Diesel generating set direct current capacitance calculation method under pulse load and diesel generating set system

Abstract

The invention relates to the technical field of direct-current power supply control, in particular to a direct-current capacitance calculation method of a diesel generating set under a pulse load and a diesel generating set system. Comprise pulse peak power, pulse period, pulse on / off time, system no-load direct current voltage, allowable minimum direct current voltage and response time of a diesel engine control unit ECU; according to the obtained parameters, equivalent discharge time needing to be provided by the energy storage capacitor is determined; and calculating the capacitance value of the energy storage capacitor according to an energy conservation relation, and connecting the calculated energy storage capacitor in parallel to a direct current bus of the generator set. In the invention, by establishing a quantitative calculation method of the direct current energy storage capacitor under the pulse load and combining a slow response control strategy of low-pass filtering of a voltage loop of the alternating current-direct current converter, the pulse transient power is borne by the capacitor, and the diesel engine stably intervenes according to self response characteristics, so that the voltage fluctuation of a direct current bus is effectively inhibited; and engine rotating speed impact and mechanical stress are reduced.

Description

Technical Field

[0001] This invention relates to a method for calculating the DC capacitor of a diesel generator set under pulse load and a diesel generator set system, belonging to the field of DC power supply control technology. Background Technology

[0002] Radar and laser weapons are both pulsed loads. The power amplitude of a pulsed load is much greater than its average power, and its power demand changes drastically in a very short time. Figure 1 As shown, the pulse load is powered by a diesel generator set. At the moment the pulse load is applied, the crankshaft of the diesel engine will be subjected to a huge reverse braking torque. When the load is removed, an acceleration torque will be generated.

[0003] This periodic and intense alternating torque load may lead to problems such as increased crankshaft torsional vibration, unstable engine speed, poor combustion, and thermal load shock, affecting engine life and reliability.

[0004] Existing technologies mainly employ two solutions to address the adverse effects of pulse loads on engines. One is to select an ultra-large diesel generator set, that is, to select a diesel engine with a power level sufficient to cover the peak power of the pulse. The disadvantages are high cost and low efficiency. Although it can barely drive the pulse load, there are still torque shocks and speed fluctuations when the load changes abruptly, only to a lesser extent.

[0005] Secondly, there is the option of adding an energy storage system, such as an energy storage capacitor, to a diesel generator set. When a pulse load occurs, the energy storage capacitor provides the required huge power instantaneously. During the intervals between pulse loads, the electricity generated by the diesel generator set, in addition to supplying other equipment, slowly charges the energy storage capacitor to prepare for the next pulse. The advantage is that it isolates the fast pulse load from the slow-responding diesel engine, resulting in smooth operation of the diesel engine with minimal mechanical stress and thermal load, and its lifespan and reliability returning to normal levels. However, the disadvantage is that there is no reasonable method for calculating the capacitance of the energy storage capacitor. If it is too small, it will have no effect; if it is too large, it will lead to a large system size and high cost. Furthermore, the control strategy of the AC / DC converter inside the diesel generator set needs to be coordinated with the energy storage capacitor to achieve the isolation of the fast pulse load from the slow-responding diesel engine. Therefore, it is urgent to improve the calculation method of the DC capacitor of a diesel generator set under a pulse load to solve the above-mentioned problems. Summary of the Invention

[0006] The purpose of this invention is to provide a method for calculating the DC capacitor of a diesel generator set under pulsed load. This addresses the problem of existing technologies that primarily employ two approaches to mitigate the adverse effects of pulsed loads on the engine. One approach involves selecting an oversized diesel generator set, i.e., choosing a diesel engine with a power rating sufficient to cover the peak power of the pulse. The disadvantages are high cost and low efficiency. While this method can barely handle the pulsed load, torque surges and speed fluctuations still occur during sudden load changes, albeit to a lesser extent. The second approach involves adding an energy storage system, such as an energy storage capacitor, to the diesel generator set. When the pulsed load occurs, the energy storage capacitor provides the required massive power instantaneously. During the intermittent period, the electricity generated by the diesel generator set, in addition to supplying other equipment, will slowly charge the energy storage capacitor to prepare for the next pulse. The advantage is that it isolates the fast pulse load from the slow-response diesel engine, resulting in smooth operation of the diesel engine with minimal mechanical stress and thermal load, and its lifespan and reliability returning to normal levels. However, the disadvantage is that there is no reasonable method for calculating the capacitance value of the energy storage capacitor. If it is too small, it will have no effect, while if it is too large, it will lead to a large system size and high price. Furthermore, the control strategy of the AC-DC converter inside the diesel generator set needs to be coordinated with the energy storage capacitor to achieve the problem of isolating the fast pulse load from the slow-response diesel engine.

[0007] To achieve the above objectives, this invention provides a technical solution for a diesel generator set system adapted to a method for calculating the DC capacitance of a diesel generator set under pulse load:

[0008] A method for calculating the DC capacitance of a diesel generator set under pulsed load includes the following steps: obtaining pulsed load parameters, including pulsed peak power. Pulse period and pulse on / off time, system no-load DC voltage Minimum allowable DC voltage and the response time of the diesel engine control unit (ECU) Based on the obtained parameters, determine the equivalent discharge time that the energy storage capacitor needs to provide. The capacitance C of the energy storage capacitor is calculated according to the law of conservation of energy, using the following formula: The calculated energy storage capacitor is connected in parallel to the DC bus of the generator set; dual closed-loop vector control is implemented on the AC / DC converter: the outer loop is the DC voltage loop, and the inner loop is the current loop; a low-pass filter is introduced into the DC voltage feedback loop, the timing of which is based on the response time of the diesel engine ECU. design.

[0009] Furthermore, the equivalent discharge time t is the time required for the diesel engine to generate a pulse and for its output power to partially or fully compensate for the pulse load. This time can be taken as the ECU response time. Integer multiples of or values ​​determined by system simulation / experience.

[0010] Furthermore, the parameters used to calculate the energy storage capacitor , , , Through real-time measurement or input from system design values; when the pulse load is a periodic pulse, Take the peak power of the pulse. This can be taken as the time interval from the start of the pulse to the effective output of the diesel engine reaching a certain percentage, or to ensure that the minimum voltage is ≥ Minimum time required.

[0011] Furthermore, the time constant or cutoff frequency of the low-pass filter is set to be approximately equal to the diesel engine ECU response time τ.

[0012] Furthermore, the voltage loop PI controller of the AC / DC converter, in conjunction with the low-pass filter, regulates the DC voltage reference along a slow trajectory when the pulsed load is on, while the energy storage capacitor provides transient power. When the pulsed load is off or the engine output resumes, the converter charges the energy storage capacitor according to the PI controller output, ensuring the capacitor recovers to its normal value before the next pulse. Nearby voltage.

[0013] Furthermore, the method for calculating the DC capacitor of a diesel generator set under pulsed load is implemented through a diesel generator set system. This system includes: a permanent magnet generator, an AC / DC converter, a DC bus, a parallel energy storage capacitor, and a control unit. The control unit is configured to execute the method described in any one of claims 1 to 5. The AC / DC converter employs dual closed-loop vector control; the DC voltage feedback is low-pass filtered before entering the outer loop PI controller, and the inner loop is a current closed loop. The parameters of the low-pass filter are based on the response time of the diesel engine ECU. set up;

[0014] The capacitance C of the energy storage capacitor is rounded down from the actual capacitance value and combined with multiple parallel capacitors in the system to meet the requirements of size, ESR and withstand voltage; the system is also equipped with capacitor overcharge and over-discharge protection and voltage equalization measures.

[0015] Furthermore, the control unit includes a charging and discharging strategy: during the pulse load interval, the AC-DC converter charges the energy storage capacitor with a controlled current, and the charging current is determined by the voltage loop PI and the charging limit logic; under long-term load or continuous high load conditions, the control unit limits pulse triggering or issues a derating / alarm based on the diesel engine output capacity.

[0016] Furthermore, it is suitable for scenarios that power radar, laser weapons, or other short-pulse, high-peak-power pulse loads.

[0017] This invention has at least the following beneficial effects:

[0018] This invention establishes a quantitative calculation method for DC energy storage capacitors under pulsed loads and combines it with a slow-response control strategy of low-pass filtering in the AC / DC converter voltage loop. This allows the capacitor to bear the transient power of the pulses, while the diesel engine smoothly engages according to its own response characteristics. This effectively suppresses DC bus voltage fluctuations, reduces engine speed impact and mechanical stress, and improves the stability, reliability, and engineering applicability of the generator set under high-peak pulsed load conditions. Attached Figure Description

[0019] Figure 1 This is an example diagram of the pulse load of the present invention;

[0020] Figure 2 This is a block diagram of the diesel generator set system of the present invention;

[0021] Figure 3 This is a schematic diagram of the AC / DC converter control strategy of the present invention;

[0022] Figure 4 This is a schematic diagram of the output voltage curve considering the response time of a diesel engine under pulse load according to the present invention. Detailed Implementation

[0023] The following will describe in detail the implementation of this application with reference to the accompanying drawings and embodiments, so that the implementation process of how this application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0024] like Figures 1-4 As shown in the figure, this embodiment provides a method for calculating the DC capacitor of a diesel generator set under pulsed load, which isolates the fast pulsed load from the slow-responding diesel engine. The method includes the following steps: obtaining pulsed load parameters, including pulsed peak power. Pulse period and pulse on / off time, system no-load DC voltage Minimum allowable DC voltage and the response time of the diesel engine control unit (ECU) Based on the obtained parameters, determine the equivalent discharge time that the energy storage capacitor needs to provide. The capacitance C of the energy storage capacitor is calculated according to the law of conservation of energy, using the following formula: The calculated energy storage capacitor is connected in parallel to the DC bus of the generator set; dual closed-loop vector control is implemented on the AC / DC converter: the outer loop is the DC voltage loop, and the inner loop is the current loop; a low-pass filter is introduced into the DC voltage feedback loop, and the timing of the low-pass filter is based on the response time of the diesel engine ECU. This design aims to make the AC / DC converter unresponsive or slow-responding to high-frequency, rapid power changes in pulsed loads. By combining a capacitor calculation formula based on energy conservation with low-pass filter slow-response control, the capacitor size can be precisely determined, ensuring that the capacitor absorbs transient impacts during engine response. This maintains the DC bus voltage within a safe range, reduces the impact of diesel engine transient load fluctuations on the unit's mechanics and speed control system, and improves the system's anti-pulse interference capability and overall reliability.

[0025] As a further implementation of this scheme, the equivalent discharge time t is the time required for the diesel engine to generate a pulse and for its output power to partially or fully compensate for the pulse load. This time can be taken as the ECU response time. The value is an integer multiple of the specified value or determined by system simulation / experience to ensure that the DC voltage does not fall below a certain value within time t. The capacitor design has both engineering feasibility and conservative margin, taking into account both short-term transient protection and long-term system stability, which helps to reduce simulation-measurement deviation and improve the safety margin of the design.

[0026] As a further implementation of this scheme, the parameters used to calculate the energy storage capacitor are as follows: , , , Through real-time measurement or input from system design values; when the pulse load is a periodic pulse, Take the peak power of the pulse. This can be taken as the time interval from the start of the pulse until the effective output of the diesel engine reaches a certain percentage (e.g., 40%, 80%), or to ensure that the minimum voltage is ≥ The minimum required time allows parameters to be input from real-time measurements or design values, taking into account both static design and online adaptive adjustment, thus improving the applicability of the method; different criteria (peak / percentage response) are considered for periodic pulses, thereby achieving a more reasonable trade-off between capacitance and control under different operating conditions;

[0027] As a further implementation of this solution, the time constant or cutoff frequency of the low-pass filter is set to be approximately equal to the response time τ of the diesel engine ECU (e.g., τ≈20 ms) to suppress the fast response of the AC-DC converter within the pulse period (e.g., on the order of milliseconds). By matching the filtering characteristics with the engine response time, the converter can achieve an "invisible" or slow response to high-frequency pulses, thereby avoiding frequent intervention of the converter and motor control circuit on short pulses, reducing the computational and hardware stress on the controller, and extending the equipment life.

[0028] As a further implementation of this scheme, the voltage loop PI controller of the AC / DC converter is jointly adjusted with the low-pass filter so that when the pulse load is turned on, the converter tracks the DC voltage reference along a slow trajectory, while the energy storage capacitor provides transient power; when the pulse load is turned off or the engine output is restored, the converter charges the energy storage capacitor according to the PI controller output, so that the capacitor recovers to its normal value before the next pulse arrives. The nearby voltage and joint regulation strategy ensure closed-loop management of transient discharge and subsequent controlled charging, which not only meets the transient power supply requirements, but also prevents the capacitor from being undervoltage or over-discharged for a long time, ensuring that the capacitor and converter operate stably under multi-pulse conditions and improving the system energy management efficiency.

[0029] The above-mentioned method for calculating the DC capacitance of a diesel generator set under pulse load is implemented through a diesel generator set system, specifically as follows:

[0030] A diesel generator set system includes a permanent magnet generator, an AC / DC converter, a DC bus, a parallel energy storage capacitor, and a control unit. The control unit is configured to execute a method for calculating the DC capacitor of the diesel generator set under pulsed load. The AC / DC converter employs dual closed-loop vector control; the DC voltage feedback is passed through a low-pass filter before entering the outer loop PI controller, while the inner loop is a current closed loop. The parameters of the low-pass filter are based on the response time of the diesel engine ECU. The method is implemented as a system to facilitate engineering integration; by configuring a permanent magnet generator with a dual closed-loop vector converter, the power density and control accuracy are improved; and by using low-pass filtering and parallel capacitors to buffer pulse energy, the generator set's adaptability to high-peak pulse loads is enhanced.

[0031] The capacitance C of the energy storage capacitor is rounded up from the actual capacitance value and combined with multiple parallel capacitors in the system to meet the requirements of size, ESR and withstand voltage. The system is also equipped with capacitor overcharge and over-discharge protection and voltage equalization measures. The system takes into account the capacitor rounding and multi-stage parallel scheme for practical engineering implementation, and takes into account the equivalent series resistance (ESR), withstand voltage and size arrangement of the capacitors. The addition of protection and voltage equalization measures improves the safety, reliability and maintenance convenience of the capacitor bank.

[0032] The control unit further includes a charging and discharging strategy: during the pulse load interval, the AC-DC converter charges the energy storage capacitor with a controlled current, and the charging current is determined by the voltage loop PI and the charging limit logic; under long-term load or continuous high load conditions, the control unit limits pulse triggering or issues a derating / alarm based on the diesel engine output capacity to prevent the capacitor from discharging in large quantities for a long time, which could lead to system instability.

[0033] Suitable for scenarios that supply power to radar, laser weapons or other short-pulse, high-peak-power pulse loads, the diesel generator set maintains stable speed and output under pulse conditions through the above-mentioned energy storage capacitor calculation and AC / DC converter slow response control strategy, reducing crankshaft torsional vibration and transient mechanical / thermal stress of the engine, thereby improving the reliability and life of the engine and the whole machine.

[0034] Example

[0035] Taking a pulse load with a peak power of 160kW, a cycle of 6.7ms, a pulse load turn-on time of 2ms, and a turn-off time of 4.7ms as an example, and assuming the output voltage is 600V under no-load conditions and cannot be lower than 550V under pulse load conditions, with a diesel engine ECU response time of 20ms:

[0036] Please refer to the attached instruction manual for details. Figure 4 Regarding the output voltage curve considering the response time of a diesel engine under pulsed load;

[0037] As shown in the attached diagram, the no-load output voltage is 600V, and the minimum output voltage does not fall below 550V. Within 0-2ms, the pulse load turns on with a power of 160kW, causing the output voltage to decrease. Within 2-6.7ms, the pulse load turns off. Due to the low-pass filter in the AC / DC converter control strategy, the AC / DC converter does not respond when the output voltage decreases; therefore, the output voltage remains constant during the pulse load off phase. The output voltage change curve repeats this process until 20.1-22.1ms, when the diesel engine has responded (outputting 40kW), and the output voltage decreases by 120kW. From 22.1-26.8ms, the output voltage increases by 40kW. From 26.8-28.8ms, the output voltage continues to decrease by 120kW, but from 28.8-33.5ms, the output voltage increases by 80kW because the diesel engine can output 80kW of power at this point. Figure 4 It can be seen that the lowest output voltage occurs at 28.8ms and is greater than 550V.

[0038] To simplify the calculation of the energy storage capacitor, it is assumed that the power required by the pulse load is provided by the energy storage capacitor within 28.8ms, and that the diesel engine does not output power during this period (achieved through the low-pass filter in the AC-DC converter control strategy). Therefore, the formula for calculating the energy storage capacitor is:

[0039]

[0040] In the formula, C is the capacitance of the energy storage capacitor, P is the peak power of the pulse load, t is the discharge time of the energy storage capacitor, u1 is the initial value of the output voltage, and u2 is the minimum value of the output voltage. Calculations show that the capacitance of the energy storage capacitor is 160mF.

[0041] It should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes that element.

Claims

1. A method for calculating the DC capacitance of a diesel generator set under pulse load, characterized in that, Includes the following steps: Obtain pulse load parameters, including pulse peak power. Pulse period and pulse on / off time, system no-load DC voltage Minimum allowable DC voltage and the response time of the diesel engine control unit (ECU) ; Based on the obtained parameters, determine the equivalent discharge time that the energy storage capacitor needs to provide. ; The capacitance C of the energy storage capacitor is calculated based on the energy conservation principle using the following formula: ; The calculated energy storage capacitor is connected in parallel to the DC bus of the generator set; The AC / DC converter is subjected to dual closed-loop vector control: the outer loop is the DC voltage loop, and the inner loop is the current loop; a low-pass filter is introduced into the DC voltage feedback loop, and the timing of the low-pass filter is based on the response time of the diesel engine ECU. design.

2. The method for calculating the DC capacitance of a diesel generator set under pulse load according to claim 1, characterized in that: The equivalent discharge time t is the time required for the diesel engine to generate a pulse and for its output power to partially or fully compensate for the pulse load. This time can be taken as the ECU response time. Integer multiples of or values ​​determined by system simulation / experience.

3. The method for calculating the DC capacitance of a diesel generator set under pulse load according to claim 1, characterized in that: Parameters used to calculate energy storage capacitors , , , Through real-time measurement or input from system design values; when the pulse load is a periodic pulse, Take the peak power of the pulse. This can be taken as the time interval from the start of the pulse to the effective output of the diesel engine reaching a certain percentage, or to ensure that the minimum voltage is ≥ Minimum time required.

4. The method for calculating the DC capacitance of a diesel generator set under pulse load according to claim 1, characterized in that: The time constant or cutoff frequency of the low-pass filter is set to be approximately equal to the diesel engine ECU response time τ.

5. The method for calculating the DC capacitance of a diesel generator set under pulse load according to claim 1, characterized in that: The AC / DC converter's voltage loop PI controller and low-pass filter work together to regulate the DC voltage reference in a slow, controlled manner when the pulsed load is on, while the energy storage capacitor provides transient power. When the pulsed load is off or the engine output resumes, the converter charges the energy storage capacitor according to the PI controller output, ensuring the capacitor is restored to its normal value before the next pulse. Nearby voltage.

6. A diesel generator set system based on the method for calculating the DC capacitance of a diesel generator set under pulse load as described in any one of claims 1-5, characterized in that: The method for calculating the DC capacitor of a diesel generator set under pulsed load is implemented through a diesel generator set system. The system includes: a permanent magnet generator, an AC / DC converter, a DC bus, a parallel energy storage capacitor, and a control unit. The control unit is configured to execute the method described in any one of claims 1 to 5. Furthermore, the AC / DC converter employs dual closed-loop vector control; the DC voltage feedback is low-pass filtered before entering the outer loop PI controller, and the inner loop is a current closed loop. The parameters of the low-pass filter are based on the response time of the diesel engine ECU. set up; The capacitance C of the energy storage capacitor is rounded down from the actual capacitance value and combined with multiple parallel capacitors in the system to meet the requirements of size, ESR and withstand voltage; the system is also equipped with capacitor overcharge and over-discharge protection and voltage equalization measures.

7. A diesel generator set system according to claim 6, characterized in that: The control unit further includes a charging and discharging strategy: during the pulse load interval, the AC-DC converter charges the energy storage capacitor with a controlled current, and the charging current is determined by the voltage loop PI and the charging limit logic; under long-term load or continuous high load conditions, the control unit limits pulse triggering or issues a derating / alarm based on the diesel engine output capacity.

8. A diesel generator set system according to claim 6, characterized in that: Suitable for scenarios that power radar, laser weapons or other short-pulse, high-peak-power pulse loads.

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