JP2014189051A - Series hybrid system - Google Patents

Abstract

In a series hybrid system, an increase in DC voltage between inverters due to a sudden stop of a motor can be suppressed.
First and second inverters 14 and 16 are connected in series to an engine 11 via a generator 13. A capacitor 15 is connected between the inverters 14 and 16, and the motor 17 is controlled by the inverter 16. When the motor 17 is stopped, the DC terminals of the inverters 14 and 16 are provided with voltage detectors 24 and 34 for detecting a rise in voltage exceeding the voltage threshold. If an overvoltage is detected, the controllers 25 and 35 in the inverters 14 and 16 are provided. To prevent overvoltage by vector control of the field current.
[Selection] Figure 1

Description

  The present invention relates to a series hybrid motor control system used for general-purpose machines such as agricultural machines and mowers, and more particularly to a series hybrid system that suppresses an increase in DC voltage.

  In recent years, the movement of regulating exhaust gas has become a social trend from the viewpoint of regulating exhaust gas including greenhouse gases. In response to this movement, development of hybrid cars and electric cars is underway. On the other hand, a conventional mower and agricultural machine uses a diesel engine as a power source, and a radiator, a muffler, etc. are arranged around the engine, and a transmission is provided to transmit the power to a necessary part.

  Patent Document 1 proposes an electric agricultural machine instead of using an engine as a power source. As a power source for supplying to the load of the agricultural machine, for example, one that outputs a three-phase AC voltage at 200V is known.

  Patent Document 2 proposes a series hybrid system in which a generator is connected to an engine and a motor is controlled via an inverter. In the series hybrid system, an engine, a generator connected to the engine, a first inverter that converts AC output of the generator into DC power, and a three-phase AC motor are controlled based on the DC output from the inverter. The second inverter is controlled in series. Here, a series hybrid system in which a battery is connected between a pair of inverters or a capacitor such as a film capacitor is connected instead of the battery is known.

JP 2003-9607 A JP 2008-187794 A

  As described above, in the series hybrid system, it is necessary to mount a battery between two inverters or connect a capacitor having a relatively large capacity. This is because when the motor suddenly stops for some reason, the engine cannot be stopped rapidly, so that the electric power from the inverter is not consumed and the voltage between the inverters rapidly increases. Normally, the torque control of the inverter is performed by a managing computer via a communication circuit, so that it cannot cope with a rapid voltage increase. When a battery is connected, the battery becomes a load and can absorb a sudden rise in voltage. However, since it is necessary to use a capacitor having a high withstand voltage and a large capacity, there is a problem in that the price of the capacitor increases or the shape becomes large.

  The present invention has been made paying attention to the problems of such a conventional series hybrid system, and it is possible to increase the voltage rapidly without requiring a capacitor having a high withstand voltage and a large capacity between the inverters. The purpose is to suppress.

In order to solve this problem, a series hybrid system of the present invention includes an engine,
A three-phase generator coupled to the engine; a first inverter that drives the generator and converts a three-phase alternating current into a direct current; and a second inverter connected to a direct current output terminal of the first inverter; A three-phase AC motor controlled by the second inverter, the first and second inverters detecting a DC voltage exceeding a threshold value, and the voltage And a controller that controls the phase of the field current of the inverter when a voltage exceeding a threshold is detected by the detector, and prevents a voltage rise between the ends of the inverter.

  According to the present invention having such characteristics, since vector control is performed so as to suppress a sudden increase in voltage inside the inverter of the series hybrid system, the capacitor between the inverters does not need a large capacity, and therefore, An increase in voltage can be suppressed. Therefore, since the capacitance and breakdown voltage of the capacitor can be reduced, an effect that the price can be reduced can be obtained.

FIG. 1 is a block diagram showing the overall configuration of a series hybrid system according to an embodiment of the present invention. FIG. 2 is a block diagram showing the inverter 14 and its peripheral circuits according to this embodiment. FIG. 3 is a block diagram showing the inverter 16 and its peripheral circuits according to the present embodiment. FIG. 4A is a vector diagram showing phase control of the inverter 14. FIG. 4B is a vector diagram showing phase control of the inverter 16.

  FIG. 1 is a block diagram showing the overall configuration of a series hybrid system according to an embodiment of the present invention. In this figure, this series hybrid system has an engine 11. The power of the engine 11 is supplied to the generator 13 via the flywheel 12, and rotates the generator 13 at a constant speed.

  The generator 13 is a three-phase AC generator, and provides the first inverter 14 with a three-phase AC corresponding to the rotational speed. The inverter 14 performs three-phase AC phase control, and a second inverter 16 is connected to the output terminal of the DC voltage via a capacitor 15. A three-phase AC motor 17 is connected to the inverter 16, and an unillustrated agricultural machine, general-purpose machine or the like is driven by the motor 17. A managing computer 18 is connected to the inverters 14 and 16. The managing computer 18 controls the inverters 14 and 16 in accordance with an accelerator signal from the operation unit 19 and drives the motor 17.

  Here, a film capacitor is used as the capacitor 15. In the conventional series hybrid system, the withstand voltage and capacity of this capacitor are large. For example, a capacitor having a withstand voltage of 800 V and a capacity of 600 μF has to be used. Since the control is performed, the withstand voltage may be as low as 450 V, for example. The capacity is also smaller than that of the conventional one, for example, 500 μF.

Next, the internal configuration of the inverter 14 will be described with reference to FIG. As shown in FIG. 2, switching elements 21U and 22U, 21V and 22V, and 21W and 22W such as power MOSFETs and IGBTs are connected in parallel as shown in the figure. A diode for preventing backflow is connected to both ends of each switching element. The midpoints of the switching elements 21U and 22U, the midpoints of 21V and 22V, and the midpoints of 21W and 22W are shown in the respective phases of the generator 13. Connected and configured. Both ends of these switching transistors serve as output terminals 23a and 23b of the DC power supply.

  Between the pair of output terminals 23a and 23b, a voltage dividing circuit using resistors R1 and R2 for detecting a voltage between the terminals and a voltage detection unit 24 connected to the midpoint thereof are provided. Is connected to the controller 25. The voltage detection unit 24 outputs a detection signal to the controller 25 when the voltage between the terminals exceeds a predetermined threshold value. The controller 25 performs phase control by controlling the opening and closing timings of the six switching elements 21U to 22W according to the control from the managing computer 18, and weakens the energy when the signal from the voltage detection unit 24 is obtained. Thus, vector phase control is performed so as to be absorbed by the field.

  FIG. 3 is a diagram showing an internal configuration of the second inverter 16. Similarly to the inverter 14, the inverter 16 has switching elements 31U and 32U, 31V and 32V, 31W and 32W such as power MOSFETs and IGBTs connected in parallel as shown in the figure. A diode for preventing a backflow is connected to both ends of each switching element, and both ends of these switching transistors are input terminals 33a and 33b of a DC power source. The midpoints of the switching elements 31U and 32U, the midpoints of 31V and 32V, and the midpoints of 31W and 32W are connected to each phase of the motor 17 as illustrated. Also in the inverter 16, a voltage dividing circuit by resistors R3 and R4 and a voltage detector 34 are connected to the DC input terminal. The voltage detection unit 34 outputs a detection signal to the controller 35 when the voltage between the terminals exceeds a predetermined threshold value. The controller 35 controls the opening and closing timings of the six switching elements 31U to 33W according to the control from the managing computer 18 to perform phase control, and weakens the energy when a signal from the voltage detection unit 34 is obtained. Thus, vector phase control is performed so as to be absorbed by the field.

  Next, the operation of this embodiment will be described. In the series hybrid system in this embodiment, the signal from the accelerator is applied to the managing computer 18 via the operation unit 19, whereby phase control is performed by the controllers of the inverters 14 and 16. During normal operation, the engine 11 rotates the generator motor 13 at a constant speed via the flywheel 12. As a result, the inverter 14 generates a substantially constant DC voltage. Here, in order to control the phase of the voltage, the switching timing of each phase of the generator motor is controlled, vector control is performed, and a necessary DC voltage is obtained. This DC voltage is smoothed by the capacitor 15 and further applied to the inverter 16, and based on this, the phase of the motor 17 is controlled according to the load. In a normal constant speed, constant load driving state, the inverter 14 is controlled for the rotational phase of -Iq as indicated by a solid line vector V1 in FIG. 4A. In the inverter 16, the phase control of + Iq is performed as indicated by the solid line vector V4 in FIG. 4B.

Assume that the motor 17 is suddenly stopped due to some load. Even in such a case, the engine 11 normally rotates at a constant speed, and thus cannot be stopped rapidly. For this reason, the level of the DC voltage on the output side of the inverter 14 and the input side of the inverter 16 becomes an overvoltage. In the inverter 14, if an overvoltage occurs, the overvoltage is detected by the voltage detection unit 24 and a signal is added to the controller 25. As a result, field control is performed so that Id is negative and Iq is reduced as in vector V2 in FIG. 4A. In this way, energy is absorbed, and the increase in voltage can be reduced. Here, the vector V3 indicates a limit vector that weakens the control current. At the same time, when an overvoltage is detected by the voltage detector 34 in the inverter 16, field control is performed so that Id is negative and Iq is reduced as shown by a vector V5 in FIG. 4B. This will absorb the energy. The vector V6 indicates the limit value of the vector that weakens the field. Such vector control can prevent a sudden overvoltage and suppress an increase in voltage in the DC section. As described above, since the vector control is performed by the controllers 25 and 35 inside the inverter, the voltage increase can be suppressed in an extremely short time, for example, about 50 μs as compared with the case where the control is performed using the managing computer 18.

  Therefore, it is not necessary to connect an expensive battery between the inverters 14 and 16, and the capacitor 15 has a low withstand voltage and may have a relatively small capacity, so that the configuration can be simplified.

  In this embodiment, each of the two inverters is provided with a resistance dividing circuit and a voltage detection unit. However, if a voltage exceeding a threshold value is detected, it is sufficient to provide a signal to the controller. The two threshold values may be the same value. Alternatively, the inverters 14 and 16 and the capacitor 15 may be housed in a single casing and integrated. In this case, the resistance voltage dividing circuit and the voltage detector can be shared.

  According to the present invention, a capacitor can be reduced between inverters in a series hybrid system. Therefore, the present invention can be suitably used for various industrial machines such as agricultural machines and lawn mowers.

DESCRIPTION OF SYMBOLS 11 Engine 12 Flywheel 13 Generator 14,16 Inverter 15 Capacitor 17 Motor 18 Managing computer 19 Operation part 24,34 Voltage detection part 25,35 Controller

Claims (2)

An engine,
A three-phase generator coupled to the engine;
A first inverter that drives the generator and converts three-phase alternating current to direct current;
A second inverter connected to a DC output terminal of the first inverter;
A three-phase AC motor controlled by the second inverter,
The first and second inverters are
A voltage detector for detecting that the DC voltage has risen above the threshold;
A series hybrid system comprising: a controller that controls a phase of a field current of the inverter when a voltage exceeding a threshold is detected by the voltage detection unit, and prevents a voltage increase between terminals of the inverter.   The series hybrid system according to claim 1, wherein the voltage detection unit and the controller are included in both the first and second inverters.

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