Excitation control system for variable speed diesel generator sets in DC power distribution systems

Abstract

The invention discloses an excitation control system suitable for a variable speed diesel generator set of a DC power distribution system, which adopts a dynamic AVR regulation technology to control the DC bus voltage by regulating the output voltage of the diesel generator set; the speed reference of the diesel generator set is given by the excitation control system, so that the diesel engine can work at the optimal fuel consumption point; the diesel generator set feeds power to the DC bus through diode rectification, which has a simple structure, low cost, mature technology and no need for complex control compared to an IGBT rectifier; the excitation and parameter adaptation of the diesel generator set is achieved, and a speed reference is given to meet the DC voltage stabilization control under different loads; compared with the traditional AVR constant voltage regulation technology, the diesel engine works in a constant speed mode, especially under the condition of low power and high speed, the control mode of the variable speed diesel engine can better play its energy-saving advantage.

Description

Technical Field

[0001] The invention relates to the field of marine diesel generator system, and in particular to an excitation control system suitable for a variable speed diesel generator set in a direct current power distribution system. Background Art

[0002] With the implementation of the EEDI / EEXI index in the field of ships, energy conservation and environmental protection have become an important indicator for measuring ship performance. The DC power distribution system is increasingly widely used on ships due to its unique advantages. The traditional AVR constant voltage excitation controller is no longer particularly applicable in the DC power distribution system because the output voltage of the rectifier is only related to the output terminal voltage of the generator set and has nothing to do with the frequency. The diesel generator assembly using a variable speed governor will become more suitable for the DC power distribution system. Under the same load, low speed is more energy-efficient than high speed. The present invention is based on this output characteristic of the diesel engine and has developed an excitation control system for a variable speed diesel generator in ship DC power distribution.

[0003] Patent CN100486101C designs a control system for a variable speed diesel generator set, including speed control, excitation control and peripheral circuits of the diesel generator set. The torque vector control method is used for speed regulation of the diesel generator set, which also determines that the rectifier can only use IGBT.

[0004] In this system, the droop characteristics of the voltage at the output end of the generator set are simulated to realize the control of the DC bus voltage. Compared with patent CN100486101C, the control system will be simpler to implement. Due to the use of diode uncontrolled rectification, the system will also be more reliable and easier to maintain. Summary of the invention

[0005] The purpose of the present invention is to provide an excitation control system suitable for a variable speed diesel generator set in a DC power distribution system, which solves the problems of high control concentration and poor scalability of the variable speed diesel generator set and simplifies the complex control method in the prior art. The system uses a diode uncontrolled rectifier to connect the diesel generator set and the DC busbar, the DC output end of the diode rectifier is connected to the DC busbar through a fast fuse, and a DC support capacitor is installed at the fuse and the output end of the diode rectifier.

[0006] The present invention proposes an excitation control system suitable for a variable speed diesel generator set in a DC power distribution system, comprising one or more generator assemblies and a controller, wherein the generator assemblies are all connected to the controller, each generator assembly comprises a generator set and a diode rectifier, the diode rectifier is connected to the generator set and a DC busbar, the generator set is rectified by the diode rectifier, and power is fed to the DC busbar, the controller collects the voltage signal of the DC busbar and the output current of the diode rectifier, obtains the corresponding excitation reference current and the reference speed of the generator set, the generator assembly adopts a variable speed regulation mode, and the generator assembly adjusts the corresponding parameters according to the excitation reference current and the reference speed of the generator set.

[0007] In some embodiments, the generator set is a diesel generator set, and the diesel generator set is a synchronous generator set. The speed can be adjusted according to the load size to make the diesel generator set work at the optimal fuel consumption point.

[0008] In some embodiments, the excitation power source for the diesel generator set comes from a coaxial permanent magnet generator.

[0009] In some embodiments, each of the generator components further includes a voltage regulator and a speed regulator, wherein the voltage regulator is used to control the output voltage of the diesel generator set, and the speed regulator is used to control the rotational speed of the generator set.

[0010] In some embodiments, the voltage regulator is an automatic voltage regulator.

[0011] In some embodiments, the DC end of the diode rectifier is equipped with a fuse, and the DC output end of the diode rectifier is connected to the DC busbar via the fuse.

[0012] In some embodiments, the fuse and the diode rectifier output end are both equipped with a DC support capacitor.

[0013] In some embodiments, a three-phase AC isolating switch is provided between the generator set and the diode rectifier.

[0014] In some embodiments,

[0015] The controller includes a PI controller and a speed controller. The controller is preset with a DC busbar power current curve, obtains the output current of the diode rectifier, obtains the reference value of the DC voltage through the DC busbar power current curve, and obtains the excitation reference current through the PI controller; matches the speed range of the generator set according to the load power, and gives the reference speed of the generator set through the speed controller. In this system, the excitation current is used as the control object, the motor voltage is used as the control target, and the PI controller is used to achieve the control effect of automatic voltage stabilization under different speed loads. The reference value of the DC voltage is described by the lower vertical line related to the load size.

[0016] In some implementations, the controller is further provided with a Kalman filter and a feedforward compensation module.

[0017] The advantages of the excitation control system for a variable speed diesel generator set in a DC power distribution system described in the present invention are:

[0018] Compared with IGBT rectifier, diode rectification has simple structure, low cost, mature technology and no need for complex control;

[0019] The DC voltage regulation technology is used to realize the excitation control and parameter adaptation of the variable speed diesel generator assembly, and provide a speed reference to ensure that the diesel engine can operate at the optimal fuel consumption point under different loads, thereby achieving the goal of energy saving and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A block diagram of a variable speed diesel generator assembly applicable to a DC power distribution system in some embodiments of the present invention;

[0021] Figure 2 is a characteristic curve of a diesel generator set in some embodiments of the present invention;

[0022] Figure 3 is a curve showing the relationship between DC voltage and load power in some implementation modes of the present invention;

[0023] Figure 4 The DC voltage variation curve when two machines perform load transfer in some embodiments of the present invention;

[0024] Figure 5 FIG. 1 is a control block diagram of an adaptive control system of an excitation system in some embodiments of the present invention. DETAILED DESCRIPTION

[0025] This embodiment proposes an excitation control system for a variable speed diesel generator set in a DC power distribution system involving a DC voltage regulation technology. Figure 1 The content shown is applicable to one or more generator components and a controller 9 of an excitation control system of a variable-speed diesel generator set in a DC power distribution system. The generator components are all connected to the controller 9. Each generator component includes a generator set, a diode rectifier 5, a voltage regulator 7 and a speed governor. The voltage regulator 7 is used to control the output voltage of the generator set, and the speed governor is used to control the speed of the generator set.

[0026] The generator assembly adopts a variable speed regulation mode.

[0027] The generator set is a diesel generator set, which is a synchronous generator set. The speed can be adjusted according to the size of the power grid load so that the diesel generator set works at the best fuel consumption point. The diesel generator set includes a diesel engine 1, an electrically excited brushless synchronous generator 2 and a coaxial permanent magnet generator 3. The electrically excited brushless synchronous generator 2 is rectified by a diode rectifier 5 to feed power to the DC busbar. The DC output end of the diode rectifier 5 is connected to the DC busbar through a fuse 6. The short-circuit protection of the diode output end is achieved by setting the fuse 6. The excitation power supply of the electrically excited brushless synchronous generator 2 comes from the coaxial permanent magnet generator 3. The AC output of the coaxial permanent magnet generator 3 is rectified into DC power by a thyristor (such as a thyristor rectifier 8) to excite the generator set. The controller 9 collects the voltage signal of the DC busbar and the output current of the diode rectifier 5. Through the adjustment of the controller 9, reference signals are given respectively (the reference signal includes the excitation reference current and the reference speed of the generator set). The voltage regulator 7 and the speed regulator in the generator assembly receive the reference signal to complete the corresponding control function.

[0028] The voltage regulator 7 may be an automatic voltage regulator (AVR).

[0029] The controller 9 may include a PI controller and a speed controller. The controller 9 is preset with a DC busbar power current curve, obtains the output current of the diode rectifier, obtains the reference value of the DC voltage through the DC busbar power current curve, obtains the excitation reference current through the PI controller, and matches the speed range of the generator set according to the load power, and gives the reference speed of the generator set through the speed controller. In this system, the excitation current is used as the control object, the motor voltage is used as the control target, and the PI controller is used to achieve the control effect of automatic voltage stabilization under different speed loads. The reference value of the DC voltage is described by the lower vertical line related to the load size.

[0030] In some specific implementations, the controller 9 is also provided with a Kalman filter and a feedforward compensation module. The settings of these two modules can effectively reduce the error between the given excitation reference current and the reference speed of the generator set, ensure the adaptive effect, and better meet the DC voltage stabilization control under different loads.

[0031] A three-phase AC isolating switch 4 may be additionally provided between the generator set and the diode rectifier 5 .

[0032] Combination Figures 2 to 5 The content shown is a specific theoretical analysis of the excitation control system applicable to the variable speed diesel generator set in the DC power distribution system.

[0033] Combination Figure 2The content shown in the figure describes the relationship between the rated voltage and speed of the generator, and the rated power and speed of the generator. And it can be seen from the figure that the rated voltage and rated power of the generator are both in a linear relationship with the speed of the generator. The generator described here is the above-mentioned generator set.

[0034] Combination Figure 3 The content shown describes the demand curve for DC voltage under different loads. The DC voltage is fitted into a straight line with a droop characteristic. The higher the load rate, the lower the voltage of the DC bus. Due to the existence of DC support capacitance, its value will directly affect the size of the DC voltage. Assuming that the rated output voltage of the generator is AC690V, when the generator is fully loaded, the minimum output voltage of the DC bus is 850V (without support capacitance). Take 900V as the nominal voltage at full load, with a fluctuation of 0.5%, and obtain a maximum voltage of 905V and a minimum voltage of 895V. The nominal voltage at no load is designed to be 915V, with a fluctuation of 0.5%, and obtain a maximum voltage of 920V and a minimum voltage of 910V. You can draw the following Figure 3 As shown in the straight line. Figure 3 As shown, straight line ① is the DC overvoltage boundary, straight line ② is the DC undervoltage boundary, and straight line ③ is the allowable DC voltage. Taking the 80% load point as an example, the final DC voltage output of the diesel generator at this time ranges from 898.5V to 907.5V. Considering the 80% load of the diesel generator, the diesel engine adopts a constant torque output mode, and its speed will also be around 80% of the rated speed. By finding an approximate speed within the fluctuation range of the DC voltage as a speed reference for the diesel engine, and controlling the output voltage of the generator at the same time, the DC busbar voltage can be controlled to achieve maximum application of the energy-saving advantages of variable-speed diesel generators.

[0035] Figure 4 The figure shows the detailed process of the generator connecting to the DC grid to complete the load distribution.

[0036] Considering that the No. 1 diesel generator is outputting in an isolated grid, its load is 50%. At this time, the ship needs to connect the No. 2 diesel generator to the DC grid to share the load with the No. 1 diesel generator.

[0037] exist Figure 4 As shown in (1), straight line ③ is the DC droop line of No. 1 diesel generator. At the beginning, the isolated grid operates at a load point of 50%, and assuming that the DC voltage of the DC busbar is adjusted to 906V, when No. 2 diesel generator is connected to the grid, its droop line should be as shown by straight line ④, that is, at the moment of grid connection, the DC voltages of the two machines are the same, and the load rates are 50% and 0% respectively.

[0038] The PMS sends a load sharing command to the excitation controller to increase the output voltage of the No. 2 diesel generator. The excitation control system increases the excitation reference current of the automatic voltage regulator (AVR) on the No. 2 diesel generator, so that the DC voltage of the DC bus reaches 907V. At this time, the curve is as follows: Figure 4 As shown in (2) above, the load rates of the two are 42% and 8% respectively.

[0039] The excitation control system continues to increase the excitation reference current of the automatic voltage regulator (AVR) on the No. 2 diesel generator, repeating the above process until the DC busbar voltage reaches 910V. At this time, the droop curves of the two machines are as follows: Figure 4 As shown in (3), the droop of the two completely overlaps, and the load rate of both is 25%.

[0040] When there is a sudden increase or decrease in load on the DC power grid, the excitation systems of the two machines are required to quickly adjust the motor voltage so that the two machines can evenly share the sudden increase or decrease in load.

[0041] The control principle used by the adaptive control system of the excitation system is as follows: Figure 5 As shown. Collecting DC bus voltage , the effective voltage after DC bus filtering is obtained through Kalman filter 501 ,Will With DC voltage reference voltage The difference is input to the DC voltage PI controller 502 to obtain the excitation current At the same time, in order to cope with the sudden addition / unloading of DC load, the feedforward control of the rectifier output current is introduced to collect the diode rectifier output current Then the effective current is obtained through the Kalman filter 501 , through the feedforward compensation 503 and The sum is output to the automatic voltage regulator (AVR) as the excitation reference current. At the same time, the speed controller 504 (the existing speed controller can be directly selected) uses the effective voltage and effective current , calculate the reference speed of the generator set and output it to the speed governor to achieve speed control of the diesel generator set.

[0042] The above undisclosed matters can all be implemented using existing technologies, so they will not be elaborated here.

[0043] For ordinary technicians, several similar variations and improvements can be made without departing from the creative concept of the present invention, and these should also be regarded as the protection scope of the present invention.

Claims

1. An excitation control system suitable for a variable speed diesel generator set in a DC power distribution system, characterized in that: The invention comprises one or more generator components and a controller. The generator components are all connected to the controller. Each generator component comprises a generator set, a diode rectifier, a voltage regulator and a speed regulator. The generator set is a diesel generator set. The diode rectifier is connected to the generator set and the DC busbar. The generator set feeds power to the DC busbar after being rectified by the diode rectifier. The controller collects the voltage signal of the DC busbar and the output current of the diode rectifier to obtain the corresponding excitation reference current and the reference speed of the generator set. The generator component adopts a variable speed regulation mode. The generator component adjusts the corresponding parameters according to the excitation reference current and the reference speed of the generator set. The controller comprises a PI controller and a speed controller. The controller is preset with a DC busbar power current curve, obtains the output current of the diode rectifier, obtains the reference value of the DC voltage through the DC busbar power current curve, and obtains the excitation reference current through the PI controller. The controller is also provided with a Kalman filter and a feedforward compensation module. The voltage regulator is used to control the output terminal voltage of the diesel generator set. The voltage regulator is an automatic voltage regulator. The speed regulator is used to control the speed of the generator set. The speed range of the generator set is matched according to the load power, and the reference speed of the generator set is given through the speed controller. The control method for the excitation control system of the variable speed diesel generator set in the DC power distribution system is: Collect DC bus voltage , the effective voltage after DC bus filtering is obtained through Kalman filter ,Will With DC voltage reference voltage The difference is input to the PI controller to obtain the excitation current At the same time, in order to cope with the sudden addition / unloading of DC load, the feedforward control of the rectifier output current is introduced to collect the diode rectifier output current , and then obtain the effective current through the Kalman filter , through the feedforward compensation and The summed output is given to the automatic voltage regulator as the excitation reference current, and the speed controller uses the effective voltage and effective current , calculate the reference speed of the generator set and output it to the speed governor to achieve speed control of the diesel generator set.

2. The excitation control system for a variable speed diesel generator set in a DC power distribution system according to claim 1, wherein: The diesel generator set is a synchronous generator set.

3. The excitation control system for a variable speed diesel generator set in a DC power distribution system according to claim 2, wherein: The excitation power supply of the diesel generator set comes from a coaxial permanent magnet generator.

4. The excitation control system for a variable speed diesel generator set in a DC power distribution system according to claim 1, wherein: The DC end of the diode rectifier is equipped with a fuse, and the DC output end of the diode rectifier is connected to the DC busbar via the fuse.

5. The excitation control system for a variable speed diesel generator set in a DC power distribution system according to claim 4, wherein: The fuse and the diode rectifier output end are both equipped with a DC support capacitor.

6. The excitation control system for a variable speed diesel generator set in a DC power distribution system according to claim 1, wherein: A three-phase AC isolating switch is provided between the generator set and the diode rectifier.

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