DE102010052808A1 - Method for operating vehicle e.g. hybrid vehicle, involves setting switch of one bridge branch of quasi-Z-source inverter such that outputs are shorted together in one time period and not short-circuited in another time period - Google Patents

Abstract

A switch of one bridge branch of quasi-Z-source inverter is set such that the outputs are shorted together in one time period and not short-circuited in another time period. The current (IL1,IL2) flowing in a control circuit (15) comprising the inductors (L1,L2) is controlled by the ratio of time period at which the outputs are short-circuited and the time period at which the outputs are not short-circuited. The voltage (UC2) is applied at the capacitors (C1,C2) in a control circuit (16) based on the ratio of the time periods.

Description

The invention relates to a method for operating a vehicle with a quasi-Z source converter, a DC voltage source and a converter with at least one bridge branch, which is short-circuited as part of the method.

The electrical energy required for the operation of hybrid and electric vehicles is usually provided by a battery or an accumulator. While the battery supplies DC power, AC power is required to operate an electric motor. Therefore, in an electrically powered motor vehicle, circuitry is needed to convert DC power to AC power. For this purpose, usually three-phase pulse inverters are provided, which are operated with the pulse width modulation method (PWM method). In the case of ordinary three-phase inverters, however, the problem arises that the generated output voltage is always less than or equal to the amount of the DC voltage provided. If, for example, the voltage of the battery drops, the maximum voltage that can be supplied to the electric motor also decreases.

To address this problem, impedance inverters have been developed to increase the output voltage provided to the electrical machine. In 1 there is shown an impedance inverter known in the art, the present embodiment being referred to as Z-source converter (ZSC). The basic circuit is a combination of a passive LC network (Z network) and a three-phase pulse inverter, which in turn consists of six switches, each with an antiparallel freewheeling diode. To a battery 3 with a positive pole 13 and a negative pole 14 is connected via a first input E1 and a second input E2 a DC link with inductive and capacitive components. This comprises two inductors L ₁ and L ₂ and two capacitors C ₁ and C ₂ (DC link capacitors) connected in an X configuration. In addition, a diode D with an anode side AS and a cathode side KS follows directly on the first input E1. While the input voltage U _E is present across the inputs E1 and E2, the intermediate circuit voltage U _ZK is present across the outputs A1 and A2. The DC link with bridge forms a so-called Z-source converter 28 ,

To the outputs A1 and A2 is an inverter 2 , which in the example is a three-phase pulse inverter, connected. The inverter 2 comprises three parallel bridge branches B1, B2 and B3. Each of the bridge branches B1, B2 and B3 comprises an upper switch S _O and a lower switch S _U connected in series therewith. The switches S _O and S _U are usually designed as bipolar transistors with insulated gate electrode (so-called IGBT switch) and are particularly suitable for use at high voltages. Antiparallel to each of the switches S _O and S _U is connected as a protective diode acting freewheeling diode. To the upper switches S _O upper freewheeling diodes F _O are connected in anti-parallel, while the lower switches S _U lower freewheeling diodes F _U are connected in anti-parallel. Between the upper switches S _O and the lower switches S _U are the phases for a rotary field machine 4 tapped. The induction machine 4 then represents a three-phase load.

In the case of ordinary three-phase voltage source converters, the amplitude of the pulse-shaped output voltage can be at most as great as the amount of the intermediate circuit voltage U _ZK . Consequently, the behavior of a buck converter is present. In contrast, in a Z-source converter by timed short-circuiting of the Z-network, the time average of the intermediate circuit voltage U _ZK relative to the input voltage U _{E can be} increased. This short circuit condition is called a boost or shoot-through. The state is achieved by short-circuiting at least one of the bridge branches B1, B2 and / or B3. Thus, the Z source converter has both a deep-set and a high-set function.

As the induction machine 4 over the battery 3 (Traction battery) is powered, it can with increasing discharge of the battery 3 to a decreasing input voltage U _E and thus to a voltage dip at the induction machine 4 come. The Z-Source converter avoids this problem, in that it is the rotary field machine 4 supplied voltage via its boost converter function to the desired voltage level adapts.

The DE 10 2007 038 959 A1 describes an inverter with two DC links and a bridge branch. The first intermediate circuit in this case comprises two capacitors connected in series, which are connected to one another at a common ground terminal on the one hand and on the other hand abut against two DC voltage inputs. The bridge branch serves to convert DC voltage into AC voltage and comprises two outputs intended for delivering the AC voltage, one of which has a mains choke. Between the first intermediate circuit and the bridge branch, a second intermediate circuit is arranged, which the Bridge branch supplied with voltage and a Hochsetzmöglichkeit for the input voltage has.

From the DE 10 2008 046 301 A1 For example, an inverter system and a special method of operating the same is known. The inverter system includes an impedance inverter that is almost identical to the one in 1 constructed Z-source converter is constructed. The contained switches are controlled by a pulse width modulation signal of a controller. By suitably operating a first set of switches of the inverter on the basis of a first carrier signal and a second set of switches of the inverter on the basis of a second carrier signal can be achieved that the inductive components of the inverter can be made smaller than usual.

From the publication "J. Anderson and FZ Peng (Department of Electrical and Computer Engineering, Michigan State University): Four Quasi-Z Source Inverters, Power Electronics Specialists Conference 2008, Date: 15-19. June 2008, pages 2743-2749 " the circuit arrangement of a quasi-Z source inverter with a parallel to the diode of the quasi-Z source inverter switched feedback switch is known. It differs from the conventional Z source converter by a different component arrangement. As in 1 can also be connected to the quasi-Z source inverter output side, an inverter. It is then known to briefly short-circuit at least one of the bridge branches of the inverter and thus to control the intermediate circuit voltage. This is the same control principle as for the Z-source inverter.

It is an object of the invention to provide a method with which the power transmission between a DC voltage source and an electrical load can be improved.

This object is achieved by a method having the features of claim 1.

The method according to the invention serves to operate a vehicle with a quasi-Z source converter. A quasi-Z source inverter is an electrical circuit arrangement that serves in particular for boosting a voltage. The quasi-Z source inverter comprises a first and a second input for applying a DC voltage. This DC voltage is from a DC voltage source, for. As a battery provided. The quasi-Z source inverter also includes first and second outputs. In addition, it comprises a first and a second throttle each having a first and a second terminal side, a diode having an anode side and a cathode side and a first and a second capacitor having a first and a second terminal side. These components are connected within the quasi-Z source inverter as follows: Between the first input and the first output, the two reactors and the diode are connected in series with each other. Here, the first connection side of the first throttle is connected to the first input, while the second connection side of the first throttle is connected to the anode side. The cathode side of the diode is also connected to the first terminal side of the second choke. The second connection side of the second throttle is finally connected to the first output. The capacitors, which can also be referred to as DC link capacitors, are connected as follows: The first capacitor is connected in parallel to the diode and second choke. The second capacitor is connected so that its first terminal side is connected to the cathode side of the diode and its second terminal side is connected both to the second input and to the second output. The term throttle is generally to be understood as meaning an inductive component or a coil. The term capacitor is generally to be understood as a capacitive component.

The quasi-Z source inverter also includes a regenerative switch which is connected in anti-parallel to the diode. The regenerative switch can thus bridge the diode electrically, especially in the closed state. The regenerative switch and the diode can also be present in a common component. When closed, the regenerative switch may allow a current source connected to the first and second outputs to conduct current through the first and second inputs. This allows the quasi-Z source inverter to operate in the reverse direction. While a DC voltage source is provided at the inputs, a load is normally connected to the outputs. With the feedback switch, it is now possible that energy which is provided by the usually acting as a load device, can be fed via the feedback switch in the DC voltage source. The quasi-Z source inverter thus promotes energy efficiency and reduces power loss. Otherwise unused energy can be recycled. A equipped with such a circuit vehicle is thus energy-efficient, cheaper to operate, environmentally friendly and able to bridge with the same energy supply longer distances.

The vehicle preferably also includes a DC voltage source whose positive pole is connected to the first input of the quasi-Z source inverter is connected and whose negative pole is connected to the second input of the quasi-Z source inverter. The DC voltage source may in particular be an electrochemical cell, for. As a traction battery or fuel cell act. The vehicle preferably also includes a converter connected to the outputs of the quasi-Z source inverter. In particular, an electrical machine can then be connected to the converter. With the converter, it is possible, in particular, to have the special advantages of the circuit arrangement come into play through its suitable circuit or activation. In particular, the converter can be operated in such a way that the DC voltage provided by the DC voltage source can be boosted or boosted at the outputs of the circuit arrangement. The converter thus permits in particular a deep-set and / or high-set operation of the circuit arrangement. The voltage provided at the outputs is then in particular lower or higher than the voltage provided by the DC voltage source at the inputs. This allows the voltage to be flexibly adapted to the respective conditions. If, for example, the maximum supply voltage of the DC voltage source decreases over time, the circuit arrangement can be operated by a suitable operation of the converter in such a way that it acts as an up-converter and thereby z. B. keeps the voltage level at the outputs constant.

The converter comprises at least one bridge branch, which is connected between the first and second output of the circuit arrangement. The at least one bridge branch comprises an upper switch and a lower switch, which are connected in series with each other, wherein in each case a freewheeling diode is connected in anti-parallel to the upper and lower switch. An upper freewheeling diode is connected in anti-parallel to the upper switch, d. that is, their cathode side is connected to the first output. A lower freewheeling diode is connected in anti-parallel to the lower switch, d. h. that its anode side is connected to the second output. This embodiment of the converter allows a particularly needs-based operation of the circuit arrangement. If the upper and lower switches are closed at the same time, there will be a short circuit between the first output and the second output. This position then leads in particular to the so-called boost or shoot-through. The circuit arrangement then acts as a step-up converter or step-up converter by periodically switching on (pulse width modulation, PWD). The voltage occurring between the outputs is then higher than the voltage between the inputs during the middle or during the non-boost states. The voltage provided by the circuit arrangement can be varied almost as desired and adapted as needed. The freewheeling diodes assume a protective function and specifically prevent damage to the components of the circuit arrangement and / or the converter.

The method according to the invention now serves for operating a vehicle having a quasi-Z source converter, a DC voltage source and a converter in the described embodiment. According to the method, the switches of the at least one bridge branch are set so that the first output and the second output are short-circuited to each other over a first period of time. It then comes in particular to the so-called boost phase or the so-called shoot-through. In particular, energy supplied to the inputs from the DC voltage source is stored in the chokes. Subsequently, the switches of the at least one bridge branch are set so that the first output and the second output are not short-circuited to each other over a second period of time. If a load is applied to the converter during this second period of time, one speaks in particular of an active state. However, if there is no load on the converter during the second time period, then this state is referred to in particular as freewheeling. Both in the active state and in the freewheel, in particular, the energy stored in the chokes is transferred to the capacitors or is available to the load. The first time duration and the second time duration can in particular be set variably to one another. In particular, the ratio of the first time period to the second time duration can be set. As a result, the voltage applied across the outputs can be adjusted continuously and variably, wherein the high-setting properties of the circuit arrangement are set, depending on the choice of the respective time periods. The voltage available to a load can be adjusted very variably.

According to the invention, the current flowing through the first throttle and / or second throttle is regulated in a first control loop on the basis of the ratio of the first time duration to the second time duration. Irrespective of this, the regulation of the voltage applied to the first capacitor and / or the second capacitor in the context of a second control circuit likewise takes place by means of setting the ratio of the first time duration to the second time duration. Inductor current and capacitor voltage can be controlled independently of each other. The independent regulation of the inductor current and the capacitor voltage can be effected exclusively by selecting the time proportion of the boost phases. It is a simple, yet convenient control of the occurring voltages and currents allows.

Preferably, in this case, the first control loop forms an inner control loop, which is superimposed by the second control loop. Then, the regulation by an exclusive setting of the ratio of the first period of time to the second period of time is particularly simple and straightforward possible.

Preferably, the regenerative switch is closed at least over a partial interval of the second time period and opened during the first time period. In this case, it is particularly preferable to close the regenerative switch over the entire second period of time. In the event that a load is applied to the converter, this closing of the feedback switch is preferably carried out in particular when the double inductor current is smaller than the load current. Without closing the regenerative switch then it comes namely to the load current-related short circuit. This is an unwanted condition which occurs in particular from a change from a freewheel state or boost state to an active state. It turns on a boost state, although an active state is desired. This load-current-dependent boost state can be prevented by the regenerative switch being switched on simultaneously with the active states. A connected to the converter load can be operated very stable and trouble-free. Even in extreme situations, there are no unwanted voltage drops. The constancy of the voltage provided is ensured.

Preferably, the converter comprises at least two bridge branches, wherein in the method at least one of the bridge branches is selected, for which the upper and lower switches are set so that the first output and the second output are short-circuited to each other over the first time period, and wherein the Selection is made so that the lowest possible maximum current flows over all switches and / or free-wheeling diodes of the bridge arms. The selection of the short-circuiting bridge branch is thus in particular such that the current load of the components in the bridge branches is reduced. In this way, the life of the components can be extended. The circuit arrangement or the converter are protected without undesired defects and malfunctions occurring. The operation is extremely gentle overall.

Preferably, it can also be provided that the converter comprises at least two bridge branches and at least two of the bridge branches are selected, for each of which the upper and the lower switch are set so that the first output and the second output are short-circuited to each other over the first time period. In the event of a short circuit between the two outputs, the flowing current is then split in particular over a plurality of bridge branches, so that the components present in these bridge branches are exposed to lower current loads. Damage to the switches and / or freewheeling diodes are reliably avoided, damage is prevented and the life of the circuit arrangement and / or the converter is increased.

• 1) Einstellen des oberen und unteren Schalters, so dass der erste Ausgang und der zweite Ausgang miteinander kurzgeschlossen sind (Boost-Zustand);
• 2) Einstellen des oberen und unteren Schalters, so dass ein Strom über die Last fließt (aktiver Zustand);
• 3) Einstellen des oberen und unteren Schalters, so dass kein Strom über die Last fließt und der erste Ausgang und der zweite Ausgang nicht miteinander kurzgeschlossen sind (Freilauf-Zustand); und
• 4) Einstellen des oberen und unteren Schalters, so dass ein Strom über die Last fließt (aktiver Zustand).

Preferably, in the context of the method, a load is connected to the converter. Preferably, then, the upper and lower switches of at least one of the bridge branches are operated with the immediately consecutive steps:

• 1) setting the upper and lower switches so that the first output and the second output are shorted together (boost state);
• 2) adjusting the upper and lower switches so that a current flows across the load (active state);
• 3) setting the upper and lower switches so that no current flows across the load and the first output and the second output are not shorted together (freewheeling state); and
• 4) Adjust the upper and lower switches so that a current flows over the load (active state).

This operating method can be used in particular when the converter has only one bridge branch, and in particular functions as a DC / DC converter. The method can thus find particular application in single-phase loading. The operating method is characterized by very few switching operations, so that the switching losses can be kept low overall.

Preferably, the converter is an inverter for the multi-phase operation of an electrical machine. In particular, it can be designed so that it allows a three-phase inverter operation. The inverter then comprises a bridge branch for each phase to be generated, the individual bridge branches being all connected in parallel with one another. By suitably controlling the switches of the inverter with suitable control signals, DC voltage applied between the outputs can thus be converted into AC voltage in a suitable manner via a pulse width modulation method. The circuit then acts together with a DC voltage source and the inverter as a DC / AC converter with simultaneously hochsetzstellender functionality. Through the regenerative switch, the entire arrangement can also be operated backward. This means that an AC voltage source connected to the inverter can be used to provide DC voltage at the inputs of the circuit arrangement and so for example to charge a connected to the inputs battery.

According to an alternative embodiment of the invention, a method for operating a vehicle having a quasi-Z source converter is provided, which comprises a diode and a parallel-to-diode feedback switch, a first choke, a second choke, a first capacitor and a second capacitor includes. The vehicle comprises a DC voltage source which is connected on the input side to the quasi-Z source inverter. Furthermore, the vehicle comprises a converter, which is connected on the output side to the quasi-Z source converter and which comprises at least one bridge branch, which is connected between a first and a second output of the quasi-Z source converter. The at least one bridge branch comprises an upper and a lower switch, which are connected in series. In the context of the method, the switches of the at least one bridge branch are set so that the first output and the second output are short-circuited to each other over a first period of time and then the switches of the at least one bridge branch are set so that the first output and the second output via a second period of time are not shorted together. According to this alternative embodiment, the regenerative switch is closed at least over a partial interval of the second time period and opened during the first time period. According to the invention, the above object is also achieved by the alternative embodiment of the invention.

According to a further alternative embodiment of the invention, a method for operating a vehicle with a quasi-Z source converter is provided, which comprises a diode and a diode switch connected in parallel with the diode, a first choke, a second choke, a first capacitor and a second Capacitor includes. The vehicle comprises a DC voltage source which is connected on the input side to the quasi-Z source inverter. Furthermore, the vehicle comprises a converter, which is connected on the output side to the quasi-Z source converter and which comprises at least one bridge branch, which is connected between a first and a second output of the quasi-Z source converter. The at least one bridge branch comprises an upper and a lower switch, which are connected in series. In the context of the method, the switches of the at least one bridge branch are set so that the first output and the second output are short-circuited to each other over a first period of time and then the switches of the at least one bridge branch are set so that the first output and the second output via a second period of time are not shorted together. According to this further alternative embodiment, the converter comprises at least two bridge branches. At least one of the bridge branches is selected, for which the upper and the lower switch are set so that the first output and the second output are short-circuited to each other over the first time period, wherein the selection is made so that the lowest possible maximum current across all switches and / or free-wheeling diodes of the bridge branches flows. Preferably, it can also be provided within the scope of the further alternative embodiment that the converter comprises at least two bridge branches and at least two of the bridge branches are selected, for which in each case the upper and the lower switch are set so that the first output and the second output via the first period of time are shorted together. According to the invention, the above object is also achieved by the further alternative embodiment of the invention.

• 1) Einstellen des oberen und unteren Schalters, so dass der erste Ausgang und der zweite Ausgang miteinander kurzgeschlossen sind (Boost-Zustand);
• 2) Einstellen des oberen und unteren Schalters, so dass ein Strom über die Last fließt (aktiver Zustand);
• 3) Einstellen des oberen und unteren Schalters, so dass kein Strom über die Last fließt und der erste Ausgang und der zweite Ausgang nicht miteinander kurzgeschlossen sind (Freilauf-Zustand); und
• 4) Einstellen des oberen und unteren Schalters, so dass ein Strom über die Last fließt (aktiver Zustand).

According to another alternative embodiment of the invention, there is provided a method of operating a vehicle having a quasi-Z source inverter comprising a diode and a diode-connected regenerative switch, a first choke, a second choke, a first capacitor, and a second Capacitor includes. The vehicle comprises a DC voltage source which is connected on the input side to the quasi-Z source inverter. Furthermore, the vehicle comprises a converter, which is connected on the output side to the quasi-Z source converter and which comprises at least one bridge branch, which is connected between a first and a second output of the quasi-Z source converter. The at least one bridge branch comprises an upper and a lower switch, which are connected in series. In the context of the other alternative embodiment, the switches of the at least one bridge branch are set so that the first output and the second output are short-circuited to each other over a first period of time and then the switches of the at least one bridge branch are set so that the first output and the second Output are not shorted together over a second period of time. In the other alternative embodiment of the invention, a load is connected to the transducer. The upper and lower switches of at least one of the bridge branches are then operated with the steps following one another directly:

• 1) setting the upper and lower switches so that the first output and the second output are shorted together (boost state);
• 2) adjusting the upper and lower switches so that a current flows across the load (active state);
• 3) setting the upper and lower switches so that no current flows across the load and the first output and the second output are not shorted together (freewheeling state); and
• 4) Adjust the upper and lower switches so that a current flows over the load (active state).

According to the invention, the above object is also achieved by the other alternative embodiment.

Further features of the invention will become apparent from the claims, the figures and the description of the figures. The features and feature combinations mentioned above in the description, as well as the features and feature combinations mentioned in the description of the figures and / or the features and feature combinations shown alone in the figures, can be used not only in the respectively specified combination but also in other combinations or alone, without departing from the scope of the invention.

Reference to exemplary embodiments, the invention is explained in more detail below. Show it:

1 a circuit diagram of a Z-source inverter and a three-phase pulse inverter according to the prior art;

2 a circuit diagram of a quasi-Z source inverter and a three-phase pulse inverter according to the prior art;

3 a time course of a DC link voltage;

4A an equivalent control circuit diagram of a cascade control structure;

4B a control circuit equivalent circuit diagram for a simplified control technical model of the route;

5 a circuit diagram of a quasi-Z source inverter and a three-phase pulse inverter with a recorded current profile in the boost state with the load current of a phase in an operating point;

6 a circuit diagram of a quasi-Z source inverter and a DC / DC converter in single-phase load;

7A a schematic pulse sequence for a modulation method according to the prior art; and

7B a schematic pulse sequence for a modified modulation method.

In the figures, identical or functionally identical elements are provided with the same reference numerals.

The circuit arrangement of 2 has a similar structure as in 1 shown circuit arrangement. However, the Z source inverter is 28 through the quasi Z source inverter 1 replaced. The quasi-Z source inverter 1 includes a first input E1 and a second input E2. Above the inputs E1 and E2 is the one from the battery 3 provided input voltage U _E on. The positive pole 13 the battery 3 is connected to the first input E1. The negative pole 14 the battery 3 is connected to the second input E2. The current I _E flows via the first input E1. The quasi-Z source inverter 1 also includes a first output A1 and a second output A2. The intermediate _circuit voltage U _{ZK present} across the two outputs A1 and A2 differs from the input voltage U _E , since the quasi-Z source converter has a plurality of electrical components between the input E1 and the output A1 or the input E2 and the output A2 , A first throttle L ₁ is with its first connection side 5 connected to the first input E1. She is with her second connection side 6 connected to the anode side AS of a diode D. The cathode side KS of the diode D is on the first side 7 a second throttle 12 connected. The second connection side 8th the second throttle 12 is finally connected to the first output A1. A first capacitor C ₁ is parallel to the diode D and to the second choke 12 connected. Here he is with his first connection page 9 with the anode side AS of the diode D or the second connection side 6 the first throttle L ₁ connected. With its second connection side 10 is the first capacitor C ₁ with the first output A1 and the second connection side 8th the second throttle 12 connected. Finally, there is in the circuit arrangement of the quasi-Z source inverter 1 also a second capacitor C ₂ , whose first connection side 11 is connected to the cathode side KS of the diode D. It is therefore also with the first connection side 7 the second throttle 12 connected. The second connection side 12 of the second capacitor C ₂ is electrically connected both to the second input E2 and to the second output A2.

A special feature is that in the quasi-Z source inverter 1 Also, a regenerative switch SR is provided. It can become the regenerative switch SR act in particular to an IGBT switch. It is connected in parallel with diode D. Hereby, a regenerative capability of the power converter circuit is achieved. In the embodiment, the induction machine is 4 an electric machine of a motor vehicle, which serves to drive the motor vehicle. If the car brakes, can the induction machine 4 can also be used as a generator and provide electrical energy. This can then via the regenerative switch SR in the battery 3 be fed. Braking energy of the motor vehicle can thus recharge the battery 3 be used. For this purpose, the regenerative switch SR is closed and then bridges the diode D. The regenerative switch SR thus serves for the return of energy into the battery 3 ,

The circuit arrangement of 2 can now be operated as follows: The principle operating method is schematically in 3 shown. Plotted is the intermediate circuit voltage U _ZK applied between the first output A1 and the second output A2 in volts as a function of the time t. In the exemplary embodiment, both the upper switch S _O and the lower switch S _{U of} the first bridge branch B1 of the inverter are over a first time period T ₁ 2 closed. This short circuits the outputs A1 and A2. It comes to the so-called boost or shoot-through. From the battery 3 Provided energy is stored in the chokes L ₁ and L ₂ , while the intermediate circuit voltage U _ZK breaks down to 0 volts. In this so-called boost phase, which lasts over the period T ₁ , follows in the embodiment of 3 an active phase. This lasts over the time period T ₂ . During the active phase, the upper switch S _{O of} the first bridge branch B1 is closed, while the lower switch S _{U of} the first bridge branch B1 is opened. At the inverter 2 So there is a load in the form of the induction machine 4 at. The resulting intermediate circuit voltage U _ZK assumes a maximum value u _{ZK, max} , which results as the sum of the voltage U _C1 , the ertsen capacitor C ₁ and the voltage U _C2 on the second capacitor C ₂ . u _{ZK, max} is considerably larger than the input voltage U _E. The intermediate circuit voltage <u _ZK > averaged over the time periods T ₁ and T ₂ is also greater than the input voltage U _E. The illustrated operating method thus allows a boosting of the intermediate circuit voltage U _ZK . The stored during the boost phase in the inductors L ₁ and L ₂ energy is in the active state in the capacitors C ₁ and C ₂ and in the induction machine 4 transhipped. Alternatively, during the time period T ₂ , a so-called free-running phase may also continue. Then, the upper switch S _O and the lower switch S _{U of} the first bridge branch B1 are both opened, so that no current can flow from the Z-source network into the bridge. Freewheel energy of the inductors L ₁ and L ₂ is transferred only in the capacitors C ₁ and C. ₂ Since the time average <u _ZK > of the clocked intermediate circuit voltage U _ZK corresponds precisely to the maximum adjustable voltage space vector, it makes sense to regulate the mean value.

• – einen Führungsgrößenfilter 17 im Sollwertpfad welcher als Glied mit proportionalem Übertragungsverhalten mit Verzögerung erster Ordnung (PT₁-Glied) modelliert wird;
• – einen Spannungsregler 18, welcher als Proportional-Integral-Glied (PI-Glied) modelliert wird. Der als quasi-kontinuierlich ausgelegte Spannungsregler 18 kann außerdem durch einen anderen Reglertypen ersetzt werden. V_P,U bezeichnet die Proportionalverstärkung, T_N,U die Nachstellzeit;
• – einen Stromregler 19, der als PI-Glied modelliert wird. Der als quasi-kontinuierlich ausgelegte Stromregler 19 kann außerdem durch andere Reglertypen ersetzt werden;
• – ein Stellglied 20, das als Totzeitglied modelliert wird. Auftretende Totzeiten sind in der Übertragungsfunktion des Stellgliedes 20 zusammengefasst. Zum einen ist dies die durch die Rechenzeit und Messzeit bedingte Totzeit, zum anderen die Totzeit, die durch das Abtasthalteverhalten des Stromrichters verursacht wird;
• – die Drosseln L₁ und L₂, deren Übertragungsverhalten vereinfachend durch ein Integrierglied (I-Glied) modelliert wird;
• – das die Diode D enthaltende Verkopplungsnetzwerk;
• – die Kondensatoren C₁ und C₂, die als I-Glieder modelliert werden;
• – eine Strommessung 21, die als Proportionalglied (P-Glied) modelliert wird; und
• – eine Spannungsmessung 22, die als P-Glied modelliert wird.

To regulate the mean DC link voltage <u _ZK >, a novel cascade structure is used, which in 4A is shown. Controlled variables are the inductor currents I _L1 and I _L2 and the capacitor voltages U _C1 and U _C2 in the Z network. About an inner loop 15 In this case, the inductor currents I _L1 and I _{L2 are} regulated, while the regulation of the capacitor voltages U _C1 and U _C2 via a superimposed control loop 16 takes place. The cascade rule structure includes the following elements:

• - a guide size filter 17 in the setpoint path, which is modeled as a member with proportional transmission behavior with first-order lag (PT ₁ -element);
• - a voltage regulator 18 , which is modeled as a proportional-integral (PI) element. The quasi-continuous voltage regulator 18 can also be replaced by another type of controller. V _{P, U} denotes the proportional gain, T _{N, U} the reset time;
• - a current regulator 19 which is modeled as a PI member. The quasi-continuous current regulator 19 can also be replaced by other types of controllers;
• - an actuator 20 which is modeled as deadtime member. Occurring dead times are in the transfer function of the actuator 20 summarized. On the one hand, this is the dead time caused by the computing time and measuring time, and on the other hand the dead time, which is caused by the sample holding behavior of the power converter;
• - The chokes L ₁ and L ₂ , whose transmission behavior is simplified modeled by an integrator (I-element);
• The coupling network containing the diode D;
• The capacitors C ₁ and C ₂ , which are modeled as I-links;
• - a current measurement 21 , which is modeled as a proportional element (P-element); and
• - a voltage measurement 22 , which is modeled as a P-limb.

The inductors L ₁ and L ₂ and the capacitors C ₁ and C ₂ can also be modeled as PT ₁ members. Disturbance variables in the control loop are the DC link current I _ZK and the input voltage U _E. Since these disturbances are known by the measurement, also their feedforward control is made.

The inductor current loop, the current measurement 21 comprises, forms a first or inner loop. As part of the cascade control this subordinate inductor current control loop is superimposed on a DC link voltage control circuit, the voltage measurement 22 includes and forms a second control loop. With the subordinate inductor current control circuit, the input current I _E = I _{L1 is} controlled. U _C2 is controlled variable. For the control, only the inductor current I _L1 and the intermediate circuit voltage <u _ZK > must be measured. The only intervention in the circuit in this case takes place in the regular operation via the change of the turn-on ratio b of the boost state. b is given as follows (with the period T): T ₁ = b * T T ₂ = (1-b) * T

The cascade control structure directly controls the average intermediate circuit voltage <u _ZK >. The control can be realized, for example, at a 10 kHz PWM (Pulse Width Modulation) clock frequency. The input voltage U _E can be, for example, 400 volts. The power can be for example 10 kW.

If the first throttle L ₁ and the second throttle L _{2 have the} same inductances and the first capacitor C _{1 has} the same capacitance as the second capacitor C ₂ , the controlled system is simplified to the one in FIG 4B illustrated rule structure. The voltages across the capacitors C ₁ and C ₂ and the currents in the inductors L ₁ and L ₂ are each the same size.

Compared with the known solutions for controlling a Z-source converter, the cascade structure offers the advantage that inductor current and capacitor voltage are regulated separately from one another.

If the double choke current becomes smaller than the load current, the load current-related short-circuit occurs. The condition for this, in turn, is that the following applies to the modulation level a of the active state of the load-side actuator:

This unwanted state occurs when switching from the freewheel state or the boost state to the active state. Under these circumstances, the free-running load current does not commute at the desired time from the freewheeling diode F _O or F _U to the corresponding switch S _O or S _U , but continues to flow until the load current is less than twice the inductor current. Consequently, the boost state is set, although an active state is desired. On the one hand, this means that the desired voltage space vector can not be set by the pulse-controlled inverter and the inductor currents rise higher than required by the regulation. On the other hand, when the load current-related boost phase ends, the capacitor voltage rises higher than the voltage setpoint. This can be prevented by switching on the regenerative switch SR at the same time as the active states. The intermediate _{circuit voltage} u _ZK.max then again results from the sum of the two capacitor _voltages U _C1 and U _C2 .

The switches S _O , S _U and SR can be designed as semiconductor switches, in particular as transistors.

5 shows an example of an optimized selection of the boost branch. In the embodiment of 5 the boost state is switched via the bridge branch B3, ie the upper switch S _O and the lower switch S _U are closed. In the boost phase, the sum of double inductor current I _L (DC link current) and switch current I _S flows via the output phase connected to the short-circuited bridge branch B3. For the semiconductor component of lower switch S _U and lower freewheeling diode F _U , the following current load results: I _S = I _LOAD - 2I _L.

Depending on the sign of the currents I _L or I _S , the switches S _O or S _U or the freewheeling diode F _U are loaded to different degrees. For example, if 2I _{L is} greater in magnitude than I _LOAD and positive, the current load of freewheeling diode F will decrease. On the other hand, the current may also increase. It is desirable to have the lowest possible current load of the components in the boost phase. This is achieved by selecting the boost branch such that the superposition of the choke and load current reduces the current load on the components. In the exemplary embodiment, the short circuit takes place via the bridge branch B3, wherein currents then pass over the path 23 run.

Alternatively or additionally, two of the three bridge branches B1, B2 and B3 or even all three bridge branches B1, B2 and B3 can be short-circuited together. This leads to a further reduction of the current load in each of the individual bridge branches B1, B2 and B3, because the current is again divided due to the parallel connection.

It should be noted that when selecting the bridge branches which are shorted, the current signs and output phases must be taken into account.

The 6 to 7B show, by way of example for the single-phase load, how the switching state sequence can be optimized. Instead of the inverter 2 is now only a bridge branch B1 to the outputs A1 and A2 of the Z source inverter 1 connected. On the DC / DC converter thus formed 29 there is a burden 24 on, which is formed via an inductance L _LAST and a resistor R _LAST . Thus, the case of single-phase loading is considered. Basically, however, the following considerations are also true in the case of the three-phase load, as in the 2 is shown possible.

• – eine Boost-Phase 25. Der obere Schalter S_O und der untere Schalter S_U des Brückenzweigs B1 in 6 sind beide geschlossen;
• – eine aktive Phase 26. Der obere Schalter S_O ist geschlossen, während der untere Schalter S_U geöffnet ist;
• – eine Freilaufphase 27. Sowohl der obere Schalter S_O als auch der untere Schalter S_U sind geöffnet;
• – wiederum eine Boost-Phase 25;
• – wiederum eine Freilaufphase 27;
• – wiederum eine aktive Phase 26; und
• – wiederum eine Boost-Phase 25.

7A shows a known from the prior art modulation method or driving method for the switches S _O and S _U. So far, it is common to integrate the boost phases in the freewheeling phases, since both phases are identical to the load 24 Act. Plotted is the duty cycle TV as a function of time. Shown is an entire period for the pulse width modulation T _PWM . a, b and c are duty cycles. b results as a ratio of the first time period T ₁ to the entire period T or T _PWM . a results as the ratio of the second time duration T ₂ to the total period T or T _PWM . C is an auxiliary quantity which is defined as c = a + b. c _S and b _S are associated switching thresholds. On the timeline follow one after another:

• - a boost phase 25 , The upper switch S _O and the lower switch S _{U of} the bridge branch B1 in 6 they are both closed;
• - an active phase 26 , The upper switch S _O is closed, while the lower switch S _{U is} open;
• - a freewheeling phase 27 , Both the upper switch S _O and the lower switch S _U are open;
• - again a boost phase 25 ;
• - again a freewheeling phase 27 ;
• - again an active phase 26 ; and
• - again a boost phase 25 ,

In this type of modulation find a transition from a freewheeling phase 27 in a boost phase 25 two switching operations instead. Namely, both the upper switch S _O and the lower switch S _U are switched on or off. However, it is desirable to always have only one switchover for all switching state changes.

By the boost phase 25 between two active phases 26 is moved at all switching state transitions only one switching instead. This means that the switching frequency of the switches S _O and S _U can be reduced. This is associated with a reduction of the switching losses. The proposed new modulation scheme is schematically shown in FIG 7B shown.

Additionally is in 7B the switching state of the regenerative switch S _R drawn. Preferably, the feedback switch S _R during an active phase 26 (optionally within one freewheel) closed over the entire duration of the phase. As already explained, unwanted load current-related short circuits can be avoided in this way.

LIST OF REFERENCE NUMBERS

1

Quasi-Z-source inverter

2

inverter

3

battery

4

Induction machine

5, 6, ..., 12

terminal side

13

positive pole

14

negative pole

15, 16

loop

17

Reference value filter

18

voltage regulators

19

current regulator

20

actuator

21

current measurement

22

voltage measurement

23

path

24

load

25

boost phase

26

active phase

27

Freewheeling phase

28

Z-source inverter

29

DC / DC converter

t

Time

T, T _PWM

period

U _ZK , U _C1 , U _C2 , U _E , <u _ZK >, u _{ZK, max}

tension

I _E , I _L , I _S , I _LOAD , I _L1 , I _L2

electricity

B1, B2, B3

bridge branch

D

diode

L ₁ , L ₂

throttle

C ₁ , C ₂

capacitor

S _R

Regenerative switch

E1, E2

entrance

A1, A2

output

AS

anode side

KS

cathode side

S _O, S _U

switch

F _O , F _U

Freewheeling diode

T ₁ , T ₂

time

R _LOAD

resistance

LOAD

inductance

c _S , b _S

switching threshold

a, b, c

relationship

V _{P, U}

proportional gain

T _{N, U}

Integral

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102007038959 A1 [0007]
• DE 102008046301 A1 [0008]

Cited non-patent literature

• "J. Anderson and FZ Peng (Department of Electrical and Computer Engineering, Michigan State University): Four Quasi-Z Source Inverters, Power Electronics Specialists Conference 2008, Date: 15-19. June 2008, pages 2743-2749 " [0009]

Claims (7)

Method for operating a vehicle with a quasi-Z source converter ( 1 ), which comprises a diode (D) and a feedback switch (S _R ) connected in parallel with the diode (D), a first choke (L ₁ ), a second choke (L ₂ ), a first capacitor (C ₁ ) and a second capacitor (C ₂ ), with a DC voltage source ( 3 ), which on the input side (E1, E2) with the quasi-Z source converter ( 1 ) and with a transducer ( 2 . 29 ), which on the output side (A1, A2) with the quasi-Z source converter ( 1 ) and which comprises at least one bridge branch (B1, B2, B3) connected between a first (A1) and a second output (A2) of the quasi-Z source converter ( 1 ), wherein the at least one bridge branch (B1, B2, B3) comprises an upper (S _O ) and a lower switch (S _U ), which are connected in series, wherein in the context of the method, the switches (S _O , S _U ) of the at least one bridge branch (B1, B2, B3) are set so that the first output (A1) and the second output (A2) are short-circuited to each other over a first time period (T ₁ ) and then the switches (S _O , S _U ) of the at least one bridge branch (B1, B2, B3) are set so that the first output (A1) and the second output (A2) are not short-circuited to each other over a second period of time (T ₂ ), characterized in that the current (L _L1 or I _L2 ) flowing through the first (L ₁ ) and / or second inductor (L ₂ ) in a first control circuit ( 15 ) is regulated on the basis of the ratio of the first time duration (T ₁ ) to the second time duration (T ₂ ) and the voltage (U _C1 or U _C2 ) applied to the first (C ₁ ) and / or second capacitor (C ₂ ) in a second Control loop ( 16 ) is controlled on the basis of the ratio of the first time period (T ₁ ) to the second time duration (T ₂ ). Method according to Claim 1, characterized in that the first control loop ( 15 ) forms an inner control loop and the second control loop ( 16 ) is superimposed on the first control loop. A method according to claim 1 or 2, characterized in that the feedback switch (S _R ) is closed at least over a partial interval of the second time period (T ₂ ) and during the first time period (T ₁ ) is opened. Method according to one of the preceding claims, characterized in that the transducer ( 2 . 29 ) at least two bridge branches (B1, B2, B3) and at least one of the bridge branches (B1, B2, B3) is selected, for which the upper (S _O ) and the lower switch (S _U ) are set so that the first Output (A1) and the second output (A2) over the first period (T ₁ ) are short-circuited to each other, wherein the selection is made so that the lowest possible current across all switches (S _O , S _U ) and / or freewheeling diodes (F _O , F _U ) of the bridge branches (B1, B2, B3) flows. Method according to one of the preceding claims, characterized in that the transducer ( 2 . 29 ) at least two bridge branches (B1, B2, B3) and at least two of the bridge branches (B1, B2, B3) are selected, for each of the upper (So) and the lower switch (S _U ) are set so that the first Output (A1) and the second output (A2) over the first period (T ₁ ) are shorted together. Method according to one of the preceding claims, characterized in that a load ( 4 . 24 ) to the converter ( 2 . 29 ), wherein the switches (S _O , S _U ) of the at least one bridge branch (B1, B2, B3) are operated with the immediately following steps: 1) setting the upper (S _O ) and lower switch (S _U ), such that the first output (A1) and the second output (A2) are shorted together; 2) Adjust the upper (S _O ) and lower switch (S _U ) so that a current across the load ( 4 . 24 ) flows; 3) Adjusting the upper (S _O ) and lower switch (S _U ) so that no current flows through the load ( 4 . 24 ) and the first output (A1) and the second output (A2) are not shorted together; and 4) adjusting the upper (S _O ) and lower switch (S _U ) so that a current across the load ( 4 . 24 ) flows. Method according to one of the preceding claims, characterized in that the converter is an inverter ( 2 ) for the multiphase, in particular three-phase, operation of an electrical machine ( 4 ) and for each phase to be generated comprises a respective bridge branch (B1, B2, B3) which is connected in parallel to the bridge branches (B1, B2, B3) for the respective other phases.

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