy inverter; U PCC is the PCC voltage of the grid-forming / grid-following new energy hybrid parallel system, Z g is the grid impedance, U g is the grid voltage.

[0033] The system of the embodiment of the present invention includes a grid-following new energy grid-connected inverter considering DC side voltage control, a voltage and current dual closed-loop grid-connected new energy grid-connected inverter under virtual synchronous control, and a grid-side equivalent circuit, wherein the grid-side equivalent circuit includes a grid equivalent voltage source and a grid impedance. The method includes the following steps:

[0034] 1) The output three-phase voltage u of the grid-connected new energy inverter is obtained through the voltage sampling circuit and the current sampling circuit respectively. aM 、u bM 、u cM And the output three-phase current i aM 、i bM 、i cM , the DC side voltage u of the grid-connected new energy inverter dcL , output three-phase voltage u aL 、u bL 、u cL And the output three-phase current i aL 、i bL 、i cL ;

[0035] 2) Active power P of grid-connected new energy inverter M and its reference value P M * The reference angular frequency ω of the active control loop output can be obtained M (reference angle θ M Can be obtained by ω M Obtained by the integral link); by the PCC point voltage amplitude U M and its rated value U M * , reactive power Q M and its reference value Q M * The voltage reference value E output by the reactive control loop can be obtained M , and the calculation formulas for the two are:

[0036]

[0037] Where ω0 is the fundamental angular frequency; D p is the active damping coefficient; J is the virtual inertia; D q is the reactive damping coefficient; K is the reactive inertia coefficient.

[0038] 3) Using the reference angle θ output by the active control loop M To u aM 、u bM 、u cM and i aM 、i bM 、i cMPerform Park transformation respectively to obtain the d-axis component u of the output voltage of the grid-connected new energy inverter dM and the q-axis component u qM And the d-axis component of the output current i dM and the q-axis component i qM ; By the voltage reference value E M , output voltage d-axis component u dM and the q-axis component u qM , we can get the d-axis component i of the output current reference value of the grid-connected new energy inverter dM * and q-axis component and i qM * , and its calculation formula is:

[0039]

[0040] Among them, k pu_M and k iu_M are the proportional coefficient and integral coefficient of the voltage PI controller of the grid-connected new energy inverter, C fM It is the filter capacitance value of grid-connected new energy inverter.

[0041] 4) The d-axis component i of the output current of the grid-connected new energy inverter dM and the q-axis component i qM and its reference value i dM * and i qM * , we can get the d-axis component and q-axis component of the duty cycle of the grid-connected new energy inverter dM and d qM , and its calculation formula is:

[0042]

[0043] Among them, k pi_M and k ii_M are the proportional coefficient and integral coefficient of the current PI controller of the grid-connected new energy inverter, L fM is the filter inductance value of the grid-connected new energy inverter, V dcM is the DC side voltage value of the grid-connected new energy inverter; using the output reference angle θ M Right dM and d qM Perform the reverse Pike transform to obtain the three-phase duty cycle signal d aM , d bM , d cM , used to control the opening and closing of the switch tube of the grid-connected new energy inverter;

[0044] 5) The DC side capacitor voltage reference value u of the grid-connected new energy inverter dcL * and its actual measured value u dcL , we can get the reference value i of the output current d-axis component of the grid-connected new energy inverter dL * , and its calculation formula is:

[0045]

[0046] Among them, k pu_L and k iu_L are the proportional coefficient and integral coefficient of the DC voltage PI controller of the grid-following new energy grid-connected inverter respectively;

[0047] 6) Obtain the phase-locked angle θ through the phase-locked loop pll , and use it to convert u aL 、u bL 、u cL and i aL 、i bL 、i cL Perform Park transformation respectively to obtain the d-axis component u of the output voltage dL and the q-axis component u qL , the d-axis component of the output current i dL and the q-axis component i qL ; The d-axis and q-axis voltages u of the grid-connected new energy inverter dL and u qL and its reference value u dL * 、u qL * , d-axis and q-axis current i dL and i qL and its reference value i dL * 、i qL * , the d-axis component and q-axis component of the duty cycle of the grid-connected new energy inverter can be obtained, and the calculation formula is:

[0048]

[0049] Among them, k pi_L and k ii_L are the proportional coefficient and integral coefficient of the current PI controller of the grid-following new energy grid-connected inverter; L fL is the filter inductance value, V dcL is the DC side voltage value. Use the phase-locked frequency to dL , d qL Perform the reverse Pike transform to obtain the three-phase duty cycle signal d aL , dbL , d cL , used to control the opening and closing of the switching tube of the grid-connected new energy grid-connected inverter.

[0050] Since the control of the front-end and rear-end converters of the new energy hybrid parallel system can be studied independently, the embodiment of the present invention mainly focuses on the grid-side inverter control strategy. Therefore, the front-end of the grid-type new energy grid-connected inverter is equivalent to a controlled current source to simplify the processing. Figure 1(b) is a topological diagram of the main circuit and control structure of the grid-type new energy grid-connected inverter. dcL is the DC side capacitor, used to buffer the energy changes of the front and rear stages, u dcL and are the DC side voltage and its reference value, V dcL is the steady-state value of DC side voltage; i dcL is the controlled current source current. e aL 、e bL 、e cL is the three-phase voltage at the inverter port, i dL 、i qL and They are the inverter port output current i aL 、i bL 、i cL The actual value and reference value of the d-axis and q-axis components; u dL 、u qL The voltage at PCC point u is aL 、u bL 、u cL The d-axis and q-axis components of θ pll is the phase-locked loop output reference angle, d dL d qL They are duty cycle signals d aL d bL d cL The d-axis and q-axis components of the signal are given in Figure 2, and ω0 is the fundamental angular frequency.

[0051] The main circuit topology and control structure of the grid-connected new energy inverter are shown in Figure 1(c). For the convenience of research, the embodiment of the present invention does not consider the dynamic changes of the front stage of the grid-connected new energy inverter. The DC side uses the DC voltage V dcM Equivalent, e aM 、e bM 、e cM is the three-phase voltage of the port; i aM 、i bM 、i cM is the output current of the port, and the signal converted to the dq coordinate system is i dM 、i qM ;u aM 、u bM 、u cMis the voltage at the PCC point, which is converted to the signal u in the dq coordinate system. dM 、u qM θ M is the reference angle of the active control loop output, E M is the voltage reference value output by the reactive power control loop, d aM d bM d cM is the three-phase duty cycle signal. dM * and i qM * They are the d-axis and q-axis current reference values ​​respectively.

[0052] Figure 2 This is an execution flow chart of an embodiment of the present invention. First, the DC side voltage, three-phase output voltage and current signals of the grid-following new energy grid-connected inverter, and the three-phase output voltage and current signals of the grid-building new energy grid-connected inverter are measured respectively through voltage and current sampling circuits; the voltage signal of the grid-following new energy grid-connected inverter is phase-locked to obtain the phase-locked loop output reference angle θ pll , the active power control loop of the grid-connected new energy inverter outputs the reference angle θ M , the reference voltage E is output by the reactive power control loop M ; Use the phase-locked loop to output the reference angle θ pll Perform Park transformation on the three-phase output voltage and current of the grid-connected new energy inverter to obtain the d-axis component u of the output voltage. dL and the q-axis component u qL , the d-axis component of the output current i dL and the q-axis component i qL ; The DC side voltage u of the grid-connected new energy inverter dcL and its reference value Make a difference and input the DC voltage PI controller to output the d-axis current reference value will i dL and andi qL and Make the difference and input it into the current PI controller, and superimpose 2u on the output of d-axis and q-axis respectively dL / V dcL 、-2ω0L f u qL / V dcL and 2u qL / V dcL 、2ω0L f u dL / V dcL , and then output the d-axis component of the duty cycle d dL and the q-axis component d qL ; Use the active loop to output the reference angle θM The three-phase output voltage and current of the grid-constructing new energy grid-connected inverter are subjected to Park transformation to obtain the d-axis component u dM and the q-axis component u qM of the output voltage, the d-axis component i dM and the q-axis component i qM of the output current; the d-axis voltage u dM of the grid-constructing new energy grid-connected inverter and its reference value E M , the q-axis voltage u dM and its reference value 0 are respectively subtracted, and input into a voltage PI controller, and the d-axis current reference value i and the q-axis current reference value i are respectively output. dM and and i qM and are respectively subtracted, and -ω0C fM u qM , ω0C fM u dM are respectively superimposed, and input into a current PI controller, and the outputs of the d-axis and q-axis of the current PI controller are respectively superimposed -2ω0L fM i qM / V dcM , 2ω0L fM i dM / V dcM , and the d-axis component d dM and the q-axis component d qM of the duty ratio are further output; θ M and θ pll are used to respectively perform inverse Park transformation on the duty ratio signals in the dq coordinate system of the grid-constructing new energy grid-connected inverter and the grid-following new energy grid-connected inverter, to obtain the three-phase duty ratio signals d aM , d bM , d cM of the grid-constructing new energy grid-connected inverter and the three-phase duty ratio signals d aL , d bL , d cL of the grid-following new energy grid-connected inverter, which are respectively used to control the turn-on and turn-off of the switching tubes of the grid-constructing / grid-following new energy grid-connected inverter.

[0053] Figure 3 For SCR=7, the waveform comparison diagram of the d-axis component of the PCC point voltage of the grid-constructing / grid-following new energy hybrid grid-connected system is shown. Before the damping compensation control method is adopted, the system is in an oscillation state; after the damping compensation control method is adopted, the system changes from the oscillation state to the stable state.

[0054] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0055] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A method for suppressing subsynchronous oscillations in a grid-building / grid-following hybrid parallel system of new energy sources, wherein the grid-building / grid-following hybrid parallel system comprises a parallel-connected grid-following new energy grid-connected inverter and a grid-building new energy grid-connected inverter; characterized in that: The method comprises the following steps: S1. Obtain the three-phase voltage u output by the grid-connected new energy inverter aM 、u bM 、u cM And the output three-phase current i aM 、i bM 、i cM , the DC side voltage u of the grid-connected new energy inverter dcL , output three-phase voltage u aL 、u bL 、u cL And the output three-phase current i aL 、i bL 、i cL ; S2, active power P of grid-connected new energy inverter M and its reference value P M * Calculate the reference angular frequency ω of the active control loop output M ; The voltage amplitude U at PCC point M and its rated value U M * , reactive power Q M and its reference value Q M * Calculate the voltage reference value E output by the reactive control loop M ; S3, using the reference angle θ output by the active control loop M To u aM 、u bM 、u cM and i aM 、i bM 、i cM Perform Park transformation respectively to obtain the d-axis component u of the output voltage of the grid-connected new energy inverter dM and the q-axis component u qM , and the d-axis component of the output current i dM and the q-axis component i qM ; By the voltage reference value E M , output voltage d-axis component u dM and the q-axis component u qM , get the d-axis component i of the output current reference value of the grid-connected new energy inverter dM * and q-axis component and i qM * ; S4, the d-axis component i of the output current of the grid-connected new energy inverter dM and the q-axis component i qM andi dM Reference value i dM * and i qM Reference value i qM * , the d-axis component and q-axis component of the duty cycle of the grid-connected new energy inverter are obtained dM and d qM ; The DC side capacitor voltage reference value u of the grid-connected new energy grid-connected inverter dc * and the measured value u dc , get the reference value i of the output current d-axis component of the grid-connected new energy inverter dL * ; S5. Get the phase-locked angle θ through the phase-locked loop pll , and use the phase-locking angle θ pll will u aL 、u bL 、u cL and i aL 、i bL 、i cL Perform Park transformation respectively to obtain the d-axis component u of the output voltage dL and the q-axis component u qL , the d-axis component of the output current i dL and the q-axis component i qL ; Using the output reference angle θ M Right dM and d qM Perform the reverse Pike transform to obtain the three-phase duty cycle signal d aM , d bM , d cM , used to control the opening and closing of the switch tube of the grid-connected new energy inverter; The d-axis and q-axis voltages u of the grid-connected new energy inverter are dL and u qL and its reference value u dL * 、u qL * , d-axis and q-axis current i dL and i qL and its reference value i dL * 、i qL * , get the d-axis component d of the duty cycle of the grid-connected new energy inverter dL and the q-axis component d qL ; Using phase-locked frequency to d dL , d qL Perform the reverse Pike transform to obtain the three-phase duty cycle signal d aL , d bL , d cL , used to control the opening and closing of the switching tube of the grid-connected new energy grid-connected inverter.

2. The method for suppressing subsynchronous oscillation of a grid-forming / grid-following type new energy hybrid parallel system according to claim 1 is characterized in that: In step S2, the reference angular frequency ω M And the voltage reference value E output by the reactive power control loop M The calculation formula is: Where ω0 is the fundamental angular frequency, D p is the active damping coefficient, J is the virtual inertia, D q is the reactive damping coefficient, and K is the reactive inertia coefficient.

3. The method for suppressing subsynchronous oscillation of a grid-connected / grid-following new energy hybrid parallel system according to claim 1 is characterized in that: In step S3, the d-axis component i of the output current reference value of the grid-connected new energy inverter is dM * and q-axis component and i qM * The calculation formula is: Among them, k pu_M and k iu_M are the proportional coefficient and integral coefficient of the voltage PI controller of the grid-connected new energy inverter, C fM is the filter capacitance value of the grid-connected new energy inverter, F f (s) is the transfer function of the damping compensation controller, and ω0 is the fundamental angular frequency.

4. The method for suppressing subsynchronous oscillation of a grid-forming / grid-following type new energy hybrid parallel system according to claim 3 is characterized in that: Damping compensation controller F f The transfer function expression of (s) is: where k a 、k b is the damping compensation coefficient, ω a 、ω b is the damping compensation angular frequency, and k a >k b ,ω b >ω a .

5. The method for suppressing subsynchronous oscillation of a grid-building / grid-following type new energy hybrid parallel system according to claim 1 is characterized in that: In step S4, the d-axis component and q-axis component d of the duty cycle of the grid-connected new energy inverter are dM and d qM The calculation formula is: Among them, k pi_M and k ii_M are the proportional coefficient and integral coefficient of the current PI controller of the grid-connected new energy inverter, L fM is the filter inductance value of the grid-connected new energy inverter, V dcM is the DC side voltage value of the grid-connected new energy inverter, and ω0 is the fundamental angular frequency.

6. The method for suppressing subsynchronous oscillation of a grid-building / grid-following type new energy hybrid parallel system according to claim 1 is characterized in that: In step S4, the reference value i of the d-axis component of the output current of the grid-connected new energy inverter is dL * The calculation formula is: Among them, k pu_L and k iu_L They are respectively the proportional coefficient and integral coefficient of the DC voltage PI controller of the grid-following new energy grid-connected inverter.

7. The method for suppressing subsynchronous oscillation of a grid-connected / grid-following new energy hybrid parallel system according to claim 1 is characterized in that: The d-axis component of the duty cycle of the grid-connected new energy inverter dL and the q-axis component d qL The calculation formula is: Among them, k pi_L and k ii_L are the proportional coefficient and integral coefficient of the current PI controller of the grid-following new energy grid-connected inverter; L fL is the filter inductance value, V dcL is the DC side voltage value.

8. A subsynchronous oscillation suppression system for a grid-building / grid-following new energy hybrid parallel system, characterized in that: It includes a grid-following new energy grid-connected inverter and a grid-building new energy grid-connected inverter; the grid-following new energy grid-connected inverter and the grid-building new energy grid-connected inverter are both connected to a processor; the processor is configured or programmed to execute the steps of the method described in one of claims 1 to 7.

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