Highly coordinated rotation power generation and network construction control method of gravity energy storage system

Abstract

The application discloses a kind of height coordination rotation power generation and network control method of gravity energy storage system.System includes at least two sets of permanent magnet synchronous motor gravity energy storage power generation unit, machine side converter, public DC bus, net side converter and LCL grid-connected filter.Machine side motor hoists heavy object when lifting, and generates power to DC bus when lowering, and is controlled by DC voltage outer ring, speed ring and current loop, and the speed given is generated by voltage outer ring to adjust power generation.Power is controlled by virtual synchronous generator to net side converter, and the change of DC bus capacitor energy is fed back to active power loop, and power dynamic correction is realized.When the first unit approaches the lowest lowering height, the current speed is latched as the target speed of the second unit, and the second unit takes over the DC bus voltage control after accelerating to the target speed, and the first unit exits power generation, so as to maintain the stability of the bus voltage under the condition of power fluctuation and limited stroke, and improve the reliability of continuous grid connection.

Description

Technical Field

[0002] This invention belongs to the fields of gravity energy storage, power electronic grid-connected control and new energy frequency regulation support technology, specifically involving a highly coordinated alternating power generation and grid control method for a gravity energy storage system. Background Technology

[0004] Gravity energy storage is an energy storage technology that utilizes changes in the height of a heavy object to convert electrical energy into gravitational potential energy. During the charging phase, the system uses an electric motor or lifting mechanism to raise the object to a higher position, converting electrical energy into gravitational potential energy. During the discharging phase, the object is lowered under gravity, and a transmission mechanism drives a generator to convert the gravitational potential energy back into electrical energy, which is then output to the grid or load. Compared to electrochemical energy storage, gravity energy storage offers advantages such as long cycle life, high safety, strong capacity scalability, and good environmental adaptability, making it particularly suitable for scenarios such as mines, vertical shafts, elevator shafts, mountain elevation changes, abandoned shafts, and industrial park-level energy storage.

[0005] Existing gravity energy storage systems typically employ a full-power converter grid-connected structure: generator—machine-side converter—DC bus—grid-side converter—grid-connected filter—grid. In this structure, the generator is not directly connected to the grid; instead, it is connected to the AC system via the machine-side converter, DC bus, and grid-side converter. While this structure improves control flexibility, it also dynamically isolates the generator's mechanical inertia from the grid frequency. The machine-side converter often uses permanent magnet synchronous motor vector control, which regulates the d-axis and q-axis currents through rotor field-oriented control, ensuring the generator operates at a given speed or torque during descent. The grid-side converter typically employs a grid-following control method, obtaining the grid voltage phase through a phase-locked loop and adjusting the grid-connected active power based on the DC bus voltage deviation to maintain DC bus voltage stability.

[0006] While the aforementioned traditional control methods can achieve basic power generation and grid connection functions, they still have significant shortcomings when gravity energy storage participates in the regulation of new power systems. Firstly, traditional grid-side control primarily aims to maintain DC bus voltage stability; that is, it increases grid-connected active power when the DC bus voltage rises and decreases grid-connected active power when the DC bus voltage falls, without actively responding to grid frequency changes. This control is essentially grid-following control; the grid-side converter operates dependent on the grid voltage phase and lacks rotor motion equations, inertial response, and damping characteristics similar to synchronous generators, making it difficult to actively provide frequency support and power oscillation suppression capabilities for the AC grid.

[0007] Therefore, with the large-scale wind power, photovoltaic and other new energy sources being connected to the grid through power electronic converters and the system's equivalent inertia continuously decreasing, traditional gravity energy storage grid-connected control cannot fully leverage the supporting role of energy storage devices in grid inertia and damping.

[0008] Furthermore, a single gravity energy storage power generation unit is limited by the travel distance of the load and cannot be lowered indefinitely. When the current power generation unit approaches its minimum lowering height, it must either cease power generation or the load must be relifted. Current technologies, which rely solely on single-unit operation or simple start-stop switching, are prone to issues such as power interruption on the generator side, DC bus voltage fluctuations, and drops in grid-side active power during unit closure. Especially when the grid-side converter is tasked with supporting grid frequency or increasing active power generation, the stability and continuity of grid-side output power will be affected if the generator side input power cannot be continuously supplied. Therefore, conventional control methods relying solely on a single power generation unit are insufficient to meet the requirements for long-term, continuous, and smooth power generation from gravity energy storage.

[0009] In summary, existing gravity energy storage grid-connected control technologies have at least the following shortcomings: First, grid-side control mostly adopts grid-following control, relying on grid phase and lacking inertia and damping support capabilities; second, the full-power converter structure dynamically isolates the mechanical inertia of the generator and heavy load system from the grid frequency, failing to effectively address the problem of reduced power system inertia support capabilities after a high proportion of new energy integration; third, there is a lack of a collaborative control mechanism between the generator side and the grid side for DC bus energy balance; and fourth, single generator units have travel limitations, and traditional switching methods cannot guarantee continuous and smooth power generation and DC bus voltage. Therefore, it is necessary to propose a DC bus collaborative control and dual-motor alternating generation method for gravity energy storage systems. This method involves regulating the potential energy release rate at the generator side through DC bus voltage control during generation, improving grid-friendliness at the grid side through virtual synchronous generator control, and ensuring continuous and stable power generation through alternating takeover of multiple generator units. Summary of the Invention

[0011] The purpose of this invention is to provide a highly coordinated alternating power generation and grid control method for gravity energy storage systems, which solves the problems of generator mechanical inertia being isolated from the grid, lack of inertia support for grid-side control, insufficient coordination between generator-side speed regulation and grid-side active power output, and discontinuous power generation caused by the limited travel of a single heavy object after the existing gravity energy storage system is connected to the grid via a full-power converter.

[0012] This invention provides the following technical solution:

[0013] In a first aspect, the present invention provides a highly coordinated alternating power generation and grid control method for a gravity energy storage system. The gravity energy storage system includes at least a first power generation unit and a second power generation unit. Each power generation unit includes a weight, a transmission mechanism, a permanent magnet synchronous motor, a generator-side converter, a position detection device, and a braking protection device. Each generator-side converter is connected in parallel to a common DC bus, and the common DC bus is connected to the power grid via a grid-side converter and a grid-connected filter. A coordination controller is used to collect the common DC bus voltage, grid-side active power, weight height, power generation unit speed, and generator-side current, and to generate a generator-side speed reference value, a grid-side control command, and a power generation unit alternation command based on the collected signals.

[0014] Secondly, the present invention provides a machine-side permanent magnet synchronous motor control method, which includes a DC bus voltage outer loop, a speed loop, and a current loop. The DC bus voltage outer loop uses the deviation between the common DC bus voltage reference value and the actual value as input to generate a machine-side target speed or a target speed correction amount; the speed loop uses the deviation between the target speed and the actual speed as input to generate a torque current setpoint; the current loop generates d-axis and q-axis voltage reference values ​​based on the d-axis current setpoint and the q-axis current setpoint, and controls the machine-side converter switching devices after coordinate transformation and modulation.

[0015] Thirdly, this invention provides a method for generating a speed reference value from the outer loop of the generator-side DC bus voltage. When the grid-side active power output increases or the common DC bus voltage is lower than the reference value, the generator-side controller does not calculate the generator-side speed reference value, but directly generates the generator unit speed reference value from the outer loop of the DC bus voltage. The DC bus voltage deviation is:

[0016]

[0017] The reference value for rotational speed is:

[0018]

[0019] In the formula, U dcref U is the reference value for the common DC bus voltage. dc The actual value of the common DC bus voltage, ω*i is the reference value of the rotational speed of the i-th generating unit, and K pu and K iu These are the proportional and integral coefficients of the outer loop of the DC bus voltage, respectively, ω min and ω max These are the minimum permissible generating speed and the maximum safe speed, respectively.

[0020] Fourthly, this invention provides a machine-side speed tracking method based on FOC. The speed loop generates a q-axis current reference based on the deviation between the speed reference value and the actual speed.

[0021]

[0022] In the formula, i*q,i is the given q-axis current of the i-th power generation unit, and ω i K represents the actual rotational speed of the i-th power generation unit. pω and K iω These are the proportional and integral coefficients of the speed ring, i q,min and i q,max These are the q-axis current limits, respectively.

[0023] In the non-weakening magnetic field operating range, the d-axis current can be set as follows:

[0024]

[0025] The current loop generates machine-side d-axis and q-axis voltage reference values ​​based on the d-axis and q-axis current deviations.

[0026]

[0027] In the formula, u*d,i and u*q,i are the reference values ​​of the d-axis and q-axis voltages of the i-th power generation unit, respectively. d,i and i q,i These are the actual d-axis and q-axis currents, respectively, L d and L q These are the d-axis and q-axis inductances, respectively, and ψ f For permanent magnet flux linkage, K pd and K pq These are the proportional and integral coefficients of the current loop d-axis, respectively, K pq and K iq These are the proportional and integral coefficients of the current loop q-axis, respectively. The voltage reference value, after coordinate transformation and SVPWM modulation, generates the switching signal for the machine-side converter. This enables the permanent magnet synchronous motor to operate according to the speed reference value given by the outer loop of the DC bus voltage.

[0028] Fifthly, this invention provides a method for coordinating energy on a common DC bus. The common DC bus serves as the energy coupling link between the generator-side converter and the grid-side converter, and its energy balance relationship satisfies:

[0029]

[0030] In the formula, C dc For the common DC bus capacitor, P ms P is the sum of the generating power of all generator-side converters input to the common DC bus. gsc P represents the active power absorbed by the grid-side converter from the common DC bus and output to the AC side. lossThis is to address system power loss. When grid-side power demand increases, causing a drop in DC bus voltage, the outer loop of the generator-side DC bus voltage automatically increases the speed reference value. Simultaneously, the grid-side VSG active power loop introduces feedback on DC bus capacitor energy changes, enabling dynamic coordination between generator-side speed regulation and grid-side active power output.

[0031] Sixthly, this invention provides a grid-side virtual synchronous generator control method. The grid-side converter collects the voltage and current at the grid connection point, calculates the grid-side output active and reactive power, and the power calculation relationship is as follows:

[0032]

[0033] In the formula, u d u q Let i be the component of the grid connection point voltage in the dq coordinate system. d i q Let P be the component of the grid-connected current in the dq coordinate system. e and Q e These represent the actual active and reactive power outputs on the grid side, respectively. Grid-side virtual synchronous generator control includes active power control, reactive power control, virtual impedance control, outer voltage loop control, and inner current loop control.

[0034] The active power control employs a virtual rotor motion equation and introduces feedback on the DC bus capacitor energy change into the active power loop. The DC bus capacitor energy change is:

[0035]

[0036] The improved active power loop input is:

[0037]

[0038] The equation of motion for the virtual rotor is:

[0039]

[0040] Where, ΔE dc C represents the change in energy of the DC bus capacitor. dc For DC bus capacitor, U dc U is the DC bus voltage. dcref P is the reference value for the DC bus voltage. ref To provide the active power for the upper layer, k ω k is the active-frequency droop factor. E J represents the DC bus energy feedback coefficient. v For virtual inertia, D v For virtual damping, ω v ω0 is the virtual angular frequency, θ is the rated angular frequency, and ω is the virtual angular frequency.v For virtual phase angle, P m For input active power, P e This represents the actual active power output on the grid side. When the DC bus voltage is lower than the reference value, ΔE dc When positive, the superposition term causes the VSG active loop input to decrease as DC-side energy is insufficient; when the DC bus voltage is higher than the reference value, ΔE dc The negative value indicates that the superposition term causes the VSG active loop input to increase as the DC side energy becomes abundant.

[0041] Reactive power-voltage control uses droop and terminal voltage feedback to jointly generate virtual potential amplitude:

[0042]

[0043] In the formula: Q e Q represents the actual reactive power output on the grid side. ref To provide reactive power to the upper layer, k q E0 is the reactive power-voltage droop coefficient, and E0 is the peak value of the reference phase voltage.

[0044] After obtaining the virtual angular frequency and phase angle through active power control, and the virtual potential amplitude through reactive power control, the virtual potential is transformed to the dq coordinate system to obtain E. d and E q And enter virtual impedance control:

[0045]

[0046] Where R s and L s Virtual resistance and virtual inductance, i d and i q These are the d-axis and q-axis currents on the grid side, respectively, and u*d and u*q are the grid-side voltage reference values ​​after passing through the virtual impedance.

[0047] The grid-side voltage reference value obtained from virtual impedance control enters the outer voltage loop, and the outer voltage loop generates a current reference.

[0048]

[0049] Where i*Ld and i*Lq are the reference values ​​for the d-axis and q-axis currents on the inverter side, respectively, u d u q Let C be the component of the grid connection point voltage in the dq coordinate system, C be the filter capacitor, and k be the voltage. pu and k iu These are the proportional coefficient and integral coefficient of the grid-side voltage loop, respectively.

[0050] The inner current loop tracks the current reference and generates modulation voltage commands:

[0051]

[0052] Where i Ld and i Lq These are the actual d-axis and q-axis currents on the inverter side, respectively. f It is a filter inductor, k pi and k ii These are the proportional coefficient and integral coefficient of the grid-side current loop, respectively.

[0053] Therefore, the grid-side converter operates according to the active-frequency, reactive-voltage, virtual impedance, voltage outer loop and current inner loop structure of a virtual synchronous generator, and achieves coordination between the DC side energy state and the grid-side active loop through the change in DC bus capacitor energy.

[0054] Seventhly, the present invention provides a method for alternating power generation using dual power generation units. The alternation process includes a deceleration exit process for the current power generation unit and an acceleration takeover process for the standby power generation unit. When the weight height of the first power generation unit is less than a preset deceleration height, the coordination controller controls the first power generation unit to enter the deceleration exit state, while simultaneously controlling the second power generation unit to enter the acceleration takeover state from the standby state.

[0055] At the start of the rotation, the coordination controller latches the descent speed of the first power generation unit before it decelerates and exits, and uses this descent speed as the target speed of the second power generation unit, denoted as v. 1t1 Simultaneously, based on the remaining descent distance between the deceleration height of the first power generation unit and the ground, the deceleration required for the first power generation unit to smoothly decelerate to the ground is calculated. Taking the descent direction as positive, the acceleration of the first power generation unit during the deceleration exit process is negative, satisfying:

[0056]

[0057] The latching speed and deceleration of the first power generation unit are transmitted to the second power generation unit. The second power generation unit is initially stationary with an initial release speed of zero. Based on the deceleration amplitude transmitted from the first power generation unit, the second power generation unit generates an acceleration reference and accelerates from its stationary state to the target speed, satisfying the following:

[0058]

[0059] The velocity reference of the second power generation unit gradually increases from zero to the target velocity according to the acceleration reference, satisfying the following:

[0060]

[0061] The time required for the second power generation unit to accelerate from rest to the target speed satisfies:

[0062]

[0063] Where a1 is the acceleration during the deceleration and withdrawal process of the first power generation unit; a2 is the acceleration reference during the acceleration and takeover process of the second power generation unit; v 1t1 The lowering speed latched before the first power generation unit enters the deceleration exit state, and also serves as the target speed for the second power generation unit; h min t1 is the lowest lowering height of the first power generation unit; v is the start time of the rotation. 2ref (t) is the speed reference for the second power generation unit; t acc This is the time required for the second power generation unit to accelerate from a standstill to the target speed.

[0064] When the actual speed of the second power generation unit tracks the target speed and the common DC bus voltage meets the preset switching conditions, the coordination controller switches the second power generation unit from speed tracking mode to DC bus voltage control mode; the first power generation unit exits the power generation state, thereby realizing a smooth takeover from the first power generation unit to the second power generation unit.

[0065] In an optional embodiment, the preset switching conditions include the difference between the actual rotational speed of the second power generation unit and the target power generation rotational speed being less than a preset rotational speed threshold, and the difference between the common DC bus voltage and the reference value being less than a preset voltage threshold, i.e., satisfying the following:

[0066]

[0067] In the formula, ω2 is the target rotational speed of the second power generation unit, ω t It is the actual rotational speed of the second power generation unit, Δω th It is a preset speed threshold, ΔU th It is a preset voltage threshold.

[0068] After the above conditions are met, the power supply for the common DC bus will gradually transition from the first power generation unit to the second power generation unit, thus avoiding voltage drops and mechanical shocks on the bus caused by the standby power generation unit taking over before it reaches its full capacity.

[0069] Eighthly, the present invention provides a gravity energy storage system, the system comprising at least two gravity energy storage power generation units, a common DC bus, a grid-side converter, a grid-connected filter, and a coordination controller. The coordination controller includes a generator-side DC bus voltage outer loop control module, a generator-side speed control module, a generator-side current control module, a DC bus voltage coordination module, a grid-side virtual synchronous generator control module, a DC bus energy feedback correction module, a power generation unit status judgment module, and a dual-motor rotation control module.

[0070] Compared with the prior art, the present invention has the following beneficial effects:

[0071] (1) The present invention uses the outer loop of the DC bus voltage on the generator side to generate a speed reference value and sends it to the motor FOC control, so that the generator unit can automatically adjust the release speed in the bus voltage control mode and improve the generator side input power regulation capability.

[0072] (2) The present invention integrates the common DC bus voltage regulation, the machine-side FOC speed control and the grid-side VSG control in a coordinated design. By adjusting the machine-side speed and the grid-side energy feedback, the bus voltage fluctuation is reduced and the power transmission stability is improved.

[0073] (3) The present invention sets a power generation unit rotation control mode, so that the standby power generation unit switches from standby mode to acceleration pre-synchronization mode, and switches to bus voltage control mode after reaching the latching speed, so as to achieve smooth take-off and continuous power generation. Attached Figure Description

[0075] The accompanying drawings, as part of this invention, are provided to further illustrate the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation on the scope of protection of the invention. Clearly, the drawings described below are only some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0076] Figure 1 This is an overall topology diagram of a gravity energy storage system provided in one embodiment of the present invention;

[0077] Figure 2 This is a block diagram of a machine-side permanent magnet synchronous motor control provided in one embodiment of the present invention;

[0078] Figure 3 This is a schematic diagram of DC bus energy balance provided in one embodiment of the present invention;

[0079] Figure 4 This is a block diagram of an improved active frequency loop control in one embodiment of the present invention;

[0080] Figure 5 This is a block diagram of a grid-side virtual synchronous generator control provided in one embodiment of the present invention;

[0081] Figure 6 This is a schematic diagram of the dual-motor alternation switching state provided in one embodiment of the present invention;

[0082] Figure 7 To simulate the DC bus voltage waveform;

[0083] Figure 8 The waveforms of the network-side output power and the machine-side output power are shown in the simulation.

[0084] Figure 9The waveform diagram of the output power on the simulation network side;

[0085] Figure 10 This is a waveform diagram of the motor speed on the simulator side;

[0086] It should be noted that the above figures and text descriptions are not intended to limit the scope of the invention, but rather to illustrate the technical solutions of the invention by referring to specific embodiments. Detailed Implementation

[0088] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of protection of the present invention.

[0089] System Overall Structure Implementation Example

[0090] Reference Figure 1 An embodiment of the present invention provides a gravity energy storage system. The system includes a first gravity energy storage power generation unit, a second gravity energy storage power generation unit, a common DC bus, a grid-side converter, an LCL grid-connected filter, a power grid, and a coordination controller. The first gravity energy storage power generation unit includes a first weight, a first transmission mechanism, a first permanent magnet synchronous motor, a first machine-side converter, a first position detection device, a first speed detection device, and a first braking protection device. The second gravity energy storage power generation unit includes a second weight, a second transmission mechanism, a second permanent magnet synchronous motor, a second machine-side converter, a second position detection device, a second speed detection device, and a second braking protection device.

[0091] The DC sides of the first and second generator-side converters are connected to a common DC bus, which is then connected to the AC grid via a grid-side converter and an LCL grid-connected filter. The coordination controller is communicatively connected to the first generator-side converter, the second generator-side converter, the grid-side converter, the position detection device, the speed detection device, and the braking protection device. It is used to achieve outer-loop speed control of the generator-side DC bus voltage, control of the grid-side virtual synchronous generator, coordination of energy feedback on the common DC bus, and alternating generation control of the dual-motor system.

[0092] When the system is in the charging or lifting phase, the permanent magnet synchronous motor can operate in motor mode, lifting the heavy object through the transmission mechanism; when the system is in the discharging phase, the heavy object is lowered under the action of gravity, and the permanent magnet synchronous motor is driven to rotate through the transmission mechanism. The permanent magnet synchronous motor operates in the power generation state, and the generator-side converter inputs the generated power into the common DC bus. The grid-side converter converts the DC power into AC power and transmits it to the grid.

[0093] Example of machine-side permanent magnet synchronous motor control

[0094] Reference Figure 2 In this embodiment, the machine-side permanent magnet synchronous motor adopts a vector control structure, including a DC bus voltage outer loop, a speed loop, and a current loop. The DC bus voltage outer loop generates a speed setpoint or speed correction amount based on the deviation between the common DC bus voltage reference value and the actual value; the speed loop generates a q-axis current setpoint based on the deviation between the speed setpoint and the actual speed; the current loop generates d-axis and q-axis voltage reference values ​​based on the d-axis current setpoint and the q-axis current setpoint, and controls the machine-side converter after Park inverse transform, Clark inverse transform, and SVPWM modulation.

[0095] In this embodiment, the machine-side control does not include a machine-side DC bus voltage outer loop calculation stage. The DC bus voltage outer loop directly calculates the speed reference value based on the deviation between the common DC bus voltage reference value and the actual value, and sends this speed reference value to the motor FOC control. The voltage deviation is:

[0096]

[0097] The reference value for rotational speed is:

[0098]

[0099] In the formula, U dcref U is the reference value for the common DC bus voltage. dc The actual value of the common DC bus voltage, ω*i is the reference value of the rotational speed of the i-th generating unit, and K pu and K iu These are the proportional and integral coefficients of the outer loop of the DC bus voltage, respectively, ω min and ω max These are the minimum permissible generating speed and the maximum safe speed, respectively.

[0100] The speed reference value is fed into the speed loop of the FOC, and the speed loop outputs the q-axis current command:

[0101]

[0102] In the formula, i*q,i is the given q-axis current of the i-th power generation unit, and ω i K represents the actual rotational speed of the i-th power generation unit. pω and K iω These are the proportional and integral coefficients of the speed ring, i q,min and i q,max These are the q-axis current limits, respectively.

[0103] The current loop then generates d-axis and q-axis voltage reference values ​​based on the given d-axis and q-axis currents and the actual currents.

[0104]

[0105] In the formula, u*d,i and u*q,i are the reference values ​​of the d-axis and q-axis voltages of the i-th power generation unit, respectively. d,i and i q,i These are the actual d-axis and q-axis currents, respectively, L d and L q These are the d-axis and q-axis inductances, respectively, and ψ f For permanent magnet flux linkage, K pd and K pq These are the proportional and integral coefficients of the current loop d-axis, respectively, K pq and K iq These are the proportional and integral coefficients of the current loop q-axis, respectively.

[0106] The aforementioned voltage reference value is used to control the machine-side converter after undergoing Park inverse transformation, Clark inverse transformation, and SVPWM modulation. Therefore, the machine-side control link is: "DC bus voltage outer loop generates speed reference value — speed loop generates q-axis current setpoint — current loop generates voltage reference value — SVPWM modulation".

[0107] Common DC bus coordinated control implementation example

[0108] Reference Figure 3 and Figure 4 The common DC bus is the energy coupling link between the generator side and the grid side. The coordinating controller collects the common DC bus voltage, grid-side output active power, generator-side power generation, and operating status of each generator unit in real time, and coordinates the generator-side and grid-side control according to the DC bus energy balance relationship.

[0109] When the grid-side active power command increases, if the generator-side power generation cannot increase synchronously, the common DC bus voltage will drop. To avoid this problem, this embodiment does not include a speed reference value calculation module on the generator side; instead, the speed reference value is calculated directly from the DC bus voltage outer loop based on U. dc The change generates a speed reference value; at the same time, the DC bus capacitor energy change feedback is superimposed in the grid-side VSG active power loop, so that the grid-side active power loop can be dynamically corrected according to the DC side energy status.

[0110] In an optional embodiment, the coordination controller determines the DC-side energy state based on the change in DC bus capacitor energy. When U dc When it is below the reference value, ΔE dc When U is positive, the active loop input of the network-side VSG decreases accordingly; when U dc When it is higher than the reference value, ΔE dcWhen the value is negative, the active power loop input of the grid-side VSG increases accordingly. The generator-side section still performs FOC control based on the speed reference value output from the outer loop of the DC bus voltage.

[0111] Grid-side virtual synchronous generator control implementation example

[0112] Reference Figure 5 In this embodiment, the grid-side converter is controlled by a virtual synchronous generator. The grid-side controller collects the three-phase voltage and three-phase current at the grid connection point, obtains the voltage and current components in the dq coordinate system through coordinate transformation, and calculates the active power and reactive power.

[0113]

[0114] In the formula, u d u q Let i be the component of the grid connection point voltage in the dq coordinate system. d i q Let P be the component of the grid-connected current in the dq coordinate system. e and Q e These represent the actual active and reactive power outputs on the grid side, respectively. Grid-side virtual synchronous generator control includes active power control, reactive power control, virtual impedance control, outer voltage loop control, and inner current loop control.

[0115] Active power-frequency control employs a virtual rotor motion equation. To coordinate the grid-side active power output with the DC-side energy state, this embodiment calculates the change in DC bus capacitor energy:

[0116]

[0117] This energy change is then multiplied by the feedback coefficient and added to the VSG active power loop.

[0118]

[0119] This leads to the virtual rotor motion equation:

[0120]

[0121] Where, ΔE dc C represents the change in energy of the DC bus capacitor. dc For DC bus capacitor, U dc U is the DC bus voltage. dcref P is the reference value for the DC bus voltage. ref To provide the active power for the upper layer, k ω k is the active-frequency droop factor. E J represents the DC bus energy feedback coefficient. v For virtual inertia, D vFor virtual damping, ω v ω0 is the virtual angular frequency, θ is the rated angular frequency, and ω is the virtual angular frequency. v For virtual phase angle, P m For input active power, P e This represents the actual active power output on the grid side.

[0122] In the above structure, the DC bus voltage drop corresponds to ΔE dc A value greater than 0 reduces the active loop input of the VSG; an increase in the DC bus voltage corresponds to ΔE. dc <0, which increases the active power loop input of VSG, thereby feeding back the energy change of the common DC bus to the grid-side active power control.

[0123] Reactive-voltage control uses droop and voltage feedback to generate virtual potential amplitude:

[0124]

[0125] In the formula: Q e Q represents the actual reactive power output on the grid side. ref To provide reactive power to the upper layer, k q E0 is the reactive power-voltage droop coefficient, and E0 is the peak value of the reference phase voltage.

[0126] The virtual potential is obtained by Park transformation to obtain E d and E q And enter virtual impedance control:

[0127]

[0128] Where R s and L s Virtual resistance and virtual inductance, i d and i q These are the d-axis and q-axis currents on the grid side, respectively, and u*d and u*q are the grid-side voltage reference values ​​after passing through the virtual impedance.

[0129] The voltage reference obtained from virtual impedance control enters the outer voltage loop, and the outer voltage loop generates a current reference.

[0130]

[0131] Where i*Ld and i*Lq are the reference values ​​for the d-axis and q-axis currents on the inverter side, respectively, u d and u q These are the actual values ​​of the grid-side voltage, C is the filter capacitor, and k is the voltage level. pu and k iu These are the proportional coefficient and integral coefficient of the grid-side voltage loop, respectively.

[0132] The inner current loop tracks the current reference and outputs the modulation voltage command:

[0133]

[0134] Where i Ld and i Lq These are the actual d-axis and q-axis currents on the inverter side, respectively. f It is a filter inductor, k pi and k ii These are the proportional coefficient and integral coefficient of the grid-side current loop, respectively.

[0135] LCL Grid-connected Filtering Example

[0136] An LCL grid-connected filter is installed at the output terminal of the grid-side converter. The LCL grid-connected filter includes a converter-side inductor L1, a filter capacitor C, and a grid-side inductor L2. The converter-side inductor is used to limit the converter output current ripple, the filter capacitor is used to bypass high-frequency switching harmonics, and the grid-side inductor is used to improve the grid-connected current quality and reduce high-frequency harmonic injection into the grid.

[0137] In this invention, the LCL grid-connected filter primarily serves as the filtering interface for the grid-side converter to connect to the power grid. Its parameters can be determined based on the system's rated power, switching frequency, allowable current ripple, grid short-circuit capacity, and grid-connected power quality requirements. To improve the stability of the LCL filter near its resonant frequency, active damping with capacitor current feedback, active damping with capacitor voltage feedback, or series damping resistors can be employed. These damping methods do not alter the core scheme of this invention regarding coordinated control between the generator side and the grid side, as well as alternating generation by dual motors.

[0138] Dual-motor alternation control embodiment

[0139] Reference Figure 6 In this embodiment, the system includes at least a first power generation unit and a second power generation unit. When the first power generation unit is used as the main operating unit to generate electricity, the coordination controller collects the height of the load, the lowering speed, the speed of the permanent magnet synchronous motor, the voltage of the common DC bus, and the active power output on the grid side of the first power generation unit in real time, and determines whether the first power generation unit has entered the rotation interval based on this.

[0140] The remaining generateable energy and remaining generateable time of the first power generation unit can be expressed as:

[0141]

[0142] In the formula, E rem,i Let m be the remaining generateable energy of the i-th power generation unit. i Let g be the mass of the object, g be the acceleration due to gravity, and h be the acceleration due to gravity. i h represents the current height of the object. min,iFor the minimum lowering height, t rem,i v represents the remaining time that can generate electricity. i This represents the current speed at which the heavy object is lowered.

[0143] When the height of the load on the first power generation unit is less than the preset deceleration height, or the remaining power generation time is less than the preset threshold, the coordination controller does not directly shut down the first power generation unit. Instead, it causes the first power generation unit to enter the deceleration exit state, while simultaneously causing the second power generation unit to enter the acceleration takeover state. Before entering the acceleration takeover state, the second power generation unit can complete pre-start operations such as releasing the mechanical brake, pre-charging the machine-side converter, speed sampling confirmation, current sampling confirmation, upper and lower limit detection, and protection signal confirmation.

[0144] At the start of the rotation, t1, the coordination controller latches the lowering speed of the first power generation unit before it decelerates and exits, and uses this latched speed as the target speed of the second power generation unit, denoted as v. 1t1 Simultaneously, based on the remaining descent distance between the deceleration height of the first power generation unit and the ground, the deceleration required for smooth deceleration to the ground is calculated; taking the descent direction as positive, the acceleration of the first power generation unit during the deceleration exit process is negative, satisfying:

[0145]

[0146] The aforementioned deceleration is used to constrain the exit process of the first power generation unit, allowing it to gradually reduce its descent speed as it approaches the ground, rather than abruptly stopping upon reaching the ground. During the deceleration exit of the first power generation unit, it can still supply energy to the common DC bus via the generator-side converter and will not be immediately removed until the second power generation unit meets the takeover conditions.

[0147] The deceleration and latching speed of the first power generation unit are directly transmitted to the second power generation unit. The second power generation unit is initially stationary with an initial lowering speed of zero. It generates an acceleration reference based on the deceleration amplitude transmitted from the first power generation unit and accelerates from a stationary state to the target speed, satisfying the following conditions:

[0148]

[0149] The velocity reference of the second power generation unit gradually increases from zero to the target velocity according to the acceleration reference, satisfying the following:

[0150]

[0151] The time required for the second power generation unit to accelerate from rest to the target speed satisfies:

[0152]

[0153] Where a1 is the acceleration during the deceleration and withdrawal process of the first power generation unit; a2 is the acceleration reference during the acceleration and takeover process of the second power generation unit; v 1t1 The lowering speed latched before the first power generation unit enters the deceleration exit state, and also serves as the target speed for the second power generation unit; h min t1 is the lowest lowering height of the first power generation unit; v is the start time of the rotation. 2ref (t) is the speed reference for the second power generation unit; t acc This is the time required for the second power generation unit to accelerate from a standstill to the target speed.

[0154] During the speed tracking phase of the second power generation unit, the machine-side control of the second power generation unit uses the speed reference v 2ref (t) is used as input, and the q-axis current is controlled through the FOC speed loop and current loop to smoothly accelerate the second generator unit from a stationary state. During this stage, the second generator unit does not yet assume the main control function of the common DC bus voltage, and the first generator unit still maintains the bus power supply, thereby avoiding the bus voltage oscillation caused by the simultaneous operation of the control rights of the two generator units.

[0155] Once the actual speed of the second power generation unit reaches the target speed, the coordination controller further determines whether the common DC bus voltage meets the preset switching conditions. In one embodiment, when the difference between the actual speed of the second power generation unit and the target power generation speed is less than a preset speed threshold, and the difference between the common DC bus voltage and the reference value is less than a preset voltage threshold, the following conditions are met:

[0156]

[0157] In the formula, ω2 is the target rotational speed of the second power generation unit, ω t It is the actual rotational speed of the second power generation unit, Δω th It is a preset speed threshold, ΔU th It is a preset voltage threshold.

[0158] Once the above conditions are met, the coordinating controller switches the second generator unit from speed tracking mode to DC bus voltage control mode, allowing the outer loop of the second generator unit's DC bus voltage to directly generate its speed reference value. The second generator unit then assumes the tasks of bus voltage regulation and turbine-side power supply. Simultaneously, the first generator unit performs mechanical braking, shutdown protection, and lift reset.

[0159] Through the coordinated deceleration and acceleration phases of the above-mentioned two-stage exit and takeover, a transmission relationship is established between the exit speed and deceleration of the first power generation unit and the target speed and acceleration reference of the second power generation unit. The second power generation unit does not start after the first power generation unit stops, but accelerates in advance while the first power generation unit decelerates out; it takes over only when the second power generation unit reaches the target speed latched by the first power generation unit and the common DC bus voltage meets the conditions, thereby achieving a smooth transition of power supply from the first power generation unit to the second power generation unit.

[0160] If the system includes three or more gravity energy storage power generation units, the coordination controller can sequentially rotate between the currently operating power generation unit and the next standby power generation unit according to the same deceleration exit and acceleration takeover rules; and can select a backup power generation unit based on the remaining height, available power, mechanical status, fault status, and operating priority of each power generation unit. If a power generation unit fails, the coordination controller skips that power generation unit, and other available power generation units take over.

[0161] Figure 7 As shown, 4 seconds before the start of power generation, the DC bus voltage briefly drops as the grid-side active power output increases, but quickly recovers as the turbine-side power output increases. Conversely, when the grid-side active power decreases, the DC bus voltage briefly rises, but quickly recovers as the turbine-side power output decreases. Around 4 seconds, during the transition between the two units, the DC bus voltage experiences only brief, small fluctuations before quickly stabilizing. After the switchover ends, the second unit generates power, and the DC bus voltage remains stable regardless of grid-side output power changes. This demonstrates the effectiveness of the proposed outer-loop control and transition method for the turbine-side DC bus voltage.

[0162] Figure 8 As shown, before the rotation, the machine-side output power can track the changes in grid-side power very well. During the switching period of about 4 seconds, the second unit can accelerate according to the transmission acceleration to ensure a smooth switching. After the rotation, the machine-side output power can still track the changes in grid-side power very well.

[0163] Figure 9 and Figure 10 As shown, the speed of the permanent magnet synchronous generator on the generator side increases with the increase of grid-side output power; conversely, the speed decreases with the decrease of grid-side output power. During the switching process, the two generators operate at specified acceleration and deceleration rates to achieve smooth switching.

[0164] Alternative implementation methods

[0165] Without departing from the concept of this invention, the permanent magnet synchronous motor can be replaced with other motors suitable for variable speed power generation; the generator-side control can adopt vector control, model predictive control, or other control methods that can adjust the generator current and generator speed; the grid-side virtual synchronous generator control can be replaced with voltage-type VSG, current-type VSG, virtual oscillator control, or grid-type control methods with similar inertia support capabilities; the grid-connected filter can adopt LC filter, LC filter, or other filter structures that meet the grid-connected current quality requirements; the number of power generation units can be two, three, or more.

[0166] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of protection of this invention. For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and all such modifications and improvements should fall within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the claims.

Claims

1. A highly coordinated alternating power generation and grid control method for a gravity energy storage system, characterized in that: The gravity energy storage system includes at least a first power generation unit and a second power generation unit. Each power generation unit includes a weight, a transmission mechanism, a permanent magnet synchronous motor, and a generator-side converter. Each generator-side converter is connected in parallel to a common DC bus, which is connected to the power grid via a grid-side converter and a grid-connected filter. The method includes: acquiring the common DC bus voltage, grid-side voltage and current, grid-side active and reactive power, the height of the weight in each power generation unit, the rotational speed of the power generation unit, and the generator-side current; when the power generation unit is lowered to generate electricity, the outer loop of the generator-side DC bus voltage is based on the common DC bus voltage. The deviation directly generates the speed reference value, and through the speed loop, current loop and FOC control, generates the generator-side converter switching signal; a virtual synchronous generator is used for control in the grid-side converter, and the grid-side active power loop is dynamically corrected according to the energy status of the common DC bus; when the current generator unit approaches the minimum lowering height, the current generator unit is controlled to decelerate and exit, while the standby generator unit is controlled to accelerate to the target generator speed, and after the speed and common DC bus voltage switching conditions are met, the standby generator unit takes over the DC bus voltage control, realizing the alternating operation of generator units.

2. The method according to claim 1, characterized in that: The control structure of the machine-side permanent magnet synchronous motor includes DC bus voltage outer loop control, speed loop control, and current loop control.

3. The method according to claim 2, characterized in that: The outer loop control of the DC bus voltage uses the deviation between the reference value and the actual value of the common DC bus voltage as input to directly generate the speed reference value of the i-th generating unit. The voltage deviation is: The reference value for rotational speed is: In the formula, U dcref U is the reference value for the common DC bus voltage. dc The actual value of the common DC bus voltage, ω*i is the reference value of the rotational speed of the i-th generating unit, and K pu and K iu These are the proportional and integral coefficients of the outer loop of the DC bus voltage, respectively, ω min and ω max These are the minimum permissible generating speed and the maximum safe speed, respectively. The speed loop control generates the q-axis current input based on the deviation between the speed reference value and the actual speed. In the formula, i*q,i is the given q-axis current of the i-th power generation unit, and ω i K represents the actual rotational speed of the i-th power generation unit. pω and K iω These are the proportional and integral coefficients of the speed ring, i q,min and i q,max These are the q-axis current limits. The current loop control is based on the d-axis current setpoint, the q-axis current setpoint, and the actual d- and q-axis current generator-side converter voltage reference values; in the non-weak magnetic generation range, the d-axis current setpoint can be taken as: The current loop output can be expressed as: In the formula, u*d,i and u*q,i are the reference values ​​of the d-axis and q-axis voltages of the i-th power generation unit, respectively. d,i and i q,i These are the actual d-axis and q-axis currents, respectively, L d and L q These are the d-axis and q-axis inductances, respectively, and ψ f For permanent magnet flux linkage, K pd and K id These are the proportional and integral coefficients of the current loop d-axis, respectively, K pq and K iq These are the proportional and integral coefficients of the current loop q-axis, respectively. The voltage reference value is transformed by coordinate transformation and SVPWM modulation to generate the machine-side converter switching signal.

4. The method according to claim 1, characterized in that: The dynamic variation of the common DC bus voltage is jointly determined by the machine-side input power, the grid-side output power, and system losses, and its energy balance relationship satisfies: In the formula, C dc For DC bus capacitance, P ms P is the power generated by the common DC bus input to the generator side. gsc P is the active power output on the grid side. loss This represents the system's power loss.

5. The method according to claim 1, characterized in that: The grid-side converter employs virtual synchronous generator control, including active-frequency control, reactive-voltage control, virtual impedance control, voltage outer loop control, and current inner loop control.

6. The method according to claim 5, characterized in that: The motion equation of the virtual rotor under active-frequency control is as follows: The active power loop introduces feedback on the energy change of the DC bus capacitor, and the energy change of the DC bus satisfies: The DC bus energy change is multiplied by the feedback coefficient and then added to the active power loop to obtain the input active power: Among them, J v For virtual inertia, D v For virtual damping, ω v ω0 is the virtual angular frequency, θ is the rated angular frequency, and ω is the virtual angular frequency. v For virtual phase angle, P m For input active power, P e ΔE represents the actual active power output on the grid side. dc C represents the change in energy of the DC bus capacitor. dc For DC bus capacitor, U dc U is the DC bus voltage. dcref P is the reference value for the DC bus voltage. ref To provide the active power for the upper layer, k ω k is the active-frequency droop factor. E This is the DC bus energy feedback coefficient.

7. The method according to claim 1, characterized in that: The power generation unit rotation includes a deceleration exit process for the current power generation unit and an acceleration takeover process for the standby power generation unit. When the first power generation unit enters the deceleration exit state, the lowering speed of the first power generation unit before entering the deceleration exit state is latched, and the lowering speed is used as the target speed of the second power generation unit, denoted as v. 1t1 Simultaneously, based on the remaining descent distance between the deceleration height of the first power generation unit and the ground, calculate the deceleration required for the first power generation unit to smoothly decelerate to the ground, satisfying the following: The deceleration and latching speed of the first power generation unit are directly transmitted to the second power generation unit. The second power generation unit generates an acceleration reference based on the deceleration amplitude transmitted by the first power generation unit, and accelerates from a stationary state to the target speed, satisfying: The velocity reference of the second power generation unit gradually increases from zero to the target velocity according to the acceleration reference, satisfying the following: The time required for the second power generation unit to accelerate from rest to the target speed satisfies: Where a1 is the acceleration during the deceleration and withdrawal process of the first power generation unit, and a1 is negative when the lowering direction is positive; a2 is the acceleration reference during the acceleration and takeover process of the second power generation unit; v 1t1 The lowering speed latched before the first power generation unit enters the deceleration exit state, and also serves as the target speed for the second power generation unit; h min t1 is the lowest lowering height of the first power generation unit; v is the start time of the rotation. 2ref (t) is the speed reference for the second power generation unit; t acc The time required for the second power generation unit to accelerate from a standstill to the target speed is given. When the actual speed of the second power generation unit tracks the target speed and the common DC bus voltage meets the preset switching conditions, the second power generation unit is switched from speed tracking mode to DC bus voltage control mode, thereby realizing a smooth takeover from the first power generation unit to the second power generation unit.

8. A gravity energy storage system, characterized in that: It includes a first power generation unit, a second power generation unit, a common DC bus, a grid-side converter, a controller, and a grid-connected filter. Both the first and second power generation units include a weight, a transmission mechanism, a permanent magnet synchronous motor, and a generator-side converter. Each generator-side converter is connected in parallel to the common DC bus, and the common DC bus is connected to the power grid via the grid-side converter and the grid-connected filter. The controller includes a generator-side DC bus voltage outer loop control module, a generator-side speed control module, a generator-side current control module, a grid-side virtual synchronous generator control module, a DC bus energy feedback correction module, a height judgment module, and a dual power generation unit switching module.

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