A method for controlling parallel connection of inverter and diesel generator set in ship power system
Through voltage and current dq control and phase-locking loop technology based on the rotation coordinate system, combined with SVPWM pulse width modulation, the problem of difficult parallel control of inverter and diesel generator set and poor dynamic load adaptability is solved, and the inverter and diesel generator are realized Stable parallel operation of the unit and high-quality power supply.
Patent Information
- Application Number
- CN202011336842.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2020-11-25
- Publication Date
- 2024-12-17
- Estimated Expiration
- 2040-11-25
AI Technical Summary
The existing parallel control method of inverters and diesel generator sets is difficult to effectively cope with dynamic load characteristics and cannot guarantee the power supply quality, especially when marine inverters and diesel generator sets are operated in parallel.
Using the voltage and current dq control method based on the rotary coordinate system and the phase-locked loop, combined with the SVPWM pulse width modulation strategy, a current dual-loop control method with feedforward compensation is proposed to realize the stable parallel operation of the inverter and the diesel generator set, and pass the lock The phase loop locks the output phase of the diesel generator set to ensure synchronous operation of the inverter and the diesel generator set.
It effectively realizes the reliable parallel operation of the inverter and the diesel generator set, ensures good response to dynamic loads and power supply quality, and improves the comprehensive power allocation capability of the ship's power system.
Smart Images
Figure CN112701718B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the control of power supply equipment in a ship power system, and in particular to a method for controlling an inverter and a diesel generator set in parallel in a ship power system. Background Art
[0002] In the past, ship power systems mostly used diesel generators as the main power supply equipment. With the development of new technologies such as electric propulsion and power electronics, new medium-voltage and low-voltage DC power systems are increasingly used in new ships with their high efficiency and high power density. In these DC power systems, traditional 380V AC loads are powered by inverters. The inverter is an energy conversion device that converts the DC power of the main power grid into 380V AC power. It is one of the core devices in the ship's DC power system and the main power supply equipment for the ship's low-voltage AC power network. Ships are usually equipped with AC diesel generators as a supplement to the inverter, which can supply power to the ship's loads when the ship is moored or docked, and can also be connected in parallel with the inverter to supply power to the ship's loads when sailing. Due to the huge difference in the characteristics of diesel generators and inverters, their parallel control is difficult. Studying their parallel control methods is of great significance to realizing the comprehensive dispatch of power in the power supply network of the power system.
[0003] The inverter suitable for marine DC power system has a compact structure, and mostly uses a three-phase full bridge as the main circuit for power conversion. The output uses LCL filtering, and most of them do not have an output transformer. When the inverter is powered alone, in order to ensure the power supply quality, a voltage and current dual-loop control method is adopted. When the inverter is powered in parallel, a current tracking control method is adopted, and the output phase of the diesel generator set is locked through a phase-locked loop (PLL), so that the inverter tracks the output of the diesel generator set to achieve parallel connection.
[0004] The existing inverter parallel control methods mainly focus on the parallel control problems between inverters or between inverters and large power grids. There are very few parallel control methods for inverters and diesel generator sets with similar or even lower power. At the same time, marine inverters need to meet the power supply quality requirements when large loads are suddenly added or unloaded, which is significantly different from inverters in the land-based new energy field. The existing methods have not yet considered the dynamic load characteristics of marine inverters and diesel generator sets in parallel, and cannot guarantee the adaptability of the inverter to dynamic loads when the inverter and diesel generator set are running in parallel. Summary of the invention
[0005] The problem to be solved by the present invention is to propose a parallel control method for an inverter and a diesel generator set in a ship power system, so as to realize stable parallel operation of an inverter and a diesel generator set with large differences in power supply characteristics, ensure that the power supply quality can be guaranteed when the load is suddenly added or unloaded during parallel operation, and provide technical support for realizing the comprehensive allocation of AC network electric energy of the ship power system.
[0006] The technical points adopted by the present invention to solve the above-mentioned problems mainly include: a method for controlling the parallel connection of an inverter and a diesel generator set in a ship power system, the steps of which include:
[0007] (1) According to the circuit topology of the inverter in the ship power system, the basic control framework of the inverter is established based on the voltage and current dq control method in the rotating coordinate system, which includes the implementation of the SVPWM pulse width modulation strategy;
[0008] (2) A phase-locking method based on a synchronous rotating coordinate system and outputting the sine and cosine values of the phase angle is proposed to lock the output voltage and current phase of the diesel generator set so that the inverter output is synchronized with the diesel generator set to meet the parallel phase requirements;
[0009] (3) When the inverter is powered alone, a voltage-current dual-loop control method is adopted to obtain better power supply voltage quality; when the inverter is powered in parallel with a diesel generator set, a current dual-loop control method with feedforward compensation is proposed to achieve stable parallel operation of the two and ensure the adaptability of the inverter to dynamic loads when the inverter and diesel generator set are running in parallel.
[0010] Compared with the prior art, the present invention has the following beneficial effects:
[0011] The present invention effectively solves the problem that the inverter as the main power supply and the diesel generator set as the auxiliary power supply in the ship's DC power system have large differences in characteristics and are difficult to control in parallel. Using the parallel control algorithm in the results, the inverter and the diesel generator set can be well implemented to operate in parallel reliably, and have a good response to dynamic loads such as sudden addition and removal of loads, so that the inverter and the diesel generator set can guarantee better power supply quality after being connected in parallel. The application of the present invention can enable the power supply equipment in the ship's DC power system to have the ability of flexible scheduling, and give full play to the advantages of the comprehensive allocation of electric energy in the DC power system.
[0012] At the same time, the present invention can also be applied to the upgrading and transformation of the ship's shaft-belt power generation system. After being configured with an inverter unit, the shaft-belt power generation system can adapt to different propulsion conditions, and has a good parallel capability with the emergency or main diesel generator set, greatly improving the performance of the shaft-belt power generation system.
[0013] The phase-locking method for phase tracking of three-phase AC power grid in the present invention, in which the output is the sine and cosine values of the phase angle, is more flexible than the traditional phase-locking method for tracking the phase angle, and can also be applied to other phase tracking occasions of parallel AC power grids. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:
[0015] Figure 1 It is a three-phase voltage-source inverter circuit topology commonly used in ship power systems.
[0016] Figure 2 It is a schematic diagram of the parallel operation and control method of the inverter and diesel generator set.
[0017] Figure 3 This is the voltage and current dual-loop control block diagram when the inverter operates alone.
[0018] Figure 4 This is the current control block diagram when the inverter and diesel generator set are running in parallel.
[0019] Figure 5 This is the block diagram of the phase-locked loop based on the rotating coordinate system.
[0020] Figure 6 This is a parallel operation output voltage waveform diagram of an embodiment of the present invention.
[0021] Figure 7 7a and 7b are parallel operation output current waveform diagrams of an embodiment of the present invention.
[0022] Figure 8 The load rate curve of parallel-operated generator sets and inverters according to an embodiment of the present invention. DETAILED DESCRIPTION
[0023] The following is a detailed description of the technical points and parallel control methods:
[0024] 1) Model of three-phase inverter
[0025] The circuit topology of the three-phase inverter is as follows Figure 1 As shown in the figure, S1~S6 are IGBT modules with anti-parallel diodes, C dc is the DC side input support capacitor, L f1 , L f2 is the inductance value of the output LCL filter, R f1 , R f2 is the resistance value in the inductor, C f is the capacitance value of the LCL filter, i f1a 、i f1b 、i f1c is the three-phase current value passing through the inverter output filter inductor, i oa 、i ob 、i oc is the three-phase current value output by the inverter, U ca , U cb , U cc is the three-phase voltage value on the filter capacitor, U a , Ub , U c is the voltage value at the midpoint of the inverter bridge.
[0026] The control method of the three-phase inverter adopts the dq axis control method based on the rotating coordinate system. The three-phase voltage and current variables of the inverter are converted into variables under the dq axis of the rotating coordinate system after Clarke transformation (3s / 2s transformation) and Park transformation (2s / 2r transformation) and added to the control loop. ca , U cb , U cc After 3s / 2r transformation, it becomes U d , U q , inverter bridge midpoint voltage U a , U b , U c After 3s / 2r transformation, it becomes U d1 , U q1 , output current i oa 、i ob 、i oc After transformation, it is i od 、i oq ,i f1a 、i f1b 、i f1c After transformation, it is i fd 、i fq .
[0027] The inverter controller output is U dCtrl , U qCtrl The output is used as the input of the space vector pulse width modulation controller (SVPWM), and the output of SVPWM is the on-off control pulse of IGBT S1~S6.
[0028] Taking the inductor current and capacitor voltage of the inverter as state variables, the state equation can be obtained as follows:
[0029]
[0030] After Clarke transformation and Park transformation, the equation under the dq axis of the rotating coordinate system is decomposed into real and imaginary parts in a complex way, and then the equation is transformed into the s domain using Laplace transformation to obtain the corresponding inverter dq axis component equation as follows:
[0031]
[0032] Among them, ω is the fundamental angular frequency. The above formula is the inverter model in the dq axis of the rotating coordinate system, and is also the basis for the dq cross compensation part in the closed-loop control algorithm.
[0033] 2) When the inverter is powered alone, a voltage and current dual-loop control method based on a rotating coordinate system is used
[0034] When the inverter is powered alone, a voltage and current dual-loop control method based on a rotating coordinate system is adopted. The inverter control only requires an inverter controller and an SVPWM pulse width modulation controller. The inverter controller is as follows: Figure 3 As shown. Given the output capacitor voltage reference value U in the rotating coordinate system cd *、U cq *, usually given as U cd *=311、U cq *=0.
[0035] From formula 2, we can see that after the 3s / 2r conversion (Clarke, Park), the model of the system on the dq axis has strong coupling between the d axis and the q axis. Therefore, these related quantities are added to the controller design to eliminate the influence of coupling and realize closed-loop control of the d-axis and q-axis variables. At the same time, the capacitor voltage U is introduced into the inner loop of the inductor current in the control loop. d , U q Feedforward effect on inductor current i fd 、i fq To compensate, the capacitor voltage outer loop introduces the output current i od 、i oq Feedforward compensates the capacitor voltage, and the final control equation is:
[0036]
[0037]
[0038] Among them, U dCtrl , U qCtrl is the input of the space vector pulse width modulation SVPWM module, which obtains the on-off control pulse of the IGBT according to the dq axis voltage vector input, K up , K ui is the PI gain of the voltage outer loop, K ip , K ii is the PI gain of the current inner loop. The control system block diagram corresponding to equations 3 and 4 is as follows: Figure 3 shown.
[0039] 3) When the inverter is connected in parallel with the diesel generator set, the current loop control method based on the rotating coordinate system is adopted
[0040] When the inverter is connected in parallel with the diesel generator set, the inverter is set to current follower to control its output current to match the output current of the diesel generator set. Therefore, the current loop control method based on the rotating coordinate system is adopted. In order to ensure the control accuracy of the output current, the current double loop control is adopted. The current outer loop control equation is as follows:
[0041]
[0042] Among them, K iop , K ioi is the PI gain of the current outer loop, i d *、i q * is the output current control target value. The current control inner loop is consistent with the current inner loop of the voltage and current dual loop control, as shown in Equation 4.
[0043] 4) Power control method when the inverter and diesel generator set are connected in parallel
[0044] The system diagram when the inverter and diesel generator set are connected in parallel for power supply is as follows: Figure 2 As shown in the figure, the inverter obtains DC power from the DC main network in the ship's DC power system, converts it into AC380V, and then connects it in parallel with the diesel generator set to supply power to the ship's AC loads. Figure 2 The parallel power control module collects the voltage and current of the inverter and the diesel generator set, and calculates the output active power and reactive power of the diesel generator set and the inverter respectively. The calculation equation is as follows:
[0045]
[0046] Among them, U ac , U bc , U ab is the line voltage of three-phase AC power, i a 、i b 、i c is the line current, P is the active power, and Q is the reactive power. After calculating the active and reactive power of the inverter and the diesel generator set through the above formula, a simple proportional distribution principle is used to calculate I d *as follows:
[0047] i d *=(P dg +P inv ) / (P N1 +P N2 )*i dN
[0048] Among them, P dg , P inv is the power of the diesel generator set and inverter, P N1 , P N2 is the rated power of the diesel generator set and inverter, i dN i is the rated power output of the inverter d ,i d * is the input of the current control loop.
[0049] 5) Phase-locking method when inverter and diesel generator set are connected in parallel
[0050] When the inverter is connected in parallel with the diesel generator set, the inverter tracks the phase of the output current (or voltage) of the diesel generator set in real time through a phase-locked loop. The block diagram of the phase-locked loop module is as follows: Figure 5 As shown, Figure 5 Taking voltage phase tracking as an example, the diesel generator voltage U abc After Clarke transformation, combined with the phase-locked loop As a result, through Park transformation to the rotating coordinate system, set U d The target value of is 0. Through the PI controller, the output With diesel generator set output U abc The phase of the phase-locked loop PI gain is recorded as K pllp , K plli The Park change in the inverter control module is obtained by using a phase-locked loop This ensures that the inverter output is consistent with the diesel generator output phase.
[0051] The embodiments of the present invention are further described below with reference to the accompanying drawings.
[0052] The embodiment is a computer simulation. In the embodiment, the diesel generator set and the inverter are connected in parallel and the load is about 90kW. A 90kW load is suddenly added at 2s. The system block diagram is as follows: Figure 2 As shown, the entire simulation calculation time is 7s.
[0053] The parallel control of the inverter adopts current double closed-loop control. The control block diagram is as follows: Figure 4 As shown, the current outer loop PI gain can be taken as K iop =1, K ioi =2, the current outer loop output saturation can be set to 1.6e3, the saturation value is calculated by the inverter output current limiting protection value, and the current inner loop PI gain can be taken as K ip =500, K ii =0, the phase-locked loop PI gain can be taken as K pllp =10, K plli =50.
[0054] Figure 6 The output voltage waveforms of the diesel generator set and the inverter are captured from 0 to 1s. It can be seen from the figure that the output voltage of the diesel generator set and the output voltage of the inverter basically coincide.
[0055] Figure 7 a is the waveform of the output current a phase of the diesel generator set and inverter, Figure 7 b is Figure 7The waveform of a, which intercepts the 1.75-2.25s sudden load time period, is enlarged. Figure 7 It can be seen from a that when the load suddenly increases, due to the large difference between the output characteristics of the diesel generator set and the output characteristics of the inverter, the output current of the diesel generator set changes greatly and increases more at the moment of load change. As the output current of the inverter increases, the output current of the diesel generator set and the inverter approaches the steady-state value. The ratio of the steady-state values of the output currents of the two is the same as the ratio of the rated powers of the two. Figure 7 In b, the output current phase of the inverter and the diesel generator set is completely consistent.
[0056] Figure 8 This is the load rate curve when the diesel generator set and the inverter are connected in parallel to supply power. When the load suddenly changes, the load rate of the diesel generator set suddenly increases. As the inverter output increases, the load rate of the diesel generator set decreases rapidly and approaches the inverter load rate. Within 2 seconds after the load suddenly changes, the output load rate of the diesel generator set and the inverter can enter the range of 5% of the power distribution difference, meeting the power distribution requirements when the ship's generator sets are running in parallel.
[0057] It can be seen from the examples that the present invention can well realize the parallel operation of the inverter and the auxiliary diesel generator set in the ship's DC power system. When running in parallel, the output voltage and current phases of the two are consistent; in steady state, the load rates of the two are consistent, and the power is accurately distributed in proportion with a small power distribution difference; when a sudden load change occurs, it can quickly stabilize to a state with a small power distribution difference, ensuring the adaptability of the inverter and the diesel generator set to dynamic loads when running in parallel.
[0058] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.
Claims
1. A method for controlling the parallel connection of an inverter and a diesel generator set in a ship power system, characterized in that: The steps include: According to the circuit topology of the inverter in the ship power system, the basic control framework of the inverter is established based on the voltage and current dq control method in the rotating coordinate system, which includes the implementation of the SVPWM pulse width modulation strategy; A phase-locking method based on a synchronous rotating coordinate system and outputting the sine and cosine values of the phase angle is proposed to lock the output voltage and current phase of the diesel generator set so that the inverter output is synchronized with the diesel generator set to meet the parallel phase requirements. When the inverter is powered alone, the voltage and current dual-loop control method is used to obtain better power supply voltage quality; when the inverter and the diesel generator set are powered in parallel, the current dual-loop control method with feedforward compensation is set to achieve stable parallel operation of the two and ensure the adaptability of the inverter and the diesel generator set to dynamic loads when running in parallel; When the inverter is powered alone, the control of the inverter only requires the inverter controller and the SVPWM pulse width modulation controller; After the 3s / 2r conversion, the system model on the dq axis has a strong coupling between the d-axis and the q-axis. Therefore, these related quantities are added to the controller design to eliminate the influence of the coupling and realize the closed-loop control of the d-axis and q-axis variables. At the same time, the capacitor voltage U is introduced into the inner loop of the inductor current in the control loop. d , U q Feedforward effect on inductor current i fd 、i fq To compensate, the capacitor voltage outer loop introduces the output current i od 、i oq Feedforward compensates the capacitor voltage, and the final control equation is: Among them, U dCtrl , U qCtrl is the input of the space vector pulse width modulation SVPWM module, which obtains the on-off control pulse of the IGBT according to the dq axis voltage vector input, K up , K ui is the PI gain of the voltage outer loop, K ip , K ii is the PI gain of the current inner loop; When the inverter is connected in parallel with the diesel generator set to supply power, the inverter is set to current follower to control its output current to match the output current of the diesel generator set. Therefore, a current loop control method based on a rotating coordinate system is adopted. To ensure the control accuracy of the output current, a current dual-loop control is adopted. The current outer loop control equation is as follows: Among them, K iop , K ioi is the PI gain of the current outer loop, i d *、i q * is the output current control target value; The current control inner loop is consistent with the current inner loop of the voltage-current dual-loop control; Power control when the inverter is connected in parallel with the diesel generator set: The inverter obtains power from the DC main network in the ship's DC power system, converts it to AC380V, and then connects in parallel with the diesel generator set to supply power to the ship's AC loads; The parallel power control module collects the voltage and current of the inverter and the diesel generator set, and calculates the output active power and reactive power of the diesel generator set and the inverter respectively. The calculation equation is as follows: Among them, U ac , U bc , U ab is the line voltage of three-phase AC power, i a 、i b 、i c is the line current, P is the active power, and Q is the reactive power. After calculating the active and reactive power of the inverter and the diesel generator set through the above formula, the proportional distribution principle is adopted to calculate I d *as follows: i d *=(P dg +P inv ) / (P N1 +P N2 )*i dN Among them, P dg , P inv is the power of the diesel generator set and inverter, P N1 , P N2 is the rated power of the diesel generator set and inverter, i dN i is the rated power output of the inverter d ,i d * is the input of the current control loop; Phase-locked mode when the inverter is connected in parallel with the diesel generator set: When the inverter is connected in parallel with the diesel generator set, the inverter tracks the phase of the output current or voltage of the diesel generator set in real time through the phase-locked loop; The phase-locked loop module tracks the voltage phase and converts the diesel generator voltage Uabc through Clarke transformation and combines it with the phase-locked loop As a result, the Park transform is transformed into the rotating coordinate system, the target value of Ud is set to 0, and the output can be made to Corresponding to the phase of the diesel generator set output Uabc; the phase-locked loop PI gain is recorded as Kpllp, Kplli; the Park change in the inverter control module is obtained by the phase-locked loop This ensures that the inverter output is consistent with the diesel generator output phase.